Texas Instruments ARM Optimizing C/C++ Compiler v4.9 C/C++ Compilers User's Guide

ARM Optimizing C/C++ Compiler
v4.9
User's Guide
Literature Number: SPNU151G
August 2011
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Contents
...................................................................................................................................... 11
Introduction to the Software Development Tools ................................................................... 15
1.1
Software Development Tools Overview ................................................................................ 16
1.2
C/C++ Compiler Overview ................................................................................................ 17
1.2.1 ANSI/ISO Standard ............................................................................................... 17
1.2.2 Output Files ....................................................................................................... 18
1.2.3 Compiler Interface ................................................................................................ 18
1.2.4 Utilities ............................................................................................................. 18
Using the C/C++ Compiler .................................................................................................. 19
2.1
About the Compiler ........................................................................................................ 20
2.2
Invoking the C/C++ Compiler ............................................................................................ 20
2.3
Changing the Compiler's Behavior With Options ...................................................................... 21
2.3.1 Frequently Used Options ........................................................................................ 29
2.3.2 Miscellaneous Useful Options .................................................................................. 31
2.3.3 Run-Time Model Options ........................................................................................ 32
2.3.4 Symbolic Debugging and Profiling Options ................................................................... 34
2.3.5 Specifying Filenames ............................................................................................ 35
2.3.6 Changing How the Compiler Interprets Filenames ........................................................... 35
2.3.7 Changing How the Compiler Processes C Files ............................................................. 36
2.3.8 Changing How the Compiler Interprets and Names Extensions ........................................... 36
2.3.9 Specifying Directories ............................................................................................ 36
2.3.10 Assembler Options .............................................................................................. 37
2.3.11 Deprecated Options ............................................................................................. 38
2.4
Controlling the Compiler Through Environment Variables ........................................................... 38
2.4.1 Setting Default Compiler Options (TMS470_C_OPTION) .................................................. 38
2.4.2 Naming an Alternate Directory (TMS470_C_DIR) ........................................................... 39
2.5
Precompiled Header Support ............................................................................................ 40
2.5.1 Automatic Precompiled Header ................................................................................. 40
2.5.2 Manual Precompiled Header .................................................................................... 40
2.5.3 Additional Precompiled Header Options ....................................................................... 40
2.6
Controlling the Preprocessor ............................................................................................. 41
2.6.1 Predefined Macro Names ....................................................................................... 41
2.6.2 The Search Path for #include Files ............................................................................ 42
2.6.3 Generating a Preprocessed Listing File (--preproc_only Option) .......................................... 43
2.6.4 Continuing Compilation After Preprocessing (--preproc_with_compile Option) .......................... 44
2.6.5 Generating a Preprocessed Listing File With Comments (--preproc_with_comment Option) .......... 44
Preface
1
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2.6.6
2.7
2.8
Generating a Preprocessed Listing File With Line-Control Information (--preproc_with_line
Option) .............................................................................................................
2.6.7 Generating Preprocessed Output for a Make Utility (--preproc_dependency Option) ...................
2.6.8 Generating a List of Files Included With the #include Directive (--preproc_includes Option) ..........
2.6.9 Generating a List of Macros in a File (--preproc_macros Option) ..........................................
Understanding Diagnostic Messages ...................................................................................
2.7.1 Controlling Diagnostics ..........................................................................................
2.7.2 How You Can Use Diagnostic Suppression Options ........................................................
Other Messages ...........................................................................................................
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2.9
2.10
2.11
2.12
2.13
2.14
2.15
3
Optimizing Your Code
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
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........................................................................................................ 55
Invoking Optimization .....................................................................................................
Performing File-Level Optimization (--opt_level=3 option) ...........................................................
3.2.1 Controlling File-Level Optimization (--std_lib_func_def Options) ...........................................
3.2.2 Creating an Optimization Information File (--gen_opt_info Option) ........................................
Performing Program-Level Optimization (--program_level_compile and --opt_level=3 options) ................
3.3.1 Controlling Program-Level Optimization (--call_assumptions Option) .....................................
3.3.2 Optimization Considerations When Mixing C/C++ and Assembly .........................................
Link-Time Optimization (--opt_level=4 Option) ........................................................................
3.4.1 Option Handling ...................................................................................................
3.4.2 Incompatible Types ...............................................................................................
Accessing Aliased Variables in Optimized Code ......................................................................
Use Caution With asm Statements in Optimized Code ..............................................................
Automatic Inline Expansion (--auto_inline Option) ....................................................................
Using the Interlist Feature With Optimization ..........................................................................
Debugging and Profiling Optimized Code ..............................................................................
3.9.1 Debugging Optimized Code (--symdebug:dwarf, --symdebug:coff, and --opt_level Options) ..........
3.9.2 Profiling Optimized Code ........................................................................................
Controlling Code Size Versus Speed ...................................................................................
What Kind of Optimization Is Being Performed? ......................................................................
3.11.1 Cost-Based Register Allocation ...............................................................................
3.11.2 Alias Disambiguation ............................................................................................
3.11.3 Branch Optimizations and Control-Flow Simplification .....................................................
3.11.4 Data Flow Optimizations ........................................................................................
3.11.5 Expression Simplification .......................................................................................
3.11.6 Inline Expansion of Functions .................................................................................
3.11.7 Function Symbol Aliasing ......................................................................................
3.11.8 Induction Variables and Strength Reduction .................................................................
3.11.9 Loop-Invariant Code Motion ...................................................................................
3.11.10 Loop Rotation ...................................................................................................
3.11.11 Instruction Scheduling .........................................................................................
3.11.12 Tail Merging ....................................................................................................
3.11.13 Autoincrement Addressing ....................................................................................
3.11.14 Block Conditionalizing .........................................................................................
3.11.15 Epilog Inlining ...................................................................................................
3.11.16 Removing Comparisons to Zero .............................................................................
3.11.17 Integer Division With Constant Divisor ......................................................................
3.11.18 Branch Chaining ...............................................................................................
Linking C/C++ Code
4.1
4
Generating Cross-Reference Listing Information (--gen_acp_xref Option) ........................................
Generating a Raw Listing File (--gen_acp_raw Option) ..............................................................
Using Inline Function Expansion ........................................................................................
2.11.1 Inlining Intrinsic Operators .....................................................................................
2.11.2 Using the inline Keyword, the --no_inlining Option, and Level 3 Optimization ..........................
2.11.3 Automatic Inlining ................................................................................................
2.11.4 Inlining Restrictions .............................................................................................
Using Interlist ...............................................................................................................
Controlling Application Binary Interface ................................................................................
VFP Support ...............................................................................................................
Enabling Entry Hook and Exit Hook Functions ........................................................................
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........................................................................................................... 71
Invoking the Linker Through the Compiler (-z Option) ................................................................ 72
4.1.1 Invoking the Linker Separately ................................................................................. 72
4.1.2 Invoking the Linker as Part of the Compile Step ............................................................. 73
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4.2
4.3
5
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 Function Subsections (--gen_func_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 Global Object Constructors .....................................................................................
4.3.4 Specifying the Type of Global Variable Initialization .........................................................
4.3.5 Specifying Where to Allocate Sections in Memory ...........................................................
4.3.6 A Sample Linker Command File ................................................................................
ARM C/C++ Language Implementation
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
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................................................................................. 81
Characteristics of ARM C ................................................................................................ 82
Characteristics of ARM C++ ............................................................................................. 82
Using MISRA-C:2004 ..................................................................................................... 83
Data Types ................................................................................................................. 84
Keywords ................................................................................................................... 85
5.5.1 The const Keyword ............................................................................................... 85
5.5.2 The interrupt Keyword ........................................................................................... 85
5.5.3 The volatile Keyword ............................................................................................. 86
C++ Exception Handling .................................................................................................. 86
Register Variables and Parameters ..................................................................................... 87
5.7.1 Local Register Variables and Parameters ..................................................................... 87
5.7.2 Global Register Variables ....................................................................................... 87
The asm Statement ....................................................................................................... 88
Pragma Directives ......................................................................................................... 89
5.9.1 The CHECK_MISRA Pragma ................................................................................... 90
5.9.2 The CLINK Pragma .............................................................................................. 90
5.9.3 The CODE_SECTION Pragma ................................................................................. 90
5.9.4 The CODE_STATE Pragma .................................................................................... 91
5.9.5 The DATA_ALIGN Pragma ..................................................................................... 91
5.9.6 The DATA_SECTION Pragma .................................................................................. 92
5.9.7 The Diagnostic Message Pragmas ............................................................................. 93
5.9.8 The DUAL_STATE Pragma ..................................................................................... 93
5.9.9 The FUNC_EXT_CALLED Pragma ............................................................................ 94
5.9.10 The FUNCTION_OPTIONS Pragma .......................................................................... 94
5.9.11 The INTERRUPT Pragma ...................................................................................... 95
5.9.12 The MUST_ITERATE Pragma ................................................................................. 95
5.9.13 The NO_HOOKS Pragma ...................................................................................... 97
5.9.14 The RESET_MISRA Pragma .................................................................................. 97
5.9.15 The RETAIN Pragma ........................................................................................... 97
5.9.16 The SET_CODE_SECTION and SET_DATA_SECTION Pragmas ...................................... 98
5.9.17 The SWI_ALIAS Pragma ....................................................................................... 99
5.9.18 The TASK Pragma ............................................................................................. 100
5.9.19 The UNROLL Pragma ......................................................................................... 100
5.9.20 The WEAK Pragma ............................................................................................ 101
The _Pragma Operator .................................................................................................. 101
Application Binary Interface ............................................................................................ 102
5.11.1 TI_ARM9_ABI .................................................................................................. 102
5.11.2 TIABI ............................................................................................................. 102
5.11.3 ARM ABIv2 or EABI ........................................................................................... 103
ARM Instruction Intrinsics ............................................................................................... 104
Object File Symbol Naming Conventions (Linknames) ............................................................. 108
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5.14
5.15
5.16
5.17
5.18
6
Run-Time Environment
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
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Initializing Static and Global Variables in TIABI and TI ARM9 ABI Modes .......................................
5.14.1 Initializing Static and Global Variables With the Linker ...................................................
5.14.2 Initializing Static and Global Variables With the const Type Qualifier ..................................
Changing the ANSI/ISO C Language Mode ..........................................................................
5.15.1 Compatibility With K&R C (--kr_compatible Option) .......................................................
5.15.2 Enabling Strict ANSI/ISO Mode and Relaxed ANSI/ISO Mode (--strict_ansi and --relaxed_ansi
Options) ..........................................................................................................
5.15.3 Enabling Embedded C++ Mode (--embedded_cpp Option) ..............................................
GNU Language Extensions .............................................................................................
5.16.1 Extensions ......................................................................................................
5.16.2 Function Attributes .............................................................................................
5.16.3 Variable Attributes .............................................................................................
5.16.4 Type Attributes .................................................................................................
5.16.5 Built-In Functions ..............................................................................................
AUTOSAR ................................................................................................................
Compiler Limits ...........................................................................................................
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Memory Model ............................................................................................................
6.1.1 Sections ..........................................................................................................
6.1.2 C/C++ System Stack ...........................................................................................
6.1.3 Dynamic Memory Allocation ...................................................................................
6.1.4 Initialization of Variables in TIABI and TI_ARM9_ABI .....................................................
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 ..................................................................
6.4.5 Generating Long Calls (-ml Option) in 16-bit Mode ........................................................
Interfacing C and C++ With Assembly Language ...................................................................
6.5.1 Using Assembly Language Modules With C/C++ Code ...................................................
6.5.2 Accessing Assembly Language Variables From C/C++ ...................................................
6.5.3 Sharing C/C++ Header Files With Assembly Source ......................................................
6.5.4 Using Inline Assembly Language .............................................................................
6.5.5 Modifying Compiler Output ....................................................................................
Interrupt Handling ........................................................................................................
6.6.1 Saving Registers During Interrupts ...........................................................................
6.6.2 Using C/C++ Interrupt Routines ...............................................................................
6.6.3 Using Assembly Language Interrupt Routines ..............................................................
6.6.4 How to Map Interrupt Routines to Interrupt Vectors ........................................................
6.6.5 Using Software Interrupts ......................................................................................
6.6.6 Other Interrupt Information .....................................................................................
Intrinsic Run-Time-Support Arithmetic and Conversion Routines .................................................
6.7.1 Naming Conventions ...........................................................................................
6.7.2 CPSR Register and Interrupt Intrinsics ......................................................................
Built-In Functions .........................................................................................................
System Initialization ......................................................................................................
6.9.1 Run-Time Stack .................................................................................................
6.9.2 TIABI/TIARM9 Automatic Initialization of Variables ........................................................
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6.10
7
Using Run-Time-Support Functions and Building Libraries
7.1
7.2
7.3
7.4
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9.6
9.7
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....................................................................................................... 175
Invoking the C++ Name Demangler ................................................................................... 176
C++ Name Demangler Options ........................................................................................ 176
Sample Usage of the C++ Name Demangler ........................................................................ 177
Static Stack Depth Profiler
9.1
9.2
9.3
9.4
9.5
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.................................................. 157
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 Changes to the Run-Time-Support Libraries ................................................................
7.1.5 Nonstandard Header Files in rtssrc.zip ......................................................................
7.1.6 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 ...............................................................................
C++ Name Demangler
8.1
8.2
8.3
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6.9.3 Autoinitialization of Variables at Run Time ..................................................................
6.9.4 Initialization of Variables at Load Time .......................................................................
6.9.5 EABI Automatic Initialization of Variables ...................................................................
6.9.6 Initialization Tables .............................................................................................
6.9.7 Global Constructors .............................................................................................
Dual-State Interworking Under TIABI .................................................................................
6.10.1 Level of Dual-State Support ..................................................................................
6.10.2 Implementation .................................................................................................
................................................................................................ 179
Invoking the Static Stack Depth Profiler ..............................................................................
Stack Depth Statistics Listing ..........................................................................................
Dependencies and Limitations .........................................................................................
User Input Mechanisms .................................................................................................
Configuration File Specification ........................................................................................
9.5.1 Specify Indirect Calls ...........................................................................................
9.5.2 Specifying Reentrant Procedures .............................................................................
9.5.3 Specifying Interrupt Service Routines ........................................................................
9.5.4 Other Features ..................................................................................................
9.5.5 Tail Calls .........................................................................................................
Profiler Generated Warnings ...........................................................................................
Run-Time Support for Stack Depth Profiling .........................................................................
Glossary
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List of Figures
1-1.
ARM Software Development Flow ...................................................................................... 16
6-1.
Char and Short Data Storage Format ................................................................................. 119
6-2.
32-Bit Data Storage Format ............................................................................................ 120
6-3.
Double-Precision Floating-Point Data Storage Format
121
6-4.
Bit-Field Packing in Big-Endian and Little-Endian Formats
122
6-5.
6-6.
6-7.
6-8.
6-9.
6-10.
6-11.
6-12.
9-1.
.............................................................
........................................................
Use of the Stack During a Function Call ..............................................................................
Autoinitialization at Run Time ..........................................................................................
Initialization at Load Time ...............................................................................................
Autoinitialization at Run Time in EABI Mode .........................................................................
Initialization at Load Time in EABI Mode .............................................................................
Constructor Table for EABI Mode .....................................................................................
Format of Initialization Records in the .cinit Section ................................................................
Format of Initialization Records in the .pinit Section ................................................................
Application Call Trees ...................................................................................................
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List of Tables
Basic Options
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2-2.
Control 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.
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...........................................................................................................
Symbolic Debug Options .................................................................................................
Language Options .........................................................................................................
Parser Preprocessing Options ...........................................................................................
Predefined Symbols Options ............................................................................................
Include Options ...........................................................................................................
Diagnostics Options .......................................................................................................
Run-Time Model Options .................................................................................................
Optimization Options .....................................................................................................
Entry/Exit Hook Options ..................................................................................................
Library Function Assumptions Options ................................................................................
Assembler Options ........................................................................................................
File Type Specifier Options ..............................................................................................
Directory Specifier Options ...............................................................................................
Default File Extensions Options .........................................................................................
Command Files Options .................................................................................................
MISRA-C:2004 Options ...................................................................................................
Linker Basic Options Summary ..........................................................................................
Command File Preprocessing Options Summary .....................................................................
Diagnostic Options Summary ............................................................................................
File Search Path Options Summary ....................................................................................
Linker Output Options Summary ........................................................................................
Symbol Management Options Summary ...............................................................................
Run-Time Environment Options Summary .............................................................................
Link-Time Optimization Options Summary .............................................................................
Miscellaneous Options Summary .......................................................................................
Compiler Backwards-Compatibility Options Summary ...............................................................
Predefined ARM Macro Names .........................................................................................
Raw Listing File Identifiers ...............................................................................................
Raw Listing File Diagnostic Identifiers ..................................................................................
2-1.
List of Figures
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3-1.
Options That You Can Use With --opt_level=3 ........................................................................ 57
3-2.
Selecting a File-Level Optimization Option
3-3.
Selecting a Level for the --gen_opt_info Option ....................................................................... 57
3-4.
Selecting a Level for the --call_assumptions Option .................................................................. 58
3-5.
Special Considerations When Using the --call_assumptions Option ............................................... 59
4-1.
Initialized Sections Created by the CompilerTIABI and TI ARM9 ABI
4-2.
4-3.
5-1.
5-2.
5-3.
5-4.
5-5.
5-6.
6-1.
6-2.
6-3.
6-4.
6-5.
6-6.
6-7.
6-8.
6-9.
6-10.
6-11.
............................................................................
.............................................
Initialized Sections Created by the Compiler for EABI ...............................................................
Uninitialized Sections Created by the Compiler .......................................................................
ARM C/C++ Data Types ..................................................................................................
EABI Enumerator Types ..................................................................................................
v5e, v6, Cortex-M3, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics ........................
V5E, V6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics .....................................
v6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics ............................................
GCC Language Extensions .............................................................................................
Summary of Sections and Memory Placement ......................................................................
Data Representation in Registers and Memory .....................................................................
How Register Types Are Affected by the Conventions .............................................................
Register Usage ..........................................................................................................
VFP Register Usage .....................................................................................................
Neon Register Usage....................................................................................................
Naming Convention Prefixes ...........................................................................................
Summary of Run-Time-Support Arithmetic and Conversion Functions ...........................................
Run-Time-Support Function Register Usage Conventions .........................................................
CPSR and Interrupt C/C++ Compiler Intrinsics ......................................................................
Selecting a Level of Dual-State Support ..............................................................................
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List of Tables
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List of Tables
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Preface
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Read This First
About This Manual
The ARM Optimizing C/C++ Compiler User's Guide explains how to use these compiler tools:
• Compiler
• Library-build process
• C++ name demangler
• Static stack depth profiler
The compiler accepts C and C++ code conforming to the International Organization for Standardization
(ISO) standards for these languages. The compiler supports the 1989 version of the C language and the
1998 version of the C++ language.
This user's guide discusses the characteristics of the C/C++ compiler. It assumes that you already know
how to write 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, cruel world\n");
}
•
•
In syntax descriptions, the instruction, command, or directive is 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:
cl470 [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:
cl470 --run_linker
{--rom_model | --ram_model} filenames [--output_file= name.out]
--library= libraryname
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In assembler syntax statements, column 1 is reserved for the first character of a label or symbol. If the
label or symbol is optional, it is usually not shown. If it 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 column 1.
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
C: A Reference Manual (fourth edition), by Samuel P. Harbison, and Guy L. Steele Jr., published by
Prentice Hall, Englewood Cliffs, New Jersey
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 C Standard),
International Organization for Standardization
ISO/IEC 14882-1998, International Standard - Programming Languages - C++ (The C++ Standard),
International Organization for Standardization
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), by Brian W. Kernighan and Dennis M. Ritchie,
published by Prentice-Hall, Englewood Cliffs, New Jersey, 1988
The C++ Programming Language (second edition), Bjarne Stroustrup, published by Addison-Wesley
Publishing Company, Reading, Massachusetts, 1990
The Annotated C++ Reference Manual, Margaret A. Ellis and 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)
12
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Related Documentation From Texas Instruments
You can use the following books to supplement this user's guide:
SPNU118 — ARM Assembly Language Tools v4.6 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.
SPNU134— TMS470R1x User's Guide. Describes the TMS470R1x RISC microcontroller, its
architecture (including registers), ICEBreaker module, interfaces (memory, coprocessor, and
debugger), 16-bit and 32-bit instruction sets, and electrical specifications.
SPRAAB5— The Impact of DWARF on TI Object Files. Describes the Texas Instruments extensions to
the DWARF specification.
ARM is a registered trademark of ARM Limited.
All other trademarks are the property of their respective owners.
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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
...........................................................................................................................
Page
Software Development Tools Overview ................................................................ 16
C/C++ Compiler Overview ................................................................................... 17
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Software Development Tools Overview
1.1
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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
process
Debugging
tools
Run-timesupport
library
Executable
object file
Hex-conversion
utility
EPROM
programmer
16
Absolute lister
Cross-reference
lister
Object file
utilities
ARM
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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 object modules. The
ARM Assembly Language Tools User's Guide explains how to use the assembler.
• The linker combines object files into a single executable object module. As it creates the executable
module, it performs relocation and resolves external references. The linker accepts relocatable object
files and object libraries as input. See Chapter 4. The ARM Assembly Language Tools User's Guide
provides a complete description of the linker.
• The archiver allows you to collect a group of files into a single archive file, called a library.
Additionally, the archiver allows you to modify a library by deleting, replacing, extracting, or adding
members. One of the most useful applications of the archiver is building a library of object modules.
The ARM Assembly Language Tools User's Guide explains how to use the archiver.
• You can use the library-build process to build your own customized run-time-support library. See
Section 7.4. Standard run-time-support library functions for C and C++ are provided in the
self-contained rtssrc.zip file.
The run-time-support libraries contain the standard ISO run-time-support functions, compiler-utility
functions, floating-point arithmetic functions, and C I/O functions that are supported by the compiler.
See Chapter 7.
• The hex conversion utility converts an object file into other object formats. You can download the
converted file to an EPROM programmer. The ARM Assembly Language Tools User's Guide explains
how to use the hex conversion utility and describes all supported formats.
• 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. The ARM Assembly Language Tools User's Guide explains how to use the absolute lister.
• 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. The ARM Assembly Language Tools
User's Guide explains how to use the cross-reference utility.
• 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 stack depth profiler provides information about the maximum stack depth requirements of an
application based on the static information available in the linker output file. See Chapter 9.
• The disassembler disassembles object files. The ARM Assembly Language Tools User's Guide
explains how to use the disassembler.
• The main product of this development process is a module that can be executed in a ARM device.
1.2
C/C++ Compiler Overview
The following subsections describe the key features of the compiler.
1.2.1 ANSI/ISO Standard
These features pertain to ISO standards:
• ISO-standard C
The C/C++ compiler conforms to the ISO C standard as defined by the ISO specification and described
in the second edition of Kernighan and Ritchie's The C Programming Language (K&R). The ISO C
standard supercedes and is the same as the ANSI C standard.
• ISO-standard C++
The C/C++ compiler supports C++ as defined by the ISO C++ Standard and described in Ellis and
Stroustrup's The Annotated C++ Reference Manual (ARM). The compiler also supports embedded
C++. For a description of unsupported C++ features, see Section 5.2.
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ISO-standard run-time support
The compiler tools come with an extensive run-time library. All library functions conform to the ISO
C/C++ library standard. 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.
1.2.2 Output Files
These features pertain to output files created by the compiler:
• COFF object files
Common object file format (COFF) allows you to define your system's memory map at link time. This
maximizes performance by enabling you to link C/C++ code and data objects into specific memory
areas. COFF also supports source-level debugging.
• ELF object files
Executable and linking format (ELF) enables supporting modern language features like early template
instantiation and export inline functions support.
1.2.3 Compiler Interface
These features pertain to interfacing with the compiler:
• Compiler program
The compiler tools include a compiler program that you use to compile, optimize, assemble, and link
programs in a single step. For more information, see Section 2.1
• Flexible assembly language interface
The compiler has straightforward calling conventions, so you can write assembly and C functions that
call each other. For more information, see Chapter 6.
1.2.4 Utilities
These features pertain to the compiler utilities:
• Library-build process
The library-build process lets you custom-build object libraries from source for any combination of
run-time models. For more information, see Section 7.4.
• C++ name demangler
The C++ name demangler (dem470) is a debugging aid that translates each mangled name it detects
to its original name found in the C++ source code. For more information, see Chapter 8.
• Static stack depth profiler
The static stack depth profiler provides information about the maximum stack depth requirements of an
application based on the static information available in the linker output file. The application must be
compiled with DWARF (default) type debug information.
• 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 COFFor 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.
18
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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 object 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 ......................................
Precompiled Header Support ..............................................................................
Controlling the Preprocessor ..............................................................................
Understanding Diagnostic Messages ...................................................................
Other Messages ................................................................................................
Generating Cross-Reference Listing Information (--gen_acp_xref Option) ................
Generating a Raw Listing File (--gen_acp_raw Option) ...........................................
Using Inline Function Expansion .........................................................................
Using Interlist ...................................................................................................
Controlling Application Binary Interface ...............................................................
VFP Support .....................................................................................................
Enabling Entry Hook and Exit Hook Functions .....................................................
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Page
20
20
21
38
40
41
45
47
48
48
49
51
52
53
54
19
About the Compiler
2.1
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About the Compiler
The compiler lets you compile, 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, and 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 2.3.8 for more information.
• The linker combines object files to create an executable object file. The linker is optional, so you can
compile and assemble many modules independently and link them later. See Chapter 4 for information
about linking the files.
By default, the compiler does not invoke the linker. You can invoke the linker by using the --run_linker
compiler option.
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:
cl470 [options] [filenames] [--run_linker [link_options] object files]]
cl470
options
filenames
--run_linker
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 2-2 through Table 2-27.
One or more C/C++ source files, assembly language source files, linear
assembly files, or object 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.
Name of the additional 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:
cl470 symtab.c file.c seek.asm --run_linker --library=lnk.cmd
--library=rts16.lib --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 cl470 with no parameters on the command line.
The following apply to the compiler options:
• Options are preceded by one or two hyphens.
• Options are case sensitive.
• Options are either single letters or sequences of characters.
• Individual options cannot be combined.
• An option with a required 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. Although not recommended, you can separate the option and the
parameter with or without a space, as in --undefine name or -undefinename.
• An option with an optional parameter should be specified with an equal sign before the parameter to
clearly associate the parameter with the option. For example, the option to specify the maximum
amount of optimization can be expressed as -O=3. Although not recommended, you can specify the
parameter directly after the option, as in -O3. 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 other compile options and precede any link options.
You can define default options for the compiler by using the TMS470_C_OPTION environment variable.
For a detailed description of the environment variable, see Section 2.4.1.
Table 2-2 through Table 2-27 summarize all options (including link options). Use the references in the
tables for more complete descriptions of the options.
Table 2-1. Basic Options
Option
Alias
Effect
Section
--symdebug:dwarf
-g
Enables symbolic debugging
Section 2.3.4
Section 3.9.1
--symdebug:coff
Enables symbolic debugging using the alternate STABS debugging
format. STABS format is not supported for ELF.
Section 2.3.4
Section 3.9.1
--symdebug:none
Disables all symbolic debugging
Section 2.3.4
--symdebug:profile_coff
Enables profiling using the alternate STABS debugging format.
STABS format is not supported for ELF.
Section 2.3.4
--symdebug:skeletal
Enables minimal symbolic debugging that does not hinder
optimizations (default behavior)
Section 2.3.4
Optimization level (Default:2)
Section 3.1
--opt_level[=0-4]
-O
Table 2-2. 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 2.3.1
--run_linker
-z
Enables linking
Section 2.3.1
--skip_assembler
-n
Compiles or assembly optimizes only
Section 2.3.1
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Table 2-3. Symbolic Debug Options
Option
Alias
Effect
Section
--symdebug:dwarf
-g
Enables symbolic debugging
Section 2.3.4
Section 3.9.1
--symdebug:coff
Enables symbolic debugging using the alternate STABS debugging
format. STABS format is not supported for ELF.
Section 2.3.4
Section 3.9.1
--symdebug:none
Disables all symbolic debugging
Section 2.3.4
--symdebug:profile_coff
Enables profiling using the alternate STABS debugging format.
STABS format is not supported for ELF.
Section 2.3.4
--symdebug:skeletal
Enables minimal symbolic debugging that does not hinder
optimizations (default behavior)
Section 2.3.4
--symdebug:dwarf_subsections
=on|off
Changes how debug information is represented in the object file
Section 2.3.4
--symdebug:dwarf_version=2|3
Specifies the DWARF format version
Section 2.3.4
Table 2-4. Language Options
Option
Alias
Effect
Section
--cpp_default
-fg
Processes all source files with a C extension as C++ source files.
Section 2.3.6
Creates a precompiled header file with the name specified
Section 2.5
Enables embedded C++ mode
Section 5.15.3
--exceptions
Enables C++ exception handling
Section 5.6
--extern_c_can_throw
Allow extern C functions to propagate exceptions
--fp_mode={relaxed|strict}
Enables or disables relaxed floating-point mode
Section 2.3.2
--create_pch=filename
--embedded_cpp
-pe
--gcc
Enables support for GCC extensions
Section 5.16
--gen_asp_raw
-pl
Generates a raw listing file
Section 2.10
--gen_acp_xref
-px
Generates a cross-reference listing file
Section 2.9
--keep_unneeded_statics
Keeps unreferenced static variables.
Section 2.3.2
--kr_compatible
-pk
Allows K&R compatibility
Section 5.15.1
--multibyte_chars
-pc
Enables multibyte character support.
-
--no_inlining
-pi
Disables definition-controlled inlining (but --opt_level=3 (or -O3)
optimizations still perform automatic inlining)
Section 2.11
--no_intrinsics
-pn
Disables intrinsic functions. No predefinition of compiler-supplied
intrinsic functions.
-
--pch
Creates or uses precompiled header files
Section 2.5
--pch_dir=directory
Specifies the path where the precompiled header file resides
Section 2.5.2
--pch_verbose
Displays a message for each precompiled header file that is
considered but not used
Section 2.5.3
--program_level_compile
-pm
Combines source files to perform program-level optimization
Section 3.3
--relaxed_ansi
-pr
Enables relaxed mode; ignores strict ISO violations
Section 5.15.2
--rtti
-rtti
Enables run time type information (RTTI)
–
Instantiate all template entities with internal linkage
–
Enables strict ISO mode (for C/C++, not K&R C)
Section 5.15.2
Specifies the precompiled header file to use for this compilation
Section 2.5.2
--static_template_instantiation
--strict_ansi
--use_pch=filename
22
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Table 2-5. 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 2.6.7
--preproc_includes[=filename]
-ppi
Performs preprocessing only, but instead of writing preprocessed
output, writes a list of files included with the #include directive
Section 2.6.8
--preproc_macros[=filename]
-ppm
Performs preprocessing only. Writes list of predefined and
user-defined macros to a file with the same name as the input but
with a .pp extension.
Section 2.6.9
--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 2.6.3
--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 2.6.5
--preproc_with_compile
-ppa
Continues compilation after preprocessing
Section 2.6.4
--preproc_with_line
-ppl
Performs preprocessing only. Writes preprocessed output with
Section 2.6.6
line-control information (#line directives) to a file with the same name
as the input but with a .pp extension.
Table 2-6. Predefined Symbols Options
Option
Alias
Effect
Section
--define=name[=def]
-D
Predefines name
Section 2.3.1
--undefine=name
-U
Undefines name
Section 2.3.1
Table 2-7. Include Options
Option
Alias
Effect
Section
--include_path=directory
-I
Defines #include search path
Section 2.6.2.1
Includes filename at the beginning of compilation
Section 2.3.2
--preinclude=filename
Table 2-8. Diagnostics 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
--display_error_number
-pden
Displays a diagnostic's identifiers along with its text
Section 2.7.1
--emit_warnings_as_errors
-pdew
Treat warnings as errors
Section 2.7.1
--gen_aux_user_info
Generate user information file (.aux)
--issue_remarks
-pdr
Issues remarks (nonserious warnings)
Section 2.7.1
--no_warnings
-pdw
Suppresses warning diagnostics (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 diagnostics that display the original source with
line-wrap
Section 2.7.1
--write_diagnostics_file
-pdf
Generates a diagnostics information file. Compiler only option.
Section 2.7.1
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Table 2-9. Run-Time Model Options
Option
Alias
-ab=num
Effect
Section
Controls the depth of branch chaining optimization
Section 3.11.18
--abi={eabi|ti_arm9_abi|tiabi}
-abi
Specifies the application binary interface
Section 2.13
--align_structs=bytecount
-mw
Aligns structures on bytecount boundary
Section 2.3.3
--code_state={16|32}
-mt
Designates the ARM compilation mode
Section 2.3.3
Section 6.10.2.2
--disable_branch_chaining
Disables branch chaining optimization
Section 3.11.18
--embedded_constants={on|off}
Controls whether compiler embeds constants in functions.
Section 2.3.3
Designates the endianness of compiled code, default is big
Section 2.3.3
--enum_type={int|packed|unpacked}
Designates the underlying type of an enumeration type; default is
unpacked
Section 2.3.3
--float_support={vfpv3|vfpv3d16
|fpalib|vfplib|vfpv4spd16}
Generates vector floating-point (VFP) coprocessor instructions
Section 2.14
Enables or disables the reassociation of floating-point arithmetic
Section 2.3.3
Puts each function in a separate subsection in the object file
Section 4.2.2
-md
Disables dual-state interworking support (tiabi only)
Section 6.10.1
-ml
Uses far calls (requires -md and --code_state=16)
Section 6.4.5
-mo
Enables dynamic stack overflow checking
Section 2.3.3
-mv={4|5e|6|7A8|7M3|7M4|7R4}
Selects processor version: ARM V4 (ARM7), ARM V5e (ARM9E),
Section 2.3.3
ARM V6 (ARM11), ARM V7A8 (Cortex-A8), ARM V7M3 (Cortex-M3),
ARM V7M4 (Cortex-M4), or ARM V7R (Cortex-R4). The default is
ARM V4.
--endian={big|little}
-me
--fp_reassoc={on|off}
--gen_func_subsections={on|off}
-ms
-neon
--optimize_with_debug
-mn
--plain_char={signed|unsigned}
-mc
Enables support for the CortexA8 Neon SIMD instruction set.
Section 2.3.3
Reenables optimizations disabled with --symdebug:dwarf
Section 3.9.1
Specifies how to treat plain chars, default is unsigned
Section 2.3.3
--profile:breakpt
Enables breakpoint-based profiling
Section 2.3.4
Section 3.9.2
--profile:power
Enables power profiling
Section 2.3.4
Section 3.9.2
-rr={r5|r6|r9}
Disallows use of rx=[5,6,9] by the compiler
Section 2.3.3
--sat_reassoc={on|off}
Enables or disables the reassociation of saturating arithmetic.
Default is --sat_reassoc=off.
--small_enum
Uses the smallest possible size for the enumeration type
Section 2.3.3
--static_template_instantiation
Instantiates all template entities as needed
Section 2.3.3
--unaligned_access={on|off}
Controls generation of unaligned accesses
Section 2.3.3
--use_dead_funcs_list [=fname]
Places each function listed in the file in a separate section
Section 2.3.3
--vectorize=off
Disables vectorization of source code
Section 2.3.3
Table 2-10. Optimization Options (1)
Option
Alias
Effect
Section
--opt_level=0
-O0
Optimizes register usage
Section 3.1
--opt_level=1
-O1
Uses -O0 optimizations and optimizes locally
Section 3.1
--opt_level=2
-O2 or -O
Uses -O1 optimizations and optimizes globally (default)
Section 3.1
--opt_level=3
-O3
Uses -O2 optimizations and optimizes the file
Section 3.1
Section 3.2
--opt_level=4
-O4
Uses -O3 optimizations and performs link-time optimization
Section 3.4
--auto_inline=[size]
-oi
Sets automatic inlining size (--opt_level=3 only). If size is not
specified, the default is 1.
Section 3.7
--call_assumptions=0
-op0
Specifies that the module contains functions and variables that are
called or modified from outside the source code provided to the
compiler
Section 3.3.1
(1)
24
Note: Machine-specific options (see Table 2-9) can also affect optimization.
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Table 2-10. Optimization Options (1) (continued)
Option
Alias
Effect
--call_assumptions=1
-op1
Specifies that the module contains variables modified from outside
Section 3.3.1
the source code provided to the compiler but does not use functions
called from outside the source code
Section
--call_assumptions=2
-op2
Specifies that the module contains no functions or variables that are Section 3.3.1
called or modified from outside the source code provided to the
compiler (default)
--call_assumptions=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
Section 3.3.1
--gen_opt_info=0
-on0
Disables the optimization information file
Section 3.2.2
--gen_opt_info=1
-on1
Produces an optimization information file
Section 3.2.2
--gen_opt_info=2
-on2
Produces a verbose optimization information file
Section 3.2.2
--opt_for_speed=n
-mf
Optimizes for speed over space (0-5 range)
Section 3.10
--optimizer_interlist
-os
Interlists optimizer comments with assembly statements
Section 3.8
--remove_hooks_when_inlining
Removes entry/exit hooks for auto-inlined functions
Section 2.15
--single_inline
Inlines functions that are only called once
--aliased_variables
-ma
Indicates that a specific aliasing technique is used
Table 2-11. 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
Table 2-12. Library Function Assumptions Options
Option
Alias
--printf_support={nofloat|full|
minimal}
Effect
Section
Enables support for smaller, limited versions of the printf and sprintf
run-time-support functions.
Section 2.3.2
--std_lib_func_defined
-ol1 or -oL1
Informs the optimizer that your file declares a standard library
function
Section 3.2.1
--std_lib_func_not_defined
-ol2 or -oL2
Informs the optimizer that your file does not declare or alter library
functions. Overrides the -ol0 and -ol1 options (default).
Section 3.2.1
--std_lib_func_redefined
-ol0 or -oL0
Informs the optimizer that your file alters a standard library function
Section 3.2.1
Table 2-13. Assembler Options
Option
Alias
Effect
Section
--keep_asm
-k
Keeps the assembly language (.asm) file
Section 2.3.10
--asm_listing
-al
Generates an assembly listing file
Section 2.3.10
--c_src_interlist
-ss
Interlists C source and assembly statements
Section 2.12
Section 3.8
--src_interlist
-s
Interlists optimizer comments (if available) and assembly source
statements; otherwise interlists C and assembly source statements
Section 2.3.1
--absolute_listing
-aa
Enables absolute listing
Section 2.3.10
--asm_define=name[=def]
-ad
Sets the name symbol
Section 2.3.10
--asm_dependency
-apd
Performs preprocessing; lists only assembly dependencies
Section 2.3.10
--asm_includes
-api
Performs preprocessing; lists only included #include files
Section 2.3.10
--asm_undefine=name
-au
Undefines the predefined constant name
Section 2.3.10
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Table 2-13. Assembler Options (continued)
Option
Alias
--code_state={16|32}
Effect
Section
Begins assembling instructions as 16- or 32-bit instructions.
Section 2.3.10
--copy_file=filename
-ahc
Copies the specified file for the assembly module
Section 2.3.10
--cross_reference
-ax
Generates the cross-reference file
Section 2.3.10
Controls assembly optimization of 32-bit Thumb2 into 16-bit Thumb
instructions
Section 2.3.10
--force_thumb2_mode={true|false}
--include_file=filename
Includes the specified file for the assembly module
Section 2.3.10
--max_branch_chain=num
-ahi
Controls the depth of branch chaining through the assembler
Section 3.11.18
--no_const_clink
Stops generation of .clink directives for const global arrays.
Section 2.3.2
--output_all_syms
-as
Puts labels in the symbol table
Section 2.3.10
--syms_ignore_case
-ac
Makes case insignificant in assembly source files
Section 2.3.10
Generates UAL syntax
Section 2.3.10
--ual
Table 2-14. 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 2.3.6
--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 2.3.6
--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 2.3.6
--obj_file=filename
-fo
Identifies filename as an object code file regardless of its extension. Section 2.3.6
By default, the compiler and linker treat .obj files as object code files.
Table 2-15. Directory Specifier Options
Option
Alias
Effect
--abs_directory=directory
-fb
Specifies an absolute listing file directory. By default, the compiler
uses the .obj directory.
Section 2.3.9
--asm_directory=directory
-fs
Specifies an assembly file directory. By default, the compiler uses
the current directory.
Section 2.3.9
--list_directory=directory
-ff
Specifies an assembly listing file and cross-reference listing file
directory By default, the compiler uses the .obj directory.
Section 2.3.9
--obj_directory=directory
-fr
Specifies an object file directory. By default, the compiler uses the
current directory.
Section 2.3.9
--output_file=filename
-fe
Specifies a compilation output file name; can override
--obj_directory.
Section 2.3.9
Specifies a preprocessor file directory. By default, the compiler uses
the current directory.
Section 2.3.9
--pp_directory=dir
--temp_directory=directory
-ft
Section
Specifies a temporary file directory. By default, the compiler uses the Section 2.3.9
current directory.
Table 2-16. Default File Extensions Options
Option
Alias
Effect
Section
--asm_extension=[.]extension
-ea
Sets a default extension for assembly source files
Section 2.3.8
--c_extension=[.]extension
-ec
Sets a default extension for C source files
Section 2.3.8
--cpp_extension=[.]extension
-ep
Sets a default extension for C++ source files
Section 2.3.8
--listing_extension=[.]extension
-es
Sets a default extension for listing files
Section 2.3.8
--obj_extension=[.]extension
-eo
Sets a default extension for object files
Section 2.3.8
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Table 2-17. 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 2.3.1
Table 2-18. MISRA-C:2004 Options
Option
Effect
Section
--check_misra[={all|required|
advisory|none|rulespec}]
Alias
Enables checking of the specified MISRA-C:2004 rules. Default is
all.
Section 2.3.2
--misra_advisory={error|warning|
remark|suppress}
Sets the diagnostic severity for advisory MISRA-C:2004 rules
Section 2.3.2
--misra_required={error|warning|
remark|suppress}
Sets the diagnostic severity for required MISRA-C:2004 rules
Section 2.3.2
The following tables list the linker options. See the ARM Assembly Language Tools User's Guide for
details on these options.
Table 2-19. Linker Basic Options Summary
Option
Alias
Description
--output_file=file
-o
Names the executable output module. The default filename is a.out.
--map_file=file
-m
Produces a map or listing of the input and output sections, including holes, and places
the listing in filename
--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
--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
Table 2-20. Command File Preprocessing Options Summary
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 2-21. Diagnostic Options Summary
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_warnings_as_errors
-pdew
Treat warnings as errors
--issue_remarks
Issues remarks (nonserious warnings)
--no_demangle
Disables demangling of symbol names in diagnostics
--no_warnings
Suppresses warning diagnostics (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
Provides verbose diagnostics that display the original source with line-wrap
--warn_sections
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-w
Displays a message when an undefined output section is created
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Table 2-22. File Search Path Options Summary
Option
Alias
Description
--library=file
-l
Names an archive library or link command file as linker input
--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.
--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
--disable_auto_rts
Disables the automatic selection of a run-time-support library
Table 2-23. Linker Output Options Summary
Option
Alias
Description
--output_file=file
-o
Names the executable output module. The default filename is a.out.
--map_file=file
-m
Produces a map or listing of the input and output sections, including holes, and places
the listing in filename
--absolute_exe
-a
Produces an absolute, executable module. This is the default; if neither --absolute_exe
nor --relocatable is specified, the linker acts as if --absolute_exe were specified.
--generate_dead_funcs_list
Writes a list of the dead functions that were removed by the linker to file fname.
--mapfile_contents=attribute
Controls the information that appears in the map file.
--relocatable
-r
--rom
Produces a nonexecutable, relocatable output module
Creates a ROM object
--run_abs
-abs
--xml_link_info=file
Produces an absolute listing file
Generates a well-formed XML file containing detailed information about the result of a
link
Table 2-24. Symbol Management Options Summary
Option
Alias
Description
--entry_point=symbol
-e
Defines a global symbol that specifies the primary entry point for the output module
--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_sym_merge
-b
Disables merge of symbolic debugging information in COFF object files
--no_sym_table
-s
Strips symbol table information and line number entries from the output module
--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
-u
--unhide=pattern
Adds symbol to the symbol table as an unresolved symbol
Excludes symbols that match the specified pattern from being hidden
Table 2-25. Run-Time Environment Options Summary
Option
Alias
Description
--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
--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
--arg_size=size
--args
Reserve size bytes for the argc/argv memory area
-be32
28
Forces the linker to generate BE-32 object code.
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Table 2-25. Run-Time Environment Options Summary (continued)
Option
Alias
-be8
Description
Forces the linker to generate BE-8 object code.
--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
Generates far call trampolines (argument is optional, is "on" by default)
--trampolines[=off|on]
Table 2-26. Link-Time Optimization Options Summary
Option
Description
--cinit_compression[=compression_kind]
Specifies the type of compression to apply to the c auto initialization data. Default is rle.
--compress_dwarf[=off|on]
Aggressively reduces the size of DWARF information from input object files. Default is
on.
--copy_compression[=compression_kind]
Compresses data copied by linker copy tables. Default is rle.
--unused_section_elimination[=off|on]
Eliminates sections that are not needed in the executable module. Default is on.
Table 2-27. Miscellaneous Options Summary
Option
Alias
--disable_clink
-j
Description
Disables conditional linking of COFF object modules
--linker_help
[-]-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
--zero_init=[off|on]
Controls preinitialization of uninitialized variables. Default is on.
2.3.1 Frequently Used Options
Following are detailed descriptions of options that you will probably use frequently:
--c_src_interlist
--cmd_file=filename
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 3.8. 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:
cl470 --cmd_file=file1 --cmd_file=file2 file3
--compile_only
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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 TMS470_C_OPTION
environment variable and you do not want to link. See Section 4.1.3.
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--define=name[=def]
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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:
•
--gen_aux_user_info
--help
--include_path=directory
--keep_asm
--quiet
--run_linker
--skip_assembler
--src_interlist
--tool_version
--undefine=name
--verbose
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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 and appends the .aux extension.
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 2.6.2.1.
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.
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2.3.2 Miscellaneous Useful Options
Following are detailed descriptions of miscellaneous options:
--check_misra={all|required|
advisory|none|rulespec}
--fp_mode={relaxed|strict}
Displays the specified amount or type of MISRA-C documentation. The
rulespec parameter is a comma-separated list of specifiers. See
Section 5.3 for details.
Supports relaxed floating-point mode. In this mode, if the result of a
double-precision floating-point expression is assigned to a
single-precision floating-point or an integer, the computations in the
expression are converted to single-precision computations. Any
double-precision constants in the expression are also converted to
single-precision if they can be correctly represented as single-precision
constants. This behavior does not conform with ISO; but it results in
faster code, with some loss in accuracy. In the following example, where
N is a number, iN=integer variable, fN=float variable, dN=double
variable:
il = f1 + f2 * 5.0 -> +, * are float, 5.0 is converted to 5.0f
il = d1 + d2 * d3 -> +, * are float
f1 = f2 + f3 * 1.1; -> +, * are float, 1.1 is converted to 1
--fp_reassoc={on|off}
--keep_unneeded_statics
--no_const_clink
--misra_advisory={error|
warning|remark|suppress}
--misra_required={error|
warning|remark|suppress}
--preinclude=filename
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To enable relaxed floating-point mode use the --fp_mode=relaxed option,
which also sets --fp_reassoc=on. To disable relaxed floating-point mode
use the --fp_mode=strict option, which also sets --fp_reassoc=off. The
default behavior is --fp_mode=strict.
If --strict_ansi is specified, --fp_mode=strict is set automatically. You can
enable the relaxed floating-point mode with strict ANSI mode by
specifying --fp_mode=relaxed after --strict_ansi. The relaxed
floating-point mode is enabled by default for ARM when the ABI chosen
is EABI(--abi=eabi), and the Strict ANSI mode (-ps) is not selected. In all
other cases, the default floating-point mode is strict.
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.
Does not delete unreferenced static variables. The parser by default
remarks about and then removes any unreferenced static variables. The
--keep_unneeded_statics option keeps the parser from deleting
unreferenced static variables and any static functions that are referenced
by these variable definitions. Unreferenced static functions will still be
removed.
Tells the compiler to not generate .clink directives for const global arrays.
By default, these arrays are placed in a .const subsection and
conditionally linked.
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 and sprintf
run-time-support functions. The valid values are:
• full: Supports all format specifiers. This is the default.
• nofloat: Excludes support for printing floating point values. Supports all
format specifiers except %f, %g, %G, %e, and %E.
• minimal: Supports the printing 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}
2.3.3 Run-Time Model Options
These options are specific to the ARM toolset. See the referenced sections for more information.
-ab=num
--abi={eabi|ti_arm9_abi|tiabi}
Controls the depth of branch chaining. See Section 3.11.18.
Specifies application binary interface (ABI). Default support is for
ARM architectures version 5e and version 6 (ti_arm9_abi). By default,
the linker generates either a BLX instruction or a veneer if there is a
mode change. Therefore, no label prefixes ($ for 16-BIS or _ for
32-BIS) are generated. Thus, new object files do not link with older
object files. The--abi=eabi option specifies the ABI defined by the
industry consortium founded by ARM Limited. The --abi=tiabi option
preserves the old behavior (prefixes) for compatibility with object files
produced prior to version 4.1.0. See Section 2.13 .
--align_structs=bytecount
Forces alignment of structures to a minimum bytecount-byte
boundary, where bytecount is a power of 2. To align all structs to a
word boundary use --align_structs=4. All structs in the file will contain
the bytecount minimum alignment, including nested structs. Only a
minimum alignment is set, the data structures are not packed. Your
program may break if one file is compiled with --align_structs and
another is not, or is a different alignment is used. The offsets of a
nested switch could be incorrect if different alignments are used.
--code_state={16|32}
Generates 16-bit Thumb code. By default, 32-bit code is generated.
When CortexR4, CortexM3, or CortexA8 architecture support is
chosen, the --code_state (or -mt) option generates Thumb-2 code.
For details on indirect calls in 16-bit versus 32-bit code, see
Section 6.10.2.2.
--disable_branch_chaining
Disables the branch chaining optimization. See Section 3.11.18.
--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 only available on Cortex-M devices.
--endian={big|little}
Designates big- or little-endian format for the compiled code. By
default, big-endian format is used.
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--enum_type={int|packed|
unpacked}
--float_support={vfpv3|
vfpv3d16|fpalib|vfplib|
vfpv4spd16}
-md
-ml
-mo
-mv={4|5e|6|7A8|7M3|7M4|7R4}
--neon
--plain_char={signed|unsigned}
-r={r5|r6|r9}
--small_enum
--static_template_instantiation
--unaligned_access={on|off}
--use_dead_funcs_list[=fname]
--vectorize=off
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Designates the underlying type of an enumeration type. The default is
unpacked, which designates the underlying type as int if the
enumerator constants can be represented in int. In C++, the
underlying type is long long if an enumerator constant cannot be
represented by int or unsigned int.
Using --enum_type=packed forces the enumeration type to be
packed, which designates the underlying type of the enumeration is
chosen to be the smallest integer that accommodates the enumerator
constants.
Using --enum_type=int designates the underlying type to always int.
An enumerator with a value outside int range generates an error.
Generates vector floating-point (VFP) coprocessor instructions for
various versions and libraries. See Section 2.14.
Disables dual-state interworking support. See Section 6.10.1.
Use long calls (requires -md and --code_state). See Section 6.4.5.
Enables dynamic stack overflow checking.
Selects processor version: ARM V4 (ARM7), ARM V5e (ARM9E),
ARM V6 (ARM11), ARM V7A8 (Cortex-A8), ARM V7M3 (Cortex-M3),
ARM V7M4 (Cortex-M4), OR ARM V7R (Cortex-R4), . 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.
Specifies how to treat C/C++ plain char variables, default is unsigned.
Disallows use of rx=[5|6|9] by the compiler.
By default, the ARM compiler uses 32 bits for every enum. When you
use the --small_enum option, the smallest possible byte size for the
enumeration type is used. For example, enum example_enum {first =
-128, second = 0, third = 127} uses only one byte instead of 32 bits
when the --small_enum option is used. Similarly, enum a_short_enum
{bottom = -32768, middle = 0, top = 32767} fits into two bytes instead
of four. Do not link object files compiled with the --small_enum option
with object files that have been 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.
Instantiates all template entities in the current file as needed though
the parser. These instantiations are also given internal (static)
linkage.
Controls whether or not the compiler generates unaligned accesses.
By default, unaligned accesses are turned on for all Cortex devices.
Places each function listed in the file in a separate section. The
functions are placed in the fname section, if specified.
Disables the vectorization of source code. The optimizer automatically
vectorizes code when -mv7A8 --neon is specified.
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2.3.4 Symbolic Debugging and Profiling Options
The following options are used to select symbolic debugging or profiling:
--profile:breakpt
Disables optimizations that would cause incorrect behavior when using a
breakpoint-based profiler.
--profile:power
Enables power profiling support by inserting NOPs into the frame code.
These NOPs can then be instrumented by the power profiling tooling to
track the power usage of functions. If the power profiling tool is not used,
this option increases the cycle count of each function because of the
NOPs. The --profile:power option also disables optimizations that cannot
be handled by the power-profiler.
--symdebug:coff
Enables symbolic debugging using the alternate STABS debugging
format. This may be necessary to allow debugging with older debuggers
or custom tools, which do not read the DWARF format. STABS format is
not supported for ELF.
--symdebug:dwarf
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. The --symdebug:dwarf option
disables many code generator optimizations, because they disrupt the
debugger. You can use the --symdebug:dwarf option with the --opt_level
(aliased as -O) option to maximize the amount of optimization that is
compatible with debugging (see Section 3.9.1).
For more information on the DWARF debug format, see The DWARF
Debugging Standard.
--symdebug:dwarf_
Changes the way the debug information is represented in the object file.
subsections=on|off
When the option is set to on, the resulting object file supports a rapid
form of type merging in the debugging information that is done in the
linker. If you have been using the --no_sym_merge linker option to
disable type merging of the debugging information in order to reduce link
time at the cost of increased .out file size, recompiling with
--symdebug:dwarf_subsections=on can realize a reasonable link time
without increasing the .out file size. The default behavior is off.
--symdebug:dwarf_
Specifies the DWARF debugging format version (2 or 3) to be generated
version={2|3}
when --symdebug:dwarf or --symdebug:skeletal is specified. By default,
the compiler generates DWARF version 3 debug information. For more
information on TI extensions to the DWARF language, see The Impact of
DWARF on TI Object Files (SPRAAB5).
--symdebug:none
Disables all symbolic debugging output. This option is not recommended;
it prevents debugging and most performance analysis capabilities.
--symdebug:profile_coff
Adds the necessary debug directives to the object file which are needed
by the profiler to allow function level profiling with minimal impact on
optimization (when used). Using --symdebug:coff may hinder some
optimizations to ensure that debug ability is maintained, while this option
will not hinder optimization. STABS format is not supported for ELF.
You can set breakpoints and profile on function-level boundaries in Code
Composer Studio, but you cannot single-step through code as with full
debug ability.
--symdebug:skeletal
Generates as much symbolic debugging information as possible without
hindering optimization. Generally, this consists of global-scope
information only. This option reflects the default behavior of the compiler.
See Section 2.3.11 for a list of deprecated symbolic debugging options.
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2.3.5 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 .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 2.3.6. 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 2.3.9.
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:
cl470 *.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.
2.3.6 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
for
for
for
an assembly language source file
a C source file
a C++ source file
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:
cl470 --c_file=file.s --asm_file=assy
You cannot use the filename options with wildcard specifications.
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2.3.7 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 2.3.8 for more information about filename extension
conventions.
2.3.8 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:
cl470 --asm_extension=.rrr --obj_extension=.o fit.rrr
The period (.) in the extension is optional. You can also write the example above as:
cl470 --asm_extension=rrr --obj_extension=o fit.rrr
2.3.9 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:
--asm_directory=directory
Specifies a directory for assembly files. For example:
--list_directory=directory
Specifies the destination directory for assembly listing files and
cross-reference listing files. The default is to use the same directory as
the object file directory. For example:
cl470 --abs_directory=d:\abso_list
cl470 --asm_directory=d:\assembly
cl470 --list_directory=d:\listing
--obj_directory=directory
Specifies a directory for object files. For example:
cl470 --obj_directory=d:\object
--output_file=filename
Specifies a compilation output file name; can override --obj_directory . For
example:
cl470 --output_file=transfer
--pp_directory=directory
Specifies a preprocessor file directory for object files (default is .). For
example:
--temp_directory=directory
Specifies a directory for temporary intermediate files. For example:
cl470 --pp_directory=d:\preproc
cl470 --temp_directory=d:\temp
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2.3.10 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
--asm_define=name[=def]
Generates a listing with absolute addresses rather than section-relative
offsets.
Predefines the constant name for the assembler; produces a .set directive
for a constant or a .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:
•
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}
--copy_file=filename
--cross_reference
--force_thumb2_mode=
{true|false}
--include_file=filename
--max_branch_chain
--output_all_syms
--syms_ignore_case
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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
CortexR4, CortexM3, or CortexA8 architecture support is chosen, the
--code_state (or -mt) option generates Thumb-2 code. For details on
indirect calls in 16-bit versus 32-bit code, see Section 6.10.2.2.
Copies the specified file for the assembly module; acts like a .copy
directive. The file is inserted before source file statements. The copied file
appears in the assembly listing files.
Produces a symbolic cross-reference in the listing file.
Alters default assembler behavior. By default, for C or C++ code, the
assembler optimizes 32-bit Thumb2 instructions when possible. For
hand-coded assembly code, the assembler does not optimize 32-bit
Thumb2 instructions.
If you require no assembly optimization of 32-bit instructions for C or C++,
use --force_thumb2_mode=true. If you require assembly optimization of
32-bit instructions in assembly files, use --force_thumb2_mode=false.
Includes the specified file for the assembly module; acts like a .include
directive. The file is included before source file statements. The included
file does not appear in the assembly listing files.
Controls the depth of branch chaining through the assembler. See
Section 3.11.18.
Puts labels in the symbol table. Label definitions are written to the COFF
symbol table for use with symbolic debugging.
Makes letter case insignificant in the assembly language source files. For
example, --syms_ignore_case makes the symbols ABC and abc
equivalent. If you do not use this option, case is significant (this is the
default).
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--ual
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Accepts UAL syntax when assembling for ARMv6 and earlier
architectures. UAL syntax is the default for ARMv7 and later architectures.
2.3.11 Deprecated Options
Several compiler options have been deprecated. The compiler continues to accept these options, but they
are not recommended for use. Future releases of the tools will not support these options. Table 2-28 lists
the deprecated options and the options that have replaced them.
Table 2-28. Compiler Backwards-Compatibility Options Summary
Old Option
Effect
-gp
Allows function-level profiling of optimized code
New Option
--symdebug:dwarf or -g
-gt
Enables symbolic debugging using the alternate STABS
debugging format
--symdebug:coff
-gw
Enables symbolic debugging using the DWARF debugging
format
--symdebug:dwarf or -g
Additionally, the --symdebug:profile_coff option has been added to enable function-level profiling of
optimized code with symbolic debugging using the STABS debugging format (the --symdebug:coff or -gt
option).
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 the device-specific
environment variables instead.
2.4.1 Setting Default Compiler Options (TMS470_C_OPTION)
You might find it useful to set the compiler, assembler, and linker default options using the
TMS470_C_OPTION environment variable. If you do this, the compiler uses the default options and/or
input filenames that you name TMS470_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 TMS470_C_OPTION environment variable and processes it.
The table below shows how to set the TMS470_C_OPTION environment variable. Select the command for
your operating system:
Operating System
Enter
UNIX (Bourne shell)
TMS470_C_OPTION=" option1 [option2 . . .]"; export TMS470_C_OPTION
Windows
set TMS470_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
TMS470_C_OPTION environment variable as follows:
set TMS470_C_OPTION=--quiet --src_interlist --run_linker
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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 TMS470_C_OPTION are passed to the linker. Thus, you can use
the TMS470_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 TMS470_C_OPTION is set as shown above:
cl470
cl470
cl470
cl470
*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.
2.4.2 Naming an Alternate Directory (TMS470_C_DIR)
The linker uses the TMS470_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)
TMS470_C_DIR=" pathname1 ; pathname2 ;..." ; export TMS470_C_DIR
Windows
set TMS470_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 TMS470_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 TMS470_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 TMS470_C_DIR
Windows
set TMS470_C_DIR=
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Precompiled Header Support
2.5
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Precompiled Header Support
Precompiled header files may reduce the compile time for applications whose source files share a
common set of headers, or a single file which has a large set of header files. Using precompiled headers,
some recompilation is avoided thus saving compilation time.
There are two ways to use precompiled header files. One is the automatic precompiled header file
processing and the other is called the manual precompiled header file processing.
2.5.1 Automatic Precompiled Header
The option to turn on automatic precompiled header processing is: --pch. Under this option, the compile
step takes a snapshot of all the code prior to the header stop point, and dump it out to a file with suffix
.pch. This snapshot does not have to be recompiled in the future compilations of this file or compilations of
files with the same header files.
The stop point typically is the first token in the primary source file that does not belong to a preprocessing
directive. For example, in the following the stopping point is before int i:
#include "x.h"
#include "y.h"
int i;
Carefully organizing the include directives across multiple files so that their header files maximize common
usage can increase the compile time savings when using precompiled headers.
A precompiled header file is produced only if the header stop point and the code prior to it meet certain
requirements.
2.5.2 Manual Precompiled Header
You can manually control the creation and use of precompiled headers by using several command line
options. You specify a precompiled header file with a specific filename as follows:
--create_pch=filename
The --use_pch=filename option specifies that the indicated precompiled header file should be used for this
compilation. If this precompiled header file is invalid, if its prefix does not match the prefix for the current
primary source file for example, a warning is issued and the header file is not used.
If --create_pch=filename or --use_pch=filename is used with --pch_dir, the indicated filename, which can
be a path name, is tacked on to the directory name, unless the filename is an absolute path name.
The --create_pch, --use_pch, and --pch options cannot be used together. If more than one of these
options is specified, only the last one is applied. In manual mode, the header stop points are determined
in the same way as in automatic mode. The precompiled header file applicability is determined in the
same manner.
2.5.3 Additional Precompiled Header Options
The --pch_verbose option displays a message for each precompiled header file that is considered but not
used. The --pch_dir=pathname option specifies the path where the precompiled header file resides.
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2.6
Controlling the Preprocessor
This section describes specific 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.
2.6.1 Predefined Macro Names
The compiler maintains and recognizes the predefined macro names listed in Table 2-29.
Table 2-29. Predefined ARM Macro Names
Macro Name
Description
_ _16bis_ _
Defined if 16-BIS state is selected (the -mt option is used); otherwise, it is undefined.
_ _32bis_ _
Defined if 32-BIS state is selected (the -mt option is not used); otherwise, it is undefined.
_ _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 indicate that compiler conforms to ISO C Standard. See Section 5.1 for
exceptions to ISO C conformance.
_ _STDC_VERSION_ _
C standard macro
_ _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_GNU_ATTIBUTE_SUPPORT_ _
Defined if GCC extensions are enabled (the --gcc option is used); otherwise, it is
undefined.
_ _TI_STRICT_ANSI_MODE__
Defined if strict ANSI/ISO mode is enabled (the --strict_ansi option is used); otherwise, it
is undefined.
_ _TI_EABI_SUPPORT_ _
Defined to 1 if the EABI ABI is enabled (the --abi=eabi option is used); 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_NEON_SUPPORT_ _
Defined to 1 if NEON SIMD extension is targeted (the --neon option is used); otherwise, it
is undefined.
_ _TI_ TMS470_V4_ _
Defined to 1 if the v4 architecture (ARM7) is targeted (the -mv4 option is used); otherwise,
it is undefined.
_ _TI_ TMS470_V5_ _
Defined to 1 if the v5E architecture (ARM9E) is targeted (the -mv5e option is used);
otherwise, it is undefined.
_ _TI_ TMS470_V6_ _
Defined to 1 if the v6 architecture (ARM11) is targeted (the -mv6 option is used);
otherwise, it is undefined.
_ _TI_ TMS470_V7_ _
Defined to 1 if any v7 architecture (Cortex) is targeted; otherwise, it is undefined.
_ _TI_ TMS470_V7A8_ _
Defined to 1 if the v7A8 architecture (Cortex-A8) is targeted (the -mv7A8 option is used);
otherwise, it is undefined.
_ _TI_ TMS470_V7M3_ _
Defined to 1 if the v7M3 architecture (Cortex-M3) is targeted (the -mv7M3 option is used);
otherwise, it is undefined.
_ _TI_ TMS470_V7R4_ _
Defined to 1 if the v7R4 architecture (Cortex-R4) is targeted (the -mv7R4 option is used);
otherwise, it is undefined.
(1)
Specified by the ISO standard
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Table 2-29. Predefined ARM Macro Names (continued)
Macro Name
Description
_ _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.
_ _TIME_ _ (1)
Expands to the compilation time in the form "hh:mm:ss"
_ _TMS470_ _
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.
_INLINE
Expands to 1 if optimization is used (--opt_level or -O option); undefined otherwise.
Regardless of any optimization, always undefined when --no_inlining is used.
_little_endian_ _
Defined if little-endian mode is selected (the --endian=little option is used); otherwise, it is
undefined.
You can use the names listed in Table 2-29 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");
2.6.2 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 TMS470_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 TMS470_C_DIR environment variable.
See Section 2.6.2.1 for information on using the --include_path option. See Section 2.4.2 for more
information on input file directories.
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2.6.2.1
Changing 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
cl470 --include_path=/tools/files source.c
Windows
cl470 --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 TMS470_C_DIR
environment variable.
For example, if you set up TMS470_C_DIR with the following command:
TMS470_C_DIR "/usr/include;/usr/ucb"; export TMS470_C_DIR
or invoke the compiler with the following command:
cl470 --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
2.6.3 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.
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2.6.4 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.
2.6.5 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.
2.6.6 Generating a Preprocessed Listing File With Line-Control Information
(--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.
2.6.7 Generating Preprocessed Output for a Make Utility (--preproc_dependency Option)
The --preproc_dependency option performs preprocessing only, but instead of writing preprocessed
output, 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 with a .pp
extension.
2.6.8 Generating a List of Files Included With the #include Directive (--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.
2.6.9 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. 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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2.7
Understanding Diagnostic Messages
One of the compiler's primary functions is to report diagnostics for the source program. The new linker
also reports diagnostics. 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
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
Diagnostic messages have an associated 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
continues, but object code is not generated.
• A warning indicates something that is valid but questionable. Compilation continues and object code is
generated (if no errors are detected).
• A remark is less serious than a warning. It indicates something that is valid and probably intended, but
may need to be checked. 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.
Diagnostics 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 line is omitted. Use the --verbose_diagnostics compiler option to enable the display
of 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 diagnostics 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 an error is determined to be discretionary based on the error severity associated with 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)"
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function "f(float)"
argument types are: (double)
f(1.5);
^
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 Diagnostics
The C/C++ compiler provides diagnostic options to control compiler- and linker-generated diagnostics. 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
diagnostics.
--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 diagnostics.
--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 diagnostics.
--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 diagnostics.
--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 (nonserious warnings), which are suppressed by default.
--no_warnings
Suppresses warning diagnostics (errors are still issued).
--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 diagnostics that display the original source with line-wrap
and indicate the position of the error in the source line
--write_diagnostics_file Produces a diagnostics information file with the same source file name with an
.err extension. (The --write_diagnostics_file option is not supported by the
linker.)
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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 now produces no diagnostic messages (because remarks are
disabled by default).
Although this type of control is useful, it can also be extremely dangerous. The compiler often emits
messages that indicate a less than obvious problem. Be careful to analyze all diagnostics emitted before
using the suppression options.
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.
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Generating Cross-Reference Listing Information (--gen_acp_xref Option)
2.9
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Generating Cross-Reference Listing Information (--gen_acp_xref Option)
The --gen_acp_xref option generates a cross-reference listing file that contains reference information for
each identifier in the source file. (The --gen_acp_xref option is separate from --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.
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_acp_raw Option)
The --gen_acp_raw 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
• Diagnostics
• 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 2-30.
Table 2-30. 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:
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Table 2-30. Raw Listing File Identifiers (continued)
Identifier
Definition
1 = entry into an include file
2 = exit from an include file
The --gen_acp_raw option also includes diagnostic identifiers as defined in Table 2-31.
Table 2-31. 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 2-31 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
Diagnostics 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, the C/C++ source code for the function is inserted at the point of the call.
This is known as inline function expansion. Inline function expansion is advantageous in short functions for
the following reasons:
Inline function expansion is performed in one of the following ways:
• Intrinsic operators are inlined by default.
• Code is compiled with definition-controlled inlining.
• When the optimizer is invoked with the --opt_level=3 option (-O3), automatic inline expansion is
performed at call sites to small functions. For more information about automatic inline function
expansion, see Section 3.7.
NOTE:
Function Inlining Can Greatly Increase Code Size
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.
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2.11.1 Inlining Intrinsic Operators
An operator is intrinsic if it can be implemented very efficiently with the target's instruction set. The
compiler automatically inlines the intrinsic operators of the target system by default. Inlining happens
whether or not you use the optimizer and whether or not you use any compiler or optimizer options on the
command line. These functions are considered the intrinsic operators:
• abs
• labs
• fabs
2.11.2 Using the inline Keyword, the --no_inlining Option, and Level 3 Optimization
Definition-controlled inline function expansion is performed when you invoke the compiler with optimization
and the compiler encounters the inline keyword in code. Functions with a variable number of arguments
are not inlined. In addition, a limit is placed on the depth of inlining for recursive or nonleaf functions.
Inlining should be used for small functions or functions that are called in a few places (though the compiler
does not enforce this). You can control this type of function inlining with the inline keyword.
The inline keyword specifies that a function is expanded inline at the point at which it is called, rather than
by using standard calling procedures.
The semantics of the inline keyword follows that described in the C++ standard. The inline keyword is
identically supported in C as a language extension. Because it is a language extension that could conflict
with a strictly conforming program, however, the keyword is disabled in strict ANSI C mode (when you use
the --strict_ansi compiler option). If you want to use definition-controlled inlining while in strict ANSI C
mode, use the alternate keyword _ _inline.
When you want to compile without definition-controlled inlining, use the --no_inlining option.
NOTE:
Using the --no_inlining Option With Level 3 Optimizations
When you use the --no_inlining option with --opt_level=3 (aliased as -O3) optimizations,
automatic inlining is still performed.
2.11.3 Automatic Inlining
When optimizing with the --opt_level=3 or --opt_level=2 option (aliased as -O3 or -O2), the compiler
automatically inlines certain functions. For more information, see Section 3.7.
2.11.4 Inlining Restrictions
There are several restrictions on what functions can be inlined for both automatic inlining and
definition-controlled inlining. Functions with local static variables or a variable number of arguments are
not inlined, with the exception of functions declared as static inline. In functions declared as static inline,
expansion occurs despite the presence of local static variables. In addition, a limit is placed on the depth
of inlining for recursive or nonleaf functions. Furthermore, inlining should be used for small functions or
functions that are called in a few places (though the compiler does not enforce this).
At
•
•
•
•
•
•
•
•
•
50
a given call site, a function may be disqualified from inlining if it:
Is not defined in the current compilation unit
Never returns
Is recursive
Has a FUNC_CANNOT_INLINE pragma
Has a variable length argument list
Has a different number of arguments than the call site
Has an argument whose type is incompatible with the corresponding call site argument
Has a class, structe or union parameter
Contains a volatile local variable or argument
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•
•
•
•
•
Is
Is
Is
Is
Is
not
not
not
not
not
declared
declared
declared
declared
declared
inline
inline
inline
inline
inline
and
and
and
and
and
contains an asm() statement that is not a comment
it is main()
it is an interrupt function
returns void but its return value is needed.
will require too much stack space for local array or structure variables.
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:
cl470 --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 3.8.
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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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 code to link together,
regardless of its source, and allows the resulting executable to run on any system that supports that ABI
Object modules conforming to different ABIs cannot be linked together. The linker detects this situation
and generates an error.
The ARM compiler supports three ABIs. The ABI is chosen through the --abi option as follows:
• TI ARM9 ABI (--abi=ti_arm9_abi)
The TI ARM9 ABI is the default ABI for the ARM compiler. If no --abi option is specified, the compiler
uses the TI ARM9 ABI. The object format, procedure calling conventions and all the other details of
this ABI are documented throughout this document and in the ARM Assembly Language Tools User's
Guide.
• TIABI (--abi=tiabi)
The TIABI is an obsolete ABI and is provided only for backward compatibility. You must enable this
ABI if you are linking object code or object libraries that have been compiled with an older compiler
(ARM 2.x compilers). You must also enable this ABI if you are compiling hand-coded assembly source
files that were initially written for a ARM 2.x compiler. The TIABI mode is only supported on the ARM7
(v4) architecture.
• ARM ABIv2 or EABI (--abi=eabi)
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 different ABIs, see Section 5.11.
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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:
vfpv3— VFPv3 architecture and instruction set
vfpv3d16— VFPv3d16 architecture and instruction set
vfpv4spd16 — VFPv4-SP architecture and instruction set
fpalib— FPA endianness is used to store double-precision floating-point values (most significant word
occupies the lower memory address).
vfplib— VFP endianness is used to store double-precision floating-point values (endianness used is that
of the memory system). All VFP coprocessors use this endianness to represent doubles.
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 7.1.6 for information on library-naming conventions.
• The compiler follows the VFP argument passing and returning calling convention for qualified VFP
arguments.
• Object files compiled with VFP support cannot be linked with objects not compiled with VFP support
whether the object files use floating-point computation or not. For correct linking of object code
compiled with VFP, all libraries and modules must be compiled with VFP support.
• Currently, the compiler generates only scalar VFP instructions. The vectorization component will be
available in future releases.
• 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_COPROC_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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53
Enabling Entry Hook and Exit Hook Functions
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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 5.9.13 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, software pipelining, 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
...........................................................................................................................
Invoking Optimization ........................................................................................
Performing File-Level Optimization (--opt_level=3 option) ......................................
Performing Program-Level Optimization (--program_level_compile and
--opt_level=3 options) ........................................................................................
Link-Time Optimization (--opt_level=4 Option) ......................................................
Accessing Aliased Variables in Optimized Code ...................................................
Use Caution With asm Statements in Optimized Code ...........................................
Automatic Inline Expansion (--auto_inline Option) .................................................
Using the Interlist Feature With Optimization ........................................................
Debugging and Profiling Optimized Code .............................................................
Controlling Code Size Versus Speed ...................................................................
What Kind of Optimization Is Being Performed? ...................................................
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Invoking Optimization
3.1
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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 high-level
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, and 3), which controls the type and degree of 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
The optimizer uses --opt_level=2 (-O2) as the default if you use --opt_level (-O) without an optimization
level.
• --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 3.2 and Section 3.3 for more information.
• --opt_level=4 or -O4
Performs link-time optimization. See Section 3.4 for details.
The levels of optimizations described above 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.
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3.2
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. 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
Have files that redeclare standard library functions
--std_lib_func_defined
--std_lib_func_redefined
Section 3.2.1
Want to create an optimization information file
--gen_opt_level=n
Section 3.2.2
Want to compile multiple source files
--program_level_compile
Section 3.3
3.2.1 Controlling File-Level Optimization (--std_lib_func_def Options)
When you invoke the compiler with the --opt_level=3 option, some of the optimizations use known
properties of the standard library functions. If your file redeclares any of these standard library functions,
these optimizations become ineffective. Use Table 3-2 to select the appropriate file-level optimization
option.
Table 3-2. Selecting a File-Level Optimization Option
If Your Source File...
Use this Option
Declares a function with the same name as a standard library function
--std_lib_func_redefined
Contains but does not alter functions declared in the standard library
--std_lib_func_defined
Does not alter standard library functions, but you used the --std_lib_func_redefined or
--std_lib_func_defined option in a command file or an environment variable. The
--std_lib_func_not_defined option restores the default behavior of the optimizer.
--std_lib_func_not_defined
3.2.2 Creating an Optimization Information File (--gen_opt_info Option)
When you invoke the compiler with the --opt_level=3 option, 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 3-3 to select the appropriate level to
append to the option.
Table 3-3. Selecting a Level for the --gen_opt_info Option
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_level=0
Want to produce an optimization information file
--gen_opt_level=1
Want to produce a verbose optimization information file
--gen_opt_level=2
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Performing Program-Level Optimization (--program_level_compile and --opt_level=3 options)
3.3
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Performing 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). 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 file-level 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.
To see which program-level optimizations the compiler is applying, use the --gen_opt_level=2 option to
generate an information file. See Section 3.2.2 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.
3.3.1 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 3-4 to select the appropriate level to append to the --call_assumptions option.
Table 3-4. 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 3-5 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 3-5. Special Considerations When Using the --call_assumptions Option
If Your Option 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 functions are
not identified by the FUNC_EXT_CALLED pragma
Reverts to --call_assumptions=0
--call_assumptions=1 or
--call_assumptions=2
No interrupt function is defined
Reverts to --call_assumptions=0
--call_assumptions=1 or
--call_assumptions=2
Functions are 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 3.3.2 for information about
these situations.
3.3.2 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 5.9.9)
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 3.3.1).
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. See Section 3.3.1 for
information about the --call_assumptions=2 option.
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.
See Section 3.3.1 for information about the --call_assumptions=n option.
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Link-Time Optimization (--opt_level=4 Option)
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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++.
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.
3.4
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.
Link-time optimization provides the same optimization opportunities as program level optimization
(Section 3.3), with 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
user-generated 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.
3.4.1 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 effect 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.
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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.
3.4.2 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.
3.5
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.
3.6
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.
3.7
Automatic Inline Expansion (--auto_inline Option)
When optimizing with the --opt_level=3 option or --opt_level=2 option (aliased as -O3 and -O2,
respectively), 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.
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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.
When deciding what to inline, the compiler collects all eligible call-sites in the module being compiled and
sorts them by the estimated benefit over cost. Functions declared static inline are ordered first, then leaf
functions, then all others eligible. Functions that are too big are not included.
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 auto-inlines aggressively if compiling for performance.
• At --opt_level=2, the compiler only automatically inlines small functions.
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 2.11.4.
Optimization Level 3 or 2 and Inlining
NOTE: In order to turn on automatic inlining, you must use the --opt_level=3 option or --opt_level=2
option. At --opt_level=2, only small functions are auto-inlined. If you desire the --opt_level=3
or 2 optimizations, but not automatic inlining, use --auto_inline=0 with the --opt_level=3 or 2
option.
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 and --no_inlining options. These options, used together,
cause the compiler to inline intrinsics only.
3.8
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.
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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.
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:
;** 5
;** 6
STMFD
SP!, {LR}
----------------------ADR
A1, SL1
BL
_printf
----------------------MOV
A1, #0
LDMFD
SP!, {PC}
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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Debugging and Profiling Optimized Code
3.9
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Debugging and Profiling Optimized Code
Debugging fully optimized code is not recommended, because the compiler's extensive rearrangement of
code and the many-to-many allocation of variables to registers often make it difficult to correlate source
code with object code. Profiling code that has been built with the --symdebug:dwarf (aliased as -g) option
or the --symdebug:coff option (STABS debug) is not recommended either, because these options can
significantly degrade performance. To remedy these problems, you can use the options described in the
following sections to optimize your code in such a way that you can still debug or profile the code.
3.9.1 Debugging Optimized Code (--symdebug:dwarf, --symdebug:coff, and --opt_level
Options)
To debug optimized code, use the --opt_level (aliased as -O) option in conjunction with one of the
symbolic debugging options (--symdebug:dwarf or --symdebug:coff). The symbolic debugging options
generate directives that are used by the C/C++ source-level debugger, but they disable many compiler
optimizations. When you use the --opt_level option (which invokes optimization) with the
--symdebug:dwarf or --symdebug:coff option, you turn on the maximum amount of optimization that is
compatible with debugging.
If you want to use symbolic debugging and still generate fully optimized code, use the
--optimize_with_debug option. This option reenables the optimizations disabled by --symdebug:dwarf or
--symdebug:coff. However, if you use the --optimize_with_debug option, portions of the debugger's
functionality will be unreliable.
If you are having trouble debugging loops in your code, you can use the --disable_software_pipelining
option to turn off software pipelining. See for more information.
Symbolic Debugging Options Affect Performance and Code Size
NOTE: Using the --symdebug:dwarf or --symdebug:coff option can cause a significant performance
and code size degradation of your code. Use these optionsthis option for debugging only.
Using --symdebug:dwarf or --symdebug:coff when profiling is not recommended.
3.9.2 Profiling Optimized Code
To profile optimized code, use optimization (--opt_level=0 through --opt_level=3) without any debug option.
By default, the compiler generates a minimal amount of debug information without affecting optimizations,
code size, or performance.
If you have a breakpoint-based profiler, use the --profile:breakpt option with the --opt_level option. The
--profile:breakpt option disables optimizations that would cause incorrect behavior when using a
breakpoint-based profiler.
If you have a power profiler, use the --profile:power option with the --opt_level option. The --profile:power
option produces instrument code for the power profiler.
If you need to profile code at a finer grain that the function level in Code Composer Studio, you can use
the --symdebug:dwarf or --symdebug:coff option, although this is not recommended. You might see a
significant performance degradation because the compiler cannot use all optimizations with
--symdebug:dwarf or --symdebug:coff. It is recommended that outside of Code Composer Studio, you use
the clock( ) function.
Profile Points
NOTE: In Code Composer Studio, when symbolic debugging is not used, profile points can only be
set at the beginning and end of functions.
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3.10 Controlling Code Size Versus Speed
The latest mechanism for controlling the goal of optimizations in the compiler is represented by the
--opt_for_speed=num option. The num denotes the level of optimization (0-5), which controls the type and
degree of code size or code speed optimization:
• --opt_for_speed=0
Enables optimizations geared towards improving the code size with a high risk of worsening or
impacting performance.
• --opt_for_speed=1
Enables optimizations geared towards improving the code size with a medium risk of worsening or
impacting performance.
• --opt_for_speed=2
Enables optimizations geared towards improving the code size with a low risk of worsening or
impacting performance.
• --opt_for_speed=3
Enables optimizations geared towards improving the code performance/speed with a low risk of
worsening or impacting code size.
• --opt_for_speed=4
Enables optimizations geared towards improving the code performance/speed with a medium risk of
worsening or impacting code size.
• --opt_for_speed=5
Enables optimizations geared towards improving the code performance/speed with a high risk of
worsening or impacting code size.
If you specify the option without a parameter, the default setting is --opt_for_speed=4. However, the
default behavior of the compiler is as if --opt_for_speed=1 were specified.
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What Kind of Optimization Is Being Performed?
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3.11 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 3.11.1
Alias disambiguation
Section 3.11.1
Branch optimizations and control-flow simplification
Section 3.11.3
Data flow optimizations
• Copy propagation
• Common subexpression elimination
• Redundant assignment elimination
Section 3.11.4
Expression simplification
Section 3.11.5
Inline expansion of functions
Section 3.11.6
Function Symbol Aliasing
Section 3.11.7
Induction variable optimizations and strength reduction
Section 3.11.8
Loop-invariant code motion
Section 3.11.9
Loop rotation
Section 3.11.10
Instruction scheduling
Section 3.11.11
470-Specific Optimization
See
Tail merging
Section 3.11.12
Autoincrement addressing
Section 3.11.13
Block conditionalizing
Section 3.11.14
Epilog inlining
Section 3.11.15
Removing comparisons to zero
Section 3.11.16
Integer division with constant divisor
Section 3.11.17
Branch chaining
Section 3.11.18
3.11.1 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 software pipeline, unroll, or eliminate the loop. Strength reduction turns the array
references into efficient pointer references with autoincrements.
3.11.2 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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3.11.3 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.
3.11.4 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.
3.11.5 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.
3.11.6 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.
3.11.7 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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3.11.8 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
loop-control variable, allowing its elimination.
3.11.9 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.
3.11.10 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.
3.11.11 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 pipeline latencies. It can also be used to
reduce code size.
3.11.12 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.
3.11.13 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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3.11.14 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
3.11.15 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.
3.11.16 Removing Comparisons to Zero
Because most of the 32-bit instructions and some of the 16-bit instructions can modify the status register,
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.
3.11.17 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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3.11.18 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 use the compiler --ab=num option to control the depth of branch chaining. The depth is
determined by the value of num. A value of zero tells the compiler not to perform branch chaining. A
negative value results in an assembler warning and the branch chaining depth defaults to zero.
Alternatively, you can use the assembler --max_branch_chain=num option.
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.
Branch chaining is disabled by the --disable_branch_chaining option.
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Linking C/C++ Code
The C/C++ compiler and assembly language 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) ........................................... 72
Linker Code Optimizations ................................................................................. 74
Controlling the Linking Process .......................................................................... 75
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Invoking the Linker Through the Compiler (-z Option)
4.1
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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:
cl470 --run_linker {--rom_model | --ram_model} filenames
[options] [--output_file= name.out] --library= library [lnk.cmd]
cl470 --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 cl470 --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 extension for all input files is .obj; 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-time-support 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
run-time-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.
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 modules prog1.obj, prog2.obj, and prog3.obj, with an
executable filename of prog.out with the command:
cl470 --run_linker --rom_model prog1 prog2 prog3 --output_file=prog.out
--library=rts16.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:
cl470filenames [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 modules prog1.c, prog2.c, and prog3.c, with an
executable filename of prog.out with the command:
cl470 prog1.c prog2.c prog3.c --run_linker --rom_model --output_file=prog.out --library=rts16.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 TMS470_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
TMS470_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 options are used to further optimize your code.
4.2.1 Generate List of Dead Functions (--generate_dead_funcs_list Option)
NOTE: Does this option apply to ARP32? So far only C6x and C28x do not support
--generate_dead_funcs_list.
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:
cl470 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:
cl470 --run_linker file1.obj file2.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:
cl470 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:
cl470 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:
cl470 --run_linker file1.obj file2.obj
Alternatively, you can combine steps 3 and 4 into one step. For example:
cl470 file1.c file2.c --use_dead_funcs_list=feedback.txt --run_linker
NOTE:
Dead Functions Feedback
The feedback file generated with the -gen_dead_funcs_list option is version controlled. It
must be generated by the linker in order to be processed correctly by the compiler.
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4.2.2 Generating Function Subsections (--gen_func_subsections Compiler Option)
When the linker places code into an executable file, it allocates all the functions in a single source file as a
group. This means that if any function in a file needs to be linked into an executable, then all the functions
in the file are linked in. This can be undesirable if a file contains many functions and only a few are
required for an executable.
This situation may exist in libraries where a single file contains multiple functions, but the application only
needs a subset of those functions. An example is a library .obj file that contains a signed divide routine
and an unsigned divide routine. If the application requires only signed division, then only the signed divide
routine is required for linking. By default, both the signed and unsigned routines are linked in since they
exist in the same .obj file.
The --gen_func_subsections compiler option remedies this problem by placing each function in a file in its
own subsection. Thus, only the functions that are referenced in the application are linked into the final
executable. This can result in an overall code size reduction.
In addition to placing each function in a separate subsection, the compiler also annotates that subsection
with a conditional linking directive, .clink. This directive marks the section as a candidate to be removed if
it is not referenced by any other section in the program. The compiler does not place a .clink directive in a
subsection for a trap or interrupt function, as these may be needed by a program even though there is no
symbolic reference to them anywhere in the program.
If a section that has been marked for conditional linking is never referenced by any other section in the
program, that section is removed from the program. Conditional linking is disabled when performing a
partial link or when relocation information is kept with the output of the link. Conditional linking can also be
disabled with the --disable_clink link option.
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 include a run-time-support library in the linker process. The following sections describe two
methods for including the run-time-support library.
4.3.1.1
Manual Run-Time-Support Library Selection
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. You must use the
--library linker option to specify which ARM run-time-support library to use. The --library option also tells
the linker to look at the --search_path options and then the TMS470_C_DIR environment variable to find
an archive path or object file. To use the --library linker option, type on the command line:
cl470 --run_linker {--rom_model | --ram_model} filenames --library= libraryname
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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.
4.3.1.2
Automatic Run-Time-Support Library Selection
If the --rom_model or --ram_model option is specified during the linker 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 best compatible run-time-support library for your program. The chosen run-time-support library
is linked in as if it was specified with the --library option last on the command line. Alternatively, you can
always force the linker to choose an appropriate run-time-support library by specifying “libc.a” as an
argument to the --library option, or when specifying the run-time-support library name explicitly in a linker
command file.
The automatic selection of a run-time-support library can be disabled with 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, you must specify the name of the desired run-time-support library using the --library option and in
your linker command files when necessary.
Example 4-1. Using the --issue_remarks Option
cl470 --abi=eabi --code_state=16 --issue_remarks main.c --run_linker --rom_model
<Linking>
remark: linking in "libc.a"
remark: linking in "rtsv4_T_be_eabi.lib" in place of "libc.a"
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 and secondary system 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 main
8. Call exit when main returns
A sample bootstrap routine is _c_int00, provided in boot.obj in the run-time support object libraries. The
entry point is usually set to the starting address of the bootstrap routine.
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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.
4.3.3 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 main( ) is called.
Global destructors are invoked during exit( ), similar to functions registered through atexit( ).
discusses the format of the global constructor table for TIABI and TI ARM9 ABI modes and Section 6.9.7
for EABI mode.
4.3.4 Specifying the Type of Global Variable Initialization
The C/C++ compiler produces data tables for initializing global variables. Section 6.9.6 discusses the
format of these initialization tables for TIABI and TI_ARM9_ABI. Section 6.9.5.4 discusses the format of
these initialization tables for EABI. 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 6.9.3).
• Global variables are initialized at load time. Use the --ram_model linker option (see Section 6.9.4).
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). The following list outlines the linking
conventions for TIABI and TI_ARM9_ABI used with --rom_model or --ram_model:
• The symbol _c_int00 is defined as the program entry point; it identifies the beginning of the C/C++ boot
routine in boot.obj. When you use --rom_model or --ram_model, _c_int00 is automatically referenced,
ensuring that boot.obj is automatically linked in from the run-time-support library.
• The initialization output section is padded with a termination record so that the loader (load-time
initialization) or the boot routine (run-time initialization) knows when to stop reading the initialization
tables.
• The global constructor output section is padded with a termination record.
• When initializing at load time (the --ram_model option), the following occur:
– The linker sets the initialization table symbol to -1. This indicates that the initialization tables are not
in memory, so no initialization is performed at run time.
– The STYP_COPY flag is set in the initialization table section header. STYP_COPY is the special
attribute that tells the loader to perform autoinitialization directly and not to load the initialization
table into memory. The linker does not allocate space in memory for the initialization table.
• When autoinitializing at run time (--rom_model option), the linker defines the initialization table symbol
as the starting address of the initialization table. The boot routine uses this symbol as the starting point
for autoinitialization.
• The linker defines the starting address of the global constructor table. The boot routine uses this
symbol as the beginning of the table of global constructors.
For details on linking conventions for EABI used with --rom_model and --ram_model, see Section 6.9.5.3
and Section 6.9.5.5, respectively.
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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.
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4.3.5 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.
The compiler creates two basic kinds of sections: initialized and uninitialized. Table 4-1 summarizes the
initialized sections created under the TIABI and TI ARM9 ABI modes. Table 4-2 summarizes the initialized
sections created under the EABI mode. Table 4-3 summarizes the uninitialized sections. Be aware that
the TIABI and TI ARM9 ABI, and EABI .cinit tables have different formats.
Table 4-1. Initialized Sections Created by the Compiler
TIABI and TI ARM9 ABI
Name
Contents
.cinit
Tables for explicitly initialized global and static variables
.const
Global and static const variables that are explicitly initialized and contain string
literals
.pinit
Table of constructors to be called at startup
.switch
.text
Executable code and constants
Table 4-2. Initialized Sections Created by the Compiler for EABI
Name
Contents
.cinit
Tables for explicitly initialized global and static variables
.const
Global and static const variables that are explicitly initialized and contain string
literals
.data
Global and static non-const variables that are explicitly initialized
.init_array
Table of constructors to be called at startup
.text
Executable code and constants
Table 4-3. Uninitialized Sections Created by the Compiler
Name
Contents
.bss
Global and static variables
.stack
Stack
.sysmem
Memory for malloc functions (heap)
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. See
Section 6.1.1 for a complete description of how the compiler uses these sections.
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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4.3.6 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:
cl470 --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
80
:
:
:
:
{}
{}
{}
{}
>
>
>
>
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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ARM C/C++ Language Implementation
The C/C++ compiler supports the C/C++ language standard that was developed by a committee of the
American National Standards Institute (ANSI) and subsequently adopted by the International Standards
Organization (IS0).
The C++ language supported by the ARM is defined by the ANSI/ISO/IEC 14882:1998 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
...........................................................................................................................
Page
Characteristics of ARM C ................................................................................... 82
Characteristics of ARM C++ ................................................................................ 82
Using MISRA-C:2004 .......................................................................................... 83
Data Types ....................................................................................................... 84
Keywords ......................................................................................................... 85
C++ Exception Handling ..................................................................................... 86
Register Variables and Parameters ...................................................................... 87
The asm Statement ............................................................................................ 88
Pragma Directives ............................................................................................. 89
The _Pragma Operator ..................................................................................... 101
Application Binary Interface .............................................................................. 102
ARM Instruction Intrinsics ................................................................................ 104
Object File Symbol Naming Conventions (Linknames) ......................................... 108
Initializing Static and Global Variables in TIABI and TI ARM9 ABI Modes ............... 109
Changing the ANSI/ISO C Language Mode .......................................................... 110
GNU Language Extensions ............................................................................... 112
AUTOSAR ....................................................................................................... 114
Compiler Limits ............................................................................................... 114
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Characteristics of ARM C
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Characteristics of ARM C
The compiler supports the C language as defined by ISO/IEC 9899:1990, which is equivalent to American
National Standard for Information Systems-Programming Language C X3.159-1989 standard, commonly
referred to as C89, published by the American National Standards Institute. The compiler can also accept
many of the language extensions found in the GNU C compiler (see Section 5.16). The compiler does not
support C99.
The ANSI/ISO standard identifies some features of the C language that are affected by characteristics of
the target processor, run-time environment, or host environment. For reasons of efficiency or practicality,
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 and multi-byte 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. So-called multi-byte characters are limited to single characters. There are no shift states.
The mapping between multi-byte characters and wide characters is simple equivalence; that is, each
wide character maps to and from exactly a single multi-byte character having the same value.
• 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
hard-coded to the behavior of the C locale, and attempting to install a different locale by way of a call
to setlocale() will return NULL.
5.2
Characteristics of ARM C++
The ARM compiler supports C++ as defined in the ANSI/ISO/IEC 14882:1998 standard, including these
features:
• Complete C++ standard library support, with exceptions noted below.
• Templates
• Exceptions, which are enabled with the --exceptions option; see Section 5.6.
• Run-time type information (RTTI), which can be enabled with the --rtti compiler option.
The exceptions to the standard are as follows:
• The compiler does not support embedded C++ run-time-support libraries.
• The <complex> header and its functions are not included in the library.
• The 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
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.
• For TIABI only: If the definition of an inline function contains a static variable, and it appears in multiple
compilation units (usually because it’s a member function of a class defined in a header file), the
compiler generates multiple copies of the static variable rather than resolving them to a single
definition. The compiler emits a warning (#1369) in such cases.
• Two-phase name binding in templates, as described in [tesp.res] and [temp.dep] of the standard, is not
implemented.
• The export keyword for templates is not implemented.
• A typedef of a function type cannot include member function cv-qualifiers.
• A partial specialization of a class member template cannot be added outside of the class definition.
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5.3
Using MISRA-C:2004
You can alter your code to work with the MISRA-C:2004 rules. The following enable/disable the rules:
• The --check_misra option enables checking of the specified MISRA-C:2004 rules.
• The CHECK_MISRA pragma enables/disables MISRA-C:2004 rules at the source level. This pragma is
equivalent to using the --check_misra option. See Section 5.9.1.
• RESET_MISRA pragma resets the specified MISRA-C:2004 rules to the state they were before any
CHECK_MISRA pragmas were processed. See Section 5.9.14.
The syntax of the option and pragmas are:
--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 these specifiers:
[-]X
[-]X-Z
[-]X.A
[-]X.A-C
Enable
Enable
Enable
Enable
(or
(or
(or
(or
disable)
disable)
disable)
disable)
all rules in topic X.
all rules in topics X through Z.
rule A in topic X.
rules A through C in topic X.
Example: --check_misra=1-5,-1.1,7.2-4
• Checks topics 1 through 5
• Disables rule 1.1 (all other rules from topic 1 remain enabled)
• Checks rules 2 through 4 in topic 7
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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Data Types
5.4
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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.
Table 5-1. ARM C/C++ Data Types
Range
Type
Size
Representation
Minimum
Maximum
signed char
8 bits
ASCII
-128
127
char, unsigned char, bool
8 bits
ASCII
0
255
short, signed short
16 bits
2s complement
-32 768
32 767
unsigned short, wchar_t
16 bits
Binary
0
65 535
int, signed int
32 bits
2s complement
-2 147 483 648
2 147 483 647
unsigned int
32 bits
Binary
0
4 294 967 295
long, signed long
32 bits
2s complement
-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
2s complement
-9 223 372 036 854 775 808
9 223 372 036 854 775 807
unsigned long long
64 bits
Binary
0
18 446 744 073 709 551 615
enum (TIABI and
TI_ARM9_ABI only) See
Table 5-2 for EABI values.
32 bits
2s complement
-2 147 483 648
2 147 483 647
float
32 bits
IEEE 32-bit
1.175 494e-38 (1)
3.40 282 346e+38
double
64 bits
(2)
IEEE 64-bit
2.22 507 385e-308 (1)
1.79 769 313e+308
long double
64 bits (2)
IEEE 64-bit
2.22 507 385e-308 (1)
1.79 769 313e+308
pointers, references, pointer to
data members
32 bits
Binary
0
0xFFFFFFFF
(1)
(2)
Figures are minimum precision.
In TIARM9 ABI mode, 64-bit data is aligned on a 32-bit boundary. In EABI mode, 64-bit data is aligned on a 64-bit boundary.
In EABI mode, 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. EABI Enumerator Types
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
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 =
blue
=
yellow =
red
=
-200,
1,
2,
60000
}
For example, the following code results in an enumerator type of short:
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enum COLORS
{ green =
blue
=
yellow =
red
=
5.5
-200,
1,
2,
3 }
Keywords
The ARM C/C++ compiler supports the standard const and volatile keywords. In addition, the C/C++
compiler extends the C/C++ language through the support of the interrupt keyword.
5.5.1 The const Keyword
The C/C++ compiler supports the ANSI/ISO standard keyword const. This keyword gives you greater
optimization and control over allocation of storage 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.
If you define an object as const, the .const section allocates storage for the object. The const data storage
allocation rule has two exceptions:
• If the keyword volatile is also specified in the definition of an object (for example, volatile const int x).
Volatile keywords are assumed to be allocated to RAM. (The program does not modify a const volatile
object, but something external to the program might.)
• If the object has automatic storage (function scope).
In both cases, the storage for the object is the same as if the const keyword were not used.
The placement of the const keyword within a definition is important. For example, the first statement below
defines a constant pointer p to a variable int. The second statement defines a variable 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};
5.5.2 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.
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 function main. Because it has no caller, c_int00
does not save any registers.
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Use the alternate keyword, __interrupt, if you are writing code for strict ANSI/ISO mode (using the
--strict_ansi compiler option).
HWI Objects and the interrupt Keyword
NOTE: The interrupt keyword must not be used when 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.
5.5.3 The volatile Keyword
The compiler analyzes data flow to avoid memory accesses whenever possible. If you have code that
depends on memory accesses exactly as written in the C/C++ code, you must use the volatile keyword to
identify these accesses. A variable qualified with a volatile keyword is allocated to an uninitialized section
(as opposed to a register). The compiler does not optimize out any references to volatile variables.
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
single-memory 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.
5.6
C++ Exception Handling
The compiler supports all the C++ exception handling features as defined by the ANSI/ISO 14882 C++
Standard. More details are discussed in 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 a particular file. Mixing exception-enabled object files
and libraries with object files and libraries that do not have exceptions enabled can lead to undefined
behavior. Also, when using --exceptions, you need to link with run-time-support libraries whose name
contains _eh. These libraries contain functions that implement exception handling.
Using --exceptions causes
Using --exceptions causes the compiler to insert exception handling code. This code will increase the
code size of the program, particularly for TIABI and TI_ARM9_ABI modes. In addition, TIABI and
TI_ARM9_ABI will increase the execution time, even if an exception is never thrown. EABI will not
increase code size as much, and has a minimal execution time cost if exceptions are never thrown, but
will slightly increase the data size for the exception-handling tables.
See Section 7.1 for details on the run-time libraries.
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5.7
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.
5.7.1 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.
5.7.2 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.
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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.
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.
5.8
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—the asm
statement. The asm (or __asm) statement provides access to hardware features that C/C++ cannot
provide. The asm statement is syntactically like 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 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.
Use the alternate statement __asm("assembler text") if you are writing code for strict ANSI/ISO C mode
(using the --strict_ansi option).
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NOTE:
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.
5.9
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:
• CHECK_MISRA (See Section 5.9.1)
• CLINK (See Section 5.9.2)
• CODE_SECTION (See Section 5.9.3)
• CODE_STATE (See Section 5.9.4)
• DATA_ALIGN (See Section 5.9.5)
• DATA_SECTION (See Section 5.9.6)
• DIAG_SUPPRESS, DIAG_REMARK, DIAG_WARNING, DIAG_ERROR, and DIAG_DEFAULT (See
Section 5.9.7)
• DUAL_STATE (See Section 5.9.8)
• FUNC_EXT_CALLED (See Section 5.9.9)
• FUNCTION_OPTIONS (See Section 5.9.10)
• INTERRUPT (See Section 5.9.11)
• MUST_ITERATE (See Section 5.9.12)
• NO_HOOKS (See Section 5.9.13)
• RESET_MISRA (See Section 5.9.14)
• RETAIN (See Section 5.9.15)
• SET_CODE_SECTION (See Section 5.9.16)
• SET_DATA_SECTION (See Section 5.9.16)
• SWI_ALIAS (See Section 5.9.17)
• TASK (See Section 5.9.18)
• UNROLL (See Section 5.9.19)
• WEAK (See Section 5.9.20)
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 the pragmas that apply to functions or symbols (except CLINK and RETAIN), the syntax for the
pragmas 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. In C++, the name is omitted; the pragma applies to the
declaration of the object or function that follows it.
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5.9.1 The CHECK_MISRA Pragma
The CHECK_MISRA pragma enables/disables MISRA-C:2004 rules at the source level. This pragma is
equivalent to using the --check_misra option.
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 specifiers. See Section 5.3 for details.
The RESET_MISRA pragma can be used to reset any CHECK_MISRA pragmas; see Section 5.9.14.
5.9.2 The CLINK Pragma
The CLINK pragma can be applied to a code or data symbol. It causes a .clink directive to be generated
into the section that contains the definition of the symbol. The .clink directive indicates to the linker that the
section is eligible for removal during conditional linking. Therefore, if the section is not referenced by any
other section in the application that is being compiled and linked, it will not be included in the output file
result of the link.
The syntax of the pragma in C/C++ is:
#pragma CLINK (symbol )
The RETAIN pragma has the opposite effect of the CLINK pragma. See Section 5.9.15 for more details.
5.9.3 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 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 " )
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 following examples demonstrate the use of the CODE_SECTION pragma.
Example 5-1. Using the CODE_SECTION Pragma C Source File
#pragma CODE_SECTION(fn, "my_sect")
int fn(int x)
{
return x;
}
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Example 5-2. Generated Assembly Code From Example 5-1
.sect
"my_sect"
.align
4
.clink
.armfunc fn
.state32
.global
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
5.9.4 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 );
5.9.5 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 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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5.9.6 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 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 " );
The DATA_SECTION pragma is useful if you have data objects that you want to link into an area separate
from the .bss section. If you allocate a global variable using a DATA_SECTION pragma and you want to
reference the variable in C code, you must declare the variable as extern far.
Example 5-3 through Example 5-5 demonstrate the use of the DATA_SECTION pragma.
Example 5-3. Using the DATA_SECTION Pragma C Source File
#pragma DATA_SECTION(bufferB, "my_sect")
char bufferA[512];
char bufferB[512];
Example 5-4. Using the DATA_SECTION Pragma C++ Source File
char bufferA[512];
#pragma DATA_SECTION("my_sect")
char bufferB[512];
Example 5-5. Using the DATA_SECTION Pragma Assembly Source File
.global
.bss
.global
_bufferB: .usect
92
_bufferA
_bufferA,512,4
_bufferB
"my_sect",512,4
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5.9.7 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
The syntax of the pragmas in C is:
#pragma DIAG_XXX [=]num[, num2, num3...]
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 diagnostics 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 along with the message when the -pden command line option is
specified.
5.9.8 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 6.10.
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5.9.9 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 by hand-coded assembly instead of main.
The FUNC_EXT_CALLED pragma specifies to the optimizer to keep these C functions or any other
functions that 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 that you want to keep. In C,
the argument func is the name of the function that you do not want removed. 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;
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 3.3.2.
5.9.10 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" );
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5.9.11 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 )] ;
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 V7M3 architecture, the interrupt_type can be nothing (default) or SWI. The M3 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 M3, C SWI handlers cannot return values).
HWI Objects and the INTERRUPT Pragma
NOTE: The INTERRUPT pragma must not be used when 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.
5.9.12 The MUST_ITERATE Pragma
The MUST_ITERATE pragma specifies to the compiler certain properties of a loop. You guarantee that
these properties are always true. Through the use of the MUST_ITERATE pragma, you can guarantee
that a loop executes a specific number of times. Anytime 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, software pipelining and 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 and PROB_ITERATE, can appear between
the MUST_ITERATE pragma and the loop.
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5.9.12.1 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.
5.9.12.2 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 software pipelined 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. For example:
pragma MUST_ITERATE(8, 48, 8);
for(i = 0; i < trip_count; i++)
{ ...
This example tells the compiler that the loop executes between 8 and 48 times and that 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.
You should also consider using MUST_ITERATE for loops with complicated bounds. In the following
example:
for(i2 = ipos[2]; i2 < 40; i2 += 5)
{ ...
The compiler would have to generate a divide function call to determine, at run time, the exact number of
iterations performed. The compiler will not do this. In this case, using MUST_ITERATE to specify that the
loop always executes eight times allows the compiler to attempt to generate a software pipelined loop:
#pragma MUST_ITERATE(8, 8);
for(i2 = ipos[2]; i2 < 40; i2 += 5)
96
{ ...
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5.9.13 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.
5.9.14 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 5.9.1) 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 syntax of the pragma in C is:
#pragma RESET_MISRA (" {all|required|advisory|rulespec} " )
The rulespec parameter is a comma-separated list of specifiers. See Section 5.3 for details.
5.9.15 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 syntax of the pragma in C/C++ is:
#pragma RETAIN ( symbol )
The CLINK pragma has the opposite effect of the RETAIN pragma. See Section 5.9.2 for more details.
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5.9.16 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 5-6 x and y are put in the section mydata. To reset the current section to the default used by
the compiler, a blank paramater 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 5-6. 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 5-7. Setting a Section With SET_CODE_SECTION Pragma
#pragma SET_CODE_SECTION("func1")
extern void func1();
#pragma SET_CODE_SECTION()
...
void func1() { ... }
In Example 5-7 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 5-8. 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 5-8 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 implictly
created objects, such as implicit constructors and virtual function tables.
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5.9.17 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 more information about using software interrupts, including restrictions on passing arguments and
register usage, see Section 6.6.5.
Example 5-9. 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 5-10. 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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Pragma Directives
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5.9.18 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
5.9.19 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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5.9.20 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.
5.10 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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Application Binary Interface
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5.11 Application Binary Interface
Selecting one of the three ABIs supported by the ARM compiler is discussed in Section 2.13.
An ABI should define how functions that are written separately, and compiled or assembled separately
can work together. This involves standardizing the data type representation, register conventions, and
function structure and calling conventions. It should define linkname generation from C symbol names. It
should define the object module format and the debug format. It should document how the system is
initialized. In the case of C++ it should define C++ name mangling and exception handling support.
5.11.1 TI_ARM9_ABI
The TI ARM9 ABI is the default mode of the compiler. This ABI is documented throughout this document
and the Assembly Language Tools User's Guide. Refer to the following sections for more information:
Section
Section
Section
Section
Section
5.4
6.2
6.3
6.4
6.9
Data Types
Object Representation
Register Conventions
Function Structure and Calling Conventions
System Initialization
In the TI ARM9 ABI, the link step generates any necessary code when cross-mode calls are made. No
extra code needs to be written to handle the transfer from arm-mode to thumb-mode, or vice-versa.
However, all 32-bit and 16-bit assembly routines must be explicitly identified using the .armfunc and
.thumbfunc assembler directives. These directives are required for the link step to properly generate dual
mode code. Assembly code without these directives may result in compiler errors and incorrect execution.
Refer to the Assembly Language Tools User's Guide for details on the .armfunc and .thumbfunc
directives.
The __TI_ARM9ABI_ASSEMBLER predefined symbol is set to 1 if compiling for TI ARM9 ABI and is set
to 0 otherwise. To write code that can be used with multiple ABIs, the assembly code must use this
predefined symbol to make the code conditional.
All function names are prefixed with the '_' (underscore) for both 16-bit mode (thumb) or 32-bit mode
(arm). If you are writing hand-coded assembly routines, you must use only the underscore prefix.
For example, if function (foo) is to be defined in 16-bit mode, and the code needs to be assembled for TI
ARM9 ABI and TI ABI, this is the desired assembly sequence:
.if __TI_ARM9ABI_ASSEMBLER
.thumbfunc _foo
.endif
.if __TIARM9ABI_ASSEMBLER
_foo:
.else
$foo:
.endif
5.11.2 TIABI
The TIABI mode is the ABI of older TI 2.x ARM compilers. You must enable this ABI (--abi=tiabi) if you are
linking object code or object libraries that have been compiled with an older compiler. You must also
enable this ABI if you are compiling hand-coded assembly source files that were initially written for a TI 2.x
ARM compiler. The TIABI mode cannot be used with any architecture option for ARM9E or higher.
The only difference between TIABI mode and TI ARM9 ABI mode is that in TIABI the link step cannot
generate the code to support cross-mode calls. The compiler generates veneers to support-cross mode
calls. Refer to Section 6.10 for more information.
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5.11.3 ARM ABIv2 or EABI
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 and the documentation is a reference point for those writing utilities that require
an understanding of the ABI. The complete ARM ABI specifications can be found at
http://www.arm.com/products/DevTools/ABI.html.
• 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 6.9.5.
The __TI_EABI_ASSEMBLER predefined symbol is set to 1 if compiling for EABI and is set to 0
otherwise.
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ARM Instruction Intrinsics
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5.12 ARM Instruction Intrinsics
Assembly instructions can be generated using the intrinsics in the following tables.
Table 5-3. v5e, v6, Cortex-M3, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics
C/C++ Compiler Intrinsic
Assembly
Instruction
Description
int dst = _norm(int src );
CLZ dst , src
Normalize floating point
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 =_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 _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 _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 =_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 =_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 _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 _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.
Table 5-4. V5E, V6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics
C/C++ Compiler Intrinsic
Assembly
Instruction
Description
int dst =_sadd(int src1 , int src2 );
QADD dst , src1 , src2
Saturated add
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 =_smac(int src1 , int src2 );
SMULBB tmp , src1 , src2
QDADD dst , dst , tmp
Saturated multiply-accumulate
int dst =_smlabb(int src1 , int src2 , int acc );
SMLABB dst , src1 , src2
Signed multiply-accumulate bottom halfwords
int dst =_smlabt(int src1 , int src2 , int acc );
SMLABT dst , src1 , src2
Signed multiply-accumulate bottom and top
halfwords
long long dst =_smlalbb(int src1 , int src2 );
SMLALBB dstlo , dsthi , src1 , src2
Signed multiply-long and accumulate bottom
halfwords
long long dst =_smlalbt(int src1 , int src2 );
SMLALBT dstlo , dsthi , src1 , src2
Signed multiply-long and accumulate bottom
and top halfwords
long long dst =_smlaltb(int src1 , int src2 );
SMLALTB dstlo , dsthi , src1 , src2
Signed multiply-long and accumulate top and
bottom halfwords
long long dst =_smlaltt(int src1 , int src2 );
SMLALTT dstlo , dsthi , src1 , src2
Signed multiply-long and accumulate top
halfwords
int dst =_smlatb(int src1 , int src2 , int acc );
SMLATB dst , src1 , src2
Signed multiply-accumulate top and bottom
halfwords
int dst =_smlatt(int src1 , int src2 , int acc );
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 =_smpy(int src1 , int src2 );
SMULBB dst , src1 , src2
QADD dst , dst , dst
Saturated multiply
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Table 5-4. V5E, V6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics (continued)
Assembly
Instruction
C/C++ Compiler Intrinsic
Description
int dst =_smsub(int src1 , int src2 );
SMULBB tmp , src1 , src2
QDSUB dst , dst , tmp
Saturated multiply-subtract
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 =_ssub(int src1 , int src2 );
QSUB dst , src1 , src2
Saturated subtract
int dst = _subc(int src1 , int src2 );
SUBC dst , src1 , src2
Subtract with carry
Table 5-5. v6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics
C/C++ Compiler Intrinsic
Assembly
Instruction
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
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
Description
int dst = _qadd8(int src1 , int src2 );
QADD8 dst , src1 , src2
Performs four signed saturated 8-bit additions
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 = _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 = _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 = _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 = _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.
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
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.
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Table 5-5. v6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics (continued)
Assembly
Instruction
C/C++ Compiler Intrinsic
long long dst _smlald(long long acc , int src1 ,
int src2 );
SMLALD dst , src1 , src2
Description
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.
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
32-bits of the result.
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 _smuad(int src1 , int src2 , int acc );
SMUAD dst , src1 , src2 , acc
Performs two signed 16-bit multiplications on
the top and bottom halfwords and adds the
products.
int dst _smuadx(int src1 , int src2 , int acc );
SMUADX dst , src1 , src2 , acc
Same as _smuad except the halfwords in src2
are exchange before the multiplication.
int dst _smusd(int src1 , int src2 , int acc );
SMUSD dst , src1 , src2 , acc
Performs two signed 16-bit multiplications on
the top and bottom halfwords and subtracts the
products.
int dst _smusadx(int src1 , int src2 , int acc );
SMUSDX dst , src1 , src2 , acc
Same as _smusd except the halfwords in src2
are exchange before the multiplication.
int dst =_ssat16(int src , int bitpos );
SSAT16 dst , #bitpos
Performs two halfword saturations to a
selectable signed range specified by bitpos
Performs two signed halfword subtractions
int dst = _ssub16(int src1 , int src2 );
SSUB16 dst , src1 , src2
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 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.
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Table 5-5. v6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics (continued)
C/C++ Compiler Intrinsic
Assembly
Instruction
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 _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 = _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.
Description
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 = _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 = _uaddsubx(int src1 , int src2 );
UASX dst , src1 , src2
Exchange halfwords of src2, add the top
halfwords and subtract the bottom halfwords
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 = _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
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.
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Object File Symbol Naming Conventions (Linknames)
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Table 5-5. v6, Cortex-M4, Cortex-R4, and Cortex-A8 C/C++ Compiler Intrinsics (continued)
C/C++ Compiler Intrinsic
Assembly
Instruction
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 _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.
Description
5.13 Object File Symbol Naming Conventions (Linknames)
Each externally visible identifier is assigned a unique symbol name to be used in the object file, a
so-called 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. This algorithm may mangle the name.
In TIABI, the linkname for all objects is the same as the name in the C source with an added underscore
prefix. For C functions, an underscore is prefixed for 32-bit mode and 16-bit mode functions with the TI
ARM9 ABI (--abi=ti_arm9_abi) mode. In the backward-compatible TIABI mode (--abi=tiabi), the names of
32-bit mode functions are prefixed with an underscore and 16-bit mode functions are prefixed with a dollar
sign ($). This prevents any C identifier from colliding with any identifier in the assembly code namespace,
such as an assembler keyword.
In EABI, no prefix is used. If a C identifier would collide with an assembler keyword, the compiler will
escape 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.
C++ functions have the same initial character: an underscore for the TI ARM9 ABI, or an underscore or
dollar sign for the TIABI. Additionally, the function name is mangled further. 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 TIABI or TI ARM9 ABI, the mangling algorithm used closely follows that described in The Annotated
Reference Manual (ARM).
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.
For EABI, the mangling algorithm follows that described in the Itanium C++ ABI
(http://www.codesourcery.com/cxx-abi/abi.html).
int foo(int i) { } would be mangled "_Z3fooi"
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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 http://www.arm.com/products/DevTools/ABI.html for details.
5.14 Initializing Static and Global Variables in TIABI and TI ARM9 ABI Modes
The ANSI/ISO C standard specifies that global (extern) and static variables without explicit initializations
must be initialized to 0 before the program begins running. This task is typically done when the program is
loaded. Because the loading process is heavily dependent on the specific environment of the target
application system, the compiler itself makes no provision for initializing to 0 otherwise uninitialized static
storage class variables at run time. It is up to your application to fulfill this requirement.
Initialize Global Objects
NOTE: You should explicitly initialize all global objects which you expected the compiler would set
to zero by default.
5.14.1 Initializing Static and Global Variables With the Linker
If your loader does not preinitialize variables, you can use the linker to preinitialize the variables to 0 in the
object file. For example, in the linker command file, use a fill value of 0 in the .bss section:
SECTIONS
{
...
.bss: {} = 0x00;
...
}
Because the linker writes a complete load image of the zeroed .bss section into the output COFF file, this
method can have the unwanted effect of significantly increasing the size of the output file (but not the
program).
If you burn your application into ROM, you should explicitly initialize variables that require initialization.
The preceding method initializes .bss to 0 only at load time, not at system reset or power up. To make
these variables 0 at run time, explicitly define them in your code.
For more information about linker command files and the SECTIONS directive, see the linker description
information in the ARM Assembly Language Tools User's Guide.
5.14.2 Initializing Static and Global Variables With the const Type Qualifier
Static and global variables of type const without explicit initializations are similar to other static and global
variables because they might not be preinitialized to 0 (for the same reasons discussed in Section 5.14).
For example:
const int zero;
/*
may not be initialized to 0
*/
However, the initialization of const global and static variables is different because these variables are
declared and initialized in a section called .const. For example:
const int zero = 0
/*
guaranteed to be 0
*/
This corresponds to an entry in the .const section:
.sect
_zero
.word
.const
0
This feature is particularly useful for declaring a large table of constants, because neither time nor space
is wasted at system startup to initialize the table. Additionally, the linker can be used to place the .const
section in ROM.
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You can use the DATA_SECTION pragma to put the variable in a section other than .const. For example,
the following C code:
#pragma DATA_SECTION (var, ".mysect");
const int zero=0;
is compiled into this assembly code:
.sect
_zero
.word
.mysect
0
5.15 Changing the ANSI/ISO C Language Mode
The --kr_compatible, --relaxed_ansi, and --strict_ansi options let you specify how the C/C++ compiler
interprets your source code. You can compile your source code in the following modes:
• Normal ANSI/ISO mode
• K&R C mode
• Relaxed ANSI/ISO mode
• Strict ANSI/ISO mode
The default is normal ANSI/ISO mode. Under normal ANSI/ISO mode, most ANSI/ISO violations are
emitted as errors. Strict ANSI/ISO violations (those idioms and allowances commonly accepted by C/C++
compilers, although violations with a strict interpretation of ANSI/ISO), however, are emitted as warnings.
Language extensions, even those that conflict with ANSI/ISO C, are enabled.
K&R C mode does not apply to C++ code.
5.15.1 Compatibility With K&R C (--kr_compatible Option)
The ANSI/ISO C/C++ language is a superset of the de facto C standard defined in Kernighan and
Ritchie's The C Programming Language. Most programs written for other non-ANSI/ISO compilers
correctly compile and run without modification.
There are subtle changes, however, in the language that can affect existing code. Appendix C in The C
Programming Language (second edition, referred to in this manual as K&R) summarizes the differences
between ANSI/ISO C and the first edition's C standard (the first edition is referred to in this manual as
K&R C).
To simplify the process of compiling existing C programs with the ANSI/ISO C/C++ compiler, the compiler
has a K&R option (--kr_compatible) that modifies some semantic rules of the language for compatibility
with older code. In general, the --kr_compatible option relaxes requirements that are stricter for ANSI/ISO
C than for K&R C. The --kr_compatible option does not disable any new features of the language such as
function prototypes, enumerations, initializations, or preprocessor constructs. Instead, --kr_compatible
simply liberalizes the ANSI/ISO rules without revoking any of the features.
The specific differences between the ANSI/ISO version of C and the K&R version of C are as follows:
• The integral promotion rules have changed regarding promoting an unsigned type to a wider signed
type. Under K&R C, the result type was an unsigned version of the wider type; under ANSI/ISO, the
result type is a signed version of the wider type. This affects operations that perform differently when
applied to signed or unsigned operands; namely, comparisons, division (and mod), and right shift:
unsigned short u;
int i;
if (u < i)
•
ANSI/ISO prohibits combining two pointers to different types in an operation. In most K&R compilers,
this situation produces only a warning. Such cases are still diagnosed when --kr_compatible is used,
but with less severity:
int *p;
char *q = p;
•
/* error without --kr_compatible, warning with --kr_compatible */
External declarations with no type or storage class (only an identifier) are illegal in ANSI/ISO but legal
in K&R:
a;
110
/* SIGNED comparison, unless --kr_compatible used */
/* illegal unless --kr_compatible used */
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•
ANSI/ISO interprets file scope definitions that have no initializers as tentative definitions. In a single
module, multiple definitions of this form are fused together into a single definition. Under K&R, each
definition is treated as a separate definition, resulting in multiple definitions of the same object and
usually an error. For example:
int a;
int a;
•
extern int a;
static int a;
•
/* same as 'q' if --kr_compatible used, error if not */
ANSI/ISO specifies that bit fields must be of type int or unsigned. With --kr_compatible, bit fields can
be legally defined with any integral type. For example:
struct s
{
short f : 2;
};
•
/* illegal unless --kr_compatible used */
Unrecognized escape sequences in string and character constants are explicitly illegal under ANSI/ISO
but ignored under K&R:
char c = '\q';
•
/* illegal if --kr_compatible used, OK if not */
Under ANSI/ISO, the result of these two definitions is a single definition for the object a. For most K&R
compilers, this sequence is illegal, because int a is defined twice.
ANSI/ISO prohibits, but K&R allows objects with external linkage to be redeclared as static:
/* illegal unless --kr_compatible used */
K&R syntax allows a trailing comma in enumerator lists:
enum { a, b, c, }; /* illegal unless --kr_compatible used */
•
K&R syntax allows trailing tokens on preprocessor directives:
#endif NAME
/* illegal unless --kr_compatible used */
5.15.2 Enabling Strict ANSI/ISO Mode and Relaxed ANSI/ISO Mode (--strict_ansi and
--relaxed_ansi Options)
Use the --strict_ansi option when you want to compile under strict ANSI/ISO mode. In this mode, error
messages are provided when non-ANSI/ISO features are used, and language extensions that could
invalidate a strictly conforming program are disabled. Examples of such extensions are the inline and asm
keywords.
Use the --relaxed_ansi option when you want the compiler to ignore strict ANSI/ISO violations rather than
emit a warning (as occurs in normal ANSI/ISO mode) or an error message (as occurs in strict ANSI/ISO
mode). In relaxed ANSI/ISO mode, the compiler accepts extensions to the ANSI/ISO C standard, even
when they conflict with ANSI/ISO C. The GCC language extensions described in Section 5.16 are
available in relaxed ANSI/ISO mode.
5.15.3 Enabling Embedded C++ Mode (--embedded_cpp Option)
The compiler supports the compilation of embedded C++. In this mode, some features of C++ are
removed that are of less value or too expensive to support in an embedded system. When compiling for
embedded C++, the compiler generates diagnostics for the use of omitted features.
Embedded C++ is enabled by compiling with the --embedded_cpp option.
Embedded C++ omits these C++ features:
• Templates
• Exception handling
• Run-time type information
• The new cast syntax
• The keyword mutable
• Multiple inheritance
• Virtual inheritance
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Under the standard definition of embedded C++, namespaces and using-declarations are not supported.
The ARM compiler nevertheless allows these features under embedded C++ because the C++
run-time-support library makes use of them. Furthermore, these features impose no run-time penalty.
The compiler does not support embedded C++ run-time-support libraries.
5.16 GNU 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 3.4) can be found
at the GNU web site, http://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/C-Extensions.html.
Most of these extensions are also available for C++ source code.
5.16.1 Extensions
Most of the GCC language extensions are available in the TI compiler when compiling in relaxed ANSI
mode (--relaxed_ansi) or if the --gcc option is used.
The extensions that the TI compiler supports are listed in Table 5-6, which is based on the list of
extensions found at the GNU web site. The shaded rows describe extensions that are not supported.
Table 5-6. 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
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.
(1)
Feature defined for GCC 3.0; definition and examples at http://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc/C-Extensions.html
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Table 5-6. GCC Language Extensions (continued)
Extensions
Descriptions
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
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 5.16.5)
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
5.16.2 Function Attributes
The following function attributes are supported: always_inline, const, constructor, deprecated, format,
format_arg, malloc, noinline, noreturn, pure, section, unused, used and warn_unused_result.
In addition, the visibility function attribute is supported for EABI mode (--abi=eabi).
The format attribute is applied to the declarations of printf, fprintf, sprintf, snprintf, vprintf, vfprintf, vsprintf,
vsnprintf, scanf, fscanf and sscan 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.
The malloc attribute is applied to the declarations of malloc, calloc, realloc and memalign in stdlib.h.
5.16.3 Variable Attributes
The following variable attributes are supported: aligned, deprecated, mode, packed, section,
transparent_union, unused, and used.
The used attribute is defined in GCC 4.2 (see
http://gcc.gnu.org/onlinedocs/gcc-4.2.4/gcc/Variable-Attributes.html#Variable-Attributes).
The packed attribute for structure and union types is available only when there is hardware support for
unaligned accesses. This means when --unaligned_access=on, which it is by default for the Cortex
devices (A8, R4, M3, M4).
In addition, the weak variable attribute is supported for EABI mode (--abi=eabi).
5.16.4 Type Attributes
The following type attributes are supported: aligned, deprecated, packed, transparent_union, and unused.
In addition, the visibility type attribute is supported for EABI mode (--abi=eabi).
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AUTOSAR
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The packed attribute on struct and union types is available only for target architectures that have hardware
support for unaligned access.
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.
5.16.5 Built-In Functions
The following builtin functions are supported: __builtin_abs, __builtin_classify_type, __builtin_constant_p,
__builtin_expect, __builtin_fabs, __builtin_fabsf, __builtin_frame_address, __builtin_labs, __builtin_llabs,
__builtin_sqrt, __builtin_sqrtf, __builtin_memcpy, and __builtin_return_address.
The __builtin_frame_address function returns zero unless the argument is a constant zero.
The __builtin_return_address function always returns zero.
5.17 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
run-time-support header files.
More information on AUTOSAR can be found at http://www.autosar.org.
5.18 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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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
...........................................................................................................................
Memory Model .................................................................................................
Object Representation ......................................................................................
Register Conventions .......................................................................................
Function Structure and Calling Conventions .......................................................
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 ..................................................................
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116
118
125
128
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135
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141
141
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Memory Model
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 module information in the ARM Assembly
Language Tools User's Guide.
There are two basic types of sections:
• Initialized sections contain data or executable code. The C/C++ compiler creates the following
initialized sections:
– For TIABI and TI_ARM9_ABI only, the .cinit section contains tables for initializing variables and
constants.
– The .pinit section for TIABI and TI_ARM9_ABI, or the .init_array section for EABI, contains
global constructor tables.
– For EABI only, the .data section contains initialized global and static variables.
– The .const section contains string constants, switch tables, 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 as well as string literals and compiler-generated
constants.
• 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 TIABI and TI_ARM9_ABI only, the .bss section reserves space for global and static variables.
At boot or load time, the C/C++ boot routine or the loader copies data out of the .cinit section
(which can be in ROM) and stores it in the .bss section.
– For EABI only, the .bss section reserves space for uninitialized global and static variables.
– The .stack section reserves memory for the C/C++ software stack.
– The .sysmem section reserves space for dynamic memory allocation. The reserved 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.
The assembler creates the default sections .text, .bss, and .data. The C/C++ compiler, however, does not
use the .data section. You can instruct the compiler to create additional sections by using the
CODE_SECTION and DATA_SECTION pragmas (see Section 5.9.3 and Section 5.9.6).
The linker takes the individual sections from different modules 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.
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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
ROM or 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, __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 if 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, __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.
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));
6.1.4 Initialization of Variables in TIABI and TI_ARM9_ABI
The C/C++ compiler produces code that is suitable for use as firmware in a ROM-based system. In such a
system, the initialization tables in the .cinit section are stored in ROM. At system initialization time, the
C/C++ boot routine copies data from these tables (in ROM) to the initialized variables in .bss (RAM).
In situations where a program is loaded directly from an object file into memory and run, you can avoid
having the .cinit section occupy space in memory. A loader can read the initialization tables directly from
the object file (instead of from ROM) and perform the initialization directly at load time instead of at run
time. You can specify this to the linker by using the --ram_model link option. For more information, see
Section 6.9.
6.2
Object Representation
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
enum (TIABI and TI_ARM9_ABI
only) (2)
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
unsigned long long
Even/odd register pair
64 bits aligned to 32-bit (word) boundary
float
Bits 0-31 of register
32 bits aligned to 32-bit (word) boundary
(1)
(2)
118
16 bits aligned to 16-bit (halfword) boundary
Negative values are sign-extended to bit 31.
For enum information for EABI mode, see Table 5-2.
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Table 6-2. Data Representation in Registers and Memory (continued)
Data Type
Register Storage
Memory Storage
double
Register pair
64 bits aligned to 32-bit (word) boundary
long double
Register pair
64 bits aligned to 32-bit (word) boundary
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.
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
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
31
0
0
0
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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enum (TIABI or TI_ARM9_ABI), float, int, and long Data Types (signed and unsigned)
The int, unsigned int, enum, 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
little-endian 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.
Enums in EABI Mode
NOTE: Enumerations have a different representation in EABI mode; see Table 5-2.
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, enum, 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 nonvirtual. The parameter f is the pointer to the member
function if it is nonvirtual, 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 handled differently in TIABI and TI ARM9 ABI, and EABI modes. Section 6.2.2.1 details how
bit fields are handled in all modes. Section 6.2.2.2 details how bit fields differ in EABI mode.
6.2.2.1
Generic 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.
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.
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
Byte 2
Byte 3
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
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
X
X
Little-endian register
MS
X
X
LS
E
8
E
7
E
6
E
5
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
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6.2.2.2
EABI Bit Field Differences
Bit fields are handled differently in TIABI and TI ARM9 ABI modes versus EABI mode in these ways:
• In the TIABI and TI ARM9 ABI plain int bit fields are signed. In EABI they are unsigned. Consider the
following C code:
struct st
{
int a:5;
} S;
foo()
{
if (S.a < 0)
bar();
}
•
•
•
In EABI bar () is never called as bit field 'a' is unsigned. Use signed int if you need a signed bit field in
EABI mode.
In TIABI and TI ARM9 ABI, bit fields of type long long are not allowed. In EABI, long long bit fields are
supported.
In TIABI and TI ARM9 ABI, all bit fields are treated as signed or unsigned int type. In EABI, bit fields
are treated as the declared type.
In TIABI and TI ARM9 ABI, the size and alignment a bit field contributes to the struct containing it
depends on the number of bits in the bit field. In EABI, 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};
•
In TIABI and TI ARM9 ABI, this struct takes up 1 byte and is aligned at 1 byte. In EABI, this struct uses
up 4 bytes and is aligned at 4 bytes.
In TIABI and TI ARM9 ABI, unnamed bit fields are zero-sized bit fields do not affect the struct or union
alignment. In EABI, such fields affect the alignment of the struct or union. For example, consider the
struct:
struct st{char a:4; int :22;};
•
In TIABI and TI ARM9 ABI, this struct uses 4 bytes and is aligned at a 1-byte boundary. In EABI, this
struct uses 4 bytes and is aligned at a 4-byte boundary.
With EABI, 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.
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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 6.9.
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';
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6.3
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
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)
(1)
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
Usage
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
FPSCR
S0
Preserved by Function
(1)
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
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
(1)
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)
The child function refers to the function being called.
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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 at http://www.arm.com/products/DevTools/ABI.html.
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.
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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
SP
Caller’s
argument
block
Argument 5...
argument n
Caller’s
local variables
Caller’s
local variables
High
Register
save area
SP
Argument 1 →
Argument 2 →
Argument 3 →
Argument 4 →
AP
register R0
register R1
register R2
register R3
Register
save area
High
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 6.10 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-on-entry 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 6.6.
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 .
8. The called function restores all registers saved in .
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 (points to
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.
6.4.5 Generating Long Calls (-ml Option) in 16-bit Mode
You can use the -ml option when compiling C/C++ code to produce long calls in 16-bit mode. You must
also use the -mt (16-bit mode) and -md (no dual state) options, or -ml (long call) has no effect.
The ARM C/C++ compiler normally uses the BL assembly instruction when making procedure calls in
16-bit mode. In object code, this is translated into two 16-bit BL instructions, each of which has 11 bits for
the offset. Adding the two together, plus the assumed zero bit, gives only 23 bits of offset for a call. This is
not enough when applications have widely disbursed areas of memory in which instructions reside.
The -ml option uses the BX instruction instead of the BL instruction. The BX instruction is less efficient. It
requires a load instruction which uses a word of memory to load the destination address into a register, a
move instruction to save the return address, and a BX instruction to make procedure calls.
6.5
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 6.5.1).
• Use assembly language variables and constants in C/C++ source (see Section 6.5.2).
• Use inline assembly language embedded directly in the C/C++ source (see Section 6.5.4).
• Modify the assembly language code that the compiler produces (see Section 6.5.5).
6.5.1 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 6.6.
• 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.
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•
•
•
•
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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 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 are writing assembly language
code, you must use the same linknames as those assigned by the compiler. See Section 5.13 for more
information.
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.
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.
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6.5.2 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
constant.
6.5.2.1
Accessing Assembly Language Global Variables
Accessing uninitialized 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.
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
* Note the use of underscores in the following lines
.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;
6.5.2.2
/* External variable */
/* Use the variable */
Accessing Assembly Language Constants
You can define global constants in assembly language by using the .set, .def, and .global directives, 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 normal variables defined in C/C++ or assembly language, the symbol table contains the address of
the value of the variable. For assembler constants, however, the symbol table contains the value of the
constant. The compiler cannot tell which items in the symbol table are values and which are addresses.
If you try to access an assembler (or linker) constant by name, the compiler attempts to fetch a value from
the address represented in the symbol table. To prevent this unwanted fetch, you must use the & (address
of) operator to get the value. In other words, if x is an assembly language constant, its value in C/C++ is
&x.
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 */
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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.
6.5.3 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.
6.5.4 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 5.8.
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.
6.5.5 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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6.6
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.
6.6.1 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 5.9.11. For information about banked registers, see the TMS470R1x User's Guide.
6.6.2 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 5.9.11 and Section 5.5.2, respectively.
6.6.3 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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6.6.4 How to Map Interrupt Routines to Interrupt Vectors
To map 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.
NOTE:
Prefixing C/C++ Interrupt Routines
Remember, if you are using C/C++ interrupt routines, you must use the proper linkname. So
for TIABI and TI ARM9 ABI use _c_intIRQ instead of c_intIRQ, for example, for a function
defined in C scope.
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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6.6.5 Using Software Interrupts
A software interrupt 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.
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 5.9.17.
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.
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.
6.6.6 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 explicitly.
• 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 changes to 32-bit. Therefore, the interrupt vectors
must always contain branches to 32-bit state code. If the interrupt handler is a 16-bit state C/C++
function, the entry for the interrupt vector must be a branch to the interrupt routine's dual-state veneer
(see Section 6.10).
• 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.
• 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 6.6.1 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 6.6.1.
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Intrinsic Run-Time-Support Arithmetic and Conversion Routines
6.7
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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. The compiler uses a preset naming convention for each of these routines, as
described in Section 6.7.1 for the TIABI and TI ARM9 ABI modes. Refer to
http://www.arm.com/products/DevTools/ABI.html for information on the EABI mode.
6.7.1 Naming Conventions
For the TIABI and TI ARM9 ABI modes, the names of the intrinsic run-time-support arithmetic and
conversion routines are made up of two parts:
• The prefix indicates the type of the routine and the state from which it can be called. Table 6-7 lists the
possible prefixes.
• The root indicates the operation performed by the routine. Table 6-8 lists the possible roots.
The prefixes from Table 6-7 are combined with the roots from Table 6-8 to form the function names listed
in Table 6-9.
Table 6-7. Naming Convention Prefixes
Prefix
Type of Operation
State Called From
FD$
Double-precision floating point
16-BIS
FD_
Double-precision floating point
32-BIS
FS$
Single-precision floating point
16_BIS
FS_
Single-precision floating point
32_BIS
I$
Signed integer
16_BIS
I_
Signed integer
32-BIS
U$
Unsigned integer
16-BIS
U_
Unsigned integer
32-BIS
Table 6-8. Summary of Run-Time-Support Arithmetic and Conversion Functions
Type of Usage
Root
Operation Performed
ADD
CMP
DIV
Division
X
X
MOD
Modulus
X
X
int
single
double
Addition
X
X
Comparison
X
X
X
X
MUL
Multiplication
X
X
SUB
Subtraction
X
X
TOI
Conversion to signed integer
X
X
TOU
Conversion to unsigned integer
X
X
TOFS
Conversion to single-precision floating point
X
X
TOFD
Conversion to double-precision floating point
X
X
(1)
138
uint
(1)
X
uint
int
X
X
indicates that the combination is supported
unsigned integer
single
single-precision floating point
signed integer
double double-precision floating point
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The source files for these functions are in the rtsc.src and rtscpp.src libraries. The source code has
comments that describe the operation of the functions. You can extract, inspect, and modify any of these
functions; be sure you follow the register usage conventions summarized in Table 6-9.
Table 6-9. Run-Time-Support Function Register Usage Conventions
Inputs
Function
Operand1
Output
Source Filename
FS$TOI
R0
Operand2
R0
fs_toi16.asm
FS_TOI
R0
R0
fs_toi32.asm
FD$TOI
R0:R1
R0
fd_toi16.asm
FSD_TOI
R0:R1
R0
fd_toi32.asm
FS$TOU
R0
R0
fs_tou16.asm
FS_TOU
R0
R0
fs_tou32.asm
FD$TOU
R0:R1
R0
fd_tou16.asm
FD_TOU
R0:R1
R0
fd_tou32.asm
I$TOFS
R0
R0
i_tofs16.asm
I_TOFS
R0
R0
i_tofs32.asm
U$TOFS
R0
R0
u_tofs16.asm
U_TOFS
R0
R0
u_tofs32.asm
FD$TOFS
R0:R1
R0
fd_tos16.asm
FD_TOFS
R0:R1
R0
fs_tos32.asm
I$TOFD
R0
R0:R1
i_tofd16.asm
I_TOFD
R0
R0:R1
i_tofd32.asm
U$TOFD
R0
R0:R1
u_tofd16.asm
U_TOFD
R0
R0:R1
u_tofd32.asm
FS$TOFD
R0
R0:R1
fs_tofd16.asm
FS_TOFD
R0
R0:R1
fs_tofd32.asm
FS$ADD
R0
R1 (1)
R0
fs_add16.asm
FS_ADD
R0
R1
(1)
R0
fs_add32.asm
FD$ADD
R0:R1
R2:R3 (1)
R0:R1
fd_add16.asm
FD_ADD
R0:R1
R2:R3 (1)
R0:R1
fd_add32.asm
FS$SUV
R0
R1
R0
fs_add16.asm
FS_SUB
R0
R1
R0
fs_add32.asm
FD$SUB
R0:R1
R2:R3 (1)
R0:R1
fd_add`6.asm
FD_SUB
R0:R1
R2:R3 (1)
R0:R1
fd_add32.asm
(1)
FS$MUL
R0
R1
R0
fs_mul16.asm
FS_MUL
R0
R1 (1)
R0
fs_mul32.asm
FD$MUL
R0:R1
R2:R3 (1)
R0:R1
fd_mul16.asm
FD_MUL
R0:R1
R2:R3
(1)
R0:R1
fd_mul32.asm
FS$DIV
R0
R1
R0
fs_div16.asm
FS_DIV
R0
R1
R0
fs_div32.asm
FD$DIV
R0:R1
R2:R3 (1)
R0:R1
fd_div16.asm
FD_DIV
R0:R1
R2:R3
(1)
R0:R1
fs_div32.asm
I$DIV
R0
R1
R1
i_div16.asm
I_DIV
R0
R1
R1
i_div32.asm
U$DIV
R0
R1
R1
u_div16.asm
U_DIV
R0
R1
R1
u_div32.asm
I$MOD
R0
R1
R0
i_mod16.asm
I_MOD
R0
R1
R0
i_mod32.asm
U$MOD
R0
R1
R0
u_mod16.asm
(1)
Value in the register is preserved.
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Table 6-9. Run-Time-Support Function Register Usage Conventions (continued)
Inputs
Function
Operand1
Operand2
Output
Source Filename
U_MOD
R0
R1
R0
u_mod32.asm
FS$CMP
R0
R1 (1)
CPSR
fs_cmp16.asm
FS_CMP
R0
R1 (1)
CPSR
fs_omp32.asm
FD$CMP
R0:R1 (1)
R2:R3 (1)
CPSR
fd_cmp16.asm
FD_CMP
(1)
(1)
CPSR
fd_cmp32.asm
R0:R1
R2:R3
6.7.2 CPSR Register and Interrupt Intrinsics
The intrinsics in Table 6-10 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.
Table 6-10. CPSR and Interrupt C/C++ Compiler Intrinsics
140
C/C++ Compiler Intrinsic
Assembly
Instruction
void _call_swi(uint src );
SWI $ src
Call a software interrupt. The src must be an
immediate.
dst = uint _disable_FIQ( ) ;
MRS dst , CPSR
ORR tmp , dst , #0x40
MSR CPSR , tmp
Disable FIQ interrupts and return previous CPSR
value.
dst = uint _disable_interrupts( ) ;
MRS dst , CPSR
ORR tmp , dst , #0xc0
MSR CPSR , tmp
Disable all interrupts and return previous CPSR value.
dst = uint _disable_IRQ( ) ;
MRS dst , CPSR
ORR tmp , dst , #0x80
MSR CPSR , tmp
Disable IRQ interrupts and return previous CPSR
value.
dst = uint _enable_FIQ( ) ;
MRS dst , CPSR
BIC tmp , dst , #0x40
MSR CPSR , tmp
Enable FIQ interrupts and return previous CPSR value.
dst = uint _enable_interrupts( ) ;
MRS dst , CPSR
BIC tmp , dst , #0xc0
MSR CPSR , tmp
Enable all interrupts and return previous CPSR value.
dst = uint _enable_IRQ( ) ;
MRS dst , CPSR
BIC tmp , dst , #0x80
MSR CPSR , tmp
Enable IRQ interrupts and return previous CPSR value.
Description
dst = uint _get_CPSR( ) ;
MRS dst , CPSR
Get the CPSR register.
void _set_CPSR(uint src );
void _restore_interupts(uint src );
MSR CPSR , src
Set the CPSR register.
void _set_CPSR_flg(uint src );
MSR dst , CPSR
Set the CPSR flag bits. The src is rotated by the
intrinsic.
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6.8
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);
6.9
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 modules. 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 module 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). In EABI mode, 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 6.9.2 for
TIABI and TI_ARM9_ABI modes and Section 6.9.5 for EABI mode.
• Calls C++ initialization routines for file scope construction from the global constructor table. For
more information, see Section 6.9.5.6 for EABI mode and Section 6.9.7 for TIABI and TI ARM9 ABI
modes.
3. Calls the function main 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.
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6.9.1 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.
6.9.2 TIABI/TIARM9 Automatic Initialization of Variables
Some global variables 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.
The TIABI/TIARM9 compiler builds tables in a special section called .cinit that contains data for initializing
global and static variables. Each compiled module contains these initialization tables. The linker combines
them into a single table (a single .cinit section). The boot routine or a loader uses this table to initialize all
the system variables.
Initializing Variables
NOTE: In ANSI/ISO C, global and static variables that are not explicitly initialized must be set to 0
before program execution. The TIABI/TIARM9 C/C++ compiler does not perform any
preinitialization of uninitialized variables. Explicitly initialize any variable that must have an
initial value of 0.
Global variables are either autoinitialized at run time or at load time; see Section 6.9.3 and Section 6.9.4.
Also see Section 5.14.
6.9.3 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 .cinit section is loaded into memory along with all the other initialized sections, and
global variables are initialized at run time. The linker defines a special symbol called cinit that points to the
beginning of the initialization tables in memory. When the program begins running, the C/C++ boot routine
copies data from the tables (pointed to by .cinit) into the specified variables in the .bss section. This allows
initialization data to be stored in ROM and copied to RAM each time the program starts.
Figure 6-6 illustrates autoinitialization at run time. Use this method in any system where your application
runs from code burned into ROM.
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Figure 6-6. Autoinitialization at Run Time
Object file
Memory
cint
.cinit
section
Loader
Initialization
tables
(EXT_MEM)
Boot
routine
.bss
section
(D_MEM)
6.9.4 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.
When you use the --ram_model link option, the linker sets the STYP_COPY bit in the .cinit section's
header. This tells the loader not to load the .cinit section into memory. (The .cinit section occupies no
space in the memory map.) The linker also sets the cinit symbol to -1 (normally, cinit points to the
beginning of the initialization tables). This indicates to the boot routine that the initialization tables are not
present in memory; accordingly, no run-time initialization is performed at boot time.
A loader (which is not part of the compiler package) must be able to perform the following tasks to use
initialization at load time:
• Detect the presence of the .cinit section in the object file
• Determine that STYP_COPY is set in the .cinit section header, so that it knows not to copy the .cinit
section into memory
• Understand the format of the initialization tables
Figure 6-7 illustrates the initialization of variables at load time.
Figure 6-7. Initialization at Load Time
Object file
.cinit
Memory
Loader
.bss
Regardless of the use of the --rom_model or --ram_model options, the .pinit section is always loaded and
processed at run time.
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6.9.5 EABI 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.
6.9.5.1
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++ EABI compiler supports preinitialization of uninitialized variables by default. This
can be turned off by specifying the linker option --zero_init=off. TI ARM9 ABI does not support zero
initialization.
6.9.5.2
EABI Direct Initialization
The EABI 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 6.9.5.5.
In the run-time initialization model, the linker uses the data in these sections to create initialization data
and an additional initialization table. The boot routine processes the initialization table to copy data from
load addresses to run addresses. See Section 6.9.5.3.
6.9.5.3
Autoinitialization of Variables at Run Time in EABI Mode
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 an 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 6-8 illustrates autoinitialization at run time in EABI Mode. Use this method in any system where
your application runs from code burned into ROM.
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Figure 6-8. Autoinitialization at Run Time in EABI Mode
Object file
Memory
C auto init
table and data
(ROM)
(.cinit section)
Loader
C auto init
table and data
(ROM)
Boot
routine
.data
uninitialized
(RAM)
6.9.5.4
Autoinitialization Tables
In EABI mode, the compiled modules (.obj 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.
Migration from COFF to ELF Initialization
NOTE: The name .cinit is used primarily to simplify migration from COFF to ELF format and the
.cinit section created by the linker has nothing in common (except the name) with the COFF
cinit records.
The autoinitialization table has the following format:
_TI_CINIT_Base:
32-bit load address
32-bit run address
32-bit load address
32-bit run address
_TI_CINT_Limit:
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
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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
8-bit index is also depicted for each format.
6.9.5.4.1 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.
6.9.5.4.2 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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6.9.5.4.3 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).
5. If L > 0 and L < 4 copy D to the output buffer L times. Go to step 2.
6. If L = 4 read the next byte (B'). Copy B' to the output buffer L times. Go to step 2.
7. Read the next 16 bits (LL).
8. Read the next byte (C).
9. If C != 0 copy C to the output buffer L times. Go to step 2.
10. End of processing.
The run-time support library has a routine __TI_decompress_rle() 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.
6.9.5.4.4 Lempel-Ziv Strore and 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.
6.9.5.4.5 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.
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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);
}
}
6.9.5.5
Initialization of Variables at Load Time in EABI Mode
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.
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 compile modules 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.
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Figure 6-9 illustrates the initialization of variables at load time in EABI mode.
Figure 6-9. Initialization at Load Time in EABI Mode
Object file
.data
section
Memory
Loader
.data section
(initialized)
(RAM)
6.9.5.6
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 6-10. Constructor Table for EABI Mode
SHT$$INIT_ARRAY$$Base:
Address of constructor 1
Address of constructor 2
Address of constructor n
SHT$$INIT_ARRAY$$Limit:
6.9.6 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 6-11 shows the format of the .cinit section and the
initialization records.
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Figure 6-11. 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
150
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 6-12). The constructors appear in the table after the .cinit initialization.
Figure 6-12. 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 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 5.5.1.
6.9.7 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 .pinit. The linker combines the .pinit section form each input file to form a single table in the
.pinit section. The boot routine uses this table to execute the constructors.
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6.10 Dual-State Interworking Under TIABI
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 (see
Section 5.11.2) 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.
6.10.1 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 6-11 to determine the best level of support to use for your code.
Table 6-11. 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 5.9.8 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.
6.10.2 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.
6.10.2.1 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
32-bit function refer to the entry point beginning with an underscore.
6.10.2.2 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 -mt option, which creates 16-bit
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 -mt 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 tasks that a C/C++ program performs (such as I/O, dynamic memory allocation, string
operations, and trigonometric functions) are not part of the C/C++ language itself. However, the ANSI/ISO
C standard defines a set of run-time-support functions that perform these tasks. The C/C++ compiler
implements the complete ISO standard library except for those facilities that handle exception conditions
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 inSection 7.1 and
Section 7.2.
A library-build process is provided with the code generation tools that lets you create customized
run-time-support libraries. This process is described in Section 7.4 .
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 ......................................................................................
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158
161
173
174
157
C and C++ Run-Time Support Libraries
7.1
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C and C++ Run-Time Support Libraries
ARM compiler releases include pre-built run-time 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 7.4 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
• Intrinsic arithmetic routines
• System startup routine, _c_int00
• Functions and macros that allow C/C++ to access specific instructions
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
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 in Section 5.1.
The C++ library included with the compiler is licensed from Dinkumware, Ltd. The Dinkumware C++ library
is a fully conforming, industry-leading implementation of the standard C++ library.
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
0-201-37926-0
• The C++ Programming Language (Third or Special Editions), Bjarne Stroustrup, Addison-Wesley,
ISBN 0-201-88954-4 or 0-201-70073-5
• Dinkumware's online reference at http://dinkumware.com/manuals
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.
You should specify libraries last on the linker command line because the linker searches a library for
unresolved references when it encounters the library on the command line. You can also use the
--reread_libs linker option to force repeated searches of each library until the linker can resolve no more
references.
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.
7.1.2 Header Files
To include the correct set of header files depending on which library you are using, you can set the
TMS470_C_DIR environment variable to the include directory where the tools are installed. The source for
the libraries is included in the rtssrc.zip file. See Section 7.4 for details on rebuilding.
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7.1.3 Modifying a Library Function
You can inspect or modify library functions by unzipping the source file (rtssrc.zip), changing the specific
function file, and rebuilding the library. When extracted (with any standard unzip tool on windows, linux, or
unix), this zip file will recreate the run-time source tree for the run-time library.
You can also build a new library this way, rather than rebuilding into rts16.lib. See Section 7.4.
7.1.4 Changes to the Run-Time-Support Libraries
The following changes and additions apply to the run-time-support libraries in the /lib subdirectory of the
release package.
7.1.4.1
Minimal Support for Internationalization
The library now 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 multi-byte 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.
So-called multi-byte characters are limited to single characters. There are no shift states. The mapping
between multi-byte characters and wide characters is simple equivalence; that is, each wide character
maps to and from exactly a single multi-byte character having the same value.
• 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
hard-coded to the behavior of the C locale, and attempting to install a different locale via a call to
setlocale() will return NULL.
7.1.4.2
Allowable Number of Open Files
In the <stdio.h> header file, the value for the macro FOPEN_MAX has been changed from 12 to 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.
7.1.5 Nonstandard Header Files in rtssrc.zip
The rtssrc.zip self-processing zip file 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.
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7.1.6 Library Naming Conventions
The run-time support libraries now have the following naming scheme:
rtsArchVersion_mode_endian[_n][_vn]_abi[_eh].lib
ArchVersion
mode
endian
n
vn
abi
eh
160
The version of the ARM architecture that the library was built for. This can be one of the
following: v4, v5, v6, v7A8, v7R4, 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, where n designates the version. Current values
are:
2
VFPv2
3
VFPv3
3D16 VFPv3D16
Indicates the application binary interface (ABI) used:
eabi
tiarm7
tiarm9
Indicates the library has exception handling support
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7.2
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
high-level 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);
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 theARM 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
todal). 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 2-19.
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The C I/O Functions
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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-time-support library:
cl470 main.c --run_linker --heap_size=400 --library=rts16.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.
7.2.2 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
(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
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 chose 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. It need not be unique across devices. Only the
low-level I/O functions will see this device file descriptor; the low-level function open will
assign its own unique file descriptor.
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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 * bu , 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 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 by 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
low-level routines. Use other names for the device-level functions that you write.
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add_device — Add Device to Device Table
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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 rtssrc.zip
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
The function returns one of the following values:
0
if successful
-1
on failure
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add_device — Add Device to Device Table
Example
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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)
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7.3
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, 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
single-threaded model is assumed, and the critical section primitives are not employed. In a multi-threaded
system such as 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 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 which do not use the BIOS
LCK 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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Library-Build Process
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Library-Build Process
When using the C/C++ compiler, you can compile your code under a number of different configurations
and options that are not necessarily compatible with one another. Because it would be cumbersome to
include all possible combinations in individual run-time-support libraries, this package includes a basic
run-time-support library, rts16.lib. Also included are library versions that support various ARM devices and
versions that support C++ exception handling.
You can also build your own run-time-support libraries using the self-contained run-time-support build
process, which is found in rtssrc.zip. This process is described in this chapter and the archiver described
in the ARM Assembly Language Tools User's Guide.
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 support items are required:
• Perl version 5.6 or later available as perl
Perl is a high-level programming language designed for process, file, and text manipulation. It is:
– Generally available from http://www.perl.org/get.htm
– Available from ActiveState.com as ActivePerl for the PC
– Available as part of the Cygwin package for the PC
It must be installed and added to PATH so it is available at the command-line prompt as perl. To
ensure perl is available, open a Command Prompt window and execute:
perl -v
•
No special or additional Perl modules are required beyond the standard perl module distribution.
GNU-compatible command-line make tool, such as gmake
More information is available from GNU at http://www.gnu.org/software/ make. This file requires a host
C compiler to build. GNU make (gmake) is shipped as part of Code Composer Studio on Windows.
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
built for Windows32 when the following is executed from the Command Prompt window:
gmake -h
7.4.2 Using the Library-Build Process
Once the perl and gmake tools are available, unzip the rtssrc.zip into a new, empty directory. See the
Makefile for additional information on how to customize a library build by modifying the LIBLIST and/or the
OPT_XXX macros
Once the desired changes have been made, simply use the following syntax from the command-line while
in the rtssrc.zip top level directory to rebuild the selected rtsname library.
gmake rtsname
To use custom options to rebuild a library, simply change the list of options for the appropriate base listed
in Section 7.1.6 and then rebuild the library. See the tables in Section 2.3 for a summary of available
generic and C6000-specific options.
To build an library with a completely different set of options, define a new OPT_XXX base, choose the
type of library per Section 7.1.6, and then rebuild the library. Not all library types are supported by all
targets. You may need to make changes to targets_rts_cfg.pm to ensure the proper files are included in
your custom library.
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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 signature in its link-level name. The process of encoding the signature into the
linkname is often referred to as name mangling. When you inspect mangled names, such as in assembly
files or linker output, 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
8.3
...........................................................................................................................
Page
Invoking the C++ Name Demangler .................................................................... 176
C++ Name Demangler Options .......................................................................... 176
Sample Usage of the C++ Name Demangler ........................................................ 177
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Invoking the C++ Name Demangler
The syntax for invoking the C++ name demangler is:
dem470 [options ] [filenames]
dem470
options
filenames
Command that invokes the C++ name demangler.
Options affect how the name demangler behaves. Options can appear anywhere on the
command line. (Options are discussed in Section 8.2.)
Text input files, such as the assembly file output by the compiler, the assembler listing file,
and the linker map file. If no filenames are specified on the command line, dem470 uses
standard in.
By default, the C++ name demangler outputs to standard out. You can use the -o file option if you want to
output to a file.
8.2
C++ Name Demangler Options
The following options apply only to the C++ name demangler:
--abi=eabi
-h
-o file
-u
-v
176
C++ Name Demangler
Demangles EABI identifiers
Prints a help screen that provides an online summary of the C++ name demangler
options
Outputs to the given file rather than to standard out
Specifies that external names do not have a C++ prefix
Enables verbose mode (outputs a banner)
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8.3
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
calories_in_a_banana__Fv:
;* --------------------------------------------------------------------------*
SUB.W
#4,SP
MOV.W
SP,r12
; |10|
ADD.W
#2,r12
; |10|
CALL
#__ct__6bananaFv
; |10|
; |10|
MOV.W
SP,r12
; |11|
ADD.W
#2,r12
; |11|
CALL
#calories__6bananaFv ; |11|
; |11|
MOV.W
r12,0(SP)
; |11|
MOV.W
SP,r12
; |11|
ADD.W
#2,r12
; |11|
MOV.W
#2,r13
; |11|
CALL
#__dt__6bananaFv
; |11|
; |11|
MOV.W
0(SP),r12
; |11|
ADD.W
#4,SP
RET
Executing the C++ name demangler demangles all names that it believes to be mangled. Enter:
dem470 calories_in_a_banana.asm
The result is shown in Example 8-3. The linknames in Example 8-2 ___ct__6bananaFv,
_calories__6bananaFv, and ___dt__6bananaFv are demangled.
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Example 8-3. Result After Running the C++ Name Demangler
calories_in_a_banana():
;* --------------------------------------------------------------------------*
SUB.W
#4,SP
MOV.W
SP,r12
; |10|
ADD.W
#2,r12
; |10|
CALL
#banana::banana()
; |10|
; |10|
MOV.W
SP,r12
; |11|
ADD.W
#2,r12
; |11|
CALL
#banana::calories() ; |11|
; |11|
MOV.W
r12,0(SP)
; |11|
MOV.W
SP,r12
; |11|
ADD.W
#2,r12
; |11|
MOV.W
#2,r13
; |11|
CALL
#banana::~banana()
; |11|
; |11|
MOV.W
0(SP),r12
; |11|
ADD.W
#4,SP
RET
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Chapter 9
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Static Stack Depth Profiler
The static stack depth profiler provides information about the maximum stack depth requirements of an
application based on the static information available in the linker output file. The application must be
compiled with DWARF (default) type debug information under the TIABI (COFF) mode.
The profiler is a stand-alone application called sdp470. The profiler takes a linked output file as input and
produces a listing that details the stack usage of all of the functions defined in the application. If an
application contains indirect calls and/or reentrant procedures, then a configuration file should also be
provided as input to the profiler.
Topic
...........................................................................................................................
9.1
9.2
9.3
9.4
9.5
9.6
9.7
Invoking the Static Stack Depth Profiler .............................................................
Stack Depth Statistics Listing ...........................................................................
Dependencies and Limitations ..........................................................................
User Input Mechanisms ....................................................................................
Configuration File Specification ........................................................................
Profiler Generated Warnings .............................................................................
Run-Time Support for Stack Depth Profiling .......................................................
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Page
180
180
182
182
183
186
186
179
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9.1
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Invoking the Static Stack Depth Profiler
The syntax for invoking the static stack depth profiler is as follows:
sdp470 [-c config] outfile
sdp470
-c config
outfile
Command that runs the compiler and the assembler
Identifies a configuration file to be used by the profiler to supply information about
indirectly called functions and reentrant procedures. For more information, see
Section 9.5.
Identifies the linked output file for an application to be analyzed by the profiler. This file
contains debug information about all functions included in the final link of an
application.
The entry point, or root function, is identified in the linked output file. The profiler uses the same method to
determine the entry point as the linker:
1. A global symbol identified with -e linker command option
2. The value of the _c_int00 symbol (if present)
3. The value of the _main or $main symbol (if present)
4. Address 0x0 (the default)
9.2
Stack Depth Statistics Listing
Each segment of the listing details the stack usage for a particular function in the application. Function
segments are listed in order, beginning with the function that has the highest total stack need.
The first line in a segment provides details about a given parent function. The first line in a function
segment provides information on the stack space needed by the function and its total stack usage
estimate (the function's stack usage plus the worst stack usage of its callees).
Subsequent lines in a function segment list the callees of the parent function listed in the first line of the
segment. The callees are listed in order from highest to lowest stack usage.
Figure 9-1 illustrates the application call trees for an example application:
Figure 9-1. Application Call Trees
_c_int00:0
_ISR1:16
_main:8
_F:4
_A:12
_G:12
_C:16
_B:8
Example 9-1 shows the function segment listings for the application illustrated in Figure 9-1.
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Example 9-1. Profile of the Application Call Trees Figure
*******************************************************************
* Static Stack Depth Analysis Profile
*******************************************************************
FCN:cint00
stack usage: 0, total stack need:
28
_main
stack usage: 8, subtree stack need: 28
===================================================================
FCN:_main
stack usage: 8, total stack need:
28
_A
stack usage: 12, subtree stack need: 20
_C
stack usage: 16, subtree stack need: 16
===================================================================
FCN:_ISR1
stack usage: 16, total stack need:
28
_G
stack usage: 12, subtree stack need: 12
_F
stack usage: 4, subtree stack need:
4
===================================================================
FCN:_A
stack usage: 12, total stack need:
20
_B
stack usage: 8, subtree stack need:
8
===================================================================
FCN:_C
stack usage: 16, total stack need:
16
===================================================================
FCN:_G
stack usage: 12, total stack need:
12
===================================================================
FCN:_B
stack usage: 8, total stack need:
8
===================================================================
FCN:_F
stack usage: 4, total stack need:
4
===================================================================
A summary of the application's stack depth requirements is provided at the end of the listing. The
summary states an estimate of the stack depth usage from each function in the application that does not
have a parent. You can derive a worst case estimate of an application's stack depth using the information
provided in the listing in combination with your knowledge of which functions are interrupts (and which
stack mode those interrupts assume).
For example, a summary of Example 9-1 looks like this:
================ROOT FUNCTIONS==============================
_c_int00
total stack need:
28 bytes
_ISR1
total stack need:
28 bytes
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Dependencies and Limitations
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Dependencies and Limitations
The profiler constructs a call tree based on the DWARF debug information provided in the linker output
file. The tree is annotated with the stack usage information that the profiler derives from the function's
debug information.
There are several significant limitations to the profiler's ability to complete this information:
• Hand-coded assembly functions and stack usage information for those functions
• Indirectly called functions and their callers
• Reentrant functions and their depth of recursion
The profiler relies on your input to supply this information in the application source code and in the
configuration file (specified with the -c option). The assembler processes the assembly source code
annotations (.asmfunc/.endasmfunc directives) and encodes the information into the linked output file in a
form that the profiler can understand. You must also provide a configuration file to identify indirect calls
and reentrant procedures to the profiler. The profiler uses this configuration file to annotate the call graph
that it constructed from the linked output file for the application.
The accuracy of the stack depth estimate is heavily dependent on the accuracy of the information you
provide. You must actively maintain this information throughout the life of a given application.
9.4
User Input Mechanisms
The assembler supports the .asmfunc and .endasmfunc assembler directives for identifying the beginning
and end of an assembly function. The .asmfunc directive has an optional parameter for specifying the
stack space needed for an assembly function.
For example, you could write a function, $foo(), which uses 12 bytes of stack space, as shown in
Example 9-2:
Example 9-2. An Assembly Function
$foo:
.global
.asmfunc
PUSH
[]
POP
MOV
.endasmfunc
$foo
stack_usage(12)
{ R4, R5, R6 }
{ R4, R5, R6 }
PC, LR
The .asmfunc and .endasmfunc directives identify the entry and exit points of the function. This
information and the fact that $foo uses 12 bytes of stack space are then encoded into the debug
information. Assembler functions must be annotated with these directives to be considered for stack depth
analysis and profile report.
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9.5
Configuration File Specification
The stack depth profiler enables you to specify indirect calls and reentrant procedures using a
configuration file. The configuration file is input to the profiler, along with the executable to be analyzed.
The profiler applies the configuration information to the stack depth information extracted from the
executable and reports the total stack usage.
9.5.1 Specify Indirect Calls
The configuration file is composed of a series of sections delimited by the section type. Each section
contains information for a specific section type. As shown in Example 9-3, the section specifying indirectly
called functions is delimited by <INDIRECT> and </INDIRECT>, and contains information on the set of
procedures called indirectly.
Example 9-3. Specifying Indirect Calls
<INDIRECT>
func1: callee1[(mode)],callee2[(mode)],[],calleeN[(mode)]
func2: callee1[(mode)],[],calleeN[(mode)]
[]
funcm: callee1[(mode)],[],calleeN[(mode)]
</INDIRECT>
The keywords <INDIRECT> and </INDIRECT> delimit an indirect callee section. Each line in the section
begins with the name of a calling procedure, func, followed by a colon (:), which is then followed by a list
of functions that are called indirectly from func. Each entry in the indirect callee list consists of the callee
name, and an optional mode (in parentheses) in which the callee was compiled.
The profiler recognizes the specification of one of three modes: ARM, THUMB, and DUAL (default). If a
mode is not specified, the profiler will assume DUAL mode. For DUAL mode callee functions, the profiler
automatically adds the names of the callees (in ARM and THUMB modes) to the callee list for func. In this
example, function bar is specified as a callee in DUAL mode, and both _bar and $bar are added to the
callee list for main:
<INDIRECT>
main:foo(ARM),bar
</INDIRECT>
Each indirect call can be specified on a separate line within an indirect call section:
<INDIRECT>
main:foo(ARM),
main:bar
</INDIRECT>
The profiler performs no semantic checks on the information input via the configuration file. That is, it does
not check to determine if the procedures listed in the callee list or the caller list exist or if they exist in the
mode specified. The profiler checks, however, for available debug information for a function and generates
a warning if none is found.
The profiler declares the following types of loads of PC (in ARM) mode as indirect call points, where #imm
is an immediate value.
LDR{B,H} PC,[reg,#imm]
However, loads of PC with register offsets are not identified as call points since such loads are used
generally for switch table jumps.
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9.5.2 Specifying Reentrant Procedures
Reentrant functions present a difficult problem to the profiler's ability to accurately estimate the worst-case
space requirement of an application. One difficulty with reentrant functions is that the depth of recursion is
often data-dependent. You may not be able to accurately inform the profiler about the depth of recursion
without knowing in advance all of the input data sets that will be used in the application. Another difficulty
is the presence of multiple recursive functions in a call-graph, which would make it hard to determine the
recursive behavior of each function in the call-graph.
In light of these difficulties, no automated analysis is performed to determine the presence of reentrant
functions or their nature. Instead, we must input the maximum recursive depth of a function. The profiler
assumes that your input is correct and reliable. It issues a warning and warns if there is no apparent
recursion in the call graph for a function and recursion depth that has been specified. Beyond the required
analysis to issue such a warning, the profiler does not perform any analysis on reentrant calls.
The configuration file issued to specify the list of reentrant procedures in the application. The syntax is:
<REENTRANT>
func1 ( depth )
func2 ( depth )
</REENTRANT>
The reentrant section is delimited by the <REENTRANT> and </REENTRANT> keywords as shown
above. Each line in the section consists of a function name followed by the recursion depth (in
parentheses) to be assumed for the function. The depth value should be a valid, non-negative integer.
The profiler multiplies the stack size of the function by its specified depth to obtain the final stack usage
requirement for the function. For example,
<REENTRANT>
foo(5)
</REENTRANT>
For this example, the profiler determines that the static stack usage requirement of foo is 100, the
maximum dynamic requirement of foo would be 100*5 = 500. The depth of a function defaults to 1 in the
absence of a depth field.
The profiler does not make any effort to determine if the procedure specified in the reentrant section is
indeed recursive. It assumes that the input is correct and reliable.
9.5.3 Specifying Interrupt Service Routines
Interrupt service routines (ISRs), are used to handle interrupts. An interrupt service routine is a special
root function that is usually not directly called from the application. In ARM, an interrupt request can be
serviced by an ISR in any of the six modes. Each mode typically uses a different stack area for the
interrupt handler. The SDA can output the stack requirements of an ISR if you identify ISRs and their
modes of operations. This is the syntax for specifying an ISR and its mode:
<INTERRUPT>
routine_name ( mode )
</INTERRUPT>
In the syntax, routine_name is the name of the ISR and mode can be one of the following:
irq
fiq
svc
abt
sys
und
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general purpose interrupt
data transfer or channel process
operating system protected mode
data or instruction prefetch abort
privileged user mode for the operating system
undefined instruction
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Configuration File Specification
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The stack space requirement for ISRs is output after the stack space requirements for routines directly
called by the application.
9.5.4 Other Features
The configuration file supports all preprocessing directives supported by cl470. The configuration file
should be processed using the cl470 preprocessor before being input to the profiler. For example, file
config1 contains the following <INDIRECT> lines and file config2 contains the following <REENTRANT>
lines:
<INDIRECT>
main:foo,
</INDIRECT>
#include "config2"
<REENTRANT>
foo(5)
</REENTRANT>
The cl470 preprocessor can be used to combine the two config files. For example:
cl470 --preproc_only config1
The preprocessor adds or replaces the file suffix with .pp. In the above example, the combined config files
will be found in the file "config1.pp". The profiler supports C++ style comments. All characters following the
// symbol to the end of the line (new line character) are ignored. The // can appear anywhere in a
configuration file. For example:
<INDIRECT>
// This is a comment
main:foo
// End of indirect callee list
</INDIRECT>
The configuration file does not permit nesting of sections. For example, the following specification is
illegal:
<INDIRECT>
foo:bar
<REENTRANT>
foo(5)
</REENTRANT>
</INDIRECT>
The profiler performs no semantic checks on the information specified in the configuration file and
assumes that the information provided is correct and valid. It is your responsibility to ensure the validity of
information specified in the configuration file.
9.5.5 Tail Calls
A tail call is code that branches to a routine foo() at the end of routine bar() so that control returns directly
to bar's caller at the end of foo()). The SDA handles tail calls by identifying tail call points as both call point
and return points. The pseudo assembly instruction CRET is used for representing tail calls.
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Profiler Generated Warnings
The static stack depth profiler detects the following situations and issues a warning in each case:
• A function contains an indirect branch (branch to the contents of a register) and there are no
<INDIRECT>entries for the function in the configuration file, the profiler issues a warning that a
potential indirect call has been observed and this caller/callee pair is not specified in the configuration
file. Not all indirect branches are function calls; e.g., in 32-BIS mode, long branches are achieved
through indirect branches.
• A set of indirect callees for a function is not specified and the profiler observes no indirect branches in
the function, it issues a warning indicating the absence of indirect calls.
• A function's call graph has a link back to the function indicating potential recursion and no recursion
depth is specified, the profiler issues a warning indicating that the function is reentrant. A warning and
not an error is issued since a function could have an apparent recursion and not a real one.
• The profiler discovers no links back to the function in a call-graph and a recursion depth is specified, it
issues a warning.
• No stack usage information for a function is found.
• No debug information for a function is found.
• The profiler generates a potential indirect callee warning for each routine compiled in dual mode. This
is because, in dual mode, each call to an external routine is performed by jumping to the RTS routine
IND_CALL or IND$CALL (depending on the mode of the caller).
• The profiler generates potential indirect callee warnings for routines in the RTS library.
9.7
Run-Time Support for Stack Depth Profiling
The ARM compiler provides a debug option to determine the maximum stack usage of an application. If
the application is compiled with the -debug:sdp option, the compiler places a call to a stack depth
bookkeeping routine (C_SDPBK for 32-BIS and C$SDPBK for 16-BIS), immediately after the frame has
been allocated for a function. This bookkeeping routine tracks the maximum stack usage for each
function. There is a profiled version of the run-time support library that can be linked when -debug:sdp is
turned on. This enables you to determine the complete stack usage of an application that contains
run-time support utilities (such as I/O utilities).
There is an overhead associated with the -debug:sdp option. The link register (LR) is always saved when
this option is turned on, since all functions in the application call the bookkeeping routine.
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Glossary
absolute lister— A debugging tool that allows you to create assembler listings that contain absolute
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.
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.
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.
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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. These files are relocatable in memory space.
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 linking 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 module— A linked object file that can be executed in a target system.
expression— A constant, a symbol, or a series of constants and symbols separated by arithmetic
operators.
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).
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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 module.
input section— A section from an object file that will be linked into an executable module.
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 object module that can be allocated
into system memory and executed by the device.
listing file— An output file, created by the assembler, that 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 module 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.
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.
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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, that 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.
object module— A linked, executable object file that can be downloaded and executed on a target
system.
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 module— A linked, executable object file that is downloaded and executed on a target system.
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.
pipelining— A technique where a second instruction begins executing before the first instruction has
been completed. You can have several instructions in the pipeline, each at a different processing
stage.,filter4,filter5,filter7
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.
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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).
run-time-support library— A library file, rts.src, that 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.
software pipelining— A technique used by the C/C++ optimizer to schedule instructions from a loop so
that multiple iterations of the loop execute in parallel.
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 a simulator or an emulator.
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.
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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
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