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Directives

5. Anything following a

; character is considered to be a comment, except in GNU compatibility mode, where

; is a statement separator.

12.1.7 Data Alignment

The assembler's default alignment is on a natural boundary for the data size and for the target processor family. To turn off this default alignment, use the alignment

keyword argument with to the

. option

directive.

NOTE

The assembler does not align data automatically in the

.debug

section.

12.2 Directives

• Some directives may not be available for the assembler for your target processor.

• The default starting character for most directives is the period (.). However, if you clear the Directives begin with '.' checkbox of the Assembler settings panel, you can omit the period.

• You can use the C/C++ preprocessor format to specify several preprocessor directives .

Explanations are in these sections:

•

Macro Directives

•

Conditional Preprocessor Directives

•

Section Control Directives

•

Scope Control Directives

•

Symbol Definition Directives

•

Data Declaration Directives

•

Assembler Control Directives

•

Debugging Directives

12.2.1 Macro Directives

These directives let you create macros:

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•

•

•

•

For more information on macros, see

"Macros" .

12.2.1.1 macro

Starts the definition of a macro.

label .macro [ parameter ] [ ,parameter ] ...

Parameters

label

Name you give the macro.

parameter

Optional parameter for the macro.

12.2.1.2 endm

Ends the definition of a macro.

.endm

12.2.1.3 mexit

Stops macro execution before it reaches the .endm directive. Program execution continues with the statement that follows the macro call.

.mexit

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12.2.1.4 #define

Defines a C pre-processor macro with the specified parameters. Note that the C preprocessor is run on the assembler file before normal assembly. C pre-processor macros should not be confused with normal macros declared using the

MACRO

and

ENDM

directives.

#define

name [ (

parms) ]

assembly_statement [ ; ] [ \ ]

assembly_statement

parms ::=

parameter [ ,

parameter ]...

Parameters

name

Name you give the macro.

parms

List of parameters, separated by commas.

assembly_statement

Any valid assembly statement.

Remarks

To extend an assembly_statement, type a backslash (\) and continue the statement on the next line. To specify multiple assembly statements in the macro, type a semicolon and backslash (;\), then type a new assembly statement on the next line. If the assembler is in

GNU mode, multiple statements can be on one line of code - separate them with semicolon characters (;).

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NOTE

For more information, see

"Using the #define Directive" on page 181

Chapter 12 Assembler

12.2.2 Conditional Preprocessor Directives

Conditional directives let you control whether compilation includes a block of code.

These directives let you make multiple builds that are slightly different.

You must use conditional directives together to form a complete block. Several conditional directives are variations of

.if

that make it easier to establish blocks that test strings for equality, test whether a symbol is defined, and so on.

NOTE

You can use the C/C++ preprocessor format to specify these conditional directives:

#if #ifdef #ifndef

#else #elif #endif

With two exceptions, these directives function identically whether their starting character is a pound sign (#) or a period.

The exceptions are:

1. You cannot use the pound sign format in a macro.

2. The period form of

#elif

.elseif

The conditional preprocessor directives are:

•

•

•

•

•

•

•

•

Compatibility Conditional Directives

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12.2.2.1 if

Starts a conditional assembly block, making assembly conditional on the truth of a boolean expression.

.if bool-expr

Parameter

bool-expr

Any boolean expression.

Remarks

If bool-expr

is true, the assembler processes the statements of the block. If bool-expr

is false, the assembler skips the statements of the block.

Each

.if

directive must have a matching

.endif

directive.

12.2.2.2 ifdef

Starts a conditional assembly block, making assembly conditional on the definition of a symbol.

#ifdef symbol

Parameter

symbol

Any valid symbol.

Remarks

If previous code includes a definition for symbol

, the assembler processes the statements of the block. If symbol

is not defined, the assembler skips the statements of the block.

Each

.ifdef

directive must have a matching

.endif

directive.

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12.2.2.3 ifndef

Starts a conditional assembly block, making assembly conditional on a symbol not being defined.

.ifndef symbol

Parameter

symbol

Any valid symbol.

Remarks

If previous code does not include a definition for symbol

, the assembler processes the statements of the block. If there is a definition for symbol

, the assembler skips the statements of the block.

Each

.ifndef

directive must have a matching

.endif

directive.

12.2.2.4 ifc

Starts a conditional assembly block, making assembly conditional on the equality of two strings.

.ifc string1, string2

Parameters

string1

Any valid string.

string2

Any valid string.

Remarks

If string1 and string2 are equal, the assembler processes the statements of the block. (The equality comparison is case-sensitive.) If the strings are not equal, the assembler skips the statements of the block.

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Each

.ifc

directive must have a matching

.endif

directive.

12.2.2.5 ifnc

Starts a conditional assembly block, making assembly conditional on the inequality of two strings.

.ifnc string1, string2

Parameters

string1

Any valid string.

string2

Any valid string.

Remarks

If string1 and string2 are not equal, the assembler processes the statements of the block.

(The inequality comparison is case-sensitive.) If the strings are equal, the assembler skips the statements of the block.

Each

.ifnc

directive must have a matching

.endif

directive.

12.2.2.6 endif

Ends a conditional assembly block. A matching

.endif

directive is mandatory for each type of

.if

directive.

.endif

12.2.2.7 elseif

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Starts an alternative conditional assembly block, making assembly conditional on the truth of a boolean expression.

.elseif bool-expr

Parameter

bool-expr

Any boolean expression.

Remarks

If bool-expr

is true, the assembler processes the statements of the block. If bool-expr

is false, the assembler skips the statements of the block.

You can use this directive to create a logical, multilevel if-then-else statement, according to this syntax:

.if bool-expr statement-group

[ .elseif bool-expr statement-group ]...

[ .else statement-group ]

.endif

(In this syntax, statement-group

is any group of assembly-language statements.)

The

.elseif

directive can be part of more complicated logical structures, such as:

.if bool-expr-1

statement-group-1

.elseif bool-expr-2

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statement-group-2

.elseif bool-expr-3

statement-group-3

.elseif bool-expr-4

statement-group-4

.else

statement-group-5

.endif

• If this structure's bool-expr-1

is true, the assembler executes the statement-group-1 assembly-language statements, then goes to the

.endif

directive.

• If bool-expr-1

is false, the assembler skips statement-group-1

, executing the first

.elseif

directive. If bool-expr-2

is true, the assembler executes statement-group-2

, then goes to the

.endif

directive.

• If bool-expr-2

also is false, the assembler skips statement-group-2

, executing the second

.elseif

directive.

• The assembler continues evaluating the boolean expressions of succeeding

.elseif

directives until it comes to a boolean expression that is true.

• If none of the boolean expressions are true, the assembler processes statement-group-5

, because this structure includes an

.else

directive. (If none of the boolean values were true and there were no

.else

directive, the assembler would not process any of the statement groups.)

12.2.2.8 else

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Starts an alternative conditional assembly block.

.else

Remarks

This directive is optional. The assembler processes the statements of the alternative conditional assembly block only if the expressions for an

.if

directive and any associated

.elseif

directives are false.

12.2.3 Compatibility Conditional Directives

For compatibility with other assemblers, the assembler supports these additional conditional directives:

•

.ifeq if equal

•

.ifne if not equal

•

.iflt if less than

•

.ifle if less than or equal

•

.ifgt if greater than

•

.ifge if greater than or equal

12.2.3.1 .ifeq if equal

Starts a conditional assembly block, making assembly conditional on a string value being equal to zero.

.ifeq string

Parameter

string

Any valid string.

Remarks

If the string

value equals 0, the assembler processes the statements of the block. If the string

value does not equal 0, the assembler skips the statements of the block.

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12.2.3.2 .ifne if not equal

Starts a conditional assembly block, making assembly conditional on a string value not being equal to zero.

.ifne string

Parameter

string

Any valid string.

Remarks

If the string value is not equal to 0, the assembler processes the statements of the block. If the string

value does equal 0, the assembler skips the statements of the block.

12.2.3.3 .iflt if less than

Starts a conditional assembly block, making assembly conditional on a string value being less than zero.

.iflt string

Parameter

string

Any valid string.

Remarks

If the string

value is less than 0, the assembler processes the statements of the block. If the string

value equals or exceeds 0, the assembler skips the statements of the block.

12.2.3.4 .ifle if less than or equal

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Starts a conditional assembly block, making assembly conditional on a string value being less than or equal to zero.

.ifle string

Parameter

string

Any valid string.

Remarks

If the string value is less than or equal to 0, the assembler processes the statements of the block. If the string

value is greater than 0, the assembler skips the statements of the block.

12.2.3.5 .ifgt if greater than

Starts a conditional assembly block, making assembly conditional on a string value being greater than zero.

.ifgt string

Parameter

string

Any valid string.

Remarks

If the string

value is greater than 0, the assembler processes the statements of the block. If the string value is less than or equal to 0, the assembler skips the statements of the block.

12.2.3.6 .ifge if greater than or equal

Starts a conditional assembly block, making assembly conditional on a the string value being greater than or equal to zero.

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.ifge string

Parameter

string

Any valid string.

Remarks

If the string

value is greater than or equal to 0, the assembler processes the statements of the block. If the string

value is less than 0, the assembler skips the statements of the block.

12.2.4 Section Control Directives

These directives identify the different sections of an assembly file:

•

•

•

•

•

•

•

•

•

•

•

12.2.4.1 text

Specifies an executable code section; must be in front of the actual code in a file.

.text

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12.2.4.2 data

Specifies an initialized read-write data section.

.data

12.2.4.3 rodata

Specifies an initialized read-only data section.

.rodata

12.2.4.4 bss

Specifies an uninitialized read-write data section.

.bss

12.2.4.5 sdata

Specifies a small data section as initialized and read-write.

.sdata

12.2.4.6 sdata2

Specifies a small data section as initialized and read-only.

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.sdata2

12.2.4.7 sbss

Specifies a small data section as uninitialized and read-write.

.sbss

12.2.4.8 text_vle

Specifies a Variable length encoded section as read/execute.

.text_vle

12.2.4.9 debug

Specifies a debug section.

.debug

Remarks

If you enable the debugger, the assembler automatically generates some debug information for your project. However, you can use special directives in the debug section that provide the debugger with more detailed information. For more information on the debug directives, see

"Debugging Directives".

12.2.4.10 previous

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Reverts to the previous section; toggles between the current section and the previous section.

.previous

12.2.4.11 offset

Starts a record definition, which extends to the start of the next section.

.offset [expression]

Parameter

expression

Optional initial location-counter value.

Remarks

Table 12-6 lists the only directives your can use inside a record.

Table 12-6. Directives within a Record

.align

.ascii

.asciz

.byte

.double

.equ

.float

.long

.org

.set

.short

.space

.textequ

Data declaration directives such as

.byte

and

.short

update the location counter, but do not allocate any storage.

Example

Figure 12-1 shows a sample record definition.

Figure 12-1. Record Definition with Offset Directive

.offset

top: .short 0 left: .short 0 bottom: .short 0 right: .short 0

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rectSize .equ *

12.2.4.12 section

Defines a section of an ELF (Executable and Linkable Format) object file.

.section name [,alignment [,type [,flags]]]

Parameters

name

Name of the section.

alignment

Alignment boundary.

type

Numeric value for the ELF section type, per Table 12-7 . The default type

value is

(SHT_PROGBITS).

flags

Numeric value for the ELF section flags, per Table 12-8 . The default flags

value is

0x00000002, 0x00000001

: (SHF_ALLOC+SHF_WRITE).

Table 12-7. ELF Section Header Types (SHT)

Type

NULL

PROGBITS

SYMTAB

STRTAB

RELA

HASH

DYNAMIC

NOTE

Name Meaning

Section header is inactive.

Section contains information that the program defines.

Section contains a symbol table.

Section contains a string table.

Section contains relocation entries with explicit addends.

Section contains a symbol hash table.

Section contains information used for dynamic linking.

Section contains information that marks the file, often for compatibility purposes between programs.

Table continues on the next page...

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0x00000001

0x00000002

0x00000004

0xF0000000

Flag

Type

Chapter 12 Assembler

Table 12-7. ELF Section Header Types (SHT) (continued)

NOBITS

REL

SHLIB

DYNSYM

Name Meaning

Section occupies no space in the object file.

Section contains relocation entries without explicit addends.

Section has unspecified semantics, so does not conform to the Application

Binary Interface (ABI) standard.

Section contains a minimal set of symbols for dynamic linking.

Table 12-8. ELF Section Header Flags (SHF)

WRITE

ALLOC

EXECINSTR

MASKPROC

Name Meaning

Section contains data that is writable during execution.

Section occupies memory during execution.

Section contains executable machine instructions.

Bits this mask specifies are reserved for processor-specific purposes.

Remark

Use this directive to create arbitrary relocatable sections, including sections to be loaded at an absolute address.

Possiblesyntaxforms

The section directive accepts a number of different syntax forms, partly for convenience and partly for compatibility with other assemblers. A section declaration requires four pieces of information: a section name, alignment, ELF section type (for example,

SHT_PROGBITS) and ELF section flags (for example, SHF_ALLOC

+SHF_EXECINSTR).

The possible syntax forms are as follows:

• Specify built-in section name.

.section text

This example specifies a built-in section name text

. Equivalently, .text is also a valid syntax form.

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Table 12-9 provides a list of all the possible values, together with their ELF types and ELF Section Header Flags.

.text

.data

.rodata

.bss

.sdata

.sdata0

.sdata2

.sbss

.sbss0

.sbss2

.debug

.text_vle

Name

Table 12-9. Built-in Section names with their ELF Types and

Flags

.PPC.EMB.sdata0

.PPC.EMB.sbss0

ELF Type

SHT_PROGBITS

SHT_NOBITS

SHT_PROGBITS

SHT_NOBITS

SHT_PROGBITS

ELF Flag

SHF_ALLOC

+SHF_EXECINSTR

SHF_ALLOC+SHF_WRITE

SHF_ALLOC

SHF_ALLOC+SHF_WRITE

SHF_ALLOC

SHF_ALLOC+SHF_WRITE

SHF_ALLOC

+SHF_EXECINSTR+

SHF_PE_EXECINSTR

SHF_ALLOC+SHF_WRITE

In general, .text is for instructions, .data for initialised data, .rodata for read-only data

(constants) and .bss for uninitialised data. The additional forms like .sdata are for small data areas. The built-in section names are architecture-specific, and are intended to make access to data more efficient. The alignment used for these sections is architecture-specific and is usually 4.

• Specify your own section name but get the attributes of the built-in section type.

.section mySection,text

This example is equivalent to writing .text except that the section will be called mySection.

• Specify the alignment, and optionally the ELF type and flags.

.section name [,alignment [,type [,flags]]]

In the syntax above, if the alignment is not specified it defaults to 16. If the type or flags are not specified, the defaults are as follows:

• If the name parameter is a built-in section name, the type and the flags are taken as specified in the Table 12-9 . For example, in the syntax form.section text,8 the

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type is SHT_PROGBITS and the flags value is SHF_ALLOC

+SHF_EXECINSTR.

• In all other cases, the default type is SHT_PROGBITS and the default flags value is SHF_ALLOC+SHF_WRITE, corresponding to a writeable data section.

• Specify the type and flags parameters in pre-defined characters, optionally in double quotes.

.section mySection,4,"rx" or .section mySection,4,rx

The values are additive. For example, rx is equivalent to SHF_ALLOC

+SHF_WRITE+SHF_EXECINSTR

NOTE

If the syntax doesn't specify a type it defaults to

SHT_PROGBITS

Table 12-10 provides a list of all the possible characters and their corresponding ELF

Type and ELF Flags.

r w x d m b c

Table 12-10. Characters and their corresponding ELF Type and ELF

Flags

Character

ELF Type

SHT_NOBITS

SHT_PROGBITS

ELF Flag

SHF_ALLOC+SHF_WRITE

SHF_ALLOC

+SHF_EXECINSTR

SHF_ALLOC+SHF_WRITE

SHF_ALLOC+SHF_WRITE+

SHF_EXECINSTR

SHF_ALLOC

SHF_ALLOC+SHF_WRITE

SHF_ALLOC

+SHF_EXECINSTR

12.2.5 Scope Control Directives

These directives let you import and export labels:

•

global

•

extern

•

public

For more information on labels, see "Labels".

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NOTE

You cannot import or export equates or local labels.

12.2.5.1 global

Tells the assembler to export the specified labels, that is, make them available to other files.

.global label [ ,label ]...

Parameter

label

Any valid label.

12.2.5.2 extern

Tells the assembler to import the specified labels, that is, find the definitions in another file.

.extern label [ ,label ]...

Parameter

label

Any valid label.

12.2.5.3 public

Declares specified labels to be public.

.public label [ ,label ]...

Parameter

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label

Any valid label.

Remarks

If the labels already are defined in the same file, the assembler exports them (makes them available to other files). If the labels are not already defined, the assembler imports them

(finds their definitions in another file).

12.2.6 Symbol Definition Directives

These directives let you create equates:

•

•

•

•

12.2.6.1 set

Defines an equate, assigning an initial value. You can change this value at a later time.

equate .set expression

Parameters

equate

Name of the equate.

expression

Temporary initial value for the equate.

12.2.6.2 equal sign (=)

Defines an equate, assigning an initial value. You can change this value at a later time.

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equate = expression

Parameters

equate

Name of the equate.

expression

Temporary initial value for the equate.

Remarks

This directive is equivalent to

.set

. It is available only for compatibility with assemblers provided by other companies.

12.2.6.3 equ

Defines an equate, assigning a permanent value. You cannot change this value at a later time.

equate .equ expression

Parameters

equate

Name of the equate.

expression

Permanent value for the equate.

12.2.6.4 textequ

Defines a text equate, assigning a string value.

equate .textequ "string"

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Parameters

equate

Name of the equate.

string

String value for the equate, in double quotes.

Remarks

This directive helps port existing code. You can use it to give new names to machine instructions, directives, and operands.

Upon finding a text equate, the assembler replaces it with the string value before performing any other processing on that source line.

Examples

dc.b .textequ ".byte"

endc .textequ ".endif"

12.2.7 Data Declaration Directives

These directive types initialize data:

•

Integer Directives

•

String Directives

•

Floating-Point Directives

12.2.7.1 Integer Directives

These directives let you initialize blocks of integer data:

•

byte

•

fill

•

incbin

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•

long

•

short

•

space

12.2.7.1.1 byte

Declares an initialized block of bytes.

[ label ] .byte expression [ ,expression ]...

Parameters

label

Name of the block of bytes.

expression

Value for one byte of the block; must fit into one byte.

12.2.7.1.2 fill

Declares a block of bytes, initializing each byte to zero.

[ label ] .fill expression

Parameters

label

Name of the block of bytes.

expression

Number of bytes in the block.

12.2.7.1.3 incbin

Tells the assembler to include the binary content of the specified file.

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. incbin filename[,start[,length]]

Parameters

filename

Name of a binary file.

start

Offset from start of file at which to begin including data.

length

Number of bytes of data to include.

Remarks

This directive is useful when you wish to include arbitrary data directly in the program being assembled, e.g.

logoPicture: .incbin "CompanyLogo.jpg"

12.2.7.1.4 long

Declares an initialized block of 32-bit short integers.

[ label ] .long expression [ ,expression ]...

Parameters

label

Name of the block of integers.

expression

Value for 32 bits of the block; must fit into 32 bits.

12.2.7.1.5 short

Declares an initialized block of 16-bit short integers.

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[ label ] .short expression [ ,expression ]...

Parameters

label

Name of the block of integers.

expression

Value for 16 bits of the block; must fit into 16 bits.

12.2.7.1.6 space

Declares a block of bytes, initializing each byte to zero.

[ label ] .space expression

Parameters

label

Name of the block of bytes.

expression

Number of bytes in the block.

12.2.7.2 String Directives

These directives initialize blocks of character data:

•

ascii

•

asciz

A string can contain any of the escape sequences Table 12-11 lists.

Table 12-11. Escape sequences

Sequence Description

Backspace

Line feed (ASCII character 10)

Table continues on the next page...

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\nnn

Table 12-11. Escape sequences (continued)

Sequence Description

Return (ASCII character 13)

Tab

Double quote

Backslash

Octal value of \nnn

12.2.7.2.1 ascii

Declares a block of storage for a string; the assembler allocates a byte for each character.

[ label ] .ascii "string"

Parameters

label

Name of the storage block.

string

String value to be stored, in double quotes.

12.2.7.2.2 asciz

Declares a zero-terminated block of storage for a string.

[ label ] .asciz "string"

Parameters

label

Name of the storage block.

string

String value to be stored, in double quotes.

Remarks

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The assembler allocates a byte for each string

character. The assembler then allocates an extra byte at the end, initializing this extra byte to zero.

12.2.7.3 Floating-Point Directives

These directives initialize blocks of floating-point data:

•

float

•

double

12.2.7.3.1 float

Declares an initialized block of 32-bit, floating-point numbers; the assembler allocates 32 bits for each value.

[ label ] .float value [ ,value ]...

Parameters

label

Name of the storage block.

value

Floating-point value; must fit into 32 bits.

12.2.7.3.2 double

Declares an initialized block of 64-bit, floating-point numbers; the assembler allocates 64 bits for each value.

[ label ] .double value [ ,value ]...

Parameters

label

Name of the storage block.

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value

Floating-point value; must fit into 64 bits.

12.2.8 Assembler Control Directives

These directives let you control code assembly:

•

•

•

•

•

•

•

12.2.8.1 align

Aligns the location counter to the next multiple of the specified power of 2.

.align expression

Parameter

expression

Power of 2, such as 2, 4, 8, 16, or 32.

12.2.8.2 endian

Specifies byte ordering for the target processor; valid only for processors that permit change of endianness.

.endian big | little

Parameters

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Directives

big

Big-endian specifier.

little

Little-endian specifier.

12.2.8.3 error

Prints the specified error message to the IDE Errors and Warnings window.

.error "error"

Parameter

error

Error message, in double quotes.

12.2.8.4 include

Tells the assembler to take input from the specified file.

.include filename

Parameter

filename

Name of an input file.

Remarks

When the assembler reaches the end of the specified file, it takes input from the assembly statement line that follows the

.include

directive. The specified file can itself contain an

.include

directive that specifies yet another input file.

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12.2.8.5 pragma

Tells the assembler to use a particular pragma setting as it assembles code.

.pragma pragma-type setting

Parameters

pragma-type

Type of pragma.

setting

Setting value.

12.2.8.6 org

Changes the location-counter value, relative to the base of the current section.

.org expression

Parameter

expression

New value for the location counter; must be greater than the current location-counter value.

Remarks

Addresses of subsequent assembly statements begin at the new expression value for the location counter, but this value is relative to the base of the current section.

Example

Listing 12-1 on page 197 , the label

Alpha

reflects the value of

.text + 0x1000

. If the linker places the

.text

section at

0x10000000

, the runtime

Alpha

value is

0x10001000

Listing 12-1. Address-Change Example

.text

.org 0x1000

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Alpha:

...

blr

NOTE

You must use the CodeWarrior IDE and linker to place code at an absolute address.

12.2.8.7 option

Sets an assembler control option as Table 12-12 describes.

.option keyword setting

Parameters

keyword

Control option.

setting

Setting value appropriate for the option: OFF, ON, RESET, or a particular number value.

RESET returns the option to its previous setting.

Table 12-12. Option Keywords

Keyword Description

alignment off | on | reset branchsize 8 | 16 | 32 case off | on | reset colon off | on | reset

Controls data alignment on a natural boundary. Does not correspond to any option of the Assembler settings panel.

Specifies the size of forward branch displacement. Applies only to x86 and

68K assemblers. Does not correspond to any option of the Assembler settings panel.

Specifies case sensitivity for identifiers.

Corresponds to the Case-sensitive identifiers checkbox of the Assembler settings panel.

Specifies whether labels must end with a colon (:). The OFF setting means that you can omit the ending colon from label names that start in the first column.

Table continues on the next page...

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Table 12-12. Option Keywords (continued)

Keyword

Description

Corresponds to the Labels must end with ':' checkbox of the Assembler settings panel.

Controls $AT use in macros. The OFF setting means that the assembler issues a warning if a macro uses $AT. Applies only to the MIPS Assembler.

Controls period usage for directives. The

ON setting means that each directive must start with a period. Corresponds to the Directives begin with '.' checkbox of the Assembler settings panel.

Controls NOP instructions after jumps and branches. The ON setting means that the assembler inserts a NOP instruction, possibly preventing pipeline problems. The OFF setting means that the assembler does not insert a NOP instruction, so that you can specify a different instruction after jumps and branches. Applies only to the MIPS

Assembler.

Controls spaces in operand fields. The

OFF setting means that a space in an operand field starts a comment.

Corresponds to the Allow space in operand field checkbox of the Assembler settings panel.

12.2.9 Debugging Directives

When you enable the debugger, the assembler automatically generates some debug information for your project. However, you can use these directives in the debug section to provide additional information to the debugger:

•

•

•

•

•

NOTE

These debugging directives are valid only in the