Texas Instruments | ARM Optimizing C/C Compiler v18.1.0.LTS (Rev. R) | User Guides | Texas Instruments ARM Optimizing C/C Compiler v19.6.0.STS (Rev. U) User guides

Texas Instruments ARM Optimizing C/C   Compiler v19.6.0.STS (Rev. U) User guides
ARM Optimizing C/C++ Compiler
v19.6.0.STS
User's Guide
Literature Number: SPNU151U
January 1998 – Revised June 2019
Contents
Preface ........................................................................................................................................ 9
1
Introduction to the Software Development Tools .................................................................... 12
1.1
1.2
1.3
1.4
1.5
2
13
15
15
15
16
Using the C/C++ Compiler ................................................................................................... 17
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2
Software Development Tools Overview .................................................................................
Compiler Interface ..........................................................................................................
ANSI/ISO Standard ........................................................................................................
Output Files .................................................................................................................
Utilities .......................................................................................................................
About the Compiler.........................................................................................................
Invoking the C/C++ Compiler .............................................................................................
Changing the Compiler's Behavior with Options .......................................................................
2.3.1 Linker Options .....................................................................................................
2.3.2 Frequently Used Options .........................................................................................
2.3.3 Miscellaneous Useful Options ...................................................................................
2.3.4 Run-Time Model Options .........................................................................................
2.3.5 Symbolic Debugging and Profiling Options ....................................................................
2.3.6 Specifying Filenames .............................................................................................
2.3.7 Changing How the Compiler Interprets Filenames ...........................................................
2.3.8 Changing How the Compiler Processes C Files ..............................................................
2.3.9 Changing How the Compiler Interprets and Names Extensions ............................................
2.3.10 Specifying Directories............................................................................................
2.3.11 Assembler Options ...............................................................................................
2.3.12 Deprecated Options ..............................................................................................
Controlling the Compiler Through Environment Variables ............................................................
2.4.1 Setting Default Compiler Options (TI_ARM_C_OPTION)....................................................
2.4.2 Naming One or More Alternate Directories (TI_ARM_C_DIR) ..............................................
Controlling the Preprocessor .............................................................................................
2.5.1 Predefined Macro Names ........................................................................................
2.5.2 The Search Path for #include Files .............................................................................
2.5.3 Support for the #warning and #warn Directives ...............................................................
2.5.4 Generating a Preprocessed Listing File (--preproc_only Option) ...........................................
2.5.5 Continuing Compilation After Preprocessing (--preproc_with_compile Option) ...........................
2.5.6 Generating a Preprocessed Listing File with Comments (--preproc_with_comment Option) ...........
2.5.7 Generating Preprocessed Listing with Line-Control Details (--preproc_with_line Option) ...............
2.5.8 Generating Preprocessed Output for a Make Utility (--preproc_dependency Option) ...................
2.5.9 Generating a List of Files Included with #include (--preproc_includes Option) ...........................
2.5.10 Generating a List of Macros in a File (--preproc_macros Option) .........................................
Passing Arguments to main() .............................................................................................
Understanding Diagnostic Messages ....................................................................................
2.7.1 Controlling Diagnostic Messages ...............................................................................
2.7.2 How You Can Use Diagnostic Suppression Options .........................................................
Other Messages ............................................................................................................
Generating Cross-Reference Listing Information (--gen_cross_reference Option) ................................
Generating a Raw Listing File (--gen_preprocessor_listing Option) .................................................
Using Inline Function Expansion .........................................................................................
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2.12
2.13
2.14
2.15
3
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51
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55
Optimizing Your Code ......................................................................................................... 56
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
4
2.11.1 Inlining Intrinsic Operators ......................................................................................
2.11.2 Inlining Restrictions ..............................................................................................
Using Interlist ...............................................................................................................
Controlling Application Binary Interface .................................................................................
VFP Support ................................................................................................................
Enabling Entry Hook and Exit Hook Functions .........................................................................
Invoking Optimization ......................................................................................................
Controlling Code Size Versus Speed ...................................................................................
Performing File-Level Optimization (--opt_level=3 option) ............................................................
3.3.1 Creating an Optimization Information File (--gen_opt_info Option) .........................................
Program-Level Optimization (--program_level_compile and --opt_level=3 options) ...............................
3.4.1 Controlling Program-Level Optimization (--call_assumptions Option) ......................................
3.4.2 Optimization Considerations When Mixing C/C++ and Assembly ..........................................
Automatic Inline Expansion (--auto_inline Option) .....................................................................
Link-Time Optimization (--opt_level=4 Option) .........................................................................
3.6.1 Option Handling ...................................................................................................
3.6.2 Incompatible Types ...............................................................................................
Using Feedback Directed Optimization..................................................................................
3.7.1 Feedback Directed Optimization ................................................................................
3.7.2 Profile Data Decoder ..............................................................................................
3.7.3 Feedback Directed Optimization API ...........................................................................
3.7.4 Feedback Directed Optimization Summary ....................................................................
Using Profile Information to Analyze Code Coverage .................................................................
3.8.1 Code Coverage ....................................................................................................
3.8.2 Related Features and Capabilities ..............................................................................
Accessing Aliased Variables in Optimized Code .......................................................................
Use Caution With asm Statements in Optimized Code ...............................................................
Using the Interlist Feature With Optimization ...........................................................................
Debugging and Profiling Optimized Code ...............................................................................
3.12.1 Profiling Optimized Code ........................................................................................
What Kind of Optimization Is Being Performed? .......................................................................
3.13.1 Cost-Based Register Allocation ................................................................................
3.13.2 Alias Disambiguation ............................................................................................
3.13.3 Branch Optimizations and Control-Flow Simplification ......................................................
3.13.4 Data Flow Optimizations ........................................................................................
3.13.5 Expression Simplification ........................................................................................
3.13.6 Inline Expansion of Functions ..................................................................................
3.13.7 Function Symbol Aliasing .......................................................................................
3.13.8 Induction Variables and Strength Reduction .................................................................
3.13.9 Loop-Invariant Code Motion ....................................................................................
3.13.10 Loop Rotation ...................................................................................................
3.13.11 Instruction Scheduling ..........................................................................................
3.13.12 Tail Merging .....................................................................................................
3.13.13 Autoincrement Addressing ....................................................................................
3.13.14 Block Conditionalizing ..........................................................................................
3.13.15 Epilog Inlining ...................................................................................................
3.13.16 Removing Comparisons to Zero ..............................................................................
3.13.17 Integer Division With Constant Divisor .......................................................................
3.13.18 Branch Chaining ................................................................................................
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Linking C/C++ Code ............................................................................................................ 77
4.1
Invoking the Linker Through the Compiler (-z Option) ................................................................ 78
4.1.1 Invoking the Linker Separately .................................................................................. 78
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4.2
4.3
5
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C/C++ Language Implementation .......................................................................................... 85
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
4
4.1.2 Invoking the Linker as Part of the Compile Step ..............................................................
4.1.3 Disabling the Linker (--compile_only Compiler Option) ......................................................
Linker Code Optimizations ................................................................................................
4.2.1 Generate List of Dead Functions (--generate_dead_funcs_list Option) ....................................
4.2.2 Generating Aggregate Data Subsections (--gen_data_subsections Compiler Option) ..................
Controlling the Linking Process ..........................................................................................
4.3.1 Including the Run-Time-Support Library .......................................................................
4.3.2 Run-Time Initialization ............................................................................................
4.3.3 Initialization of Cinit and Watchdog Timer Hold ...............................................................
4.3.4 Global Object Constructors ......................................................................................
4.3.5 Specifying the Type of Global Variable Initialization ..........................................................
4.3.6 Specifying Where to Allocate Sections in Memory ...........................................................
4.3.7 A Sample Linker Command File ................................................................................
Characteristics of ARM C ................................................................................................. 86
5.1.1 Implementation-Defined Behavior ............................................................................... 86
Characteristics of ARM C++ .............................................................................................. 91
Using MISRA C 2004 ...................................................................................................... 92
Using the ULP Advisor .................................................................................................... 93
Data Types .................................................................................................................. 94
5.5.1 Size of Enum Types .............................................................................................. 95
File Encodings and Character Sets ...................................................................................... 96
Keywords .................................................................................................................... 96
5.7.1 The const Keyword................................................................................................ 96
5.7.2 The __interrupt Keyword ......................................................................................... 97
5.7.3 The volatile Keyword .............................................................................................. 98
C++ Exception Handling................................................................................................... 99
Register Variables and Parameters .................................................................................... 100
5.9.1 Local Register Variables and Parameters .................................................................... 100
5.9.2 Global Register Variables....................................................................................... 100
The __asm Statement .................................................................................................... 101
Pragma Directives ........................................................................................................ 102
5.11.1 The CALLS Pragma ............................................................................................ 103
5.11.2 The CHECK_MISRA Pragma ................................................................................. 103
5.11.3 The CHECK_ULP Pragma .................................................................................... 104
5.11.4 The CODE_ALIGN Pragma ................................................................................... 104
5.11.5 The CODE_SECTION Pragma ............................................................................... 104
5.11.6 The CODE_STATE Pragma .................................................................................. 106
5.11.7 The DATA_ALIGN Pragma .................................................................................... 106
5.11.8 The DATA_SECTION Pragma ................................................................................ 107
5.11.9 The Diagnostic Message Pragmas ........................................................................... 108
5.11.10 The DUAL_STATE Pragma .................................................................................. 108
5.11.11 The FORCEINLINE Pragma ................................................................................. 109
5.11.12 The FORCEINLINE_RECURSIVE Pragma ................................................................ 109
5.11.13 The FUNC_ALWAYS_INLINE Pragma..................................................................... 109
5.11.14 The FUNC_CANNOT_INLINE Pragma .................................................................... 110
5.11.15 The FUNC_EXT_CALLED Pragma ......................................................................... 110
5.11.16 The FUNCTION_OPTIONS Pragma ....................................................................... 111
5.11.17 The INTERRUPT Pragma.................................................................................... 111
5.11.18 The LOCATION Pragma ..................................................................................... 112
5.11.19 The MUST_ITERATE Pragma .............................................................................. 113
5.11.20 The NOINIT and PERSISTENT Pragmas ................................................................. 114
5.11.21 The NOINLINE Pragma ...................................................................................... 115
Contents
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5.12
5.13
5.14
5.15
5.16
5.17
5.18
5.19
6
5.11.22 The NO_HOOKS Pragma ....................................................................................
5.11.23 The pack Pragma .............................................................................................
5.11.24 The RESET_MISRA Pragma ................................................................................
5.11.25 The RESET_ULP Pragma ...................................................................................
5.11.26 The RETAIN Pragma .........................................................................................
5.11.27 The SET_CODE_SECTION and SET_DATA_SECTION Pragmas ....................................
5.11.28 The SWI_ALIAS Pragma .....................................................................................
5.11.29 The TASK Pragma ............................................................................................
5.11.30 The UNROLL Pragma ........................................................................................
5.11.31 The WEAK Pragma ...........................................................................................
The _Pragma Operator ..................................................................................................
Application Binary Interface .............................................................................................
ARM Instruction Intrinsics................................................................................................
Object File Symbol Naming Conventions (Linknames) ..............................................................
Changing the ANSI/ISO C/C++ Language Mode .....................................................................
5.16.1 C99 Support (--c99) ............................................................................................
5.16.2 C11 Support (--c11) ............................................................................................
5.16.3 Strict ANSI Mode and Relaxed ANSI Mode (--strict_ansi and --relaxed_ansi) .........................
GNU, Clang, and ACLE Language Extensions .......................................................................
5.17.1 Extensions .......................................................................................................
5.17.2 Function Attributes ..............................................................................................
5.17.3 Variable Attributes ..............................................................................................
5.17.4 Type Attributes ..................................................................................................
5.17.5 Built-In Functions ...............................................................................................
AUTOSAR .................................................................................................................
Compiler Limits ............................................................................................................
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Run-Time Environment ...................................................................................................... 141
6.1
6.2
6.3
6.4
6.5
6.6
6.7
Memory Model ............................................................................................................
6.1.1 Sections ...........................................................................................................
6.1.2 C/C++ System Stack ............................................................................................
6.1.3 Dynamic Memory Allocation ....................................................................................
Object Representation ...................................................................................................
6.2.1 Data Type Storage...............................................................................................
6.2.2 Bit Fields ..........................................................................................................
6.2.3 Character String Constants .....................................................................................
Register Conventions ....................................................................................................
Function Structure and Calling Conventions ..........................................................................
6.4.1 How a Function Makes a Call ..................................................................................
6.4.2 How a Called Function Responds .............................................................................
6.4.3 C Exception Handler Calling Convention .....................................................................
6.4.4 Accessing Arguments and Local Variables...................................................................
Accessing Linker Symbols in C and C++ ..............................................................................
Interfacing C and C++ With Assembly Language ....................................................................
6.6.1 Using Assembly Language Modules With C/C++ Code ....................................................
6.6.2 Accessing Assembly Language Functions From C/C++ ...................................................
6.6.3 Accessing Assembly Language Variables From C/C++ ....................................................
6.6.4 Sharing C/C++ Header Files With Assembly Source .......................................................
6.6.5 Using Inline Assembly Language ..............................................................................
6.6.6 Modifying Compiler Output .....................................................................................
Interrupt Handling .........................................................................................................
6.7.1 Saving Registers During Interrupts ............................................................................
6.7.2 Using C/C++ Interrupt Routines ...............................................................................
6.7.3 Using Assembly Language Interrupt Routines ...............................................................
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Contents
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6.8
6.9
6.10
6.11
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Using Run-Time-Support Functions and Building Libraries ................................................... 178
7.1
7.2
7.3
7.4
8
6.7.4 How to Map Interrupt Routines to Interrupt Vectors.........................................................
6.7.5 Using Software Interrupts .......................................................................................
6.7.6 Other Interrupt Information .....................................................................................
Intrinsic Run-Time-Support Arithmetic and Conversion Routines ..................................................
6.8.1 CPSR Register and Interrupt Intrinsics .......................................................................
Built-In Functions .........................................................................................................
System Initialization ......................................................................................................
6.10.1 Boot Hook Functions for System Pre-Initialization .........................................................
6.10.2 Run-Time Stack .................................................................................................
6.10.3 Automatic Initialization of Variables ..........................................................................
6.10.4 Initialization Tables .............................................................................................
Dual-State Interworking Under TIABI (Deprecated) ..................................................................
6.11.1 Level of Dual-State Support ...................................................................................
6.11.2 Implementation ..................................................................................................
C and C++ Run-Time Support Libraries ...............................................................................
7.1.1 Linking Code With the Object Library .........................................................................
7.1.2 Header Files ......................................................................................................
7.1.3 Modifying a Library Function ...................................................................................
7.1.4 Support for String Handling.....................................................................................
7.1.5 Minimal Support for Internationalization ......................................................................
7.1.6 Allowable Number of Open Files ..............................................................................
7.1.7 Nonstandard Header Files in the Source Tree ..............................................................
7.1.8 Library Naming Conventions ...................................................................................
The C I/O Functions ......................................................................................................
7.2.1 High-Level I/O Functions .......................................................................................
7.2.2 Overview of Low-Level I/O Implementation ..................................................................
7.2.3 Device-Driver Level I/O Functions .............................................................................
7.2.4 Adding a User-Defined Device Driver for C I/O ..............................................................
7.2.5 The device Prefix ................................................................................................
Handling Reentrancy (_register_lock() and _register_unlock() Functions) ........................................
Library-Build Process.....................................................................................................
7.4.1 Required Non-Texas Instruments Software ..................................................................
7.4.2 Using the Library-Build Process ...............................................................................
7.4.3 Extending mklib ..................................................................................................
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C++ Name Demangler ........................................................................................................ 199
8.1
8.2
Invoking the C++ Name Demangler .................................................................................... 200
Sample Usage of the C++ Name Demangler ......................................................................... 201
A
Glossary .......................................................................................................................... 202
B
............................................................................................................... 202
Revision History ............................................................................................................... 207
B.1
Recent Revisions ......................................................................................................... 207
6
Contents
A.1
Terminology
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List of Figures
1-1.
ARM Software Development Flow ....................................................................................... 13
6-1.
Char and Short Data Storage Format .................................................................................. 145
6-2.
32-Bit Data Storage Format ............................................................................................. 146
6-3.
Double-Precision Floating-Point Data Storage Format .............................................................. 147
6-4.
Bit-Field Packing in Big-Endian and Little-Endian Formats ......................................................... 149
6-5.
Use of the Stack During a Function Call ............................................................................... 154
6-6.
Autoinitialization at Run Time ........................................................................................... 167
6-7.
Initialization at Load Time
6-8.
Constructor Table ......................................................................................................... 171
6-9.
Format of Initialization Records in the .cinit Section ................................................................. 172
6-10.
Format of Initialization Records in the .pinit Section ................................................................. 173
...............................................................................................
171
List of Tables
.........................................................................................................
......................................................................................................
Advanced Optimization Options .........................................................................................
Debug Options ..............................................................................................................
Include Options ............................................................................................................
ULP Advisor Options .......................................................................................................
Control Options ............................................................................................................
Language Options ..........................................................................................................
Parser Preprocessing Options ............................................................................................
Predefined Macro Options ...............................................................................................
Diagnostic Message Options .............................................................................................
Supplemental Information Options ......................................................................................
Run-Time Model Options ..................................................................................................
Entry/Exit Hook Options ...................................................................................................
Feedback Options .........................................................................................................
Assembler Options .........................................................................................................
File Type Specifier Options ...............................................................................................
Directory Specifier Options................................................................................................
Default File Extensions Options ..........................................................................................
Command Files Options ...................................................................................................
MISRA-C 2004 Options ...................................................................................................
Linker Basic Options .......................................................................................................
File Search Path Options ..................................................................................................
Command File Preprocessing Options ..................................................................................
Diagnostic Message Options .............................................................................................
Linker Output Options .....................................................................................................
Symbol Management Options ............................................................................................
Run-Time Environment Options ..........................................................................................
Miscellaneous Options.....................................................................................................
Predefined ARM Macro Names ..........................................................................................
ACLE Pre-Defined Macros ................................................................................................
Raw Listing File Identifiers ................................................................................................
Raw Listing File Diagnostic Identifiers ...................................................................................
Options That You Can Use With --opt_level=3 .........................................................................
2-1.
Processor Options
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2-2.
Optimization Options
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2-3.
2-4.
2-5.
2-6.
2-7.
2-8.
2-9.
2-10.
2-11.
2-12.
2-13.
2-14.
2-15.
2-16.
2-17.
2-18.
2-19.
2-20.
2-21.
2-22.
2-23.
2-24.
2-25.
2-26.
2-27.
2-28.
2-29.
2-30.
2-31.
2-32.
2-33.
3-1.
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List of Figures
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3-2.
Selecting a Level for the --gen_opt_info Option ........................................................................ 58
3-3.
Selecting a Level for the --call_assumptions Option................................................................... 59
3-4.
Special Considerations When Using the --call_assumptions Option ................................................ 60
4-1.
Initialized Sections Created by the Compiler ........................................................................... 83
4-2.
Uninitialized Sections Created by the Compiler ........................................................................ 83
5-1.
ARM C/C++ Data Types................................................................................................... 94
5-2.
Enumerator Types.......................................................................................................... 94
5-3.
ARM Intrinsic Support by Target ........................................................................................ 122
5-4.
ARM Compiler Intrinsics ................................................................................................. 125
5-5.
GCC Language Extensions
6-1.
Summary of Sections and Memory Placement ....................................................................... 143
6-2.
Data Representation in Registers and Memory
6-3.
How Register Types Are Affected by the Conventions .............................................................. 150
6-4.
...........................................................................................................
VFP Register Usage......................................................................................................
Neon Register Usage ....................................................................................................
CPSR and Interrupt C/C++ Compiler Intrinsics .......................................................................
Selecting a Level of Dual-State Support ...............................................................................
The mklib Program Options .............................................................................................
Revision History ...........................................................................................................
6-5.
6-6.
6-7.
6-8.
7-1.
B-1.
8
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......................................................................
Register Usage
List of Tables
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Preface
SPNU151U – January 1998 – Revised June 2019
Read This First
About This Manual
The ARM Optimizing C/C++ Compiler User's Guide explains how to use the following Texas Instruments
Code Generation compiler tools:
• Compiler
• Library build utility
• C++ name demangler
The TI compiler accepts C and C++ code conforming to the International Organization for Standardization
(ISO) standards for these languages. The compiler supports the 1989, 1999, and 2011 versions of the C
language and the 2014 version of the C++ language.
This user's guide discusses the characteristics of the TI C/C++ compiler. It assumes that you already
know how to write C/C++ programs. The C Programming Language (second edition), by Brian W.
Kernighan and Dennis M. Ritchie, describes C based on the ISO C standard. You can use the Kernighan
and Ritchie (hereafter referred to as K&R) book as a supplement to this manual. References to K&R C (as
opposed to ISO C) in this manual refer to the C language as defined in the first edition of Kernighan and
Ritchie's The C Programming Language.
Notational Conventions
This document uses the following conventions:
• Program listings, program examples, and interactive displays are shown in a special typeface.
Interactive displays use a bold version of the special typeface to distinguish commands that you enter
from items that the system displays (such as prompts, command output, error messages, etc.). Here is
a sample of C code:
#include <stdio.h>
main()
{
printf("Hello World\n");
}
•
•
In syntax descriptions, instructions, commands, and directives are in a bold typeface and parameters
are in an italic typeface. Portions of a syntax that are in bold should be entered as shown; portions of a
syntax that are in italics describe the type of information that should be entered.
Square brackets ( [ and ] ) identify an optional parameter. If you use an optional parameter, you specify
the information within the brackets. Unless the square brackets are in the bold typeface, do not enter
the brackets themselves. The following is an example of a command that has an optional parameter:
armcl [options] [filenames] [--run_linker [link_options] [object files]]
•
Braces ( { and } ) indicate that you must choose one of the parameters within the braces; you do not
enter the braces themselves. This is an example of a command with braces that are not included in the
actual syntax but indicate that you must specify either the --rom_model or --ram_model option:
armcl --run_linker
{--rom_model | --ram_model} filenames [--output_file= name.out]
--library= libraryname
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Related Documentation
•
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In assembler syntax statements, the leftmost column is reserved for the first character of a label or
symbol. If the label or symbol is optional, it is usually not shown. If a label or symbol is a required
parameter, it is shown starting against the left margin of the box, as in the example below. No
instruction, command, directive, or parameter, other than a symbol or label, can begin in the leftmost
column.
symbol .usect "section name", size in bytes[, alignment]
•
•
•
Some directives can have a varying number of parameters. For example, the .byte directive. This
syntax is shown as [, ..., parameter].
The ARM® 16-bit instruction set is referred to as 16-BIS.
The ARM 32-bit instruction set is referred to as 32-BIS.
Related Documentation
You can use the following books to supplement this user's guide:
ANSI X3.159-1989, Programming Language - C (Alternate version of the 1989 C Standard), American
National Standards Institute
ISO/IEC 9899:1989, International Standard - Programming Languages - C (The 1989 C Standard),
International Organization for Standardization
ISO/IEC 9899:1999, International Standard - Programming Languages - C (The 1999 C Standard),
International Organization for Standardization
ISO/IEC 9899:2011, International Standard - Programming Languages - C (The 2011 C Standard),
International Organization for Standardization
ISO/IEC 14882-2014, International Standard - Programming Languages - C++ (The 2014 C++
Standard), International Organization for Standardization
The C Programming Language (second edition), by Brian W. Kernighan and Dennis M. Ritchie,
published by Prentice-Hall, Englewood Cliffs, New Jersey, 1988
The Annotated C++ Reference Manual, Margaret A. Ellis and Bjarne Stroustrup, published by AddisonWesley Publishing Company, Reading, Massachusetts, 1990
C: A Reference Manual (fourth edition), by Samuel P. Harbison, and Guy L. Steele Jr., published by
Prentice Hall, Englewood Cliffs, New Jersey
Programming Embedded Systems in C and C++, by Michael Barr, Andy Oram (Editor), published by
O'Reilly & Associates; ISBN: 1565923545, February 1999
Programming in C, Steve G. Kochan, Hayden Book Company
The C++ Programming Language (second edition), Bjarne Stroustrup, published by Addison-Wesley
Publishing Company, Reading, Massachusetts, 1990
Tool Interface Standards (TIS) DWARF Debugging Information Format Specification Version 2.0,
TIS Committee, 1995
DWARF Debugging Information Format Version 3, DWARF Debugging Information Format Workgroup,
Free Standards Group, 2005 (http://dwarfstd.org)
DWARF Debugging Information Format Version 4, DWARF Debugging Information Format Workgroup,
Free Standards Group, 2010 (http://dwarfstd.org)
System V ABI specification (http://www.sco.com/developers/gabi/)
ARM C Language Extensions (ACLE) specification (ACLE Version ACLE Q2 2017)
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Related Documentation From Texas Instruments
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Related Documentation From Texas Instruments
See the following resources for further information about the TI Code Generation Tools:
• Texas Instruments Wiki: Compiler topics
• Texas Instruments E2E Community: Compiler forum
You can use the following documents to supplement this user's guide:
SPNU118 — ARM Assembly Language Tools User's Guide. Describes the assembly language tools
(assembler, linker, and other tools used to develop assembly language code), assembler directives,
macros, common object file format, and symbolic debugging directives for the ARM devices.
SPRAAB5 — The Impact of DWARF on TI Object Files. Describes the Texas Instruments extensions to
the DWARF specification.
SPRUEX3— TI SYS/BIOS Real-time Operating System User's Guide. SYS/BIOS gives application
developers the ability to develop embedded real-time software. SYS/BIOS is a scalable real-time
kernel. It is designed to be used by applications that require real-time scheduling and
synchronization or real-time instrumentation. SYS/BIOS provides preemptive multithreading,
hardware abstraction, real-time analysis, and configuration tools.
Trademarks
Code Composer Studio is a trademark of Texas Instruments.
ARM is a registered trademark of ARM Limited.
All other trademarks are the property of their respective owners.
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11
Chapter 1
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Introduction to the Software Development Tools
The ARM® is supported by a set of software development tools, which includes an optimizing C/C++
compiler, an assembler, a linker, and assorted utilities.
This chapter provides an overview of these tools and introduces the features of the optimizing C/C++
compiler. The assembler and linker are discussed in detail in the ARM Assembly Language Tools User's
Guide.
Topic
1.1
1.2
1.3
1.4
1.5
12
...........................................................................................................................
Software Development Tools Overview .................................................................
Compiler Interface ..............................................................................................
ANSI/ISO Standard .............................................................................................
Output Files .......................................................................................................
Utilities .............................................................................................................
Introduction to the Software Development Tools
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1.1
Software Development Tools Overview
Figure 1-1 illustrates the software development flow. The shaded portion of the figure highlights the most
common path of software development for C language programs. The other portions are peripheral
functions that enhance the development process.
Figure 1-1. ARM Software Development Flow
C/C++
source
files
Macro
source
files
C/C++
compiler
Archiver
Assembler
source
Macro
library
Assembler
Archiver
Object
files
Library of
object
files
Linker
C/C++ name
demangling
utility
Library-build
utility
Debugging
tools
Run-timesupport
library
Executable
object file
Hex-conversion
utility
EPROM
programmer
Absolute lister
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lister
Object file
utilities
ARM
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Software Development Tools Overview
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The following list describes the tools that are shown in Figure 1-1:
• The compiler accepts C/C++ source code and produces ARM assembly language source code. See
Chapter 2.
• The assembler translates assembly language source files into machine language relocatable object
files. See the ARM Assembly Language Tools User's Guide.
• The linker combines relocatable object files into a single absolute executable object file. As it creates
the executable file, it performs relocation and resolves external references. The linker accepts
relocatable object files and object libraries as input. See Chapter 4 for an overview of the linker. See
the ARM Assembly Language Tools User's Guide for details.
• The archiver allows you to collect a group of files into a single archive file, called a library. The
archiver allows you to modify such libraries by deleting, replacing, extracting, or adding members. One
of the most useful applications of the archiver is building a library of object files. See the ARM
Assembly Language Tools User's Guide.
• The run-time-support libraries contain the standard ISO C and C++ library functions, compiler-utility
functions, floating-point arithmetic functions, and C I/O functions that are supported by the compiler.
See Chapter 7.
The library-build utility automatically builds the run-time-support library if compiler and linker options
require a custom version of the library. See Section 7.4. Source code for the standard run-time-support
library functions for C and C++ is provided in the lib\src subdirectory of the directory where the
compiler is installed.
• The hex conversion utility converts an object file into other object formats. You can download the
converted file to an EPROM programmer. See the ARM Assembly Language Tools User's Guide.
• The absolute lister accepts linked object files as input and creates .abs files as output. You can
assemble these .abs files to produce a listing that contains absolute, rather than relative, addresses.
Without the absolute lister, producing such a listing would be tedious and would require many manual
operations. See the ARM Assembly Language Tools User's Guide.
• The cross-reference lister uses object files to produce a cross-reference listing showing symbols,
their definitions, and their references in the linked source files. See the ARM Assembly Language
Tools User's Guide.
• The C++ name demangler is a debugging aid that converts names mangled by the compiler back to
their original names as declared in the C++ source code. As shown in Figure 1-1, you can use the C++
name demangler on the assembly file that is output by the compiler; you can also use this utility on the
assembler listing file and the linker map file. See Chapter 8.
• The disassembler decodes object files to show the assembly instructions that they represent. See the
ARM Assembly Language Tools User's Guide.
• The main product of this development process is an executable object file that can be executed on a
ARM device.
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Compiler Interface
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1.2
Compiler Interface
The compiler is a command-line program named armcl. This program can compile, optimize, assemble,
and link programs in a single step. Within Code Composer Studio™, the compiler is run automatically to
perform the steps needed to build a project.
For more information about compiling a program, see Section 2.1
The compiler has straightforward calling conventions, so you can write assembly and C functions that call
each other. For more information about calling conventions, see Chapter 6.
1.3
ANSI/ISO Standard
The compiler supports the 1989, 1999, and 2011 versions of the C language and the 2014 version of the
C++ language. The C and C++ language features in the compiler are implemented in conformance with
the following ISO standards:
• ISO-standard C
The C compiler supports the 1989, 1999, and 2011 versions of the C language.
– C89. Compiling with the --c89 option causes the compiler to conform to the ISO/IEC 9899:1990 C
standard, which was previously ratified as ANSI X3.159-1989. The names "C89" and "C90" refer to
the same programming language. "C89" is used in this document.
– C99. Compiling with the --c99 option causes the compiler to conform to the ISO/IEC 9899:1999 C
standard.
– C11. Compiling with the --c11 option causes the compiler to conform to the ISO/IEC 9899:2011 C
standard.
The C language is also described in the second edition of Kernighan and Ritchie's The C Programming
Language (K&R).
• ISO-standard C++
The compiler uses the C++14 version of the C++ standard. Previously, C++03 was used. See the C++
Standard ISO/IEC 14882:2014. For a description of unsupported C++ features, see Section 5.2.
• ISO-standard run-time support
The compiler tools come with an extensive run-time library. Library functions conform to the ISO C/C++
library standard unless otherwise stated. The library includes functions for standard input and output,
string manipulation, dynamic memory allocation, data conversion, timekeeping, trigonometry, and
exponential and hyperbolic functions. Functions for signal handling are not included, because these
are target-system specific. For more information, see Chapter 7.
See Section 5.16 for command line options to select the C or C++ standard your code uses.
1.4
Output Files
The following types of output files are created by the compiler:
• ELF object files. Executable and Linking Format (ELF) enables supporting modern language features
like early template instantiation and exporting inline functions. The ELF format for ARM is part of the
Application Binary Interface (ABI) specification, which is documented in the ARM Infocenter.
COFF object files and the legacy TIABI and TI ARM9 ABI modes are not supported in v15.6.0.STS and
later versions of the TI Code Generation Tools. If you would like to produce COFF output files, please use
v5.2 of the ARM Code Generation Tools and refer to SPNU151J for documentation.
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Utilities
1.5
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Utilities
These features are compiler utilities:
• Library-build utility
The library-build utility lets you custom-build object libraries from source for any combination of runtime models. For more information, see Section 7.4.
• C++ name demangler
The C++ name demangler (armdem) is a debugging aid that translates each mangled name it detects
in compiler-generated assembly code, disassembly output, or compiler diagnostic messages to its
original name found in the C++ source code. For more information, see Chapter 8.
• Hex conversion utility
For stand-alone embedded applications, the compiler has the ability to place all code and initialization
data into ROM, allowing C/C++ code to run from reset. The ELF files output by the compiler can be
converted to EPROM programmer data files by using the hex conversion utility, as described in the
ARM Assembly Language Tools User's Guide.
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Chapter 2
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Using the C/C++ Compiler
The compiler translates your source program into machine language object code that the ARM can
execute. Source code must be compiled, assembled, and linked to create an executable file. All of these
steps are executed at once by using the compiler.
Topic
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
2.14
2.15
...........................................................................................................................
About the Compiler ............................................................................................
Invoking the C/C++ Compiler ...............................................................................
Changing the Compiler's Behavior with Options ....................................................
Controlling the Compiler Through Environment Variables ......................................
Controlling the Preprocessor ...............................................................................
Passing Arguments to main() ..............................................................................
Understanding Diagnostic Messages ....................................................................
Other Messages .................................................................................................
Generating Cross-Reference Listing Information (--gen_cross_reference Option) ......
Generating a Raw Listing File (--gen_preprocessor_listing Option) ..........................
Using Inline Function Expansion..........................................................................
Using Interlist ....................................................................................................
Controlling Application Binary Interface ...............................................................
VFP Support ......................................................................................................
Enabling Entry Hook and Exit Hook Functions ......................................................
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44
44
47
47
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49
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53
54
55
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About the Compiler
2.1
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About the Compiler
The compiler lets you compile, optimize, assemble, and optionally link in one step. The compiler performs
the following steps on one or more source modules:
• The compiler accepts C/C++ source code and assembly code. It produces object code.
You can compile C, C++, and assembly files in a single command. The compiler uses the filename
extensions to distinguish between different file types. See Section 2.3.9 for more information.
• The linker combines object files to create an executable or relinkablean executable file. The link step
is optional, so you can compile and assemble many modules independently and link them later. See
Chapter 4 for information about linking the files.
Invoking the Linker
NOTE: By default, the compiler does not invoke the linker. You can invoke the linker by using the -run_linker (-z)compiler option. See Section 4.1.1 for details.
For a complete description of the assembler and the linker, see the ARM Assembly Language Tools
User's Guide.
2.2
Invoking the C/C++ Compiler
To invoke the compiler, enter:
armcl [options] [filenames] [--run_linker [link_options] object files]]
armcl
options
filenames
--run_linker (-z)
link_options
object files
Command that runs the compiler and the assembler.
Options that affect the way the compiler processes input files. The options are listed
in Table 2-7 through Table 2-29.
One or more C/C++ source files and assembly language source files.
Option that invokes the linker. The --run_linker option's short form is -z. See
Chapter 4 for more information.
Options that control the linking process.
Names of the object files for the linking process.
The arguments to the compiler are of three types:
• Compiler options
• Link options
• Filenames
The --run_linker option indicates linking is to be performed. If the --run_linker option is used, any compiler
options must precede the --run_linker option, and all link options must follow the --run_linker option.
Source code filenames must be placed before the --run_linker option. Additional object file filenames can
be placed after the --run_linker option.
For example, if you want to compile two files named symtab.c and file.c, assemble a third file named
seek.asm, and link to create an executable program called myprogram.out, you will enter:
armcl symtab.c file.c seek.asm --run_linker --library=lnk.cmd
--output_file=myprogram.out
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2.3
Changing the Compiler's Behavior with Options
Options control the operation of the compiler. This section provides a description of option conventions
and an option summary table. It also provides detailed descriptions of the most frequently used options,
including options used for type-checking and assembling.
For a help screen summary of the options, enter armcl with no parameters on the command line.
The following apply to the compiler options:
• There are typically two ways of specifying a given option. The "long form" uses a two hyphen prefix
and is usually a more descriptive name. The "short form" uses a single hyphen prefix and a
combination of letters and numbers that are not always intuitive.
• Options are usually case sensitive.
• Individual options cannot be combined.
• An option with a parameter should be specified with an equal sign before the parameter to clearly
associate the parameter with the option. For example, the option to undefine a constant can be
expressed as --undefine=name. Likewise, the option to specify the maximum amount of optimization
can be expressed as -O=3. You can also specify a parameter directly after certain options, for example
-O3 is the same as -O=3. No space is allowed between the option and the optional parameter, so -O 3
is not accepted.
• Files and options except the --run_linker option can occur in any order. The --run_linker option must
follow all compiler options and precede any linker options.
You can define default options for the compiler by using the TI_ARM_C_OPTION environment variable.
For a detailed description of the environment variable, see Section 2.4.1.
Table 2-7 through Table 2-29 summarize all options (including link options). Use the references in the
tables for more complete descriptions of the options.
Table 2-1. Processor Options
Option
Alias
Effect
Section
--silicon_version={ 4 | 5e | 6 | 6M0 |
7A8 | 7M3 | 7M4 | 7R4 | 7R5 }
-mv
Selects processor version: ARM V4 (ARM7), ARM V5e (ARM9E),
Section 2.3.4
ARM V6 (ARM11), ARM V6M0 (Cortex-M0), ARM V7A8 (Cortex-A8),
ARM V7M3 (Cortex-M3), ARM V7M4 (Cortex-M4), ARM V7R4
(Cortex-R4), or ARM V7R5 (Cortex-R5). The default is ARM V4.
--code_state={ 16 | 32 }
Designates the ARM compilation mode.
Section 2.3.4
--float_support={ vfpv2 | vfpv3 |
vfpv3d16 | fpv4spd16 | none )
Generates vector floating-point (VFP) coprocessor instructions.
Section 2.14
Designates little-endian code. The default is big-endian.
Section 2.3.4
--little_endian or --endian={ big |
little }
-me
Table 2-2. Optimization Options (1)
Option
Alias
--opt_level=off
Effect
Section
Disables all optimization.
Section 3.1
--opt_level=n
-On
Level 0 (-O0) optimizes register usage only.
Level 1 (-O1) uses Level 0 optimizations and optimizes locally.
Level 2 (-O2) uses Level 1 optimizations and optimizes globally.
Level 3 (-O3) uses Level 2 optimizations and optimizes the file
(default if option not used).
Level 4 (-O4) uses Level 3 optimizations and performs link-time
optimization.
Section 3.1,
Section 3.3,
Section 3.6
--opt_for_speed[=n]
-mf
Controls the tradeoff between size and speed (0-5 range). If this
option is specified without n, the default value is 4. If this option is
not specified, the default setting is 1.
Section 3.2
(1)
Note: Machine-specific options (see Table 2-13) can also affect optimization.
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Table 2-3. Advanced Optimization Options
(1)
Option
Alias
Effect
Section
--auto_inline=[size]
-oi
Sets automatic inlining size (--opt_level=3 only). If size is not
specified, the default is 1.
Section 3.5
--call_assumptions=n
-opn
Level 0 (-op0) specifies that the module contains functions and
Section 3.4.1
variables that are called or modified from outside the source code
provided to the compiler.
Level 1 (-op1) specifies that the module contains variables modified
from outside the source code provided to the compiler but does not
use functions called from outside the source code.
Level 2 (-op2) specifies that the module contains no functions or
variables that are called or modified from outside the source code
provided to the compiler (default).
Level 3 (-op3) specifies that the module contains functions that are
called from outside the source code provided to the compiler but
does not use variables modified from outside the source code.
--disable_inlining
Prevents any inlining from occurring.
Section 2.11
--fp_mode={relaxed|strict}
Enables or disables relaxed floating-point mode.
Section 2.3.3
--fp_reassoc={on|off}
Enables or disables the reassociation of floating-point arithmetic.
Section 2.3.3
--gen_opt_info=n
-onn
Level 0 (-on0) disables the optimization information file.
Level 1 (-on2) produces an optimization information file.
Level 2 (-on2) produces a verbose optimization information file.
Section 3.3.1
--optimizer_interlist
-os
Interlists optimizer comments with assembly statements.
Section 3.11
--program_level_compile
-pm
Combines source files to perform program-level optimization.
Section 3.4
Enables or disables the reassociation of saturating arithmetic.
Default is --sat_reassoc=off.
Section 2.3.3
Indicates that a specific aliasing technique is used.
Section 3.9
--sat_reassoc={on|off}
--aliased_variables
(1)
-ma
Note: Machine-specific options (see Table 2-13) can also affect optimization.
Table 2-4. Debug Options
Option
Alias
Effect
Section
--symdebug:dwarf
-g
Default behavior. Enables symbolic debugging. The generation of
debug information does not impact optimization. Therefore,
generating debug information is enabled by default.
Section 2.3.5
Section 3.12
--symdebug:dwarf_version=2|3|4
Specifies the DWARF format version.
Section 2.3.5
--symdebug:none
Disables all symbolic debugging.
Section 2.3.5
Section 3.12
--symdebug:skeletal
(Deprecated; has no effect.)
Table 2-5. Include Options
Option
Alias
Effect
Section
--include_path=directory
-I
Adds the specified directory to the #include search path.
Section 2.5.2.1
Includes filename at the beginning of compilation.
Section 2.3.3
--preinclude=filename
Table 2-6. ULP Advisor Options
Option
Effect
Section
--advice:power[={all|none|rulespec}]
Enables checking the specified ULP Advisor rules. (Default is all.)
Section 2.3.3
--advice:power_severity={error|
warning|remark|suppress}
Sets the diagnostic severity for ULP Advisor rules.
Section 2.3.3
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Table 2-7. Control Options
Option
Alias
Effect
Section
--compile_only
-c
Disables linking (negates --run_linker).
Section 4.1.3
--help
-h
Prints (on the standard output device) a description of the options
understood by the compiler.
Section 2.3.2
--run_linker
-z
Causes the linker to be invoked from the compiler command line.
Section 2.3.2
--skip_assembler
-n
Compiles C/C++ source file, producing an assembly language output Section 2.3.2
file. The assembler is not run and no object file is produced.
Table 2-8. Language Options
Option
Effect
Section
--c89
Processes C files according to the ISO C89 standard.
Section 5.16
--c99
Processes C files according to the ISO C99 standard.
Section 5.16
--c11
Processes C files according to the ISO C11 standard.
Section 5.16
--c++14
Processes C++ files according to the ISO C++14 standard.
The --c++03 option has been deprecated.
Section 5.16
--cpp_default
Alias
Processes all source files with a C extension as C++ source files.
Section 2.3.7
--enum_type={int|packed}
Designates the underlying type of an enumeration type.
Section 2.3.4
--exceptions
Enables C++ exception handling.
Section 5.8
--extern_c_can_throw
Allow extern C functions to propagate exceptions.
--
--float_operations_allowed
={none|all|32|64}
Restricts the types of floating point operations allowed.
Section 2.3.3
Generates a cross-reference listing file (.crl).
Section 2.9
Specify the number of template instantiations that may be in
progress at any given time. Use 0 to specify an unlimited number.
Section 2.3.4
Specifies how to treat plain chars, default is unsigned.
Section 2.3.4
Enables support for smaller, limited versions of the printf function
family (sprintf, fprintf, etc.) and the scanf function family (sscanf,
fscanf, etc.) run-time-support functions.
Section 2.3.3
--gen_cross_reference
-fg
-px
--pending_instantiations=#
--plain_char={signed|unsigned}
-mc
--printf_support={nofloat|full|
minimal}
--relaxed_ansi
-pr
Enables relaxed mode; ignores strict ISO violations. This is on by
default. To disable this mode, use the --strict_ansi option.
Section 5.16.3
--rtti
-rtti
Enables C++ run-time type information (RTTI).
–-
--strict_ansi
-ps
Enables strict ANSI/ISO mode (for C/C++, not for K&R C). In this
mode, language extensions that conflict with ANSI/ISO C/C++ are
disabled. In strict ANSI/ISO mode, most ANSI/ISO violations are
reported as errors. Violations that are considered discretionary may
be reported as warnings instead.
Section 5.16.3
Sets the size of the C/C++ type wchar_t. Default is 16 bits.
Section 2.3.4
--wchar_t={32|16}
Table 2-9. Parser Preprocessing Options
Option
Alias
Effect
Section
--preproc_dependency[=filename]
-ppd
Performs preprocessing only, but instead of writing preprocessed
output, writes a list of dependency lines suitable for input to a
standard make utility.
Section 2.5.8
--preproc_includes[=filename]
-ppi
Performs preprocessing only, but instead of writing preprocessed
output, writes a list of files included with the #include directive.
Section 2.5.9
--preproc_macros[=filename]
-ppm
Performs preprocessing only. Writes list of predefined and userdefined macros to a file with the same name as the input but with a
.pp extension.
Section 2.5.10
--preproc_only
-ppo
Performs preprocessing only. Writes preprocessed output to a file
with the same name as the input but with a .pp extension.
Section 2.5.4
--preproc_with_comment
-ppc
Performs preprocessing only. Writes preprocessed output, keeping
the comments, to a file with the same name as the input but with a
.pp extension.
Section 2.5.6
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Table 2-9. Parser Preprocessing Options (continued)
Option
Alias
Effect
Section
--preproc_with_compile
-ppa
Continues compilation after preprocessing with any of the -pp<x>
options that normally disable compilation.
Section 2.5.5
--preproc_with_line
-ppl
Performs preprocessing only. Writes preprocessed output with linecontrol information (#line directives) to a file with the same name as
the input but with a .pp extension.
Section 2.5.7
Table 2-10. Predefined Macro Options
Option
Alias
Effect
Section
--define=name[=def]
-D
Predefines name.
Section 2.3.2
--undefine=name
-U
Undefines name.
Section 2.3.2
Table 2-11. Diagnostic Message Options
Option
Alias
--compiler_revision
Effect
Section
Prints out the compiler release revision and exits.
--
--diag_error=num
-pdse
Categorizes the diagnostic identified by num as an error.
Section 2.7.1
--diag_remark=num
-pdsr
Categorizes the diagnostic identified by num as a remark.
Section 2.7.1
--diag_suppress=num
-pds
Suppresses the diagnostic identified by num.
Section 2.7.1
--diag_warning=num
-pdsw
Categorizes the diagnostic identified by num as a warning.
Section 2.7.1
--diag_wrap={on|off}
Wrap diagnostic messages (default is on). Note that this commandline option cannot be used within the Code Composer Studio IDE.
--display_error_number
-pden
Displays a diagnostic's identifiers along with its text. Note that this
command-line option cannot be used within the Code Composer
Studio IDE.
Section 2.7.1
--emit_warnings_as_errors
-pdew
Treat warnings as errors.
Section 2.7.1
Generate user information file (.aux).
Section 2.3.2
--gen_func_info_listing
--issue_remarks
-pdr
Issues remarks (non-serious warnings).
Section 2.7.1
--no_warnings
-pdw
Suppresses diagnostic warnings (errors are still issued).
Section 2.7.1
--quiet
-q
Suppresses progress messages (quiet).
--
--set_error_limit=num
-pdel
Sets the error limit to num. The compiler abandons compiling after
this number of errors. (The default is 100.)
Section 2.7.1
--super_quiet
-qq
Super quiet mode.
--
--tool_version
-version
Displays version number for each tool.
--
--verbose
Display banner and function progress information.
--
--verbose_diagnostics
-pdv
Provides verbose diagnostic messages that display the original
source with line-wrap. Note that this command-line option cannot be
used within the Code Composer Studio IDE.
Section 2.7.1
--write_diagnostics_file
-pdf
Generates a diagnostic message information file. Compiler only
Section 2.7.1
option. Note that this command-line option cannot be used within the
Code Composer Studio IDE.
Table 2-12. Supplemental Information Options
Option
Alias
Effect
Section
--gen_preprocessor_listing
-pl
Generates a raw listing file (.rl).
Section 2.10
Generates section size information, including sizes for sections
containing executable code and constants, constant or initialized
data (global and static variables), and uninitialized data. (Default is
off if this option is not included on the command line. Default is on if
this option is used with no value specified.)
Section 2.7.1
--section_sizes={on|off}
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Table 2-13. Run-Time Model Options
Option
Alias
Effect
Section
--common={on|off}
On by default. When on, uninitialized file scope variables are emitted Section 2.3.4
as common symbols. When off, common symbols are not created.
--embedded_constants={on|off}
Controls whether compiler embeds constants in functions.
Section 2.3.4
--gen_data_subsections={on|off}
Place all aggregate data (arrays, structs, and unions) into
subsections. This gives the linker more control over removing
unused data during the final link step. The default is on.
Section 4.2.2
--global_register={r5|r6|r9}
Disallows use of rx=[5,6,9] by the compiler.
Section 2.3.4
-neon
-rr
Enables support for the Cortex-A8 Neon SIMD instruction set.
Section 2.3.4
--ramfunc={on|off}
If set to on, specifies that all functions should be placed in the
.TI.ramfunc section, which is placed in RAM.
Section 2.3.4
--unaligned_access={on|off}
Controls generation of unaligned accesses.
Section 2.3.4
--use_dead_funcs_list [=fname]
Places each function listed in the file in a separate section.
Section 2.3.4
Table 2-14. Entry/Exit Hook Options
Option
Effect
Section
--entry_hook[=name]
Alias
Enables entry hooks.
Section 2.15
--entry_parm={none|name|
address}
Specifies the parameters to the function to the --entry_hook option.
Section 2.15
--exit_hook[=name]
Enables exit hooks.
Section 2.15
--exit_parm={none|name|address}
Specifies the parameters to the function to the --exit_hook option.
Section 2.15
--remove_hooks_when_inlining
Removes entry/exit hooks for auto-inlined functions.
Section 2.15
Table 2-15. Feedback Options
Option
Effect
Section
--analyze=codecov
Alias
Generate analysis info from profile data.
Section 3.8.2.2
--analyze_only
Only generate analysis.
Section 3.8.2.2
--gen_profile_info
Generates instrumentation code to collect profile information.
Section 3.7.1.3
--use_profile_info=file1[, file2,...]
Specifies the profile information file(s).
Section 3.7.1.3
Table 2-16. Assembler Options
Option
Alias
Effect
Section
--keep_asm
-k
Keeps the assembly language (.asm) file.
Section 2.3.11
--asm_listing
-al
Generates an assembly listing file.
Section 2.3.11
--c_src_interlist
-ss
Interlists C source and assembly statements.
Section 2.12
Section 3.11
--src_interlist
-s
Interlists optimizer comments (if available) and assembly source
statements; otherwise interlists C and assembly source statements.
Section 2.3.2
--absolute_listing
-aa
Enables absolute listing.
Section 2.3.11
--asm_define=name[=def]
-ad
Sets the name symbol.
Section 2.3.11
--asm_dependency
-apd
Performs preprocessing; lists only assembly dependencies.
Section 2.3.11
--asm_includes
-api
Performs preprocessing; lists only included #include files.
Section 2.3.11
--asm_undefine=name
-au
Undefines the predefined constant name.
Section 2.3.11
Begins assembling instructions as 16- or 32-bit instructions.
Section 2.3.11
--code_state={16|32}
--asm_listing_cross_reference
-ax
Generates the cross-reference file.
Section 2.3.11
--include_file=filename
-ahi
Includes the specified file for the assembly module.
Section 2.3.11
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Table 2-17. File Type Specifier Options
Option
Alias
Effect
Section
--asm_file=filename
-fa
Identifies filename as an assembly source file regardless of its
extension. By default, the compiler and assembler treat .asm files as
assembly source files.
Section 2.3.7
--c_file=filename
-fc
Identifies filename as a C source file regardless of its extension. By
default, the compiler treats .c files as C source files.
Section 2.3.7
--cpp_file=filename
-fp
Identifies filename as a C++ file, regardless of its extension. By
default, the compiler treats .C, .cpp, .cc and .cxx files as a C++ files.
Section 2.3.7
--obj_file=filename
-fo
Identifies filename as an object code file regardless of its extension. Section 2.3.7
By default, the compiler and linker treat .obj files as object code files,
including both *.c.obj and *.cpp.obj files.
Table 2-18. Directory Specifier Options
Option
Alias
Effect
--abs_directory=directory
-fb
Specifies an absolute listing file directory. By default, the compiler
uses the object file directory.
Section 2.3.10
--asm_directory=directory
-fs
Specifies an assembly file directory. By default, the compiler uses
the current directory.
Section 2.3.10
--list_directory=directory
-ff
Specifies an assembly listing file and cross-reference listing file
directory By default, the compiler uses the object file directory.
Section 2.3.10
--obj_directory=directory
-fr
Specifies an object file directory. By default, the compiler uses the
current directory.
Section 2.3.10
--output_file=filename
-fe
Specifies a compilation output file name; can override -obj_directory.
Section 2.3.10
Specifies a preprocessor file directory. By default, the compiler uses
the current directory.
Section 2.3.10
--pp_directory=dir
--temp_directory=directory
-ft
Section
Specifies a temporary file directory. By default, the compiler uses the Section 2.3.10
current directory.
Table 2-19. Default File Extensions Options
Option
Alias
Effect
Section
--asm_extension=[.]extension
-ea
Sets a default extension for assembly source files.
Section 2.3.9
--c_extension=[.]extension
-ec
Sets a default extension for C source files.
Section 2.3.9
--cpp_extension=[.]extension
-ep
Sets a default extension for C++ source files.
Section 2.3.9
--listing_extension=[.]extension
-es
Sets a default extension for listing files.
Section 2.3.9
--obj_extension=[.]extension
-eo
Sets a default extension for object files.
Section 2.3.9
Table 2-20. Command Files Options
Option
Alias
Effect
Section
--cmd_file=filename
-@
Interprets contents of a file as an extension to the command line.
Multiple -@ instances can be used.
Section 2.3.2
Table 2-21. MISRA-C 2004 Options
Option
Effect
Section
--check_misra[={all|required|
advisory|none|rulespec}]
Enables checking of the specified MISRA-C:2004 rules. Default is
all.
Section 2.3.3
--misra_advisory={error|warning|
remark|suppress}
Sets the diagnostic severity for advisory MISRA-C:2004 rules.
Section 2.3.3
--misra_required={error|warning|
remark|suppress}
Sets the diagnostic severity for required MISRA-C:2004 rules.
Section 2.3.3
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2.3.1 Linker Options
The following tables list the linker options. See Chapter 4 of this document and the ARM Assembly
Language Tools User's Guide for details on these options.
Table 2-22. Linker Basic Options
Option
Alias
Description
--run_linker
-z
Enables linking.
--output_file=file
-o
Names the executable output file. The default filename is a .out file.
--map_file=file
-m
Produces a map or listing of the input and output sections, including holes, and places
the listing in file.
--stack_size=size
[-]-stack
Sets C system stack size to size bytes and defines a global symbol that specifies the
stack size. Default = 2K bytes.
--heap_size=size
[-]-heap
Sets heap size (for the dynamic memory allocation in C) to size bytes and defines a
global symbol that specifies the heap size. Default = 2K bytes.
Table 2-23. File Search Path Options
Option
Alias
Description
--library=file
-l
Names an archive library or link command file as linker input.
--disable_auto_rts
Disables the automatic selection of a run-time-support library. See Section 4.3.1.1.
--priority
-priority
Satisfies unresolved references by the first library that contains a definition for that
symbol.
--reread_libs
-x
Forces rereading of libraries, which resolves back references.
--search_path=pathname
-I
Alters library-search algorithms to look in a directory named with pathname before
looking in the default location. This option must appear before the --library option.
Table 2-24. Command File Preprocessing Options
Option
Alias
Description
--define=name=value
Predefines name as a preprocessor macro.
--undefine=name
Removes the preprocessor macro name.
--disable_pp
Disables preprocessing for command files.
Table 2-25. Diagnostic Message Options
Option
Alias
Description
--diag_error=num
Categorizes the diagnostic identified by num as an error.
--diag_remark=num
Categorizes the diagnostic identified by num as a remark.
--diag_suppress=num
Suppresses the diagnostic identified by num.
--diag_warning=num
Categorizes the diagnostic identified by num as a warning.
--display_error_number
Displays a diagnostic's identifiers along with its text.
--emit_references:file[=file]
Emits a file containing section information. The information includes section size,
symbols defined, and references to symbols.
--emit_warnings_as_errors
-pdew
Treat warnings as errors.
--issue_remarks
Issues remarks (non-serious warnings).
--no_demangle
Disables demangling of symbol names in diagnostic messages.
--no_warnings
Suppresses diagnostic warnings (errors are still issued).
--set_error_limit=count
Sets the error limit to count. The linker abandons linking after this number of errors. (The
default is 100.)
--verbose_diagnostics
--warn_sections
Provides verbose diagnostic messages that display the original source with line-wrap.
-w
Displays a message when an undefined output section is created.
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Table 2-26. Linker Output Options
Option
Alias
Description
--absolute_exe
-a
Produces an absolute, executable object file. This is the default; if neither --absolute_exe
nor --relocatable is specified, the linker acts as if --absolute_exe were specified.
--ecc={ on | off }
Enable linker-generated Error Correcting Codes (ECC). The default is off.
--ecc:data_error
Inject specified errors into the output file for testing.
--ecc:ecc_error
Inject specified errors into the Error Correcting Code (ECC) for testing.
--generate_dead_funcs_list
Writes a list of the dead functions that were removed by the linker to file fname.
--mapfile_contents=attribute
--relocatable
Controls the information that appears in the map file.
-r
Produces a nonexecutable, relocatable output object file.
--rom
Creates a ROM object.
--run_abs
-abs
Produces an absolute listing file.
--xml_link_info=file
Generates a well-formed XML file containing detailed information about the result of a
link.
Table 2-27. Symbol Management Options
Option
Alias
Description
--entry_point=symbol
-e
Defines a global symbol that specifies the primary entry point for the executable object
file.
--globalize=pattern
Changes the symbol linkage to global for symbols that match pattern.
--hide=pattern
Hides symbols that match the specified pattern.
--localize=pattern
Make the symbols that match the specified pattern local.
--make_global=symbol
-g
Makes symbol global (overrides -h).
--make_static
-h
Makes all global symbols static.
--no_symtable
-s
Strips symbol table information and line number entries from the executable object file.
--retain
Retains a list of sections that otherwise would be discarded.
--scan_libraries
-scanlibs
--symbol_map=refname=defname
--undef_sym=symbol
Scans all libraries for duplicate symbol definitions.
Specifies a symbol mapping; references to the refname symbol are replaced with
references to the defname symbol. The --symbol_map option is supported when used
with --opt_level=4.
-u
Adds symbol to the symbol table as an unresolved symbol.
--unhide=pattern
Excludes symbols that match the specified pattern from being hidden.
Table 2-28. Run-Time Environment Options
Option
Alias
Description
--arg_size=size
--args
Reserve size bytes for the argc/argv memory area.
--cinit_hold_wdt={on|off}
Link in an RTS auto-initialization routine that either holds (on) or does not hold (off) the
watchdog timer during cinit auto-initialization. See Section 4.3.3.
-be32
Forces the linker to generate BE-32 object code.
-be8
Forces the linker to generate BE-8 object code.
--cinit_compression[=type]
Specifies the type of compression to apply to the C auto initialization data. The default if
this option is specified with no type is lzss for Lempel-Ziv-Storer-Szymanski
compression.
--copy_compression[=type]
Compresses data copied by linker copy tables. The default if this option is specified with
no type is lzss for Lempel-Ziv-Storer-Szymanski compression.
--fill_value=value
-f
Sets default fill value for holes within output sections
--ram_model
-cr
Initializes variables at load time.
--rom_model
-c
Autoinitializes variables at run time.
--trampolines[=off|on]
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Generates far call trampolines (argument is optional, is "on" by default).
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Table 2-29. Miscellaneous Options
Option
Alias
Description
--compress_dwarf[=off|on]
--linker_help
Aggressively reduces the size of DWARF information from input object files. Default is
on.
[-]-help
Displays information about syntax and available options.
--minimize_trampolines
Places sections to minimize number of far trampolines required.
--preferred_order=function
Prioritizes placement of functions.
--strict_compatibility[=off|on]
Performs more conservative and rigorous compatibility checking of input object files.
Default is on.
--trampoline_min_spacing
When trampoline reservations are spaced more closely than the specified limit, tries to
make them adjacent.
--unused_section_elimination[=off|on]
Eliminates sections that are not needed in the executable module. Default is on.
--zero_init=[off|on]
Controls preinitialization of uninitialized variables. Default is on.
2.3.2 Frequently Used Options
Following are detailed descriptions of options that you will probably use frequently:
--c_src_interlist
Invokes the interlist feature, which interweaves original C/C++ source
with compiler-generated assembly language. The interlisted C
statements may appear to be out of sequence. You can use the interlist
feature with the optimizer by combining the --optimizer_interlist and -c_src_interlist options. See Section 3.11. The --c_src_interlist option can
have a negative performance and/or code size impact.
Appends the contents of a file to the option set. You can use this option
to avoid limitations on command line length or C style comments
imposed by the host operating system. Use a # or ; at the beginning of a
line in the command file to include comments. You can also include
comments by delimiting them with /* and */. To specify options, surround
hyphens with quotation marks. For example, "--"quiet.
You can use the --cmd_file option multiple times to specify multiple files.
For instance, the following indicates that file3 should be compiled as
source and file1 and file2 are --cmd_file files:
--cmd_file=filename
armcl --cmd_file=file1 --cmd_file=file2 file3
--compile_only
Suppresses the linker and overrides the --run_linker option, which
specifies linking. The --compile_only option's short form is -c. Use this
option when you have --run_linker specified in the TI_ARM_C_OPTION
environment variable and you do not want to link. See Section 4.1.3.
Predefines the constant name for the preprocessor. This is equivalent to
inserting #define name def at the top of each C source file. If the
optional[=def] is omitted, the name is set to 1. The --define option's short
form is -D.
If you want to define a quoted string and keep the quotation marks, do
one of the following:
--define=name[=def]
•
For Windows, use --define=name="\"string def\"". For example, -define=car="\"sedan\""
• For UNIX, use --define=name='"string def"'. For example, -define=car='"sedan"'
• For Code Composer Studio, enter the definition in a file and include
that file with the --cmd_file option.
Generates a user information file with a .aux file extension. The file
contains linker call graph information on a per-file level.
--gen_func_info_listing
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--help
--include_path=directory
--keep_asm
--quiet
--run_linker
--skip_assembler
--src_interlist
--tool_version
--undefine=name
--verbose
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Displays the syntax for invoking the compiler and lists available options.
If the --help option is followed by another option or phrase, detailed
information about the option or phrase is displayed. For example, to see
information about debugging options use --help debug.
Adds directory to the list of directories that the compiler searches for
#include files. The --include_path option's short form is -I. You can use
this option several times to define several directories; be sure to
separate the --include_path options with spaces. If you do not specify a
directory name, the preprocessor ignores the --include_path option. See
Section 2.5.2.1.
Retains the assembly language output from the compiler or assembly
optimizer. Normally, the compiler deletes the output assembly language
file after assembly is complete. The --keep_asm option's short form is -k.
Suppresses banners and progress information from all the tools. Only
source filenames and error messages are output. The --quiet option's
short form is -q.
Runs the linker on the specified object files. The --run_linker option and
its parameters follow all other options on the command line. All
arguments that follow --run_linker are passed to the linker. The -run_linker option's short form is -z. See Section 4.1.
Compiles only. The specified source files are compiled but not
assembled or linked. The --skip_assembler option's short form is -n. This
option overrides --run_linker. The output is assembly language output
from the compiler.
Invokes the interlist feature, which interweaves optimizer comments or
C/C++ source with assembly source. If the optimizer is invoked (-opt_level=n option), optimizer comments are interlisted with the
assembly language output of the compiler, which may rearrange code
significantly. If the optimizer is not invoked, C/C++ source statements are
interlisted with the assembly language output of the compiler, which
allows you to inspect the code generated for each C/C++ statement. The
--src_interlist option implies the --keep_asm option. The --src_interlist
option's short form is -s.
Prints the version number for each tool in the compiler. No compiling
occurs.
Undefines the predefined constant name. This option overrides any -define options for the specified constant. The --undefine option's short
form is -U.
Displays progress information and toolset version while compiling.
Resets the --quiet option.
2.3.3 Miscellaneous Useful Options
Following are detailed descriptions of miscellaneous options:
--advice:power={all|none|
rulespec}
Enables checking code against ULP (ultra low power) Advisor rules
for possible power inefficiencies. More detailed information can be
found at www.ti.com/ulpadvisor. The rulespec parameter is a commaseparated list of specifiers. See Section 5.4 for details.
--advice:power_severity={error| Sets the diagnostic severity for ULP Advisor rules.
warning|remark|suppress}
--check_misra={all|required|
Displays the specified amount or type of MISRA-C documentation.
advisory|none|rulespec}
This option must be used if you want to enable use of the
CHECK_MISRA and RESET_MISRA pragmas within the source
code. The rulespec parameter is a comma-separated list of specifiers.
See Section 5.3 for details.
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--float_operations_allowed=
{none|all|32|64}
--fp_mode={relaxed|strict}
--fp_reassoc={on|off}
--misra_advisory={error|
warning|remark|suppress}
--misra_required={error|
warning|remark|suppress}
--preinclude=filename
Restricts the type of floating point operations allowed in the
application. The default is all. If set to none, 32, or 64, the application
is checked for operations that will be performed at runtime. For
example, if --float_operations_allowed=32 is specified on the
command line, the compiler issues an error if a double precision
operation will be generated. This can be used to ensure that double
precision operations are not accidentally introduced into an
application. The checks are performed after relaxed mode
optimizations have been performed, so illegal operations that are
completely removed result in no diagnostic messages.
The default floating-point mode is strict. To enable relaxed floatingpoint mode use the --fp_mode=relaxed option. Relaxed floating-point
mode causes double-precision floating-point computations and
storage to be converted to single-precision floating-point or integers
where possible. This behavior does not conform with ISO, but it
results in faster code, with some loss in accuracy. The following
specific changes occur in relaxed mode:
• If the result of a double-precision floating-point expression is
assigned to a single-precision floating-point or an integer or
immediately used in a single-precision context, the computations in
the expression are converted to single-precision computations.
Double-precision constants in the expression are also converted to
single-precision if they can be correctly represented as singleprecision constants.
• Calls to double-precision functions in math.h are converted to their
single-precision counterparts if all arguments are single-precision
and the result is used in a single-precision context. The math.h
header file must be included for this optimization to work.
• Division by a constant is converted to inverse multiplication.
• Calls to sqrt, sqrtf, and sqrtl are converted directly to the VSQRT
instruction. In this case errno will not be set for negative inputs.
• Certain C standard float functions--such as sqrt, sin, cos, atan, and
atan2--are redirected to optimized inline functions where possible.
Enables or disables the reassociation of floating-point arithmetic. If -fp_mode=relaxed is specified, --fp_reassoc=on is set automatically. If
--strict_ansi is set, --fp_reassoc=off is set since reassociation of
floating-point arithmetic is an ANSI violation.
Because floating-point values are of limited precision, and because
floating-point operations round, floating-point arithmetic is neither
associative nor distributive. For instance, (1 + 3e100) - 3e100 is not
equal to 1 + (3e100 - 3e100). If strictly following IEEE 754, the
compiler cannot, in general, reassociate floating-point operations.
Using --fp_reassoc=on allows the compiler to perform the algebraic
reassociation, at the cost of a small amount of precision for some
operations.
Sets the diagnostic severity for advisory MISRA-C:2004 rules.
Sets the diagnostic severity for required MISRA-C:2004 rules.
Includes the source code of filename at the beginning of the
compilation. This can be used to establish standard macro definitions.
The filename is searched for in the directories on the include search
list. The files are processed in the order in which they were specified.
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--printf_support={full|
nofloat|minimal}
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Enables support for smaller, limited versions of the printf function
family (sprintf, fprintf, etc.) and the scanf function family (sscanf,
fscanf, etc.) run-time-support functions. The valid values are:
• full: Supports all format specifiers. This is the default.
• nofloat: Excludes support for printing and scanning floating-point
values. Supports all format specifiers except %a, %A, %f, %F, %g,
%G, %e, and %E.
• minimal: Supports the printing and scanning of integer, char, or
string values without width or precision flags. Specifically, only
the %%, %d, %o, %c, %s, and %x format specifiers are supported
There is no run-time error checking to detect if a format specifier is
used for which support is not included. The --printf_support option
precedes the --run_linker option, and must be used when performing
the final link.
Enables or disables the reassociation of saturating arithmetic.
--sat_reassoc={on|off}
2.3.4 Run-Time Model Options
These options are specific to the ARM toolset. See the referenced sections for more information. ARMspecific assembler options are listed in Section 2.3.11.
The ARM compiler now supports only the Embedded Application Binary Interface (EABI) ABI, which uses
the ELF object format and the DWARF debug format. If you want support for the legacy COFF ABI, please
use the ARM v5.2 Code Generation Tools and refer to SPNU151J and SPNU118J for documentation.
--code_state={16|32}
Generates 16-bit Thumb code. By default, 32-bit code is generated.
When Cortex-R4, Cortex-M0, Cortex-M3, or Cortex-A8 architecture
support is chosen, the --code_state option generates Thumb-2 code.
For details on indirect calls in 16-bit versus 32-bit code, see
Section 6.11.2.2.
--common={on|off}
When on (the default), uninitialized file scope variables are emitted as
common symbols. When off, common symbols are not created. The
benefit of allowing common symbols to be created is that generated
code can remove unused variables that would otherwise increase the
size of the .bss section. (Uninitialized variables of a size larger than
32 bytes are separately optimized through placement in separate
subsections that can be omitted from a link.) Variables cannot be
common symbols if they are assigned to a section other than .bss or
are defined relative to another common symbol.
--embedded_constants={on|off} By default the compiler embeds constants in functions. These
constants can include literals, addresses, strings, etc. This is a
problem if you wants to prevent reads from a memory region that
contains only executable code. To enable the generation of "execute
only code", the compiler provides the --embedded_constants=[on|off]
option. If the option is not specified, it is assumed to be on. The
option is available on the following devices: Cortex-A8, Cortex-M3,
Cortex-M4, and Cortex-R4.
--endian={ big | little }
Designates big- or little-endian format for the compiled code. By
default, big-endian format is used.
--enum_type={int|packed}
Designates the underlying type of an enumeration type. The default is
packed, which causes the underlying enumeration type to be the
smallest integer type that accommodates the enumeration constants.
Using --enum_type=int causes the underlying type to always be int.
An enumeration constant with a value outside the int range generates
an error.
--float_support={ vfpv2 | vfpv3 | Generates vector floating-point (VFP) coprocessor instructions for
vfpv3d16 | fpv4spd16 | none }
various versions and libraries. See Section 2.14.
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--global_register={r5|r6|r9}
-md
-mv={4|5e|6|6M0|7A8|7M3
|7M4|7R4|7R5}
--neon
--pending_instantiations=#
--plain_char={signed|unsigned}
--ramfunc={on|off}
--silicon_version
--unaligned_access={on|off}
Disallows use of rx=[5|6|9] by the compiler.
Disables dual-state interworking support. See Section 6.11.1.
Selects processor version: ARM V4 (ARM7), ARM V5e (ARM9E),
ARM V6 (ARM11), ARM V6M0 (Cortex-M0), ARM V7A8 (Cortex-A8),
ARM V7M3 (Cortex-M3), ARM V7M4 (Cortex-M4), ARM V7R4
(Cortex-R4), or ARM V7R5 (Cortex-R5). The default is ARM V4.
The compiler can generate code using the SIMD instructions
available in the Neon extension to the version 7 ARM architecture.
The optimizer attempts to vectorize source code in order to take
advantage of these SIMD instructions. In order to generate vectorized
SIMD Neon code, select the version 7 architecture with the -mv=7A8
option and enable Neon instruction support with the --neon option.
The optimizer is used to vectorize the source code. At least level 2
optimization (--opt_level=2 or O2) is required, although level 3 (-opt_level=3) is recommended along with the --opt_for_speed option.
Specify the number of template instantiations that may be in progress
at any given time. Use 0 to specify an unlimited number.
Specifies how to treat C/C++ plain char variables. Default is
unsigned.
If set to on, specifies that all functions should be placed in the
.TI.ramfunc section, which is placed in RAM. If set to off, only
functions with the ramfunc function attribute are treated this way. See
Section 5.17.2.
Newer TI linker command files support the --ramfunc option
automatically by placing functions in the .TI.ramfunc section. If you
have a linker command file that does not include a section
specification for the .TI.ramfunc section, you can modify the linker
command file to place this section in RAM. See the ARM Assembly
Language Tools User's Guide for details on section placement.
Selects the instruction set version. The options are:
• 4 = ARM V4 (ARM7) This is the default.
• 5e = ARM V5e (ARM9E)
• 6 = ARM V6 (ARM11)
• 6M0 = ARM V6M0 (Cortex-M0)
• 7A8 = ARM V7A8 (Cortex-A8)
• 7M3 = ARM V7M3 (Cortex-M3)
• 7M4 = ARM V7M4 (Cortex-M4)
• 7R4 = ARM V7R4 (Cortex-R4),
• 7R5 = ARM V7R5 (Cortex-R5)
Using the --silicon_version=7M4 option automatically sets the -float_support=fpv4spd16 option. To disable hardware floating point
support, use the --float_support=none option.
Informs the compiler that the target device supports unaligned
memory accesses. Typically data is aligned to its size boundary. For
instance 32-bit data is aligned on a 32-bit boundary, 16-bit data on a
16-bit boundary, and 8-bit data on an 8-bit boundary. If this option is
set to on, it tells the compiler it is legal to generate load and store
instructions for data that falls on an unaligned boundary (32-bit data
on a 16-bit boundary). Cases where unaligned data accesses can
occur include calls to memcpy() and accessing packed structs. This
option is on by default for all Cortex devices.
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--use_dead_funcs_list[=fname]
--wchar_t={32|16}
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Places each function listed in the file in a separate section. The
functions are placed in the fname section, if specified. This option and
--generate_dead_funcs_list are not recommended within the Code
Composer Studio IDE. Instead, consider using --opt_level=4, -program_level_compile, and/or --gen_func_subsections.
Sets the size (in bits) of the C/C++ type wchar_t. By default the
compiler generates 16-bit wchar_t. 16-bit wchar_t objects are not
compatible with the 32-bit wchar_t objects; an error is generated if
they are combined.
2.3.5 Symbolic Debugging and Profiling Options
The following options are used to select symbolic debugging or profiling:
--symdebug:dwarf
--symdebug:dwarf_
version={2|3|4}
--symdebug:none
--symdebug:skeletal
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(Default) Generates directives that are used by the C/C++ source-level
debugger and enables assembly source debugging in the assembler.
The --symdebug:dwarf option's short form is -g. See Section 3.12.
For more information on the DWARF debug format, see The DWARF
Debugging Standard.
Specifies the DWARF debugging format version (2, 3, or 4) to be
generated when --symdebug:dwarf (the default) is specified. By default,
the compiler generates DWARF version 3 debug information. DWARF
versions 2, 3, and 4 may be intermixed safely. When DWARF 4 is used,
type information is placed in the .debug_types section. At link time,
duplicate type information will be removed. This method of type merging
is superior to those used in DWARF 2 or 3 and will result in a smaller
executable. In addition, DWARF 4 reduces the size of intermediate
object files in comparison to DWARF 3. For more information on TI
extensions to the DWARF language, see The Impact of DWARF on TI
Object Files (SPRAAB5).
Disables all symbolic debugging output. This option is not recommended;
it prevents debugging and most performance analysis capabilities.
Deprecated. Has no effect.
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2.3.6 Specifying Filenames
The input files that you specify on the command line can be C source files, C++ source files, assembly
source files, or object files. The compiler uses filename extensions to determine the file type.
Extension
File Type
.asm, .abs, or .s* (extension begins with s)
Assembly source
.c
C source
.C
Depends on operating system
.cpp, .cxx, .cc
C++ source
.obj .c.obj .cpp.obj .o* .dll .so
Object
NOTE:
Case Sensitivity in Filename Extensions
Case sensitivity in filename extensions is determined by your operating system. If your
operating system is not case sensitive, a file with a .C extension is interpreted as a C file. If
your operating system is case sensitive, a file with a .C extension is interpreted as a C++ file.
For information about how you can alter the way that the compiler interprets individual filenames, see
Section 2.3.7. For information about how you can alter the way that the compiler interprets and names the
extensions of assembly source and object files, see Section 2.3.10.
You can use wildcard characters to compile or assemble multiple files. Wildcard specifications vary by
system; use the appropriate form listed in your operating system manual. For example, to compile all of
the files in a directory with the extension .cpp, enter the following:
armcl *.cpp
NOTE:
No Default Extension for Source Files is Assumed
If you list a filename called example on the command line, the compiler assumes that the
entire filename is example not example.c. No default extensions are added onto files that do
not contain an extension.
2.3.7 Changing How the Compiler Interprets Filenames
You can use options to change how the compiler interprets your filenames. If the extensions that you use
are different from those recognized by the compiler, you can use the filename options to specify the type
of file. You can insert an optional space between the option and the filename. Select the appropriate
option for the type of file you want to specify:
--asm_file=filename
--c_file=filename
--cpp_file=filename
--obj_file=filename
for an assembly language source file
for a C source file
for a C++ source file
for an object file
For example, if you have a C source file called file.s and an assembly language source file called assy,
use the --asm_file and --c_file options to force the correct interpretation:
armcl --c_file=file.s --asm_file=assy
You cannot use the filename options with wildcard specifications.
NOTE: The default file extensions for object files created by the compiler have been changed in
order to prevent conflicts when C and C++ files have the same names. Object files
generated from C source files have the .c.obj extension. Object files generated from C++
source files have the .cpp.obj extension.
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2.3.8 Changing How the Compiler Processes C Files
The --cpp_default option causes the compiler to process C files as C++ files. By default, the compiler
treats files with a .c extension as C files. See Section 2.3.9 for more information about filename extension
conventions.
2.3.9 Changing How the Compiler Interprets and Names Extensions
You can use options to change how the compiler program interprets filename extensions and names the
extensions of the files that it creates. The filename extension options must precede the filenames they
apply to on the command line. You can use wildcard specifications with these options. An extension can
be up to nine characters in length. Select the appropriate option for the type of extension you want to
specify:
--asm_extension=new extension
--c_extension=new extension
--cpp_extension=new extension
--listing_extension=new extension
--obj_extension=new extension
for an assembly language file
for a C source file
for a C++ source file
sets default extension for listing files
for an object file
The following example assembles the file fit.rrr and creates an object file named fit.o:
armcl --asm_extension=.rrr --obj_extension=.o fit.rrr
The period (.) in the extension is optional. You can also write the example above as:
armcl --asm_extension=rrr --obj_extension=o fit.rrr
2.3.10 Specifying Directories
By default, the compiler program places the object, assembly, and temporary files that it creates into the
current directory. If you want the compiler program to place these files in different directories, use the
following options:
--abs_directory=directory
Specifies the destination directory for absolute listing files. The default is
to use the same directory as the object file directory. For example:
armcl --abs_directory=d:\abso_list
--asm_directory=directory
Specifies a directory for assembly files. For example:
armcl --asm_directory=d:\assembly
--list_directory=directory
Specifies the destination directory for assembly listing files and crossreference listing files. The default is to use the same directory as the
object file directory. For example:
armcl --list_directory=d:\listing
--obj_directory=directory
Specifies a directory for object files. For example:
armcl --obj_directory=d:\object
--output_file=filename
Specifies a compilation output file name; can override --obj_directory . For
example:
armcl --output_file=transfer
--pp_directory=directory
Specifies a preprocessor file directory for object files (default is .). For
example:
armcl --pp_directory=d:\preproc
--temp_directory=directory
Specifies a directory for temporary intermediate files. For example:
armcl --temp_directory=d:\temp
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2.3.11 Assembler Options
Following are assembler options that you can use with the compiler. For more information, see the ARM
Assembly Language Tools User's Guide.
--absolute_listing
Generates a listing with absolute addresses rather than sectionrelative offsets.
Predefines the constant name for the assembler; produces a .set
directive for a constant or an .arg directive for a string. If the optional
[=def] is omitted, the name is set to 1. If you want to define a quoted
string and keep the quotation marks, do one of the following:
--asm_define=name[=def]
•
•
For Windows, use --asm_define=name="\"string def\"". For
example: --asm_define=car="\"sedan\""
For UNIX, use --asm_define=name='"string def"'. For example: -asm_define=car='"sedan"'
•
--asm_dependency
--asm_includes
--asm_listing
--asm_undefine=name
--code_state={16|32}
--asm_listing_cross_reference
--include_file=filename
For Code Composer Studio, enter the definition in a file and
include that file with the --cmd_file option.
Performs preprocessing for assembly files, but instead of writing
preprocessed output, writes a list of dependency lines suitable for
input to a standard make utility. The list is written to a file with the
same name as the source file but with a .ppa extension.
Performs preprocessing for assembly files, but instead of writing
preprocessed output, writes a list of files included with the #include
directive. The list is written to a file with the same name as the
source file but with a .ppa extension.
Produces an assembly listing file.
Undefines the predefined constant name. This option overrides any -asm_define options for the specified name.
Generates 16-bit Thumb code. By default, 32-bit code is generated.
When Cortex-R4, Cortex-M0, Cortex-M3, or Cortex-A8 architecture
support is chosen, the --code_state option generates Thumb-2 code.
For details on indirect calls in 16-bit versus 32-bit code, see
Section 6.11.2.2.
Produces a symbolic cross-reference in the listing file.
Includes the specified file for the assembly module; acts like an
.include directive. The file is included before source file statements.
The included file does not appear in the assembly listing files.
2.3.12 Deprecated Options
Several compiler options have been deprecated, removed, or renamed. The compiler continues to accept
some of the deprecated options, but they are not recommended for use. See the Compiler Option Cleanup
wiki page for a list of deprecated and removed options, options that have been removed from CCS, and
options that have been renamed.
2.4
Controlling the Compiler Through Environment Variables
An environment variable is a system symbol that you define and assign a string to. Setting environment
variables is useful when you want to run the compiler repeatedly without re-entering options, input
filenames, or pathnames.
NOTE:
C_OPTION and C_DIR -- The C_OPTION and C_DIR environment variables are
deprecated. Use device-specific environment variables instead.
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2.4.1 Setting Default Compiler Options (TI_ARM_C_OPTION)
You might find it useful to set the compiler, assembler, and linker default options using the
TI_ARM_C_OPTION environment variable. If you do this, the compiler uses the default options and/or
input filenames that you name TI_ARM_C_OPTION every time you run the compiler.
Setting the default options with these environment variables is useful when you want to run the compiler
repeatedly with the same set of options and/or input files. After the compiler reads the command line and
the input filenames, it looks for the TI_ARM_C_OPTION environment variable and processes it.
The table below shows how to set the TI_ARM_C_OPTION environment variable. Select the command for
your operating system:
Operating System
Enter
UNIX (Bourne shell)
TI_ARM_C_OPTION=" option1 [option2 . . .]"; export TI_ARM_C_OPTION
Windows
set TI_ARM_C_OPTION= option1 [option2 . . .]
Environment variable options are specified in the same way and have the same meaning as they do on
the command line. For example, if you want to always run quietly (the --quiet option), enable C/C++
source interlisting (the --src_interlist option), and link (the --run_linker option) for Windows, set up the
TI_ARM_C_OPTION environment variable as follows:
set TI_ARM_C_OPTION=--quiet --src_interlist --run_linker
NOTE: The TI_ARM_C_OPTION environment variable takes precedence over the older
TMS470_C_OPTION environment variable if both are defined. If only TMS470_C_OPTION is
set, it will continue to be used.
In the following examples, each time you run the compiler, it runs the linker. Any options following -run_linker on the command line or in TI_ARM_C_OPTION are passed to the linker. Thus, you can use the
TI_ARM_C_OPTION environment variable to specify default compiler and linker options and then specify
additional compiler and linker options on the command line. If you have set --run_linker in the environment
variable and want to compile only, use the compiler --compile_only option. These additional examples
assume TI_ARM_C_OPTION is set as shown above:
armcl
armcl
armcl
armcl
*c
; compiles and links
--compile_only *.c
; only compiles
*.c --run_linker lnk.cmd
; compiles and links using a command file
--compile_only *.c --run_linker lnk.cmd
; only compiles (--compile_only overrides --run_linker)
For details on compiler options, see Section 2.3. For details on linker options, see the Linker Description
chapter in the ARM Assembly Language Tools User's Guide.
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2.4.2 Naming One or More Alternate Directories (TI_ARM_C_DIR)
The linker uses the TI_ARM_C_DIR environment variable to name alternate directories that contain object
libraries. The command syntaxes for assigning the environment variable are:
Operating System
Enter
UNIX (Bourne shell)
TI_ARM_C_DIR=" pathname1 ; pathname2 ;..."; export TI_ARM_C_DIR
Windows
set TI_ARM_C_DIR= pathname1 ; pathname2 ;...
The pathnames are directories that contain input files. The pathnames must follow these constraints:
• Pathnames must be separated with a semicolon.
• Spaces or tabs at the beginning or end of a path are ignored. For example, the space before and after
the semicolon in the following is ignored:
set TI_ARM_C_DIR=c:\path\one\to\tools ; c:\path\two\to\tools
•
Spaces and tabs are allowed within paths to accommodate Windows directories that contain spaces.
For example, the pathnames in the following are valid:
set TI_ARM_C_DIR=c:\first path\to\tools;d:\second path\to\tools
The environment variable remains set until you reboot the system or reset the variable by entering:
Operating System
Enter
UNIX (Bourne shell)
unset TI_ARM_C_DIR
Windows
set TI_ARM_C_DIR=
NOTE: The TI_ARM_C_DIR environment variable takes precedence over the older TMS470_C_DIR
environment variable if both are defined. If only TMS470_C_DIR is set, it will continue to be
used.
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Controlling the Preprocessor
This section describes features that control the preprocessor, which is part of the parser. A general
description of C preprocessing is in section A12 of K&R. The C/C++ compiler includes standard C/C++
preprocessing functions, which are built into the first pass of the compiler. The preprocessor handles:
• Macro definitions and expansions
• #include files
• Conditional compilation
• Various preprocessor directives, specified in the source file as lines beginning with the # character
The preprocessor produces self-explanatory error messages. The line number and the filename where the
error occurred are printed along with a diagnostic message.
2.5.1 Predefined Macro Names
The compiler maintains and recognizes the predefined macro names listed in Table 2-30.
Table 2-30. Predefined ARM Macro Names
Macro Name
Description
_ _16bis_ _
Defined if 16-BIS state is selected (the -code_state=16 option is used); otherwise, it is
undefined.
_ _32bis_ _
Defined if 32-BIS state is selected (the -code_state=16 option is not used); otherwise, it
is undefined.
_AEABI_PORTABILITY_LEVEL
Define to 1 to enable full object file portability when headers files are included. Define to
0 to require full C standard compatibility. See the ARM standard for details.
_ _DATE_ _ (1)
Expands to the compilation date in the form mmm dd yyyy
_ _FILE_ _ (1)
Expands to the current source filename
_ _LINE_ _ (1)
Expands to the current line number
_ _signed_chars_ _
Defined if char types are signed by default
_ _STDC_ _ (1)
Defined to 1 to indicate that compiler conforms to ISO C Standard. See Section 5.1 for
exceptions to ISO C conformance.
_ _STDC_VERSION_ _
C standard macro.
_ _STDC_HOSTED_ _
C standard macro. Always defined to 1.
_ _STDC_NO_THREADS_ _
C standard macro. Always defined to 1.
_ _TI_COMPILER_VERSION_ _
Defined to a 7-9 digit integer, depending on if X has 1, 2, or 3 digits. The number does
not contain a decimal. For example, version 3.2.1 is represented as 3002001. The
leading zeros are dropped to prevent the number being interpreted as an octal.
_ _TI_EABI_SUPPORT_ _
Defined to 1 if the EABI ABI is enabled (this is the default); otherwise, it is undefined.
_ _TI_FPALIB_SUPPORT_ _
Defined to 1 if the FPA endianness is used to store double-precision floating-point
values; otherwise, it is undefined.
_ _TI_GNU_ATTRIBUTE_SUPPORT_ _ Defined to 1 if GCC extensions are enabled (which is the default)
_ _TI_NEON_SUPPORT_ _
Defined to 1 if NEON SIMD extension is targeted (the --neon option is used); otherwise,
it is undefined.
_ _TI_STRICT_ANSI_MODE_ _
Defined to 1 if strict ANSI/ISO mode is enabled (the --strict_ansi option is used);
otherwise, it is defined as 0.
_ _TI_STRICT_FP_MODE_ _
Defined to 1 if --fp_mode=strict is used (default); otherwise, it is defined as 0.
_ _TI_ ARM_V4_ _
Defined to 1 if the v4 architecture (ARM7) is targeted (the -mv4 option is used);
otherwise, it is undefined.
_ _TI_ ARM_V5_ _
Defined to 1 if the v5E architecture (ARM9E) is targeted (the -mv5e option is used);
otherwise, it is undefined.
_ _TI_ ARM_V6_ _
Defined to 1 if the v6 architecture (ARM11) is targeted (the -mv6 option is used);
otherwise, it is undefined.
_ _TI_ ARM_V6M0_ _
Defined to 1 if the v6M0 architecture (Cortex-M0) is targeted (the -mv6M0 option is
used); otherwise, it is undefined.
_ _TI_ ARM_V7_ _
Defined to 1 if any v7 architecture (Cortex) is targeted; otherwise, it is undefined.
(1)
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Table 2-30. Predefined ARM Macro Names (continued)
Macro Name
Description
_ _TI_ ARM_V7A8_ _
Defined to 1 if the v7A8 architecture (Cortex-A8) is targeted (the -mv7A8 option is used);
otherwise, it is undefined.
_ _TI_ ARM_V7M3_ _
Defined to 1 if the v7M3 architecture (Cortex-M3) is targeted (the -mv7M3 option is
used); otherwise, it is undefined.
_ _TI_ ARM_V7M4_ _
Defined to 1 if the v7M4 architecture (Cortex-M4) is targeted (the -mv7M4 option is
used); otherwise, it is undefined.
_ _TI_ ARM_V7R4_ _
Defined to 1 if the v7R4 architecture (Cortex-R4) is targeted (the -mv7R4 option is
used); otherwise, it is undefined.
_ _TI_ ARM_V7R5_ _
Defined to 1 if the v7R5 architecture (Cortex-R5) is targeted (the -mv7R5 option is
used); otherwise, it is undefined.
_ _TI_VFP_SUPPORT_ _
Defined to 1 if the VFP coprocessor is enabled (any --float_support option is used);
otherwise, it is undefined.
_ _TI_VFPLIB_SUPPORT_ _
Defined to 1 if the VFP endianness is used to store double-precision floating-point
values; otherwise, it is undefined.
_ _TI_VFPV3_SUPPORT_ _
Defined to 1 if the VFP coprocessor is enabled (the --float_support=vfpv3 option is
used); otherwise, it is undefined.
_ _TI_VFPV3D16_SUPPORT_ _
Defined to 1 if the VFP coprocessor is enabled (the --float_support=vfpv3d16 option is
used); otherwise, it is undefined.
_ _TI_FPV4SPD16_SUPPORT_ _
Defined to 1 if the VFP coprocessor is enabled (the --float_support=fpv4spd16 option is
used); otherwise, it is undefined.
_ _TI_WCHAR_T_BITS_ _
Set to the type of wchar_t.
_ _TIME_ _ (1)
Expands to the compilation time in the form "hh:mm:ss"
_ _TI_ ARM_ _
Always defined
_ _unsigned_chars_ _
Defined if char types are unsigned by default (default)
_ _big_endian_ _
Defined if big-endian mode is selected (the --endian=big option is used or the -endian=little option is not used); otherwise, it is undefined.
_ _WCHAR_T_TYPE_ _
Set to the type of wchar_t.
_INLINE
Expands to 1 if optimization is used (--opt_level or -O option); undefined otherwise.
_ _little_endian_ _
Defined if little-endian mode is selected (the --endian=little option is used); otherwise, it
is undefined.
NOTE: Macros with names that contain _ _TI_ARM are duplicates of the older _ _TI_TMS470
macros. For example, _ _TI_ARM_V7_ _ is the newer name for the _ _TI_TMS470_V7_ _
macro. The old macro names still exist and can continue to be used.
You can use the names listed in Table 2-30 in the same manner as any other defined name. For example,
printf ( "%s %s" , __TIME__ , __DATE__);
translates to a line such as:
printf ("%s %s" , "13:58:17", "Jan 14 1997");
In addition, the ARM C Language Extensions (ACLE) v2.0 specification describes macros that identify
features of the ARM architecture and how the C/C++ implementation uses the architecture. All ACLE
predefined macros begin with the prefix __ARM. Table 2-31 lists the macros mentioned in the ACLE
specification and the section of the specification that provides more information. Some macros are
undefined because they are not applicable for any Cortex-M or Cortex-R processor variant.
Table 2-31. ACLE Pre-Defined Macros
Macro Name
Description
Section in ACLE
Specification
__ARM_32BIT_STATE
Defined as 1 if the compiler is generating code for an ARM
32-bit processor variant (-mv6m0, -mv7m3, -mv7m4, mv7a8, -mv7r4, and -mv7r5); undefined otherwise.
(Section 5.4.1)
__ARM_64BIT_STATE
Undefined
(Section 5.4.1)
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Table 2-31. ACLE Pre-Defined Macros (continued)
40
Macro Name
Description
Section in ACLE
Specification
__ARM_ACLE
Defined as 200 for all Cortex-M and Cortex-R processor
variants (-mv6m0, -mv7m3, -mv7m4, -mv7r4, and -mv7r5).
(Sections 3.4, 5.2)
__ARM_ALIGN_MAX_PWR
Not supported
(Section 6.5.2)
__ARM_ALIGN_MAX_STACK_PWR
Not supported
(Section 6.5.3)
__ARM_ARCH
Identifies the version of ARM architecture selected on the
compiler command line.
• 4 indicates -mv4
• 5 indicates -mv5e
• 6 indicates -mv6 or -mv6m0
• 7 indicates -mv7a8, -mv7m3, -mv7m4, -mv7r4, or mv7r5
(Section 5.1)
__ARM_ARCH_ISA_A64
Undefined
(Section 5.4.1)
__ARM_ARCH_ISA_ARM
Defined as 1 if the compiler is generating code for a
processor variant that supports the ARM instruction set (mv7a8, -mv7r4, and -mv7r5); undefined otherwise.
(Section 5.4.1)
__ARM_ARCH_ISA_THUMB
Defined as 1 if the compiler is generating code for a
(Section 5.4.1)
processor variant that supports the THUMB-1 instruction set.
Defined as 2 if the compiler is generating code for a
processor variant that supports the THUMB-2 instruction set;
undefined otherwise.
__ARM_ARCH_PROFILE
Not supported
(Section 5.4.2)
__ARM_BIG_ENDIAN
Defined as 1 by default; not defined if --little-endian (-me)
option is used.
(Section 5.3)
__ARM_FEATURE_CLZ
Defined as 1 if the compiler is generating code for a
(Section 5.4.5)
processor variant that supports the CLZ instruction (-mv7m3,
-mv7m4, -mv7a8, -mv7r4, and -mv7r5); undefined otherwise.
__ARM_FEATURE_COPROC
Not supported
(Section 5.9)
__ARM_FEATURE_CRC32
Undefined
(Section 5.5.8)
__ARM_FEATURE_CRYPTO
Undefined
(Section 5.5.7)
__ARM_FEATURE_DIRECTED_ROUNDING
Undefined
(Section 5.5.9)
__ARM_FEATURE_DSP
Defined as 1 if the compiler is generating code for a CortexM or Cortex-R processor that supports DSP
instructions/intrinsics (-mv7m4, -mv7r4, and -mv7r5);
undefined otherwise.
(Section 5.4.7)
__ARM_FEATURE_FMA
Not supported
(Section 5.5.3)
__ARM_FEATURE_FP16_SCALAR_
ARITHMETIC
Undefined
(Sections 3.4,
5.5.13)
__ARM_FEATURE_FP16_VECTOR_
ARITHMETIC
Undefined
(Section 5.5.13)
__ARM_FEATURE_IDIV
Not supported
(Section 5.4.10)
__ARM_FEATURE_JCVT
Undefined
(Section 5.5.14)
__ARM_FEATURE_LDREX
Undefined
(Section 5.4.4)
__ARM_FEATURE_NUMERIC_MAXMIN
Undefined
(Section 5.5.10)
__ARM_FEATURE_QBIT
Not supported
(Section 5.4.6)
__ARM_FEATURE_QRDMX
Undefined
(Section 5.5.12)
__ARM_FEATURE_SAT
Defined as 1 if the compiler is generating code for a
processor variant that supports SSAT/USAT
instructions/intrinsics (-mv7m3, -mv7m4, -mv7a8, -mv7r4,
and -mv7r5); undefined otherwise.
(Section 5.4.8)
__ARM_FEATURE_SIMD32
Defined as 1 if the compiler is generating code for a
processor variant that supports all SIMD
instructions/intrinsics (-mv7m4, -mv7r4, and -mv7r5);
undefined otherwise.
(Section 5.4.9)
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Table 2-31. ACLE Pre-Defined Macros (continued)
Macro Name
Description
Section in ACLE
Specification
__ARM_FEATURE_UNALIGNED
Defined as 1 if the compiler is generating code for a
(Section 5.4.3)
processor variant that supports unaligned access to memory
(-mv7m3, -mv7m4, -mv7a8, -mv7r4, and -mv7r5); undefined
otherwise.
__ARM_FP
Defined as 6 for --float_support={fpv4spd16 | fpv5spd16}.
Defined as 12 for --float_support={vfpv2 | vfpv3 | vfpv3d16};
undefined otherwise.
(Section 5.5.1)
__ARM_FP16_ARGS
Defined as 1 if a 16-bit float type can be used for an
argument and/or result; undefined otherwise.
(Section 5.5.11)
__ARM_FP16_FORMAT_ALTERNATIVE
Undefined
(Section 5.5.2)
__ARM_FP16_FORMAT_IEEE
Defined as 1 if the IEEE format for 16-bit floating-point
(according to IEEE 754-2008 standard) is used; undefined
otherwise.
(Section 5.5.2)
__ARM_FP_FAST
Not supported
(Section 5.6)
__ARM_FP_FENV_ROUNDING
Not supported
(Section 5.6)
__ARM_NEON
Undefined
(Sections 3.4, 5.5.4)
__ARM_NEON_FP
Undefined
(Section 5.5.5)
__ARM_PCS
Defined as 1 if the compiler can assume the default
(Section 5.7)
procedure calling standard for a translation unit conforms to
the "base procedure call standard" as prescribed in the ARM
Architecture Procedure Call Standard (AAPCS) specification
(-mv7m3, -mv7m4, -mv7r4, and -mv7r5); undefined
otherwise.
__ARM_PCS_AAPCS64
Undefined
(Section 5.7)
__ARM_PCS_VFP
Defined as 1 if the default procedure calling convention is to
pass floating-point arguments / return values in hardware
floating-point registers; undefined otherwise.
(Section 5.7)
__ARM_ROPI
Undefined
(Section 5.8)
__ARM_RWPI
Undefined
(Section 5.8)
__ARM_SIZEOF_MINIMAL_ENUM
Defined to the smallest possible enum type size (1 byte for
(Section 3.1.1)
packed, 4 bytes for int). This mirrors the -enum_type=[packed | int] option where packed is the default.
__ARM_SIZEOF_WCHAR_T
Defined as 2 if --wchar_t=16 (default). Defined as 4 if -wchar_t=32.
(Section 3.1.1)
__ARM_WMMX
Undefined
(Section 5.5.6)
__STDC_IEC_559__
Undefined
(Section 5.6)
__SUPPORT_SNAN__
Not supported
(Section 5.6)
2.5.2 The Search Path for #include Files
The #include preprocessor directive tells the compiler to read source statements from another file. When
specifying the file, you can enclose the filename in double quotes or in angle brackets. The filename can
be a complete pathname, partial path information, or a filename with no path information.
• If you enclose the filename in double quotes (" "), the compiler searches for the file in the following
directories in this order:
1. The directory of the file that contains the #include directive and in the directories of any files that
contain that file.
2. Directories named with the --include_path option.
3. Directories set with the TI_ARM_C_DIR environment variable.
• If you enclose the filename in angle brackets (< >), the compiler searches for the file in the following
directories in this order:
1. Directories named with the --include_path option.
2. Directories set with the TI_ARM_C_DIR environment variable.
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See Section 2.5.2.1 for information on using the --include_path option. See Section 2.4.2 for more
information on input file directories.
2.5.2.1
Adding a Directory to the #include File Search Path (--include_path Option)
The --include_path option names an alternate directory that contains #include files. The --include_path
option's short form is -I. The format of the --include_path option is:
--include_path=directory1 [--include_path= directory2 ...]
There is no limit to the number of --include_path options per invocation of the compiler; each -include_path option names one directory. In C source, you can use the #include directive without
specifying any directory information for the file; instead, you can specify the directory information with the -include_path option.
For example, assume that a file called source.c is in the current directory. The file source.c contains the
following directive statement:
#include "alt.h"
Assume that the complete pathname for alt.h is:
UNIX
Windows
/tools/files/alt.h
c:\tools\files\alt.h
The table below shows how to invoke the compiler. Select the command for your operating system:
Operating System
Enter
UNIX
armcl --include_path=/tools/files source.c
Windows
armcl --include_path=c:\tools\files source.c
NOTE:
Specifying Path Information in Angle Brackets
If you specify the path information in angle brackets, the compiler applies that information
relative to the path information specified with --include_path options and the TI_ARM_C_DIR
environment variable.
For example, if you set up TI_ARM_C_DIR with the following command:
TI_ARM_C_DIR "/usr/include;/usr/ucb"; export TI_ARM_C_DIR
or invoke the compiler with the following command:
armcl --include_path=/usr/include file.c
and file.c contains this line:
#include <sys/proc.h>
the result is that the included file is in the following path:
/usr/include/sys/proc.h
2.5.3 Support for the #warning and #warn Directives
In strict ANSI mode, the TI preprocessor allows you to use the #warn directive to cause the preprocessor
to issue a warning and continue preprocessing. The #warn directive is equivalent to the #warning directive
supported by GCC, IAR, and other compilers.
If you use the --relaxed_ansi option (on by default), both the #warn and #warning preprocessor directives
are supported.
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2.5.4 Generating a Preprocessed Listing File (--preproc_only Option)
The --preproc_only option allows you to generate a preprocessed version of your source file with an
extension of .pp. The compiler's preprocessing functions perform the following operations on the source
file:
• Each source line ending in a backslash (\) is joined with the following line.
• Trigraph sequences are expanded.
• Comments are removed.
• #include files are copied into the file.
• Macro definitions are processed.
• All macros are expanded.
• All other preprocessing directives, including #line directives and conditional compilation, are expanded.
The --preproc_only option is useful when creating a source file for a technical support case or to ask a
question about your code. It allows you to reduce the test case to a single source file, because #include
files are incorporated when the preprocessor runs.
2.5.5 Continuing Compilation After Preprocessing (--preproc_with_compile Option)
If you are preprocessing, the preprocessor performs preprocessing only; it does not compile your source
code. To override this feature and continue to compile after your source code is preprocessed, use the -preproc_with_compile option along with the other preprocessing options. For example, use -preproc_with_compile with --preproc_only to perform preprocessing, write preprocessed output to a file
with a .pp extension, and compile your source code.
2.5.6 Generating a Preprocessed Listing File with Comments (--preproc_with_comment
Option)
The --preproc_with_comment option performs all of the preprocessing functions except removing
comments and generates a preprocessed version of your source file with a .pp extension. Use the -preproc_with_comment option instead of the --preproc_only option if you want to keep the comments.
2.5.7 Generating Preprocessed Listing with Line-Control Details (--preproc_with_line Option)
By default, the preprocessed output file contains no preprocessor directives. To include the #line
directives, use the --preproc_with_line option. The --preproc_with_line option performs preprocessing only
and writes preprocessed output with line-control information (#line directives) to a file named as the
source file but with a .pp extension.
2.5.8 Generating Preprocessed Output for a Make Utility (--preproc_dependency Option)
The --preproc_dependency option performs preprocessing only. Instead of writing preprocessed output, it
writes a list of dependency lines suitable for input to a standard make utility. If you do not supply an
optional filename, the list is written to a file with the same name as the source file but a .pp extension.
2.5.9 Generating a List of Files Included with #include (--preproc_includes Option)
The --preproc_includes option performs preprocessing only, but instead of writing preprocessed output,
writes a list of files included with the #include directive. If you do not supply an optional filename, the list is
written to a file with the same name as the source file but with a .pp extension.
2.5.10 Generating a List of Macros in a File (--preproc_macros Option)
The --preproc_macros option generates a list of all predefined and user-defined macros. If you do not
supply an optional filename, the list is written to a file with the same name as the source file but with a .pp
extension.
The output includes only those files directly included by the source file. Predefined macros are listed first
and indicated by the comment /* Predefined */. User-defined macros are listed next and indicated by the
source filename.
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Passing Arguments to main()
Some programs pass arguments to main() via argc and argv. This presents special challenges in an
embedded program that is not run from the command line. In general, argc and argv are made available
to your program through the .args section. There are various ways to populate the contents of this section
for use by your program.
To cause the linker to allocate an .args section of the appropriate size, use the --arg_size=size linker
option. This option tells the linker to allocate an uninitialized section named .args, which can be used by
the loader to pass arguments from the command line of the loader to the program. The size is the number
of bytes to be allocated. When you use the --arg_size option, the linker defines the __c_args__ symbol to
contain the address of the .args section.
It is the responsibility of the loader to populate the .args section. The loader and the target boot code can
use the .args section and the __c_args__ symbol to determine whether and how to pass arguments from
the host to the target program. The format of the arguments is an array of pointers to char on the target.
Due to variations in loaders, it is not specified how the loader determines which arguments to pass to the
target.
If you are using Code Composer Studio to run your application, you can use the Scripting Console tool to
populate the .args section. To open this tool, choose View > Scripting Console from the CCS menus.
You can use the loadProg command to load an object file and its associated symbol table into memory
and pass an array of arguments to main(). These arguments are automatically written to the allocated
.args section.
The loadProg syntax is as follows, where file is an executable file and args is an object array of
arguments. Use JavaScript to declare the array of arguments before using this command.
loadProg(file, args)
The .args section is loaded with the following data for non-SYS/BIOS-based executables, where each
element in the argv[] array contains a string corresponding to that argument:
Int argc;
Char * argv[0];
Char * argv[1];
...
Char * argv[n];
For SYS/BIOS-based executables, the elements in the .args section are as follows:
Int argc;
Char ** argv;
Char * envp;
Char * argv[0];
Char * argv[1];
...
Char * argv[n];
/* points to argv[0] */
/* ignored by loadProg command */
For more details, see the "Scripting Console" topic in the TI Processors Wiki.
2.7
Understanding Diagnostic Messages
One of the primary functions of the compiler and linker is to report diagnostic messages for the source
program. A diagnostic message indicates that something may be wrong with the program. When the
compiler or linker detects a suspect condition, it displays a message in the following format:
"file.c", line n : diagnostic severity : diagnostic message
"file.c"
line n :
diagnostic severity
diagnostic message
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The
The
The
The
name of the file involved
line number where the diagnostic applies
diagnostic message severity (severity category descriptions follow)
text that describes the problem
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Diagnostic messages have a severity, as follows:
• A fatal error indicates a problem so severe that the compilation cannot continue. Examples of such
problems include command-line errors, internal errors, and missing include files. If multiple source files
are being compiled, any source files after the current one will not be compiled.
• An error indicates a violation of the syntax or semantic rules of the C/C++ language. Compilation may
continue, but object code is not generated.
• A warning indicates something that is likely to be a problem, but cannot be proven to be an error. For
example, the compiler emits a warning for an unused variable. An unused variable does not affect
program execution, but its existence suggests that you might have meant to use it. Compilation
continues and object code is generated (if no errors are detected).
• A remark is less serious than a warning. It may indicate something that is a potential problem in rare
cases, or the remark may be strictly informational. Compilation continues and object code is generated
(if no errors are detected). By default, remarks are not issued. Use the --issue_remarks compiler option
to enable remarks.
• Advice provides information about recommended usage. It is not provided in the same way as the
other diagnostic categories described here. Instead, it is only available in Code Composer Studio in the
Advice area, which is a tab that appears next to the Problems tab. This advice cannot be controlled or
accessed via the command line. The advice provided includes suggested settings for the --opt_level
and --opt_for_speed options. In addition, messages about suggested code changes from the ULP
(Ultra-Low Power) Advisor are provided in this tab.
Diagnostic messages are written to standard error with a form like the following example:
"test.c", line 5: error: a break statement may only be used within a loop or switch
break;
^
By default, the source code line is not printed. Use the --verbose_diagnostics compiler option to display
the source line and the error position. The above example makes use of this option.
The message identifies the file and line involved in the diagnostic, and the source line itself (with the
position indicated by the ^ character) follows the message. If several diagnostic messages apply to one
source line, each diagnostic has the form shown; the text of the source line is displayed several times,
with an appropriate position indicated each time.
Long messages are wrapped to additional lines, when necessary.
You can use the --display_error_number command-line option to request that the diagnostic's numeric
identifier be included in the diagnostic message. When displayed, the diagnostic identifier also indicates
whether the diagnostic can have its severity overridden on the command line. If the severity can be
overridden, the diagnostic identifier includes the suffix -D (for discretionary); otherwise, no suffix is
present. For example:
"Test_name.c", line 7: error #64-D: declaration does not declare anything
struct {};
^
"Test_name.c", line 9: error #77: this declaration has no storage class or type specifier
xxxxx;
^
Because errors are determined to be discretionary based on the severity in a specific context, an error can
be discretionary in some cases and not in others. All warnings and remarks are discretionary.
For some messages, a list of entities (functions, local variables, source files, etc.) is useful; the entities are
listed following the initial error message:
"test.c", line 4: error: more than one instance of overloaded function "f"
matches the argument list:
function "f(int)"
function "f(float)"
argument types are: (double)
f(1.5);
^
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In some cases, additional context information is provided. Specifically, the context information is useful
when the front end issues a diagnostic while doing a template instantiation or while generating a
constructor, destructor, or assignment operator function. For example:
"test.c", line 7: error: "A::A()" is inaccessible
B x;
^
detected during implicit generation of "B::B()" at line 7
Without the context information, it is difficult to determine to what the error refers.
2.7.1 Controlling Diagnostic Messages
The C/C++ compiler provides diagnostic options to control compiler- and linker-generated diagnostic
messages. The diagnostic options must be specified before the --run_linker option.
--diag_error=num
Categorizes the diagnostic identified by num as an error. To determine the
numeric identifier of a diagnostic message, use the --display_error_number
option first in a separate compile. Then use --diag_error=num to recategorize
the diagnostic as an error. You can only alter the severity of discretionary
diagnostic messages.
--diag_remark=num
Categorizes the diagnostic identified by num as a remark. To determine the
numeric identifier of a diagnostic message, use the --display_error_number
option first in a separate compile. Then use --diag_remark=num to
recategorize the diagnostic as a remark. You can only alter the severity of
discretionary diagnostic messages.
--diag_suppress=num
Suppresses the diagnostic identified by num. To determine the numeric
identifier of a diagnostic message, use the --display_error_number option first
in a separate compile. Then use --diag_suppress=num to suppress the
diagnostic. You can only suppress discretionary diagnostic messages.
--diag_warning=num
Categorizes the diagnostic identified by num as a warning. To determine the
numeric identifier of a diagnostic message, use the --display_error_number
option first in a separate compile. Then use --diag_warning=num to
recategorize the diagnostic as a warning. You can only alter the severity of
discretionary diagnostic messages.
--display_error_number Displays a diagnostic's numeric identifier along with its text. Use this option in
determining which arguments you need to supply to the diagnostic
suppression options (--diag_suppress, --diag_error, --diag_remark, and -diag_warning). This option also indicates whether a diagnostic is discretionary.
A discretionary diagnostic is one whose severity can be overridden. A
discretionary diagnostic includes the suffix -D; otherwise, no suffix is present.
See Section 2.7.
--emit_warnings_as_
Treats all warnings as errors. This option cannot be used with the -errors
no_warnings option. The --diag_remark option takes precedence over this
option. This option takes precedence over the --diag_warning option.
--issue_remarks
Issues remarks (non-serious warnings), which are suppressed by default.
--no_warnings
Suppresses diagnostic warnings (errors are still issued).
--section_sizes={on|off} Generates section size information, including sizes for sections containing
executable code and constants, constant or initialized data (global and static
variables), and uninitialized data. Section size information is output during
both the assembly and linking phases. This option should be placed on the
command line with the compiler options (that is, before the --run_linker or --z
option).
--set_error_limit=num
Sets the error limit to num, which can be any decimal value. The compiler
abandons compiling after this number of errors. (The default is 100.)
--verbose_diagnostics Provides verbose diagnostic messages that display the original source with
line-wrap and indicate the position of the error in the source line. Note that this
command-line option cannot be used within the Code Composer Studio IDE.
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--write_diagnostics_file Produces a diagnostic message information file with the same source file
name with an .err extension. (The --write_diagnostics_file option is not
supported by the linker.) Note that this command-line option cannot be used
within the Code Composer Studio IDE.
2.7.2 How You Can Use Diagnostic Suppression Options
The following example demonstrates how you can control diagnostic messages issued by the compiler.
You control the linker diagnostic messages in a similar manner.
int one();
int I;
int main()
{
switch (I){
case 1;
return one ();
break;
default:
return 0;
break;
}
}
If you invoke the compiler with the --quiet option, this is the result:
"err.c", line 9: warning: statement is unreachable
"err.c", line 12: warning: statement is unreachable
Because it is standard programming practice to include break statements at the end of each case arm to
avoid the fall-through condition, these warnings can be ignored. Using the --display_error_number option,
you can find out the diagnostic identifier for these warnings. Here is the result:
[err.c]
"err.c", line 9: warning #111-D: statement is unreachable
"err.c", line 12: warning #111-D: statement is unreachable
Next, you can use the diagnostic identifier of 111 as the argument to the --diag_remark option to treat this
warning as a remark. This compilation produces no diagnostic messages (because remarks are disabled
by default).
NOTE: You can suppress any non-fatal errors, but be careful to make sure you only suppress
diagnostic messages that you understand and are known not to affect the correctness of
your program.
2.8
Other Messages
Other error messages that are unrelated to the source, such as incorrect command-line syntax or inability
to find specified files, are usually fatal. They are identified by the symbol >> preceding the message.
2.9
Generating Cross-Reference Listing Information (--gen_cross_reference Option)
The --gen_cross_reference option generates a cross-reference listing file that contains reference
information for each identifier in the source file. (The --gen_cross_reference option is separate from -asm_listing_cross_reference, which is an assembler rather than a compiler option.) The cross-reference
listing file has the same name as the source file with a .crl extension.
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The information in the cross-reference listing file is displayed in the following format:
sym-id name X filename line number column number
sym-id
name
X
filename
line number
column number
An integer uniquely assigned to each identifier
The identifier name
One of the following values:
D
Definition
d
Declaration (not a definition)
M
Modification
A
Address taken
U
Used
C
Changed (used and modified in a single operation)
R
Any other kind of reference
E
Error; reference is indeterminate
The source file
The line number in the source file
The column number in the source file
2.10 Generating a Raw Listing File (--gen_preprocessor_listing Option)
The --gen_preprocessor_listing option generates a raw listing file that can help you understand how the
compiler is preprocessing your source file. Whereas the preprocessed listing file (generated with the -preproc_only, --preproc_with_comment, --preproc_with_line, and --preproc_dependency preprocessor
options) shows a preprocessed version of your source file, a raw listing file provides a comparison
between the original source line and the preprocessed output. The raw listing file has the same name as
the corresponding source file with an .rl extension.
The raw listing file contains the following information:
• Each original source line
• Transitions into and out of include files
• Diagnostic messages
• Preprocessed source line if nontrivial processing was performed (comment removal is considered
trivial; other preprocessing is nontrivial)
Each source line in the raw listing file begins with one of the identifiers listed in Table 2-32.
Table 2-32. Raw Listing File Identifiers
Identifier
Definition
N
Normal line of source
X
Expanded line of source. It appears immediately following the normal line of source
if nontrivial preprocessing occurs.
S
Skipped source line (false #if clause)
L
Change in source position, given in the following format:
L line number filename key
Where line number is the line number in the source file. The key is present only
when the change is due to entry/exit of an include file. Possible values of key are:
1 = entry into an include file
2 = exit from an include file
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The --gen_preprocessor_listing option also includes diagnostic identifiers as defined in Table 2-33.
Table 2-33. Raw Listing File Diagnostic Identifiers
Diagnostic Identifier
Definition
E
Error
F
Fatal
R
Remark
W
Warning
Diagnostic raw listing information is displayed in the following format:
S filename line number column number diagnostic
S
filename
line number
column number
diagnostic
One of the identifiers in Table 2-33 that indicates the severity of the diagnostic
The source file
The line number in the source file
The column number in the source file
The message text for the diagnostic
Diagnostic messages after the end of file are indicated as the last line of the file with a column number of
0. When diagnostic message text requires more than one line, each subsequent line contains the same
file, line, and column information but uses a lowercase version of the diagnostic identifier. For more
information about diagnostic messages, see Section 2.7.
2.11 Using Inline Function Expansion
When an inline function is called, a copy of the C/C++ source code for the function is inserted at the point
of the call. This is known as inline function expansion, commonly called function inlining or just inlining.
Inline function expansion can speed up execution by eliminating function call overhead. This is particularly
beneficial for very small functions that are called frequently. Function inlining involves a tradeoff between
execution speed and code size, because the code is duplicated at each function call site. Large functions
that are called in many places are poor candidates for inlining.
NOTE: Excessive Inlining Can Degrade Performance
Excessive inlining can make the compiler dramatically slower and degrade the performance
of generated code.
Function inlining is triggered by the following situations:
• The use of built-in intrinsic operations. Intrinsic operations look like function calls, and are inlined
automatically, even though no function body exists.
• Use of the inline keyword or the equivalent __inline keyword. Functions declared with the inline
keyword may be inlined by the compiler if you set --opt_level=0 or greater. The inline keyword is a
suggestion from the programmer to the compiler. Even if your optimization level is high, inlining is still
optional for the compiler. The compiler decides whether to inline a function based on the length of the
function, the number of times it is called, your --opt_for_speed setting, and any contents of the function
that disqualify it from inlining (see Section 2.11.2). Functions can be inlined at --opt_level=0 or above if
the function body is visible in the same module or if -pm is also used and the function is visible in one
of the modules being compiled. Functions may be inlined at link time if the file containing the definition
and the call site were both compiled with --opt_level=4. Functions defined as both static and inline are
more likely to be inlined.
• When --opt_level=3 or greater is used, the compiler may automatically inline eligible functions even if
they are not declared as inline functions. The same list of decision factors listed for functions explicitly
defined with the inline keyword is used. For more about automatic function inlining, see Section 3.5.
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Using Inline Function Expansion
•
•
•
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The pragma FUNC_ALWAYS_INLINE (Section 5.11.13) and the equivalent always_inline attribute
(Section 5.17.2) force a function to be inlined (where it is legal to do so) unless --opt_level=off. That is,
the pragma FUNC_ALWAYS_INLINE forces function inlining even if the function is not declared as
inline and the --opt_level=0 or --opt_level=1.
The FORCEINLINE pragma (Section 5.11.11) forces functions to be inlined in the annotated
statement. That is, it has no effect on those functions in general, only on function calls in a single
statement. The FORCEINLINE_RECURSIVE pragma forces inlining not only of calls visible in the
statement, but also in the inlined bodies of calls from that statement.
The --disable_inlining option prevents any inlining. The pragma FUNC_CANNOT_INLINE prevents a
function from being inlined. The NOINLINE pragma prevents calls within a single statement from being
inlined. (NOINLINE is the inverse of the FORCEINLINE pragma.)
NOTE: Function Inlining Can Greatly Increase Code Size
Function inlining increases code size, especially inlining a function that is called in a number
of places. Function inlining is optimal for functions that are called only from a small number
of places and for small functions.
The semantics of the inline keyword in C code follow the C99 standard. The semantics of the inline
keyword in C++ code follow the C++ standard.
The inline keyword is supported in all C++ modes, in relaxed ANSI mode for all C standards, and in
strict ANSI mode for C99 and C11. It is disabled in strict ANSI mode for C89, because it is a language
extension that could conflict with a strictly conforming program. If you want to define inline functions while
in strict ANSI C89 mode, use the alternate keyword __inline.
Compiler options that affect inlining are: --opt_level, --auto_inline, --remove_hooks_when_inlining, -opt_for_speed, and --disable_inlining.
2.11.1 Inlining Intrinsic Operators
The compiler has a number of built-in function-like operations called intrinsics. The implementation of an
intrinsic function is handled by the compiler, which substitutes a sequence of instructions for the function
call. This is similar to the way inline functions are handled; however, because the compiler knows the code
of the intrinsic function, it can perform better optimization.
Intrinsics are inlined whether or not you use the optimizer. For details about intrinsics, and a list of the
intrinsics, see Section 5.14. In addition to those listed, abs and memcpy are implemented as intrinsics.
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2.11.2 Inlining Restrictions
The compiler makes decisions about which functions to inline based on the factors mentioned in
Section 2.11. In addition, there are several restrictions that can disqualify a function from being inlined by
automatic inlining or inline keyword-based inlining.
The compiler will leave calls as they are if the function:
• Has a different number of arguments than the call site
• Has an argument whose type is incompatible with the corresponding call site argument
• Is not declared inline and returns void but its return value is needed
• Is an ARM function with different code-state than its caller
The compiler will also not inline a call if the function has features that create difficult situations for the
compiler:
• Has a variable-length argument list
• Never returns
• Is a recursive or non-leaf function that exceeds the depth limit
• Is not declared inline and contains an asm() statement that is not a comment
• Is an interrupt function
• Is the main() function
• Is not declared inline and will require too much stack space for local array or structure variables
• Contains a volatile local variable or argument
• Is a C++ function that contains a catch
• Is not defined in the current compilation unit and -O4 optimization is not used
A call in a statement that is annotated with a NOINLINE pragma will not be inlined, regardless of other
indications (including a FUNC_ALWAYS_INLINE pragma or always_inline attribute on the called function).
A call in a statement that is annotated with a FORCEINLINE pragma will always be inlined, if it is not
disqualified for one of the reasons above, even if the called function has a FUNC_CANNOT_INLINE
pragma or cannot_inline attribute.
In other words, a statement-level pragma overrides a function-level pragma or attribute. If both NOINLINE
and FORCEINLINE apply to the same statement, then the one that appears first will be used and the rest
will be ignored.
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Using Interlist
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2.12 Using Interlist
The compiler tools include a feature that interlists C/C++ source statements into the assembly language
output of the compiler. The interlist feature enables you to inspect the assembly code generated for each
C statement. The interlist behaves differently, depending on whether or not the optimizer is used, and
depending on which options you specify.
The easiest way to invoke the interlist feature is to use the --c_src_interlist option. To compile and run the
interlist on a program called function.c, enter:
armcl --c_src_interlist function
The --c_src_interlist option prevents the compiler from deleting the interlisted assembly language output
file. The output assembly file, function.asm, is assembled normally.
When you invoke the interlist feature without the optimizer, the interlist runs as a separate pass between
the code generator and the assembler. It reads both the assembly and C/C++ source files, merges them,
and writes the C/C++ statements into the assembly file as comments.
Using the --c_src_interlist option can cause performance and/or code size degradation.
Example 2-1 shows a typical interlisted assembly file.
For more information about using the interlist feature with the optimizer, see Section 3.11.
Example 2‑1. An Interlisted Assembly Language File
_main:
STMFD
SP!, {LR}
;-----------------------------------------------------------------------------;
5 | printf("Hello, world\n");
;-----------------------------------------------------------------------------ADR
A1, SL1
BL
_printf
;-----------------------------------------------------------------------------;
6 | return 0;
;-----------------------------------------------------------------------------MOV
A1, #0
LDMFD
SP!, {PC}
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Controlling Application Binary Interface
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2.13 Controlling Application Binary Interface
Application Binary Interface (ABI) defines the low level interface between object files, and between an
executable and its execution environment. An ABI allows ABI-compliant object files to be linked together,
regardless of their source, and allows the resulting executable to run on any system that supports that
ABI.
Object files conforming to different ABIs cannot be linked together. The linker detects this situation and
generates an error.
The ARM compiler now supports only the Embedded Application Binary Interface (EABI) ABI, which uses
the ELF object format and the DWARF debug format. If you want support for the legacy TI_ARM9_ABI
and TIARM ABIs, please use the ARM v5.2 Code Generation Tools and refer to SPNU151J and
SPNU118J for documentation.
An industry consortium founded by ARM Ltd defined a standard ABI for binary code intended for the ARM
architecture. This ABI is called the Application Binary Interface (ABI) for the ARM Architecture Version 2
(ARM ABIv2). This ABI is also referred to as Embedded Application Binary Interface (EABI). The terms
ABIv2 and EABI can be used interchangeably.
For more details on the ABI, see Section 5.13.
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VFP Support
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2.14 VFP Support
The compiler includes support for generating vector floating-point (VFP) co-processor instructions through
the --float_support=vfp option. The VFP co-processor is available in many variants of ARM11 and higher.
The valid vfp entries are:
vfpv2— Allows generation of floating point instructions for ARM9E.
vfpv3— Allows generation of floating point instructions for Cortex-A8.
vfpv3d16— Allows generation of floating point instructions for Cortex-R4.
fpv4spd16 — Allows generation of floating point instructions for Cortex-M4.
none — Disables hardware floating point support. Specifies that the compiler implements floating point
operations in software.
Using the --silicon_version=7M4 command-line option automatically sets the --float_support=fpv4spd16
option. To disable hardware floating point support, use the --float_support=none option.
This is the current support for VFP:
• You must link any VFP compiled code with a separate version of the run-time support library. See
Section 7.1.8 for information on library-naming conventions.
• The compiler follows the VFP argument passing and returning calling convention for qualified VFP
arguments.
• Object files that do not contain any functions with floating point arguments or return values can be
linked with both VFP and non-VFP files.
• Object files that do contain functions with floating point arguments or return values can only be linked
with objects that were compiled with matching VFP support.
• All hand-coded VFP assembly must follow VFP calling conventions and EABI conventions to correctly
compile and link. In addition to these, the appropriate VFP build attributes for EABI must be correctly
set.
• The compile-time predefined macro __TI_VFP_SUPPORT__ can be used for conditionally
compiling/assembling user code. VFP-specific user code can use this macro to ensure that the
conditionally included code is compiled only when VFP is enabled.
Refer to the ARM architecture manual for more details on the VFPv3 and VFPv3D16 architectures and
ISAs. Refer to the ARM AAPCS and EABI documents for more details on VFP calling conventions and
build attributes.
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2.15 Enabling Entry Hook and Exit Hook Functions
An entry hook is a routine that is called upon entry to each function in the program. An exit hook is a
routine that is called upon exit of each function. Applications for hooks include debugging, trace, profiling,
and stack overflow checking.
Entry and exit hooks are enabled using the following options:
--entry_hook[=name]
--entry_parm{=name|
address|none}
--exit_hook[=name]
--exit_parm{=name|
address|none}
Enables entry hooks. If specified, the hook function is called name. Otherwise,
the default entry hook function name is __entry_hook.
Specify the parameters to the hook function. The name parameter specifies
that the name of the calling function is passed to the hook function as an
argument. In this case the signature for the hook function is: void hook(const
char *name);
The address parameter specifies that the address of the calling function is
passed to the hook function. In this case the signature for the hook function is:
void hook(void (*addr)());
The none parameter specifies that the hook is called with no parameters. This
is the default. In this case the signature for the hook function is: void
hook(void);
Enables exit hooks. If specified, the hook function is called name. Otherwise,
the default exit hook function name is __exit_hook.
Specify the parameters to the hook function. The name parameter specifies
that the name of the calling function is passed to the hook function as an
argument. In this case the signature for the hook function is: void hook(const
char *name);
The address parameter specifies that the address of the calling function is
passed to the hook function. In this case the signature for the hook function is:
void hook(void (*addr)());
The none parameter specifies that the hook is called with no parameters. This
is the default. In this case the signature for the hook function is: void
hook(void);
The presence of the hook options creates an implicit declaration of the hook function with the given
signature. If a declaration or definition of the hook function appears in the compilation unit compiled with
the options, it must agree with the signatures listed above.
In C++, the hooks are declared extern "C". Thus you can define them in C (or assembly) without being
concerned with name mangling.
Hooks can be declared inline, in which case the compiler tries to inline them using the same criteria as
other inline functions.
Entry hooks and exit hooks are independent. You can enable one but not the other, or both. The same
function can be used as both the entry and exit hook.
You must take care to avoid recursive calls to hook functions. The hook function should not call any
function which itself has hook calls inserted. To help prevent this, hooks are not generated for inline
functions, or for the hook functions themselves.
You can use the --remove_hooks_when_inlining option to remove entry/exit hooks for functions that are
auto-inlined by the optimizer.
See Section 5.11.22 for information about the NO_HOOKS pragma.
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Chapter 3
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Optimizing Your Code
The compiler tools can perform many optimizations to improve the execution speed and reduce the size of
C and C++ programs by simplifying loops, rearranging statements and expressions, and allocating
variables into registers.
This chapter describes how to invoke different levels of optimization and describes which optimizations are
performed at each level. This chapter also describes how you can use the Interlist feature when
performing optimization and how you can profile or debug optimized code.
Topic
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
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...........................................................................................................................
Invoking Optimization .........................................................................................
Controlling Code Size Versus Speed ...................................................................
Performing File-Level Optimization (--opt_level=3 option) .......................................
Program-Level Optimization (--program_level_compile and --opt_level=3 options).....
Automatic Inline Expansion (--auto_inline Option)..................................................
Link-Time Optimization (--opt_level=4 Option) .......................................................
Using Feedback Directed Optimization .................................................................
Using Profile Information to Analyze Code Coverage .............................................
Accessing Aliased Variables in Optimized Code ....................................................
Use Caution With asm Statements in Optimized Code ............................................
Using the Interlist Feature With Optimization .........................................................
Debugging and Profiling Optimized Code..............................................................
What Kind of Optimization Is Being Performed? ....................................................
Optimizing Your Code
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62
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69
69
69
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3.1
Invoking Optimization
The C/C++ compiler is able to perform various optimizations. High-level optimizations are performed in the
optimizer and low-level, target-specific optimizations occur in the code generator. Use higher optimization
levels, such as --opt_level=2 and --opt_level=3, to achieve optimal code.
The easiest way to invoke optimization is to use the compiler program, specifying the --opt_level=n option
on the compiler command line. You can use -On to alias the --opt_level option. The n denotes the level of
optimization (0, 1, 2, 3, and 4), which controls the type and degree of optimization.
• --opt_level=off or -Ooff
– Performs no optimization
• --opt_level=0 or -O0
– Performs control-flow-graph simplification
– Allocates variables to registers
– Performs loop rotation
– Eliminates unused code
– Simplifies expressions and statements
– Expands calls to functions declared inline
• --opt_level=1 or -O1
Performs all --opt_level=0 (-O0) optimizations, plus:
– Performs local copy/constant propagation
– Removes unused assignments
– Eliminates local common expressions
• --opt_level=2 or -O2
Performs all --opt_level=1 (-O1) optimizations, plus:
– Performs loop optimizations
– Eliminates global common subexpressions
– Eliminates global unused assignments
– Performs loop unrolling
• --opt_level=3 or -O3
Performs all --opt_level=2 (-O2) optimizations, plus:
– Removes all functions that are never called
– Simplifies functions with return values that are never used
– Inlines calls to small functions
– Reorders function declarations; the called functions attributes are known when the caller is
optimized
– Propagates arguments into function bodies when all calls pass the same value in the same
argument position
– Identifies file-level variable characteristics
If you use --opt_level=3 (-O3), see Section 3.3 and Section 3.4 for more information.
• --opt_level=4 or -O4
Performs link-time optimization. See Section 3.6 for details.
For information about how the --opt_level option along with the --opt_for_speed option and various
pragmas affect inlining, see Section 2.11.
By default, debugging is enabled and the default optimization level is unaffected by the generation of
debug information.
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The levels of optimizations are performed by the stand-alone optimization pass. The code generator
performs several additional optimizations, particularly processor-specific optimizations. It does so
regardless of whether you invoke the optimizer. These optimizations are always enabled, although they
are more effective when the optimizer is used.
3.2
Controlling Code Size Versus Speed
To balance the tradeoff between code size and speed, use the --opt_for_speed option. The level of
optimization (0-5) controls the type and degree of code size or code speed optimization:
• --opt_for_speed=0
Optimizes code size with a high risk of worsening or impacting performance.
• --opt_for_speed=1
Optimizes code size with a medium risk of worsening or impacting performance.
• --opt_for_speed=2
Optimizes code size with a low risk of worsening or impacting performance.
• --opt_for_speed=3
Optimizes code performance/speed with a low risk of worsening or impacting code size.
• --opt_for_speed=4
Optimizes code performance/speed with a medium risk of worsening or impacting code size.
• --opt_for_speed=5
Optimizes code performance/speed with a high risk of worsening or impacting code size.
If you specify the --opt_for_speed option without a parameter, the default setting is --opt_for_speed=4. If
you do not specify the --opt_for_speed option, the default setting is 1
The best performance for caching devices has been observed with --opt_for_speed set to level 1 or 2.
3.3
Performing File-Level Optimization (--opt_level=3 option)
The --opt_level=3 option (aliased as the -O3 option) instructs the compiler to perform file-level
optimization. This is the default optimization level. You can use the --opt_level=3 option alone to perform
general file-level optimization, or you can combine it with other options to perform more specific
optimizations. The options listed in Table 3-1 work with --opt_level=3 to perform the indicated optimization:
Table 3-1. Options That You Can Use With --opt_level=3
If You ...
Use this Option
See
Want to create an optimization information file
--gen_opt_level=n
Section 3.3.1
Want to compile multiple source files
--program_level_compile
Section 3.4
3.3.1 Creating an Optimization Information File (--gen_opt_info Option)
When you invoke the compiler with the --opt_level=3 option (the default), you can use the --gen_opt_info
option to create an optimization information file that you can read. The number following the option
denotes the level (0, 1, or 2). The resulting file has an .nfo extension. Use Table 3-2 to select the
appropriate level to append to the option.
Table 3-2. Selecting a Level for the --gen_opt_info Option
58
If you...
Use this option
Do not want to produce an information file, but you used the --gen_opt_level=1 or --gen_opt_level=2
option in a command file or an environment variable. The --gen_opt_level=0 option restores the
default behavior of the optimizer.
--gen_opt_info=0
Want to produce an optimization information file
--gen_opt_info=1
Want to produce a verbose optimization information file
--gen_opt_info=2
Optimizing Your Code
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3.4
Program-Level Optimization (--program_level_compile and --opt_level=3 options)
You can specify program-level optimization by using the --program_level_compile option with the -opt_level=3 option (aliased as -O3). (If you use --opt_level=4 (-O4), the --program_level_compile option
cannot be used, because link-time optimization provides the same optimization opportunities as program
level optimization.)
With program-level optimization, all of your source files are compiled into one intermediate file called a
module. The module moves to the optimization and code generation passes of the compiler. Because the
compiler can see the entire program, it performs several optimizations that are rarely applied during filelevel optimization:
• If a particular argument in a function always has the same value, the compiler replaces the argument
with the value and passes the value instead of the argument.
• If a return value of a function is never used, the compiler deletes the return code in the function.
• If a function is not called directly or indirectly by main(), the compiler removes the function.
The --program_level_compile option requires use of --opt_level=3 or higher in order to perform these
optimizations.
To see which program-level optimizations the compiler is applying, use the --gen_opt_level=2 option to
generate an information file. See Section 3.3.1 for more information.
In Code Composer Studio, when the --program_level_compile option is used, C and C++ files that have
the same options are compiled together. However, if any file has a file-specific option that is not selected
as a project-wide option, that file is compiled separately. For example, if every C and C++ file in your
project has a different set of file-specific options, each is compiled separately, even though program-level
optimization has been specified. To compile all C and C++ files together, make sure the files do not have
file-specific options. Be aware that compiling C and C++ files together may not be safe if previously you
used a file-specific option.
Compiling Files With the --program_level_compile and --keep_asm Options
NOTE: If you compile all files with the --program_level_compile and --keep_asm options, the
compiler produces only one .asm file, not one for each corresponding source file.
3.4.1 Controlling Program-Level Optimization (--call_assumptions Option)
You can control program-level optimization, which you invoke with --program_level_compile --opt_level=3,
by using the --call_assumptions option. Specifically, the --call_assumptions option indicates if functions in
other modules can call a module's external functions or modify a module's external variables. The number
following --call_assumptions indicates the level you set for the module that you are allowing to be called or
modified. The --opt_level=3 option combines this information with its own file-level analysis to decide
whether to treat this module's external function and variable declarations as if they had been declared
static. Use Table 3-3 to select the appropriate level to append to the --call_assumptions option.
Table 3-3. Selecting a Level for the --call_assumptions Option
If Your Module …
Use this Option
Has functions that are called from other modules and global variables that are modified in other
modules
--call_assumptions=0
Does not have functions that are called by other modules but has global variables that are modified in
other modules
--call_assumptions=1
Does not have functions that are called by other modules or global variables that are modified in other
modules
--call_assumptions=2
Has functions that are called from other modules but does not have global variables that are modified
in other modules
--call_assumptions=3
In certain circumstances, the compiler reverts to a different --call_assumptions level from the one you
specified, or it might disable program-level optimization altogether. Table 3-4 lists the combinations of -call_assumptions levels and conditions that cause the compiler to revert to other --call_assumptions
levels.
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Table 3-4. Special Considerations When Using the --call_assumptions Option
If --call_assumptions is...
Under these Conditions...
Then the --call_assumptions
Level...
Not specified
The --opt_level=3 optimization level was specified
Defaults to --call_assumptions=2
Not specified
The compiler sees calls to outside functions under the -opt_level=3 optimization level
Reverts to --call_assumptions=0
Not specified
Main is not defined
Reverts to --call_assumptions=0
--call_assumptions=1 or
--call_assumptions=2
No function has main defined as an entry point, and no interrupt
functions are defined, and no functions are identified by the
FUNC_EXT_CALLED pragma
Reverts to --call_assumptions=0
--call_assumptions=1 or
--call_assumptions=2
A main function is defined, or, an interrupt function is defined, or a
function is identified by the FUNC_EXT_CALLED pragma
Remains --call_assumptions=1
or --call_assumptions=2
--call_assumptions=3
Any condition
Remains --call_assumptions=3
In some situations when you use --program_level_compile and --opt_level=3, you must use a -call_assumptions option or the FUNC_EXT_CALLED pragma. See Section 3.4.2 for information about
these situations.
3.4.2 Optimization Considerations When Mixing C/C++ and Assembly
If you have any assembly functions in your program, you need to exercise caution when using the -program_level_compile option. The compiler recognizes only the C/C++ source code and not any
assembly code that might be present. Because the compiler does not recognize the assembly code calls
and variable modifications to C/C++ functions, the --program_level_compile option optimizes out those
C/C++ functions. To keep these functions, place the FUNC_EXT_CALLED pragma (see Section 5.11.15)
before any declaration or reference to a function that you want to keep.
Another approach you can take when you use assembly functions in your program is to use the -call_assumptions=n option with the --program_level_compile and --opt_level=3 options. See Section 3.4.1
for information about the --call_assumptions=n option.
In general, you achieve the best results through judicious use of the FUNC_EXT_CALLED pragma in
combination with --program_level_compile --opt_level=3 and --call_assumptions=1 or -call_assumptions=2.
If any of the following situations apply to your application, use the suggested solution:
Situation — Your application consists of C/C++ source code that calls assembly functions. Those
assembly functions do not call any C/C++ functions or modify any C/C++ variables.
Solution — Compile with --program_level_compile --opt_level=3 --call_assumptions=2 to tell the compiler
that outside functions do not call C/C++ functions or modify C/C++ variables.
If you compile with the --program_level_compile --opt_level=3 options only, the compiler reverts
from the default optimization level (--call_assumptions=2) to --call_assumptions=0. The compiler
uses --call_assumptions=0, because it presumes that the calls to the assembly language functions
that have a definition in C/C++ may call other C/C++ functions or modify C/C++ variables.
Situation — Your application consists of C/C++ source code that calls assembly functions. The assembly
language functions do not call C/C++ functions, but they modify C/C++ variables.
Solution — Try both of these solutions and choose the one that works best with your code:
• Compile with --program_level_compile --opt_level=3 --call_assumptions=1.
• Add the volatile keyword to those variables that may be modified by the assembly functions and
compile with --program_level_compile --opt_level=3 --call_assumptions=2.
Situation — Your application consists of C/C++ source code and assembly source code. The assembly
functions are interrupt service routines that call C/C++ functions; the C/C++ functions that the
assembly functions call are never called from C/C++. These C/C++ functions act like main: they
function as entry points into C/C++.
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Solution — Add the volatile keyword to the C/C++ variables that may be modified by the interrupts. Then,
you can optimize your code in one of these ways:
• You achieve the best optimization by applying the FUNC_EXT_CALLED pragma to all of the
entry-point functions called from the assembly language interrupts, and then compiling with -program_level_compile --opt_level=3 --call_assumptions=2. Be sure that you use the pragma
with all of the entry-point functions. If you do not, the compiler might remove the entry-point
functions that are not preceded by the FUNC_EXT_CALLED pragma.
• Compile with --program_level_compile --opt_level=3 --call_assumptions=3. Because you do not
use the FUNC_EXT_CALLED pragma, you must use the --call_assumptions=3 option, which is
less aggressive than the --call_assumptions=2 option, and your optimization may not be as
effective.
Keep in mind that if you use --program_level_compile --opt_level=3 without additional options, the
compiler removes the C functions that the assembly functions call. Use the FUNC_EXT_CALLED
pragma to keep these functions.
3.5
Automatic Inline Expansion (--auto_inline Option)
When optimizing with the --opt_level=3 option (aliased as -O3), the compiler automatically inlines small
functions. A command-line option, --auto_inline=size, specifies the size threshold for automatic inlining.
This option controls only the inlining of functions that are not explicitly declared as inline.
When the --auto_inline option is not used, the compiler sets the size limit based on the optimization level
and the optimization goal (performance versus code size). If the -auto_inline size parameter is set to 0,
automatic inline expansion is disabled. If the --auto_inline size parameter is set to a non-zero integer, the
compiler automatically inlines any function smaller than size. (This is a change from previous releases,
which inlined functions for which the product of the function size and the number of calls to it was less
than size. The new scheme is simpler, but will usually lead to more inlining for a given value of size.)
The compiler measures the size of a function in arbitrary units; however the optimizer information file
(created with the --gen_opt_info=1 or --gen_opt_info=2 option) reports the size of each function in the
same units that the --auto_inline option uses. When --auto_inline is used, the compiler does not attempt to
prevent inlining that causes excessive growth in compile time or size; use with care.
When --auto_inline option is not used, the decision to inline a function at a particular call-site is based on
an algorithm that attempts to optimize benefit and cost. The compiler inlines eligible functions at call-sites
until a limit on size or compilation time is reached.
Inlining behavior varies, depending on which compile-time options are specified:
• The code size limit is smaller when compiling for code size rather than performance. The --auto_inline
option overrides this size limit.
• At --opt_level=3, the compiler automatically inlines small functions.
• At --opt_level=4, the compiler auto-inlines aggressively if compiling for performance.
For information about interactions between command-line options, pragmas, and keywords that affect
inlining, see Section 2.11.
Some Functions Cannot Be Inlined
NOTE: For a call-site to be considered for inlining, it must be legal to inline the function and inlining
must not be disabled in some way. See the inlining restrictions in Section 2.11.2.
Optimization Level 3 and Inlining
NOTE: In order to turn on automatic inlining, you must use the --opt_level=3 option. If you desire the
--opt_level=3 optimizations, but not automatic inlining, use --auto_inline=0 with the -opt_level=3 option.
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Inlining and Code Size
NOTE: Expanding functions inline increases code size, especially inlining a function that is called in
a number of places. Function inlining is optimal for functions that are called only from a small
number of places and for small functions. To prevent increases in code size because of
inlining, use the --auto_inline=0 option. This option causes the compiler to inline intrinsics
only.
3.6
Link-Time Optimization (--opt_level=4 Option)
Link-time optimization is an optimization mode that allows the compiler to have visibility of the entire
program. The optimization occurs at link-time instead of compile-time like other optimization levels.
Link-time optimization is invoked by using the --opt_level=4 option. This option must be used in both the
compilation and linking steps. At compile time, the compiler embeds an intermediate representation of the
file being compiled into the resulting object file. At link-time this representation is extracted from every
object file which contains it, and is used to optimize the entire program.
If you use --opt_level=4 (-O4), the --program_level_compile option cannot also be used, because link-time
optimization provides the same optimization opportunities as program level optimization (Section 3.4).
Link-time optimization provides the following benefits:
• Each source file can be compiled separately. One issue with program-level compilation is that it
requires all source files to be passed to the compiler at one time. This often requires significant
modification of a customer's build process. With link-time optimization, all files can be compiled
separately.
• References to C/C++ symbols from assembly are handled automatically. When doing program-level
compilation, the compiler has no knowledge of whether a symbol is referenced externally. When
performing link-time optimization during a final link, the linker can determine which symbols are
referenced externally and prevent eliminating them during optimization.
• Third party object files can participate in optimization. If a third party vendor provides object files that
were compiled with the --opt_level=4 option, those files participate in optimization along with usergenerated files. This includes object files supplied as part of the TI run-time support. Object files that
were not compiled with –opt_level=4 can still be used in a link that is performing link-time optimization.
Those files that were not compiled with –opt_level=4 do not participate in the optimization.
• Source files can be compiled with different option sets. With program-level compilation, all source files
must be compiled with the same option set. With link-time optimization files can be compiled with
different options. If the compiler determines that two options are incompatible, it issues an error.
3.6.1 Option Handling
When performing link-time optimization, source files can be compiled with different options. When
possible, the options that were used during compilation are used during link-time optimization. For options
which apply at the program level, --auto_inline for instance, the options used to compile the main function
are used. If main is not included in link-time optimization, the option set used for the first object file
specified on the command line is used. Some options, --opt_for_speed for instance, can affect a wide
range of optimizations. For these options, the program-level behavior is derived from main, and the local
optimizations are obtained from the original option set.
Some options are incompatible when performing link-time optimization. These are usually options which
conflict on the command line as well, but can also be options that cannot be handled during link-time
optimization.
3.6.2 Incompatible Types
During a normal link, the linker does not check to make sure that each symbol was declared with the
same type in different files. This is not necessary during a normal link. When performing link-time
optimization, however, the linker must ensure that all symbols are declared with compatible types in
different source files. If a symbol is found which has incompatible types, an error is issued. The rules for
compatible types are derived from the C and C++ standards.
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3.7
Using Feedback Directed Optimization
Feedback directed optimization provides a method for finding frequently executed paths in an application
using compiler-based instrumentation. This information is fed back to the compiler and is used to perform
optimizations. This information is also used to provide you with information about application behavior.
3.7.1 Feedback Directed Optimization
Feedback directed optimization uses run-time feedback to identify and optimize frequently executed
program paths. Feedback directed optimization is a two-phase process.
3.7.1.1
Phase 1 -- Collect Program Profile Information
In this phase the compiler is invoked with the option --gen_profile_info, which instructs the compiler to add
instrumentation code to collect profile information. The compiler inserts a minimal amount of
instrumentation code to determine control flow frequencies. Memory is allocated to store counter
information.
The instrumented application program is executed on the target using representative input data sets. The
input data sets should correlate closely with the way the program is expected to be used in the end
product environment. When the program completes, a run-time-support function writes the collected
information into a profile data file called a PDAT file. Multiple executions of the program using different
input data sets can be performed and in such cases, the run-time-support function appends the collected
information into the PDAT file. The resulting PDAT file is post-processed using a tool called the Profile
Data Decoder or armpdd. The armpdd tool consolidates multiple data sets and formats the data into a
feedback file (PRF file, see Section 3.7.2) for consumption by phase 2 of feedback directed optimization.
3.7.1.2
Phase 2 -- Use Application Profile Information for Optimization
In this phase, the compiler is invoked with the --use_profile_info=file.prf option, which reads the specified
PRF file generated in phase 1. In phase 2, optimization decisions are made using the data generated
during phase 1. The profile feedback file is used to guide program optimization. The compiler optimizes
frequently executed program paths more aggressively.
The compiler uses data in the profile feedback file to guide certain optimizations of frequently executed
program paths.
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3.7.1.3
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Generating and Using Profile Information
There are two options that control feedback directed optimization:
--gen_profile_info
--use_profile_info
3.7.1.4
tells the compiler to add instrumentation code to collect profile information. When
the program executes the run-time-support exit() function, the profile data is
written to a PDAT file. This option applies to all the C/C++ source files being
compiled on the command-line.
If the environment variable TI_PROFDATA on the host is set, the data is written
into the specified file. Otherwise, it uses the default filename: pprofout.pdat. The
full pathname of the PDAT file (including the directory name) can be specified
using the TI_PROFDATA host environment variable.
By default, the RTS profile data output routine uses the C I/O mechanism to write
data to the PDAT file. You can install a device handler for the PPHNDL device to
re-direct the profile data to a custom device driver routine. For example, this could
be used to send the profile data to a device that does not use a file system.
Feedback directed optimization requires you to turn on at least some debug
information when using the --gen_profile_info option. This enables the compiler to
output debug information that allows armpdd to correlate compiled functions and
their associated profile data.
specifies the profile information file(s) to use for performing phase 2 of feedback
directed optimization. More than one profile information file can be specified on the
command line; the compiler uses all input data from multiple information files. The
syntax for the option is:
--use_profile_info==file1[, file2, ..., filen]
If no filename is specified, the compiler looks for a file named pprofout.prf in the
directory where the compiler in invoked.
Example Use of Feedback Directed Optimization
These steps illustrate the creation and use of feedback directed optimization.
1. Generate profile information.
armcl --opt_level=2 --gen_profile_info foo.c --run_linker --output_file=foo.out
--library=lnk.cmd --library=rtsv4_A_be_eabi.lib
2. Execute the application.
The execution of the application creates a PDAT file named pprofout.pdat in the current (host)
directory. The application can be run on target hardware connected to a host machine.
3. Process the profile data.
After running the application with multiple data-sets, run armpdd on the PDAT files to create a profile
information (PRF) file to be used with --use_profile_info.
armpdd -e foo.out -o pprofout.prf pprofout.pdat
4. Re-compile using the profile feedback file.
armcl --opt_level=2 --use_profile_info=pprofout.prf foo.c --run_linker
--output_file=foo.out --library=lnk.cmd --library=rtsv4_A_be_eabi.lib
3.7.1.5
The .ppdata Section
The profile information collected in phase 1 is stored in the .ppdata section, which must be allocated into
target memory. The .ppdata section contains profiler counters for all functions compiled with -gen_profile_info. The default lnk.cmd file in has directives to place the .ppdata section in data memory. If
the link command file has no section directive for allocating .ppdata section, the link step places the
.ppdata section in a writable memory range.
The .ppdata section must be allocated memory in multiples of 32 bytes. Please refer to the linker
command file in the distribution for example usage.
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3.7.1.6
Feedback Directed Optimization and Code Size Tune
Feedback directed optimization is different from the Code Size Tune feature in Code Composer Studio
(CCS). The code size tune feature uses CCS profiling to select specific compilation options for each
function in order to minimize code size while still maintaining a specific performance point. Code size tune
is coarse-grained, since it is selecting an option set for the whole function. Feedback directed optimization
selects different optimization goals along specific regions within a function.
3.7.1.7
Instrumented Program Execution Overhead
During profile collection, the execution time of the application may increase. The amount of increase
depends on the size of the application and the number of files in the application compiled for profiling.
The profiling counters increase the code and data size of the application. Consider using the option when
using profiling to mitigate the code size increase. This has no effect on the accuracy of the profile data
being collected. Since profiling only counts execution frequency and not cycle counts, code size
optimization flags do not affect profiler measurements.
3.7.1.8
Invalid Profile Data
When recompiling with --use_profile_info, the profile information is invalid in the following cases:
• The source file name changed between the generation of profile information (gen-profile) and the use
of the profile information (use-profile).
• The source code was modified since gen-profile. In this case, profile information is invalid for the
modified functions.
• Certain compiler options used with gen-profile are different from those with used with use-profile. In
particular, options that affect parser behavior could invalidate profile data during use-profile. In general,
using different optimization options during use-profile should not affect the validity of profile data.
3.7.2 Profile Data Decoder
The code generation tools include a tool called the Profile Data Decoder or armpdd, which is used for post
processing profile data (PDAT) files. The armpdd tool generates a profile feedback (PRF) file. See
Section 3.7.1 for a discussion of where armpdd fits in the profiling flow. The armpdd tool is invoked with
this syntax:
armpdd -e exec.out -o application.prf filename .pdat
-a
-e exec.out
-o application.prf
filename .pdat
Computes the average of the data values in the data sets instead of
accumulating data values
Specifies exec.out is the name of the application executable.
Specifies application.prf is the formatted profile feedback file that is used as the
argument to --use_profile_info during recompilation. If no output file is specified,
the default output filename is pprofout.prf.
Is the name of the profile data file generated by the run-time-support function.
This is the default name and it can be overridden by using the host environment
variable TI_PROFDATA.
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The run-time-support function and armpdd append to their respective output files and do not overwrite
them. This enables collection of data sets from multiple runs of the application.
Profile Data Decoder Requirements
NOTE: Your application must be compiled with at least DWARF debug support to enable feedback
directed optimization. When compiling for feedback directed optimization, the armpdd tool
relies on basic debug information about each function in generating the formatted .prf file.
The pprofout.pdat file generated by the run-time support is a raw data file of a fixed format
understood only by armpdd. You should not modify this file in any way.
3.7.3 Feedback Directed Optimization API
There are two user interfaces to the profiler mechanism. You can start and stop profiling in your
application by using the following run-time-support calls.
• _TI_start_pprof_collection()
This interface informs the run-time support that you wish to start profiling collection from this point on
and causes the run-time support to clear all profiling counters in the application (that is, discard old
counter values).
• _TI_stop_pprof_collection()
This interface directs the run-time support to stop profiling collection and output profiling data into the
output file (into the default file or one specified by the TI_PROFDATA host environment variable). The
run-time support also disables any further output of profile data into the output file during exit(), unless
you call _TI_start_pprof_collection() again.
3.7.4 Feedback Directed Optimization Summary
Options
--gen_profile_info
--use_profile_info=file.prf
--analyze=codecov
--analyze_only
Adds instrumentation to the compiled code. Execution of the code results in
profile data being emitted to a PDAT file.
Uses profile information for optimization and/or generating code coverage
information.
Generates a code coverage information file and continues with profile-based
compilation. Must be used with --use_profile_info.
Generates only a code coverage information file. Must be used with -use_profile_info. You must specify both --analyze=codecov and -analyze_only to do code coverage analysis of the instrumented application.
Host Environment Variables
TI_PROFDATA
TI_COVDIR
TI_COVDATA
Writes profile data into the specified file
Creates code coverage files in the specified directory
Writes code coverage data into the specified file
API
_TI_start_pprof_collection() Clears the profile counters to file
_TI_stop_pprof_collection() Writes out all profile counters to file
PPHDNL
Device driver handle for low-level C I/O based driver for writing out profile
data from a target program.
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Files Created
*.pdat
*.prf
3.8
Profile data file, which is created by executing an instrumented program and
used as input to the profile data decoder
Profiling feedback file, which is created by the profile data decoder and
used as input to the re-compilation step
Using Profile Information to Analyze Code Coverage
You can use the analysis information from the Profile Data Decoder to analyze code coverage.
3.8.1 Code Coverage
The information collected during feedback directed optimization can be used for generating code coverage
reports. As with feedback directed optimization, the program must be compiled with the --gen_profile_info
option.
Code coverage conveys the execution count of each line of source code in the file being compiled, using
data collected during profiling.
3.8.1.1
Phase1 -- Collect Program Profile Information
In this phase the compiler is invoked with the option --gen_profile_info, which instructs the compiler to add
instrumentation code to collect profile information. The compiler inserts a minimal amount of
instrumentation code to determine control flow frequencies. Memory is allocated to store counter
information.
The instrumented application program is executed on the target using representative input data sets. The
input data sets should correlate closely with the way the program is expected to be used in the end
product environment. When the program completes, a run-time-support function writes the collected
information into a profile data file called a PDAT file. Multiple executions of the program using different
input data sets can be performed and in such cases, the run-time-support function appends the collected
information into the PDAT file. The resulting PDAT file is post-processed using a tool called the Profile
Data Decoder or armpdd. The armpdd tool consolidates multiple data sets and formats the data into a
feedback file (PRF file, see Section 3.7.2) for consumption by phase 2 of feedback directed optimization.
3.8.1.2
Phase 2 -- Generate Code Coverage Reports
In this phase, the compiler is invoked with the --use_profile_info=file.prf option, which indicates that the
compiler should read the specified PRF file generated in phase 1. The application must also be compiled
with either the --codecov or --onlycodecov option; the compiler generates a code-coverage info file. The -codecov option directs the compiler to continue compilation after generating code-coverage information,
while the --onlycodecov option stops the compiler after generating code-coverage data. For example:
armcl --opt_level=2 --use_profile_info=pprofout.prf --onlycodecov foo.c
You can specify two environment variables to control the destination of the code-coverage information file.
• The TI_COVDIR environment variable specifies the directory where the code-coverage file should be
generated. The default is the directory where the compiler is invoked.
• The TI_COVDATA environment variable specifies the name of the code-coverage data file generated
by the compiler. the default is filename.csv where filename is the base-name of the file being compiled.
For example, if foo.c is being compiled, the default code-coverage data file name is foo.csv.
If the code-coverage data file already exists, the compiler appends the new dataset at the end of the file.
Code-coverage data is a comma-separated list of data items that can be conveniently handled by dataprocessing tools and scripting languages. The following is the format of code-coverage data:
"filename-with-full-path","funcname",line#,column#,exec-frequency,"comments"
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"filename-with-full-path"
"funcname"
line#
column#
exec-frequency
"comments"
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Full pathname of the file corresponding to the entry
Name of the function
Line number of the source line corresponding to frequency data
Column number of the source line
Execution frequency of the line
Intermediate-level representation of the source-code generated by the parser
The full filename, function name, and comments appear within quotation marks ("). For example:
"/some_dir/zlib/arm/deflate.c","_deflateInit2_",216,5,1,"( strm->zalloc )"
Other tools, such as a spreadsheet program, can be used to format and view the code coverage data.
3.8.2 Related Features and Capabilities
The code generation tools provide some features and capabilities that can be used in conjunction with
code coverage analysis. The following is a summary:
3.8.2.1
Path Profiler
The code generation tools include a path profiling utility, armpprof, that is run from the compiler, armcl.
The armpprof utility is invoked by the compiler when the --gen_profile or the --use_profile command is
used from the compiler command line:
armcl --gen_profile ... file.c
armcl --use_profile ... file.c
For further information about profile-based optimization and a more detailed description of the profiling
infrastructure, see Section 3.7.
3.8.2.2
Analysis Options
The path profiling utility, armpprof, appends code coverage information to existing CSV (comma separated
values) files that contain the same type of analysis information.
The utility checks to make sure that an existing CSV file contains analysis information that is consistent
with the type of analysis information it is being asked to generate. Attempts to mix code coverage and
other analysis information in the same output CSV file will be detected, and armpprof will emit a fatal error
and abort.
--analyze=codecov
Instructs the compiler to generate code coverage analysis information. This
option replaces the previous --codecov option.
Halts compilation after generation of analysis information is completed.
--analyze_only
3.8.2.3
Environment Variables
To assist with the management of output CSV analysis files, armpprof supports this environment variable:
TI_ANALYSIS_DIR
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Specifies the directory in which the output analysis file will be generated.
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3.9
Accessing Aliased Variables in Optimized Code
Aliasing occurs when a single object can be accessed in more than one way, such as when two pointers
point to the same object or when a pointer points to a named object. Aliasing can disrupt optimization
because any indirect reference can refer to another object. The optimizer analyzes the code to determine
where aliasing can and cannot occur, then optimizes as much as possible while still preserving the
correctness of the program. The optimizer behaves conservatively. If there is a chance that two pointers
are pointing to the same object, then the optimizer assumes that the pointers do point to the same object.
The compiler assumes that if the address of a local variable is passed to a function, the function changes
the local variable by writing through the pointer. This makes the local variable's address unavailable for
use elsewhere after returning. For example, the called function cannot assign the local variable's address
to a global variable or return the local variable's address. In cases where this assumption is invalid, use
the --aliased_variables compiler option to force the compiler to assume worst-case aliasing. In worst-case
aliasing, any indirect reference can refer to such a variable.
3.10 Use Caution With asm Statements in Optimized Code
You must be extremely careful when using asm (inline assembly) statements in optimized code. The
compiler rearranges code segments, uses registers freely, and can completely remove variables or
expressions. Although the compiler never optimizes out an asm statement (except when it is
unreachable), the surrounding environment where the assembly code is inserted can differ significantly
from the original C/C++ source code.
It is usually safe to use asm statements to manipulate hardware controls such as interrupt masks, but asm
statements that attempt to interface with the C/C++ environment or access C/C++ variables can have
unexpected results. After compilation, check the assembly output to make sure your asm statements are
correct and maintain the integrity of the program.
3.11 Using the Interlist Feature With Optimization
You control the output of the interlist feature when compiling with optimization (the --opt_level=n or -On
option) with the --optimizer_interlist and --c_src_interlist options.
• The --optimizer_interlist option interlists compiler comments with assembly source statements.
• The --c_src_interlist and --optimizer_interlist options together interlist the compiler comments and the
original C/C++ source with the assembly code.
When you use the --optimizer_interlist option with optimization, the interlist feature does not run as a
separate pass. Instead, the compiler inserts comments into the code, indicating how the compiler has
rearranged and optimized the code. These comments appear in the assembly language file as comments
starting with ;**. The C/C++ source code is not interlisted, unless you use the --c_src_interlist option also.
The interlist feature can affect optimized code because it might prevent some optimization from crossing
C/C++ statement boundaries. Optimization makes normal source interlisting impractical, because the
compiler extensively rearranges your program. Therefore, when you use the --optimizer_interlist option,
the compiler writes reconstructed C/C++ statements.
Example 3-1 shows a function that has been compiled with optimization (--opt_level=2) and the -optimizer_interlist option. The assembly file contains compiler comments interlisted with assembly code.
Impact on Performance and Code Size
NOTE: The --c_src_interlist option can have a negative effect on performance and code size.
When you use the --c_src_interlist and --optimizer_interlist options with optimization, the compiler inserts
its comments and the interlist feature runs before the assembler, merging the original C/C++ source into
the assembly file.
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Example 3-2 shows the function from Example 3-1 compiled with the optimization (--opt_level=2) and the -c_src_interlist and --optimizer_interlist options. The assembly file contains compiler comments and C
source interlisted with assembly code.
Example 3‑1. The Function From Example 2-1 Compiled With the -O2 and --optimizer_interlist Options
_main:
STMFD
SP!, {LR}
----------------------ADR
A1, SL1
BL
_printf
----------------------MOV
A1, #0
LDMFD
SP!, {PC}
;** 5
;** 6
printf("Hello, world\n");
return 0;
Example 3‑2. The Function From Example 2-1 Compiled with the --opt_level=2, --optimizer_interlist, and -c_src_interlist Options
_main:
STMFD
SP!, {LR}
;** 5
----------------------printf("Hello, world\n");
;-----------------------------------------------------------------------------;
5 | printf("Hello, world\n");
;-----------------------------------------------------------------------------ADR
A1, SL1
BL
_printf
;** 6
----------------------return 0;
;-----------------------------------------------------------------------------;
6 | return 0;
;-----------------------------------------------------------------------------MOV
A1, #0
LDMFD
SP!, {PC}
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3.12 Debugging and Profiling Optimized Code
The compiler generates symbolic debugging information by default at all optimization levels. Generating
debug information does not affect compiler optimization or generated code. However, higher levels of
optimization negatively impact the debugging experience due to the code transformations that are done.
For the best debugging experience use --opt_level=off.
The default optimization level depends on the use of the --symdebug:dwarf (-g) option. If -symdebug:dwarf is specified, the default optimization level is off. Otherwise the default optimization level is
3.
Debug information increases the size of object files, but it does not affect the size of code or data on the
target. If object file size is a concern and debugging is not needed, use --symdebug:none to disable the
generation of debug information.
3.12.1 Profiling Optimized Code
To profile optimized code, use optimization (--opt_level=0 through --opt_level=3).
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3.13 What Kind of Optimization Is Being Performed?
The ARM C/C++ compiler uses a variety of optimization techniques to improve the execution speed of
your C/C++ programs and to reduce their size.
Following are some of the optimizations performed by the compiler:
Optimization
See
Cost-based register allocation
Section 3.13.1
Alias disambiguation
Section 3.13.1
Branch optimizations and control-flow simplification
Section 3.13.3
Data flow optimizations
• Copy propagation
• Common subexpression elimination
• Redundant assignment elimination
Section 3.13.4
Expression simplification
Section 3.13.5
Inline expansion of functions
Section 3.13.6
Function Symbol Aliasing
Section 3.13.7
Induction variable optimizations and strength reduction
Section 3.13.8
Loop-invariant code motion
Section 3.13.9
Loop rotation
Section 3.13.10
Instruction scheduling
Section 3.13.11
ARM-Specific Optimization
See
Tail merging
Section 3.13.12
Autoincrement addressing
Section 3.13.13
Block conditionalizing
Section 3.13.14
Epilog inlining
Section 3.13.15
Removing comparisons to zero
Section 3.13.16
Integer division with constant divisor
Section 3.13.17
Branch chaining
Section 3.13.18
3.13.1 Cost-Based Register Allocation
The compiler, when optimization is enabled, allocates registers to user variables and compiler temporary
values according to their type, use, and frequency. Variables used within loops are weighted to have
priority over others, and those variables whose uses do not overlap can be allocated to the same register.
Induction variable elimination and loop test replacement allow the compiler to recognize the loop as a
simple counting loop and unroll or eliminate the loop. Strength reduction turns the array references into
efficient pointer references with autoincrements.
3.13.2 Alias Disambiguation
C and C++ programs generally use many pointer variables. Frequently, compilers are unable to determine
whether or not two or more I values (lowercase L: symbols, pointer references, or structure references)
refer to the same memory location. This aliasing of memory locations often prevents the compiler from
retaining values in registers because it cannot be sure that the register and memory continue to hold the
same values over time.
Alias disambiguation is a technique that determines when two pointer expressions cannot point to the
same location, allowing the compiler to freely optimize such expressions.
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3.13.3 Branch Optimizations and Control-Flow Simplification
The compiler analyzes the branching behavior of a program and rearranges the linear sequences of
operations (basic blocks) to remove branches or redundant conditions. Unreachable code is deleted,
branches to branches are bypassed, and conditional branches over unconditional branches are simplified
to a single conditional branch.
When the value of a condition is determined at compile time (through copy propagation or other data flow
analysis), the compiler can delete a conditional branch. Switch case lists are analyzed in the same way as
conditional branches and are sometimes eliminated entirely. Some simple control flow constructs are
reduced to conditional instructions, totally eliminating the need for branches.
3.13.4 Data Flow Optimizations
Collectively, the following data flow optimizations replace expressions with less costly ones, detect and
remove unnecessary assignments, and avoid operations that produce values that are already computed.
The compiler with optimization enabled performs these data flow optimizations both locally (within basic
blocks) and globally (across entire functions).
• Copy propagation. Following an assignment to a variable, the compiler replaces references to the
variable with its value. The value can be another variable, a constant, or a common subexpression.
This can result in increased opportunities for constant folding, common subexpression elimination, or
even total elimination of the variable.
• Common subexpression elimination. When two or more expressions produce the same value, the
compiler computes the value once, saves it, and reuses it.
• Redundant assignment elimination. Often, copy propagation and common subexpression elimination
optimizations result in unnecessary assignments to variables (variables with no subsequent reference
before another assignment or before the end of the function). The compiler removes these dead
assignments.
3.13.5 Expression Simplification
For optimal evaluation, the compiler simplifies expressions into equivalent forms, requiring fewer
instructions or registers. Operations between constants are folded into single constants. For example, a =
(b + 4) - (c + 1) becomes a = b - c + 3.
3.13.6 Inline Expansion of Functions
The compiler replaces calls to small functions with inline code, saving the overhead associated with a
function call as well as providing increased opportunities to apply other optimizations.
For information about interactions between command-line options, pragmas, and keywords that affect
inlining, see Section 2.11.
3.13.7 Function Symbol Aliasing
The compiler recognizes a function whose definition contains only a call to another function. If the two
functions have the same signature (same return value and same number of parameters with the same
type, in the same order), then the compiler can make the calling function an alias of the called function.
For example, consider the following:
int bbb(int arg1, char *arg2);
int aaa(int n, char *str)
{
return bbb(n, str);
}
For this example, the compiler makes aaa an alias of bbb, so that at link time all calls to function aaa
should be redirected to bbb. If the linker can successfully redirect all references to aaa, then the body of
function aaa can be removed and the symbol aaa is defined at the same address as bbb.
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For information about using the GCC function attribute syntax to declare function aliases, see
Section 5.17.2
3.13.8 Induction Variables and Strength Reduction
Induction variables are variables whose value within a loop is directly related to the number of executions
of the loop. Array indices and control variables for loops are often induction variables.
Strength reduction is the process of replacing inefficient expressions involving induction variables with
more efficient expressions. For example, code that indexes into a sequence of array elements is replaced
with code that increments a pointer through the array.
Induction variable analysis and strength reduction together often remove all references to your loopcontrol variable, allowing its elimination.
3.13.9 Loop-Invariant Code Motion
This optimization identifies expressions within loops that always compute to the same value. The
computation is moved in front of the loop, and each occurrence of the expression in the loop is replaced
by a reference to the precomputed value.
3.13.10 Loop Rotation
The compiler evaluates loop conditionals at the bottom of loops, saving an extra branch out of the loop. In
many cases, the initial entry conditional check and the branch are optimized out.
3.13.11 Instruction Scheduling
The compiler performs instruction scheduling, which is the rearranging of machine instructions in such a
way that improves performance while maintaining the semantics of the original order. Instruction
scheduling is used to improve instruction parallelism and hide latencies. It can also be used to reduce
code size.
3.13.12 Tail Merging
If you are optimizing for code size, tail merging can be very effective for some functions. Tail merging finds
basic blocks that end in an identical sequence of instructions and have a common destination. If such a
set of blocks is found, the sequence of identical instructions is made into its own block. These instructions
are then removed from the set of blocks and replaced with branches to the newly created block. Thus,
there is only one copy of the sequence of instructions, rather than one for each block in the set.
3.13.13 Autoincrement Addressing
For pointer expressions of the form *p++, the compiler uses efficient ARM autoincrement addressing
modes. In many cases, where code steps through an array in a loop such as below, the loop optimizations
convert the array references to indirect references through autoincremented register variable pointers.
for (I = 0; I <N; ++I) a(I)...
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3.13.14 Block Conditionalizing
Because all 32-bit instructions can be conditional, branches can be removed by conditionalizing
instructions.
In Example 3-3, the branch around the add and the branch around the subtract are removed by simply
conditionalizing the add and the subtract.
Example 3-3. Block Conditionalizing C Source
int main(int a)
{
if (a < 0)
a = a-3;
else
a = a*3;
return ++a;
}
Example 3-4. C/C++ Compiler Output for Example 3-3
;*********************************************************
;* FUNCTION DEF: _main
*
;*********************************************************
_main:
CMP
A1, #0
ADDPL
A1, A1, A1, LSL #1
SUBMI
A1, A1, #3
ADD
A1, A1, #1
BX
LR
3.13.15 Epilog Inlining
If the epilog of a function is a single instruction, that instruction replaces all branches to the epilog. This
increases execution speed by removing the branch.
3.13.16 Removing Comparisons to Zero
Because most of the 32-bit instructions and some of the 16-bit instructions can modify the status register
when the result of their operation is 0, explicit comparisons to 0 may be unnecessary. The ARM C/C++
compiler removes comparisons to 0 if a previous instruction can be modified to set the status register
appropriately.
3.13.17 Integer Division With Constant Divisor
The optimizer attempts to rewrite integer divide operations with constant divisors. The integer divides are
rewritten as a multiply with the reciprocal of the divisor. This occurs at optimization level 2 (--opt_level=2
or -O2) and higher. You must also compile with the --opt_for_speed option, which selects compile for
speed.
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3.13.18 Branch Chaining
Branching to branches that jump to the desired target is called branch chaining. Branch chaining is
supported in 16-BIS mode only. Consider this code sequence:
LAB1:
LAB2:
BR L10
....
BR L10
....
L10:
If L10 is far away from LAB1 (large offset), the assembler converts BR into a sequence of branch around
and unconditional branches, resulting in a sequence of two instructions that are either four or six bytes
long. Instead, if the branch at LAB1 can jump to LAB2, and LAB2 is close enough that BR can be
replaced by a single short branch instruction, the resulting code is smaller as the BR in LAB1 would be
converted into one instruction that is two bytes long. LAB2 can in turn jump to another branch if L10 is too
far away from LAB2. Thus, branch chaining can be extended to arbitrary depths.
When you compile in thumb mode (--code_state=16) and for code size (--opt_for_speed is not used), the
compiler generates two psuedo instructions:
• BTcc instead of BRcc. The format is BRcc target, #[depth].
The #depth is an optional argument. If depth is not specified, it is set to the default branch chaining
depth. If specified, the chaining depth for this branch instruction is set to #depth. The assembler issues
a warning if #depth is less than zero and sets the branch chaining depth for this instruction to zero.
• BQcc instead of Bcc. The format is BQcc target , #[depth].
The #depth is the same as for the BTcc psuedo instruction.
The BT pseudo instruction replaces the BR (pseudo branch) instruction. Similarly, BQ replaces B. The
assembler performs branch chain optimizations for these instructions, if branch chaining is enabled. The
assembler replaces the BT and BQ jump targets with the offset to the branch to which these instructions
jump.
The default branch chaining depth is 10. This limit is designed to prevent longer branch chains from
impeding performance.
You can the BT and BQ instructions in assembly language programs to enable the assembler to perform
branch chaining. You can control the branch chaining depth for each instruction by specifying the
(optional) #depth argument. You must use the BR and B instructions to prevent branch chaining for any
BT or BQ branches.
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Chapter 4
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Linking C/C++ Code
The C/C++ Code Generation Tools provide two methods for linking your programs:
• You can compile individual modules and link them together. This method is especially useful when you
have multiple source files.
• You can compile and link in one step. This method is useful when you have a single source module.
This chapter describes how to invoke the linker with each method. It also discusses special requirements
of linking C/C++ code, including the run-time-support libraries, specifying the type of initialization, and
allocating the program into memory. For a complete description of the linker, see the ARM Assembly
Language Tools User's Guide.
Topic
4.1
4.2
4.3
...........................................................................................................................
Page
Invoking the Linker Through the Compiler (-z Option) ............................................ 78
Linker Code Optimizations .................................................................................. 80
Controlling the Linking Process ........................................................................... 81
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Invoking the Linker Through the Compiler (-z Option)
This section explains how to invoke the linker after you have compiled and assembled your programs: as
a separate step or as part of the compile step.
4.1.1 Invoking the Linker Separately
This is the general syntax for linking C/C++ programs as a separate step:
armcl --run_linker {--rom_model | --ram_model} filenames
[options] [--output_file= name.out] --library= library [lnk.cmd]
armcl --run_linker
--rom_model | --ram_model
filenames
options
--output_file= name.out
--library= library
lnk.cmd
The command that invokes the linker.
Options that tell the linker to use special conventions defined by the
C/C++ environment. When you use armcl --run_linker, you must use -rom_model or --ram_model. The --rom_model option uses
automatic variable initialization at run time; the --ram_model option
uses variable initialization at load time.
Names of object files, linker command files, or archive libraries. The
default extensions for input files are .c.obj (for C source files) and
.cpp.obj (for C++ source files). Any other extension must be explicitly
specified. The linker can determine whether the input file is an object
or ASCII file that contains linker commands. The default output
filename is a.out, unless you use the --output_file option to name the
output file.
Options affect how the linker handles your object files. Linker options
can only appear after the --run_linker option on the command line,
but otherwise may be in any order. (Options are discussed in detail in
the ARM Assembly Language Tools User's Guide.)
Names the output file.
Identifies the appropriate archive library containing C/C++ run-timesupport and floating-point math functions, or linker command files. If
you are linking C/C++ code, you must use a run-time-support library.
You can use the libraries included with the compiler, or you can
create your own run-time-support library. If you have specified a runtime-support library in a linker command file, you do not need this
parameter. The --library option's short form is -l.
Contains options, filenames, directives, or commands for the linker.
NOTE: The default file extensions for object files created by the compiler have been changed.
Object files generated from C source files have the .c.obj extension. Object files generated
from C++ source files have the .cpp.obj extension.
When you specify a library as linker input, the linker includes and links only those library members that
resolve undefined references. The linker uses a default allocation algorithm to allocate your program into
memory. You can use the MEMORY and SECTIONS directives in the linker command file to customize
the allocation process. For information, see the ARM Assembly Language Tools User's Guide.
You can link a C/C++ program consisting of object files prog1.c.obj, prog2.c.obj, and prog3.cpp.obj, with
an executable object file filename of prog.out with the command:
armcl --run_linker --rom_model prog1 prog2 prog3 --output_file=prog.out
--library=rtsv4_A_be_eabi.lib
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4.1.2 Invoking the Linker as Part of the Compile Step
This is the general syntax for linking C/C++ programs as part of the compile step:
armcl filenames [options] --run_linker
{--rom_model | --ram_model} filenames
[options] [--output_file= name.out] --library= library [lnk.cmd]
The --run_linker option divides the command line into the compiler options (the options before -run_linker) and the linker options (the options following --run_linker). The --run_linker option must follow all
source files and compiler options on the command line.
All arguments that follow --run_linker on the command line are passed to the linker. These arguments can
be linker command files, additional object files, linker options, or libraries. These arguments are the same
as described in Section 4.1.1.
All arguments that precede --run_linker on the command line are compiler arguments. These arguments
can be C/C++ source files, assembly files, or compiler options. These arguments are described in
Section 2.2.
You can compile and link a C/C++ program consisting of object files prog1.c, prog2.c, and prog3.c, with an
executable object file filename of prog.out with the command:
armcl prog1.c prog2.c prog3.c --run_linker --rom_model --output_file=prog.out
--library=rtsv4_A_be_eabi.lib
NOTE:
Order of Processing Arguments in the Linker
The order in which the linker processes arguments is important. The compiler passes
arguments to the linker in the following order:
1. Object filenames from the command line
2. Arguments following the --run_linker option on the command line
3. Arguments following the --run_linker option from the TI_ARM_C_OPTION environment
variable
4.1.3 Disabling the Linker (--compile_only Compiler Option)
You can override the --run_linker option by using the --compile_only compiler option. The -run_linker
option's short form is -z and the --compile_only option's short form is -c.
The --compile_only option is especially helpful if you specify the --run_linker option in the
TI_ARM_C_OPTION environment variable and want to selectively disable linking with the --compile_only
option on the command line.
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Linker Code Optimizations
These techniques are used to further optimize your code.
4.2.1 Generate List of Dead Functions (--generate_dead_funcs_list Option)
In order to facilitate the removal of unused code, the linker generates a feedback file containing a list of
functions that are never referenced. The feedback file must be used the next time you compile the source
files. The syntax for the --generate_dead_funcs_list option is:
--generate_dead_funcs_list= filename
If filename is not specified, a default filename of dead_funcs.txt is used.
Proper creation and use of the feedback file entails the following steps:
1. Compile all source files using the --gen_func_subsections compiler option. For example:
armcl file1.c file2.c --gen_func_subsections
2. During the linker, use the --generate_dead_funcs_list option to generate the feedback file based on the
generated object files. For example:
armcl --run_linker file1.c.obj file2.c.obj --generate_dead_funcs_list=feedback.txt
Alternatively, you can combine steps 1 and 2 into one step. When you do this, you are not required to
specify --gen_func_subsections when compiling the source files as this is done for you automatically.
For example:
armcl file1.c file2.c --run_linker --generate_dead_funcs_list=feedback.txt
3. Once you have the feedback file, rebuild the source. Give the feedback file to the compiler using the -use_dead_funcs_list option. This option forces each dead function listed in the file into its own
subsection. For example:
armcl file1.c file2.c --use_dead_funcs_list=feedback.txt
4. Invoke the linker with the newly built object files. The linker removes the subsections. For example:
armcl --run_linker file1.c.obj file2.c.obj
Alternatively, you can combine steps 3 and 4 into one step. For example:
armcl file1.c file2.c --use_dead_funcs_list=feedback.txt --run_linker
NOTE:
Dead Functions Feedback
The format of the feedback file generated with --generate_dead_funcs_list is tightly
controlled. It must be generated by the linker in order to be processed correctly by the
compiler. The format of this file may change over time, so the file contains a version format
number to allow backward compatibility.
4.2.2 Generating Aggregate Data Subsections (--gen_data_subsections Compiler Option)
Similarly to code sections described in the previous section, data can either be placed in a single section
or multiple sections. The benefit of multiple data sections is that the linker may omit unused data
structures from the executable. By default, the --gen_data_subsections option is on. This option causes
aggregate data—arrays, structs, and unions—to be placed in separate subsections of the data section.
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4.3
Controlling the Linking Process
Regardless of the method you choose for invoking the linker, special requirements apply when linking
C/C++ programs. You must:
• Include the compiler's run-time-support library
• Specify the type of boot-time initialization
• Determine how you want to allocate your program into memory
This section discusses how these factors are controlled and provides an example of the standard default
linker command file. For more information about how to operate the linker, see the linker description in the
ARM Assembly Language Tools User's Guide.
4.3.1 Including the Run-Time-Support Library
You must link all C/C++ programs with a run-time-support library. The library contains standard C/C++
functions as well as functions used by the compiler to manage the C/C++ environment. The following
sections describe two methods for including the run-time-support library.
4.3.1.1
Automatic Run-Time-Support Library Selection
The linker assumes you are using the C and C++ conventions if either the --rom_model or --ram_model
linker option is specified, or if the link step includes the compile step for a C or C++ file, or if you link
against the index library libc.a.
If the linker assumes you are using the C and C++ conventions and the entry point for the program
(normally c_int00) is not resolved by any specified object file or library, the linker attempts to automatically
include the most compatible run-time-support library for your program. The run-time-support library chosen
by the compiler is searched after any other libraries specified with the --library option on the command line
or in the linker command file. If libc.a is explicitly used, the appropriate run-time-support library is included
in the search order where libc.a is specified.
You can disable the automatic selection of a run-time-support library by using the --disable_auto_rts
option.
If the --issue_remarks option is specified before the --run_linker option during the linker, a remark is
generated indicating which run-time support library was linked in. If a different run-time-support library is
desired than the one reported by --issue_remarks, you must specify the name of the desired run-timesupport library using the --library option and in your linker command files when necessary.
Example 4-1. Using the --issue_remarks Option
armcl --code_state=16 --issue_remarks main.c --run_linker --rom_model
<Linking>
remark: linking in "libc.a"
remark: linking in "rtsv4_A_be_eabi.lib" in place of "libc.a"
4.3.1.2
Manual Run-Time-Support Library Selection
You can bypass automatic library selection by explicitly specifying the desired run-time-support library to
use. Use the --library linker option to specify the name of the library. The linker will search the path
specified by the --search_path option and then the TI_ARM_C_DIR environment variable for the named
library. You can use the --library linker option on the command line or in a command file.
armcl --run_linker {--rom_model | --ram_model} filenames --library= libraryname
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Library Order for Searching for Symbols
Generally, you should specify the run-time-support library as the last name on the command line because
the linker searches libraries for unresolved references in the order that files are specified on the command
line. If any object files follow a library, references from those object files to that library are not resolved.
You can use the --reread_libs option to force the linker to reread all libraries until references are resolved.
Whenever you specify a library as linker input, the linker includes and links only those library members
that resolve undefined references.
By default, if a library introduces an unresolved reference and multiple libraries have a definition for it, then
the definition from the same library that introduced the unresolved reference is used. Use the --priority
option if you want the linker to use the definition from the first library on the command line that contains
the definition.
4.3.2 Run-Time Initialization
You must link all C/C++ programs with code to initialize and execute the program called a bootstrap
routine. The bootstrap routine is responsible for the following tasks:
1. Switch to user mode and sets up the user mode stack
2. Set up status and configuration registers
3. Set up the stack
4. Process special binit copy table, if present.
5. Process the run-time initialization table to autoinitialize global variables (when using the --rom_model
option)
6. Call all global constructors
7. Call the main() function
8. Call exit() when main() returns
NOTE:
The _c_int00 Symbol
If you use the --ram_model or --rom_model link option, _c_int00 is automatically defined as
the entry point for the program. Otherwise, an entry point is not automatically selected and
you will receive a linker warning.
4.3.3 Initialization of Cinit and Watchdog Timer Hold
You can use the --cinit_hold_wdt option to specify whether the watchdog timer should be held (on) or not
held (off) during cinit auto-initialization. Setting this option causes an RTS auto-initialization routine to be
linked in with the program to handle the desired watchdog timer behavior.
4.3.4 Global Object Constructors
Global C++ variables that have constructors and destructors require their constructors to be called during
program initialization and their destructors to be called during program termination. The C++ compiler
produces a table of constructors to be called at startup.
Constructors for global objects from a single module are invoked in the order declared in the source code,
but the relative order of objects from different object files is unspecified.
Global constructors are called after initialization of other global variables and before the main() function is
called. Global destructors are invoked during the exit run-time support function, similar to functions
registered through atexit.
Section 6.10.3.6 discusses the format of the global constructor table for EABI mode.
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4.3.5 Specifying the Type of Global Variable Initialization
The C/C++ compiler produces data tables for initializing global variables. Section 6.10.3.4 discusses the
format of these initialization tables. The initialization tables are used in one of the following ways:
• Global variables are initialized at run time. Use the --rom_model linker option (see Section 6.10.3.3).
• Global variables are initialized at load time. Use the --ram_model linker option (see Section 6.10.3.5).
When you link a C/C++ program, you must use either the --rom_model or --ram_model option. These
options tell the linker to select initialization at run time or load time. When you compile and link programs,
the --rom_model option is the default. If used, the --rom_model option must follow the --run_linker option
(see Section 4.1). For details on linking conventions for EABI used with --rom_model and --ram_model,
see Section 6.10.3.3 and Section 6.10.3.5, respectively.
NOTE:
Boot Loader
A loader is not included as part of the C/C++ compiler tools. You can use the ARM simulator
or emulator with the source debugger as a loader. See the "Program Loading and Running"
chapter of the ARM Assembly Language Tools User's Guide for more about boot loading.
4.3.6 Specifying Where to Allocate Sections in Memory
The compiler produces relocatable blocks of code and data. These blocks, called sections, are allocated
in memory in a variety of ways to conform to a variety of system configurations. See Section 6.1.1 for a
complete description of how the compiler uses these sections.
The compiler creates two basic kinds of sections: initialized and uninitialized. Table 4-1 summarizes the
initialized sections. Table 4-2 summarizes the uninitialized sections.
Table 4-1. Initialized Sections Created by the Compiler
Name
Contents
.binit
Boot time copy tables (See the Assembly Language Tools User's Guide for information on BINIT in
linker command files.)
.cinit
Tables for explicitly initialized global and static variables.
.const
Global and static const variables that are explicitly initialized.
.data
Global and static non-const variables that are explicitly initialized.
.init_array
Table of constructors to be called at startup.
.ovly
Copy tables other than boot time (.binit) copy tables. Read-only data.
.text
Executable code and constants. Also contains string literals and switch tables. See Section 6.1.1 for
exceptions.
.TI.crctab
Generated CRC checking tables. Read-only data.
Table 4-2. Uninitialized Sections Created by the Compiler
Name
Contents
.bss
Uninitialized global and static variables
.cio
Buffers for stdio functions from the run-time support library
.stack
Stack
.sysmem
Memory pool (heap) for dynamic memory allocation (malloc, etc)
When you link your program, you must specify where to allocate the sections in memory. In general,
initialized sections are linked into ROM or RAM; uninitialized sections are linked into RAM.
The linker provides MEMORY and SECTIONS directives for allocating sections. For more information
about allocating sections into memory, see the ARM Assembly Language Tools User's Guide.
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4.3.7 A Sample Linker Command File
Example 4-2 shows a typical linker command file that links a 32-bit C program. The command file in this
example is named lnk32.cmd and lists several link options:
--rom_model
--stack_size
--heap_size
Tells the linker to use autoinitialization at run time
Tells the linker to set the C stack size at 0x8000 bytes
Tells the linker to set the heap size to 0x2000 bytes
To link the program, use the following syntax:
armcl --run_linker object_file(s) --output_file outfile --map_file mapfile lnk32.cmd
Example 4-2. Linker Command File
--rom_model
--stack_size=0x8000
--heap_size=0x2000
/* LINK USING C CONVENTIONS
/* SOFTWARE STACK SIZE
/* HEAP AREA SIZE
*/
*/
*/
/* SPECIFY THE SYSTEM MEMORY MAP */
MEMORY
{
P_MEM
D_MEM
}
: org = 0x00000000
: org = 0x00030000
len = 0x00030000
len = 0x00050000
/* PROGRAM MEMORY (ROM) */
/* DATA MEMORY
(RAM) */
/* SPECIFY THE SECTIONS ALLOCATION INTO MEMORY */
SECTIONS
{
.intvecs
.bss
.sysmem
.stack
.text
.cinit
.const
.pinit
84
:
:
:
:
{}
{}
{}
{}
>
>
>
>
0x0
D_MEM
D_MEM
D_MEM
/*
/*
/*
/*
INTERRUPT VECTORS
GLOBAL & STATIC VARS
DYNAMIC MEMORY ALLOCATION AREA
SOFTWARE SYSTEM STACK
*/
*/
*/
*/
:
:
:
:
{}
{}
{}
{}
>
>
>
>
P_MEM
P_MEM
P_MEM
P_MEM
/*
/*
/*
/*
CODE
INITIALIZATION TABLES
CONSTANT DATA
TEMPLATE INITIALIZATION TABLES
*/
*/
*/
*/
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Chapter 5
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C/C++ Language Implementation
The C language supported by the ARM was developed by a committee of the American National
Standards Institute (ANSI) and subsequently adopted by the International Standards Organization (ISO).
The C++ language supported by the ARM is defined by the ANSI/ISO/IEC 14882:2014 standard with
certain exceptions.
Topic
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
5.12
5.13
5.14
5.15
5.16
5.17
5.18
5.19
...........................................................................................................................
Page
Characteristics of ARM C .................................................................................... 86
Characteristics of ARM C++................................................................................. 91
Using MISRA C 2004 ........................................................................................... 92
Using the ULP Advisor........................................................................................ 93
Data Types ........................................................................................................ 94
File Encodings and Character Sets ...................................................................... 96
Keywords .......................................................................................................... 96
C++ Exception Handling ...................................................................................... 99
Register Variables and Parameters ..................................................................... 100
The __asm Statement ........................................................................................ 101
Pragma Directives ............................................................................................ 102
The _Pragma Operator ...................................................................................... 121
Application Binary Interface ............................................................................... 122
ARM Instruction Intrinsics ................................................................................. 122
Object File Symbol Naming Conventions (Linknames) .......................................... 131
Changing the ANSI/ISO C/C++ Language Mode .................................................... 131
GNU, Clang, and ACLE Language Extensions ...................................................... 134
AUTOSAR ........................................................................................................ 139
Compiler Limits ................................................................................................ 140
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Characteristics of ARM C
The C compiler supports the 1989 and 1999 versions of the C language:
• C89. Compiling with the --c89 option causes the compiler to conform to the ISO/IEC 9899:1990 C
standard, which was previously ratified as ANSI X3.159-1989. The names "C89" and "C90" refer to the
same programming language. "C89" is used in this document.
• C99. Compiling with the --c99 option causes the compiler to conform to the ISO/IEC 9899:1999 C
standard.
• C11. Compiling with the --c11 option causes the compiler to conform to the ISO/IEC 9899:2011 C
standard.
The C language is also described in the second edition of Kernighan and Ritchie's The C Programming
Language (K&R). The compiler can also accept many of the language extensions found in the GNU C
compiler (see Section 5.17).
The compiler supports some features of C99 and C11 in the default relaxed ANSI mode with C89 support.
It supports all language features of C99 in C99 mode and all language features of C11 in C11 mode. See
Section 5.16.
The atomic operations in C11 are supported in the relaxed ANSI mode (on by default) and in C11 mode
as follows:
• On ARM V7A8 (Cortex-A8), ARM V7M3 (Cortex-M3), ARM V7M4 (Cortex-M4), ARM V7R4 (CortexR4), and ARM V7R5 (Cortex-R5)), atomic operations are implemented using processor-supported
exclusive access instructions.
• On ARM V6M0 (Cortex-M0), atomic operations are implemented by disabling interrupts across the
operation.
• On ARM V4 (ARM7), ARM V5e (ARM9E), and ARM V6 (ARM11), atomic operations are not
supported.
In addition, the compiler supports many of the features described in the ARM C Language Extensions
(ACLE) specification. These features are applicable for the Cortex-M and Cortex-R processor variants.
ACLE support affects the pre-defined macros (Table 2-31), function attributes (Section 5.17.2), and
intrinsics (Section 5.14) you may use in C/C++ code. These features are implemented in order to support
the development of source code that can be compiled using ACLE-compliant compilers from multiple
vendors for a variety of ARM processors.
The ANSI/ISO standard identifies some features of the C language that may be affected by characteristics
of the target processor, run-time environment, or host environment. This set of features can differ among
standard compilers.
Unsupported features of the C library are:
• The run-time library has minimal support for wide characters. The type wchar_t is implemented as
unsigned short (16 bits), but can be an int if you set the --wchar_t=32 option. The wide character set is
equivalent to the set of values of type char. The library includes the header files <wchar.h> and
<wctype.h>, but does not include all the functions specified in the standard. See Section 5.6 for
information about extended and multibyte character sets.
• The run-time library includes the header file <locale.h>, but with a minimal implementation. The only
supported locale is the C locale. That is, library behavior that is specified to vary by locale is hardcoded to the behavior of the C locale, and attempting to install a different locale by way of a call to
setlocale() will return NULL.
• Some run-time functions and features in the C99/C11 specifications are not supported. See
Section 5.16.
5.1.1 Implementation-Defined Behavior
The C standard requires that conforming implementations provide documentation on how the compiler
handles instances of implementation-defined behavior.
The TI compiler officially supports a freestanding environment. The C standard does not require a
freestanding environment to supply every C feature; in particular the library need not be complete.
However, the TI compiler strives to provide most features of a hosted environment.
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The section numbers in the lists that follow correspond to section numbers in Appendix J of the C99
standard. The numbers in parentheses at the end of each item are sections in the C99 standard that
discuss the topic. Certain items listed in Appendix J of the C99 standard have been omitted from this list.
J.3.1 Translation
• The compiler and related tools emit diagnostic messages with several distinct formats. Diagnostic
messages are emitted to stderr; any text on stderr may be assumed to be a diagnostic. If any errors
are present, the tool will exit with an exit status indicating failure (non-zero). (3.10, 5.1.1.3)
• Nonempty sequences of white-space characters are preserved and are not replaced by a single space
character in translation phase 3. (5.1.1.2)
J.3.2 Environment
• The compiler does not support multibyte characters in identifiers, string literals, or character constants.
There is no mapping from multibyte characters to the source character set. However, the compiler
accepts multibyte characters in comments. See Section 5.6 for details. (5.1.1.2)
• The name of the function called at program startup is "main" (5.1.2.1)
• Program termination does not affect the environment; there is no way to return an exit code to the
environment. By default, the program is known to have halted when execution reaches the special
C$$EXIT label. (5.1.2.1)
• In relaxed ANSI mode, the compiler accepts "void main(void)" and "void main(int argc, char *argv[])" as
alternate definitions of main. The alternate definitions are rejected in strict ANSI mode. (5.1.2.2.1)
• If space is provided for program arguments at link time with the --args option and the program is run
under a system that can populate the .args section (such as CCS), argv[0] will contain the filename of
the executable, argv[1] through argv[argc-1] will contain the command-line arguments to the program,
and argv[argc] will be NULL. Otherwise, the value of argv and argc are undefined. (5.1.2.2.1)
• Interactive devices include stdin, stdout, and stderr (when attached to a system that honors CIO
requests). Interactive devices are not limited to those output locations; the program may access
hardware peripherals that interact with the external state. (5.1.2.3)
• Signals are not supported. The function signal is not supported. (7.14) (7.14.1.1)
• The library function getenv is implemented through the CIO interface. If the program is run under a
system that supports CIO, the system performs getenv calls on the host system and passes the result
back to the program. Otherwise the operation of getenv is undefined. No method of changing the
environment from inside the target program is provided. (7.20.4.5)
• The system function is not supported. (7.20.4.6).
J.3.3. Identifiers
• The compiler does not support multibyte characters in identifiers. See Section 5.6 for details. (6.4.2)
• The number of significant initial characters in an identifier is unlimited. (5.2.4.1, 6.4.2)
J.3.4 Characters
• The number of bits in a byte (CHAR_BIT) is 8. See Section 5.5 for details about data types. (3.6)
• The execution character set is the same as the basic execution character set: plain ASCII. Characters
in the ISO 8859 extended character set are also supported. (5.2.1)
• The values produced for the standard alphabetic escape sequences are as follows: (5.2.2)
Escape Sequence ASCII Meaning
Integer Value
\a
BEL (bell)
7
\b
BS (backspace)
8
\f
FF (form feed)
12
\n
LF (line feed)
10
\r
CR (carriage
return)
13
\t
HT (horizontal tab)
9
\v
VT (vertical tab)
11
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•
•
•
•
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The value of a char object into which any character other than a member of the basic execution
character set has been stored is the ASCII value of that character. (6.2.5)
Plain char is identical to unsigned char, but can be changed to signed char with the -plain_char=signed option. (6.2.5, 6.3.1.1)
The source character set and execution character set are both plain ASCII, so the mapping between
them is one-to-one. The compiler accepts multibyte characters in comments. See Section 5.6 for
details. (6.4.4.4, 5.1.1.2)
The compiler currently supports only one locale, "C". (6.4.4.4).
The compiler currently supports only one locale, "C". (6.4.5).
J.3.5 Integers
• No extended integer types are provided. (6.2.5)
• Negative values for signed integer types are represented as two's complement, and there are no trap
representations. (6.2.6.2)
• No extended integer types are provided, so there is no change to the integer ranks. (6.3.1.1)
• When an integer is converted to a signed integer type which cannot represent the value, the value is
truncated (without raising a signal) by discarding the bits which cannot be stored in the destination
type; the lowest bits are not modified. (6.3.1.3)
• Right shift of a signed integer value performs an arithmetic (signed) shift. The bitwise operations other
than right shift operate on the bits in exactly the same way as on an unsigned value. That is, after the
usual arithmetic conversions, the bitwise operation is performed without regard to the format of the
integer type, in particular the sign bit. (6.5)
J.3.6 Floating point
• The accuracy of floating-point operations (+ - * /) is bit-exact. The accuracy of library functions that
return floating-point results is not specified. (5.2.4.2.2)
• The compiler does not provide non-standard values for FLT_ROUNDS (5.2.4.2.2)
• The compiler does not provide non-standard negative values of FLT_EVAL_METHOD (5.2.4.2.2)
• The rounding direction when an integer is converted to a floating-point number is IEEE-754 "round to
even". (6.3.1.4)
• The rounding direction when a floating-point number is converted to a narrower floating-point number
is IEEE-754 "round to even". (6.3.1.5)
• For floating-point constants that are not exactly representable, the implementation uses the nearest
representable value. (6.4.4.2)
• The compiler does not contract float expressions. (6.5)
• The default state for the FENV_ACCESS pragma is off. (7.6.1)
• The TI compiler does not define any additional float exceptions (7.6, 7.12)
• The default state for the FP_CONTRACT pragma is off. (7.12.2)
• The "inexact" floating-point exception cannot be raised if the rounded result equals the mathematical
result. (F.9)
• The "underflow" and "inexact" floating-point exceptions cannot be raised if the result is tiny but not
inexact. (F.9)
J.3.7 Arrays and pointers
• When converting a pointer to an integer or vice versa, the pointer is considered an unsigned integer of
the same size, and the normal integer conversion rules apply.
• When converting a pointer to an integer or vice versa, if the bitwise representation of the destination
can hold all of the bits in the bitwise representation of the source, the bits are copied exactly. (6.3.2.3)
• The size of the result of subtracting two pointers to elements of the same array is the size of ptrdiff_t,
which is defined in Section 5.5. (6.5.6)
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J.3.8 Hints
• When the optimizer is used, the register storage-class specifier is ignored. When the optimizer is not
used, the compiler will preferentially place register storage class objects into registers to the extent
possible. The compiler reserves the right to place any register storage class object somewhere other
than a register. (6.7.1)
• The inline function specifier is ignored unless the optimizer is used. For other restrictions on inlining,
see Section 2.11.2. (6.7.4)
J.3.9 Structures, unions, enumerations, and bit-fields
• A "plain" int bit-field is treated as a signed int bit-field. (6.7.2, 6.7.2.1)
• In addition to _Bool, signed int, and unsigned int, the compiler allows char, signed char, unsigned char,
signed short, unsigned shot, signed long, unsigned long, signed long long, unsigned long long, and
enum types as bit-field types. (6.7.2.1)
• Bit-fields may not straddle a storage-unit boundary.(6.7.2.1)
• Bit-fields are allocated in endianness order within a unit. See Section 6.2.2. (6.7.2.1)
• Non-bit-field members of structures are aligned as specified in Section 6.2.1. (6.7.2.1)
• The integer type underlying each enumerated type is described in Section 5.5.1. (6.7.2.2)
J.3.10 Qualifiers
• The TI compiler does not shrink or grow volatile accesses. It is the user's responsibility to make sure
the access size is appropriate for devices that only tolerate accesses of certain widths. The TI compiler
does not change the number of accesses to a volatile variable unless absolutely necessary. This is
significant for read-modify-write expressions such as += ; for an architecture which does not have a
corresponding read-modify-write instruction, the compiler will be forced to use two accesses, one for
the read and one for the write. Even for architectures with such instructions, it is not guaranteed that
the compiler will be able to map such expressions to an instruction with a single memory operand. It is
not guaranteed that the memory system will lock that memory location for the duration of the
instruction. In a multi-core system, some other core may write the location after a RMW instruction
reads it, but before it writes the result. The TI compiler will not reorder two volatile accesses, but it may
reorder a volatile and a non-volatile access, so volatile cannot be used to create a critical section. Use
some sort of lock if you need to create a critical section. (6.7.3)
J.3.11 Preprocessing directives
• Include directives may have one of two forms, " " or < >. For both forms, the compiler will look for a
real file on-disk by that name using the include file search path. See Section 2.5.2. (6.4.7).
• The value of a character constant in a constant expression that controls conditional inclusion matches
the value of the same character constant in the execution character set (both are ASCII). (6.10.1).
• The compiler uses the file search path to search for an included < > delimited header file. See
Section 2.5.2. (6.10.2).
• he compiler uses the file search path to search for an included " " delimited header file. See
Section 2.5.2. (6.10.2). (6.10.2).
• There is no arbitrary nesting limit for #include processing. (6.10.2).
• See Section 5.11 for a description of the recognized non-standard pragmas. (6.10.6).
• The date and time of translation are always available from the host. (6.10.8).
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J.3.12 Library functions
• Almost all of the library functions required for a hosted implementation are provided by the TI library,
with exceptions noted in Section 5.16.1. (5.1.2.1).
• The format of the diagnostic printed by the assert macro is "Assertion failed, (assertion macro
argument), file file, line line". (7.2.1.1).
• No strings other than "C" and "" may be passed as the second argument to the setlocale function
(7.11.1.1).
• No signal handling is supported. (7.14.1.1).
• The +INF, -INF, +inf, -inf, NAN, and nan styles can be used to print an infinity or NaN. (7.19.6.1,
7.24.2.1).
• The output for %p conversion in the fprintf or fwprintf function is the same as %x of the appropriate
size. (7.19.6.1, 7.24.2.1).
• The termination status returned to the host environment by the abort, exit, or _Exit function is not
returned to the host environment. (7.20.4.1, 7.20.4.3, 7.20.4.4).
• The system function is not supported. (7.20.4.6).
J.3.13 Architecture
• The values or expressions assigned to the macros specified in the headers float.h, limits.h, and stdint.h
are described along with the sizes and format of integer types are described in Section 5.5. (5.2.4.2,
7.18.2, 7.18.3)
• The number, order, and encoding of bytes in any object are described in Section 6.2.1. (6.2.6.1)
• The value of the result of the sizeof operator is the storage size for each type, in terms of bytes. See
Section 6.2.1. (6.5.3.4)
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5.2
Characteristics of ARM C++
The ARM compiler supports C++ as defined in the ANSI/ISO/IEC 14882:2014 standard (C++14), including
these features:
• Complete C++ standard library support, with exceptions noted below.
• Templates
• Exceptions, which are enabled with the --exceptions option; see Section 5.8.
• Run-time type information (RTTI), which can be enabled with the --rtti compiler option.
The compiler supports the 2014 standard of C++ as standardized by the ISO. However, the following
features are not implemented or fully supported:
• The compiler does not support embedded C++ run-time-support libraries.
• The library supports wide chars (wchar_t), in that template functions and classes that are defined for
char are also available for wchar_t. For example, wide char stream classes wios, wiostream,
wstreambuf and so on (corresponding to char classes ios, iostream, streambuf) are implemented.
However, there is no low-level file I/O for wide chars. Also, the C library interface to wide char support
(through the C++ headers <cwchar> and <cwctype>) is limited as described above in the C library.
• Constant expressions for target-specific types are only partially supported.
• New character types (introduced in the C++11 standard) are not supported.
• Unicode string literals (introduced in the C++11 standard) are not supported.
• Universal character names in literals (introduced in the C++11 standard) are not supported.
• Strong compare and exchange (introduced in the C++11 standard) are not supported.
• Bidirectional fences (introduced in the C++11 standard) are not supported.
• Memory model (introduced in the C++11 standard) is not supported.
• Propagating exceptions (introduced in the C++11 standard) is not supported.
• Thread-local storage (introduced in the C++11 standard) is not supported.
• Dynamic initialization and destruction with concurrency (introduced in the C++11 standard) is not
supported.
The changes made in order to support C++14 may cause "undefined symbol" errors to occur if you link
with a C++ object file or library that was compiled with an older version of the compiler. If such linktime
errors occur, recompile your C++ code using the --no_demangle command-line option. If any undefined
symbol names begin with _Z or _ZVT, recompile the entire application, including object files and libraries.
If you do not have source code for the libraries, download a newly-compiled version of the library.
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Using MISRA C 2004
MISRA C is a set of software development guidelines for the C programming language. It promotes best
practices in developing safety-related electronic systems in road vehicles and other embedded systems.
MISRA C was originally launched in 1998 by the Motor Industry Software Reliability Association, and has
since been adopted across a wide variety of industries. A subsequent update to the guidelines was
publishes as MISRA C:2004
You can alter your code to work with the MISRA C:2004 rules. The following options and pragmas can be
used to enable/disable rules:
• The --check_misra option enables checking of the specified MISRA C:2004 rules. This compiler option
must be used if you want to enable further control over checking using the CHECK_MISRA and
RESET_MISRA pragmas.
• The CHECK_MISRA pragma enables/disables MISRA C:2004 rules at the source level. See
Section 5.11.2.
• The RESET_MISRA pragma resets the specified MISRA C:2004 rules to their state before any
CHECK_MISRA pragmas were processed. See Section 5.11.24.
The syntax of the option and the pragmas is:
--check_misra={all|required|advisory|none|rulespec}
#pragma CHECK_MISRA ("{all|required|advisory|none|rulespec}")
#pragma RESET_MISRA ("{all|required|advisory|rulespec}")
The rulespec parameter is a comma-separated list of rule numbers to enable or disable.
Example: --check_misra=1.1,1.4,1.5,2.1,2.7,7.1,7.2,8.4
• Enables checking of rules 1.1, 1.4, 1.5, 2.1, 2.7, 7.1, 7.2, and 8.4.
Example: #pragma CHECK_MISRA("-7.1,-7.2,-8.4")
• Disables checking of rules 7.1, 7.2, and 8.4.
A typical use case is to use the --check_misra option on the command line to specify the rules that should
be checked in most of your code. Then, use the CHECK_MISRA pragma with a rulespec to activate or
deactivate certain rules for a particular region of code.
Two options control the severity of certain MISRA C:2004 rules:
• The --misra_required option sets the diagnostic severity for required MISRA C:2004 rules.
• The --misra_advisory option sets the diagnostic severity for advisory MISRA C:2004 rules.
The syntax for these options is:
--misra_advisory={error|warning|remark|suppress}
--misra_required={error|warning|remark|suppress}
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5.4
Using the ULP Advisor
You can get feedback about your code from the ULP (Ultra-Low Power) Advisor. For a list and
descriptions of the ULP rules, see www.ti.com/ulpadvisor. You can enable/disable the rules using any of
the following. Using multiple --advice options on the command line is permitted.
• The --advice:power option lets you specify which rules to check.
• The --advice:power_severity option lets you specify whether ULP Advisor rule violations are errors,
warnings, remarks, or not reported.
• The CHECK_ULP pragma enables/disables ULP Advisor rules at the source level. This pragma has
the same effect as using the --advice:power option. See Section 5.11.3.
• The RESET_ULP pragma resets the specified ULP Advisor rules to their state before any
CHECK_ULP pragmas were processed. See Section 5.11.25.
The --advice:power option enables checking specified ULP Advisor rules. The syntax is:
--advice:power={all|none|rulespec}
The rulespec parameter is a comma-separated list of rule numbers to enable. For example, -advice:power=1.1,7.2,7.3,7.4 enables rules 1.1, 7.2, 7.3, and 7.4.
The --advice:power_severity option sets the diagnostic severity for ULP Advisor rules. The syntax is:
--advice:power_severity={error|warning|remark|suppress}
The syntax of the pragmas is:
#pragma CHECK_ULP ("{all|none|rulespec}")
#pragma RESET_ULP ("{all|rulespec}")
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Data Types
Table 5-1 lists the size, representation, and range of each scalar data type for the ARM compiler. Many of
the range values are available as standard macros in the header file limits.h.
The storage and alignment of data types is described in Section 6.2.1.
Table 5-1. ARM C/C++ Data Types
Range
Type
Size
Representation
Minimum
Maximum
signed char
8 bits
ASCII
-128
127
(1)
8 bits
ASCII
0
unsigned char
8 bits
ASCII
0
255
bool, _Bool
8 bits
ASCII
0 (false)
1(true)
short, signed short
16 bits
Binary
-32 768
32 767
16 bits
Binary
0
65 535
int, signed int
32 bits
Binary
-2 147 483 648
2 147 483 647
unsigned int
32 bits
Binary
0
4 294 967 295
long, signed long
32 bits
Binary
-2 147 483 648
2 147 483 647
unsigned long
32 bits
Binary
0
4 294 967 295
long long, signed long long
64 bits
(3)
Binary
-9 223 372 036 854 775 808
9 223 372 036 854 775 807
unsigned long long
64 bits (3)
Binary
0
18 446 744 073 709 551 615
enum (TI_ARM9_ABI and
TIABI only) (4)
32 bits
Binary
-2 147 483 648
2 147 483 647
float
32 bits
char
unsigned short, wchar_t
(2)
(1)
255
(1)
IEEE 32-bit
1.175 494e-38 (5)
3.40 282 346e+38
double
64 bits
(3)
IEEE 64-bit
2.22 507 385e-308 (5)
1.79 769 313e+308
long double
64 bits (3)
IEEE 64-bit
2.22 507 385e-308 (5)
1.79 769 313e+308
pointers, references, pointer to
data members
32 bits
Binary
0
0xFFFFFFFF
(1)
(2)
(3)
(4)
(5)
"Plain" char has the same representation as either signed char or unsigned char. The --plain_char option specifies whether
"plain" char is signed or unsigned. The default is unsigned.
This is the default type for wchar_t. You can use the --wchar_t option to change the wchar_t type to a 32-bit unsigned int type.
64-bit data is aligned on a 64-bit boundary.
For details about the size of an enum type, see Section 5.5.1. Also see Table 5-2 for sizes.
Figures are minimum precision.
Negative values for signed types are represented using two's complement.
The type of the storage container for an enumerated type is the smallest integer type that contains all the
enumerated values. The container types for enumerators are shown in Table 5-2.
Table 5-2. Enumerator Types
94
Lower Bound Range
Upper Bound Range
Enumerator Type
0 to 255
0 to 255
unsigned char
-128 to 1
-128 to 127
signed char
0 to 65 535
256 to 65 535
unsigned short
-128 to 1
128 to 32 767
short, signed short
-32 768 to -129
-32 768 to 32 767
0 to 4 294 967 295
2 147 483 648 to 4 294 967 295
unsigned int
-32 768 to -1
32 767 to 2 147 483 647
int, signed int
-2 147 483 648 to -32 769
-2 147 483 648 to 2 147 483 647
0 to 2 147 483 647
65 536 to 2 147 483 647
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The compiler determines the type based on the range of the lowest and highest elements of the
enumerator. For example, the following code results in an enumerator type of int:
{
enum COLORS
green = -200,
blue
= 1,
yellow = 2,
red
= 60000
};
The following code results in an enumerator type of short:
{
enum COLORS
green = -200,
blue
= 1,
yellow = 2,
red
= 3
};
5.5.1 Size of Enum Types
An enum type is represented by an underlying integer type. The size of the integer type and whether it is
signed is based on the range of values of the enumerated constants.
In strict C89/C99/C11 mode, the compiler allows only enumeration constants with values that will fit in "int"
or "unsigned int".
For C++ and relaxed C89/C99/C11, the compiler allows enumeration constants up to the largest integral
type (64 bits). The default, which is recommended, is for the underlying type to be the first type in the
following list in which all the enumerated constant values can be represented: int, unsigned int, long,
unsigned long, long long, unsigned long long.
If you use the --small_enum option, the smallest possible byte size for the enumeration type is used. The
underlying type is the first type in the following list in which all the enumerated constant values can be
represented: signed char, unsigned char, short, unsigned short, int, unsigned int, long, unsigned long, long
long, unsigned long long.
The following enum uses 8 bits instead of 32 bits when the --small_enum option is used.
enum example_enum {
first = -128,
second = 0,
third = 127
};
The following enum fits into 16 bits instead of 32 when the --small_enum option is used.
enum a_short_enum {
bottom = -32768,
middle = 0,
top = 32767
};
NOTE: Do not link object files compiled with the --small_enum option with object files that were
compiled without it. If you use the --small_enum option, you must use it with all of your
C/C++ files; otherwise, you will encounter errors that cannot be detected until run time.
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File Encodings and Character Sets
The compiler accepts source files with one of two distinct encodings:
• UTF-8 with Byte Order Mark (BOM). These files may contain extended (multibyte) characters in
C/C++ comments. In all other contexts—including string constants, identifiers, assembly files, and
linker command files—only 7-bit ASCII characters are supported.
• Plain ASCII files. These files must contain only 7-bit ASCII characters.
To choose the UTF-8 encoding in Code Composer Studio, open the Preferences dialog, select General >
Workspace, and set the Text File Encoding to UTF-8.
If you use an editor that does not have a "plain ASCII" encoding mode, you can use Windows-1252 (also
called CP-1252) or ISO-8859-1 (also called Latin 1), both of which accept all 7-bit ASCII characters.
However, the compiler may not accept extended characters in these encodings, so you should not use
extended characters, even in comments.
Wide character (wchar_t) types and operations are supported by the compiler. However, wide character
strings may not contain characters beyond 7-bit ASCII. The encoding of wide characters is 7-bit ASCII, 0
extended to the width of the wchar_t type.
5.7
Keywords
The ARM C/C++ compiler supports all of the standard C89 keywords, including const, volatile, and
register. It supports all of the standard C99 keywords, including inline and restrict. It supports all of the
standard C11 keywords. It also supports TI extension keywords __interrupt, and __asm. Some keywords
are not available in strict ANSI mode.
The following keywords may appear in other target documentation and require the same treatment as the
interrupt and restrict keywords:
• trap
• reentrant
• cregister
5.7.1 The const Keyword
The C/C++ compiler supports the ANSI/ISO standard keyword const in all modes. This keyword gives you
greater optimization and control over allocation for certain data objects. You can apply the const qualifier
to the definition of any variable or array to ensure that its value is not altered.
Global objects qualified as const are placed in the .const section. The linker allocates the .const section
from ROM or FLASH, which are typically more plentiful than RAM. The const data storage allocation rule
has the following exceptions:
• If volatile is also specified in the object definition. For example, volatile const int x. Volatile
keywords are assumed to be allocated to RAM. (The program is not allowed to modify a const volatile
object, but something external to the program might.)
• If the object has automatic storage (function scope).
• If the object is a C++ object with a "mutable" member.
• If the object is initialized with a value that is not known at compile time (such as the value of another
variable).
In these cases, the storage for the object is the same as if the const keyword were not used.
The placement of the const keyword is important. For example, the first statement below defines a
constant pointer p to a modifiable int. The second statement defines a modifiable pointer q to a constant
int:
int * const p = &x;
const int * q = &x;
Using the const keyword, you can define large constant tables and allocate them into system ROM. For
example, to allocate a ROM table, you could use the following definition:
const int digits[] = {0,1,2,3,4,5,6,7,8,9};
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5.7.2 The __interrupt Keyword
The compiler extends the C/C++ language by adding the __interrupt keyword, which specifies that a
function is treated as an interrupt function. This keyword is an IRQ interrupt. The alternate keyword,
"interrupt", may also be used except in strict ANSI C or C++ modes.
Note that the interrupt function attribute described in Section 5.11.17 is the recommended syntax for
declaring interrupt functions.
Functions that handle interrupts follow special register-saving rules and a special return sequence. The
implementation stresses safety. The interrupt routine does not assume that the C run-time conventions for
the various CPU register and status bits are in effect; instead, it re-establishes any values assumed by the
run-time environment. When C/C++ code is interrupted, the interrupt routine must preserve the contents of
all machine registers that are used by the routine or by any function called by the routine. When you use
the __interrupt keyword with the definition of the function, the compiler generates register saves based on
the rules for interrupt functions and the special return sequence for interrupts.
You can only use the __interrupt keyword with a function that is defined to return void and that has no
parameters. The body of the interrupt function can have local variables and is free to use the stack or
global variables. For example:
__interrupt void int_handler()
{
unsigned int flags;
...
}
The name c_int00 is the C/C++ entry point. This name is reserved for the system reset interrupt. This
special interrupt routine initializes the system and calls the main() function. Because it has no caller,
c_int00 does not save any registers.
Hwi Objects and the __interrupt Keyword
NOTE: The __interrupt keyword must not be used when SYS/BIOS Hwi objects are used in
conjunction with C functions. The Hwi_enter/Hwi_exit macros and the Hwi dispatcher already
contain this functionality, and the use of the C modifier can cause unwanted conflicts.
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5.7.3 The volatile Keyword
The C/C++ compiler supports the volatile keyword in all modes. In addition, the __volatile keyword is
supported in relaxed ANSI mode for C89, C99, C11, and C++.
The volatile keyword indicates to the compiler that there is something about how the variable is accessed
that requires that the compiler not use overly-clever optimization on expressions involving that variable.
For example, the variable may also be accessed by an external program, an interrupt, another thread, or a
peripheral device.
The compiler eliminates redundant memory accesses whenever possible, using data flow analysis to
figure out when it is legal. However, some memory accesses may be special in some way that the
compiler cannot see, and in such cases you should use the volatile keyword to prevent the compiler from
optimizing away something important. The compiler does not optimize out any accesses to variables
declared volatile. The number of volatile reads and writes will be exactly as they appear in the C/C++
code, no more and no less and in the same order.
Any variable which might be modified by something external to the obvious control flow of the program
(such as an interrupt service routine) must be declared volatile. This tells the compiler that an interrupt
function might modify the value at any time, so the compiler should not perform optimizations which will
change the number or order of accesses of that variable. This is the primary purpose of the volatile
keyword. In the following example, the loop intends to wait for a location to be read as 0xFF:
unsigned int *ctrl;
while (*ctrl !=0xFF);
However, in this example, *ctrl is a loop-invariant expression, so the loop is optimized down to a singlememory read. To get the desired result, define ctrl as:
volatile unsigned int *ctrl;
Here the *ctrl pointer is intended to reference a hardware location, such as an interrupt flag.
The volatile keyword must also be used when accessing memory locations that represent memorymapped peripheral devices. Such memory locations might change value in ways that the compiler cannot
predict. These locations might change if accessed, or when some other memory location is accessed, or
when some signal occurs.
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Volatile must also be used for local variables in a function which calls setjmp, if the value of the local
variables needs to remain valid if a longjmp occurs.
Example 5-1. Volatile for Local Variables With setjmp
#include <stdlib.h>
jmp_buf context;
void function()
{
volatile int x = 3;
switch(setjmp(context))
{
case 0: setup(); break;
default:
{
/* We only reach here if longjmp occurs. Because x's lifetime begins before setjmp
and lasts through longjmp, the C standard requires x be declared "volatile". */
printf("x == %d\n", x);
break;
}
}
}
5.8
C++ Exception Handling
The compiler supports the C++ exception handling features defined by the ANSI/ISO 14882 C++
Standard. See The C++ Programming Language, Third Edition by Bjarne Stroustrup.
The compiler --exceptions option enables exception handling. The compiler’s default is no exception
handling support.
For exceptions to work correctly, all C++ files in the application must be compiled with the --exceptions
option, regardless of whether exceptions occur in that file. Mixing exception-enabled and exceptiondisabled object files and libraries can lead to undefined behavior.
Exception handling requires support in the run-time-support library, which come in exception-enabled and
exception-disabled forms; you must link with the correct form. When using automatic library selection (the
default), the linker automatically selects the correct library Section 4.3.1.1. If you select the library
manually, you must use run-time-support libraries whose name contains _eh if you enable exceptions.
Using the --exceptions option causes the compiler to insert exception handling code. This code will
increase the size of the program, but EABI does not increase the code size much, and has a minimal
execution time cost if exceptions are never thrown. It slightly increases the data size for the exceptionhandling tables.
See Section 7.1 for details on the run-time libraries.
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Register Variables and Parameters
The C/C++ compiler allows the use of the keyword register on global and local register variables and
parameters. This section describes the compiler implementation for this qualifier.
5.9.1 Local Register Variables and Parameters
The C/C++ compiler treats register variables (variables defined with the register keyword) differently,
depending on whether you use the --opt_level (-O) option.
• Compiling with optimization
The compiler ignores any register definitions and allocates registers to variables and temporary values
by using an algorithm that makes the most efficient use of registers.
• Compiling without optimization
If you use the register keyword, you can suggest variables as candidates for allocation into registers.
The compiler uses the same set of registers for allocating temporary expression results as it uses for
allocating register variables.
The compiler attempts to honor all register definitions. If the compiler runs out of appropriate registers, it
frees a register by moving its contents to memory. If you define too many objects as register variables,
you limit the number of registers the compiler has for temporary expression results. This limit causes
excessive movement of register contents to memory.
Any object with a scalar type (integral, floating point, or pointer) can be defined as a register variable. The
register designator is ignored for objects of other types, such as arrays.
The register storage class is meaningful for parameters as well as local variables. Normally, in a function,
some of the parameters are copied to a location on the stack where they are referenced during the
function body. The compiler copies a register parameter to a register instead of the stack, which speeds
access to the parameter within the function.
For more information about register conventions, see Section 6.3.
5.9.2 Global Register Variables
The C/C++ compiler extends the C language by adding a special convention to the register storage class
specifier to allow the allocation of global registers. This special global declaration has the form:
register type regid
The regid parameter can be __R5, __R6, or __R9. The identifiers _ _R5, _ _R6, and _ _R9 are each
bound to their corresponding register R5, R6 and R9, respectively.
When you use this declaration at the file level, the register is permanently reserved from any other use by
the optimizer and code generator for that file. You cannot assign an initial value to the register. You can
use a #define directive to assign a meaningful name to the register; for example:
register struct data_struct *__R5
#define data_pointer __R5
data_pointer->element;
data_pointer++;
There are two reasons that you would be likely to use a global register variable:
• You are using a global variable throughout your program, and it would significantly reduce code size
and execution speed to assign this variable to a register permanently.
• You are using an interrupt service routine that is called so frequently that it would significantly reduce
execution speed if the routine did not have to save and restore the register(s) it uses every time it is
called.
You need to consider very carefully the implications of reserving a global register variable. Registers are a
precious resource to the compiler, and using this feature indiscriminately may result in poorer code.
You also need to consider carefully how code with a globally declared register variable interacts with other
code, including library functions, that does not recognize the restriction placed on the register.
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Because the registers that can be global register variables are save-on-entry registers, a normal function
call and return does not affect the value in the register and neither does a normal interrupt. However,
when you mix code that has a globally declared register variable with code that does not have the register
reserved, it is still possible for the value in the register to become corrupted. To avoid the possibility of
corruption, you must follow these rules:
• Functions that alter global register variables cannot be called by functions that are not aware of the
global register. Use the -r shell option to reserve the register in code that is not aware of the global
register declaration. You must be careful if you pass a pointer to a function as an argument. If the
passed function alters the global register variable and the called function saves the register, the value
in the register will be corrupted.
• You cannot access a global register variable in an interrupt service routine unless you recompile all
code, including all libraries, to reserve the register. This is because the interrupt routine can be called
from any point in the program.
• The longjmp ( ) function restores global register variables to the values they had at the setjmp ( )
location. If this presents a problem in your code, you must alter the code for the function and recompile
rts.src.
The -r register compiler command-line option allows you to prevent the compiler from using the named
register. This lets you reserve the named register in modules that do not have the global register
variable declaration, such as the run-time-support libraries, if you need to compile the modules to
prevent some of the above occurrences.
5.10 The __asm Statement
The C/C++ compiler can embed assembly language instructions or directives directly into the assembly
language output of the compiler. This capability is an extension to the C/C++ language implemented
through the __asm keyword. The __asm keyword provides access to hardware features that C/C++
cannot provide.
The alternate keyword, "asm", may also be used except in strict ANSI C mode. It is available in relaxed C
and C++ modes.
Using __asm is syntactically performed as a call to a function named __asm, with one string constant
argument:
__asm(" assembler text ");
The compiler copies the argument string directly into your output file. The assembler text must be
enclosed in double quotes. All the usual character string escape codes retain their definitions. For
example, you can insert a .byte directive that contains quotes as follows:
__asm("STR: .byte \"abc\"");
The naked function attribute can be used to identify functions that are written as embedded assembly
functions using __asm statements. See Section 5.17.2.
The inserted code must be a legal assembly language statement. Like all assembly language statements,
the line of code inside the quotes must begin with a label, a blank, a tab, or a comment (asterisk or
semicolon). The compiler performs no checking on the string; if there is an error, the assembler detects it.
For more information about the assembly language statements, see the ARM Assembly Language Tools
User's Guide.
The __asm statements do not follow the syntactic restrictions of normal C/C++ statements. Each can
appear as a statement or a declaration, even outside of blocks. This is useful for inserting directives at the
very beginning of a compiled module.
The __asm statement does not provide any way to refer to local variables. If your assembly code needs to
refer to local variables, you will need to write the entire function in assembly code.
For more information, refer to Section 6.6.5.
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Avoid Disrupting the C/C++ Environment With asm Statements
Be careful not to disrupt the C/C++ environment with __asm statements. The compiler does
not check the inserted instructions. Inserting jumps and labels into C/C++ code can cause
unpredictable results in variables manipulated in or around the inserted code. Directives that
change sections or otherwise affect the assembly environment can also be troublesome.
Be especially careful when you use optimization with __asm statements. Although the
compiler cannot remove __asm statements, it can significantly rearrange the code order near
them and cause undesired results.
5.11 Pragma Directives
Pragma directives tell the compiler how to treat a certain function, object, or section of code. The ARM
C/C++ compiler supports the following pragmas:
• CALLS (See Section 5.11.1)
• CHECK_MISRA (See Section 5.11.2)
• CHECK_ULP (See Section 5.11.3)
• CODE_ALIGN (See Section 5.11.4)
• CODE_SECTION (See Section 5.11.5)
• CODE_STATE (See Section 5.11.6)
• DATA_ALIGN (See Section 5.11.7)
• DATA_SECTION (See Section 5.11.8)
• diag_suppress, diag_remark, diag_warning, diag_error, diag_default, diag_push, diag_pop (See
Section 5.11.9)
• DUAL_STATE (See Section 5.11.10)
• FORCEINLINE (See Section 5.11.11)
• FORCEINLINE_RECURSIVE (See Section 5.11.12)
• FUNC_ALWAYS_INLINE (See Section 5.11.13)
• FUNC_CANNOT_INLINE (See Section 5.11.14)
• FUNC_EXT_CALLED (See Section 5.11.15)
• FUNCTION_OPTIONS (See Section 5.11.16)
• INTERRUPT (See Section 5.11.17)
• LOCATION (See Section 5.11.18)
• MUST_ITERATE (See Section 5.11.19)
• NOINIT (See Section 5.11.20)
• NOINLINE (See Section 5.11.21)
• NO_HOOKS (See Section 5.11.22)
• pack (See Section 5.11.23)
• PERSISTENT (See Section 5.11.20)
• RESET_MISRA (See Section 5.11.24)
• RESET_ULP (See Section 5.11.25)
• RETAIN (See Section 5.11.26)
• SET_CODE_SECTION (See Section 5.11.27)
• SET_DATA_SECTION (See Section 5.11.27)
• SWI_ALIAS (See Section 5.11.28)
• TASK (See Section 5.11.29)
• UNROLL (See Section 5.11.30)
• WEAK (See Section 5.11.31)
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The arguments func and symbol cannot be defined or declared inside the body of a function. You must
specify the pragma outside the body of a function; and the pragma specification must occur before any
declaration, definition, or reference to the func or symbol argument. If you do not follow these rules, the
compiler issues a warning and may ignore the pragma.
For pragmas that apply to functions or symbols, the syntax differs between C and C++.
• In C, you must supply the name of the object or function to which you are applying the pragma as the
first argument. Because the entity operated on is specified, a pragma in C can appear some distance
way from the definition of that entity.
• In C++, pragmas are positional. They do not name the entity on which they operate as an argument.
Instead, they always operate on the next entity defined after the pragma.
5.11.1 The CALLS Pragma
The CALLS pragma specifies a set of functions that can be called indirectly from a specified calling
function.
The CALLS pragma is used by the compiler to embed debug information about indirect calls in object files.
Using the CALLS pragma on functions that make indirect calls enables such indirect calls to be included in
calculations for such functions' inclusive stack sizes. For more information on generating function stack
usage information, see the -cg option of the Object File Display Utility in the "Invoking the Object File
Display Utility" section of the ARM Assembly Language Tools User's Guide.
The CALLS pragma can precede either the calling function's definition or its declaration. In C, the pragma
must have at least 2 arguments—the first argument is the calling function, followed by at least one
function that will be indirectly called from the calling function. In C++, the pragma applies to the next
function declared or defined, and the pragma must have at least one argument.
The syntax for the CALLS pragma in C is as follows. This indicates that calling_function can indirectly call
function_1 through function_n.
#pragma CALLS ( calling_function, function_1, function_2, ..., function_n )
The syntax for the CALLS pragma in C++ is:
#pragma CALLS ( function_1_mangled_name, ..., function_n_mangled_name )
Note that in C++, the arguments to the CALLS pragma must be the full mangled names for the functions
that can be indirectly called from the calling function.
The GCC-style "calls" function attribute (see Section 5.17.2), which has the same effect as the CALLS
pragma, has the following syntax:
__attribute__((calls("function_1","function_2",..., "function_n")))
5.11.2 The CHECK_MISRA Pragma
The CHECK_MISRA pragma enables/disables MISRA C:2004 rules at the source level. The compiler
option --check_misra must be used to enable checking in order for this pragma to function at the source
level.
The syntax of the pragma in C is:
#pragma CHECK_MISRA (" {all|required|advisory|none|rulespec} ")
The rulespec parameter is a comma-separated list of rule numbers. See Section 5.3 for details.
The RESET_MISRA pragma can be used to reset any CHECK_MISRA pragmas; see Section 5.11.24.
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5.11.3 The CHECK_ULP Pragma
The CHECK_ULP pragma enables/disables ULP Advisor rules at the source level. This pragma has the
same effect as using the --advice:power option.
The syntax of the pragma in C is:
#pragma CHECK_ULP (" {all|none|rulespec} ")
The rulespec parameter is a comma-separated list of rule numbers. See Section 5.4 for the syntax. See
www.ti.com/ulpadvisor for a list of rules.
The RESET_ULP pragma can be used to reset any CHECK_ULP pragmas; see Section 5.11.25.
5.11.4 The CODE_ALIGN Pragma
The CODE_ALIGN pragma aligns func along the specified alignment. The alignment constant must be a
power of 2. The CODE_ALIGN pragma is useful if you have functions that you want to start at a certain
boundary.
The CODE_ALIGN pragma has the same effect as using the GCC-style aligned function attribute. See
Section 5.17.2.
The syntax of the pragma in C is:
#pragma CODE_ALIGN ( func, constant )
The syntax of the pragma in C++ is:
#pragma CODE_ALIGN ( constant )
5.11.5 The CODE_SECTION Pragma
The CODE_SECTION pragma allocates space for the symbol in C, or the next symbol declared in C++, in
a section named section name.
The CODE_SECTION pragma is useful if you have code objects that you want to link into an area
separate from the .text section.
The CODE_SECTION pragma has the same effect as using the GCC-style section function attribute.
See Section 5.17.2.
The syntax of the pragma in C is:
#pragma CODE_SECTION (symbol , "section name ")
The syntax of the pragma in C++ is:
#pragma CODE_SECTION (" section name ")
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The following example demonstrates the use of the CODE_SECTION pragma.
Example 5-2. Using the CODE_SECTION Pragma C Source File
#pragma CODE_SECTION(fn, "my_sect")
int fn(int x)
{
return x;
}
Example 5-3. Generated Assembly Code From Example 5-2
.sect
.align
.state32
.global
"my_sect"
4
fn
;*****************************************************************************
;* FUNCTION NAME: fn
*
;*
*
;*
Regs Modified
: SP
*
;*
Regs Used
: A1,SP
*
;*
Local Frame Size : 0 Args + 4 Auto + 0 Save = 4 byte
*
;*****************************************************************************
fn:
;* --------------------------------------------------------------------------*
SUB
SP, SP, #8
STR
A1, [SP, #0]
; |4|
ADD
SP, SP, #8
BX
LR
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5.11.6 The CODE_STATE Pragma
The CODE_STATE pragma overrides the compilation state of a file, at the function level. For example, if a
file is compiled in thumb mode, but you want a function in that file to be compiled in 32-bit mode, you
would add this pragma in the file. The compilation state for the function is changed to 16-bit mode (thumb)
or 32-bit mode.
The syntax of the pragma is C is:
#pragma CODE_STATE ( function , {16|32} )
The syntax of the pragma in C++ is:
#pragma CODE_STATE ( code state )
5.11.7 The DATA_ALIGN Pragma
The DATA_ALIGN pragma aligns the symbol in C, or the next symbol declared in C++, to an alignment
boundary. The alignment boundary is the maximum of the symbol's default alignment value or the value of
the constant in bytes. The constant must be a power of 2. The maximum alignment is 32768.
The DATA_ALIGN pragma cannot be used to reduce an object's natural alignment.
Using the DATA_ALIGN pragma has the same effect as using the GCC-style aligned variable attribute.
See Section 5.17.3.
The syntax of the pragma in C is:
#pragma DATA_ALIGN ( symbol , constant )
The syntax of the pragma in C++ is:
#pragma DATA_ALIGN ( constant )
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5.11.8 The DATA_SECTION Pragma
The DATA_SECTION pragma allocates space for the symbol in C, or the next symbol declared in C++, in
a section named section name.
The DATA_SECTION pragma is useful if you have data objects that you want to link into an area separate
from the .bss section.
Using the DATA_SECTION pragma has the same effect as using the GCC-style section variable
attribute. See Section 5.17.3.
The syntax of the pragma in C is:
#pragma DATA_SECTION ( symbol , " section name ")
The syntax of the pragma in C++ is:
#pragma DATA_SECTION (" section name ")
Example 5-4 through Example 5-6 demonstrate the use of the DATA_SECTION pragma.
Example 5-4. Using the DATA_SECTION Pragma C Source File
#pragma DATA_SECTION(bufferB, "my_sect")
char bufferA[512];
char bufferB[512];
Example 5-5. Using the DATA_SECTION Pragma C++ Source File
char bufferA[512];
#pragma DATA_SECTION("my_sect")
char bufferB[512];
Example 5-6. Using the DATA_SECTION Pragma Assembly Source File
.global
.bss
.global
_bufferB: .usect
_bufferA
_bufferA,512,4
_bufferB
"my_sect",512,4
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5.11.9 The Diagnostic Message Pragmas
The following pragmas can be used to control diagnostic messages in the same ways as the
corresponding command line options:
Pragma
Option
Description
diag_suppress num
-pds=num[, num2, num3...]
Suppress diagnostic num
diag_remark num
-pdsr=num[, num2, num3...]
Treat diagnostic num as a remark
diag_warning num
-pdsw=num[, num2, num3...]
Treat diagnostic num as a warning
diag_error num
-pdse=num[, num2, num3...]
Treat diagnostic num as an error
diag_default num
n/a
Use default severity of the diagnostic
diag_push
n/a
Push the current diagnostics severity state to store it for later use.
diag_pop
n/a
Pop the most recent diagnostic severity state stored with #pragma
diag_push to be the current setting.
The syntax of the diag_suppress, diag_remark, diag_warning, and diag_error pragmas in C is:
#pragma diag_xxx [=]num[, num2, num3...]
Notice that the names of these pragmas are in lowercase.
The diagnostic affected (num) is specified using either an error number or an error tag name. The equal
sign (=) is optional. Any diagnostic can be overridden to be an error, but only diagnostic messages with a
severity of discretionary error or below can have their severity reduced to a warning or below, or be
suppressed. The diag_default pragma is used to return the severity of a diagnostic to the one that was in
effect before any pragmas were issued (i.e., the normal severity of the message as modified by any
command-line options).
The diagnostic identifier number is output with the message when you use the -pden command line
option. The following example suppresses a diagnostic message and then restores the previous
diagnostics severity state:
#pragma
#pragma
#pragma
#pragma
diag_push
diag_suppress 551
CHECK_MISRA("-9.1")
diag_pop
5.11.10 The DUAL_STATE Pragma
By default (that is, without the compiler -md option), all functions with external linkage support dual-state
interworking. This support assumes that most calls do not require a state change and are therefore
optimized (in terms of code size and execution speed) for calls not requiring a state change. Using the
DUAL_STATE pragma does not change the functionality of the dual-state support, but it does assert that
calls to the applied function often require a state change. Therefore, such support is optimized for state
changes.
The pragma must appear before any declaration or reference to the function that you want to keep. In C,
the argument func is the name of the function. In C++, the pragma applies to the next function declared.
The syntax of the pragma in C is:
#pragma DUAL_STATE ( func )
The syntax of the pragma in C++ is:
#pragma DUAL_STATE
For more information on dual-state interworking, see Section 6.11.
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5.11.11 The FORCEINLINE Pragma
The FORCEINLINE pragma can be placed before a statement to force any function calls made in that
statement to be inlined. It has no effect on other calls to the same functions.
The compiler only inlines a function if it is legal to inline the function. Functions are never inlined if the
compiler is invoked with the --opt_level=off option. A function can be inlined even if the function is not
declared with the inline keyword. A function can be inlined even if the compiler is not invoked with any -opt_level command-line option.
The syntax of the pragma in C/C++ is:
#pragma FORCEINLINE
For example, in the following example, the mytest() and getname() functions are inlined, but the error()
function is not.
#pragma FORCEINLINE
if (!mytest(getname(myvar))) {
error();
}
Placing the FORCEINLINE pragma before the call to error() would inline that function but not the others.
For information about interactions between command-line options, pragmas, and keywords that affect
inlining, see Section 2.11.
Notice that the FORCEINLINE, FORCEINLINE_RECURSIVE, and NOINLINE pragmas affect only the
C/C++ statement that follows the pragma. The FUNC_ALWAYS_INLINE and FUNC_CANNOT_INLINE
pragmas affect an entire function.
5.11.12 The FORCEINLINE_RECURSIVE Pragma
The FORCEINLINE_RECURSIVE can be placed before a statement to force any function calls made in
that statement to be inlined along with any calls made from those functions. That is, calls that are not
visible in the statement but are called as a result of the statement will be inlined.
The syntax of the pragma in C/C++ is:
#pragma FORCEINLINE_RECURSIVE
For information about interactions between command-line options, pragmas, and keywords that affect
inlining, see Section 2.11.
5.11.13 The FUNC_ALWAYS_INLINE Pragma
The FUNC_ALWAYS_INLINE pragma instructs the compiler to always inline the named function.
The compiler only inlines a function if it is legal to inline the function. Functions are never inlined if the
compiler is invoked with the --opt_level=off option. A function can be inlined even if the function is not
declared with the inline keyword. A function can be inlined even if the compiler is not invoked with any -opt_level command-line option. See Section 2.11 for details about interaction between various types of
inlining.
This pragma must appear before any declaration or reference to the function that you want to inline. In C,
the argument func is the name of the function that will be inlined. In C++, the pragma applies to the next
function declared.
The FUNC_ALWAYS_INLINE pragma has the same effect as using the GCC-style always_inline
function attribute. See Section 5.17.2.
The syntax of the pragma in C is:
#pragma FUNC_ALWAYS_INLINE ( func )
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The syntax of the pragma in C++ is:
#pragma FUNC_ALWAYS_INLINE
The following example uses this pragma:
#pragma FUNC_ALWAYS_INLINE(functionThatMustGetInlined)
static inline void functionThatMustGetInlined(void) {
P1OUT |= 0x01;
P1OUT &= ~0x01;
}
Use Caution with the FUNC_ALWAYS_INLINE Pragma
NOTE: The FUNC_ALWAYS_INLINE pragma overrides the compiler's inlining decisions. Overuse of
this pragma could result in increased compilation times or memory usage, potentially enough
to consume all available memory and result in compilation tool failures.
5.11.14 The FUNC_CANNOT_INLINE Pragma
The FUNC_CANNOT_INLINE pragma instructs the compiler that the named function cannot be expanded
inline. Any function named with this pragma overrides any inlining you designate in any other way, such as
using the inline keyword. Automatic inlining is also overridden with this pragma; see Section 2.11.
The pragma must appear before any declaration or reference to the function that you want to keep. In C,
the argument func is the name of the function that cannot be inlined. In C++, the pragma applies to the
next function declared.
The FUNC_CANNOT_INLINE pragma has the same effect as using the GCC-style noinline function
attribute. See Section 5.17.2.
The syntax of the pragma in C is:
#pragma FUNC_CANNOT_INLINE ( func )
The syntax of the pragma in C++ is:
#pragma FUNC_CANNOT_INLINE
5.11.15 The FUNC_EXT_CALLED Pragma
When you use the --program_level_compile option, the compiler uses program-level optimization. When
you use this type of optimization, the compiler removes any function that is not called, directly or indirectly,
by main(). You might have C/C++ functions that are called instead of main().
The FUNC_EXT_CALLED pragma specifies that the optimizer should keep these C functions or any
functions these C/C++ functions call. These functions act as entry points into C/C++. The pragma must
appear before any declaration or reference to the function to keep. In C, the argument func is the name of
the function to keep. In C++, the pragma applies to the next function declared.
The syntax of the pragma in C is:
#pragma FUNC_EXT_CALLED ( func )
The syntax of the pragma in C++ is:
#pragma FUNC_EXT_CALLED
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Except for _c_int00, which is the name reserved for the system reset interrupt for C/C++programs, the
name of the interrupt (the func argument) does not need to conform to a naming convention.
When you use program-level optimization, you may need to use the FUNC_EXT_CALLED pragma with
certain options. See Section 3.4.2.
5.11.16 The FUNCTION_OPTIONS Pragma
The FUNCTION_OPTIONS pragma allows you to compile a specific function in a C or C++ file with
additional command-line compiler options. The affected function will be compiled as if the specified list of
options appeared on the command line after all other compiler options. In C, the pragma is applied to the
function specified. In C++, the pragma is applied to the next function.
The syntax of the pragma in C is:
#pragma FUNCTION_OPTIONS ( func, "additional options" )
The syntax of the pragma in C++ is:
#pragma FUNCTION_OPTIONS( "additional options" )
Supported options for this pragma are --opt_level, --auto_inline, --code_state, and --opt_for_speed. In
order to use --opt_level and --auto_inline with the FUNCTION_OPTIONS pragma, the compiler must be
invoked with some optimization level (that is, at least --opt_level=0).
5.11.17 The INTERRUPT Pragma
The INTERRUPT pragma enables you to handle interrupts directly with C code. The pragma specifies that
the function is an interrupt. The type of interrupt is specified by the pragma; the IRQ (interrupt request)
interrupt type is assumed if none is given.
The syntax of the pragma in C is:
#pragma INTERRUPT ( func [, interrupt_type] )
The syntax of the pragma in C++ is:
#pragma INTERRUPT [( interrupt_type )]
void func( void )
The GCC interrupt attribute syntax, which has the same effects as the INTERRUPT pragma, is as follows.
Note that the interrupt attribute can precede either the function's definition or its declaration.
__attribute__((interrupt[( "interrupt_type" )] )) void func( void )
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In C, the argument func is the name of a function. In C++, the pragma applies to the next function
declared. The optional argument interrupt_type specifies an interrupt type. The registers that are saved
and the return sequence depend upon the interrupt type. If the interrupt type is omitted from the interrupt
pragma, the interrupt type IRQ is assumed. These are the valid interrupt types:
Interrupt Type
Description
DABT
Data abort
FIQ
Fast interrupt request
IRQ
Interrupt request
PABT
Prefetch abort
RESET
System reset
SWI
Software interrupt
UDEF
Undefined instruction
Except for _c_int00, which is the name reserved for the system reset interrupt for C programs, the name
of the interrupt (the func argument) does not need to conform to a naming convention.
For the Cortex-M architectures, the interrupt_type can be nothing (default) or SWI. The hardware performs
the necessary saving and restoring of context for interrupts. Therefore, the compiler does not distinguish
between the different interrupt types. The only exception is for software interrupts (SWIs) which are
allowed to have arguments (for Cortex-M architectures, C SWI handlers cannot return values).
Hwi Objects and the INTERRUPT Pragma
NOTE: The INTERRUPT pragma must not be used when SYS/BIOS Hwi objects are used in
conjunction with C functions. The Hwi_enter/Hwi_exit macros and the Hwi dispatcher contain
this functionality, and the use of the C modifier can cause negative results.
5.11.18 The LOCATION Pragma
The compiler supports the ability to specify the run-time address of a variable at the source level. This can
be accomplished with the LOCATION pragma or the GCC-style location attribute.
The LOCATION pragma has the same effect as using the GCC-style location function attribute. See
Section 5.17.2.
The syntax of the pragma in C is:
#pragma LOCATION( x , address )
int x
The syntax of the pragmas in C++ is:
#pragma LOCATION(address )
int x
The syntax of the GCC-style attribute (see Section 5.17.3) is:
int x __attribute__((location(address )))
The NOINIT pragma may be used in conjunction with the LOCATION pragma to map variables to special
memory locations; see Section 5.11.20.
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5.11.19 The MUST_ITERATE Pragma
The MUST_ITERATE pragma specifies to the compiler certain properties of a loop. When you use this
pragma, you are guaranteeing to the compiler that a loop executes a specific number of times or a
number of times within a specified range.
Any time the UNROLL pragma is applied to a loop, MUST_ITERATE should be applied to the same loop.
For loops the MUST_ITERATE pragma's third argument, multiple, is the most important and should
always be specified.
Furthermore, the MUST_ITERATE pragma should be applied to any other loops as often as possible. This
is because the information provided via the pragma (especially the minimum number of iterations) aids the
compiler in choosing the best loops and loop transformations (that is, nested loop transformations). It also
helps the compiler reduce code size.
No statements are allowed between the MUST_ITERATE pragma and the for, while, or do-while loop to
which it applies. However, other pragmas, such as UNROLL, can appear between the MUST_ITERATE
pragma and the loop.
5.11.19.1 The MUST_ITERATE Pragma Syntax
The syntax of the pragma for C and C++ is:
#pragma MUST_ITERATE ( min, max, multiple )
The arguments min and max are programmer-guaranteed minimum and maximum trip counts. The trip
count is the number of times a loop iterates. The trip count of the loop must be evenly divisible by multiple.
All arguments are optional. For example, if the trip count could be 5 or greater, you can specify the
argument list as follows:
#pragma MUST_ITERATE(5)
However, if the trip count could be any nonzero multiple of 5, the pragma would look like this:
#pragma MUST_ITERATE(5, , 5) /* Note the blank field for max */
It is sometimes necessary for you to provide min and multiple in order for the compiler to perform
unrolling. This is especially the case when the compiler cannot easily determine how many iterations the
loop will perform (that is, the loop has a complex exit condition).
When specifying a multiple via the MUST_ITERATE pragma, results of the program are undefined if the
trip count is not evenly divisible by multiple. Also, results of the program are undefined if the trip count is
less than the minimum or greater than the maximum specified.
If no min is specified, zero is used. If no max is specified, the largest possible number is used. If multiple
MUST_ITERATE pragmas are specified for the same loop, the smallest max and largest min are used.
5.11.19.2 Using MUST_ITERATE to Expand Compiler Knowledge of Loops
Through the use of the MUST_ITERATE pragma, you can guarantee that a loop executes a certain
number of times. The example below tells the compiler that the loop is guaranteed to run exactly 10 times:
#pragma MUST_ITERATE(10,10)
for(i = 0; i < trip_count; i++)
{ ...
In this example, the compiler attempts to generate a loop even without the pragma. However, if
MUST_ITERATE is not specified for a loop such as this, the compiler generates code to bypass the loop,
to account for the possibility of 0 iterations. With the pragma specification, the compiler knows that the
loop iterates at least once and can eliminate the loop-bypassing code.
MUST_ITERATE can specify a range for the trip count as well as a factor of the trip count. The following
example tells the compiler that the loop executes between 8 and 48 times and the trip_count variable is a
multiple of 8 (8, 16, 24, 32, 40, 48). The multiple argument allows the compiler to unroll the loop.
#pragma MUST_ITERATE(8, 48, 8)
for(i = 0; i < trip_count; i++)
{ ...
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You should consider using MUST_ITERATE for loops with complicated bounds. In the following example,
the compiler would have to generate a divide function call to determine, at run time, the number of
iterations performed.
for(i2 = ipos[2]; i2 < 40; i2 += 5)
{ ...
The compiler will not do the above. In this case, using MUST_ITERATE to specify that the loop always
executes eight times allows the compiler to attempt to generate a loop:
#pragma MUST_ITERATE(8, 8)
for(i2 = ipos[2]; i2 < 40; i2 += 5)
{ ...
5.11.20 The NOINIT and PERSISTENT Pragmas
Global and static variables are zero-initialized by default. However, in applications that use non-volatile
memory, it may be desirable to have variables that are not initialized. Noinit variables are global or static
variables that are not zero-initialized at startup or reset.
Variables can be declared as noinit or persistent using either pragmas or variable attributes. See
Section 5.17.3 for information about using variable attributes in declarations.
Noinit and persistent variables behave identically with the exception of whether or not they are initialized
at load time.
• The NOINIT pragma may be used only with uninitialized variables. It prevents such variables from
being set to 0 during a reset. It may be used in conjunction with the LOCATION pragma to map
variables to special memory locations, like memory-mapped registers, without generating unwanted
writes.
• The PERSISTENT pragma may be used only with statically-initialized variables. It prevents such
variables from being initialized during a reset. Persistent variables disable startup initialization; they are
given an initial value when the code is loaded, but are never again initialized.
By default, noinit or persistent variables are placed in sections named .TI.noinit and .TI.persistent,
respectively. The location of these sections is controlled by the linker command file. Typically .TI.persistent
sections are placed in FRAM for devices that support FRAM and .TI.noinit sections are placed in RAM.
NOTE: When using these pragmas in non-volatile FRAM memory, the memory region could be
protected against unintended writes through the device's Memory Protection Unit. Some
devices have memory protection enabled by default. Please see the information about
memory protection in the datasheet for your device. If the Memory Protection Unit is enabled,
it first needs to be disabled before modifying the variables.
If you are using non-volatile RAM, you can define a persistent variable with an initial value of zero loaded
into RAM. The program can increment that variable over time as a counter, and that count will not
disappear if the device loses power and restarts, because the memory is non-volatile and the boot
routines do not initialize it back to zero. For example:
#pragma PERSISTENT(x)
#pragma location = 0xC200
int x = 0;
// memory address in RAM
void main() {
run_init();
while (1) {
run_actions(x);
__delay_cycles(1000000);
x++;
}
}
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The syntax of the pragmas in C is:
#pragma NOINIT (x )
int x;
#pragma PERSISTENT (x )
int x=10;
The syntax of the pragmas in C++ is:
#pragma NOINIT
int x;
#pragma PERSISTENT
int x=10;
The syntax of the GCC attributes is:
int x __attribute__((noinit));
int x __attribute__((persistent)) = 0;
5.11.21 The NOINLINE Pragma
The NOINLINE pragma can be placed before a statement to prevent any function calls made in that
statement from being inlined. It has no effect on other calls to the same functions.
The syntax of the pragma in C/C++ is:
#pragma NOINLINE
For information about interactions between command-line options, pragmas, and keywords that affect
inlining, see Section 2.11.
5.11.22 The NO_HOOKS Pragma
The NO_HOOKS pragma prevents entry and exit hook calls from being generated for a function.
The syntax of the pragma in C is:
#pragma NO_HOOKS ( func )
The syntax of the pragma in C++ is:
#pragma NO_HOOKS
See Section 2.15 for details on entry and exit hooks.
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5.11.23 The pack Pragma
The pack pragma can be used to control the alignment of fields within a class, struct, or union type. The
syntax of the pragma in C/C++ can be any of the following.
#pragma pack (n)
The above form of the pack pragma affects all class, struct, or union type declarations that follow this
pragma in a file. It forces the maximum alignment of each field to be the value specified by n. Valid values
for n are 1, 2, 4, 8, and 16 bytes.
#pragma pack ( push, n)
#pragma pack ( pop )
The above form of the pack pragma affects only class, struct, and union type declarations between push
and pop directives. (A pop directive with no prior push results in a warning diagnostic from the compiler.)
The maximum alignment of all fields declared is n. Valid values for n are 1, 2, 4, 8, and 16 bytes.
#pragma pack ( show )
The above form of the pack pragma sends a warning diagnostic to stderr to record the current state of the
pack pragma stack. You can use this form while debugging.
For more about packed fields, see Section 5.17.4.
5.11.24 The RESET_MISRA Pragma
The RESET_MISRA pragma resets the specified MISRA C:2004 rules to the state they were before any
CHECK_MISRA pragmas (see Section 5.11.2) were processed. For instance, if a rule was enabled on the
command line but disabled in the source, the RESET_MISRA pragma resets it to enabled. This pragma
accepts the same format as the --check_misra option, except for the "none" keyword.
The --check_misra compiler command-line option must be used to enable MISRA C:2004 rule checking in
order for this pragma to function at the source level.
The syntax of the pragma in C is:
#pragma RESET_MISRA (" {all|required|advisory|rulespec} ")
The rulespec parameter is a comma-separated list of rule numbers. See Section 5.3 for details.
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5.11.25 The RESET_ULP Pragma
The RESET_ULP pragma resets the specified ULP Advisor rules to the state they were before any
CHECK_ULP pragmas (see Section 5.11.3) were processed. For instance, if a rule was enabled on the
command line but disabled in the source, the RESET_ULP pragma resets it to enabled. This pragma
accepts the same format as the --advice:power option, except for the "none" keyword.
The syntax of the pragma in C is:
#pragma RESET_ULP (" {all|rulespec} ")
The rulespec parameter is a comma-separated list of rule numbers. See Section 5.4 for details. See
www.ti.com/ulpadvisor for a list of rules.
5.11.26 The RETAIN Pragma
The RETAIN pragma can be applied to a code or data symbol.
It causes a .retain directive to be generated into the section that contains the definition of the symbol. The
.retain directive indicates to the linker that the section is ineligible for removal during conditional linking.
Therefore, regardless whether or not the section is referenced by another section in the application that is
being compiled and linked, it will be included in the output file result of the link.
The RETAIN pragma has the same effect as using the retain function or variable attribute. See
Section 5.17.2 and Section 5.17.3, respectively.
The syntax of the pragma in C is:
#pragma RETAIN ( symbol )
The syntax of the pragma in C++ is:
#pragma RETAIN
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5.11.27 The SET_CODE_SECTION and SET_DATA_SECTION Pragmas
These pragmas can be used to set the section for all declarations below the pragma.
The syntax of the pragmas in C/C++ is:
#pragma SET_CODE_SECTION ("section name")
#pragma SET_DATA_SECTION ("section name")
In Example 5-7 x and y are put in the section mydata. To reset the current section to the default used by
the compiler, a blank parameter should be passed to the pragma. An easy way to think of the pragma is
that it is like applying the CODE_SECTION or DATA_SECTION pragma to all symbols below it.
Example 5-7. Setting Section With SET_DATA_SECTION Pragma
#pragma SET_DATA_SECTION("mydata")
int x;
int y;
#pragma SET_DATA_SECTION()
The pragmas apply to both declarations and definitions. If applied to a declaration and not the definition,
the pragma that is active at the declaration is used to set the section for that symbol. Here is an example:
Example 5-8. Setting a Section With SET_CODE_SECTION Pragma
#pragma SET_CODE_SECTION("func1")
extern void func1();
#pragma SET_CODE_SECTION()
...
void func1() { ... }
In Example 5-8 func1 is placed in section func1. If conflicting sections are specified at the declaration and
definition, a diagnostic is issued.
The current CODE_SECTION and DATA_SECTION pragmas and GCC attributes can be used to override
the SET_CODE_SECTION and SET_DATA_SECTION pragmas. For example:
Example 5-9. Overriding SET_DATA_SECTION Setting
#pragma DATA_SECTION(x, "x_data")
#pragma SET_DATA_SECTION("mydata")
int x;
int y;
#pragma SET_DATA_SECTION()
In Example 5-9 x is placed in x_data and y is placed in mydata. No diagnostic is issued for this case.
The pragmas work for both C and C++. In C++, the pragmas are ignored for templates and for implicitly
created objects, such as implicit constructors and virtual function tables.
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5.11.28 The SWI_ALIAS Pragma
The SWI_ALIAS pragma allows you to refer to a particular software interrupt as a function name and to
invocations of the software interrupt as function calls. Since the function name is simply an alias for the
software interrupt, no function definition exists for the function name.
The syntax of the pragma in C is:
#pragma SWI_ALIAS( func , swi_number )
The syntax of the pragma in C++ is:
#pragma SWI_ALIAS( swi_number )
Calls to the applied function are compiled as software interrupts whose number is swi_number. The
swi_number variable must be an integer constant.
A function prototype must exist for the alias and it must occur after the pragma and before the alias is
used. Software interrupts whose number is not known until run time are not supported.
For information about using the GCC function attribute syntax to declare function aliases, see
Section 5.17.2.
For more information about using software interrupts, including restrictions on passing arguments and
register usage, see Section 6.7.5.
Example 5-10. Using the SWI_ALIAS Pragma C Source File
#pragma SWI_ALIAS(put, 48)
/* #pragma SWI_ALIAS(48) for C++ */
int put (char *key, int value);
void error();
main()
{
if (!put("one", 1))
error();
}
/* calling "put" invokes SWI #48 with 2 arguments */
/* and returns a result.
*/
Example 5-11. Generated Assembly File
;***************************************************************
;* FUNCTION DEF: _main
*
;***************************************************************
_main:
STMFD
SP!, {LR}
ADR
A1, SL1
MOV
A2, #1
SWI
#48
; SWI #48 is generated for the function call
CMP
A1, #0
BLEQ
_error
MOV
A1, #0
LDMFD
SP!, {PC}
SL1:
.string "one",0
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5.11.29 The TASK Pragma
The TASK pragma specifies that the function to which it is applied is a task. Tasks are functions that are
called but never return. Typically, they consist of an infinite loop that simply dispatches other activities.
Because they never return, there is no need to save (and therefore restore) registers that would otherwise
be saved and restored. This can save RAM space, as well as some code space.
The syntax of the pragma in C is:
#pragma TASK( func )
The syntax of the pragma in C++ is:
#pragma TASK
5.11.30 The UNROLL Pragma
The UNROLL pragma specifies to the compiler how many times a loop should be unrolled. The optimizer
must be invoked (use --opt_level=[1|2|3] or -O1, -O2, or -O3) in order for pragma-specified loop unrolling
to take place. The compiler has the option of ignoring this pragma.
No statements are allowed between the UNROLL pragma and the for, while, or do-while loop to which it
applies. However, other pragmas, such as MUST_ITERATE, can appear between the UNROLL pragma
and the loop.
The syntax of the pragma for C and C++ is:
#pragma UNROLL( n )
If possible, the compiler unrolls the loop so there are n copies of the original loop. The compiler only
unrolls if it can determine that unrolling by a factor of n is safe. In order to increase the chances the loop is
unrolled, the compiler needs to know certain properties:
• The loop iterates a multiple of n times. This information can be specified to the compiler via the
multiple argument in the MUST_ITERATE pragma.
• The smallest possible number of iterations of the loop
• The largest possible number of iterations of the loop
The compiler can sometimes obtain this information itself by analyzing the code. However, sometimes the
compiler can be overly conservative in its assumptions and therefore generates more code than is
necessary when unrolling. This can also lead to not unrolling at all. Furthermore, if the mechanism that
determines when the loop should exit is complex, the compiler may not be able to determine these
properties of the loop. In these cases, you must tell the compiler the properties of the loop by using the
MUST_ITERATE pragma.
Specifying #pragma UNROLL(1) asks that the loop not be unrolled. Automatic loop unrolling also is not
performed in this case.
If multiple UNROLL pragmas are specified for the same loop, it is undefined which pragma is used, if any.
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5.11.31 The WEAK Pragma
The WEAK pragma gives weak binding to a symbol.
The syntax of the pragma in C is:
#pragma WEAK ( symbol )
The syntax of the pragma in C++ is:
#pragma WEAK
The WEAK pragma makes symbol a weak reference if it is a reference, or a weak definition, if it is a
definition. The symbol can be a data or function variable. In effect, unresolved weak references do not
cause linker errors and do not have any effect at run time. The following apply for weak references:
• Libraries are not searched to resolve weak references. It is not an error for a weak reference to remain
unresolved.
• During linking, the value of an undefined weak reference is:
– Zero if the relocation type is absolute
– The address of the place if the relocation type is PC-relative
– The address of the nominal base address if the relocation type is base-relative.
A weak definition does not change the rules by which object files are selected from libraries. However, if a
link set contains both a weak definition and a non-weak definition, the non-weak definition is always used.
The WEAK pragma has the same effect as using the weak function or variable attribute. See
Section 5.17.2 and Section 5.17.3, respectively.
5.12 The _Pragma Operator
The ARM C/C++ compiler supports the C99 preprocessor _Pragma() operator. This preprocessor operator
is similar to #pragma directives. However, _Pragma can be used in preprocessing macros (#defines).
The syntax of the operator is:
_Pragma (" string_literal ");
The argument string_literal is interpreted in the same way the tokens following a #pragma directive are
processed. The string_literal must be enclosed in quotes. A quotation mark that is part of the string_literal
must be preceded by a backward slash.
You can use the _Pragma operator to express #pragma directives in macros. For example, the
DATA_SECTION syntax:
#pragma DATA_SECTION( func ," section ")
Is represented by the _Pragma() operator syntax:
_Pragma ("DATA_SECTION( func ,\" section \")")
The following code illustrates using _Pragma to specify the DATA_SECTION pragma in a macro:
...
#define EMIT_PRAGMA(x) _Pragma(#x)
#define COLLECT_DATA(var) EMIT_PRAGMA(DATA_SECTION(var,"mysection"))
COLLECT_DATA(x)
int x;
...
The EMIT_PRAGMA macro is needed to properly expand the quotes that are required to surround the
section argument to the DATA_SECTION pragma.
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5.13 Application Binary Interface
An Application Binary Interface (ABI) defines how functions that are written separately and compiled or
assembled separately can work together. This involves standardizing data type storage, register
conventions, and function structure and calling conventions. It should define linkname generation from C
symbols. It defines the object file format and the debug format. It should document how the system is
initialized. In the case of C++ it defines C++ name mangling and exception handling support.
The COFF ABI is not supported in v15.6.0.STS and later versions of the TI Code Generation Tools. If you
want to produce COFF output files, please use v5.2 of the ARM tools and see SPRU151J.
The ARM ABIv2 has become an industry standard for the ARM architecture. It has these advantages:
• It enables interlinking of objects built with different tool chains. For example, this enables a library built
with RVCT to be linked in with an application built with the ARM 4.6 toolset.
• It is well documented. The complete ARM ABI specifications are in the ARM Information Center.
• It is modern. EABI requires ELF object file format which enables supporting modern language features
like early template instantiation and export inline functions support.
ARM ABIv2 allows a vendor to define the system initialization in the bare-metal mode. TI-specific
information on EABI mode is described in Section 6.10.3. The __TI_EABI_ASSEMBLER predefined
symbol is set to 1 if compiling for EABI.
5.14 ARM Instruction Intrinsics
Assembly instructions can be generated using the intrinsics in the following tables. Table 5-3 shows which
intrinsics are available on the different ARM targets. Table 5-4 shows the calling syntax for each intrinsic,
along with the corresponding assembly instruction and a description. Additional intrinsices for getting and
setting the CPSR register and to enable/disable interrupts are provided in Section 6.8.1.
Table 5-3. ARM Intrinsic Support by Target
C/C++ Compiler
Intrinsic
ARM V5e
(ARM9E)
ARM V6
(ARM11)
_ _clz
yes
yes
ARM V6M0
(Cortex-M0)
ARM V7M3
(Cortex-M3)
ARM V7M4
(Cortex-M4)
ARM V7R
(Cortex-R4)
ARM V7A8
(Cortex-A8)
yes
yes
yes
yes
yes
_ _delay_cycles
yes
yes
yes
_ _get_MSP
yes
yes
yes
yes
_ _get_PRIMASK
yes
yes
_ _ldrex
yes
yes
yes
yes
yes
_ _ldrexb
yes
yes
yes
yes
yes
_ _ldrexd
yes
yes
yes
_ _ldrexh
yes
yes
yes
yes
yes
_ _MCR
yes
yes
yes
yes
yes
yes
_ _MRC
yes
yes
yes
yes
yes
yes
_ _ nop
yes
yes
yes
yes
yes
yes
_norm
yes
yes
yes
yes
yes
yes
yes
_ _rev
yes
yes
yes
yes
yes
_ _rev16
yes
yes
yes
yes
yes
_ _revsh
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
_ _rbit
yes
_ _ror
yes
yes
yes
yes
_pkhbt
yes
yes
yes
yes
_pkhtb
yes
yes
yes
yes
_qadd16
yes
yes
yes
yes
_qadd8
yes
yes
yes
yes
_qaddsubx
yes
yes
yes
yes
_qsub16
yes
yes
yes
yes
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Table 5-3. ARM Intrinsic Support by Target (continued)
C/C++ Compiler
Intrinsic
ARM V5e
(ARM9E)
ARM V6
(ARM11)
ARM V6M0
(Cortex-M0)
ARM V7M3
(Cortex-M3)
ARM V7M4
(Cortex-M4)
ARM V7R
(Cortex-R4)
ARM V7A8
(Cortex-A8)
_qsub8
yes
yes
yes
yes
_qsubaddx
yes
yes
yes
yes
yes
yes
yes
yes
_sadd16
yes
yes
yes
yes
_sadd8
yes
yes
yes
yes
_saddsubx
yes
yes
yes
yes
_sadd
yes
_sdadd
yes
yes
yes
yes
yes
_sdsub
yes
yes
yes
yes
yes
yes
yes
yes
yes
_sel
_ _set_MSP
_ _set_PRIMASK
yes
yes
yes
yes
yes
yes
_shadd16
yes
yes
yes
yes
_shadd8
yes
yes
yes
yes
_shsub16
yes
yes
yes
yes
_shsub8
yes
yes
yes
yes
_smac
yes
yes
yes
yes
yes
_smlabb
yes
yes
yes
yes
yes
_smlabt
yes
yes
yes
yes
yes
_smlad
yes
yes
yes
yes
_smladx
yes
yes
yes
yes
_smlalbb
yes
yes
yes
yes
yes
_smlalbt
yes
yes
yes
yes
yes
_smlald
yes
yes
yes
yes
_smlaldx
yes
yes
yes
yes
_smlaltb
yes
yes
yes
yes
yes
_smlaltt
yes
yes
yes
yes
yes
_smlatb
yes
yes
yes
yes
yes
_smlatt
yes
yes
yes
yes
yes
_smlawb
yes
yes
yes
yes
yes
_smlawt
yes
yes
yes
yes
yes
_smlsd
yes
yes
yes
yes
_smlsdx
yes
yes
yes
yes
_smlsld
yes
yes
yes
yes
_smlsldx
yes
yes
yes
yes
_smmla
yes
yes
yes
yes
_smmlar
yes
yes
yes
yes
_smmls
yes
yes
yes
yes
_smmlsr
yes
yes
yes
yes
_smmul
yes
yes
yes
yes
_smmulr
yes
yes
yes
yes
_smuad
yes
yes
yes
yes
_smuadx
yes
yes
yes
yes
_smusd
yes
yes
yes
yes
_smusdx
yes
yes
yes
yes
_smpy
yes
yes
yes
yes
yes
_smsub
yes
yes
yes
yes
yes
_smulbb
yes
yes
yes
yes
yes
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Table 5-3. ARM Intrinsic Support by Target (continued)
C/C++ Compiler
Intrinsic
ARM V5e
(ARM9E)
ARM V6
(ARM11)
_smulbt
yes
_smultb
yes
_smultt
ARM V7M4
(Cortex-M4)
ARM V7R
(Cortex-R4)
ARM V7A8
(Cortex-A8)
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
_smulwb
yes
yes
yes
yes
yes
_smulwt
yes
yes
yes
yes
yes
_ _sqrt
yes
yes
yes
yes
_ _sqrtf
yes
yes
yes
yes
yes
_ssat16
ARM V6M0
(Cortex-M0)
ARM V7M3
(Cortex-M3)
yes
yes
yes
_ssata
yes
yes
yes
yes
yes
yes
yes
_ssatl
yes
yes
yes
yes
yes
yes
_ssub
yes
yes
yes
yes
yes
_ssub16
yes
yes
yes
yes
_ssub8
yes
yes
yes
yes
_ssubaddx
yes
yes
yes
yes
_ _strex
yes
yes
yes
yes
yes
_ _strexb
yes
yes
yes
yes
yes
_ _strexd
yes
yes
yes
_ _strexh
yes
yes
yes
yes
yes
yes
yes
_sxtab
yes
yes
yes
yes
_sxtab16
yes
yes
yes
yes
_sxtah
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
_subc
yes
yes
_sxtb
yes
_sxtb16
_sxth
yes
yes
yes
yes
yes
yes
yes
_uadd16
yes
yes
yes
yes
yes
_uadd8
yes
yes
yes
yes
_uaddsubx
yes
yes
yes
yes
_uhadd16
yes
yes
yes
yes
_uhadd8
yes
yes
yes
yes
_uhsub16
yes
yes
yes
yes
_uhsub8
yes
yes
yes
yes
_umaal
yes
yes
yes
yes
_uqadd16
yes
yes
yes
yes
_uqadd8
yes
yes
yes
yes
_uqaddsubx
yes
yes
yes
yes
_uqsub16
yes
yes
yes
yes
_uqsub8
yes
yes
yes
yes
_uqsubaddx
yes
yes
yes
yes
_usad8
yes
yes
yes
yes
_usat16
yes
yes
yes
yes
yes
_usata
yes
yes
yes
yes
yes
yes
yes
_usatl
yes
yes
yes
yes
yes
yes
_usub16
yes
yes
yes
yes
_usub8
yes
yes
yes
yes
_usubaddx
yes
yes
yes
yes
_uxtab
yes
yes
yes
yes
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Table 5-3. ARM Intrinsic Support by Target (continued)
C/C++ Compiler
Intrinsic
ARM V5e
(ARM9E)
ARM V6
(ARM11)
ARM V6M0
(Cortex-M0)
ARM V7M3
(Cortex-M3)
ARM V7M4
(Cortex-M4)
ARM V7R
(Cortex-R4)
ARM V7A8
(Cortex-A8)
_uxtab16
yes
yes
yes
yes
_uxtah
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
_uxtb
yes
_uxtb16
_uxth
yes
yes
yes
yes
yes
yes
yes
_ _wfe
yes
yes
yes
yes
yes
yes
yes
_ _wfi
yes
yes
yes
yes
yes
Table 5-4 shows the calling syntax for each intrinsic, along with the corresponding assembly instruction
and a description. See Table 5-3 for a list of which intrinsics are available on the different ARM targets.
Additional intrinsices for getting and setting the CPSR register and to enable/disable interrupts are
provided in Section 6.8.1.
Table 5-4. ARM Compiler Intrinsics
C/C++ Compiler Intrinsic
Assembly
Instruction
Description
int count = _ _clz(int src );
CLZ count , src
Returns the count of leading zeros.
void _ _delay_cycles( unsigned int cycles );
varies
Delays execution for the specified number of
cycles. The number of cycles must be a
constant.
The __delay_cycles intrinsic inserts code to
consume precisely the number of specified
cycles with no side effects. The number of
cycles delayed must be a compile-time
constant.
Note: Cycle timing is based on 0 wait states.
Results vary with additional wait states. The
implementation does not account for dynamic
prediction. Lower delay cycle counts may be
less accurate given pipeline flush behaviors.
unsigned int dst = _ _get_MSP(void );
MRS dst , MSP
Returns the current value of the Main Stack
Pointer.
unsigned int dst = _ _get_PRIMASK(void );
MRS dst , PRIMASK
Returns the current value of the Priority Mask
Register. If this value is 1, activation of all
exceptions with configurable priority is
prevented.
unsigned int dest = _ _ldrex(void* src );
LDREX dst , src
Loads data from memory address containing
word (32-bit) data
unsigned int dest= _ _ldrexb(void* src );
LDREXB dst , src
Loads data from memory address containing
byte data
unsigned long long dest = _ _ldrexd(void*
src );
LDREXD dst , src
Loads data from memory address with long
long support
unsigned int dest = _ _ldrexh(void* src );
LDREXH dst , src
Loads data from memory address containing
halfword (16-bit) data
void __MCR (unsigned int coproc, unsigned int
opc1, unsigned int src, unsigned int
coproc_reg1, unsigned int coproc_reg2,
unsigned int opc2);
MCR coproc, opc1, src,
CR<coproc_reg1>, CR<coproc_reg2>,
opc2
Access the coprocessor registers
unsigned int __MRC(unsigned int coproc,
unsigned int opc1, unsigned int coproc_reg1,
unsigned int coproc_reg2, unsigned int opc2);
MRCcoproc, opc1, src,
CR<coproc_reg1>, CR<coproc_reg2>,
opc2
Access the coprocessor registers
void _ _nop( void );
NOP
Perform an instruction that does nothing.
int dst = _norm(int src );
CLZ dst , src
Count leading zero bits. This intrinsic can be
used when implementing integer normalization.
int dst = _pkhbt(int src1 , int src2 , int shift );
PKHBT dst , src1 , src2 , #shift
Combine bottom halfword of src1 with shifted
top halfword of src2
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Table 5-4. ARM Compiler Intrinsics (continued)
C/C++ Compiler Intrinsic
Assembly
Instruction
nt dst = _pkhtb(int src1 , int src2 , int shift );
PKHTB dst , src1 , src2 , #shift
Combine top halfword of src1 with shifted
bottom halfword of src2
int dst = _qadd16(int src1 , int src2 );
QADD16 dst , src1 , src2
Performs two signed halfword saturated
additions
int dst = _qadd8(int src1 , int src2 );
QADD8 dst , src1 , src2
Performs four signed saturated 8-bit additions
int dst = _qaddsubx(int src1 , int src2 );
QASX dst , src1 , src2
Exchange halfwords of src2, perform signed
saturated addition on the top halfwords and
signed saturated subtraction on the bottom
halfwords.
int dst = _qsub16(int src1 , int src2 );
QSUB16 dst , src1 , src2
Performs two signed saturated halfword
subtractions
int dst = _qsub8(int src1 , int src2 );
QSUB8 dst , src1 , src2
Performs four signed saturated 8-bit
subtractions
int dst = _qsubaddx(int src1 , int src2 );
QSAX dst , src1 , src2
Exchange halfwords of src2, perform signed
saturated subtraction on top halfwords and
signed saturated addition on bottom halfwords
int dst = _ _rbit(int src );
RBIT dst , src
Reverses the bit order in a word.
int dst = _ _rev(int src );
REV dst , src
Reverses byte order in a word. That is,
converts 32-bit data between big-endian and
little-endian or vice versa.
int dst = _ _rev16(int src );
REV16 dst , src
Reverses byte order in each byte in a word
independently. That is, converts 16-bit data
between big-endian and little-endian or vice
versa.
int dst = _ _revsh(int src );
REVSH dst , src
Reverses byte order in the lower byte of a
word, and extends the sign to 32 bits. That is,
converts 16-bit signed data to 32-bit signed
data, while also converting between big-endian
and little-endian or vice versa.
int dst = _ _ror(int src , int shift );
ROR dst , src , shift
Rotates the value to the right by the number of
bits specified. Bits rotated off the right end are
placed into empty bits on the left.
int dst =_sadd(int src1 , int src2 );
QADD dst , src1 , src2
Saturated add
int dst = _sadd16(int src1 , int src2 );
SADD16 dst , src1 , src2
Performs two signed halfword additions
int dst = _sadd8(int src1 , int src2 );
SADD8 dst , src1 , src2
Performs four signed 8-bit additions
int dst = _saddsubx(int src1 , int src2 );
SASX dst , src1 , src2
Exchange halfwords of src2, add the top
halfwords and subtract the bottom halfwords
int dst =_sdadd(int src1 , int src2 );
QDADD dst , src1 , src2
Saturated double-add
int dst =_sdsub(int src1 , int src2 );
QDSUB dst , src1 , src2
Saturated double-subtract
int dst = _sel(int src1 , int src2 );
SEL dst , src1 , src2
Selects byte n from src1 if GE bit n is set or
from src2 if GE bit n is not set, where n ranges
from 0 to 3.
void _ _set_MSP(unsigned int src);
MSR MSP, src
Sets the value of the Main Stack Pointer to src.
unsigned int dst = _ _set_PRIMASK(unsigned
int src);
MRS dst , PRIMASK (optional)
MSR PRIMASK, src
Sets the Priority Mask Register to the src value
and returns the value as it was prior to being
set as dst. Setting this register to 1 prevents
the activation of all exceptions with configurable
priority.
int dst = _shadd16(int src1 , int src2 );
SHADD16 dst , src1 , src2
Performs two signed halfword additions and
halves the results
int dst = _shadd8(int src1 , int src2 );
SHADD8 dst , src1 , src2
Performs four signed 8-bit additions and halves
the results
int dst = _shsub16(int src1 , int src2 );
SHSUB16 dst , src1 , src2
Performs two signed halfword subtractions and
halves the results
int dst = _shsub8int src1 , int src2 );
SHSUB8 dst , src1 , src2
Performs four signed 8-bit subtractions and
halves the results
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Table 5-4. ARM Compiler Intrinsics (continued)
Assembly
Instruction
C/C++ Compiler Intrinsic
Description
int dst =_smac(int dst, int src1 , int src2 );
SMULBB tmp , src1 , src2
QDADD dst , dst , tmp
Saturated multiply-accumulate
int dst =_smlabb(int dst , short src1 , short
src2 );
SMLABB dst , src1 , src2
Signed multiply-accumulate bottom halfwords
int dst =_smlabt(int dst , short src1 , int src2 );
SMLABT dst , src1 , src2
Signed multiply-accumulate bottom and top
halfwords
int dst _smlad(int src1 , int src2 , int acc );
SMLAD dst , src1 , src2 , acc
Performs two signed 16-bit multiplications on
the top and bottom halfwords of src1 and src2
and adds the results to acc.
int dst _smladx(int src1 , int src2 , int acc );
SMLADX dst , src1 , src2 , acc
Same as _smlad except the halfwords in src2
are exchange before the multiplication.
long long dst =_smlalbb(long long dst , short
src1 , short src2 );
SMLALBB dstlo , dsthi , src1 , src2
Signed multiply-long and accumulate bottom
halfwords
long long dst =_smlalbt(long long dst , short
src1 , int src2 );
SMLALBT dstlo , dsthi , src1 , src2
Signed multiply-long and accumulate bottom
and top halfwords
long long dst _smlald(long long acc , int src1 ,
int src2 );
SMLALD dst , src1 , src2
Performs two 16-bit multiplication on the top
and bottom halfwords of src1 and src2 and
adds the results to the 64-bit acc operand
long long dst _smlaldx(long long acc , int src1 , SMLALDX dst , src1 , src2
int src2 );
Same as _smlald except the halfwords in src2
are exchanged.
long long dst =_smlaltb(long long dst , int
src1 , short src2 );
Signed multiply-long and accumulate top and
bottom halfwords
SMLALTB dstlo , dsthi , src1 , src2
long long dst =_smlaltt(long long dst , int src1 , SMLALTT dstlo , dsthi , src1 , src2
int src2 );
Signed multiply-long and accumulate top
halfwords
int dst =_smlatb(int dst , int src1 , short src2 );
SMLATB dst , src1 , src2
Signed multiply-accumulate top and bottom
halfwords
int dst =_smlatt(int dst , int src1 , int src2 );
SMLATT dst , src1 , src2
Signed multiply-accumulate top halfwords
int dst _smlawb(int src1 , short src2 , int acc );
SMLAWB dst , src1 , src2
Signed multiply-accumulate word and bottom
halfword
int dst _smlawt(int src1 , short src2 , int acc );
SMLAWT dst , src1 , src2
Signed multiply-accumulate word and top
halfword
int dst _smlsd(int src1 , int src2 , int acc );
SMLSD dst , src1 , src2 , acc
Performs two signed 16-bit multiplications on
the top and bottom halfwords of src1 and src2
and adds the difference of the results to acc.
int dst _smlsdx(int src1 , int src2 , int acc );
SMLSDX dst , src1 , src2 , acc
Same as _smlsd except the halfwords in src2
are exchange before the multiplication.
long long dst _smlsld(long long acc , int src1 ,
int src2 );
SMLSLD dst , src1 , src2
Performs two 16-bit multiplication on the top
and bottom halfwords of src1 and src2 and
adds the difference of the results to the 64-bit
acc operand.
long long dst _smlsldx(long long acc , int src1 , SMLSLDX dst , src1 , src2
int src2 );
Same as _smlsld except the halfwords in src2
are exchanged.
int dst _smmla(int src1 , int src2 , int acc );
SMMLA dst , src1 , src2 , acc
Performs a signed multiplication on src1 and
src2, extracts the most significant 32 bits of the
result, and adds an accumulate value.
int dst _smmlar(int src1 , int src2 , int acc );
SMMLAR dst , src1 , src2 , acc
Same as _smmla execpt the result is rounded
instead of being truncated.
int dst _smmls(int src1 , int src2 , int acc );
SMMLS dst , src1 , src2 , acc
Performs a signed multiplication on src1 and
src2, subtracts the result from an accumulate
value that is shifted left by 32 bits, and extracts
the most significant 32 bits of the result of the
subtraction.
int dst _smmlsr(int src1 , int src2 , int acc );
SMMLSR dst , src1 , src2 , acc
Same as _smmls except the result is rounded
instead of being truncated.
int dst _smmul(int src1 , int src2 , int acc );
SMMUL dst , src1 , src2 , acc
Performs a signed 32-bit multiplication on src1
and src2 and extracts the most significant 32bits of the result.
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Table 5-4. ARM Compiler Intrinsics (continued)
C/C++ Compiler Intrinsic
Assembly
Instruction
int dst _smmulr(int src1 , int src2 , int acc );
SMMULR dst , src1 , src2 , acc
Same as _smmul except the result is rounded
instead of being truncated.
int dst =_smpy(int src1 , int src2 );
SMULBB dst , src1 , src2
QADD dst , dst , dst
Saturated multiply
int dst =_smsub(int src1 , int src2 );
SMULBB tmp , src1 , src2
QDSUB dst , dst , tmp
Saturated multiply-subtract
int dst _smuad(int src1 , int src2 );
SMUAD dst , src1 , src2
Performs two signed 16-bit multiplications on
the top and bottom halfwords and adds the
products.
int dst _smuadx(int src1 , int src2 );
SMUADX dst , src1 , src2
Same as _smuad except the halfwords in src2
are exchange before the multiplication.
int dst =_smulbb(int src1 , int src2 );
SMULBB dst , src1 , src2
Signed multiply bottom halfwords
int dst =_smulbt(int src1 , int src2 );
SMULBT dst , src1 , src2
Signed multiply bottom and top halfwords
int dst =_smultb(int src1 , int src2 );
SMULTB dst , src1 , src2
Signed multiply top and bottom halfwords
int dst =_smultt(int src1 , int src2 );
SMULTT dst , src1 , src2
Signed multiply top halfwords
int dst _smulwb(int src1 , short src2 , int acc );
SMULWB dst , src1 , src2
Signed multiply word and bottom halfword
int dst _smulwt(int src1 , short src2 , int acc );
SMULWT dst , src1 , src2
Signed multiply word and top halfword
int dst _smusd(int src1 , int src2 );
SMUSD dst , src1 , src2
Performs two signed 16-bit multiplications on
the top and bottom halfwords and subtracts the
products.
int dst _smusdx(int src1 , int src2 );
SMUSDX dst , src1 , src2
Same as _smusd except the halfwords in src2
are exchanged before the multiplication.
double __sqrt( double );
VSQRT dst , src1
Return the square root of the specified double.
This intrinsic is directly replaced with the
VSQRT instruction if --fp_mode=relaxed. If
strict floating point mode is used, the function
must also set an errno if a domain error occurs.
float __sqrtf( float );
VSQRT dst , src1
Return the square root of the specified float.
This intrinsic is directly replaced with the
VSQRT instruction if --fp_mode=relaxed. If
strict floating point mode is used, the function
must also set an errno if a domain error occurs.
int dst =_ssat16(int src , int bitpos );
SSAT16 dst , #bitpos
Performs two halfword saturations to a
selectable signed range specified by bitpos
int dst =_ssata(int src , int shift , int bitpos );
SSAT dst , #bitpos, src, ASR #shift
Right shifts src and saturates to a selectable
signed range specified by bitpos
int dst =_ssatl(int src , int shift , int bitpos );
SSAT dst , #bitpos, src, LSL #shift
Left shifts src and saturates to a selectable
signed range specified by bitpos
int dst =_ssub(int src1 , int src2 );
QSUB dst , src1 , src2
Saturated subtract
int dst = _ssub16(int src1 , int src2 );
SSUB16 dst , src1 , src2
Performs two signed halfword subtractions
int dst = _ssub8(int src1 , int src2 );
SSUB8 dst , src1 , src2
Performs four signed 8-bit subtractions
int dst = _ssubaddx(int src1 , int src2 );
SSAX dst , src1 , src2
Exchange halfwords of src2, subtract the top
halfwords and add the bottom halfwords
int status = _ _strex(unsigned int src, void*
dst );
STREX status , src , dest
Stores word (32-bit) data in memory address
int status = _ _strexb(unsigned char src, void*
dst );
STREXB status , src , dest
Stores byte data in memory address
int status = _ _strexd(unsigned long long src,
void* dst );
STREXD status , src , dest
Stores long long data in memory address
int status = _ _strexh(unsigned short src, void*
dst );
STREXH status , src , dest
Stores halfword (16-bit) data in memory
address
int dst = _subc(int src1 , int src2 );
SUBC dst , src1 , src2
Subtract with carry
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Table 5-4. ARM Compiler Intrinsics (continued)
C/C++ Compiler Intrinsic
Assembly
Instruction
int dst _sxtab(int src1 , int src2 , int rotamt );
SXTAB dst , src1 , src2 , ROR #rotamt
Extracts an optionally rotated 8-bit value from
src2 and sign extends it to 32 bits, then adds
the value to src1. The rotation amount can be
0, 8, 16, or 24.
int dst _sxtab16(int src1 , int src2 , int rotamt );
SXTAB16 dst , src1 , src2 , ROR
#rotamt
Extracts two optionally rotated 8-bit values from
src2 and sign extends them to 16 bits each,
then adds the values to the two 16-bit values in
src1. The rotation amount should be 0, 8, 16, or
24.
int dst _sxtah(int src1 , int src2 , int rotamt );
SXTAH dst , src1 , src2 , ROR #rotamt
Extracts an optionally rotated 16-bit value from
src2 and sign extends it to 32 bits, then adds
the result to src1. The rotation amount can be
0, 8, 16, or 32.
int dst _sxtb(int src1 , int rotamt );
SXTB dst , src1 , ROR #rotamt
Extracts an optionally rotated 8-bit value from
src1 and sign extends it to 32 bits. The rotation
amount can be 0, 8, 16, or 24.
int dst _sxtb16(int src1 , int rotamt );
SXTAB16 dst , src1 , ROR #rotamt
Extracts two optionally rotated 8-bit values from
src1 and sign extends them to 16-bits. The
rotation amount can be 0, 8, 16, or 24.
int dst _sxth(int src1 , int rotamt );
SXTH dst , src1 , ROR #rotamt
Extracts an optionally rotated 16-bit value from
src2 and sign extends it to 32 bits. The rotation
amount can be 0, 8, 16, or 24.
int dst = _uadd16(int src1 , int src2 );
UADD16 dst , src1 , src2
Performs two unsigned halfword additions
int dst = _uadd8(int src1 , int src2 );
UADD8 dst , src1 , src2
Performs four unsigned 8-bit additions
int dst = _uaddsubx(int src1 , int src2 );
UASX dst , src1 , src2
Exchange halfwords of src2, add the top
halfwords and subtract the bottom halfwords
int dst = _uhadd16(int src1 , int src2 );
UHADD16 dst , src1 , src2
Performs two unsigned halfword additions and
halves the results
int dst = _uhadd8(int src1 , int src2 );
UHADD8 dst , src1 , src2
Performs four unsigned 8-bit additions and
halves the results
int dst = _uhsub16(int src1 , int src2 );
UHSUB16 dst , src1 , src2
Performs two unsigned halfword subtractions
and halves the results
int dst = _uhsub8(int src1 , int src2 );
UHSUB8 dst , src1 , src2
Performs four unsigned 8-bit subtractions and
halves the results
int dst = _umaal(long long acc , int src1 , int
src2 );
UMAAL dst1 , dst2 , src1 , src2
Performs an unsigned 32-bit multiplication on
src1 and src2, then adds two unsigned 32-bit
values in acc.
int dst = _uqadd16(int src1 , int src2 );
UQADD16 dst , src1 , src2
Performs two unsigned halfword saturated
additions
int dst = _uqadd8(int src1 , int src2 );
UQADD8 dst , src1 , src2
Performs four unsigned saturated 8-bit
additions
int dst = _uqaddsubx(int src1 , int src2 );
UQASX dst , src1 , src2
Exchange halfwords of src2, perform unsigned
saturated addition on the top halfwords and
unsigned saturated subtraction on the bottom
halfwords.
int dst = _uqsub16(int src1 , int src2 );
UQSUB16 dst , src1 , src2
Performs two unsigned saturated halfword
subtractions
int dst = _uqsub8(int src1 , int src2 );
UQSUB8 dst , src1 , src2
Performs four unsigned saturated 8-bit
subtractions
int dst = _uqsubaddx(int src1 , int src2 );
UQSAX dst , src1 , src2
Exchange halfwords of src2, perform unsigned
saturated subtraction on top halfwords and
unsigned saturated addition on bottom
halfwords
int dst = _usad8(int src1 , int src2 );
USAD8 dst , src1 , src2
Performs four unsigned 8-bit subtractions, and
adds the absolute value of the differences
together.
int dst =_usat16(int src , int bitpos );
USAT16 dst , #bitpos
Performs two halfword saturations to a
selectable unsigned range specified by bitpos
Description
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Table 5-4. ARM Compiler Intrinsics (continued)
C/C++ Compiler Intrinsic
Assembly
Instruction
int dst =_usata(int src , int shift , int bitpos );
USAT dst , #bitpos, src, ASR #shift
Right shifts src and saturates to a selectable
unsigned range specified by bitpos
int dst =_usatl(int src , int shift , int bitpos );
USAT dst , #bitpos, src, LSL #shift
Left shifts src and saturates to a selectable
unsigned range specified by bitpos
int dst = _usub16(int src1 , int src2 );
USUB16 dst , src1 , src2
Performs two unsigned halfword subtractions
int dst = _usub8(int src1 , int src2 );
USUB8 dst , src1 , src2
Performs four unsigned 8-bit subtractions
int dst = _usubaddx(int src1 , int src2 );
USAX dst , src1 , src2
Exchange halfwords of src2, subtract the top
halfwords and add the bottom halfwords
int dst _uxtab(int src1 , int src2 , int rotamt );
UXTAB dst , src1 , src2 , ROR #rotamt
Extracts an optionally rotated 8-bit value from
src2 and zero extends it to 32 bits, then adds
the value to src1. The rotation amount can be
0, 8, 16, or 24.
int dst _uxtab16(int src1 , int src2 , int rotamt );
UXTAB16 dst , src1 , src2 , ROR
#rotamt
Extracts two optionally rotated 8-bit values from
src2 and zero extends them to 16 bits each,
then adds the values to the two 16-bit values in
src1. The rotation amount should be 0, 8, 16, or
24.
int dst _uxtah(int src1 , int src2 , int rotamt );
UXTAH dst , src1 , src2 , ROR #rotamt
Extracts an optionally rotated 16-bit value from
src2 and zero extends it to 32 bits, then adds
the result to src1. The rotation amount can be
0, 8, 16, or 32.
int dst _uxtb(int src1 , int rotamt );
UXTB dst , src1 , ROR #rotamt
Extracts an optionally rotated 8-bit value from
src2 and zero extends it to 32 bits. The rotation
amount can be 0, 8, 16, or 24.
int dst _uxtb16(int src1 , int rotamt );
UXTB16 dst , src1 , ROR #rotamt
Extracts two optionally rotated 8-bit values from
src1 and zero extends them to 16-bits. The
rotation amount can be 0, 8, 16, or 24.
int dst _uxth(int src1 , int rotamt );
UXTH dst , src1 , ROR #rotamt
Extracts an optionally rotated 16-bit value from
src2 and zero extends it to 32 bits. The rotation
amount can be 0, 8, 16, or 24.
void _ _wfe( void );
WFE
Wait for event. Save power by waiting for an
exception or event..
void _ _wfi( void );
WFI
Wait for interrupt. Enter standby, dormant or
shutdown mode, where an interrupt is required
to wake-up the processor.
Description
In addition, the compiler supports many of the intrinsics described in the ARM C Language Extensions
(ACLE) specification. These intrinsics are applicable for the Cortex-M and Cortex-R processor variants.
The ACLE intrinsics are implemented in order to support the development of source code that can be
compiled using ACLE-compliant compilers from multiple vendors for a variety of ARM processors. A
number of the intrinsics are duplicates of intrinsics listed in the previous table but with slightly different
names (such as one vs. two leading underscores).
The compiler does not support all of the ACLE intrinsics listed in the ACLE specification. For example, the
__cls, __clsl, and __clsll ACLE intrinsics are not supported, because the CLS instruction is not available
on the Cortex-M or Cortex-R architectures.
In order to use the ACLE intrinsics, your code must include the provided arm_acle.h header file. For
details about the ACLE intrinsics, see the ACLE specification. For information about which ACLE intrinsics
are supported, see the arm_acle.h file. Where applicable, the declarations of ACLE intrinsics that are not
supported are enclosed in comments in that header file along with a brief explanation of why the intrinsic
is not supported and a reference to the appropriate section in the ACLE specification where the intrinsic is
described.
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5.15 Object File Symbol Naming Conventions (Linknames)
Each externally visible identifier is assigned a unique symbol name to be used in the object file, a socalled linkname. This name is assigned by the compiler according to an algorithm which depends on the
name, type, and source language of the symbol. This algorithm may add a prefix to the identifier (typically
an underscore), and it may mangle the name.
User-defined symbols in C code and in assembly code are stored in the same namespace, which means
you are responsible for making sure that your C identifiers do not collide with your assembly code
identifiers. You may have identifiers that collide with assembly keywords (for instance, register names); in
this case, the compiler automatically uses an escape sequence to prevent the collision. The compiler
escapes the identifier with double parallel bars, which instructs the assembler not to treat the identifier as
a keyword. You are responsible for making sure that C identifiers do not collide with user-defined
assembly code identifiers.
Name mangling encodes the types of the parameters of a function in the linkname for a function. Name
mangling only occurs for C++ functions which are not declared 'extern "C"'. Mangling allows function
overloading, operator overloading, and type-safe linking. Be aware that the return value of the function is
not encoded in the mangled name, as C++ functions cannot be overloaded based on the return value.
For example, the general form of a C++ linkname for a 32-bit function named func is:
__func__F parmcodes
Where parmcodes is a sequence of letters that encodes the parameter types of func.
For this simple C++ source file:
int foo(int I){ }
//global C++ function compiled in 16-bit mode
This is the resulting assembly code:
$__foo__Fi
The linkname of foo is $__foo__Fi, indicating that foo is a 16-bit function that takes a single argument of
type int. To aid inspection and debugging, a name demangling utility is provided that demangles names
into those found in the original C++ source. See Chapter 8 for more information.
The mangling algorithm follows that described in the Itanium C++ ABI (http://www.codesourcery.com/cxxabi/abi.html).
int foo(int i) { } would be mangled "_Z3fooi"
EABI Mode C++ Demangling
NOTE: The EABI mode has a different C++ demangling scheme. For instance, there is no prefix
(either _ or $). Please refer to the ARM Information Center for details.
5.16 Changing the ANSI/ISO C/C++ Language Mode
The language mode command-line options determine how the compiler interprets your source code. You
specify one option to identify which language standard your code follows. You can also specify a separate
option to specify how strictly the compiler should expect your code to conform to the standard.
Specify one of the following language options to control the language standard that the compiler expects
the source to follow. The options are:
• ANSI/ISO C89 (--c89, default for C files)
• ANSI/ISO C99 (--c99, see Section 5.16.1.)
• ANSI/ISO C11 (--c11, see Section 5.16.2)
• ISO C++14 (--c++14, used for all C++ files, see Section 5.2.)
Use one of the following options to specify how strictly the code conforms to the standard:
• Relaxed ANSI/ISO (--relaxed_ansi or -pr) This is the default.
• Strict ANSI/ISO (--strict_ansi or -ps)
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The default is relaxed ANSI/ISO mode. Under relaxed ANSI/ISO mode, the compiler accepts language
extensions that could potentially conflict with ANSI/ISO C/C++. Under strict ANSI mode, these language
extensions are suppressed so that the compiler will accept all strictly conforming programs. (See
Section 5.16.3.)
If you want to link object files created with the TI CodeGen tools with object files generated by other
compiler tool chains, the ARM standard specifies that you should define the
_AEABI_PORTABILITY_LEVEL preprocessor symbol as follows before #including any standard header
files, such as <stdlib.h>.
#define _AEABI_PORTABILITY_LEVEL 1
This definition enables full portability. Defining the symbol to 0 specifies that the "C standard" portability
level will be used.
5.16.1 C99 Support (--c99)
The compiler supports the 1999 standard of C as standardized by the ISO. However, the following list of
run-time functions and features are not implemented or fully supported:
• inttypes.h
– wcstoimax() / wcstoumax()
• stdio.h
– The %e specifier may produce "-0" when "0" is expected by the standard
– snprintf() does not properly pad with spaces when writing to a wide character array
• stdlib.h
– vfscanf() / vscanf() / vsscanf() return value on floating point matching failure is incorrect
• wchar.h
– getws() / fputws()
– mbrlen()
– mbsrtowcs()
– wcscat()
– wcschr()
– wcscmp() / wcsncmp()
– wcscpy() / wcsncpy()
– wcsftime()
– wcsrtombs()
– wcsstr()
– wcstok()
– wcsxfrm()
– Wide character print / scan functions
– Wide character conversion functions
5.16.2 C11 Support (--c11)
The compiler supports the 2011 standard of C as standardized by the ISO. However, in addition to the list
in Section 5.16.1, the following run-time functions and features are not implemented or fully supported in
C11 mode:
• threads.h
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5.16.3 Strict ANSI Mode and Relaxed ANSI Mode (--strict_ansi and --relaxed_ansi)
Under relaxed ANSI/ISO mode (the default), the compiler accepts language extensions that could
potentially conflict with a strictly conforming ANSI/ISO C/C++ program. Under strict ANSI mode, these
language extensions are suppressed so that the compiler will accept all strictly conforming programs.
Use the --strict_ansi option when you know your program is a conforming program and it will not compile
in relaxed mode. In this mode, language extensions that conflict with ANSI/ISO C/C++ are disabled and
the compiler will emit error messages where the standard requires it to do so. Violations that are
considered discretionary by the standard may be emitted as warnings instead.
Examples:
The following is strictly conforming C code, but will not be accepted by the compiler in the default relaxed
mode. To get the compiler to accept this code, use strict ANSI mode. The compiler will suppress the
interrupt keyword language exception, and interrupt may then be used as an identifier in the code.
int main()
{
int interrupt = 0;
return 0;
}
The following is not strictly conforming code. The compiler will not accept this code in strict ANSI mode.
To get the compiler to accept it, use relaxed ANSI mode. The compiler will provide the interrupt keyword
extension and will accept the code.
interrupt void isr(void);
int main()
{
return 0;
}
The following code is accepted in all modes. The __interrupt keyword does not conflict with the ANSI/ISO
C standard, so it is always available as a language extension.
__interrupt void isr(void);
int main()
{
return 0;
}
The default mode is relaxed ANSI. This mode can be selected with the --relaxed_ansi (or -pr) option.
Relaxed ANSI mode accepts the broadest range of programs. It accepts all TI language extensions, even
those which conflict with ANSI/ISO, and ignores some ANSI/ISO violations for which the compiler can do
something reasonable. Some GCC language extensions described in Section 5.17 may conflict with strict
ANSI/ISO standards, but many do not conflict with the standards.
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5.17 GNU, Clang, and ACLE Language Extensions
The GNU compiler collection (GCC) defines a number of language features not found in the ANSI/ISO C
and C++ standards. The definition and examples of these extensions (for GCC version 4.7) can be found
at the GNU web site, http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/C-Extensions.html#C-Extensions. Most of
these extensions are also available for C++ source code.
The compiler also supports the following Clang macro extensions, which are described in the Clang 6
Documentation:
• __has_feature (up to tests described for Clang 3.5)
• __has_extension (up to tests described for Clang 3.5)
• __has_include
• __has_include_next
• __has_builtin (see Section 5.17.5)
• __has_attribute
In addition, the compiler supports many of the features described in the ARM C Language Extensions
(ACLE) specification. These features are applicable for the Cortex-M and Cortex-R processor variants.
ACLE support affects the pre-defined macros (Table 2-31), function attributes (Section 5.17.2), and
intrinsics (Section 5.14) you may use in C/C++ code. These features are implemented in order to support
the development of source code that can be compiled using ACLE-compliant compilers from multiple
vendors for a variety of ARM processors.
5.17.1 Extensions
Most of the GCC language extensions are available in the TI compiler when compiling in relaxed ANSI
mode (--relaxed_ansi).
The extensions that the TI compiler supports are listed in Table 5-5, which is based on the list of
extensions found at the GNU web site. The shaded rows describe extensions that are not supported.
Table 5-5. GCC Language Extensions
Extensions
Descriptions
Statement expressions
Putting statements and declarations inside expressions (useful for creating smart 'safe' macros)
Local labels
Labels local to a statement expression
Labels as values
Pointers to labels and computed gotos
Nested functions
As in Algol and Pascal, lexical scoping of functions
Constructing calls
Dispatching a call to another function
Naming types (1)
Giving a name to the type of an expression
typeof operator
typeof referring to the type of an expression
Generalized lvalues
Using question mark (?) and comma (,) and casts in lvalues
Conditionals
Omitting the middle operand of a ?: expression
long long
Double long word integers and long long int type
Hex floats
Hexadecimal floating-point constants
Complex
Data types for complex numbers
Zero length
Zero-length arrays
Variadic macros
Macros with a variable number of arguments
Variable length
Arrays whose length is computed at run time
Empty structures
Structures with no members
Subscripting
Any array can be subscripted, even if it is not an lvalue.
Escaped newlines
Slightly looser rules for escaped newlines
Multi-line strings (1)
String literals with embedded newlines
Pointer arithmetic
Arithmetic on void pointers and function pointers
(1)
Feature defined for GCC 3.0; definition and examples at http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/C-Extensions.html#CExtensions
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Table 5-5. GCC Language Extensions (continued)
Extensions
Descriptions
Initializers
Non-constant initializers
Compound literals
Compound literals give structures, unions, or arrays as values
Designated initializers
Labeling elements of initializers
Cast to union
Casting to union type from any member of the union
Case ranges
'Case 1 ... 9' and such
Mixed declarations
Mixing declarations and code
Function attributes
Declaring that functions have no side effects, or that they can never return
Attribute syntax
Formal syntax for attributes
Function prototypes
Prototype declarations and old-style definitions
C++ comments
C++ comments are recognized.
Dollar signs
A dollar sign is allowed in identifiers.
Character escapes
The character ESC is represented as \e
Variable attributes
Specifying the attributes of variables
Type attributes
Specifying the attributes of types
Alignment
Inquiring about the alignment of a type or variable
Inline
Defining inline functions (as fast as macros)
Assembly labels
Specifying the assembler name to use for a C symbol
Extended asm
Assembler instructions with C operands
Constraints
Constraints for asm operands
Wrapper headers
Wrapper header files can include another version of the header file using #include_next
Alternate keywords
Header files can use __const__, __asm__, etc
Explicit reg vars
Defining variables residing in specified registers
Incomplete enum types
Define an enum tag without specifying its possible values
Function names
Printable strings which are the name of the current function
Return address
Getting the return or frame address of a function (limited support)
Other built-ins
Other built-in functions (see Section 5.17.5)
Vector extensions
Using vector instructions through built-in functions
Target built-ins
Built-in functions specific to particular targets
Pragmas
Pragmas accepted by GCC
Unnamed fields
Unnamed struct/union fields within structs/unions
Thread-local
Per-thread variables
Binary constants
Binary constants using the '0b' prefix.
5.17.2 Function Attributes
The following GCC function attributes are supported:
• alias
• aligned
• always_inline
• calls
• const
• constructor
• deprecated
• format
• format_arg
• interrupt
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•
•
•
•
•
•
•
•
•
•
•
•
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malloc
naked
noinline
noreturn
pure
ramfunc
section
target
unused
used
warn_unused_result
weak
The following additional TI-specific function attribute is supported:
• retain
For example, this function declaration uses the alias attribute to make "my_alias" a function alias for the
"myFunc" function:
void my_alias() __attribute__((alias("myFunc")));
The aligned function attribute has the same effect as the CODE_ALIGN pragma. See Section 5.11.4
The always_inline function attribute has the same effect as the FUNC_ALWAYS_INLINE pragma. See
Section 5.11.13
The calls attribute has the same effect as the CALLS pragma, which is described in Section 5.11.1.
The format attribute is applied to the declarations of printf, fprintf, sprintf, snprintf, vprintf, vfprintf, vsprintf,
vsnprintf, scanf, fscanf, vfscanf, vscanf, vsscanf, and sscanf in stdio.h. Thus when GCC extensions are
enabled, the data arguments of these functions are type checked against the format specifiers in the
format string argument and warnings are issued when there is a mismatch. These warnings can be
suppressed in the usual ways if they are not desired.
See Section 5.11.17 for more about using the interrupt function attribute.
The malloc attribute is applied to the declarations of malloc, calloc, realloc and memalign in stdlib.h.
The naked attribute identifies functions that are written as embedded assembly functions using __asm
statements. The compiler does not generate prologue and epilog sequences for such functions. See
Section 5.10.
The noinline function attribute has the same effect as the FUNC_CANNOT_INLINE pragma. See
Section 5.11.14
The ramfunc attribute specifies that a function will be placed in and executed from RAM. The ramfunc
attribute allows the compiler to optimize functions for RAM execution, as well as to automatically copy
functions to RAM on flash-based devices. For example:
__attribute__((ramfunc))
void f(void) {
...
}
The --ramfunc=on option specifies that all functions compiled with this option are placed in and executed
from RAM, even if this function attribute is not used.
Newer TI linker command files support the ramfunc attribute automatically by placing functions with this
attribute in the .TI.ramfunc section. If you have a linker command file that does not include a section
specification for the .TI.ramfunc section, you can modify the linker command file to place this section in
RAM. See the Placing functions in RAM wiki page for more about the ramfunc attribute and option. See
the ARM Assembly Language Tools User's Guide for details on section placement.
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The target attribute causes the function to be compiled in either ARM (32-bit) or Thumb (16-bit) mode.
The target attribute has the same effect as using the CODE_STATE pragma. The following examples use
the target attribute.
__attribute__((target("arm"))) void foo(int arg1, int arg2)
__attribute__((target("thumb"))) void foo(int arg1, int arg2)
Note that the "pcs" attribute described in the ACLE specification is not supported.
The retain attribute has the same effect as the RETAIN pragma (Section 5.11.26). That is, the section that
contains the function will not be omitted from conditionally linked output even if it is not referenced
elsewhere in the application.
The section attribute when used on a function has the same effect as the CODE_SECTION pragma. See
Section 5.11.5
The weak attribute has the same effect as the WEAK pragma (Section 5.11.31).
5.17.3 Variable Attributes
The following variable attributes are supported:
• aligned
• deprecated
• location
• mode
• noinit
• packed
• persistent
• retain
• section
• transparent_union
• unused
• used
• weak
The aligned attribute when used on a variable has the same effect as the DATA_ALIGN pragma. See
Section 5.11.7
The location attribute has the same effect as the LOCATION pragma. See Section 5.11.18.
The noinit and persistent attributes apply to the ROM initialization model and allow an application to
avoid initializing certain global variables during a reset. The alternative RAM initialization model initializes
variables only when the image is loaded; no variables are initialized during a reset. See the "RAM Model
vs. ROM Model" section and its subsections in the ARM Assembly Language Tools User's Guide.
The noinit attribute can be used on uninitialized variables; it prevents those variables from being set to 0
during a reset. The persistent attribute can be used on initialized variables; it prevents those variables
from being initialized during a reset. By default, variables marked noinit or persistent will be placed in
sections named .TI.noinit and .TI.persistent, respectively. The location of these sections is
controlled by the linker command file. Typically .TI.persistent sections are placed in FRAM for devices that
support FRAM and .TI.noinit sections are placed in RAM. Also see Section 5.11.20.
The packed attribute may be applied to individual fields within a struct or union. The packed attribute is
supported on all ARM targets. See the description of the --unaligned_access option for more information
on how the compiler accesses unaligned data.
The retain attribute has the same effect as the RETAIN pragma (Section 5.11.26). That is, the section that
contains the variable will not be omitted from conditionally linked output even if it is not referenced
elsewhere in the application.
The section attribute when used on a variable has the same effect as the DATA_SECTION pragma. See
Section 5.11.8
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The used attribute is defined in GCC 4.2 (see http://gcc.gnu.org/onlinedocs/gcc-4.2.4/gcc/VariableAttributes.html#Variable-Attributes).
The weak attribute has the same effect as the WEAK pragma (Section 5.11.31).
5.17.4 Type Attributes
The following type attributes are supported:
• aligned
• deprecated
• packed
• transparent_union
• unused
The packed attribute is supported for struct and union types. It is supported on all ARM targets if the -relaxed_ansi option is used. See the description of the --unaligned_access option for more information on
how the compiler accesses unaligned data.
Members of a packed structure are stored as closely to each other as possible, omitting additional bytes of
padding usually added to preserve word-alignment. For example, assuming a word-size of 4 bytes
ordinarily has 3 bytes of padding between members c1 and i, and another 3 bytes of trailing padding after
member c2, leading to a total size of 12 bytes:
struct unpacked_struct { char c1; int i; char c2;};
However, the members of a packed struct are byte-aligned. Thus the following does not have any bytes of
padding between or after members and totals 6 bytes:
struct __attribute__((__packed__)) packed_struct { char c1; int i; char c2; };
Subsequently, packed structures in an array are packed together without trailing padding between array
elements.
Bit fields of a packed structure are bit-aligned. The byte alignment of adjacent struct members that are not
bit fields does not change. However, there are no bits of padding between adjacent bit fields.
The packed attribute can only be applied to the original definition of a structure or union type. It cannot be
applied with a typedef to a non-packed structure that has already been defined, nor can it be applied to
the declaration of a struct or union object. Therefore, any given structure or union type can only be packed
or non-packed, and all objects of that type will inherit its packed or non-packed attribute.
The packed attribute is not applied recursively to structure types that are contained within a packed
structure. Thus, in the following example the member s retains the same internal layout as in the first
example above. There is no padding between c and s, so s falls on an unaligned boundary:
struct __attribute__((__packed__)) outer_packed_struct { char c; struct unpacked_struct s; };
It is illegal to implicitly or explicitly cast the address of a packed struct member as a pointer to any nonpacked type except an unsigned char. In the following example, p1, p2, and the call to foo are all illegal.
void foo(int *param);
struct packed_struct ps;
int *p1 = &ps.i;
int *p2 = (int *)&ps.i;
foo(&ps.i);
However, it is legal to explicitly cast the address of a packed struct member as a pointer to an unsigned
char:
unsigned char *pc = (unsigned char *)&ps.i;
The TI compiler also supports an unpacked attribute for an enumeration type to allow you to indicate that
the representation is to be an integer type that is no smaller than int; in other words, it is not packed.
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5.17.5 Built-In Functions
The following built-in functions are supported:
• __builtin_abs()
• __builtin_constant_p()
• __builtin_expect()
• __builtin_fabs()
• __builtin_fabsf()
• __builtin_frame_address()
• __builtin_labs()
• __builtin_llabs()
• __builtin_sqrt()
• __builtin_sqrtf()
• __builtin_memcpy()
• __builtin_return_address()
The __builtin_frame_address() function always returns zero unless the argument is a constant zero.
The __builtin_sqrt() and __builtin_sqrtf() functions are supported only when hardware floating point
support is enabled. In addition, the __builtin_sqrt() function is not supported if --float_support is set to
fpv4spd16.
When calling built-in functions that may be unavailable at run-time, use the Clang __has_builtin macro as
shown in the following example to make sure the function is supported:
#if __has_builtin(__builtin_sqrt)
double estimate = __builtin_sqrt(x);
#else
double estimate = fast_approximate_sqrt(x);
#endif
If the built-in function is supported and the device has the appropriate hardware support, the built-in
function will invoke the hardware support.
If the built-in function is supported but the device does not have the appropriate hardware enabled, the
built-in function will usually become a call to an RTS library function. For example, __builtin_sqrt() will
become a call to the library function sqrt().
The __builtin_return_address() function always returns zero.
5.18 AUTOSAR
The ARM compiler supports the AUTOSAR 3.1 standard by providing the following header files:
• Compiler.h
• Platform_Types.h
• Std_Types.h
• Compiler_Cfg.h
Compiler_Cfg.h is an empty file, the contents of which should be provided by the end user. The provided
file contains information on what the contents of the file should look like. It is included by Compiler.h. If a
new Compiler_Cfg.h file is provided by the user, its include path must come before the path to the runtime-support header files.
More information on AUTOSAR can be found at http://www.autosar.org.
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5.19 Compiler Limits
Due to the variety of host systems supported by the C/C++ compiler and the limitations of some of these
systems, the compiler may not be able to successfully compile source files that are excessively large or
complex. In general, exceeding such a system limit prevents continued compilation, so the compiler aborts
immediately after printing the error message. Simplify the program to avoid exceeding a system limit.
Some systems do not allow filenames longer than 500 characters. Make sure your filenames are shorter
than 500.
The compiler has no arbitrary limits but is limited by the amount of memory available on the host system.
On smaller host systems such as PCs, the optimizer may run out of memory. If this occurs, the optimizer
terminates and the shell continues compiling the file with the code generator. This results in a file compiled
with no optimization. The optimizer compiles one function at a time, so the most likely cause of this is a
large or extremely complex function in your source module. To correct the problem, your options are:
• Don't optimize the module in question.
• Identify the function that caused the problem and break it down into smaller functions.
• Extract the function from the module and place it in a separate module that can be compiled without
optimization so that the remaining functions can be optimized.
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Chapter 6
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Run-Time Environment
This chapter describes the ARM C/C++ run-time environment. To ensure successful execution of C/C++
programs, it is critical that all run-time code maintain this environment. It is also important to follow the
guidelines in this chapter if you write assembly language functions that interface with C/C++ code.
Topic
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
...........................................................................................................................
Memory Model..................................................................................................
Object Representation.......................................................................................
Register Conventions........................................................................................
Function Structure and Calling Conventions........................................................
Accessing Linker Symbols in C and C++ .............................................................
Interfacing C and C++ With Assembly Language ..................................................
Interrupt Handling.............................................................................................
Intrinsic Run-Time-Support Arithmetic and Conversion Routines ...........................
Built-In Functions .............................................................................................
System Initialization ..........................................................................................
Dual-State Interworking Under TIABI (Deprecated) ...............................................
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6.1
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Memory Model
The ARM compiler treats memory as a single linear block that is partitioned into subblocks of code and
data. Each subblock of code or data generated by a C program is placed in its own continuous memory
space. The compiler assumes that a full 32-bit address space is available in target memory.
The Linker Defines the Memory Map
NOTE: The linker, not the compiler, defines the memory map and allocates code and data into
target memory. The compiler assumes nothing about the types of memory available, about
any locations not available for code or data (holes), or about any locations reserved for I/O or
control purposes. The compiler produces relocatable code that allows the linker to allocate
code and data into the appropriate memory spaces. For example, you can use the linker to
allocate global variables into on-chip RAM or to allocate executable code into external ROM.
You can allocate each block of code or data individually into memory, but this is not a
general practice (an exception to this is memory-mapped I/O, although you can access
physical memory locations with C/C++ pointer types).
6.1.1 Sections
The compiler produces relocatable blocks of code and data called sections. The sections are allocated
into memory in a variety of ways to conform to a variety of system configurations. For more information
about sections and allocating them, see the introductory object file information in the ARM Assembly
Language Tools User's Guide.
There are two basic types of sections:
• Initialized sections contain data or executable code. Initialized sections are usually, but not always,
read-only. The C/C++ compiler creates the following initialized sections:
– The .binit section contains boot time copy tables. This is a read-only section. For details on BINIT,
see the ARM Assembly Language Tools User's Guide.
– The .init_array section contains global constructor tables.
– The .ovly section contains copy tables for unions in which different sections have the same run
address. This is a read-only section.
– The .data section contains initialized global and static variables.
– The .const section contains read-only data, typically string constants and static-scoped objects
defined with the C/C++ qualifier const. Note that not all static-scoped objects marked "const" are
placed in the .const section (see Section 5.7.1). This is a read-only section.
– contains string constants and data defined with the C/C++ qualifier const (provided the constant is
not also defined as volatile).
– The .text section contains all the executable code. It also contains string literals, switch tables, and
compiler-generated constants. This section is usually read-only. Note that some string literals may
instead be placed in .const:.string. The placement of string literals depends on the size of the string
and the use of the --embedded_constants option.
– The .TI.crctab section contains CRC checking tables. This is a read-only section.
• Uninitialized sections reserve space in memory (usually RAM). A program can use this space at run
time to create and store variables. The compiler creates the following uninitialized sections:
– For EABI only, the .bss section reserves space for uninitialized global and static variables.
Uninitialized variables that are also unused are usually created as common symbols (unless you
specify --common=off) instead of being placed in .bss so that they can be excluded from the
resulting application.
– The .stack section reserves memory for the C/C++ software stack.
– The .sysmem section reserves space for dynamic memory allocation. This space is used by
dynamic memory allocation routines, such as malloc(), calloc(), realloc(), or new(). If a C/C++
program does not use these functions, the compiler does not create the .sysmem section.
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The assembler creates the default sections .text, .bss, and .data. You can instruct the compiler to create
additional sections by using the CODE_SECTION and DATA_SECTION pragmas (see Section 5.11.5 and
Section 5.11.8).
The linker takes the individual sections from different object files and combines sections that have the
same name. The resulting output sections and the appropriate placement in memory for each section are
listed in Table 6-1. You can place these output sections anywhere in the address space as needed to
meet system requirements.
Table 6-1. Summary of Sections and Memory Placement
Section
Type of Memory
Section
Type of Memory
.bss
RAM
.pinit
ROM or RAM
.cinit
ROM or RAM
.stack
RAM
.const
ROM or RAM
.sysmem
RAM
.data
RAM
.text
ROM or RAM
.init_array
ROM or RAM
You can use the SECTIONS directive in the linker command file to customize the section-allocation
process. For more information about allocating sections into memory, see the linker description chapter in
the ARM Assembly Language Tools User's Guide.
6.1.2 C/C++ System Stack
The C/C++ compiler uses a stack to:
• Allocate local variables
• Pass arguments to functions
• Save register contents
The run-time stack grows from the high addresses to the low addresses. The compiler uses the R13
register to manage this stack. R13 is the stack pointer (SP), which points to the next unused location on
the stack.
The linker sets the stack size, creates a global symbol, __TI_STACK_SIZE, and assigns it a value equal
to the stack size in bytes. The default stack size is 2048 bytes. You can change the stack size at link time
by using the --stack_size option with the linker command. For more information on the --stack_size option,
see the linker description chapter in the ARM Assembly Language Tools User's Guide.
At system initialization, SP is set to a designated address for the top of the stack. This address is the first
location past the end of the .stack section. Since the position of the stack depends on where the .stack
section is allocated, the actual address of the stack is determined at link time.
The C/C++ environment automatically decrements SP at the entry to a function to reserve all the space
necessary for the execution of that function. The stack pointer is incremented at the exit of the function to
restore the stack to the state before the function was entered. If you interface assembly language routines
to C/C++ programs, be sure to restore the stack pointer to the same state it was in before the function
was entered.
For more information about using the stack pointer, see Section 6.3; for more information about the stack,
see Section 6.4.
Stack Overflow
NOTE: The compiler provides no means to check for stack overflow during compilation or at run
time. A stack overflow disrupts the run-time environment, causing your program to fail. Be
sure to allow enough space for the stack to grow. You can use the --entry_hook option to
add code to the beginning of each function to check for stack overflow; see Section 2.15.
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6.1.3 Dynamic Memory Allocation
The run-time-support library supplied with the ARM compiler contains several functions (such as malloc,
calloc, and realloc) that allow you to allocate memory dynamically for variables at run time.
Memory is allocated from a global pool, or heap, that is defined in the .sysmem section. You can set the
size of the .sysmem section by using the --heap_size=size option with the linker command. The linker also
creates a global symbol, __TI_SYSMEM_SIZE, and assigns it a value equal to the size of the heap in
bytes. The default size is 2048 bytes. For more information on the --heap_size option, see the linker
description chapter in the ARM Assembly Language Tools User's Guide.
If you use any C I/O function, the RTS library allocates an I/O buffer for each file you access. This buffer
will be a bit larger than BUFSIZ, which is defined in stdio.h and defaults to 256. Make sure you allocate a
heap large enough for these buffers or use setvbuf to change the buffer to a statically-allocated buffer.
Dynamically allocated objects are not addressed directly (they are always accessed with pointers) and the
memory pool is in a separate section (.sysmem); therefore, the dynamic memory pool can have a size
limited only by the amount of available memory in your system. To conserve space in the .bss section,
you can allocate large arrays from the heap instead of defining them as global or static. For example,
instead of a definition such as:
struct big table[100];
Use a pointer and call the malloc function:
struct big *table
table = (struct big *)malloc(100*sizeof(struct big));
When allocating from a heap, make sure the size of the heap is large enough for the allocation. This is
particularly important when allocating variable-length arrays.
6.2
Object Representation
For general information about data types, see Section 5.5. This section explains how various data objects
are sized, aligned, and accessed.
6.2.1 Data Type Storage
Table 6-2 lists register and memory storage for various data types:
Table 6-2. Data Representation in Registers and Memory
Data Type
Register Storage
Memory Storage
char, signed char
Bits 0-7 of register (1)
8 bits aligned to 8-bit boundary
unsigned char, bool
Bits 0-7 of register
8 bits aligned to 8-bit boundary
(1)
short, signed short
Bits 0-15 of register
unsigned short, wchar_t
Bits 0-15 of register
16 bits aligned to 16-bit (halfword) boundary
int, signed int
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
unsigned int
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
long, signed long
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
unsigned long
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
long long
Even/odd register pair
64 bits aligned to 32-bit (word) boundary (2)
unsigned long long
Even/odd register pair
64 bits aligned to 32-bit (word) boundary (2)
float
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
double
Register pair
64 bits aligned to 32-bit (word) boundary (2)
long double
Register pair
64 bits aligned to 32-bit (word) boundary (2)
struct
Members are stored as their individual types
require.
Members are stored as their individual types
require; aligned according to the member with the
most restrictive alignment requirement.
(1)
(2)
144
16 bits aligned to 16-bit (halfword) boundary
Negative values are sign-extended to bit 31.
64-bit data is aligned on a 64-bit boundary.
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Table 6-2. Data Representation in Registers and Memory (continued)
Data Type
Register Storage
Memory Storage
array
Members are stored as their individual types
require.
Members are stored as their individual types
require; aligned to 32-bit (word) boundary. All
arrays inside a structure are aligned according to
the type of each element in the array.
pointer to data member
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
pointer to member function
Components stored as their individual types require 64 bits aligned to 32-bit (word) boundary
For details about the size of an enum type, see Table 5-2.
6.2.1.1
char and short Data Types (signed and unsigned)
The char and unsigned char data types are stored in memory as a single byte and are loaded to and
stored from bits 0-7 of a register (see Figure 6-1). Objects defined as short or unsigned short are stored in
memory as two bytes at a halfword (2 byte) aligned address and they are loaded to and stored from bits
0-15 of a register (see Figure 6-1).
Figure 6-1. Char and Short Data Storage Format
Signed 8-bit char
MS
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
31
S
LS
I
I
I
I
I
7
I
0
Unsigned 8-bit char
MS
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
31
U
LS
U
U
U
U
U
7
U
0
Signed 16-bit short
MS
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
31
S
LS
I
I
I
I
I
I
I
I
I
I
I
I
I
I
15
I
0
Unsigned 16-bit short
MS
0
0
0
0
0
0
0
0
0
0
0
31
0
0
0
0
0
U
LS
U
U
U
U
U
U
U
U
U
U
U
U
U
15
U
U
0
LEGEND: S = sign, I = signed integer, U = unsigned integer, MS = most significant, LS = least significant
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float, int, and long Data Types (signed and unsigned)
The int, unsigned int, float, long and unsigned long data types are stored in memory as 32-bit objects at
word (4 byte) aligned addresses. Objects of these types are loaded to and stored from bits 0-31 of a
register, as shown in Figure 6-2. In big-endian mode, 4-byte objects are loaded to registers by moving the
first byte (that is, the lower address) of memory to bits 24-31 of the register, moving the second byte of
memory to bits 16-23, moving the third byte to bits 8-15, and moving the fourth byte to bits 0-7. In littleendian mode, 4-byte objects are loaded to registers by moving the first byte (that is, the lower address) of
memory to bits 0-7 of the register, moving the second byte to bits 8-15, moving the third byte to bits 16-23,
and moving the fourth byte to bits 24-31.
Figure 6-2. 32-Bit Data Storage Format
Single-precision floating char
MS
S
E
E
E
E
E
E
E
31
E
M
LS
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
23
M
0
Signed 32-bit integer or long char
MS
S
LS
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
31
I
0
Unsigned 32-bit integer or long
MS
U
LS
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
31
U
0
LEGEND: S = sign, M = Mantissa, U = unsigned integer, E = exponent, I = signed integer, MS = most significant, LS = least significant
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6.2.1.3
double, long double, and long long Data Types (signed and unsigned)
Double, long double, long long and unsigned long long data types are stored in memory in a pair of
registers and are always referenced as a pair. These types are stored as 64-bit objects at word (4 byte)
aligned addresses. For FPA mode, the word at the lowest address contains the sign bit, the exponent, and
the most significant part of the mantissa. The word at the higher address contains the least significant part
of the mantissa. This is true regardless of the endianness of the target. For VFP mode, the words are
ordered based upon the endianness of the target.
Objects of this type are loaded into and stored in register pairs, as shown in Figure 6-3. The most
significant memory word contains the sign bit, exponent, and the most significant part of the mantissa. The
least significant memory word contains the least significant part of the mantissa.
Figure 6-3. Double-Precision Floating-Point Data Storage Format
Address x
MS
S
E
E
E
E
E
E
E
E
E
E
E
31
E
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
20
M
0
Address x+ 4
LS
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
31
M
0
LEGEND: S = sign, M = mantissa, E = exponent, MS = most significant, LS = least significant
6.2.1.4
Pointer to Data Member Types
Pointer to data member objects are stored in memory like an unsigned int (32 bit) integral type. Its value is
the byte offset to the data member in the class, plus 1. The zero value is reserved to represent the NULL
pointer to the data member.
6.2.1.5
Pointer to Member Function Types
Pointer to member function objects are stored as a structure with three members, and the layout is
equivalent to:
struct {
short int d;
short int i;
union {
void (f) ();
long 0; }
};
The parameter d is the offset to be added to the beginning of the class object for this pointer. The
parameter I is the index into the virtual function table, offset by 1. The index enables the NULL pointer to
be represented. Its value is -1 if the function is non-virtual. The parameter f is the pointer to the member
function if it is non-virtual, when I is 0. The 0 is the offset to the virtual function pointer within the class
object.
6.2.1.6
Structure and Array Alignment
Structures are aligned according to the member with the most restrictive alignment requirement.
Structures are padded so that the size of the structure is a multiple of its alignment. Arrays are always
word aligned. Elements of arrays are stored in the same manner as if they were individual objects.
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6.2.2 Bit Fields
Bit fields are the only objects that are packed within a byte. That is, two bit fields can be stored in the
same byte. Bit fields can range in size from 1 to 32 bits, but they never span a 4-byte boundary.
For big-endian mode, bit fields are packed into registers from most significant bit (MSB) to least significant
bit (LSB) in the order in which they are defined. Bit fields are packed in memory from most significant byte
(MSbyte) to least significant byte (LSbyte). For little-endian mode, bit fields are packed into registers from
the LSB to the MSB in the order in which they are defined, and packed in memory from LSbyte to MSbyte.
Here are some details about how bit fields are handled:
• Plain int bit fields are unsigned. Consider the following C code:
struct st
{
int a:5;
} S;
foo()
{
if (S.a < 0)
bar();
}
•
•
•
In this example, bar () is never called as bit field 'a' is unsigned. Use signed int if you need a signed bit
field.
Bit fields of type long long are supported.
Bit fields are treated as the declared type.
The size and alignment of the struct containing the bit field depends on the declared type of the bit
field. For example, consider the struct:
struct st {int a:4};
•
This struct uses up 4 bytes and is aligned at 4 bytes.
Unnamed bit fields affect the alignment of the struct or union. For example, consider the struct:
struct st{char a:4; int :22;};
•
This struct uses 4 bytes and is aligned at a 4-byte boundary.
Bit fields declared volatile are accessed according to the bit field's declared type. A volatile bit field
reference generates exactly one reference to its storage; multiple volatile bit field accesses are not
merged.
Figure 6-4 illustrates bit-field packing, using the following bit field definitions:
struct{
int
int
int
int
int
}x;
A:7
B:10
C:3
D:2
E:9
A0 represents the least significant bit of the field A; A1 represents the next least significant bit, etc. Again,
storage of bit fields in memory is done with a byte-by-byte, rather than bit-by-bit, transfer.
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Figure 6-4. Bit-Field Packing in Big-Endian and Little-Endian Formats
Big-endian register
MS
A
6
LS
A
5
A
4
A
3
A
2
A
1
A
0
B
9
B
8
B
7
B
6
B
5
B
4
B
3
B
2
B
1
B
0
C
2
C
1
C
0
D
1
D
0
E
8
E
7
E
6
E
5
E
4
E
3
E
2
E
1
E
0
31
X
X
0
Big-endian memory
Byte 0
A
6
A
5
A
4
A
3
A
2
Byte 1
A
1
A
0
B
9
B
8
B
7
B
6
B
5
B
4
Byte 2
B
3
B
2
B
1
B
0
C
2
C
1
C
0
D
1
Byte 3
D
0
E
8
E
7
E
6
E
5
E
4
E
3
E
2
E
1
E
0
X
X
Little-endian register
MS
X
X
LS
E
8
E
7
E
6
E
5
E
4
E
3
E
2
E
1
E
0
D
1
D
0
C
2
C
1
C
0
B
9
B
8
B
7
B
6
B
5
B
4
B
3
B
2
B
1
B
0
A
6
A
5
A
4
A
3
A
2
A
1
31
A
0
0
Little-endian memory
Byte 0
B
0
A
6
A
5
A
4
A
3
Byte 1
A
2
A
1
A
0
B
8
B
7
B
6
B
5
B
4
Byte 2
B
3
B
2
B
1
E
1
E
0
D
1
D
0
C
2
Byte 3
C
1
C
0
B
9
X
X
E
8
E
7
E
6
E
5
E
4
E
3
E
2
LEGEND: X = not used, MS = most significant, LS = least significant
6.2.3 Character String Constants
In C, a character string constant is used in one of the following ways:
• To initialize an array of characters. For example:
char s[] = "abc";
•
When a string is used as an initializer, it is simply treated as an initialized array; each character is a
separate initializer. For more information about initialization, see Section 6.10.
In an expression. For example:
strcpy (s, "abc");
When a string is used in an expression, the string itself is defined in the .const section with the .string
assembler directive, along with a unique label that points to the string; the terminating 0 byte is
included. For example, the following lines define the string abc, and the terminating 0 byte (the label
SL5 points to the string):
.sect
".const"
SL5: .string "abc",0
String labels have the form SLn, where n is a number assigned by the compiler to make the label
unique. The number begins at 0 and is increased by 1 for each string defined. All strings used in a
source module are defined at the end of the compiled assembly language module.
The label SLn represents the address of the string constant. The compiler uses this label to reference
the string expression.
Because strings are stored in the .const section (possibly in ROM) and shared, it is bad practice for a
program to modify a string constant. The following code is an example of incorrect string use:
const char
a[1] = 'x';
*a = "abc"
/* Incorrect! undefined behavior */
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Register Conventions
Strict conventions associate specific registers with specific operations in the C/C++ environment. If you
plan to interface an assembly language routine to a C/C++ program, you must understand and follow
these register conventions.
The register conventions dictate how the compiler uses registers and how values are preserved across
function calls. Table 6-3 shows the types of registers affected by these conventions.Table 6-4 summarizes
how the compiler uses registers and whether their values are preserved across calls. For information
about how values are preserved across calls, see Section 6.4.
Table 6-3. How Register Types Are Affected by the Conventions
Register Type
Description
Argument register
Passes arguments during a function call
Return register
Holds the return value from a function call
Expression register
Holds a value
Argument pointer
Used as a base value from which a function's parameters (incoming
arguments) are accessed
Stack pointer
Holds the address of the top of the software stack
Link register
Contains the return address of a function call
Program counter
Contains the current address of code being executed
Table 6-4. Register Usage
Register
Alias
Usage
Preserved by Function (1)
R0
A1
Argument register, return register, expression register
Parent
R1
A2
Argument register, return register, expression register
Parent
R2
A3
Argument register, expression register
Parent
R3
A4
Argument register, expression register
Parent
R4
V1
Expression register
Child
R5
V2
Expression register
Child
R6
V3
Expression register
Child
R7
V4, AP
Expression register, argument pointer
Child
R8
V5
Expression register
Child
R9
V6
Expression register
Child
R10
V7
Expression register
Child
R11
V8
Expression register
Child
R12
V9, 1P
Expression register, instruction pointer
Parent
R13
SP
Stack pointer
Child (2)
R14
LR
Link register, expression register
Child
R15
PC
Program counter
N/A
CPSR
Current program status register
Child
SPSR
Saved program status register
Child
(1)
(2)
The parent function refers to the function making the function call. The child function refers to the function being called.
The SP is preserved by the convention that everything pushed on the stack is popped off before returning.
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Table 6-5. VFP Register Usage
32-Bit Register
64-Bit Register
FPSCR
S0
Usage
Preserved by Function (1)
Status register
N/A
D0
Floating-point expression, return values, pass arguments
N/A
D1
Floating-point expression, return values, pass arguments
N/A
D2
Floating-point expression, return values, pass arguments
N/A
D3
Floating-point expression, return values, pass arguments
N/A
D4
Floating-point expression, pass arguments
N/A
D5
Floating-point expression, pass arguments
N/A
D6
Floating-point expression, pass arguments
N/A
D7
Floating-point expression, pass arguments
N/A
D8
Floating-point expression
Child
D9
Floating-point expression
Child
D10
Floating-point expression
Child
D11
Floating-point expression
Child
D12
Floating-point expression
Child
D13
Floating-point expression
Child
D14
Floating-point expression
Child
D15
Floating-point expression
Child
D16-D31
Floating-point expression
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20
S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
(1)
The child function refers to the function being called.
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Table 6-6. Neon Register Usage
64-Bit Register
Quad Register
Usage
Preserved by Function (1)
D0
Q0
SIMD register
N/A
Q1
SIMD register
N/A
Q2
SIMD register
N/A
Q3
SIMD register
N/A
Q4
SIMD register
Child
Q5
SIMD register
Child
Q6
SIMD register
Child
Q7
SIMD register
Child
Q8
SIMD register
N/A
Q9
SIMD register
N/A
Q10
SIMD register
N/A
Q11
SIMD register
N/A
Q12
SIMD register
N/A
Q13
SIMD register
N/A
Q14
SIMD register
N/A
Q15
SIMD register
N/A
Status register
N/A
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
D19
D20
D21
D22
D23
D24
D25
D26
D27
D28
D29
D30
D31
FPSCR
(1)
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6.4
Function Structure and Calling Conventions
The C/C++ compiler imposes a strict set of rules on function calls. Except for special run-time support
functions, any function that calls or is called by a C/C++ function must follow these rules. Failure to adhere
to these rules can disrupt the C/C++ environment and cause a program to fail.
The following sections use this terminology to describe the function-calling conventions of the C/C++
compiler:
• Argument block. The part of the local frame used to pass arguments to other functions. Arguments
are passed to a function by moving them into the argument block rather than pushing them on the
stack. The local frame and argument block are allocated at the same time.
• Register save area. The part of the local frame that is used to save the registers when the program
calls the function and restore them when the program exits the function.
• Save-on-call registers. Registers R0-R3 and R12 (alternate names are A1-A4 and V9). The called
function does not preserve the values in these registers; therefore, the calling function must save them
if their values need to be preserved.
• Save-on-entry registers. Registers R4-R11 and R14 (alternate names are V1 to V8 and LR). It is the
called function's responsibility to preserve the values in these registers. If the called function modifies
these registers, it saves them when it gains control and preserves them when it returns control to the
calling function.
For details on the calling conventions in EABI mode or when using a VFP coprocessor, refer to the EABI
documentation located in the ARM Information Center.
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Figure 6-5 illustrates a typical function call. In this example, arguments are passed to the function, and the
function uses local variables and calls another function. The first four arguments are passed to registers
R0-R3. This example also shows allocation of a local frame and argument block for the called function.
Functions that have no local variables and do not require an argument block do not allocate a local frame.
Figure 6-5. Use of the Stack During a Function Call
Move arguments to
argument block;
call function
Before call
Low
Allocate new frame and
argument block
Low
Low
Callee’s
argument
block
SP
Callee’s
local variables
Register
save area
Caller’s
argument
block
SP
Argument 5...
argument n
Caller’s
local variables
Caller’s
local variables
High
Register
save area
High
SP
Argument 1 →
Argument 2 →
Argument 3 →
Argument 4 →
AP
register R0
register R1
register R2
register R3
Register
save area
High
Argument 5...
argument n
Caller’s
local variables
Register
save area
Legend: AP: argument pointer
SP: stack pointer
6.4.1 How a Function Makes a Call
A function (parent function) performs the following tasks when it calls another function (child function).
1. The calling function (parent) is responsible for preserving any save-on-call registers across the call that
are live across the call. (The save-on-call registers are R0-R3 and R12 (alternate names are A1-A4
and V9).)
2. If the called function (child) returns a structure, the caller allocates space for the structure and passes
the address of that space to the called function as the first argument.
3. The caller places the first arguments in registers R0-R3, in that order. The caller moves the remaining
arguments to the argument block in reverse order, placing the leftmost remaining argument at the
lowest address. Thus, the leftmost remaining argument is placed at the top of the stack.
4. If arguments were stored onto the argument block in step 3, the caller reserves a word in the argument
block for dual-state support. (See Section 6.11 for more information.)
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6.4.2 How a Called Function Responds
A called function (child function) must perform the following tasks:
1. If the function is declared with an ellipsis, it can be called with a variable number of arguments. The
called function pushes these arguments on the stack if they meet both of these criteria:
• The argument includes or follows the last explicitly declared argument.
• The argument is passed in a register.
2. The called function pushes register values of all the registers that are modified by the function and that
must be preserved upon exit of the function onto the stack. Normally, these registers are the save-onentry registers (R4-R11 and R14 (alternate names are V1 to V8 and LR)) and the link register (R14) if
the function contains calls. If the function is an interrupt, additional registers may need to be preserved.
For more information, see Section 6.7.
3. The called function allocates memory for the local variables and argument block by subtracting a
constant from the SP. This constant is computed with the following formula:
size of all local variables + max = constant
The max argument specifies the size of all parameters placed in the argument block for each call.
4. The called function executes the code for the function.
5. If the called function returns a value, it places the value in R0 (or R0 and R1 values).
6. If the called function returns a structure, it copies the structure to the memory block that the first
argument, R0, points to. If the caller does not use the return value, R0 is set to 0. This directs the
called function not to copy the return structure.
In this way, the caller can be smart about telling the called function where to return the structure. For
example, in the statement s = f(x), where s is a structure and f is a function that returns a structure, the
caller can simply pass the address of s as the first argument and call f. The function f then copies the
return structure directly into s, performing the assignment automatically.
You must be careful to properly declare functions that return structures, both at the point where they
are called (so the caller properly sets up the first argument) and at the point where they are declared
(so the function knows to copy the result).
7. The called function deallocates the frame and argument block by adding the constant computed in
Step 3.
8. The called function restores all registers that were saved in Step 2.
9. The called function ( _f) loads the program counter (PC) with the return address.
The following example is typical of how a called function responds to a call:
STMFD
SUB
...
ADD
LDMFD
;
SP!, {V1, V2, V3, LR} ;
SP, SP, #16
;
;
SP, SP, #16
;
SP!, {V1, V2, V3, PC} ;
;
called function entry point
save V1, V2, V3, and LR
allocate frame
body of the function
deallocate frame
restore V1, V2, V3, and store LR
in the PC, causing a return
6.4.3 C Exception Handler Calling Convention
If a C exception handler calls other functions, the following must take place:
• The handler must set its own stack pointer.
• The handler saves all of the registers not preserved by the call: R0-R3, R-12, LR (R8-R12 saved by
hardware for FIQ)
• Re-entrant exception handlers must save SPSR and LR.
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6.4.4 Accessing Arguments and Local Variables
A function accesses its local nonregister variables indirectly through the stack pointer (SP or R13) and its
stack arguments indirectly through the argument pointer (AP). If all stack arguments can be referenced
with the SP, they are, and the AP is not reserved. The SP always points to the top of the stack (the most
recently pushed value) and the AP points to the leftmost stack argument (the one closest to the top of the
stack). For example:
LDR
LDR
A2 [SP, #4]
A1 [AP, #0]
; load local var from stack
; load argument from stack
Since the stack grows toward smaller addresses, the local and argument data on the stack for the C/C++
function is accessed with a positive offset from the SP or the AP register.
6.5
Accessing Linker Symbols in C and C++
See the section on "Using Linker Symbols in C/C++ Applications" in the ARM Assembly Language Tools
User's Guide for information about referring to linker symbols in C/C++ code.
6.6
Interfacing C and C++ With Assembly Language
The following are ways to use assembly language with C/C++ code:
• Use separate modules of assembled code and link them with compiled C/C++ modules (see
Section 6.6.1).
• Use assembly language variables and constants in C/C++ source (see Section 6.6.3).
• Use inline assembly language embedded directly in the C/C++ source (see Section 6.6.5).
• Modify the assembly language code that the compiler produces (see Section 6.6.6).
6.6.1 Using Assembly Language Modules With C/C++ Code
Interfacing C/C++ with assembly language functions is straightforward if you follow the calling conventions
defined in Section 6.4, and the register conventions defined in Section 6.3. C/C++ code can access
variables and call functions defined in assembly language, and assembly code can access C/C++
variables and call C/C++ functions.
Follow these guidelines to interface assembly language and C:
• You must preserve any dedicated registers modified by a function. Dedicated registers include:
– Save-on-entry registers (R4-R11 (alternate names are V1 to V8 and LR))
– Stack pointer (SP or R13)
If the SP is used normally, it does not need to be explicitly preserved. In other words, the assembly
function is free to use the stack as long as anything that is pushed onto the stack is popped back off
before the function returns (thus preserving SP).
Any register that is not dedicated can be used freely without first being saved.
• Interrupt routines must save all the registers they use. For more information, see Section 6.7.
• When you call a C/C++ function from assembly language, load the designated registers with
arguments and push the remaining arguments onto the stack as described in Section 6.4.1.
Remember that a function can alter any register not designated as being preserved without having to
restore it. If the contents of any of these registers must be preserved across the call, you must
explicitly save them.
• Functions must return values correctly according to their C/C++ declarations. Double values are
returned in R0 and R1, and structures are returned as described in Step 2 of Section 6.4.1. Any other
values are returned in R0.
• No assembly module should use the .cinit section for any purpose other than autoinitialization of global
variables. The C/C++ startup routine assumes that the .cinit section consists entirely of initialization
tables. Disrupting the tables by putting other information in .cinit can cause unpredictable results.
• The compiler assigns linknames to all external objects. Thus, when you write assembly language code,
you must use the same linknames as those assigned by the compiler. See Section 5.15 for details.
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•
Any object or function declared in assembly language that is accessed or called from C/C++ must be
declared with the .def or .global directive in the assembly language modifier. This declares the symbol
as external and allows the linker to resolve references to it.
Likewise, to access a C/C++ function or object from assembly language, declare the C/C++ object with
the .ref or .global directive in the assembly language module. This creates an undeclared external
reference that the linker resolves.
6.6.2 Accessing Assembly Language Functions From C/C++
Functions defined in C++ that will be called from assembly should be defined as extern "C" in the C++ file.
Functions defined in assembly that will be called from C++ must be prototyped as extern "C" in C++.
Example 6-1 illustrates a C++ function called main, which calls an assembly language function called
asmfunc, Example 6-2. The asmfunc function takes its single argument, adds it to the C++ global variable
called gvar, and returns the result.
Example 6-1. Calling an Assembly Language Function From a C/C++ Program
extern "C" {
extern int asmfunc(int a); /* declare external asm function */
int gvar = 0;
/* define global variable
*/
}
void main()
{
int I = 5;
I = asmfunc(I);
/* call function normally
*/
Example 6-2. Assembly Language Program Called by Example 6-1
.global asmfunc
.global gvar
asmfunc:
gvar_a
LDR
LDR
ADD
STR
MOV
.field
r1, gvar_a
r2, [r1, #0]
r0, r0, r2
r0, [r1, #0]
pc, lr
gvar, 32
In the C++ program in Example 6-1, the extern "C" declaration tells the compiler to use C naming
conventions (that is, no name mangling). When the linker resolves the .global _asmfunc reference, the
corresponding definition in the assembly file will match.
The parameter i is passed in R0, and the result is returned in R0. R1 holds the address of the global gvar.
R2 holds the value of gvar before adding the value i to it.
6.6.3 Accessing Assembly Language Variables From C/C++
It is sometimes useful for a C/C++ program to access variables or constants defined in assembly
language. There are several methods that you can use to accomplish this, depending on where and how
the item is defined: a variable defined in the .bss section, a variable not defined in the .bss section, or a
linker symbol.
6.6.3.1
Accessing Assembly Language Global Variables
Accessing variables from the .bss section or a section named with .usect is straightforward:
1. Use the .bss or .usect directive to define the variable.
2. Use the .def or .global directive to make the definition external.
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3. Use the appropriate linkname in assembly language.
4. In C/C++, declare the variable as extern and access it normally.
Example 6-4 and Example 6-3 show how you can access a variable defined in .bss.
Example 6-3. Assembly Language Variable Program
.bss
.global
var,4,4
var
; Define the variable
; Declare the variable as external
Example 6-4. C Program to Access Assembly Language From Example 6-3
extern int var;
var = 1;
6.6.3.2
/* External variable */
/* Use the variable */
Accessing Assembly Language Constants
You can define global constants in assembly language by using the .set directive in combination with
either the .def or .global directive, or you can define them in a linker command file using a linker
assignment statement. These constants are accessible from C/C++ only with the use of special operators.
For variables defined in C/C++ or assembly language, the symbol table contains the address of the value
contained by the variable. When you access an assembly variable by name from C/C++, the compiler gets
the value using the address in the symbol table.
For assembly constants, however, the symbol table contains the actual value of the constant. The
compiler cannot tell which items in the symbol table are addresses and which are values. If you access an
assembly (or linker) constant by name, the compiler tries to use the value in the symbol table as an
address to fetch a value. To prevent this behavior, you must use the & (address of) operator to get the
value (_symval). In other words, if x is an assembly language constant, its value in C/C++ is &x. See the
section on "Using Linker Symbols in C/C++ Applications" in the ARM Assembly Language Tools User's
Guide for more examples that use _symval.
For more about symbols and the symbol table, refer to the section on "Symbols" in the ARM Assembly
Language Tools User's Guide.
You can use casts and #defines to ease the use of these symbols in your program, as in Example 6-5 and
Example 6-6.
Example 6-5. Accessing an Assembly Language Constant From C
extern int table_size;
/*external ref */
#define TABLE_SIZE ((int) (&table_size))
.
/* use cast to hide address-of */
.
.
for (I=0; i<TABLE_SIZE; ++I) /* use like normal symbol */
Example 6-6. Assembly Language Program for Example 6-5
_table_size
.set
10000
; define the constant
.global _table_size ; make it global
Because you are referencing only the symbol's value as stored in the symbol table, the symbol's declared
type is unimportant. In Example 6-5, int is used. You can reference linker-defined symbols in a similar
manner.
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6.6.4 Sharing C/C++ Header Files With Assembly Source
You can use the .cdecls assembler directive to share C headers containing declarations and prototypes
between C and assembly code. Any legal C/C++ can be used in a .cdecls block and the C/C++
declarations will cause suitable assembly to be generated automatically, allowing you to reference the
C/C++ constructs in assembly code. For more information, see the C/C++ header files chapter in the ARM
Assembly Language Tools User's Guide.
6.6.5 Using Inline Assembly Language
Within a C/C++ program, you can use the asm statement to insert a single line of assembly language into
the assembly language file created by the compiler. A series of asm statements places sequential lines of
assembly language into the compiler output with no intervening code. For more information, see
Section 5.10.
The asm statement is useful for inserting comments in the compiler output. Simply start the assembly
code string with a semicolon (;) as shown below:
asm(";*** this is an assembly language comment");
NOTE:
Using the asm Statement
Keep the following in mind when using the asm statement:
•
Be extremely careful not to disrupt the C/C++ environment. The compiler does not check
or analyze the inserted instructions.
•
Avoid inserting jumps or labels into C/C++ code because they can produce
unpredictable results by confusing the register-tracking algorithms that the code
generator uses.
•
Do not change the value of a C/C++ variable when using an asm statement. This is
because the compiler does not verify such statements. They are inserted as is into the
assembly code, and potentially can cause problems if you are not sure of their effect.
•
Do not use the asm statement to insert assembler directives that change the assembly
environment.
•
Avoid creating assembly macros in C code and compiling with the --symdebug:dwarf (or
-g) option. The C environment’s debug information and the assembly macro expansion
are not compatible.
6.6.6 Modifying Compiler Output
You can inspect and change the compiler's assembly language output by compiling the source and then
editing the assembly output file before assembling it. The C/C++ interlist feature can help you inspect
compiler output. See Section 2.12.
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Interrupt Handling
As long as you follow the guidelines in this section, you can interrupt and return to C/C++ code without
disrupting the C/C++ environment. When the C/C++ environment is initialized, the startup routine does not
enable or disable interrupts. If the system is initialized by way of a hardware reset, interrupts are disabled.
If your system uses interrupts, you must handle any required enabling or masking of interrupts. Such
operations have no effect on the C/C++ environment and are easily incorporated with asm statements or
calling an assembly language function.
6.7.1 Saving Registers During Interrupts
When C/C++ code is interrupted, the interrupt routine must preserve the contents of all machine registers
that are used by the routine or by any functions called by the routine. With the exception of banked
registers, register preservation must be explicitly handled by the interrupt routine.
All banked registers are automatically preserved by the hardware (except for interrupts that are reentrant.
If you write interrupt routines that are reentrant, you must add code that preserves the interrupt's banked
registers.) Each interrupt type has a set of banked registers. For information about the interrupt types, see
Section 5.11.17.
6.7.2 Using C/C++ Interrupt Routines
When C/C++ code is interrupted, the interrupt routine must preserve the contents of all machine registers
that are used by the routine or by any functions called by the routine. Register preservation must be
explicitly handled by the interrupt routine.
__interrupt void example (void)
{
...
}
If a C/C++ interrupt routine does not call any other functions, only those registers that the interrupt handler
uses are saved and restored. However, if a C/C++ interrupt routine does call other functions, these
functions can modify unknown registers that the interrupt handler does not use. For this reason, the
routine saves all the save-on-call registers if any other functions are called. (This excludes banked
registers.) Do not call interrupt handling functions directly.
Interrupts can be handled directly with C/C++ functions by using the INTERRUPT pragma or the
__interrupt keyword. For information, see Section 5.11.17 and Section 5.7.2, respectively.
6.7.3 Using Assembly Language Interrupt Routines
You can handle interrupts with assembly language code as long as you follow the same register
conventions the compiler does. Like all assembly functions, interrupt routines can use the stack, access
global C/C++ variables, and call C/C++ functions normally. When calling C/C++ functions, be sure that
any save-on-call registers are preserved before the call because the C/C++ function can modify any of
these registers. You do not need to save save-on-entry registers because they are preserved by the called
C/C++ function.
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6.7.4 How to Map Interrupt Routines to Interrupt Vectors
NOTE: This section does not apply to Cortex-M devices.
To map Cortex-A interrupt routines to interrupt vectors you need to include a intvecs.asm file. This file will
contain assembly language directives that can be used to set up the ARM's interrupt vectors with
branches to your interrupt routines. Follow these steps to use this file:
1. Using Example 6-7 as a guide, create intvecs.asm and include your interrupt routines. For each
routine:
a. At the beginning of the file, add a .global directive that names the routine.
b. Modify the appropriate .word directive to create a branch to the name of your routine.
2. Assemble and link intvecs.asm with your applications code and with the compiler's linker control file
(lnk16.cmd or lnk32.cmd). The control file contains a SECTIONS directive that maps the .intvecs
section into the memory locations 0x00-0x1F.
For example, on an ARM v4 target, if you have written a C interrupt routine for the IRQ interrupt called
c_intIRQ and an assembly language routine for the FIQ interrupt called tim1_int, you should create
intvecs.asm as in Example 6-7.
Example 6-7. Sample intvecs.asm File
.if __TI_EABI_ASSEMBLER
.asg c_intIRQ, C_INTIRQ
.else
.asg _c_intIRQ, C_INTIRQ
.endif
.global _c_int00
.global C_INTIRQ
.global tim1_int
.sect ".intvecs"
B _c_int00 ; reset interrupt
.word 0 ; undefined instruction interrupt
.word 0 ; software interrupt
.word 0 ; abort (prefetch) interrupt
.word 0 ; abort (data) interrupt
.word 0 ; reserved
B C_INTIRQ ; IRQ interrupt
B tim1_int ; FIQ interrupt
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6.7.5 Using Software Interrupts
A software interrupt (SWI) is a synchronous exception generated by the execution of a particular
instruction. Applications use software interrupts to request services from a protected system, such as an
operating system, which can perform the services only while in a supervisor mode. Some ARM
documentation uses the term Supervisor Calls (SVC) instead of "software interrupt".
A C/C++ application can invoke a software interrupt by associating a software interrupt number with a
function name through use of the SWI_ALIAS pragma and then calling the software interrupt as if it were a
function. For information, see Section 5.11.28.
Since a call to the software interrupt function represents an invocation of the software interrupt, passing
and returning data to and from a software interrupt is specified as normal function parameter passing with
the following restriction:
All arguments passed to a software interrupt must reside in the four argument registers (R0-R3). No
arguments can be passed by way of a software stack. Thus, only four arguments can be passed unless:
• Floating-point doubles are passed, in which case each double occupies two registers.
• Structures are returned, in which case the address of the returned structure occupies the first
argument register.
For Cortex-M architectures, C SWI handlers cannot return values. Values may be returned by SWI
handlers on other architectures.
The C/C++ compiler also treats the register usage of a called software interrupt the same as a called
function. It assumes that all save-on-entry registers () are preserved by the software interrupt and that
save-on-call registers (the remainder of the registers) can be altered by the software interrupt.
6.7.6 Other Interrupt Information
An interrupt routine can perform any task performed by any other function, including accessing global
variables, allocating local variables, and calling other functions.
When you write interrupt routines, keep the following points in mind:
• It is your responsibility to handle any special masking of interrupts.
• A C/C++ interrupt routine cannot be called directly from C/C++ code.
• In a system reset interrupt, such as c_int00, you cannot assume that the run-time environment is set
up; therefore, you cannot allocate local variables, and you cannot save any information on the run-time
stack.
• In assembly language, remember to precede the name of a C/C++ interrupt with the appropriate
linkname. For example, refer to c_int00 as _c_int00.
• When an interrupt occurs, the state of the processor (ARM or Thumb mode) is dependent on the
device you are using. The compiler allows interrupt handlers to be defined in ARM or Thumb-2 mode.
You should ensure the interrupt handler uses the proper mode for the device.
• The FIQ, supervisor, abort, IRQ, and undefined modes have separate stacks that are not automatically
set up by the C/C++ run-time environment. If you have interrupt routines in one of these modes, you
must set up the software stack for that mode. However, ARM Cortex-M processors have two stacks,
and the main stack (MSP), which is used by IRQ (the only interrupt type for Cortex-M), is automatically
handled by the compiler.
• Interrupt routines are not reentrant. If an interrupt routine enables interrupts of its type, it must save a
copy of the return address and SPSR (the saved program status register) before doing so.
• Because a software interrupt is synchronous, the register saving conventions discussed in
Section 6.7.1 can be less restrictive as long as the system is designed for this. A software interrupt
routine generated by the compiler, however, follows the conventions in Section 6.7.1.
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6.8
Intrinsic Run-Time-Support Arithmetic and Conversion Routines
The intrinsic run-time-support library contains a number of assembly language routines that provide
arithmetic and conversion capability for C/C++ operations that the 32-bit and 16-bit instruction sets do not
provide. These routines include integer division, integer modulus, and floating-point operations.
There are two versions of each of the routines:
• A 16-bit version to be called only from the 16-BIS (bit instruction set) state
• A 32-bit version only to be called from the 32-BIS state
These routines do not follow the standard C/C++ calling conventions in that the naming and register
conventions are not upheld. Refer to the ARM Information Center for information on the EABI naming
conventions.
6.8.1 CPSR Register and Interrupt Intrinsics
The intrinsics in Table 6-7 enable you to get/set the CPSR register and to enable/disable interrupts. All but
the _call_swi() function are only available when compiling in ARM mode. Additional intrinsices for ARM
assembly instructions are provided in Section 5.14.
Table 6-7. CPSR and Interrupt C/C++ Compiler Intrinsics
C/C++ Compiler Intrinsic
Assembly
Instruction
void _call_swi(unsigned int src );
SWI $ src
Call a software interrupt. The src must be an
immediate.
unsigned int dst = _disable_FIQ( ) ;
Cortex-R4/A8:
MRS dst, FAULTMASK
CPSID f
Disable FIQ interrupts and return previous
FAULTMASK or CPSR setting.
unsigned int dst =
_disable_interrupts( ) ;
Cortex-M0:
MRS dst, PRIMASK
CPSID i
Cortex-M3/M4/R4/A8:
MRS dst, FAULTMASK
CPSID f
Disable all interrupts and return previous PRIMASK
or FAULTMASK setting. The assembly instructions
are dependent on the architecture.
unsigned int dst = _disable_IRQ( ) ;
MRS dst, PRIMASK
CPSID i
Disable IRQ interrupts and return previous PRIMASK
setting.
unsigned int dst = _enable_FIQ( ) ;
Cortex-R4/A8:
MRS dst, FAULTMASK
CPSIE f
Enable FIQ interrupts and return previous
FAULTMASK or CPSR setting.
unsigned int dst =
_enable_interrupts( ) ;
Cortex-M0:
MRS dst, PRIMASK
CPSIE i
Cortex-M3/M4/R4/A8:
MRS dst, FAULTMASK
CPSIE f
Enable all interrupts and return previous PRIMASK or
FAULTMASK setting. The assembly instructions are
dependent on the architecture.
unsigned int dst = _enable_IRQ( ) ;
MRS dst, PRIMASK
CPSIE i
Enable IRQ interrupts and return previous PRIMASK
setting.
unsigned int dst = _get_CPSR( ) ;
MRS dst , CPSR
Get the CPSR register.
void _restore_interupts(unsigned int
src );
Cortex-M0:
MSR PRIMASK src
Cortex-M3/M4:
MSR FAULTMASK src
Cortex-R4:
MSR CPSR_cf , src
Restores interrupts to state indicated by value
returned from _disable_interrupts. The assembly
instructions are dependent on the architecture.
void _set_CPSR(unsigned int src );
MSR CPSR , src
Set the CPSR register.
void _set_CPSR_flg(unsigned int src );
MSR dst , CPSR
Set the CPSR flag bits. The src is rotated by the
intrinsic.
unsigned int dst =
_set_interrupt_priority( unsigned int
src ) ;
Cortex-M0/M3/M4 only:
MRS dst, BASEPRI
MSR BASEPRI, src
Set interrupt priority and return the previous setting.
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Built-In Functions
Built-in functions are predefined by the compiler. They can be called like a regular function, but they do
not require a prototype or definition. The compiler supplies the proper prototype and definition.
The ARM compiler supports the following built-in functions:
• The _ _curpc function, which returns the value of the program counter where it is called. The syntax of
the function is:
void *_ _curpc(void);
•
The _ _run_address_check function, which returns TRUE if the code performing the call is located at
its run-time address, as assigned by the linker. Otherwise, FALSE is returned. The syntax of the
function is:
int _ _run_address_check(void);
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6.10 System Initialization
Before you can run a C/C++ program, you must create the C/C++ run-time environment. The C/C++ boot
routine performs this task using a function called c_int00 (or _c_int00). The run-time-support source
library, rts.src, contains the source to this routine in a module named boot.c (or boot.asm).
To begin running the system, the c_int00 function can be called by reset hardware. You must link the
c_int00 function with the other object files. This occurs automatically when you use the --rom_model or -ram_model link option and include a standard run-time-support library as one of the linker input files.
When C/C++ programs are linked, the linker sets the entry point value in the executable output file to the
symbol c_int00.
The c_int00 function performs the following tasks to initialize the environment:
1. Switches to the appropriate mode, reserves space for the run-time stack, and sets up the initial value
of the stack pointer (SP). The stack is aligned on a 64-bit boundary.
2. Calls the function _ _TI_auto_init to perform the C/C++ autoinitialization.
The _ _TI_auto_init function does the following tasks:
• Processes the binit copy table, if present.
• Performs C autoinitialization of global/static variables. For more information, see Section 6.10.3.
• Calls C++ initialization routines for file scope construction from the global constructor table. For
more information, see Section 6.10.3.6.
3. Calls the main() function to run the C/C++ program.
You can replace or modify the boot routine to meet your system requirements. However, the boot routine
must perform the operations listed above to correctly initialize the C/C++ environment.
6.10.1 Boot Hook Functions for System Pre-Initialization
Boot hooks are points at which you may insert application functions into the C/C++ boot process. Default
boot hook functions are provided with the run-time support (RTS) library. However, you can implement
customized versions of these boot hook functions, which override the default boot hook functions in the
RTS library if they are linked before the run-time library. Such functions can perform any applicationspecific initialization before continuing with the C/C++ environment setup.
Note that the TI-RTOS operating system uses custom versions of the boot hook functions for system
setup, so you should be careful about overriding these functions if you are using TI-RTOS.
The following boot hook functions are available:
__mpu_init(): This function provides an interface for initializing the MPU, if MPU support is included. The
__mpu_init() function is called after the stack pointer is initialized but before any C/C++ environment setup
is performed. This function should not return a value.
_system_pre_init(): This function provides a place to perform application-specific initialization. It is
invoked after the stack pointer is initialized but before any C/C++ environment setup is performed. For
targets that include MPU support, this function is called after __mpu_init(). By default, _system_pre_init()
should return a non-zero value. The default C/C++ environment setup is bypassed if _system_pre_init()
returns 0.
_system_post_cinit(): This function is invoked during C/C++ environment setup, after C/C++ global data
is initialized but before any C++ constructors are called. This function should not return a value.
The _c_int00( ) initialization routine also provides a mechanism for an application to perform the setup (set
I/O registers, enable/disable timers, etc.) before the C/C++ environment is initialized.
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6.10.2 Run-Time Stack
The run-time stack is allocated in a single continuous block of memory and grows down from high
addresses to lower addresses. The SP points to the top of the stack.
The code does not check to see if the run-time stack overflows. Stack overflow occurs when the stack
grows beyond the limits of the memory space that was allocated for it. Be sure to allocate adequate
memory for the stack.
The stack size can be changed at link time by using the --stack_size link option on the linker command
line and specifying the stack size as a constant directly after the option.
The C/C++ boot routine shipped with the compiler sets up the user/thread mode run-time stack. If your
program uses a run-time stack when it is in other operating modes, you must also allocate space and set
up the run-time stack corresponding to those modes.
EABI requires that 64-bit data (type long long and long double) be aligned at 64-bits. This requires that the
stack be aligned at a 64-bit boundary at function entry so that local 64-bit variables are allocated in the
stack with correct alignment. The boot routine aligns the stack at a 64-bit boundary.
6.10.3 Automatic Initialization of Variables
Any global variables declared as preinitialized must have initial values assigned to them before a C/C++
program starts running. The process of retrieving these variables' data and initializing the variables with
the data is called autoinitialization. Internally, the compiler and linker coordinate to produce compressed
initialization tables. Your code should not access the initialization table.
6.10.3.1 Zero Initializing Variables
In ANSI C, global and static variables that are not explicitly initialized must be set to 0 before program
execution. The C/C++ compiler supports preinitialization of uninitialized variables by default. This can be
turned off by specifying the linker option --zero_init=off.
6.10.3.2 Direct Initialization
The compiler uses direct initialization to initialize global variables. For example, consider the following C
code:
int i
= 23;
int a[5] = { 1, 2, 3, 4, 5 };
The compiler allocates the variables 'i' and 'a[] to .data section and the initial values are placed directly.
.global i
.data
.align 4
i:
.field
23,32
; i @ 0
1,32
2,32
3,32
4,32
5,32
;
;
;
;
;
.global a
.data
.align 4
a:
.field
.field
.field
.field
.field
a[0]
a[1]
a[2]
a[3]
a[4]
@
@
@
@
@
0
32
64
96
128
Each compiled module that defines static or global variables contains these .data sections. The linker
treats the .data section like any other initialized section and creates an output section. In the load-time
initialization model, the sections are loaded into memory and used by the program. See Section 6.10.3.5.
In the run-time initialization model, the linker uses the data in these sections to create initialization data
and an additional compressed initialization table. The boot routine processes the initialization table to copy
data from load addresses to run addresses. See Section 6.10.3.3.
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6.10.3.3 Autoinitialization of Variables at Run Time
Autoinitializing variables at run time is the default method of autoinitialization. To use this method, invoke
the linker with the --rom_model option.
Using this method, the linker creates a compressed initialization table and initialization data from the direct
initialized sections in the compiled module. The table and data are used by the C/C++ boot routine to
initialize variables in RAM using the table and data in ROM.
Figure 6-6 illustrates autoinitialization at run time. Use this method in any system where your application
runs from code burned into ROM.
Figure 6-6. Autoinitialization at Run Time
Object file
C auto init
table and data
(ROM)
(.cinit section)
Memory
Loader
C auto init
table and data
(ROM)
Boot
routine
.data
uninitialized
(RAM)
6.10.3.4 Autoinitialization Tables
The compiled object files do not have initialization tables. The variables are initialized directly. The linker,
when the --rom_model option is specified, creates C auto initialization table and the initialization data. The
linker creates both the table and the initialization data in an output section named .cinit.
The autoinitialization table has the following format:
The linker defined symbols __TI_CINIT_Base and __TI_CINIT_Limit point to the start and end of the
table, respectively. Each entry in this table corresponds to one output section that needs to be initialized.
The initialization data for each output section could be encoded using different encoding.
The load address in the C auto initialization record points to initialization data with the following format:
8-bit index
Encoded data
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The first 8-bits of the initialization data is the handler index. It indexes into a handler table to get the
address of a handler function that knows how to decode the following data.
The handler table is a list of 32-bit function pointers.
_TI_Handler_Table_Base:
32-bit handler 1 address
32-bit handler n address
_TI_Handler_Table_Limit:
The encoded data that follows the 8-bit index can be in one of the following format types. For clarity the 8bit index is also depicted for each format.
6.10.3.4.1 Length Followed by Data Format
8-bit index
24-bit padding
32-bit length (N)
N byte initialization data (not compressed)
The compiler uses 24-bit padding to align the length field to a 32-bit boundary. The 32-bit length field
encodes the length of the initialization data in bytes (N). N byte initialization data is not compressed and is
copied to the run address as is.
The run-time support library has a function __TI_zero_init() to process this type of initialization data. The
first argument to this function is the address pointing to the byte after the 8-bit index. The second
argument is the run address from the C auto initialization record.
6.10.3.4.2 Zero Initialization Format
8-bit index
24-bit padding
32-bit length (N)
The compiler uses 24-bit padding to align the length field to a 32-bit boundary. The 32-bit length field
encodes the number of bytes to be zero initialized.
The run-time support library has a function __TI_zero_init() to process the zero initialization. The first
argument to this function is the address pointing to the byte after the 8-bit index. The second argument is
the run address from the C auto initialization record.
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6.10.3.4.3 Run Length Encoded (RLE) Format
8-bit index
Initialization data compressed using run length encoding
The data following the 8-bit index is compressed using Run Length Encoded (RLE) format. uses a simple
run length encoding that can be decompressed using the following algorithm:
1. Read the first byte, Delimiter (D).
2. Read the next byte (B).
3. If B != D, copy B to the output buffer and go to step 2.
4. Read the next byte (L).
a. If L == 0, then length is either a 16-bit, a 24-bit value, or we’ve reached the end of the data, read
next byte (L).
1. If L == 0, length is a 24-bit value or the end of the data is reached, read next byte (L).
a. If L == 0, the end of the data is reached, go to step 7.
b. Else L <<= 16, read next two bytes into lower 16 bits of L to complete 24-bit value for L.
2. Else L <<= 8, read next byte into lower 8 bits of L to complete 16-bit value for L.
b. Else if L > 0 and L < 4, copy D to the output buffer L times. Go to step 2.
c. Else, length is 8-bit value (L).
5. Read the next byte (C); C is the repeat character.
6. Write C to the output buffer L times; go to step 2.
7. End of processing.
The run-time support library has a routine __TI_decompress_rle24() to decompress data compressed
using RLE. The first argument to this function is the address pointing to the byte after the 8-bit index. The
second argument is the run address from the C auto initialization record.
RLE Decompression Routine
NOTE: The previous decompression routine, __TI_decompress_rle(), is included in the run-timesupport library for decompressing RLE encodings generated by older versions of the linker.
6.10.3.4.4 Lempel-Ziv-Storer-Szymanski Compression (LZSS) Format
8-bit index
Initialization data compressed using LZSS
The data following the 8-bit index is compressed using LZSS compression. The run-time support library
has the routine __TI_decompress_lzss() to decompress the data compressed using LZSS. The first
argument to this function is the address pointing to the byte after the 8-bit index. The second argument is
the run address from the C auto initialization record.
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6.10.3.4.5 Sample C Code to Process the C Autoinitialization Table
The run-time support boot routine has code to process the C autoinitialization table. The following C code
illustrates how the autoinitialization table can be processed on the target.
Example 6-8. Processing the C Autoinitialization Table
typedef void (*handler_fptr)(const unsigned char *in,
unsigned char *out);
#define
#pragma
extern
extern
extern
HANDLER_TABLE __TI_Handler_Table_Base
WEAK(HANDLER_TABLE)
unsigned int
HANDLER_TABLE;
unsigned char *__TI_CINIT_Base;
unsigned char *__TI_CINIT_Limit;
void auto_initialize()
{
unsigned char **table_ptr;
unsigned char **table_limit;
/*--------------------------------------------------------------*/
/* Check if Handler table has entries.
*/
/*--------------------------------------------------------------*/
if (&__TI_Handler_Table_Base >= &__TI_Handler_Table_Limit)
return;
/*---------------------------------------------------------------*/
/* Get the Start and End of the CINIT Table.
*/
/*---------------------------------------------------------------*/
table_ptr
= (unsigned char **)&__TI_CINIT_Base;
table_limit = (unsigned char **)&__TI_CINIT_Limit;
while (table_ptr < table_limit)
{
/*-------------------------------------------------------------*/
/* 1. Get the Load and Run address.
*/
/* 2. Read the 8-bit index from the load address.
*/
/* 3. Get the handler function pointer using the index from
*/
/*
handler table.
*/
/*-------------------------------------------------------------*/
unsigned char *load_addr
= *table_ptr++;
unsigned char *run_addr
= *table_ptr++;
unsigned char handler_idx = *load_addr++;
handler_fptr
handler
=
(handler_fptr)(&HANDLER_TABLE)[handler_idx];
/*-------------------------------------------------------------*/
/* 4. Call the handler and pass the pointer to the load data
*/
/*
after index and the run address.
*/
/*-------------------------------------------------------------*/
(*handler)((const unsigned char *)load_addr, run_addr);
}
}
6.10.3.5 Initialization of Variables at Load Time
Initialization of variables at load time enhances performance by reducing boot time and by saving the
memory used by the initialization tables. To use this method, invoke the linker with the --ram_model
option.
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When you use the --ram_model link option, the linker does not generate C autoinitialization tables and
data. The direct initialized sections (.data) in the compiled object files are combined according to the linker
command file to generate initialized output sections. The loader loads the initialized output sections into
memory. After the load, the variables are assigned their initial values.
Since the linker does not generate the C autoinitialization tables, no boot time initialization is performed.
Figure 6-7 illustrates the initialization of variables at load time.
Figure 6-7. Initialization at Load Time
Object file
.data
section
Memory
Loader
.data section
(initialized)
(RAM)
6.10.3.6 Global Constructors
All global C++ variables that have constructors must have their constructor called before main(). The
compiler builds a table of global constructor addresses that must be called, in order, before main() in a
section called .init_array. The linker combines the .init_array section form each input file to form a single
table in the .init_array section. The boot routine uses this table to execute the constructors. The linker
defines two symbols to identify the combined .init_array table as shown below. This table is not null
terminated by the linker.
Figure 6-8. Constructor Table
SHT$$INIT_ARRAY$$Base:
Address of constructor 1
Address of constructor 2
Address of constructor n
SHT$$INIT_ARRAY$$Limit:
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6.10.4 Initialization Tables
The tables in the .cinit section consist of variable-size initialization records. Each variable that must be
autoinitialized has a record in the .cinit section. Figure 6-9 shows the format of the .cinit section and the
initialization records.
Figure 6-9. Format of Initialization Records in the .cinit Section
.cinit section
Initialization record 1
Initialization record 2
Initialization record
Initialization record 3
Size in
bytes
?
Pointer to
.bss area
Initialization
data
Initialization record n
The fields of an initialization record contain the following information:
• The first field of an initialization record contains the size (in bytes) of the initialization data.The width of
this field is one word (32-bit).
• The second field contains the starting address of the area within the .bss section where the
initialization data must be copied.The width of this field is one word.
• The third field contains the data that is copied into the .bss section to initialize the variable.The width of
this field is variable.
Each variable that must be autoinitialized has an initialization record in the .cinit section.
Example 6-9 shows initialized global variables defined in C. Example 6-10 shows the corresponding
initialization table. The section .cinit:c is a subsection in the .cinit section that contains all scalar data. The
subsection is handled as one record during initialization, which minimizes the overall size of the .cinit
section.
Example 6-9. Initialized Variables Defined in C
int
int
172
i = 23;
a[5] = { 1, 2, 3, 4, 5 };
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Example 6-10. Initialized Information for Variables Defined in Example 6-9
.sect
".cinit"
; Initialization section
* Initialization record for variable i
.align
4
; align on word boundary
.field
4,32
; length of data (1 word)
.field
_i+0,32
; address of i
.field
23,32
; _i @ 0
* Initialization record for variable a
.sect
".cinit"
.align
4
; align on word boundary
.field
IR1,32
; Length of data (5 words)
.field
_a+0,32
; Address of a[ ]
.field
1,32
; _a[0] @ 0
.field
2,32
; _a[1] @ 32
.field
3,32
; _a[2] @ 64
.field
4,32
; _a[3] @ 96
.field
5,32
; _a[4] @ 128
IR1: .set
20
; set length symbol
The .cinit section must contain only initialization tables in this format. When interfacing assembly language
modules, do not use the .cinit section for any other purpose.
The table in the .pinit section simply consists of a list of addresses of constructors to be called (see
Figure 6-10). The constructors appear in the table after the .cinit initialization.
Figure 6-10. Format of Initialization Records in the .pinit Section
.pinit section
Address of constructor 1
Address of constructor 2
Address of constructor 3
•
•
•
Address of constructor n
When you use the --rom_model or --ram_model option, the linker combines the .cinit sections from all the
C/C++ modules and appends a null word to the end of the composite .cinit section. This terminating record
appears as a record with a size field of 0 and marks the end of the initialization tables.
Likewise, the --rom_model or --ram_model link option causes the linker to combine all of the .pinit sections
from all C/C++ modules and append a null word to the end of the composite .pinit section. The boot
routine knows the end of the global constructor table when it encounters a null constructor address.
The const-qualified variables are initialized differently; see Section 5.7.1.
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6.11 Dual-State Interworking Under TIABI (Deprecated)
The ARM is a unique processor in that it gives you the performance of a 32-bit architecture with the code
density of a 16-bit architecture. It supports a 16-bit instruction set and a 32-bit instruction set that allows
switching dynamically between the two sets.
The instruction set that the ARM processor uses is determined by the state of the processor. The
processor can be in 32-BIS (bit instruction set) state or 16-BIS state at any given time. The compiler
allows you to specify whether a module should be compiled in 32- or 16-BIS state and allows functions
compiled in one state to call functions compiled in the other state.
6.11.1 Level of Dual-State Support
By default, the compiler allows dual-state interworking between functions. However, the compiler allows
you to alter the level of support to meet your particular needs.
In dual-state interworking, it is the called function's responsibility to handle the proper state changes
required by the calling function. It is the calling function's responsibility to handle the proper state changes
required to indirectly call a function (call it by address). Therefore, a function supports dual-state
interworking if it provides the capability for functions requiring a state change to directly call the function
(call it by name) and provides the mechanism to indirectly call functions involving state changes.
If a function does not support dual-state interworking, it cannot be called by functions requiring a state
change and cannot indirectly call functions that support dual-state interworking. Regardless of whether a
function supports dual-state interworking or not, it can directly or indirectly call certain functions:
• Directly call a function in the same state
• Directly call a function in a different state if that function supports dual-state interworking
• Indirectly call a function in the same state if that function does not support dual-state interworking
Given this definition of dual-state support, the ARM C/C++ compiler offers three levels of support. Use
Table 6-8 to determine the best level of support to use for your code.
Table 6-8. Selecting a Level of Dual-State Support
If your code...
Use this level of support ...
Requires few state changes
Default
Requires many state changes
Optimized
Requires no state changes and has frequent indirect calls
None
Here is detailed information about each level of support:
• Default. Full dual-state interworking is supported. For each function that supports full dual-state
interworking, the compiler generates code that allows functions requiring a state change to call the
function, whether it is ever used or not. This code is placed in a different section from the section the
actual function is in. If the linker determines that this code is never referenced, it does not link it into
the final executable image. However, the mechanism used with indirect calls to support dual-state
interworking is integrated into the function and cannot be removed by the linker, even if the linker
determines that the mechanism is not needed.
• Optimized. Optimized dual-state interworking provides no additional functionality over the default level
but optimizes the dual-state support code (in terms of code size and execution speed) for the case
where a state change is required. It does this optimization by integrating the support into the function.
Use the optimized level of support only when you know that a majority of the calls to this function
require a state change. Even if the dual-state support code is never used, the linker cannot remove the
code because it is integrated into the function. To specify this level of support, use the DUAL_STATE
pragma. See Section 5.11.10 for more information.
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•
None. Dual-state interworking is disabled. This level is invoked with the -md shell option. Functions
with this support can directly call the following functions:
– Functions compiled in the same state
– Functions in a different state that support dual-state interworking
Functions with this support level can indirectly call only functions that do not require a state change
and do not support dual-state interworking. Because functions with this support level do not provide
dual-state interworking, they cannot be called by a function requiring a state change.
Use this support level if you do not require dual-state interworking, have frequent indirect calls, and
cannot tolerate the additional code size or speed incurred by the indirect calls supporting dual-state
interworking.
When a program does not require any state changes, the only difference between specifying no support
and default support is that indirect calls are more complex in the default support level.
6.11.2 Implementation
Dual-state support is implemented by providing an alternate entry point for a function. This alternate entry
point is used by functions requiring a state change. Dual-state support handles the change to the correct
state and, if needed, changes the function back to the state of the caller when it returns. Also, indirect
calls set up the return address so that once the called function returns, the state can be reliably changed
back to that of the caller.
6.11.2.1 Naming Conventions for Entry Points
The ARM compiler reserves the name space of all identifiers beginning with an underscore ( _ ) or a dollar
sign ($). In this dual-state support scheme, all 32-BIS state entry points begin with an underscore, and all
16-BIS state entry points begin with a dollar sign. All other compiler-generated identifiers, which are
independent of the state of the processor, begin with an underscore. By this convention, all direct calls
within a 16-bit function refer to the entry point beginning with a dollar sign and all direct calls within a 32bit function refer to the entry point beginning with an underscore.
6.11.2.2 Indirect Calls
Addresses of functions taken in 16-BIS state use the address of the 16-BIS state entry point to the
function (with bit 0 of the address set). Likewise, addresses of functions taken in 32-BIS state use the
address of the 32-BIS state entry point (with bit 0 of the address cleared). Then all indirect calls are
performed by loading the address of the called function into a register and executing the branch and
exchange (BX) instruction. This automatically changes the state and ensures that the code works
correctly, regardless of what state the address was in when it was taken.
The return address must also be set up so that the state of the processor is consistent and known upon
return. Bit 0 of the address is tested to determine if the BX instruction invokes a state change. If it does
not invoke a state change, the return address is set up for the state of the function. If it does invoke a
change, the return address is set up for the alternate state and code is executed to return to the function's
state.
Because the entry point into a function depends upon the state of the function that takes the address, it is
more efficient to take the address of a function when in the same state as that function. This ensures that
the address of the actual function is used, not its alternate entry point. Because the indirect call can invoke
a state change itself, entering a function through its alternate entry point, even if calling it from a different
state, is unnecessary.
Example 6-11 shows sum( ) calling max( ) with code that is compiled for the 16-BIS state and supports
dual-state interworking. The sum( ) function is compiled with the -code_state=16 option, which creates 16bit instructions for pre-UAL assembly code. (Refer to the ARM Assembly Language Tools User's Guide for
information on UAL syntax.) Example 6-14 shows the same function call with code that is compiled for the
32-BIS state and supports dual-state interworking. Function max( ) is compiled without the -code_state=16
option, creating 32-bit instructions.
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Example 6-11. C Code Compiled for 16-BIS State: sum( )
int total = 0;
sum(int val1, int val2)
{
int val = max(val1, val2);
total += val;
}
Example 6-12. 16-Bit Assembly Program for Example 6-11
;***********************************************************
;* FUNCTION VENEER: _sum
*
;***********************************************************
_sum:
.state32
STMFD sp!, {lr}
ADD
lr, pc, #1
BX
lr
.state16
BL
$sum
BX
pc
NOP
.state32
LDMFD sp!, {pc}
.state16
.sect
".text"
.global sum
;***********************************************************
;* FUNCTION DEF: $sum
*
;***********************************************************
$sum:
PUSH
{LR}
BL
$max
LDR
A2, CON1 ; {_total+0}
LDR
A3, [A2, #0]
ADD
A1, A1, A3
STR
A1, [A2, #0]
POP
{PC}
;***********************************************************
;* CONSTANT TABLE
*
;***********************************************************
.sect ".text"
.align 4
CON1: .field _total, 32
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Example 6-13. C Code Compiled for 32-BIS State: sum( )
int max(int a, int b)
{
return a < b ? b : a;
}
Example 6-14. 32-Bit Assembly Program for Example 6-13
;***********************************************************
;* FUNCTION VENEER: $max
*
;***********************************************************
$max:
.state16
BX
pc
NOP
.state32
B
_max
.text
.global _max
;***********************************************************
;* FUNCTION DEF: _max
*
;***********************************************************
_max:
CMP
A1, A2
MOVLE A1, A2
BX
LR
Since sum( ) is a 16-bit function, its entry point is $sum. Because it was compiled for dual-state
interworking, an alternate entry point, _sum, located in a different section is included. All calls to sum( )
requiring a state change use the _sum entry point.
The call to max( ) in sum( ) references $max, because sum( ) is a 16-bit function. If max( ) were a 16-bit
function, sum( ) would call the actual entry point for max( ). However, since max( ) is a 32-bit function,
$max is the alternate entry point for max( ) and handles the state change required by sum( ).
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Chapter 7
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Using Run-Time-Support Functions and Building Libraries
Some of the features of C/C++ (such as I/O, dynamic memory allocation, string operations, and
trigonometric functions) are provided as an ANSI/ISO C/C++ standard library, rather than as part of the
compiler itself. The TI implementation of this library is the run-time-support library (RTS). The C/C++
compiler implements the ISO standard library except for those facilities that handle exception conditions,
signal and locale issues (properties that depend on local language, nationality, or culture). Using the
ANSI/ISO standard library ensures a consistent set of functions that provide for greater portability.
In addition to the ANSI/ISO-specified functions, the run-time-support library includes routines that give you
processor-specific commands and direct C language I/O requests. These are detailed in Section 7.1 and
Section 7.2.
A library-build utility is provided with the code generation tools that lets you create customized run-timesupport libraries. This process is described in Section 7.4 .
178
Topic
...........................................................................................................................
7.1
7.2
7.3
7.4
C and C++ Run-Time Support Libraries ...............................................................
The C I/O Functions ..........................................................................................
Handling Reentrancy (_register_lock() and _register_unlock() Functions) ...............
Library-Build Process .......................................................................................
Using Run-Time-Support Functions and Building Libraries
Page
179
182
194
195
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7.1
C and C++ Run-Time Support Libraries
ARM compiler releases include pre-built run-time support (RTS) libraries that provide all the standard
capabilities. Separate libraries are provided for each mode, big and little endian support, each ABI
(compiler version 4.1.0 and later), various architectures, and C++ exception support. See Section 7.1.8 for
information on the library-naming conventions.
The run-time-support library contains the following:
• ANSI/ISO C/C++ standard library
• C I/O library
• Low-level support functions that provide I/O to the host operating system
• Fundamental arithmetic routines
• System startup routine, _c_int00
• Compiler helper functions (to support language features that are not directly efficiently expressible in
C/C++)
The run-time-support libraries do not contain functions involving signals and locale issues.
The C++ library supports wide chars, in that template functions and classes that are defined for char are
also available for wide char. For example, wide char stream classes wios, wiostream, wstreambuf and so
on (corresponding to char classes ios, iostream, streambuf) are implemented. However, there is no lowlevel file I/O for wide chars. Also, the C library interface to wide char support (through the C++ headers
<cwchar> and <cwctype>) is limited as described in Section 5.1.
TI does not provide documentation that covers the functionality of the C++ library. TI suggests referring to
one of the following sources:
• The Standard C++ Library: A Tutorial and Reference, Nicolai M. Josuttis, Addison-Wesley, ISBN 0201-37926-0
• The C++ Programming Language (Third or Special Editions), Bjarne Stroustrup, Addison-Wesley,
ISBN 0-201-88954-4 or 0-201-70073-5
7.1.1 Linking Code With the Object Library
When you link your program, you must specify the object library as one of the linker input files so that
references to the I/O and run-time-support functions can be resolved. You can either specify the library or
allow the compiler to select one for you. See Section 4.3.1 for further information.
When a library is linked, the linker includes only those library members required to resolve undefined
references. For more information about linking, see the ARM Assembly Language Tools User's Guide.
C, C++, and mixed C and C++ programs can use the same run-time-support library. Run-time-support
functions and variables that can be called and referenced from both C and C++ will have the same
linkage.
If you want to link object files created with the TI CodeGen tools with object files generated by other
compiler tool chains, the ARM standard specifies that you should define the
_AEABI_PORTABILITY_LEVEL preprocessor symbol as follows before #including any standard header
files, such as <stdlib.h>.
#define _AEABI_PORTABILITY_LEVEL 1
This definition enables full portability. Defining the symbol to 0 specifies that the "C standard" portability
level will be used.
7.1.2 Header Files
You must use the header files provided with the compiler run-time support when using functions from
C/C++ standard library. Set the TI_ARM_C_DIR environment variable to the include directory where the
tools are installed.
The following header files provide TI extensions to the C standard:
• cpy_tbl.h -- Declares the copy_in() RTS function, which is used to move code or data from a load
location to a separate run location at run-time. This function helps manage overlays.
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•
•
•
•
•
•
•
•
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file.h -- Declares functions used by low-level I/O functions in the RTS library.
_lock.h -- Used when declaring system-wide mutex locks. This header file is deprecated; use
_reg_mutex_api.h and _mutex.h instead.
memory.h -- Provides the memalign() function, which is not required by the C standard.
_mutex.h -- Declares functions used by the RTS library to help facilitate mutexes for specific resources
that are owned by the RTS. For example, these functions are used for heap or file table allocation.
_pthread.h -- Declares low-level mutex infrastructure functions and provides support for recursive
mutexes.
_reg_mutex_api.h -- Declares a function that can be used by an RTOS to register an underlying lock
mechanism and/or thread ID mechanism that is implemented in the RTOS but is called indirectly by the
RTS’ _mutex.h functions.
_reg_synch_api.h -- Declares a function that can be used by an RTOS to register an underlying cache
synchronization mechanism that is implemented in the RTOS but is called indirectly by the RTS’
_data_synch.h functions.
strings.h -- Provides additional string functions, including bcmp(), bcopy(), bzero(), ffs(), index(),
rindex(), strcasecmp(), and strncasecmp().
7.1.3 Modifying a Library Function
You can inspect or modify library functions by examining the source code in the lib/src subdirectory of the
compiler installation. For example, C:\ti\ccsv7\tools\compiler\arm_#.#.#\lib\src.
One you have located the relevant source code, change the specific function file and rebuild the library.
You can use this source tree to rebuild the rtsv4_A_be_eabi.lib library or to build a new library. See
Section 7.1.8 for details on library naming and Section 7.4 for details on building
7.1.4 Support for String Handling
The library includes the header files <string.h> and <strings.h>, which provide the following functions for
string handling beyond those required.
• string.h
– strdup(), which duplicates a string by dynamically allocating memory and copying the string to this
allocated memory
– strcmp() and strncmp(), which perform case-sensitive string comparisons
– memcpy(), which copies memory from one location to another
– memcmp(), which compares sections of memory
• strings.h
– bcmp(), which is equivalent to memcmp()
– bcopy(), which is equivalent to memmove()
– bzero(), which is equivalent to memset(.., 0, ...);
– ffs(), which finds the first bit set and returns the index of that bit
– index(), which is equivalent to strchr()
– rindex(), which is equivalent to strrchr()
– strcasecmp() and strncasecmp(), which perform case-insensitive string comparisons
7.1.5 Minimal Support for Internationalization
The library includes the header files <locale.h>, <wchar.h>, and <wctype.h>, which provide APIs to
support non-ASCII character sets and conventions. Our implementation of these APIs is limited in the
following ways:
• The library has minimal support for wide and multibyte characters. The type wchar_t is implemented as
int. The wide character set is equivalent to the set of values of type char. The library includes the
header files <wchar.h> and <wctype.h> but does not include all the functions specified in the standard.
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•
See Section 5.6 for more information about extended character sets.
The C library includes the header file <locale.h> but with a minimal implementation. The only
supported locale is the C locale. That is, library behavior that is specified to vary by locale is hardcoded to the behavior of the C locale, and attempting to install a different locale via a call to setlocale()
will return NULL.
7.1.6 Allowable Number of Open Files
In the <stdio.h> header file, the value for the macro FOPEN_MAX has the value of the macro _NFILE,
which is set to 10. The impact is that you can only have 10 files simultaneously open at one time
(including the pre-defined streams - stdin, stdout, stderr).
The C standard requires that the minimum value for the FOPEN_MAX macro is 8. The macro determines
the maximum number of files that can be opened at one time. The macro is defined in the stdio.h header
file and can be modified by changing the value of the _NFILE macro and recompiling the library.
7.1.7 Nonstandard Header Files in the Source Tree
The source code in the lib/src subdirectory of the compiler installation contains these non-ANSI include
files that are used to build the library:
• The values.h file contains the definitions necessary for recompiling the trigonometric and
transcendental math functions. If necessary, you can customize the functions in values.h.
• The file.h file includes macros and definitions used for low-level I/O functions.
• The format.h file includes structures and macros used in printf and scanf.
• The 470cio.h file includes low-level, target-specific C I/O macro definitions. If necessary, you can
customize 470cio.h.
• The rtti.h file includes internal function prototypes necessary to implement run-time type identification.
• The vtbl.h file contains the definition of a class's virtual function table format.
7.1.8 Library Naming Conventions
By default, the linker uses automatic library selection to select the correct run-time-support library (see
Section 4.3.1.1) for your application. If you select the library manually, you must select the matching
library using a naming scheme like the following:
rtsArchVersion_mode_endian[_n][_vn]_abi[_eh].lib
ArchVersion
mode
endian
n
vn
abi
eh
The version of the ARM architecture that the library was built for. This can be one of the
following: v4, v5, v6, v6M0, v7A8, v7R4, v7R5, or v7M3.
Indicates compilation mode:
T
Thumb mode
A
ARM mode
Indicates endianness:
le
Little-endian library
be
Big-endian library
Indicates the library contains NEON support.
Indicates the library has VFP support. n designates the version. Current values are:
2
VFPv2
3
VFPv3
3D16 VFPv3D16
Indicates the application binary interface (ABI) used. Although the TI_ARM9_ABI and
TIARM ABIs are no longer supported, the library filename still contains "_eabi" to
distinguish the EABI libraries from older libraries.
Indicates the library has exception handling support
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The C I/O Functions
7.2
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The C I/O Functions
The C I/O functions make it possible to access the host's operating system to perform I/O. The capability
to perform I/O on the host gives you more options when debugging and testing code.
The I/O functions are logically divided into layers: high level, low level, and device-driver level.
With properly written device drivers, the C-standard high-level I/O functions can be used to perform I/O on
custom user-defined devices. This provides an easy way to use the sophisticated buffering of the highlevel I/O functions on an arbitrary device.
The formatting rules for long long data types require ll (lowercase LL) in the format string. For example:
printf("%lld", 0x0011223344556677);
printf("llx", 0x0011223344556677);
Debugger Required for Default HOST
NOTE: For the default HOST device to work, there must be a debugger to handle the C I/O
requests; the default HOST device cannot work by itself in an embedded system. To work in
an embedded system, you will need to provide an appropriate driver for your system.
NOTE:
C I/O Mysteriously Fails
If there is not enough space on the heap for a C I/O buffer, operations on the file will silently
fail. If a call to printf() mysteriously fails, this may be the reason. The heap needs to be at
least large enough to allocate a block of size BUFSIZ (defined in stdio.h) for every file on
which I/O is performed, including stdout, stdin, and stderr, plus allocations performed by the
user's code, plus allocation bookkeeping overhead. Alternately, declare a char array of size
BUFSIZ and pass it to setvbuf to avoid dynamic allocation. To set the heap size, use the -heap_size option when linking (refer to the Linker Description chapter in the ARM Assembly
Language Tools User's Guide).
NOTE: Open Mysteriously Fails
The run-time support limits the total number of open files to a small number relative to
general-purpose processors. If you attempt to open more files than the maximum, you may
find that the open will mysteriously fail. You can increase the number of open files by
extracting the source code from rts.src and editing the constants controlling the size of some
of the C I/O data structures. The macro _NFILE controls how many FILE (fopen) objects can
be open at one time (stdin, stdout, and stderr count against this total). (See also
FOPEN_MAX.) The macro _NSTREAM controls how many low-level file descriptors can be
open at one time (the low-level files underlying stdin, stdout, and stderr count against this
total). The macro _NDEVICE controls how many device drivers are installed at one time (the
HOST device counts against this total).
7.2.1 High-Level I/O Functions
The high-level functions are the standard C library of stream I/O routines (printf, scanf, fopen, getchar, and
so on). These functions call one or more low-level I/O functions to carry out the high-level I/O request. The
high-level I/O routines operate on FILE pointers, also called streams.
Portable applications should use only the high-level I/O functions.
To use the high-level I/O functions:
• Include the header file stdio.h for each module that references a function.
• Allow for 320 bytes of heap space for each I/O stream used in your program. A stream is a source or
destination of data that is associated with a peripheral, such as a terminal or keyboard. Streams are
buffered using dynamically allocated memory that is taken from the heap. More heap space may be
required to support programs that use additional amounts of dynamically allocated memory (calls to
malloc()). To set the heap size, use the --heap_size option when linking; see Table 2-22.
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For example, given the following C program in a file named main.c:
#include <stdio.h>
void main()
{
FILE *fid;
fid = fopen("myfile","w");
fprintf(fid,"Hello, world\n");
fclose(fid);
printf("Hello again, world\n");
}
Issuing the following compiler command compiles, links, and creates the file main.out from the run-timesupport library:
armcl main.c --run_linker --heap_size=400 --library=rtsv4_A_be_eabi.lib --output_file=main.out
Executing main.out results in
Hello, world
being output to a file and
Hello again, world
being output to your host's stdout window.
7.2.1.1
Formatting and the Format Conversion Buffer
The internal routine behind the C I/O functions—such as printf(), vsnprintf(), and snprintf()—reserves stack
space for a format conversion buffer. The buffer size is set by the macro
FORMAT_CONVERSION_BUFFER, which is defined in format.h. Consider the following issues before
reducing the size of this buffer:
• The default buffer size is 510 bytes. If MINIMAL is defined, the size is set to 32, which allows integer
values without width specifiers to be printed.
• Each conversion specified with %xxxx (except %s) must fit in FORMAT_CONVERSION_BUFSIZE.
This means any individual formatted float or integer value, accounting for width and precision
specifiers, needs to fit in the buffer. Since the actual value of any representable number should easily
fit, the main concern is ensuring the width and/or precision size meets the constraints.
• The length of converted strings using %s are unaffected by any change in
FORMAT_CONVERSION_BUFSIZE. For example, you can specify printf("%s value is %d",
some_really_long_string, intval) without a problem.
•
•
The constraint is for each individual item being converted. For example a format string of
%d item1 %f item2 %e item3 does not need to fit in the buffer. Instead, each converted item
specified with a % format must fit.
There is no buffer overrun check.
7.2.2 Overview of Low-Level I/O Implementation
The low-level functions are comprised of seven basic I/O functions: open, read, write, close, lseek,
rename, and unlink. These low-level routines provide the interface between the high-level functions and
the device-level drivers that actually perform the I/O command on the specified device.
The low-level functions are designed to be appropriate for all I/O methods, even those which are not
actually disk files. Abstractly, all I/O channels can be treated as files, although some operations (such as
lseek) may not be appropriate. See Section 7.2.3 for more details.
The low-level functions are inspired by, but not identical to, the POSIX functions of the same names.
The low-level functions operate on file descriptors. A file descriptor is an integer returned by open,
representing an opened file. Multiple file descriptors may be associated with a file; each has its own
independent file position indicator.
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open — Open File for I/O
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open
Open File for I/O
Syntax
#include <file.h>
int open (const char * path , unsigned flags , int file_descriptor );
Description
The open function opens the file specified by path and prepares it for I/O.
• The path is the filename of the file to be opened, including an optional directory path
and an optional device specifier (see Section 7.2.5).
• The flags are attributes that specify how the file is manipulated. The flags are
specified using the following symbols:
O_RDONLY
O_WRONLY
O_RDWR
O_APPEND
O_CREAT
O_TRUNC
O_BINARY
•
Return Value
184
(0x0000)
(0x0001)
(0x0002)
(0x0008)
(0x0200)
(0x0400)
(0x8000)
/*
/*
/*
/*
/*
/*
/*
open for reading */
open for writing */
open for read & write */
append on each write */
open with file create */
open with truncation */
open in binary mode */
Low-level I/O routines allow or disallow some operations depending on the flags used
when the file was opened. Some flags may not be meaningful for some devices,
depending on how the device implements files.
The file_descriptor is assigned by open to an opened file.
The next available file descriptor is assigned to each new file opened.
The function returns one of the following values:
non-negative file descriptor
if successful
-1
on failure
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close — Close File for I/O
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close
Close File for I/O
Syntax
#include <file.h>
int close (int file_descriptor );
Description
The close function closes the file associated with file_descriptor.
The file_descriptor is the number assigned by open to an opened file.
Return Value
The return value is one of the following:
0
if successful
-1
on failure
read
Read Characters from a File
Syntax
#include <file.h>
int read (int file_descriptor , char * buffer , unsigned count );
Description
The read function reads count characters into the buffer from the file associated with
file_descriptor.
• The file_descriptor is the number assigned by open to an opened file.
• The buffer is where the read characters are placed.
• The count is the number of characters to read from the file.
Return Value
The function returns one of the following values:
0
if EOF was encountered before any characters were read
#
number of characters read (may be less than count)
-1
on failure
write
Write Characters to a File
Syntax
#include <file.h>
int write (int file_descriptor , const char * buffer , unsigned count );
Description
The write function writes the number of characters specified by count from the buffer to
the file associated with file_descriptor.
• The file_descriptor is the number assigned by open to an opened file.
• The buffer is where the characters to be written are located.
• The count is the number of characters to write to the file.
Return Value
The function returns one of the following values:
#
number of characters written if successful (may be less than count)
-1
on failure
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lseek — Set File Position Indicator
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lseek
Set File Position Indicator
Syntax for C
#include <file.h>
off_t lseek (int file_descriptor , off_t offset , int origin );
Description
The lseek function sets the file position indicator for the given file to a location relative to
the specified origin. The file position indicator measures the position in characters from
the beginning of the file.
• The file_descriptor is the number assigned by open to an opened file.
• The offset indicates the relative offset from the origin in characters.
• The origin is used to indicate which of the base locations the offset is measured from.
The origin must be one of the following macros:
SEEK_SET (0x0000) Beginning of file
SEEK_CUR (0x0001) Current value of the file position indicator
SEEK_END (0x0002) End of file
Return Value
The return value is one of the following:
#
new value of the file position indicator if successful
(off_t)-1 on failure
unlink
Delete File
Syntax
#include <file.h>
int unlink (const char * path );
Description
The unlink function deletes the file specified by path. Depending on the device, a deleted
file may still remain until all file descriptors which have been opened for that file have
been closed. See Section 7.2.3.
The path is the filename of the file, including path information and optional device prefix.
(See Section 7.2.5.)
Return Value
186
The function returns one of the following values:
0
if successful
-1
on failure
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rename — Rename File
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rename
Rename File
Syntax for C
#include {<stdio.h> | <file.h>}
int rename (const char * old_name , const char * new_name );
Syntax for C++
#include {<cstdio> | <file.h>}
int std::rename (const char * old_name , const char * new_name );
Description
The rename function changes the name of a file.
• The old_name is the current name of the file.
• The new_name is the new name for the file.
NOTE: The optional device specified in the new name must match the device of
the old name. If they do not match, a file copy would be required to
perform the rename, and rename is not capable of this action.
Return Value
The function returns one of the following values:
0
if successful
-1
on failure
NOTE:
Although rename is a low-level function, it is defined by the C standard
and can be used by portable applications.
7.2.3 Device-Driver Level I/O Functions
At the next level are the device-level drivers. They map directly to the low-level I/O functions. The default
device driver is the HOST device driver, which uses the debugger to perform file operations. The HOST
device driver is automatically used for the default C streams stdin, stdout, and stderr.
The HOST device driver shares a special protocol with the debugger running on a host system so that the
host can perform the C I/O requested by the program. Instructions for C I/O operations that the program
wants to perform are encoded in a special buffer named _CIOBUF_ in the .cio section. The debugger
halts the program at a special breakpoint (C$$IO$$), reads and decodes the target memory, and performs
the requested operation. The result is encoded into _CIOBUF_, the program is resumed, and the target
decodes the result.
The HOST device is implemented with seven functions, HOSTopen, HOSTclose, HOSTread, HOSTwrite,
HOSTlseek, HOSTunlink, and HOSTrename, which perform the encoding. Each function is called from the
low-level I/O function with a similar name.
A device driver is composed of seven required functions. Not all function need to be meaningful for all
devices, but all seven must be defined. Here we show the names of all seven functions as starting with
DEV, but you may choose any name except for HOST.
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DEV_open — Open File for I/O
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DEV_open
Open File for I/O
Syntax
int DEV_open (const char * path , unsigned flags , int llv_fd );
Description
This function finds a file matching path and opens it for I/O as requested by flags.
• The path is the filename of the file to be opened. If the name of a file passed to open
has a device prefix, the device prefix will be stripped by open, so DEV_open will not
see it. (See Section 7.2.5 for details on the device prefix.)
• The flags are attributes that specify how the file is manipulated. The flags are
specified using the following symbols:
O_RDONLY
O_WRONLY
O_RDWR
O_APPEND
O_CREAT
O_TRUNC
O_BINARY
•
(0x0000)
(0x0001)
(0x0002)
(0x0008)
(0x0200)
(0x0400)
(0x8000)
/*
/*
/*
/*
/*
/*
/*
open for reading */
open for writing */
open for read & write */
append on each write */
open with file create */
open with truncation */
open in binary mode */
See POSIX for further explanation of the flags.
The llv_fd is treated as a suggested low-level file descriptor. This is a historical
artifact; newly-defined device drivers should ignore this argument. This differs from
the low-level I/O open function.
This function must arrange for information to be saved for each file descriptor, typically
including a file position indicator and any significant flags. For the HOST version, all the
bookkeeping is handled by the debugger running on the host machine. If the device uses
an internal buffer, the buffer can be created when a file is opened, or the buffer can be
created during a read or write.
Return Value
This function must return -1 to indicate an error if for some reason the file could not be
opened; such as the file does not exist, could not be created, or there are too many files
open. The value of errno may optionally be set to indicate the exact error (the HOST
device does not set errno). Some devices might have special failure conditions; for
instance, if a device is read-only, a file cannot be opened O_WRONLY.
On success, this function must return a non-negative file descriptor unique among all
open files handled by the specific device. The file descriptor need not be unique across
devices. The device file descriptor is used only by low-level functions when calling the
device-driver-level functions. The low-level function open allocates its own unique file
descriptor for the high-level functions to call the low-level functions. Code that uses only
high-level I/O functions need not be aware of these file descriptors.
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DEV_close — Close File for I/O
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DEV_close
Close File for I/O
Syntax
int DEV_close (int dev_fd );
Description
This function closes a valid open file descriptor.
On some devices, DEV_close may need to be responsible for checking if this is the last
file descriptor pointing to a file that was unlinked. If so, it is responsible for ensuring that
the file is actually removed from the device and the resources reclaimed, if appropriate.
Return Value
This function should return -1 to indicate an error if the file descriptor is invalid in some
way, such as being out of range or already closed, but this is not required. The user
should not call close() with an invalid file descriptor.
DEV_read
Read Characters from a File
Syntax
int DEV_read (int dev_fd , char * buf , unsigned count );
Description
The read function reads count bytes from the input file associated with dev_fd.
• The dev_fd is the number assigned by open to an opened file.
• The buf is where the read characters are placed.
• The count is the number of characters to read from the file.
Return Value
This function must return -1 to indicate an error if for some reason no bytes could be
read from the file. This could be because of an attempt to read from a O_WRONLY file,
or for device-specific reasons.
If count is 0, no bytes are read and this function returns 0.
This function returns the number of bytes read, from 0 to count. 0 indicates that EOF
was reached before any bytes were read. It is not an error to read less than count bytes;
this is common if the are not enough bytes left in the file or the request was larger than
an internal device buffer size.
DEV_write
Write Characters to a File
Syntax
int DEV_write (int dev_fd , const char * buf , unsigned count );
Description
This function writes count bytes to the output file.
• The dev_fd is the number assigned by open to an opened file.
• The buffer is where the write characters are placed.
• The count is the number of characters to write to the file.
Return Value
This function must return -1 to indicate an error if for some reason no bytes could be
written to the file. This could be because of an attempt to read from a O_RDONLY file,
or for device-specific reasons.
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DEV_lseek — Set File Position Indicator
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DEV_lseek
Set File Position Indicator
Syntax
off_t DEV_lseek (int dev_fd , off_t offset , int origin );
Description
This function sets the file's position indicator for this file descriptor as lseek.
If lseek is supported, it should not allow a seek to before the beginning of the file, but it
should support seeking past the end of the file. Such seeks do not change the size of
the file, but if it is followed by a write, the file size will increase.
Return Value
If successful, this function returns the new value of the file position indicator.
This function must return -1 to indicate an error if for some reason no bytes could be
written to the file. For many devices, the lseek operation is nonsensical (e.g. a computer
monitor).
DEV_unlink
Delete File
Syntax
int DEV_unlink (const char * path );
Description
Remove the association of the pathname with the file. This means that the file may no
longer be opened using this name, but the file may not actually be immediately removed.
Depending on the device, the file may be immediately removed, but for a device which
allows open file descriptors to point to unlinked files, the file will not actually be deleted
until the last file descriptor is closed. See Section 7.2.3.
Return Value
This function must return -1 to indicate an error if for some reason the file could not be
unlinked (delayed removal does not count as a failure to unlink.)
If successful, this function returns 0.
DEV_rename
Rename File
Syntax
int DEV_rename (const char * old_name , const char * new_name );
Description
This function changes the name associated with the file.
• The old_name is the current name of the file.
• The new_name is the new name for the file.
Return Value
This function must return -1 to indicate an error if for some reason the file could not be
renamed, such as the file doesn't exist, or the new name already exists.
NOTE: It is inadvisable to allow renaming a file so that it is on a different device.
In general this would require a whole file copy, which may be more
expensive than you expect.
If successful, this function returns 0.
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7.2.4 Adding a User-Defined Device Driver for C I/O
The function add_device allows you to add and use a device. When a device is registered with
add_device, the high-level I/O routines can be used for I/O on that device.
You can use a different protocol to communicate with any desired device and install that protocol using
add_device; however, the HOST functions should not be modified. The default streams stdin, stdout, and
stderr can be remapped to a file on a user-defined device instead of HOST by using freopen() as in
Example 7-1. If the default streams are reopened in this way, the buffering mode will change to _IOFBF
(fully buffered). To restore the default buffering behavior, call setvbuf on each reopened file with the
appropriate value (_IOLBF for stdin and stdout, _IONBF for stderr).
The default streams stdin, stdout, and stderr can be mapped to a file on a user-defined device instead of
HOST by using freopen() as shown in Example 7-1. Each function must set up and maintain its own data
structures as needed. Some function definitions perform no action and should just return.
Example 7-1. Mapping Default Streams to Device
#include <stdio.h>
#include <file.h>
#include "mydevice.h"
void main()
{
add_device("mydevice", _MSA,
MYDEVICE_open, MYDEVICE_close,
MYDEVICE_read, MYDEVICE_write,
MYDEVICE_lseek, MYDEVICE_unlink, MYDEVICE_rename);
/*-----------------------------------------------------------------------*/
/* Re-open stderr as a MYDEVICE file
*/
/*-----------------------------------------------------------------------*/
if (!freopen("mydevice:stderrfile", "w", stderr))
{
puts("Failed to freopen stderr");
exit(EXIT_FAILURE);
}
/*-----------------------------------------------------------------------*/
/* stderr should not be fully buffered; we want errors to be seen as
*/
/* soon as possible. Normally stderr is line-buffered, but this example */
/* doesn't buffer stderr at all. This means that there will be one call */
/* to write() for each character in the message.
*/
/*-----------------------------------------------------------------------*/
if (setvbuf(stderr, NULL, _IONBF, 0))
{
puts("Failed to setvbuf stderr");
exit(EXIT_FAILURE);
}
/*-----------------------------------------------------------------------*/
/* Try it out!
*/
/*-----------------------------------------------------------------------*/
printf("This goes to stdout\n");
fprintf(stderr, "This goes to stderr\n"); }
NOTE:
Use Unique Function Names
The function names open, read, write, close, lseek, rename, and unlink are used by the lowlevel routines. Use other names for the device-level functions that you write.
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Use the low-level function add_device() to add your device to the device_table. The device table is a
statically defined array that supports n devices, where n is defined by the macro _NDEVICE found in
stdio.h/cstdio.
The first entry in the device table is predefined to be the host device on which the debugger is running.
The low-level routine add_device() finds the first empty position in the device table and initializes the
device fields with the passed-in arguments. For a complete description, see the add_device function.
7.2.5 The device Prefix
A file can be opened to a user-defined device driver by using a device prefix in the pathname. The device
prefix is the device name used in the call to add_device followed by a colon. For example:
FILE *fptr = fopen("mydevice:file1", "r");
int fd = open("mydevice:file2, O_RDONLY, 0);
If no device prefix is used, the HOST device will be used to open the file.
add_device
Add Device to Device Table
Syntax for C
#include <file.h>
int add_device(char * name,
unsigned flags ,
int (* dopen )(const char *path, unsigned flags, int llv_fd),
int (* dclose )( int dev_fd),
int (* dread )(intdev_fd, char *buf, unsigned count),
int (* dwrite )(int dev_fd, const char *buf, unsigned count),
off_t (* dlseek )(int dev_fd, off_t ioffset, int origin),
int (* dunlink )(const char * path),
int (* drename )(const char *old_name, const char *new_name));
Defined in
lowlev.c (in the lib/src subdirectory of the compiler installation)
Description
The add_device function adds a device record to the device table allowing that device to
be used for I/O from C. The first entry in the device table is predefined to be the HOST
device on which the debugger is running. The function add_device() finds the first empty
position in the device table and initializes the fields of the structure that represent a
device.
To open a stream on a newly added device use fopen( ) with a string of the format
devicename : filename as the first argument.
• The name is a character string denoting the device name. The name is limited to 8
characters.
• The flags are device characteristics. The flags are as follows:
_SSA Denotes that the device supports only one open stream at a time
_MSA Denotes that the device supports multiple open streams
More flags can be added by defining them in file.h.
• The dopen, dclose, dread, dwrite, dlseek, dunlink, and drename specifiers are
function pointers to the functions in the device driver that are called by the low-level
functions to perform I/O on the specified device. You must declare these functions
with the interface specified in Section 7.2.2. The device driver for the HOST that the
ARM debugger is run on are included in the C I/O library.
Return Value
192
The function returns one of the following values:
0
if successful
-1
on failure
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Example
Example 7-2 does the following:
• Adds the device mydevice to the device table
• Opens a file named test on that device and associates it with the FILE pointer fid
• Writes the string Hello, world into the file
• Closes the file
Example 7-2 illustrates adding and using a device for C I/O:
Example 7-2. Program for C I/O Device
#include <file.h>
#include <stdio.h>
/****************************************************************************/
/* Declarations of the user-defined device drivers
*/
/****************************************************************************/
extern int
MYDEVICE_open(const char *path, unsigned flags, int fno);
extern int
MYDEVICE_close(int fno);
extern int
MYDEVICE_read(int fno, char *buffer, unsigned count);
extern int
MYDEVICE_write(int fno, const char *buffer, unsigned count);
extern off_t MYDEVICE_lseek(int fno, off_t offset, int origin);
extern int
MYDEVICE_unlink(const char *path);
extern int
MYDEVICE_rename(const char *old_name, char *new_name);
main()
{
FILE *fid;
add_device("mydevice", _MSA, MYDEVICE_open, MYDEVICE_close, MYDEVICE_read,
MYDEVICE_write, MYDEVICE_lseek, MYDEVICE_unlink, MYDEVICE_rename);
fid = fopen("mydevice:test","w");
fprintf(fid,"Hello, world\n");
fclose(fid);
}
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Handling Reentrancy (_register_lock() and _register_unlock() Functions)
The C standard assumes only one thread of execution, with the only exception being extremely narrow
support for signal handlers. The issue of reentrancy is avoided by not allowing you to do much of anything
in a signal handler. However, SYS/BIOS applications have multiple threads which need to modify the
same global program state, such as the CIO buffer, so reentrancy is a concern.
Part of the problem of reentrancy remains your responsibility, but the run-time-support environment does
provide rudimentary support for multi-threaded reentrancy by providing support for critical sections. This
implementation does not protect you from reentrancy issues such as calling run-time-support functions
from inside interrupts; this remains your responsibility.
The run-time-support environment provides hooks to install critical section primitives. By default, a singlethreaded model is assumed, and the critical section primitives are not employed. In a multi-threaded
system such as SYS/BIOS, the kernel arranges to install semaphore lock primitive functions in these
hooks, which are then called when the run-time-support enters code that needs to be protected by a
critical section.
Throughout the run-time-support environment where a global state is accessed, and thus needs to be
protected with a critical section, there are calls to the function _lock(). This calls the provided primitive, if
installed, and acquires the semaphore before proceeding. Once the critical section is finished, _unlock() is
called to release the semaphore.
Usually SYS/BIOS is responsible for creating and installing the primitives, so you do not need to take any
action. However, this mechanism can be used in multi-threaded applications that do not use the
SYS/BIOS locking mechanism.
You should not define the functions _lock() and _unlock() functions directly; instead, the installation
functions are called to instruct the run-time-support environment to use these new primitives:
void _register_lock
(void (
*lock)());
void _register_unlock(void (*unlock)());
The arguments to _register_lock() and _register_unlock() should be functions which take no arguments
and return no values, and which implement some sort of global semaphore locking:
extern volatile sig_atomic_t *sema = SHARED_SEMAPHORE_LOCATION;
static int sema_depth = 0;
static void my_lock(void)
{
while (ATOMIC_TEST_AND_SET(sema, MY_UNIQUE_ID) != MY_UNIQUE_ID);
sema_depth++;
}
static void my_unlock(void)
{
if (!--sema_depth) ATOMIC_CLEAR(sema);
}
The run-time-support nests calls to _lock(), so the primitives must keep track of the nesting level.
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7.4
Library-Build Process
When using the C/C++ compiler, you can compile your code under a large number of different
configurations and options that are not necessarily compatible with one another. Because it would be
infeasible to include all possible run-time-support library variants, compiler releases pre-build only a small
number of very commonly-used libraries.
To provide maximum flexibility, the run-time-support source code is provided as part of each compiler
release. You can build the missing libraries as desired. The linker can also automatically build missing
libraries. This is accomplished with a new library build process, the core of which is the executable mklib,
which is available beginning with CCS 5.1.
7.4.1 Required Non-Texas Instruments Software
To use the self-contained run-time-support build process to rebuild a library with custom options, the
following are required:
• sh (Bourne shell)
• gmake (GNU make 3.81 or later)
More information is available from GNU at http://www.gnu.org/software/make. GNU make (gmake) is
also available in earlier versions of Code Composer Studio. GNU make is also included in some UNIX
support packages for Windows, such as the MKS Toolkit, Cygwin, and Interix. The GNU make used on
Windows platforms should explicitly report "This program build for Windows32" when the following is
executed from the Command Prompt window:
gmake -h
All three of these programs are provided as a non-optional feature of CCS 5.1. They are also available as
part of the optional XDC Tools feature if you are using an earlier version of CCS.
The mklib program looks for these executables in the following order:
1. in your PATH
2. in the directory getenv("CCS_UTILS_DIR")/cygwin
3. in the directory getenv("CCS_UTILS_DIR")/bin
4. in the directory getenv("XDCROOT")
5. in the directory getenv("XDCROOT")/bin
If you are invoking mklib from the command line, and these executables are not in your path, you must set
the environment variable CCS_UTILS_DIR such that getenv("CCS_UTILS_DIR")/bin contains the correct
programs.
7.4.2 Using the Library-Build Process
You should normally let the linker automatically rebuild libraries as needed. If necessary, you can run
mklib directly to populate libraries. See Section 7.4.2.2 for situations when you might want to do this.
7.4.2.1
Automatic Standard Library Rebuilding by the Linker
The linker looks for run-time-support libraries primarily through the TI_ARM_C_DIR environment variable.
Typically, one of the pathnames in TI_ARM_C_DIR is your install directory/lib, which contains all of the
pre-built libraries, as well as the index library libc.a. The linker looks in TI_ARM_C_DIR to find a library
that is the best match for the build attributes of the application. The build attributes are set indirectly
according to the command-line options used to build the application. Build attributes include things like
CPU revision. If the library name is explicitly specified (e.g. -library=rtsv4_A_be_eabi), run-time support
looks for that library exactly. If the library name is not specified, the linker uses the index library libc.a to
pick an appropriate library. If the library is specified by path (e.g. –library=/foo/rtsv4_A_be_eabi), it is
assumed the library already exists and it will not be built automatically.
The index library describes a set of libraries with different build attributes. The linker will compare the build
attributes for each potential library with the build attributes of the application and will pick the best fit. For
details on the index library, see the archiver chapter in the ARM Assembly Language Tools User's Guide.
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Now that the linker has decided which library to use, it checks whether the run-time-support library is
present in TI_ARM_C_DIR . The library must be in exactly the same directory as the index library libc.a. If
the library is not present, the linker invokes mklib to build it. This happens when the library is missing,
regardless of whether the user specified the name of the library directly or allowed the linker to pick the
best library from the index library.
The mklib program builds the requested library and places it in 'lib' directory part of TI_ARM_C_DIR in the
same directory as the index library, so it is available for subsequent compilations.
Things to watch out for:
• The linker invokes mklib and waits for it to finish before finishing the link, so you will experience a onetime delay when an uncommonly-used library is built for the first time. Build times of 1-5 minutes have
been observed. This depends on the power of the host (number of CPUs, etc).
• In a shared installation, where an installation of the compiler is shared among more than one user, it is
possible that two users might cause the linker to rebuild the same library at the same time. The mklib
program tries to minimize the race condition, but it is possible one build will corrupt the other. In a
shared environment, all libraries which might be needed should be built at install time; see
Section 7.4.2.2 for instructions on invoking mklib directly to avoid this problem.
• The index library must exist, or the linker is unable to rebuild libraries automatically.
• The index library must be in a user-writable directory, or the library is not built. If the compiler
installation must be installed read-only (a good practice for shared installation), any missing libraries
must be built at installation time by invoking mklib directly.
• The mklib program is specific to a certain version of a certain library; you cannot use one compiler
version's run-time support's mklib to build a different compiler version's run-time support library.
7.4.2.2
Invoking mklib Manually
You may need to invoke mklib directly in special circumstances:
• The compiler installation directory is read-only or shared.
• You want to build a variant of the run-time-support library that is not pre-configured in the index library
libc.a or known to mklib. (e.g. a variant with source-level debugging turned on.)
7.4.2.2.1 Building Standard Libraries
You can invoke mklib directly to build any or all of the libraries indexed in the index library libc.a. The
libraries are built with the standard options for that library; the library names and the appropriate standard
option sets are known to mklib.
This is most easily done by changing the working directory to be the compiler run-time-support library
directory 'lib' and invoking the mklib executable there:
mklib --pattern=rtsv4_A_be_eabi.lib
7.4.2.2.2 Shared or Read-Only Library Directory
If the compiler tools are to be installed in shared or read-only directory, mklib cannot build the standard
libraries at link time; the libraries must be built before the library directory is made shared or read-only.
At installation time, the installing user must build all of the libraries which will be used by any user. To
build all possible libraries, change the working directory to be the compiler RTS library directory 'lib' and
invoke the mklib executable there:
mklib --all
Some targets have many libraries, so this step can take a long time. To build a subset of the libraries,
invoke mklib individually for each desired library.
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7.4.2.2.3 Building Libraries With Custom Options
You can build a library with any extra custom options desired. This is useful for building a version of the
library with silicon exception workarounds enabled. The generated library is not a standard library, and
must not be placed in the 'lib' directory. It should be placed in a directory local to the project which needs
it. To build a debugging version of the library rtsv4_A_be_eabi, change the working directory to the 'lib'
directory and run the command:
mklib --pattern=rtsv4_A_be_eabi.lib --name=rtsv4_A_be_eabi_debug.lib
--install_to=$Project/Debug --extra_options="-g"
7.4.2.2.4 The mklib Program Option Summary
Run the following command to see the full list of options. These are described in Table 7-1.
mklib --help
Table 7-1. The mklib Program Options
Option
Effect
--index=filename
The index library (libc.a) for this release. Used to find a template library for custom builds, and to find the
source files (in the lib/src subdirectory of the compiler installation). REQUIRED.
--pattern=filename
Pattern for building a library. If neither --extra_options nor --options are specified, the library will be the
standard library with the standard options for that library. If either --extra_options or --options are
specified, the library is a custom library with custom options. REQUIRED unless --all is used.
--all
Build all standard libraries at once.
--install_to=directory
The directory into which to write the library. For a standard library, this defaults to the same directory as
the index library (libc.a). For a custom library, this option is REQUIRED.
--compiler_bin_dir=
directory
The directory where the compiler executables are. When invoking mklib directly, the executables should
be in the path, but if they are not, this option must be used to tell mklib where they are. This option is
primarily for use when mklib is invoked by the linker.
--name=filename
File name for the library with no directory part. Only useful for custom libraries.
--options='str'
Options to use when building the library. The default options (see below) are replaced by this string. If
this option is used, the library will be a custom library.
--extra_options='str'
Options to use when building the library. The default options (see below) are also used. If this option is
used, the library will be a custom library.
--list_libraries
List the libraries this script is capable of building and exit. ordinary system-specific directory.
--log=filename
Save the build log as filename.
--tmpdir=directory
Use directory for scratch space instead of the ordinary system-specific directory.
--gmake=filename
Gmake-compatible program to invoke instead of "gmake"
--parallel=N
Compile N files at once ("gmake -j N").
--query=filename
Does this script know how to build FILENAME?
--help or --h
Display this help.
--quiet or --q
Operate silently.
--verbose or --v
Extra information to debug this executable.
Examples:
To build all standard libraries and place them in the compiler's library directory:
mklib --all --index=$C_DIR/lib
To build one standard library and place it in the compiler's library directory:
mklib --pattern=rtsv4_A_be_eabi.lib --index=$C_DIR/lib
To build a custom library that is just like rtsv4_A_be_eabi.lib, but has symbolic debugging support
enabled:
mklib --pattern=rts16.lib --extra_options="-g" --index=$C_DIR/lib --install_to=$Project/Debug
--name=rtsv4_A_be_eabi_debug.lib
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7.4.3 Extending mklib
The mklib API is a uniform interface that allows Code Composer Studio to build libraries without needing
to know exactly what underlying mechanism is used to build it. Each library vendor (e.g. the TI compiler)
provides a library-specific copy of 'mklib' in the library directory that can be invoked, which understands a
standardized set of options, and understands how to build the library. This allows the linker to
automatically build application-compatible versions of any vendor's library without needing to register the
library in advance, as long as the vendor supports mklib.
7.4.3.1
Underlying Mechanism
The underlying mechanism can be anything the vendor desires. For the compiler run-time-support
libraries, mklib is just a wrapper that knows how to use the files in the lib/src subdirectory of the compiler
installation and invoke gmake with the appropriate options to build each library. If necessary, mklib can be
bypassed and the Makefile used directly, but this mode of operation is not supported by TI, and you are
responsible for any changes to the Makefile. The format of the Makefile and the interface between mklib
and the Makefile is subject to change without notice. The mklib program is the forward-compatible path.
7.4.3.2
Libraries From Other Vendors
Any vendor who wishes to distribute a library that can be rebuilt automatically by the linker must provide:
• An index library (like 'libc.a', but with a different name)
• A copy of mklib specific to that library
• A copy of the library source code (in whatever format is convenient)
These things must be placed together in one directory that is part of the linker's library search path
(specified either in TI_ARM_C_DIR or with the linker --search_path option).
If mklib needs extra information that is not possible to pass as command-line options to the compiler, the
vendor will need to provide some other means of discovering the information (such as a configuration file
written by a wizard run from inside CCS).
The vendor-supplied mklib must at least accept all of the options listed in Table 7-1 without error, even if
they do not do anything.
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Chapter 8
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C++ Name Demangler
The C++ compiler implements function overloading, operator overloading, and type-safe linking by
encoding a function's prototype and namespace in its link-level name. The process of encoding the
prototype into the linkname is often referred to as name mangling. When you inspect mangled names,
such as in assembly files, disassembler output, or compiler or linker diagnostic messages, it can be
difficult to associate a mangled name with its corresponding name in the C++ source code. The C++ name
demangler is a debugging aid that translates each mangled name it detects to its original name found in
the C++ source code.
These topics tell you how to invoke and use the C++ name demangler. The C++ name demangler reads
in input, looking for mangled names. All unmangled text is copied to output unaltered. All mangled names
are demangled before being copied to output.
Topic
8.1
8.2
...........................................................................................................................
Page
Invoking the C++ Name Demangler ..................................................................... 200
Sample Usage of the C++ Name Demangler ......................................................... 201
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Invoking the C++ Name Demangler
The syntax for invoking the C++ name demangler is:
armdem [options ] [filenames]
armdem
options
filenames
Command that invokes the C++ name demangler.
Options affect how the name demangler behaves. Options can appear anywhere on the
command line.
Text input files, such as the assembly file output by the compiler, the assembler listing file,
the disassembly file, and the linker map file. If no filenames are specified on the command
line, armdem uses standard input.
By default, the C++ name demangler outputs to standard output. You can use the -o file option if you want
to output to a file.
The following options apply only to the C++ name demangler:
--debug (--d)
--diag_wrap[=on,off]
--help (-h)
--output= file (-o)
--quiet (-q)
-u
200
C++ Name Demangler
Prints debug messages.
Sets diagnostic messages to wrap at 79 columns (on, which is the default)
or not (off).
Prints a help screen that provides an online summary of the C++ name
demangler options.
Outputs to the specified file rather than to standard out.
Reduces the number of messages generated during execution.
Specifies that external names do not have a C++ prefix. (deprecated)
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8.2
Sample Usage of the C++ Name Demangler
The examples in this section illustrate the demangling process. Example 8-1 shows a sample C++
program. Example 8-2 shows the resulting assembly that is output by the compiler. In this example, the
linknames of all the functions are mangled; that is, their signature information is encoded into their names.
Example 8‑1. C++ Code for calories_in_a_banana
class banana {
public:
int calories(void);
banana();
~banana();
};
int calories_in_a_banana(void)
{
banana x;
return x.calories();
}
Example 8‑2. Resulting Assembly for calories_in_a_banana
_Z20calories_in_a_bananav:
STMFD
SP!, {A3, A4, V1, LR}
MOV
A1, SP
BL
_ZN6bananaC1Ev
BL
_ZN6banana8caloriesEv
MOV
V1, A1
MOV
A1, SP
BL
_ZN6bananaD1Ev
MOV
A1, V1
LDMFD
SP!, {A3, A4, V1, LR}
BX
LR
Executing the C++ name demangler demangles all names that it believes to be mangled. Enter:
armdem calories_in_a_banana.asm
The result is shown in Example 8-3. The linknames in Example 8-2 _ZN6bananaC1Ev,
_ZN6banana8caloriesEv, and _ZN6bananaD1Ev are demangled.
Example 8‑3. Result After Running the C++ Name Demangler
calories_in_a_banana():
STMFD
SP!, {A3, A4, V1, LR}
MOV
A1, SP
BL
banana::banana()
BL
banana::calories()
MOV
V1, A1
MOV
A1, SP
BL
banana::~banana()
MOV
A1, V1
LDMFD
SP!, {A3, A4, V1, LR}
BX
LR
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Appendix A
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Glossary
A.1
Terminology
absolute lister— A debugging tool that allows you to create assembler listings that contain absolute
addresses.
Application Binary Interface (ABI)— A standard that specifies the interface between two object
modules. An ABI specifies how functions are called and how information is passed from one
program component to another.
assignment statement— A statement that initializes a variable with a value.
autoinitialization— The process of initializing global C variables (contained in the .cinit section) before
program execution begins.
autoinitialization at run time— An autoinitialization method used by the linker when linking C code. The
linker uses this method when you invoke it with the --rom_model link option. The linker loads the
.cinit section of data tables into memory, and variables are initialized at run time.
alias disambiguation— A technique that determines when two pointer expressions cannot point to the
same location, allowing the compiler to freely optimize such expressions.
aliasing— The ability for a single object to be accessed in more than one way, such as when two
pointers point to a single object. It can disrupt optimization, because any indirect reference could
refer to any other object.
allocation— A process in which the linker calculates the final memory addresses of output sections.
ANSI— American National Standards Institute; an organization that establishes standards voluntarily
followed by industries.
archive library— A collection of individual files grouped into a single file by the archiver.
archiver— A software program that collects several individual files into a single file called an archive
library. With the archiver, you can add, delete, extract, or replace members of the archive library.
assembler— A software program that creates a machine-language program from a source file that
contains assembly language instructions, directives, and macro definitions. The assembler
substitutes absolute operation codes for symbolic operation codes and absolute or relocatable
addresses for symbolic addresses.
assignment statement— A statement that initializes a variable with a value.
autoinitialization— The process of initializing global C variables (contained in the .cinit section) before
program execution begins.
autoinitialization at run time— An autoinitialization method used by the linker when linking C code. The
linker uses this method when you invoke it with the --rom_model link option. The linker loads the
.cinit section of data tables into memory, and variables are initialized at run time.
big endian— An addressing protocol in which bytes are numbered from left to right within a word. More
significant bytes in a word have lower numbered addresses. Endian ordering is hardware-specific
and is determined at reset. See also little endian
BIS— Bit instruction set.
202
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block— A set of statements that are grouped together within braces and treated as an entity.
.bss section— One of the default object file sections. You use the assembler .bss directive to reserve a
specified amount of space in the memory map that you can use later for storing data. The .bss
section is uninitialized.
byte— Per ANSI/ISO C, the smallest addressable unit that can hold a character.
C/C++ compiler— A software program that translates C source statements into assembly language
source statements.
code generator— A compiler tool that takes the file produced by the parser or the optimizer and
produces an assembly language source file.
COFF— Common object file format; a system of object files configured according to a standard
developed by AT&T. This ABI is no longer supported.
command file— A file that contains options, filenames, directives, or commands for the linker or hex
conversion utility.
comment— A source statement (or portion of a source statement) that documents or improves
readability of a source file. Comments are not compiled, assembled, or linked; they have no effect
on the object file.
compiler program— A utility that lets you compile, assemble, and optionally link in one step. The
compiler runs one or more source modules through the compiler (including the parser, optimizer,
and code generator), the assembler, and the linker.
configured memory— Memory that the linker has specified for allocation.
constant— A type whose value cannot change.
cross-reference listing— An output file created by the assembler that lists the symbols that were
defined, what line they were defined on, which lines referenced them, and their final values.
.data section— One of the default object file sections. The .data section is an initialized section that
contains initialized data. You can use the .data directive to assemble code into the .data section.
direct call— A function call where one function calls another using the function's name.
directives— Special-purpose commands that control the actions and functions of a software tool (as
opposed to assembly language instructions, which control the actions of a device).
disambiguation— See alias disambiguation
dynamic memory allocation— A technique used by several functions (such as malloc, calloc, and
realloc) to dynamically allocate memory for variables at run time. This is accomplished by defining a
large memory pool (heap) and using the functions to allocate memory from the heap.
ELF— Executable and Linkable Format; a system of object files configured according to the System V
Application Binary Interface specification.
emulator— A hardware development system that duplicates the ARM operation.
entry point— A point in target memory where execution starts.
environment variable— A system symbol that you define and assign to a string. Environmental variables
are often included in Windows batch files or UNIX shell scripts such as .cshrc or .profile.
epilog— The portion of code in a function that restores the stack and returns.
executable object file— A linked, executable object file that is downloaded and executed on a target
system.
expression— A constant, a symbol, or a series of constants and symbols separated by arithmetic
operators.
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Terminology
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external symbol— A symbol that is used in the current program module but defined or declared in a
different program module.
file-level optimization— A level of optimization where the compiler uses the information that it has about
the entire file to optimize your code (as opposed to program-level optimization, where the compiler
uses information that it has about the entire program to optimize your code).
function inlining— The process of inserting code for a function at the point of call. This saves the
overhead of a function call and allows the optimizer to optimize the function in the context of the
surrounding code.
global symbol— A symbol that is either defined in the current module and accessed in another, or
accessed in the current module but defined in another.
high-level language debugging— The ability of a compiler to retain symbolic and high-level language
information (such as type and function definitions) so that a debugging tool can use this
information.
indirect call— A function call where one function calls another function by giving the address of the
called function.
initialization at load time— An autoinitialization method used by the linker when linking C/C++ code. The
linker uses this method when you invoke it with the --ram_model link option. This method initializes
variables at load time instead of run time.
initialized section— A section from an object file that will be linked into an executable object file.
input section— A section from an object file that will be linked into an executable object file.
integrated preprocessor— A C/C++ preprocessor that is merged with the parser, allowing for faster
compilation. Stand-alone preprocessing or preprocessed listing is also available.
interlist feature— A feature that inserts as comments your original C/C++ source statements into the
assembly language output from the assembler. The C/C++ statements are inserted next to the
equivalent assembly instructions.
intrinsics— Operators that are used like functions and produce assembly language code that would
otherwise be inexpressible in C, or would take greater time and effort to code.
ISO— International Organization for Standardization; a worldwide federation of national standards
bodies, which establishes international standards voluntarily followed by industries.
K&R C— Kernighan and Ritchie C, the de facto standard as defined in the first edition of The C
Programming Language (K&R). Most K&R C programs written for earlier, non-ISO C compilers
should correctly compile and run without modification.
label— A symbol that begins in column 1 of an assembler source statement and corresponds to the
address of that statement. A label is the only assembler statement that can begin in column 1.
linker— A software program that combines object files to form an executable object file that can be
allocated into system memory and executed by the device.
listing file— An output file, created by the assembler, which lists source statements, their line numbers,
and their effects on the section program counter (SPC).
little endian— An addressing protocol in which bytes are numbered from right to left within a word. More
significant bytes in a word have higher numbered addresses. Endian ordering is hardware-specific
and is determined at reset. See also big endian
loader— A device that places an executable object file into system memory.
loop unrolling— An optimization that expands small loops so that each iteration of the loop appears in
your code. Although loop unrolling increases code size, it can improve the performance of your
code.
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macro— A user-defined routine that can be used as an instruction.
macro call— The process of invoking a macro.
macro definition— A block of source statements that define the name and the code that make up a
macro.
macro expansion— The process of inserting source statements into your code in place of a macro call.
map file— An output file, created by the linker, which shows the memory configuration, section
composition, section allocation, symbol definitions and the addresses at which the symbols were
defined for your program.
memory map— A map of target system memory space that is partitioned into functional blocks.
name mangling— A compiler-specific feature that encodes a function name with information regarding
the function's arguments return types.
object file— An assembled or linked file that contains machine-language object code.
object library— An archive library made up of individual object files.
operand— An argument of an assembly language instruction, assembler directive, or macro directive
that supplies information to the operation performed by the instruction or directive.
optimizer— A software tool that improves the execution speed and reduces the size of C programs.
options— Command-line parameters that allow you to request additional or specific functions when you
invoke a software tool.
output section— A final, allocated section in a linked, executable module.
parser— A software tool that reads the source file, performs preprocessing functions, checks the syntax,
and produces an intermediate file used as input for the optimizer or code generator.
partitioning— The process of assigning a data path to each instruction.
pop— An operation that retrieves a data object from a stack.
pragma— A preprocessor directive that provides directions to the compiler about how to treat a particular
statement.
preprocessor— A software tool that interprets macro definitions, expands macros, interprets header
files, interprets conditional compilation, and acts upon preprocessor directives.
program-level optimization— An aggressive level of optimization where all of the source files are
compiled into one intermediate file. Because the compiler can see the entire program, several
optimizations are performed with program-level optimization that are rarely applied during file-level
optimization.
prolog— The portion of code in a function that sets up the stack.
push— An operation that places a data object on a stack for temporary storage.
quiet run— An option that suppresses the normal banner and the progress information.
raw data— Executable code or initialized data in an output section.
relocation— A process in which the linker adjusts all the references to a symbol when the symbol's
address changes.
run-time environment— The run time parameters in which your program must function. These
parameters are defined by the memory and register conventions, stack organization, function call
conventions, and system initialization.
run-time-support functions— Standard ISO functions that perform tasks that are not part of the C
language (such as memory allocation, string conversion, and string searches).
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run-time-support library— A library file, rts.src, which contains the source for the run time-support
functions.
section— A relocatable block of code or data that ultimately will be contiguous with other sections in the
memory map.
sign extend— A process that fills the unused MSBs of a value with the value's sign bit.
simulator— A software development system that simulates ARM operation.
source file— A file that contains C/C++ code or assembly language code that is compiled or assembled
to form an object file.
stand-alone preprocessor— A software tool that expands macros, #include files, and conditional
compilation as an independent program. It also performs integrated preprocessing, which includes
parsing of instructions.
static variable— A variable whose scope is confined to a function or a program. The values of static
variables are not discarded when the function or program is exited; their previous value is resumed
when the function or program is reentered.
storage class— An entry in the symbol table that indicates how to access a symbol.
string table— A table that stores symbol names that are longer than eight characters (symbol names of
eight characters or longer cannot be stored in the symbol table; instead they are stored in the string
table). The name portion of the symbol's entry points to the location of the string in the string table.
structure— A collection of one or more variables grouped together under a single name.
subsection— A relocatable block of code or data that ultimately will occupy continuous space in the
memory map. Subsections are smaller sections within larger sections. Subsections give you tighter
control of the memory map.
symbol— A string of alphanumeric characters that represents an address or a value.
symbolic debugging— The ability of a software tool to retain symbolic information that can be used by a
debugging tool such as an emulator or simulator.
target system— The system on which the object code you have developed is executed.
.text section— One of the default object file sections. The .text section is initialized and contains
executable code. You can use the .text directive to assemble code into the .text section.
trigraph sequence— A 3-character sequence that has a meaning (as defined by the ISO 646-1983
Invariant Code Set). These characters cannot be represented in the C character set and are
expanded to one character. For example, the trigraph ??' is expanded to ^.
trip count— The number of times that a loop executes before it terminates.
unconfigured memory— Memory that is not defined as part of the memory map and cannot be loaded
with code or data.
uninitialized section— A object file section that reserves space in the memory map but that has no
actual contents. These sections are built with the .bss and .usect directives.
unsigned value— A value that is treated as a nonnegative number, regardless of its actual sign.
variable— A symbol representing a quantity that can assume any of a set of values.
veneer— A sequence of instructions that serves as an alternate entry point into a routine if a state
change is required.
word— A 32-bit addressable location in target memory
206
Glossary
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Appendix B
SPNU151U – January 1998 – Revised June 2019
Revision History
B.1
Recent Revisions
Table B-1 lists significant changes made to this document. The left column identifies the first version of
this document in which that particular change appeared.
Table B-1. Revision History
Version
Added
Chapter
SPNU151U
Location
Additions / Modifications / Deletions
-- throughout --
The default file extensions for object files created by the compiler have
been changed in order to prevent conflicts when C and C++ files have
the same names. Object files generated from C source files have the
.c.obj extension. Object files generated from C++ source files have the
.cpp.obj extension.
Previous Revisions:
SPNU151T
Using the Compiler
Section 2.3.1
Added the --emit_references:file linker option.
SPNU151T
Using the Compiler
Section 2.5.1
Documented that C standard macros such as __STDC_VERSION__
are supported.
SPNU151T
C/C++ Language
Section 5.11.4
Added documentation for the CODE_ALIGN pragma.
SPNU151T
C/C++ Language
Section 5.11.20
Clarify section placement for the NOINIT and PERSISTENT pragmas.
SPNU151T
C/C++ Language
Section 5.14
Corrected syntax for the _norm intrinsic.
SPNU151T
C/C++ Language
Section 5.16.1
Updated list of C99 non-supported run-time functions.
SPNU151T
C/C++ Language
Section 5.17.2
Added documentation for the aligned, calls, naked, and weak function
attributes.
SPNU151T
C/C++ Language
Section 5.17.3
Added documentation for the location and packed variable attributes.
SPNU151T
Run-Time Support
Functions
DEV_lseek topic
Corrected syntax documented for DEV_lseek function.
SPNU151S
Introduction,
Using the Compiler,
C/C++ Language
Section 1.3,
Section 2.3,
Section 5.1, and
Section 5.16.2
Added support for C11.
SPNU151S
Using the Compiler
Section 2.3.1
Added the --ecc=on linker option, which enables ECC generation.
Note that ECC generation is now off by default.
SPNU151S
Using the Compiler
Section 2.5.1
The __TI_STRICT_ANSI_MODE__ and __TI_STRICT_FP_MODE__
macros are defined as 0 if their conditions are false.
SPNU151S
Using the Compiler,
C/C++ Language
Section 2.11 and
Section 5.11
Revised the section on inline function expansion and its subsections to
include new pragmas and changes to the compilers decision-making
about what functions to inline. The FORCEINLINE,
FORCEINLINE_RECURSIVE, and NOINLINE pragmas have been
added.
SPNU151S
C/C++ Language
Section 5.2
C++11 features related to atomics are now supported. In addition,
removed several C++ features from the exception list because they
have been supported for several releases.
SPNU151S
C/C++ Language
Section 5.6
Added information about character sets and file encoding.
SPNU151S
C/C++ Language
Section 5.14
Corrected syntax for _smac intrinsic.
SPNU151S
C/C++ Language
Section 5.17.2 and
Section 5.17.3
Added "retain" as a function attribute and variable attribute.
SPNU151S
C/C++ Language
Section 5.17.5
Clarified the availability of the __builtin_sqrt() and __builtin_sqrtf()
functions.
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Revision History 207
Recent Revisions
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Table B-1. Revision History (continued)
Version
Added
Chapter
Location
Additions / Modifications / Deletions
SPNU151R
Using the Compiler,
C/C++ Language
Section 2.3 and
Section 5.2
The compiler now follows the C++14 standard.
SPNU151R
C/C++ Language
Section 5.17
The compiler now supports several Clang __has_ macro extensions.
SPNU151R
C/C++ Language
Section 5.17.1
The wrapper header file GCC extension (#include_next) is now
supported.
SPNU151Q
Using the Compiler,
C/C++ Language
Table 2-31,
Section 5.1,
Section 5.14,
Section 5.17.2
ARM C Language Extensions (ACLE) are supported.
SPNU151Q
Using the Compiler
Section 2.14
Updated the list of settings for the --float_support option.
SPNU151Q
C/C++ Language
Section 5.2
Preliminary changes have been made in order to support C++14 in a
future release. These changes may cause linktime errors. Recompile
object files to resolve these errors.
SPNU151Q
C/C++ Language
Section 5.7.1
Clarified exceptions to const data storage set by the const keyword.
SPNU151Q
C/C++ Language
Section 5.14
Remove incorrect third parameter for the _smuad, _smuadx, _smusd,
and _smusdx intrinsics.
SPNU151P
Optimization
Section 3.7.1.4
Corrected error in command to process the profile data.
SPNU151O
Using the Compiler,
C/C++ Language
Section 2.3.3,
Section 5.3,
Section 5.11.2,
and
Section 5.11.24
Revised to state that --check_misra option is required even if the
CHECK_MISRA pragma is used.
SPNU151O
Using the Compiler,
C/C++ Language,
and
Run-Time Support
Functions
Section 2.5.1,
Section 5.16, and
Section 7.1.1
_AEABI_PORTABILITY_LEVEL can be defined to enable full object
file portability when headers files are included.
SPNU151O
Using the Compiler
Section 2.10
Corrected the document to describe the ---gen_preprocessor_listing
option. The name --gen_parser_listing was incorrect.
SPNU151N
Optimization
Section 3.7.3
Corrected function names for _TI_start_pprof_collection() and
_TI_stop_pprof_collection().
SPNU151M
Using the Compiler
Section 2.3
The default for --cinit_compression and --copy_compression has been
changed from RLE to LZSS.
Several compiler options have been deprecated, removed, or
renamed. The compiler continues to accept some of the deprecated
options, but they are not recommended for use. See the Compiler
Option Cleanup wiki page for a list of deprecated and removed
options, options that have been removed from CCS, and options that
have been renamed.
SPNU151M
Using the Compiler
SPNU151M
Using the Compiler
Section 2.5.1
The __little_endian__ and __big_endian__ macros are preceded by
two underscores.
SPNU151M
C/C++ Language
Section 5.14
The following intrinsics are supported for Cortex-M3: __ldrex,
__ldrexb, __ldrexh, __strex, __strexb, and __strexh.
SPNU151M
Run-Time
Environment
Section 6.8.1
The _enable_interrupts, _enable_IRQ, _enable_FIQ,
_disable_interrupts, _disable_IRQ, and _disable_FIQ intrinsics for
Cortex-R4 and Cortex-A8 now use the CPSIE and CPSID instructions.
SPNU151L
Using the Compiler
Section 2.3 and
Section 4.2.2
The --gen_data_subsections option has been added.
SPNU151L
Using the Compiler
Section 2.3.5
The --symdebug:dwarf_version option can be set to 4 to enable the
use of DWARF debugging format version 4.
SPNU151L
Optimization
Section 3.7 and
Section 3.8
Feedback directed optimization is described. This technique can be
used for code coverage analysis.
SPNU151L
C/C++ Language
Section 5.11.1
A CALLS pragma has been added to specify a set of functions that
can be called indirectly from a specified calling function. Using this
pragma allows such indirect calls to be included in the calculation of a
functions' inclusive stack size.
SPNU151L
C/C++ Language
Section 5.14
The following intrinsics have been added to the documentation:
__MCR, __MRC.
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Table B-1. Revision History (continued)
Version
Added
Chapter
Location
Additions / Modifications / Deletions
SPNU151L
Run-Time
Environment
Section 6.10.1
Additional boot hook functions are available. These can be customized
for use during system initialization.
SPNU151K
Introduction
Section 1.4
The COFF object file format and the TI_ARM9_ABI and TIARM ABIs
are no longer supported. The ARM Code Generation Tools now
support only the Embedded Application Binary Interface (EABI) ABI,
which works only with object files that use the ELF object file format
and the DWARF debug format. Sections of this document that referred
to the COFF format have been removed or simplified. If you would like
to produce COFF output files, please use v5.2 of the ARM Code
Generation Tools and refer to SPNU151J for documentation.
The --abi=coff, --symdebug:profile_coff, --no_sym_merge, and -diable_clink options have been deprecated.
SPNU151K
Using the Compiler
Section 2.3.4
The --ramfunc option has been added. If set, this option places all
functions in RAM.
SPNU151K
C/C++ Language
Section 5.14
The following intrinsics have been added to the documentation: __nop,
__sqrt, __sqrtf, __wfi, __wfe
SPNU151K
C/C++ Language
Section 5.17.2
The ramfunc function attribute has been added. It specifies that a
function should be placed in RAM.
SPNU151K
Run-Time Support
Functions
Section 7.1.2
Added information about header file extensions.
SPNU151J
Introduction
Section 1.3
Added support for C99 and C++03.
SPNU151J
Using the Compiler
Table 2-1
Added --endian=[big | little] option.
SPNU151J
Using the Compiler
Table 2-6,
Section 2.7, and
Section 2.3.3
Added the --advice:power and --advice:power_severity options for use
with the ULP Advisor.
SPNU151J
Using the Compiler
Table 2-8
Added support for C99 and C++03. The -gcc option has been
deprecated. The --relaxed_ansi option is now the default.
SPNU151J
Using the Compiler
Table 2-8
Removed documentation of precompiled headers, which have been
deprecated.
SPNU151J
Using the Compiler
Table 2-11 and
Section 2.7.1
Added --section_sizes option for diagnostic reporting of section sizes.
SPNU151J
Using the Compiler
Table 2-28 and
Section 4.3.3
Added the –cinit_hold_wdt linker option.
SPNU151J
Using the Compiler
Section 2.5.1
Added __TI_ ARM_V7M4__ predefined macro name for Cortex-M4.
SPNU151J
Using the Compiler
Section 2.5.3
Documented that the #warning and #warn preprocessor directives are
supported.
SPNU151J
Using the Compiler
Section 2.6
Added section on techniques for passing arguments to main().
SPNU151J
Using the Compiler
Section 2.11
Documented that the inline keyword is now enabled in all modes
except C89 strict ANSI mode.
SPNU151J
C/C++ Language
Section 5.1.1
Added section documenting implementation-defined behavior.
SPNU151J
C/C++ Language
Section 5.4
Added support for the ULP Advisor
SPNU151J
C/C++ Language
Section 5.5.1
Added documentation on the size of enum types.
C/C++ Language
Section 5.11.3,
Section 5.11.13,
Section 5.11.14,
Section 5.11.20,
and
Section 5.11.25
Added the CHECK_ULP, FUNC_ALWAYS_INLINE,
FUNC_CANNOT_INLINE, NOINIT, PERSISTENT, and RESET_ULP
pragmas.
SPNU151J
C/C++ Language
Section 5.11.17,
Section 5.11.26,
and Section 5.17.2
Added C++ syntax for the INTERRUPT and RETAIN pragmas. Also
removed unnecessary semicolons from #pragma syntax specifications.
Also the GCC interrupt and alias function attributes are now
supported.
SPNU151J
C/C++ Language
Section 5.11.9
Added the diag_push and diag_pop diagnostic message pragmas.
SPNU151J
C/C++ Language
Section 5.14
Added __delay_cycles, __get_PRIMASK, __set_PRIMASK,
__get_MSP, and __set_MSP intrinsics.
SPNU151J
C/C++ Language
Section 5.14
Corrected arguments for smlalbb, smlalbt, smlaltb, smlaltt, smlabb,
smlabt, smlatb, and smlatt intrinsics.
SPNU151J
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Revision History 209
Recent Revisions
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Table B-1. Revision History (continued)
210
Version
Added
Chapter
Location
Additions / Modifications / Deletions
SPNU151J
C/C++ Language
Section 5.16,
Section 5.16.1,
and Section 5.16.3
Added support for C99 and C++03. The --relaxed_ansi option is now
the default and --strict_ansi is the other option; "normal mode" for
standards violation strictness is no longer available.
SPNU151J
Run-Time
Environment
Section 6.5
Added reference to section on accessing linker symbols in C and C++
in the Assembly Language Tools User's Guide.
SPNU151J
Run-Time
Environment
Section 6.7.5
Added information about allowable return values from SWI handlers.
SPNU151J
Run-Time
Environment
Section 6.8.1
Added instructions for several device families for _disable_interrupts,
_enable_interrupts, and _restore_interrupts intrinsics. Added Cortex-M
support for _enable_IRQ, _disable_IRQ, and _set_interrupt_priority
intrinsics.
SPNU151J
Run-Time
Environment
Section 6.10.1
Added support for system pre-initialization.
SPNU151J
Run-Time Support
Functions
Section 7.1.3
RTS source code is no longer provided in a rtssrc.zip file. Instead, it is
located in separate files in the lib/src subdirectory of the compiler
installation.
SPNU151J
C++ Name
Demangler
Section 8.1
Corrected information about name demangler options.
SPNU151J
C++ Name
Demangler
Section 8.2
Corrected examples of resulting assembly output.
Revision History
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