Main index | Section 7 | Options |
This document is distributed under the terms of the GNU Free Documentation License. A copy of the license is included in the section entitled “GNU Free Documentation License”.
as [-a[cdhlns][=file]] [--alternate] [-D] [--defsym sym=val] [-f] [-g] [--gstabs] [--gstabs+] [--gdwarf-2] [--help] [-I dir] [-J] [-K] [-L] [--listing-lhs-width=NUM] [--listing-lhs-width2=NUM] [--listing-rhs-width=NUM] [--listing-cont-lines=NUM] [--keep-locals] [-o objfile] [-R] [--reduce-memory-overheads] [--statistics] [-v] [-version] [--version] [-W] [--warn] [--fatal-warnings] [-w] [-x] [-Z] [@FILE] [--target-help] [target-options] [--|files ...]Target ARM options: [-mcpu=processor[+extension...]] [-march=architecture[+extension...]] [-mfpu=floating-point-format] [-mfloat-abi=abi] [-meabi=ver] [-mthumb] [-EB|-EL] [-mapcs-32|-mapcs-26|-mapcs-float| -mapcs-reentrant] [-mthumb-interwork] [-k]
Target i386 options: [--32|--64] [-n] [-march=CPU] [-mtune=CPU]
Target IA-64 options: [-mconstant-gp|-mauto-pic] [-milp32|-milp64|-mlp64|-mp64] [-mle|mbe] [-mtune=itanium1|-mtune=itanium2] [-munwind-check=warning|-munwind-check=error] [-mhint.b=ok|-mhint.b=warning|-mhint.b=error] [-x|-xexplicit] [-xauto] [-xdebug]
Target MIPS options: [-nocpp] [-EL] [-EB] [-O[optimization level]] [-g[debug level]] [-G num] [-KPIC] [-call_shared] [-non_shared] [-xgot [-mvxworks-pic] [-mabi=ABI] [-32] [-n32] [-64] [-mfp32] [-mgp32] [-march=CPU] [-mtune=CPU] [-mips1] [-mips2] [-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2] [-mips64] [-mips64r2] [-construct-floats] [-no-construct-floats] [-trap] [-no-break] [-break] [-no-trap] [-mfix7000] [-mno-fix7000] [-mips16] [-no-mips16] [-msmartmips] [-mno-smartmips] [-mips3d] [-no-mips3d] [-mdmx] [-no-mdmx] [-mdsp] [-mno-dsp] [-mdspr2] [-mno-dspr2] [-mmt] [-mno-mt] [-mdebug] [-no-mdebug] [-mpdr] [-mno-pdr]
Target PowerPC options: [-mpwrx|-mpwr2|-mpwr|-m601|-mppc|-mppc32|-m603|-m604| -m403|-m405|-mppc64|-m620|-mppc64bridge|-mbooke| -mbooke32|-mbooke64] [-mcom|-many|-maltivec] [-memb] [-mregnames|-mno-regnames] [-mrelocatable|-mrelocatable-lib] [-mlittle|-mlittle-endian|-mbig|-mbig-endian] [-msolaris|-mno-solaris]
Target SPARC options: [-Av6|-Av7|-Av8|-Asparclet|-Asparclite -Av8plus|-Av8plusa|-Av9|-Av9a] [-xarch=v8plus|-xarch=v8plusa] [-bump] [-32|-64]
@ file | |
Read command-line options from
file.
The options read are inserted in place of the original @
file
option. If
file
does not exist, or cannot be read, then the option will be treated literally,
and not removed.
Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @ file options; any such options will be processed recursively.
| |
-a[cdhlmns] | |
Turn on listings, in any of a variety of ways:
| |
-ac |
omit false conditionals
|
-ad |
omit debugging directives
|
-ah |
include high-level source
|
-al |
include assembly
|
-am |
include macro expansions
|
-an |
omit forms processing
|
-as |
include symbols
|
=file | set the name of the listing file |
You may combine these options; for example, use -aln for assembly listing without forms processing. The =file option, if used, must be the last one. By itself, -a defaults to -ahls.
--alternate | |
Begin in alternate macro mode.See Section
"Altmacro".
| |
-D |
Ignored. This option is accepted for script compatibility with calls to other
assemblers.
|
--defsym sym= value | |
Define the symbol
sym
to be
value
before assembling the input file.
value
must be an integer constant. As in C, a leading
0x
indicates a hexadecimal value, and a leading
0
indicates an octal value. The value of the symbol can be overridden inside
a source file via the use of a
.set
pseudo-op.
| |
-f |
“fast”---skip whitespace and comment preprocessing (assume source is compiler
output).
|
-g
--gen-debug | |
Generate debugging information for each assembler source line using whichever
debug format is preferred by the target. This currently means either STABS,
ECOFF or DWARF2.
| |
--gstabs | |
Generate stabs debugging information for each assembler line. This may help
debugging assembler code, if the debugger can handle it.
| |
--gstabs+ | |
Generate stabs debugging information for each assembler line, with GNU extensions
that probably only gdb can handle, and that could make other debuggers crash
or refuse to read your program. This may help debugging assembler code. Currently
the only GNU extension is the location of the current working directory at
assembling time.
| |
--gdwarf-2 | |
Generate DWARF2 debugging information for each assembler line. This may help
debugging assembler code, if the debugger can handle it. Note---this option
is only supported by some targets, not all of them.
| |
--help | |
Print a summary of the command line options and exit.
| |
--target-help | |
Print a summary of all target specific options and exit.
| |
-I dir | |
Add directory
dir
to the search list for
.include
directives.
| |
-J |
Don't warn about signed overflow.
|
-K |
This option is accepted but has no effect on the machine specific family.
|
-L
--keep-locals | |
Keep (in the symbol table) local symbols. These symbols start with system-specific
local label prefixes, typically
.L
for ELF systems or
L
for traditional a.out systems.See Section
"Symbol Names".
| |
--listing-lhs-width= number | |
Set the maximum width, in words, of the output data column for an assembler
listing to
number.
| |
--listing-lhs-width2= number | |
Set the maximum width, in words, of the output data column for continuation
lines in an assembler listing to
number.
| |
--listing-rhs-width= number | |
Set the maximum width of an input source line, as displayed in a listing,
to
number
bytes.
| |
--listing-cont-lines= number | |
Set the maximum number of lines printed in a listing for a single line of
input to
number
+ 1.
| |
-o objfile | |
Name the object-file output from
as
objfile.
| |
-R |
Fold the data section into the text section.
Set the default size of GAS's hash tables to a prime number close to number. Increasing this value can reduce the length of time it takes the assembler to perform its tasks, at the expense of increasing the assembler's memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed.
|
--reduce-memory-overheads | |
This option reduces GAS's memory requirements, at the expense of making the
assembly processes slower. Currently this switch is a synonym for
--hash-size=4051,
but in the future it may have other effects as well.
| |
--statistics | |
Print the maximum space (in bytes) and total time (in seconds) used by assembly.
| |
--strip-local-absolute | |
Remove local absolute symbols from the outgoing symbol table.
| |
-v
-version | |
Print the
as
version.
| |
--version | |
Print the
as
version and exit.
| |
-W
--no-warn | |
Suppress warning messages.
| |
--fatal-warnings | |
Treat warnings as errors.
| |
--warn | |
Don't suppress warning messages or treat them as errors.
| |
-w |
Ignored.
|
-x |
Ignored.
|
-Z |
Generate an object file even after errors.
|
-- | files ... | |
Standard input, or source files to assemble.
| |
-mcpu= processor[+ extension...] | |
Specify which ARM processor variant is the target. | |
-march= architecture[+ extension...] | |
Specify which ARM architecture variant is used by the target. | |
-mfpu= floating-point-format | |
Select which Floating Point architecture is the target. | |
-mfloat-abi= abi | |
Select which floating point ABI is in use. | |
-mthumb | |
Enable Thumb only instruction decoding. | |
-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant | |
Select which procedure calling convention is in use. | |
-EB | -EL | |
Select either big-endian (-EB) or little-endian (-EL) output. | |
-mthumb-interwork | |
Specify that the code has been generated with interworking between Thumb and ARM code in mind. | |
-k | Specify that PIC code has been generated. |
The following options are available when as is configured for the SPARC architecture:
-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
-Av8plus | -Av8plusa | -Av9 | -Av9a | |
Explicitly select a variant of the SPARC architecture.
-Av8plus and -Av8plusa select a 32 bit environment. -Av9 and -Av9a select a 64 bit environment. -Av8plusa and -Av9a enable the SPARC V9 instruction set with UltraSPARC extensions.
| |
-xarch=v8plus | -xarch=v8plusa | |
For compatibility with the Solaris v9 assembler. These options are equivalent
to -Av8plus and -Av8plusa, respectively.
| |
-bump | Warn when the assembler switches to another architecture. |
The following options are available when as is configured for a mips processor.
-G num | |
This option sets the largest size of an object that can be referenced implicitly
with the
gp
register. It is only accepted for targets that use ECOFF format, such as a
DECstation running Ultrix. The default value is 8.
| |
-EB |
Generate “big endian” format output.
|
-EL |
Generate “little endian” format output.
|
-mips1
-mips2 -mips3 -mips4 -mips5 -mips32 -mips32r2 -mips64 -mips64r2 | |
Generate code for a particular mips Instruction Set Architecture level.
-mips1
is an alias for
-march=r3000,
-mips2
is an alias for
-march=r6000,
-mips3
is an alias for
-march=r4000
and
-mips4
is an alias for
-march=r8000.
-mips5,
-mips32,
-mips32r2,
-mips64,
and
-mips64r2
correspond to generic
MIPS V,
MIPS32,
MIPS32 Release 2,
MIPS64,
and
MIPS64 Release 2
ISA processors, respectively.
| |
-march= CPU | |
Generate code for a particular mips cpu.
| |
-mtune= cpu | |
Schedule and tune for a particular mips cpu.
| |
-mfix7000
-mno-fix7000 | |
Cause nops to be inserted if the read of the destination register of an mfhi
or mflo instruction occurs in the following two instructions.
| |
-mdebug
-no-mdebug | |
Cause stabs-style debugging output to go into an ECOFF-style .mdebug section
instead of the standard ELF .stabs sections.
| |
-mpdr
-mno-pdr | |
Control generation of
.pdr
sections.
| |
-mgp32
-mfp32 | |
The register sizes are normally inferred from the ISA and ABI, but these flags
force a certain group of registers to be treated as 32 bits wide at all times.
-mgp32
controls the size of general-purpose registers and
-mfp32
controls the size of floating-point registers.
| |
-mips16
-no-mips16 | |
Generate code for the MIPS 16 processor. This is equivalent to putting
.set mips16
at the start of the assembly file.
-no-mips16
turns off this option.
| |
-msmartmips
-mno-smartmips | |
Enables the SmartMIPS extension to the MIPS32 instruction set. This is equivalent
to putting
.set smartmips
at the start of the assembly file.
-mno-smartmips
turns off this option.
| |
-mips3d
-no-mips3d | |
Generate code for the MIPS-3D Application Specific Extension. This tells the
assembler to accept MIPS-3D instructions.
-no-mips3d
turns off this option.
| |
-mdmx
-no-mdmx | |
Generate code for the MDMX Application Specific Extension. This tells the
assembler to accept MDMX instructions.
-no-mdmx
turns off this option.
| |
-mdsp
-mno-dsp | |
Generate code for the DSP Release 1 Application Specific Extension. This tells
the assembler to accept DSP Release 1 instructions.
-mno-dsp
turns off this option.
| |
-mdspr2
-mno-dspr2 | |
Generate code for the DSP Release 2 Application Specific Extension. This option
implies -mdsp. This tells the assembler to accept DSP Release 2 instructions.
-mno-dspr2
turns off this option.
| |
-mmt
-mno-mt | |
Generate code for the MT Application Specific Extension. This tells the assembler
to accept MT instructions.
-mno-mt
turns off this option.
| |
--construct-floats
--no-construct-floats | |
The
--no-construct-floats
option disables the construction of double width floating point constants
by loading the two halves of the value into the two single width floating
point registers that make up the double width register. By default
--construct-floats
is selected, allowing construction of these floating point constants.
| |
--emulation= name | |
This option causes
as
to emulate
as
configured for some other target, in all respects, including output format
(choosing between ELF and ECOFF only), handling of pseudo-opcodes which may
generate debugging information or store symbol table information, and default
endianness. The available configuration names are:
mipsecoff,
mipself,
mipslecoff,
mipsbecoff,
mipslelf,
mipsbelf.
The first two do not alter the default endianness from that of the primary
target for which the assembler was configured; the others change the default
to little- or big-endian as indicated by the
b
or
l
in the name. Using
-EB
or
-EL
will override the endianness selection in any case.
This option is currently supported only when the primary target as is configured for is a mips ELF or ECOFF target. Furthermore, the primary target or others specified with --enable-targets=... at configuration time must include support for the other format, if both are to be available. For example, the Irix 5 configuration includes support for both. Eventually, this option will support more configurations, with more fine-grained control over the assembler's behavior, and will be supported for more processors.
| |
-nocpp | |
as
ignores this option. It is accepted for compatibility with the native tools.
| |
--trap
--no-trap --break --no-break | |
Control how to deal with multiplication overflow and division by zero.
--trap
or
--no-break
(which are synonyms) take a trap exception (and only work for Instruction
Set Architecture level 2 and higher);
--break
or
--no-trap
(also synonyms, and the default) take a break exception.
| |
-n | When this option is used, as will issue a warning every time it generates a nop instruction from a macro. |
We also cover special features in the machine specific configuration of as, including assembler directives.
On the other hand, this manual is not intended as an introduction to programming in assembly language---let alone programming in general! In a similar vein, we make no attempt to introduce the machine architecture; we do not describe the instruction set, standard mnemonics, registers or addressing modes that are standard to a particular architecture.
as is primarily intended to assemble the output of the GNU C compiler gcc for use by the linker ld. Nevertheless, we've tried to make as assemble correctly everything that other assemblers for the same machine would assemble.
Unlike older assemblers, as is designed to assemble a source program in one pass of the source file. This has a subtle impact on the .org directive (see Section "Org").
-- (two hyphens) by itself names the standard input file explicitly, as one of the files for as to assemble.
Except for -- any command line argument that begins with a hyphen ( -) is an option. Each option changes the behavior of as. No option changes the way another option works. An option is a - followed by one or more letters; the case of the letter is important. All options are optional.
Some options expect exactly one file name to follow them. The file name may either immediately follow the option's letter (compatible with older assemblers) or it may be the next command argument (GNU standard). These two command lines are equivalent:
as -o my-object-file.o mumble.s as -omy-object-file.o mumble.s
The source program is a concatenation of the text in all the files, in the order specified.
Each time you run as it assembles exactly one source program. The source program is made up of one or more files. (The standard input is also a file.)
You give as a command line that has zero or more input file names. The input files are read (from left file name to right). A command line argument (in any position) that has no special meaning is taken to be an input file name.
If you give as no file names it attempts to read one input file from the as standard input, which is normally your terminal. You may have to type ctl-D to tell as there is no more program to assemble.
Use -- if you need to explicitly name the standard input file in your command line.
If the source is empty, as produces a small, empty object file.
Filenames and Line-numbers
There are two ways of locating a line in the input file (or files) and either may be used in reporting error messages. One way refers to a line number in a physical file; the other refers to a line number in a “logical” file.See Section "Errors".
Physical files are those files named in the command line given to as.
Logical files are simply names declared explicitly by assembler directives; they bear no relation to physical files. Logical file names help error messages reflect the original source file, when as source is itself synthesized from other files. as understands the # directives emitted by the gcc preprocessor. See also File,, .file amp;.
The object file is meant for input to the linker ld. It contains assembled program code, information to help ld integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger.
Warning messages have the format
file_name:NNN:Warning Message Text
(where NNN is a line number). If a logical file name has been given (see Section "File") it is used for the filename, otherwise the name of the current input file is used. If a logical line number was given then it is used to calculate the number printed, otherwise the actual line in the current source file is printed. The message text is intended to be self explanatory (in the grand Unix tradition).
Error messages have the format
file_name:NNN:FATAL:Error Message TextThe file name and line number are derived as for warning messages. The actual message text may be rather less explanatory because many of them aren't supposed to happen.
If you are invoking as via the GNU C compiler, you can use the -Wa option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the -Wa) by commas. For example:
gcc -c -g -O -Wa,-alh,-L file.c
This passes two options to the assembler: -alh (emit a listing to standard output with high-level and assembly source) and -L (retain local symbols in the symbol table).
Usually you do not need to use this -Wa mechanism, since many compiler command-line options are automatically passed to the assembler by the compiler. (You can call the GNU compiler driver with the -v option to see precisely what options it passes to each compilation pass, including the assembler.)
Use the
-ac
option to omit false conditionals from a listing. Any lines which are not
assembled because of a false
.if
(or
.ifdef,
or any other conditional), or a true
.if
followed by an
.else,
will be omitted from the listing.
Use the
-ad
option to omit debugging directives from the listing.
Once you have specified one of these options, you can further control listing
output and its appearance using the directives
.list,
.nolist,
.psize,
.eject,
.title,
and
.sbttl.
The
-an
option turns off all forms processing. If you do not request listing output
with one of the
-a
options, the listing-control directives have no effect.
The letters after
-a
may be combined into one option,
e.g.,
-aln.
Note if the assembler source is coming from the standard input (e.g., because
it is being created by
gcc
and the
-pipe
command line switch is being used) then the listing will not contain any comments
or preprocessor directives. This is because the listing code buffers input
source lines from stdin only after they have been preprocessed by the assembler.
This reduces memory usage and makes the code more efficient.
"
Warning:
if you use
-f
when the files actually need to be preprocessed (if they contain comments,
for example),
as
does not work correctly.
"
Enable Listings: [-a[cdhlns]]
These options enable listing output from the assembler. By itself,
-a
requests high-level, assembly, and symbols listing. You can use other letters
to select specific options for the list:
-ah
requests a high-level language listing,
-al
requests an output-program assembly listing, and
-as
requests a symbol table listing. High-level listings require that a compiler
debugging option like
-g
be used, and that assembly listings (
-al)
be requested also.
[--alternate]
Begin in alternate macro mode, see Altmacro,,
.altmacro
amp;.
[-D]
This option has no effect whatsoever, but it is accepted to make it more likely
that scripts written for other assemblers also work with
as.
Work Faster: [-f]
-f
should only be used when assembling programs written by a (trusted) compiler.
-f
stops the assembler from doing whitespace and comment preprocessing on the
input file(s) before assembling them.See Section
"Preprocessing".
.include Search Path: [-I path]
Use this option to add a
path
to the list of directories
as
searches for files specified in
.include
directives (see Section
"Include").
You may use
[-I]
as many times as necessary to include a variety of paths. The current working
directory is always searched first; after that,
as
searches any
-I
directories in the same order as they were specified (left to right) on the
command line.
Difference Tables: [-K]
On the machine specific family, this option is allowed, but has no effect.
It is permitted for compatibility with the GNU assembler on other platforms,
where it can be used to warn when the assembler alters the machine code generated
for
.word
directives in difference tables. The machine specific family does not have
the addressing limitations that sometimes lead to this alteration on other
platforms.
--listing-lhs-width=number | |
Sets the maximum width, in words, of the first line of the hex byte dump.
This dump appears on the left hand side of the listing output.
| |
--listing-lhs-width2=number | |
Sets the maximum width, in words, of any further lines of the hex byte dump
for a given input source line. If this value is not specified, it defaults
to being the same as the value specified for
--listing-lhs-width.
If neither switch is used the default is to one.
| |
--listing-rhs-width=number | |
Sets the maximum width, in characters, of the source line that is displayed
alongside the hex dump. The default value for this parameter is 100. The source
line is displayed on the right hand side of the listing output.
| |
--listing-cont-lines=number | |
Sets the maximum number of continuation lines of hex dump that will be displayed for a given single line of source input. The default value is 4. | |
The MRI compatibility is not complete. Certain operations of the MRI assembler
depend upon its object file format, and can not be supported using other object
file formats. Supporting these would require enhancing each object file format
individually. These are:
The m68k MRI assembler supports common sections which are merged by the linker.
Other object file formats do not support this.
as
handles common sections by treating them as a single common symbol. It permits
local symbols to be defined within a common section, but it can not support
global symbols, since it has no way to describe them.
The MRI assemblers support relocations against a negated section address,
and relocations which combine the start addresses of two or more sections.
These are not support by other object file formats.
The MRI
END
pseudo-op permits the specification of a start address. This is not supported
by other object file formats. The start address may instead be specified using
the
[-e]
option to the linker, or in a linker script.
The MRI
IDNT,
.ident
and
NAME
pseudo-ops assign a module name to the output file. This is not supported
by other object file formats.
The m68k MRI
ORG
pseudo-op begins an absolute section at a given address. This differs from
the usual
as
.org
pseudo-op, which changes the location within the current section. Absolute
sections are not supported by other object file formats. The address of a
section may be assigned within a linker script.
There are some other features of the MRI assembler which are not supported
by
as,
typically either because they are difficult or because they seem of little
consequence. Some of these may be supported in future releases.
EBCDIC strings are not supported.
Packed binary coded decimal is not supported. This means that the
DC.P
and
DCB.P
pseudo-ops are not supported.
The m68k
FEQU
pseudo-op is not supported.
The m68k
NOOBJ
pseudo-op is not supported.
The m68k
OPT
branch control options---
B,
BRS,
BRB,
BRL,
and
BRW
---are ignored.
as
automatically relaxes all branches, whether forward or backward, to an appropriate
size, so these options serve no purpose.
The following m68k
OPT
list control options are ignored:
C,
CEX,
CL,
CRE,
E,
G,
I,
M,
MEX,
MC,
MD,
X.
The following m68k
OPT
options are ignored:
NEST,
O,
OLD,
OP,
P,
PCO,
PCR,
PCS,
R.
The m68k
OPT
D
option is the default, unlike the MRI assembler.
OPT NOD
may be used to turn it off.
The m68k
XREF
pseudo-op is ignored.
The i960
.debug
pseudo-op is not supported.
The i960
.extended
pseudo-op is not supported.
The various options of the i960
.list
pseudo-op are not supported.
The i960
.optimize
pseudo-op is not supported.
The i960
.output
pseudo-op is not supported.
The i960
.setreal
pseudo-op is not supported.
The rule is written to the file named in its argument.
This feature is used in the automatic updating of makefiles.
Whatever the object file is called,
as
overwrites any existing file of the same name.
When you specify
[-R]
it would be possible to generate shorter address displacements (because we
do not have to cross between text and data section). We refrain from doing
this simply for compatibility with older versions of
as.
In future,
[-R]
may work this way.
When
as
is configured for COFF or ELF output, this option is only useful if you use
sections named
.text
and
.data.
For example, it disables the exception frame optimizations which
as
normally does by default on
gcc
output.
Assemble in MRI Compatibility Mode: [-M]
The
[-M]
or
[--mri]
option selects MRI compatibility mode. This changes the syntax and pseudo-op
handling of
as
to make it compatible with the
ASM68K
or the
ASM960
(depending upon the configured target) assembler from Microtec Research. The
exact nature of the MRI syntax will not be documented here; see the MRI manuals
for more information. Note in particular that the handling of macros and macro
arguments is somewhat different. The purpose of this option is to permit assembling
existing MRI assembler code using
as.
Dependency Tracking: [--MD]
as
can generate a dependency file for the file it creates. This file consists
of a single rule suitable for
make
describing the dependencies of the main source file.
Name the Object File: [-o]
There is always one object file output when you run
as.
By default it has the name
a.out.
You use this option (which takes exactly one filename) to give the object
file a different name.
Join Data and Text Sections: [-R]
[-R]
tells
as
to write the object file as if all data-section data lives in the text section.
This is only done at the very last moment: your binary data are the same,
but data section parts are relocated differently. The data section part of
your object file is zero bytes long because all its bytes are appended to
the text section. (See Section
"Sections.")
Display Assembly Statistics: [--statistics]
Use
--statistics
to display two statistics about the resources used by
as:
the maximum amount of space allocated during the assembly (in bytes), and
the total execution time taken for the assembly (in cpu seconds).
Compatible Output: [--traditional-format]
For some targets, the output of
as
is different in some ways from the output of some existing assembler. This
switch requests
as
to use the traditional format instead.
Announce Version: [-v]
You can find out what version of as is running by including the option
-v
(which you can also spell as
-version)
on the command line.
It does not do macro processing, include file handling, or anything else you may get from your C compiler's preprocessor. You can do include file processing with the .include directive (see Section "Include"). You can use the GNU C compiler driver to get other “CPP” style preprocessing by giving the input file a .S suffix.See Section "Overall Options".
Excess whitespace, comments, and character constants cannot be used in the portions of the input text that are not preprocessed.
If the first line of an input file is #NO_APP or if you use the -f option, whitespace and comments are not removed from the input file. Within an input file, you can ask for whitespace and comment removal in specific portions of the by putting a line that says #APP before the text that may contain whitespace or comments, and putting a line that says #NO_APP after this text. This feature is mainly intend to support asm statements in compilers whose output is otherwise free of comments and whitespace.
Anything from /* through the next */ is a comment. This means you may not nest these comments.
/* The only way to include a newline ('\n') in a comment is to use this sort of comment. *//* This sort of comment does not nest. */
Anything from the line comment character to the next newline is considered a comment and is ignored. The line comment character is @ on the ARM; # on the i386 and x86-64; # for Motorola PowerPC; ! on the SPARC; see Machine Dependencies.
To be compatible with past assemblers, lines that begin with # have a special interpretation. Following the # should be an absolute expression (see Section "Expressions"): the logical line number of the next line. Then a string (see Section "Strings") is allowed: if present it is a new logical file name. The rest of the line, if any, should be whitespace.
If the first non-whitespace characters on the line are not numeric, the line is ignored. (Just like a comment.)
# This is an ordinary comment. # 42-6 "new_file_name" # New logical file name # This is logical line # 36.This feature is deprecated, and may disappear from future versions of as.
It is an error to end any statement with end-of-file: the last character of any input file should be a newline.
An empty statement is allowed, and may include whitespace. It is ignored.
A statement begins with zero or more labels, optionally followed by a key symbol which determines what kind of statement it is. The key symbol determines the syntax of the rest of the statement. If the symbol begins with a dot . then the statement is an assembler directive: typically valid for any computer. If the symbol begins with a letter the statement is an assembly language instruction: it assembles into a machine language instruction.
A label is a symbol immediately followed by a colon ( :). Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon.See Section "Labels".
label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, ...
amp;.byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value. amp;.ascii "Ring the bell\7" # A string constant. amp;.octa 0x123456789abcdef0123456789ABCDEF0 # A biGNUm. amp;.float 0f-314159265358979323846264338327\ 95028841971.693993751E-40 # - pi, a flonum.
Character Constants
There are two kinds of character constants. A character stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string literals) are potentially many bytes and their values may not be used in arithmetic expressions.
Strings
A string is written between double-quotes. It may contain double-quotes or null characters. The way to get special characters into a string is to escape these characters: precede them with a backslash \ character. For example \\ represents one backslash: the first \ is an escape which tells as to interpret the second character literally as a backslash (which prevents as from recognizing the second \ as an escape character). The complete list of escapes follows.
\b |
Mnemonic for backspace; for ASCII this is octal code 010.
|
\f |
Mnemonic for FormFeed; for ASCII this is octal code 014.
|
\n |
Mnemonic for newline; for ASCII this is octal code 012.
|
\r |
Mnemonic for carriage-Return; for ASCII this is octal code 015.
|
\t |
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
|
\ digit digit digit | |
An octal character code. The numeric code is 3 octal digits. For compatibility
with other Unix systems, 8 and 9 are accepted as digits: for example,
\008
has the value 010, and
\009
the value 011.
| |
\x hex-digits... | |
A hex character code. All trailing hex digits are combined. Either upper or
lower case
x
works.
| |
\\ |
Represents one
\
character.
|
\" |
Represents one
"
character. Needed in strings to represent this character, because an unescaped
"
would end the string.
|
\ anything-else | |
Any other character when escaped by \ gives a warning, but assembles as if the \ was not present. The idea is that if you used an escape sequence you clearly didn't want the literal interpretation of the following character. However as has no other interpretation, so as knows it is giving you the wrong code and warns you of the fact. | |
Which characters are escapable, and what those escapes represent, varies widely among assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is a subset of what most C compilers recognize. If you are in doubt, do not use an escape sequence.
Characters
A single character may be written as a single quote immediately followed by that character. The same escapes apply to characters as to strings. So if you want to write the character backslash, you must write '\\ where the first \ escapes the second \. As you can see, the quote is an acute accent, not a grave accent. A newline (or semicolon ;) immediately following an acute accent is taken as a literal character and does not count as the end of a statement. The value of a character constant in a numeric expression is the machine's byte-wide code for that character. as assumes your character code is ASCII: 'A means 65, 'B means 66, and so on.
Number Constants
as distinguishes three kinds of numbers according to how they are stored in the target machine. Integers are numbers that would fit into an int in the C language. BiGNUms are integers, but they are stored in more than 32 bits. Flonums are floating point numbers, described below.
Integers
A binary integer is 0b or 0B followed by zero or more of the binary digits 01.
An octal integer is 0 followed by zero or more of the octal digits ( 01234567).
A decimal integer starts with a non-zero digit followed by zero or more digits ( 0123456789).
A hexadecimal integer is 0x or 0X followed by one or more hexadecimal digits chosen from 0123456789abcdefABCDEF.
Integers have the usual values. To denote a negative integer, use the prefix operator - discussed under expressions (see Section "Prefix Ops").
BiGNUms
A biGNUm has the same syntax and semantics as an integer except that the number (or its negative) takes more than 32 bits to represent in binary. The distinction is made because in some places integers are permitted while biGNUms are not.
Flonums
A flonum represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by as to a generic binary floating point number of more than sufficient precision. This generic floating point number is converted to a particular computer's floating point format (or formats) by a portion of as specialized to that computer.
A flonum is written by writing (in order)
as does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running as.
The linker ld reads many object files (partial programs) and combines their contents to form a runnable program. When as emits an object file, the partial program is assumed to start at address 0. ld assigns the final addresses for the partial program, so that different partial programs do not overlap. This is actually an oversimplification, but it suffices to explain how as uses sections.
ld moves blocks of bytes of your program to their run-time addresses. These blocks slide to their run-time addresses as rigid units; their length does not change and neither does the order of bytes within them. Such a rigid unit is called a section. Assigning run-time addresses to sections is called relocation. It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses.
An object file written by as has at least three sections, any of which may be empty. These are named text, data and bss sections.
as can also generate whatever other named sections you specify using the .section directive (see Section "Section"). If you do not use any directives that place output in the .text or .data sections, these sections still exist, but are empty.
Within the object file, the text section starts at address 0, the data section follows, and the bss section follows the data section.
To let ld know which data changes when the sections are relocated, and how to change that data, as also writes to the object file details of the relocation needed. To perform relocation ld must know, each time an address in the object file is mentioned:
In fact, every address as ever uses is expressed as ( section) + ( offset into section) Further, most expressions as computes have this section-relative nature.
In this manual we use the notation { secname N }to mean “offset N into section secname amp;.”
Apart from text, data and bss sections you need to know about the absolute section. When ld mixes partial programs, addresses in the absolute section remain unchanged. For example, address {absolute 0} is “relocated” to run-time address 0 by ld. Although the linker never arranges two partial programs' data sections with overlapping addresses after linking, by definition their absolute sections must overlap. Address {absolute 239} in one part of a program is always the same address when the program is running as address {absolute 239} in any other part of the program.
The idea of sections is extended to the undefined section. Any address whose section is unknown at assembly time is by definition rendered {undefined U }---where U is filled in later. Since numbers are always defined, the only way to generate an undefined address is to mention an undefined symbol. A reference to a named common block would be such a symbol: its value is unknown at assembly time so it has section undefined.
By analogy the word section is used to describe groups of sections in the linked program. ld puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the text section of a program, meaning all the addresses of all partial programs' text sections. Likewise for data and bss sections.
Some sections are manipulated by ld; others are invented for use of as and have no meaning except during assembly.
named sections | |
These sections hold your program.
as
and
ld
treat them as separate but equal sections. Anything you can say of one section
is true of another. When the program is running, however, it is customary
for the text section to be unalterable. The text section is often shared among
processes: it contains instructions, constants and the like. The data section
of a running program is usually alterable: for example, C variables would
be stored in the data section.
| |
bss section | |
This section contains zeroed bytes when your program begins running. It is
used to hold uninitialized variables or common storage. The length of each
partial program's bss section is important, but because it starts out containing
zeroed bytes there is no need to store explicit zero bytes in the object file.
The bss section was invented to eliminate those explicit zeros from object
files.
| |
absolute section | |
Address 0 of this section is always “relocated” to runtime address 0. This is
useful if you want to refer to an address that
ld
must not change when relocating. In this sense we speak of absolute addresses
being “unrelocatable”: they do not change during relocation.
| |
undefined section | |
This “section” is a catch-all for address references to objects not in the preceding sections. | |
An idealized example of three relocatable sections follows. The example uses the traditional section names .text and .data. Memory addresses are on the horizontal axis.
+-----+----+--+ partial program # 1: |ttttt|dddd|00| +-----+----+--+text data bss seg. seg. seg.
+---+---+---+ partial program # 2: |TTT|DDD|000| +---+---+---+
+--+---+-----+--+----+---+-----+~~ linked program: | |TTT|ttttt| |dddd|DDD|00000| +--+---+-----+--+----+---+-----+~~
addresses: 0 ...
ASSEMBLER-INTERNAL-LOGIC-ERROR! | |
An internal assembler logic error has been found. This means there is a bug
in the assembler.
| |
expr section | |
The assembler stores complex expression internally as combinations of symbols. When it needs to represent an expression as a symbol, it puts it in the expr section. | |
Subsections are optional. If you do not use subsections, everything goes in subsection number zero.
Subsections appear in your object file in numeric order, lowest numbered to highest. (All this to be compatible with other people's assemblers.) The object file contains no representation of subsections; ld and other programs that manipulate object files see no trace of them. They just see all your text subsections as a text section, and all your data subsections as a data section.
To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a .text expression or a .data expression statement. You can also use the .subsection directive (see Section "SubSection") to specify a subsection: .subsection expression. Expression should be an absolute expression (see Section "Expressions"). If you just say .text then .text 0 is assumed. Likewise .data means .data 0. Assembly begins in text 0. For instance:
amp;.text 0 # The default subsection is text 0 anyway. amp;.ascii "This lives in the first text subsection. *" amp;.text 1 amp;.ascii "But this lives in the second text subsection." amp;.data 0 amp;.ascii "This lives in the data section," amp;.ascii "in the first data subsection." amp;.text 0 amp;.ascii "This lives in the first text section," amp;.ascii "immediately following the asterisk (*)."
Each section has a location counter incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to as there is no concept of a subsection location counter. There is no way to directly manipulate a location counter---but the .align directive changes it, and any label definition captures its current value. The location counter of the section where statements are being assembled is said to be the active location counter.
The .lcomm pseudo-op defines a symbol in the bss section; see Lcomm,, .lcomm amp;.
The .comm pseudo-op may be used to declare a common symbol, which is another form of uninitialized symbol; see Comm,, .comm amp;.
" Warning: as does not place symbols in the object file in the same order they were declared. This may break some debuggers. "
Case of letters is significant: foo is a different symbol name than Foo.
Each symbol has exactly one name. Each name in an assembly language program refers to exactly one symbol. You may use that symbol name any number of times in a program.
Local Symbol Names
A local symbol is any symbol beginning with certain local label prefixes. By default, the local label prefix is .L for ELF systems or L for traditional a.out systems, but each target may have its own set of local label prefixes.
Local symbols are defined and used within the assembler, but they are normally not saved in object files. Thus, they are not visible when debugging. You may use the -L option (see Section "L") to retain the local symbols in the object files.
Local Labels
Local labels help compilers and programmers use names temporarily. They create symbols which are guaranteed to be unique over the entire scope of the input source code and which can be referred to by a simple notation. To define a local label, write a label of the form N: (where N represents any positive integer). To refer to the most recent previous definition of that label write Nb, using the same number as when you defined the label. To refer to the next definition of a local label, write Nf ---the b stands for “backwards” and the f stands for “forwards”.
There is no restriction on how you can use these labels, and you can reuse them too. So that it is possible to repeatedly define the same local label (using the same number N), although you can only refer to the most recently defined local label of that number (for a backwards reference) or the next definition of a specific local label for a forward reference. It is also worth noting that the first 10 local labels ( 0: amp;....Li Sy 9: ) are implemented in a slightly more efficient manner than the others.
Here is an example:
1: branch 1f 2: branch 1b 1: branch 2f 2: branch 1b
Which is the equivalent of:
label_1: branch label_3 label_2: branch label_1 label_3: branch label_4 label_4: branch label_3
Local label names are only a notational device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names are stored in the symbol table, appear in error messages, and are optionally emitted to the object file. The names are constructed using these parts:
local label prefix | |
All local symbols begin with the system-specific local label prefix. Normally
both
as
and
ld
forget symbols that start with the local label prefix. These labels are used
for symbols you are never intended to see. If you use the
-L
option then
as
retains these symbols in the object file. If you also instruct
ld
to retain these symbols, you may use them in debugging.
| |
number | |
This is the number that was used in the local label definition. So if the
label is written
55:
then the number is
55.
| |
C-B |
This unusual character is included so you do not accidentally invent a symbol
of the same name. The character has ASCII value of
\002
(control-B).
|
ordinal number | |
This is a serial number to keep the labels distinct. The first definition of 0: gets the number 1. The 15th definition of 0: gets the number 15, and so on. Likewise the first definition of 1: gets the number 1 and its 15th definition gets 15 as well. | |
So for example, the first 1: may be named .L1C-B1, and the 44th 3: may be named .L3C-B44.
Dollar Local Labels
as also supports an even more local form of local labels called dollar labels. These labels go out of scope (i.e., they become undefined) as soon as a non-local label is defined. Thus they remain valid for only a small region of the input source code. Normal local labels, by contrast, remain in scope for the entire file, or until they are redefined by another occurrence of the same local label.
Dollar labels are defined in exactly the same way as ordinary local labels, except that instead of being terminated by a colon, they are terminated by a dollar sign, e.g., 55$.
They can also be distinguished from ordinary local labels by their transformed names which use ASCII character \001 (control-A) as the magic character to distinguish them from ordinary labels. For example, the fifth definition of 6$ may be named .L6C-A5.
If you use a symbol without defining it, as assumes zero for all these attributes, and probably won't warn you. This makes the symbol an externally defined symbol, which is generally what you would want.
Value
The value of a symbol is (usually) 32 bits. For a symbol which labels a location in the text, data, bss or absolute sections the value is the number of addresses from the start of that section to the label. Naturally for text, data and bss sections the value of a symbol changes as ld changes section base addresses during linking. Absolute symbols' values do not change during linking: that is why they are called absolute.
The value of an undefined symbol is treated in a special way. If it is 0 then the symbol is not defined in this assembler source file, and ld tries to determine its value from other files linked into the same program. You make this kind of symbol simply by mentioning a symbol name without defining it. A non-zero value represents a .comm common declaration. The value is how much common storage to reserve, in bytes (addresses). The symbol refers to the first address of the allocated storage.
Type
The type attribute of a symbol contains relocation (section) information, any flag settings indicating that a symbol is external, and (optionally), other information for linkers and debuggers. The exact format depends on the object-code output format in use.
The result of an expression must be an absolute number, or else an offset into a particular section. If an expression is not absolute, and there is not enough information when as sees the expression to know its section, a second pass over the source program might be necessary to interpret the expression---but the second pass is currently not implemented. as aborts with an error message in this situation.
Arguments
Arguments are symbols, numbers or subexpressions. In other contexts arguments are sometimes called “arithmetic operands”. In this manual, to avoid confusing them with the “instruction operands” of the machine language, we use the term “argument” to refer to parts of expressions only, reserving the word “operand” to refer only to machine instruction operands.
Symbols are evaluated to yield { section NNN }where section is one of text, data, bss, absolute, or undefined. NNN is a signed, 2's complement 32 bit integer.
Numbers are usually integers.
A number can be a flonum or biGNUm. In this case, you are warned that only the low order 32 bits are used, and as pretends these 32 bits are an integer. You may write integer-manipulating instructions that act on exotic constants, compatible with other assemblers.
Subexpressions are a left parenthesis ( followed by an integer expression, followed by a right parenthesis ); or a prefix operator followed by an argument.
Operators
Operators are arithmetic functions, like + or %. Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or followed by whitespace.
Prefix Operator
as has the following prefix operators. They each take one argument, which must be absolute.
- | Negation. Two's complement negation. |
~ | Complementation. Bitwise not. |
Infix Operators
Infix operators take two arguments, one on either side. Operators have precedence, but operations with equal precedence are performed left to right. Apart from + or [-], both arguments must be absolute, and the result is absolute.
* |
Multiplication.
|
/ |
Division.
Truncation is the same as the C operator
/
|
% |
Remainder.
|
<< | |
Shift Left.
Same as the C operator
<<.
| |
>> | |
Shift Right. Same as the C operator >>. | |
| |
Bitwise Inclusive Or.
|
& |
Bitwise And.
|
^ |
Bitwise Exclusive Or.
|
! | Bitwise Or Not. |
+ |
Addition.
If either argument is absolute, the result has the section of the other argument.
You may not add together arguments from different sections.
|
- |
Subtraction.
If the right argument is absolute, the result has the section of the left
argument. If both arguments are in the same section, the result is absolute.
You may not subtract arguments from different sections.
|
== | Is Equal To |
<>
!= | |
Is Not Equal To | |
< | Is Less Than |
> | Is Greater Than |
>= | Is Greater Than Or Equal To |
<= |
Is Less Than Or Equal To
The comparison operators can be used as infix operators. A true results has a value of -1 whereas a false result has a value of 0. Note, these operators perform signed comparisons. |
&& | |
Logical And.
| |
|| |
Logical Or.
These two logical operations can be used to combine the results of sub expressions. Note, unlike the comparison operators a true result returns a value of 1 but a false results does still return 0. Also note that the logical or operator has a slightly lower precedence than logical and.
|
This chapter discusses directives that are available regardless of the target machine configuration for the GNU assembler.
The second expression (also absolute) gives the fill value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is omitted, the
padding bytes are normally zero. However, on some systems, if the section
is marked as containing code and the fill value is omitted, the space is filled
with no-op instructions.
The third expression is also absolute, and is also optional. If it is present,
it is the maximum number of bytes that should be skipped by this alignment
directive. If doing the alignment would require skipping more bytes than the
specified maximum, then the alignment is not done at all. You can omit the
fill value (the second argument) entirely by simply using two commas after
the required alignment; this can be useful if you want the alignment to be
filled with no-op instructions when appropriate.
The way the required alignment is specified varies from system to system.
For the arc, hppa, i386 using ELF, i860, iq2000, m68k, or32, s390, sparc,
tic4x, tic80 and xtensa, the first expression is the alignment request in
bytes. For example
.align 8
advances the location counter until it is a multiple of 8. If the location
counter is already a multiple of 8, no change is needed. For the tic54x, the
first expression is the alignment request in words.
For other systems, including the i386 using a.out format, and the arm and
strongarm, it is the number of low-order zero bits the location counter must
have after advancement. For example
.align 3
advances the location counter until it a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
This inconsistency is due to the different behaviors of the various native
assemblers for these systems which GAS must emulate. GAS also provides
.balign
and
.p2align
directives, described later, which have a consistent behavior across all architectures
(but are specific to GAS).
The second expression (also absolute) gives the fill value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is omitted, the
padding bytes are normally zero. However, on some systems, if the section
is marked as containing code and the fill value is omitted, the space is filled
with no-op instructions.
The third expression is also absolute, and is also optional. If it is present,
it is the maximum number of bytes that should be skipped by this alignment
directive. If doing the alignment would require skipping more bytes than the
specified maximum, then the alignment is not done at all. You can omit the
fill value (the second argument) entirely by simply using two commas after
the required alignment; this can be useful if you want the alignment to be
filled with no-op instructions when appropriate.
The
.balignw
and
.balignl
directives are variants of the
.balign
directive. The
.balignw
directive treats the fill pattern as a two byte word value. The
.balignl
directives treats the fill pattern as a four byte longword value. For example,
.balignw 4,0x368d
will align to a multiple of 4. If it skips two bytes, they will be filled
in with the value 0x368d (the exact placement of the bytes depends upon the
endianness of the processor). If it skips 1 or 3 bytes, the fill value is
undefined.
When using ELF, the
.comm
directive takes an optional third argument. This is the desired alignment
of the symbol, specified as a byte boundary (for example, an alignment of
16 means that the least significant 4 bits of the address should be zero).
The alignment must be an absolute expression, and it must be a power of two.
If
ld
allocates uninitialized memory for the common symbol, it will use the alignment
when placing the symbol. If no alignment is specified,
as
will set the alignment to the largest power of two less than or equal to the
size of the symbol, up to a maximum of 16.
Unless
.cfi_startproc
is used along with parameter
simple
it also emits some architecture dependent initial CFI instructions.
.abort
This directive stops the assembly immediately. It is for compatibility with
other assemblers. The original idea was that the assembly language source
would be piped into the assembler. If the sender of the source quit, it could
use this directive tells
as
to quit also. One day
.abort
will not be supported.
.align abs-expr, abs-expr, abs-expr
Pad the location counter (in the current subsection) to a particular storage
boundary. The first expression (which must be absolute) is the alignment required,
as described below.
.ascii Va string ...
.ascii
expects zero or more string literals (see Section
"Strings")
separated by commas. It assembles each string (with no automatic trailing
zero byte) into consecutive addresses.
.asciz Va string ...
.asciz
is just like
.ascii,
but each string is followed by a zero byte. The “z” in
.asciz
stands for “zero”.
.balign[wl] abs-expr, abs-expr, abs-expr
Pad the location counter (in the current subsection) to a particular storage
boundary. The first expression (which must be absolute) is the alignment request
in bytes. For example
.balign 8
advances the location counter until it is a multiple of 8. If the location
counter is already a multiple of 8, no change is needed.
.byte expressions
.byte
expects zero or more expressions, separated by commas. Each expression is
assembled into the next byte.
.comm symbol, length
.comm
declares a common symbol named
symbol.
When linking, a common symbol in one object file may be merged with a defined
or common symbol of the same name in another object file. If
ld
does not see a definition for the symbol--just one or more common symbols--then
it will allocate
length
bytes of uninitialized memory.
length
must be an absolute expression. If
ld
sees multiple common symbols with the same name, and they do not all have
the same size, it will allocate space using the largest size.
.cfi_startproc [simple]
.cfi_startproc
is used at the beginning of each function that should have an entry in
.eh_frame.
It initializes some internal data structures. Don't forget to close the function
by
.cfi_endproc.
.cfi_endproc
.cfi_endproc
is used at the end of a function where it closes its unwind entry previously
opened by
.cfi_startproc,
and emits it to
.eh_frame.
.cfi_personality encoding [, exp]
.cfi_personality
defines personality routine and its encoding.
encoding
must be a constant determining how the personality should be encoded. If it
is 255 (
DW_EH_PE_omit),
second argument is not present, otherwise second argument should be a constant
or a symbol name. When using indirect encodings, the symbol provided should
be the location where personality can be loaded from, not the personality
routine itself. The default after
.cfi_startproc
is
.cfi_personality 0xff,
no personality routine.
.cfi_lsda encoding [, exp]
.cfi_lsda
defines LSDA and its encoding.
encoding
must be a constant determining how the LSDA should be encoded. If it is 255
(
DW_EH_PE_omit),
second argument is not present, otherwise second argument should be a constant
or a symbol name. The default after
.cfi_startproc
is
.cfi_lsda 0xff,
no LSDA.
.cfi_def_cfa register, offset
.cfi_def_cfa
defines a rule for computing CFA as:
take address from register and add offset to it.
.cfi_def_cfa_register register
.cfi_def_cfa_register
modifies a rule for computing CFA. From now on
register
will be used instead of the old one. Offset remains the same.
.cfi_def_cfa_offset offset
.cfi_def_cfa_offset
modifies a rule for computing CFA. Register remains the same, but
offset
is new. Note that it is the absolute offset that will be added to a defined
register to compute CFA address.
.cfi_adjust_cfa_offset offset
Same as
.cfi_def_cfa_offset
but
offset
is a relative value that is added/substracted from the previous offset.
.cfi_offset register, offset
Previous value of
register
is saved at offset
offset
from CFA.
.cfi_rel_offset register, offset
Previous value of
register
is saved at offset
offset
from the current CFA register. This is transformed to
.cfi_offset
using the known displacement of the CFA register from the CFA. This is often
easier to use, because the number will match the code it's annotating.
.cfi_register register1, register2
Previous value of
register1
is saved in register
register2.
.cfi_restore register
.cfi_restore
says that the rule for
register
is now the same as it was at the beginning of the function, after all initial
instruction added by
.cfi_startproc
were executed.
.cfi_undefined register
From now on the previous value of
register
can't be restored anymore.
.cfi_same_value register
Current value of
register
is the same like in the previous frame, i.e. no restoration needed.
.cfi_remember_state,
First save all current rules for all registers by
.cfi_remember_state,
then totally screw them up by subsequent
.cfi_*
directives and when everything is hopelessly bad, use
.cfi_restore_state
to restore the previous saved state.
.cfi_return_column register
Change return column
register,
i.e. the return address is either directly in
register
or can be accessed by rules for
register.
.cfi_signal_frame
Mark current function as signal trampoline.
.cfi_window_save
SPARC register window has been saved.
.cfi_escape expression[, ...]
Allows the user to add arbitrary bytes to the unwind info. One might use this
to add OS-specific CFI opcodes, or generic CFI opcodes that GAS does not yet
support.
basic_block | |
This option will set the
basic_block
register in the
.debug_line
state machine to
true.
| |
prologue_end | |
This option will set the
prologue_end
register in the
.debug_line
state machine to
true.
| |
epilogue_begin | |
This option will set the
epilogue_begin
register in the
.debug_line
state machine to
true.
| |
is_stmt value | |
This option will set the
is_stmt
register in the
.debug_line
state machine to
value,
which must be either 0 or 1.
| |
isa value | |
This directive will set the
isa
register in the
.debug_line
state machine to
value,
which must be an unsigned integer.
| |
Except for the contents of the error message, this is roughly equivalent to
size
and
value
are optional. If the second comma and
value
are absent,
value
is assumed zero. If the first comma and following tokens are absent,
size
is assumed to be 1.
Both spellings (
.globl
and
.global)
are accepted, for compatibility with other assemblers.
This directive overrides the named symbols default visibility (which is set
by their binding: local, global or weak). The directive sets the visibility
to
hidden
which means that the symbols are not visible to other components. Such symbols
are always considered to be
protected
as well.
This directive is a synonym for
.short.
.data subsection
.data
tells
as
to assemble the following statements onto the end of the data subsection numbered
subsection
(which is an absolute expression). If
subsection
is omitted, it defaults to zero.
.double flonums
.double
expects zero or more flonums, separated by commas. It assembles floating point
numbers.
.eject
Force a page break at this point, when generating assembly listings.
.else
.else
is part of the
as
support for conditional assembly; see If,,
.if
amp;. It marks the beginning of a section of code to be assembled if the condition
for the preceding
.if
was false.
.elseif
.elseif
is part of the
as
support for conditional assembly; see If,,
.if
amp;. It is shorthand for beginning a new
.if
block that would otherwise fill the entire
.else
section.
.end
.end
marks the end of the assembly file.
as
does not process anything in the file past the
.end
directive.
.endfunc
.endfunc
marks the end of a function specified with
.func.
.endif
.endif
is part of the
as
support for conditional assembly; it marks the end of a block of code that
is only assembled conditionally.See Section
"If".
.equ symbol, expression
This directive sets the value of
symbol
to
expression.
It is synonymous with
.set;
see Set,,
.set
amp;.
.equiv symbol, expression
The
.equiv
directive is like
.equ
and
.set,
except that the assembler will signal an error if
symbol
is already defined. Note a symbol which has been referenced but not actually
defined is considered to be undefined.
amp;.ifdef SYM
amp;.err
amp;.endif
amp;.equ SYM,VAL
plus it protects the symbol from later redefinition.
.eqv symbol, expression
The
.eqv
directive is like
.equiv,
but no attempt is made to evaluate the expression or any part of it immediately.
Instead each time the resulting symbol is used in an expression, a snapshot
of its current value is taken.
.err
If
as
assembles a
.err
directive, it will print an error message and, unless the
[-Z]
option was used, it will not generate an object file. This can be used to
signal an error in conditionally compiled code.
.error Va string
Similarly to
.err,
this directive emits an error, but you can specify a string that will be emitted
as the error message. If you don't specify the message, it defaults to
.error directive invoked in source file.
See Section.Dq Errors .
.error "This code has not been assembled and tested."
.exitm
Exit early from the current macro definition.See Section
"Macro".
.extern
.extern
is accepted in the source program---for compatibility with other assemblers---but
it is ignored.
as
treats all undefined symbols as external.
.fail expression
Generates an error or a warning. If the value of the
expression
is 500 or more,
as
will print a warning message. If the value is less than 500,
as
will print an error message. The message will include the value of
expression.
This can occasionally be useful inside complex nested macros or conditional
assembly.
.file string
.file
tells
as
that we are about to start a new logical file.
string
is the new file name. In general, the filename is recognized whether or not
it is surrounded by quotes
";
but if you wish to specify an empty file name, you must give the quotes--
.
This statement may go away in future: it is only recognized to be compatible
with old
as
programs.
.fill repeat, size, value
repeat,
size
and
value
are absolute expressions. This emits
repeat
copies of
size
bytes.
Repeat
may be zero or more.
Size
may be zero or more, but if it is more than 8, then it is deemed to have the
value 8, compatible with other people's assemblers. The contents of each
repeat
bytes is taken from an 8-byte number. The highest order 4 bytes are zero.
The lowest order 4 bytes are
value
rendered in the byte-order of an integer on the computer
as
is assembling for. Each
size
bytes in a repetition is taken from the lowest order
size
bytes of this number. Again, this bizarre behavior is compatible with other
people's assemblers.
.float flonums
This directive assembles zero or more flonums, separated by commas. It has
the same effect as
.single.
.func name[, label]
.func
emits debugging information to denote function
name,
and is ignored unless the file is assembled with debugging enabled. Only
--gstabs[+]
is currently supported.
label
is the entry point of the function and if omitted
name
prepended with the
leading char
is used.
leading char
is usually
_
or nothing, depending on the target. All functions are currently defined to
have
void
return type. The function must be terminated with
.endfunc.
.global symbol,.globl symbol
.global
makes the symbol visible to
ld.
If you define
symbol
in your partial program, its value is made available to other partial programs
that are linked with it. Otherwise,
symbol
takes its attributes from a symbol of the same name from another file linked
into the same program.
.hidden names
This is one of the ELF visibility directives. The other two are
.internal
(see Section
"Internal")
and
.protected
(see Section
"Protected").
.hword expressions
This expects zero or more
expressions,
and emits a 16 bit number for each.
.ifdef symbol | |
Assembles the following section of code if the specified
symbol
has been defined. Note a symbol which has been referenced but not yet defined
is considered to be undefined.
| |
.ifb text | |
Assembles the following section of code if the operand is blank (empty).
| |
.ifc string1, string2 | |
Assembles the following section of code if the two strings are the same. The
strings may be optionally quoted with single quotes. If they are not quoted,
the first string stops at the first comma, and the second string stops at
the end of the line. Strings which contain whitespace should be quoted. The
string comparison is case sensitive.
| |
.ifeq absolute expression | |
Assembles the following section of code if the argument is zero.
| |
.ifeqs string1, string2 | |
Another form of
.ifc.
The strings must be quoted using double quotes.
| |
.ifge absolute expression | |
Assembles the following section of code if the argument is greater than or
equal to zero.
| |
.ifgt absolute expression | |
Assembles the following section of code if the argument is greater than zero.
| |
.ifle absolute expression | |
Assembles the following section of code if the argument is less than or equal
to zero.
| |
.iflt absolute expression | |
Assembles the following section of code if the argument is less than zero.
| |
.ifnb text | |
Like
.ifb,
but the sense of the test is reversed: this assembles the following section
of code if the operand is non-blank (non-empty).
| |
.ifnc string1, string2. | |
Like
.ifc,
but the sense of the test is reversed: this assembles the following section
of code if the two strings are not the same.
| |
.ifndef symbol
.ifnotdef symbol | |
Assembles the following section of code if the specified
symbol
has not been defined. Both spelling variants are equivalent. Note a symbol
which has been referenced but not yet defined is considered to be undefined.
| |
.ifne absolute expression | |
Assembles the following section of code if the argument is not equal to zero
(in other words, this is equivalent to
.if).
| |
.ifnes string1, string2 | |
Like .ifeqs, but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same. | |
The
skip
argument skips a number of bytes from the start of the
file.
The
count
argument indicates the maximum number of bytes to read. Note that the data
is not aligned in any way, so it is the user's responsibility to make sure
that proper alignment is provided both before and after the
incbin
directive.
This directive overrides the named symbols default visibility (which is set
by their binding: local, global or weak). The directive sets the visibility
to
internal
which means that the symbols are considered to be
hidden
(i.e., not visible to other components), and that some extra, processor specific
processing must also be performed upon the symbols as well.
For example, assembling
is equivalent to assembling
For some caveats with the spelling of
symbol,
see also Macro.
For example, assembling
is equivalent to assembling
For some caveats with the spelling of
symbol,
see also the discussion atSee Section
"Macro".
.incbin Va file [, skip[, count]]
The
incbin
directive includes
file
verbatim at the current location. You can control the search paths used with
the
-I
command-line option (see Section
"Invoking").
Quotation marks are required around
file.
.include Va file
This directive provides a way to include supporting files at specified points
in your source program. The code from
file
is assembled as if it followed the point of the
.include;
when the end of the included file is reached, assembly of the original file
continues. You can control the search paths used with the
-I
command-line option (see Section
"Invoking").
Quotation marks are required around
file.
.int expressions
Expect zero or more
expressions,
of any section, separated by commas. For each expression, emit a number that,
at run time, is the value of that expression. The byte order and bit size
of the number depends on what kind of target the assembly is for.
.internal names
This is one of the ELF visibility directives. The other two are
.hidden
(see Section
"Hidden")
and
.protected
(see Section
"Protected").
.irp symbol, values...
Evaluate a sequence of statements assigning different values to
symbol.
The sequence of statements starts at the
.irp
directive, and is terminated by an
.endr
directive. For each
value,
symbol
is set to
value,
and the sequence of statements is assembled. If no
value
is listed, the sequence of statements is assembled once, with
symbol
set to the null string. To refer to
symbol
within the sequence of statements, use
\symbol.
.irp param,1,2,3
move d\param,sp@-
.endr
move d1,sp@-
move d2,sp@-
move d3,sp@-
.irpc symbol, values...
Evaluate a sequence of statements assigning different values to
symbol.
The sequence of statements starts at the
.irpc
directive, and is terminated by an
.endr
directive. For each character in
value,
symbol
is set to the character, and the sequence of statements is assembled. If no
value
is listed, the sequence of statements is assembled once, with
symbol
set to the null string. To refer to
symbol
within the sequence of statements, use
\symbol.
.irpc param,123
move d\param,sp@-
.endr
move d1,sp@-
move d2,sp@-
move d3,sp@-
.lcomm symbol, length
Reserve
length
(an absolute expression) bytes for a local common denoted by
symbol.
The section and value of
symbol
are those of the new local common. The addresses are allocated in the bss
section, so that at run-time the bytes start off zeroed.
Symbol
is not declared global (see Section
"Global"),
so is normally not visible to
ld.
.lflags
as
accepts this directive, for compatibility with other assemblers, but ignores
it.
discard | |
Silently discard duplicate sections. This is the default.
| |
one_only | |
Warn if there are duplicate sections, but still keep only one copy.
| |
same_size | |
Warn if any of the duplicates have different sizes.
| |
same_contents | |
Warn if any of the duplicates do not have exactly the same contents. | |
By default, listings are disabled. When you enable them (with the
-a
command line option;see Section
"Invoking"),
the initial value of the listing counter is one.
.ln line-number
.ln
is a synonym for
.line.
.mri val
If
val
is non-zero, this tells
as
to enter MRI mode. If
val
is zero, this tells
as
to exit MRI mode. This change affects code assembled until the next
.mri
directive, or until the end of the file.See Section
"M".
.list
Control (in conjunction with the
.nolist
directive) whether or not assembly listings are generated. These two directives
maintain an internal counter (which is zero initially).
.list
increments the counter, and
.nolist
decrements it. Assembly listings are generated whenever the counter is greater
than zero.
.long expressions
.long
is the same as
.int.
See Section.Dq Int .
.macro macname
.macro macname macargs ... | |
Begin the definition of a macro called
macname.
If your macro definition requires arguments, specify their names after the
macro name, separated by commas or spaces. You can qualify the macro argument
to indicate whether all invocations must specify a non-blank value (through
:req),
or whether it takes all of the remaining arguments (through
:vararg).
You can supply a default value for any macro argument by following the name
with
= deflt.
You cannot define two macros with the same
macname
unless it has been subject to the
.purgem
directive (see Section
"Purgem")
between the two definitions. For example, these are all valid
.macro
statements:
| |
.macro comm | |
Begin the definition of a macro called
comm,
which takes no arguments.
| |
.macro plus1 p, p1
.macro plus1 p p1 | |
Either statement begins the definition of a macro called
plus1,
which takes two arguments; within the macro definition, write
\p
or
\p1
to evaluate the arguments.
| |
.macro reserve_str p1=0 p2 | |
Begin the definition of a macro called
reserve_str,
with two arguments. The first argument has a default value, but not the second.
After the definition is complete, you can call the macro either as
reserve_str a, b
(with
\p1
evaluating to
a
and
\p2
evaluating to
b),
or as
reserve_str, b
(with
\p1
evaluating as the default, in this case
0,
and
\p2
evaluating to
b).
| |
.macro m p1:req, p2=0, p3:vararg | |
Begin the definition of a macro called
m,
with at least three arguments. The first argument must always have a value
specified, but not the second, which instead has a default value. The third
formal will get assigned all remaining arguments specified at invocation time.
When you call a macro, you can specify the argument values either by position, or by keyword. For example, sum 9,17 is equivalent to sum to=17, from=9.
| |
.macro label l \l: .endm
might not work as expected. Invoking label foo might not create a label called foo but instead just insert the text \l: into the assembler source, probably generating an error about an unrecognised identifier.
Similarly problems might occur with the period character ( .) which is often allowed inside opcode names (and hence identifier names). So for example constructing a macro to build an opcode from a base name and a length specifier like this:
.macro opcode base length \base.\length .endm
and invoking it as opcode store l will not create a store.l instruction but instead generate some kind of error as the assembler tries to interpret the text \base.\length.
There are several possible ways around this problem:
Insert white space | |
If it is possible to use white space characters then this is the simplest
solution. eg:
.macro label l \l : .endm
| |
Use\() |
The string
\()
can be used to separate the end of a macro argument from the following text.
eg:
.macro opcode base length \base\().\length .endm
|
Use the alternate macro syntax mode | |
In the alternative macro syntax mode the ampersand character (
&)
can be used as a separator. eg:
.altmacro .macro label l l&: .endm | |
Note: this problem of correctly identifying string parameters to pseudo ops also applies to the identifiers used in .irp (see Section "Irp") and .irpc (see Section "Irpc") as well.
.endm |
Mark the end of a macro definition.
|
.exitm |
Exit early from the current macro definition.
|
\@ |
as
maintains a counter of how many macros it has executed in this pseudo-variable;
you can copy that number to your output with
\@,
but
only within a macro definition.
|
LOCAL name[, ...] | |
Warning:LOCAL is only available if you select “alternate macro syntax” with--alternate or.altmacro. See Section.Dq Altmacro . | |
.altmacro
Enable alternate macro mode, enabling:
LOCAL name[, ...] | |
One additional directive,
LOCAL,
is available. It is used to generate a string replacement for each of the
name
arguments, and replace any instances of
name
in each macro expansion. The replacement string is unique in the assembly,
and different for each separate macro expansion.
LOCAL
allows you to write macros that define symbols, without fear of conflict between
separate macro expansions.
| |
String delimiters | |
You can write strings delimited in these other ways besides
Va string:
| |
' string' | |
You can delimit strings with single-quote characters.
| |
< string> | |
You can delimit strings with matching angle brackets. | |
single-character string escape | |
To include any single character literally in a string (even if the character
would otherwise have some special meaning), you can prefix the character with
!
(an exclamation mark). For example, you can write
<4.3 !> 5.4!!>
to get the literal text
4.3 > 5.4!.
| |
Expression results as strings | |
You can write % expr to evaluate the expression expr and use the result as a string. | |
The term “octa” comes from contexts in which a “word” is two bytes; hence
octa
-word for 16 bytes.
.org
may only increase the location counter, or leave it unchanged; you cannot
use
.org
to move the location counter backwards.
Because
as
tries to assemble programs in one pass,
new-lc
may not be undefined. If you really detest this restriction we eagerly await
a chance to share your improved assembler.
Beware that the origin is relative to the start of the section, not to the
start of the subsection. This is compatible with other people's assemblers.
When the location counter (of the current subsection) is advanced, the intervening
bytes are filled with
fill
which should be an absolute expression. If the comma and
fill
are omitted,
fill
defaults to zero.
The second expression (also absolute) gives the fill value to be stored in
the padding bytes. It (and the comma) may be omitted. If it is omitted, the
padding bytes are normally zero. However, on some systems, if the section
is marked as containing code and the fill value is omitted, the space is filled
with no-op instructions.
The third expression is also absolute, and is also optional. If it is present,
it is the maximum number of bytes that should be skipped by this alignment
directive. If doing the alignment would require skipping more bytes than the
specified maximum, then the alignment is not done at all. You can omit the
fill value (the second argument) entirely by simply using two commas after
the required alignment; this can be useful if you want the alignment to be
filled with no-op instructions when appropriate.
The
.p2alignw
and
.p2alignl
directives are variants of the
.p2align
directive. The
.p2alignw
directive treats the fill pattern as a two byte word value. The
.p2alignl
directives treats the fill pattern as a four byte longword value. For example,
.p2alignw 2,0x368d
will align to a multiple of 4. If it skips two bytes, they will be filled
in with the value 0x368d (the exact placement of the bytes depends upon the
endianness of the processor). If it skips 1 or 3 bytes, the fill value is
undefined.
This directive swaps the current section (and subsection) with most recently
referenced section (and subsection) prior to this one. Multiple
.previous
directives in a row will flip between two sections (and their subsections).
In terms of the section stack, this directive swaps the current section with
the top section on the section stack.
This directive replaces the current section (and subsection) with the top
section (and subsection) on the section stack. This section is popped off
the stack.
This directive overrides the named symbols default visibility (which is set
by their binding: local, global or weak). The directive sets the visibility
to
protected
which means that any references to the symbols from within the components
that defines them must be resolved to the definition in that component, even
if a definition in another component would normally preempt this.
If you do not use
.psize,
listings use a default line-count of 60. You may omit the comma and
columns
specification; the default width is 200 columns.
as
generates formfeeds whenever the specified number of lines is exceeded (or
whenever you explicitly request one, using
.eject).
If you specify
lines
as
0,
no formfeeds are generated save those explicitly specified with
.eject.
This directive pushes the current section (and subsection) onto the top of
the section stack, and then replaces the current section and subsection with
name
and
subsection.
The term “quad” comes from contexts in which a “word” is two bytes; hence
quad
-word for 8 bytes.
For example, assembling
is equivalent to assembling
.noaltmacro
Disable alternate macro mode.See Section
"Altmacro".
.nolist
Control (in conjunction with the
.list
directive) whether or not assembly listings are generated. These two directives
maintain an internal counter (which is zero initially).
.list
increments the counter, and
.nolist
decrements it. Assembly listings are generated whenever the counter is greater
than zero.
.octa biGNUms
This directive expects zero or more biGNUms, separated by commas. For each
biGNUm, it emits a 16-byte integer.
.org new-lc, fill
Advance the location counter of the current section to
new-lc.
new-lc
is either an absolute expression or an expression with the same section as
the current subsection. That is, you can't use
.org
to cross sections: if
new-lc
has the wrong section, the
.org
directive is ignored. To be compatible with former assemblers, if the section
of
new-lc
is absolute,
as
issues a warning, then pretends the section of
new-lc
is the same as the current subsection.
.p2align[wl] abs-expr, abs-expr, abs-expr
Pad the location counter (in the current subsection) to a particular storage
boundary. The first expression (which must be absolute) is the number of low-order
zero bits the location counter must have after advancement. For example
.p2align 3
advances the location counter until it a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
.previous
This is one of the ELF section stack manipulation directives. The others are
.section
(see Section
"Section"),
.subsection
(see Section
"SubSection"),
.pushsection
(see Section
"PushSection"),
and
.popsection
(see Section
"PopSection").
.popsection
This is one of the ELF section stack manipulation directives. The others are
.section
(see Section
"Section"),
.subsection
(see Section
"SubSection"),
.pushsection
(see Section
"PushSection"),
and
.previous
(see Section
"Previous").
.print string
as
will print
string
on the standard output during assembly. You must put
string
in double quotes.
.protected names
This is one of the ELF visibility directives. The other two are
.hidden
(see Section
"Hidden")
and
.internal
(see Section
"Internal").
.psize lines, columns
Use this directive to declare the number of lines---and, optionally, the number
of columns---to use for each page, when generating listings.
.purgem name
Undefine the macro
name,
so that later uses of the string will not be expanded.See Section
"Macro".
.pushsection name, subsection
This is one of the ELF section stack manipulation directives. The others are
.section
(see Section
"Section"),
.subsection
(see Section
"SubSection"),
.popsection
(see Section
"PopSection"),
and
.previous
(see Section
"Previous").
.quad biGNUms
.quad
expects zero or more biGNUms, separated by commas. For each bignum, it emits
an 8-byte integer. If the biGNUm won't fit in 8 bytes, it prints a warning
message; and just takes the lowest order 8 bytes of the biGNUm.
.reloc offset, reloc_name[, expression]
Generate a relocation at
offset
of type
reloc_name
with value
expression.
If
offset
is a number, the relocation is generated in the current section. If
offset
is an expression that resolves to a symbol plus offset, the relocation is
generated in the given symbol's section.
expression,
if present, must resolve to a symbol plus addend or to an absolute value,
but note that not all targets support an addend. e.g. ELF REL targets such
as i386 store an addend in the section contents rather than in the relocation.
This low level interface does not support addends stored in the section.
.rept count
Repeat the sequence of lines between the
.rept
directive and the next
.endr
directive
count
times.
.rept 3
.long 0
.endr
.long 0
.long 0
.long 0
a | section is allocatable |
w | section is writable |
x | section is executable |
M | section is mergeable |
S | section contains zero terminated strings |
G | section is a member of a section group |
T | section is used for thread-local-storage |
The optional type argument may contain one of the following constants:
@progbits | |
section contains data | |
@nobits | |
section does not contain data (i.e., section only occupies space) | |
@note | section contains data which is used by things other than the program |
@init_array | |
section contains an array of pointers to init functions | |
@fini_array | |
section contains an array of pointers to finish functions | |
@preinit_array | |
section contains an array of pointers to pre-init functions | |
Many targets only support the first three section types.
Note on targets where the @ character is the start of a comment (eg ARM) then another character is used instead. For example the ARM port uses the % character.
If flags contains the M symbol then the type argument must be specified as well as an extra argument--- entsize ---like this:
amp;.section name , "flags"M, @type, entsize
Sections with the M flag but not S flag must contain fixed size constants, each entsize octets long. Sections with both M and S must contain zero terminated strings where each character is entsize bytes long. The linker may remove duplicates within sections with the same name, same entity size and same flags. entsize must be an absolute expression.
If flags contains the G symbol then the type argument must be present along with an additional field like this:
amp;.section name , "flags"G, @type, GroupName[, linkage]
The GroupName field specifies the name of the section group to which this particular section belongs. The optional linkage field can contain:
comdat | |
indicates that only one copy of this section should be retained | |
.GNU.linkonce | |
an alias for comdat | |
Note: if both the M and G flags are present then the fields for the Merge flag should come first, like this:
amp;.section name , "flags"MG, @type, entsize, GroupName[, linkage]
If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to have none of the above flags: it will not be allocated in memory, nor writable, nor executable. The section will contain data.
For ELF targets, the assembler supports another type of .section directive for compatibility with the Solaris assembler:
amp;.section "name"[, flags...]
Note that the section name is quoted. There may be a sequence of comma separated flags:
#alloc | |
section is allocatable | |
#write | |
section is writable | |
#execinstr | |
section is executable | |
#tls | section is used for thread local storage |
This directive replaces the current section and subsection. See the contents of the gas testsuite directory gas/testsuite/gas/elf for some examples of how this directive and the other section stack directives work.
You may
.set
a symbol many times in the same assembly.
If you
.set
a global symbol, the value stored in the object file is the last value stored
into it.
For ELF targets, the
.size
directive is used like this:
This directive sets the size associated with a symbol
name.
The size in bytes is computed from
expression
which can make use of label arithmetic. This directive is typically used to
set the size of function symbols.
.set symbol, expression
Set the value of
symbol
to
expression.
This changes
symbol
amp;'s value and type to conform to
expression.
If
symbol
was flagged as external, it remains flagged (see Section
"Symbol Attributes").
.short expressions
This expects zero or more
expressions,
and emits a 16 bit number for each.
.single flonums
This directive assembles zero or more flonums, separated by commas. It has
the same effect as
.float.
.size
This directive is used to set the size associated with a symbol.
amp;.size name , expression
.sleb128 expressions
sleb128
stands for “signed little endian base 128.” This is a compact, variable length
representation of numbers used by the DWARF symbolic debugging format.See Section
"Uleb128".
.skip size, fill
This directive emits
size
bytes, each of value
fill.
Both
size
and
fill
are absolute expressions. If the comma and
fill
are omitted,
fill
is assumed to be zero. This is the same as
.space.
string | |
This is the symbol's name. It may contain any character except
\000,
so is more general than ordinary symbol names. Some debuggers used to code
arbitrarily complex structures into symbol names using this field.
| |
type |
An absolute expression. The symbol's type is set to the low 8 bits of this
expression. Any bit pattern is permitted, but
ld
and debuggers choke on silly bit patterns.
|
other |
An absolute expression. The symbol's “other” attribute is set to the low 8 bits
of this expression.
|
desc |
An absolute expression. The symbol's descriptor is set to the low 16 bits
of this expression.
|
value | An absolute expression which becomes the symbol's value. |
If a warning is detected while reading a .stabd, .stabn, or .stabs statement, the symbol has probably already been created; you get a half-formed symbol in your object file. This is compatible with earlier assemblers!
.stabd type, other, desc | |
The “name” of the symbol generated is not even an empty string. It is a null pointer, for compatibility. Older assemblers used a null pointer so they didn't waste space in object files with empty strings. The symbol's value is set to the location counter, relocatably. When your program is linked, the value of this symbol is the address of the location counter when the .stabd was assembled.
| |
.stabn type, other, desc, value | |
The name of the symbol is set to the empty string
.
| |
.stabs string, type, other, desc, value | |
All five fields are specified. | |
This directive replaces the current subsection with
name.
The current section is not changed. The replaced subsection is put onto the
section stack in place of the then current top of stack subsection.
For ELF targets, the
.symver
directive can be used like this:
If the symbol
name
is not defined within the file being assembled, all references to
name
will be changed to
name2@nodename.
If no reference to
name
is made,
name2@nodename
will be removed from the symbol table.
Another usage of the
.symver
directive is:
The third usage of the
.symver
directive is:
This directive affects subsequent pages, as well as the current page if it
appears within ten lines of the top of a page.
For ELF targets, the
.type
directive is used like this:
This sets the type of symbol
name
to be either a function symbol or an object symbol. There are five different
syntaxes supported for the
type description
field, in order to provide compatibility with various other assemblers.
Because some of the characters used in these syntaxes (such as
@
and
#)
are comment characters for some architectures, some of the syntaxes below
do not work on all architectures. The first variant will be accepted by the
GNU assembler on all architectures so that variant should be used for maximum
portability, if you do not need to assemble your code with other assemblers.
The syntaxes supported are:
.type <name>,#function
.type <name>,#object
.type <name>,@function
.type <name>,@object
.type <name>,%function
.type <name>,%object
.type <name>,"function"
.type <name>,"object"
On COFF targets other than PE, weak symbols are a GNU extension. This directive
sets the weak attribute on the comma separated list of symbol
names.
If the symbols do not already exist, they will be created.
On the PE target, weak symbols are supported natively as weak aliases. When
a weak symbol is created that is not an alias, GAS creates an alternate symbol
to hold the default value.
.string Va str
Copy the characters in
str
to the object file. You may specify more than one string to copy, separated
by commas. Unless otherwise specified for a particular machine, the assembler
marks the end of each string with a 0 byte. You can use any of the escape
sequences described in Strings,,Strings.
.struct expression
Switch to the absolute section, and set the section offset to
expression,
which must be an absolute expression. You might use this as follows:
.struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:
This would define the symbol
field1
to have the value 0, the symbol
field2
to have the value 4, and the symbol
field3
to have the value 8. Assembly would be left in the absolute section, and you
would need to use a
.section
directive of some sort to change to some other section before further assembly.
.subsection name
This is one of the ELF section stack manipulation directives. The others are
.section
(see Section
"Section"),
.pushsection
(see Section
"PushSection"),
.popsection
(see Section
"PopSection"),
and
.previous
(see Section
"Previous").
.symver
Use the
.symver
directive to bind symbols to specific version nodes within a source file.
This is only supported on ELF platforms, and is typically used when assembling
files to be linked into a shared library. There are cases where it may make
sense to use this in objects to be bound into an application itself so as
to override a versioned symbol from a shared library.
amp;.symver name, name2@nodename
If the symbol
name
is defined within the file being assembled, the
.symver
directive effectively creates a symbol alias with the name
name2@nodename,
and in fact the main reason that we just don't try and create a regular alias
is that the
@
character isn't permitted in symbol names. The
name2
part of the name is the actual name of the symbol by which it will be externally
referenced. The name
name
itself is merely a name of convenience that is used so that it is possible
to have definitions for multiple versions of a function within a single source
file, and so that the compiler can unambiguously know which version of a function
is being mentioned. The
nodename
portion of the alias should be the name of a node specified in the version
script supplied to the linker when building a shared library. If you are attempting
to override a versioned symbol from a shared library, then
nodename
should correspond to the nodename of the symbol you are trying to override.
amp;.symver name, name2@@nodename
In this case, the symbol
name
must exist and be defined within the file being assembled. It is similar to
name2@nodename.
The difference is
name2@@nodename
will also be used to resolve references to
name2
by the linker.
amp;.symver name, name2@@@nodename
When
name
is not defined within the file being assembled, it is treated as
name2@nodename.
When
name
is defined within the file being assembled, the symbol name,
name,
will be changed to
name2@@nodename.
.text subsection
Tells
as
to assemble the following statements onto the end of the text subsection numbered
subsection,
which is an absolute expression. If
subsection
is omitted, subsection number zero is used.
.title Va heading
Use
heading
as the title (second line, immediately after the source file name and pagenumber)
when generating assembly listings.
.type
This directive is used to set the type of a symbol.
amp;.type name , type description
.type <name> STT_FUNCTION
.type <name> STT_OBJECT
.uleb128 expressions
uleb128
stands for “unsigned little endian base 128.” This is a compact, variable length
representation of numbers used by the DWARF symbolic debugging format.See Section
"Sleb128".
.version Va string
This directive creates a
.note
section and places into it an ELF formatted note of type NT_VERSION. The note's
name is set to
string.
.vtable_entry table, offset
This directive finds or creates a symbol
table
and creates a
VTABLE_ENTRY
relocation for it with an addend of
offset.
.vtable_inherit child, parent
This directive finds the symbol
child
and finds or creates the symbol
parent
and then creates a
VTABLE_INHERIT
relocation for the parent whose addend is the value of the child symbol. As
a special case the parent name of
0
is treated as referring to the
*ABS*
section.
.warning Va string
Similar to the directive
.error
(see Section
"Error"),
but just emits a warning.
.weak names
This directive sets the weak attribute on the comma separated list of symbol
names.
If the symbols do not already exist, they will be created.
.abort
.line | |
-mcpu= processor[+ extension...] | |
This option specifies the target processor. The assembler will issue an error
message if an attempt is made to assemble an instruction which will not execute
on the target processor. The following processor names are recognized:
arm1,
arm2,
arm250,
arm3,
arm6,
arm60,
arm600,
arm610,
arm620,
arm7,
arm7m,
arm7d,
arm7dm,
arm7di,
arm7dmi,
arm70,
arm700,
arm700i,
arm710,
arm710t,
arm720,
arm720t,
arm740t,
arm710c,
arm7100,
arm7500,
arm7500fe,
arm7t,
arm7tdmi,
arm7tdmi-s,
arm8,
arm810,
strongarm,
strongarm1,
strongarm110,
strongarm1100,
strongarm1110,
arm9,
arm920,
arm920t,
arm922t,
arm940t,
arm9tdmi,
arm9e,
arm926e,
arm926ej-s,
arm946e-r0,
arm946e,
arm946e-s,
arm966e-r0,
arm966e,
arm966e-s,
arm968e-s,
arm10t,
arm10tdmi,
arm10e,
arm1020,
arm1020t,
arm1020e,
arm1022e,
arm1026ej-s,
arm1136j-s,
arm1136jf-s,
arm1156t2-s,
arm1156t2f-s,
arm1176jz-s,
arm1176jzf-s,
mpcore,
mpcorenovfp,
cortex-a8,
cortex-r4,
cortex-m3,
ep9312
(ARM920 with Cirrus Maverick coprocessor),
i80200
(Intel XScale processor)
iwmmxt
(Intel(r) XScale processor with Wireless MMX(tm) technology coprocessor) and
xscale.
The special name
all
may be used to allow the assembler to accept instructions valid for any ARM
processor.
In addition to the basic instruction set, the assembler can be told to accept various extension mnemonics that extend the processor using the co-processor instruction space. For example, -mcpu=arm920+maverick is equivalent to specifying -mcpu=ep9312. The following extensions are currently supported: +maverick +iwmmxt and +xscale.
| |
-march= architecture[+ extension...] | |
This option specifies the target architecture. The assembler will issue an
error message if an attempt is made to assemble an instruction which will
not execute on the target architecture. The following architecture names are
recognized:
armv1,
armv2,
armv2a,
armv2s,
armv3,
armv3m,
armv4,
armv4xm,
armv4t,
armv4txm,
armv5,
armv5t,
armv5txm,
armv5te,
armv5texp,
armv6,
armv6j,
armv6k,
armv6z,
armv6zk,
armv7,
armv7-a,
armv7-r,
armv7-m,
iwmmxt
and
xscale.
If both
-mcpu
and
-march
are specified, the assembler will use the setting for
-mcpu.
The architecture option can be extended with the same instruction set extension options as the -mcpu option.
| |
-mfpu= floating-point-format | |
This option specifies the floating point format to assemble for. The assembler will issue an error message if an attempt is made to assemble an instruction which will not execute on the target floating point unit. The following format options are recognized: softfpa, fpe, fpe2, fpe3, fpa, fpa10, fpa11, arm7500fe, softvfp, softvfp+vfp, vfp, vfp10, vfp10-r0, vfp9, vfpxd, arm1020t, arm1020e, arm1136jf-s and maverick. In addition to determining which instructions are assembled, this option also affects the way in which the .double assembler directive behaves when assembling little-endian code. The default is dependent on the processor selected. For Architecture 5 or later, the default is to assembler for VFP instructions; for earlier architectures the default is to assemble for FPA instructions.
| |
-mthumb | |
This option specifies that the assembler should start assembling Thumb instructions;
that is, it should behave as though the file starts with a
.code 16
directive.
| |
-mthumb-interwork | |
This option specifies that the output generated by the assembler should be
marked as supporting interworking.
| |
-mapcs[26|32] | |
This option specifies that the output generated by the assembler should be
marked as supporting the indicated version of the Arm Procedure. Calling Standard.
| |
-matpcs | |
This option specifies that the output generated by the assembler should be
marked as supporting the Arm/Thumb Procedure Calling Standard. If enabled
this option will cause the assembler to create an empty debugging section
in the object file called .arm.atpcs. Debuggers can use this to determine
the ABI being used by.
| |
-mapcs-float | |
This indicates the floating point variant of the APCS should be used. In this
variant floating point arguments are passed in FP registers rather than integer
registers.
| |
-mapcs-reentrant | |
This indicates that the reentrant variant of the APCS should be used. This
variant supports position independent code.
| |
-mfloat-abi= abi | |
This option specifies that the output generated by the assembler should be
marked as using specified floating point ABI. The following values are recognized:
soft,
softfp
and
hard.
| |
-meabi= ver | |
This option specifies which EABI version the produced object files should
conform to. The following values are recognized:
GNU,
4
and
5.
| |
-EB |
This option specifies that the output generated by the assembler should be
marked as being encoded for a big-endian processor.
|
-EL |
This option specifies that the output generated by the assembler should be
marked as being encoded for a little-endian processor.
|
-k |
This option specifies that the output of the assembler should be marked as
position-independent code (PIC).
|
The presence of a @ on a line indicates the start of a comment that extends to the end of the current line. If a # appears as the first character of a line, the whole line is treated as a comment.
The ; character can be used instead of a newline to separate statements.
Either # or $ can be used to indicate immediate operands.
*TODO* Explain about /data modifier on symbols.
Register Names
*TODO* Explain about ARM register naming, and the predefined names.
ARM relocation generation
Specific data relocations can be generated by putting the relocation name in parentheses after the symbol name. For example:
.word foo(TARGET1)
This will generate an R_ARM_TARGET1 relocation against the symbol foo. The following relocations are supported: GOT, GOTOFF, TARGET1, TARGET2, SBREL, TLSGD, TLSLDM, TLSLDO, GOTTPOFF and TPOFF.
For compatibility with older toolchains the assembler also accepts (PLT) after branch targets. This will generate the deprecated R_ARM_PLT32 relocation.
Relocations for MOVW and MOVT instructions can be generated by prefixing the value with #:lower16: and #:upper16 respectively. For example to load the 32-bit address of foo into r0:
MOVW r0, #:lower16:foo MOVT r0, #:upper16:foo
.align expression [, expression] | |
This is the generic
.align
directive. For the ARM however if the first argument is zero (ie no alignment
is needed) the assembler will behave as if the argument had been 2 (ie pad
to the next four byte boundary). This is for compatibility with ARM's own
assembler.
| |
name .req register name | |
This creates an alias for
register name
called
name.
For example:
foo .req r0
| |
.unreq alias-name | |
This undefines a register alias which was previously defined using the
req,
dn
or
qn
directives. For example:
foo .req r0 .unreq foo An error occurs if the name is undefined. Note - this pseudo op can be used to delete builtin in register name aliases (eg 'r0'). This should only be done if it is really necessary.
| |
name .dn register name[ .type][ [index]]
name .qn register name[ .type][ [index]] | |
The dn and qn directives are used to create typed and/or indexed register aliases for use in Advanced SIMD Extension (Neon) instructions. The former should be used to create aliases of double-precision registers, and the latter to create aliases of quad-precision registers. If these directives are used to create typed aliases, those aliases can be used in Neon instructions instead of writing types after the mnemonic or after each operand. For example:
x .dn d2.f32 y .dn d3.f32 z .dn d4.f32[1] vmul x,y,z This is equivalent to writing the following:
vmul.f32 d2,d3,d4[1] Aliases created using dn or qn can be destroyed using unreq.
| |
.code[16|32] | |
This directive selects the instruction set being generated. The value 16 selects
Thumb, with the value 32 selecting ARM.
| |
.thumb |
This performs the same action as
.code 16.
|
.arm |
This performs the same action as
.code 32.
|
.force_thumb | |
This directive forces the selection of Thumb instructions, even if the target
processor does not support those instructions
| |
.thumb_func | |
This directive specifies that the following symbol is the name of a Thumb
encoded function. This information is necessary in order to allow the assembler
and linker to generate correct code for interworking between Arm and Thumb
instructions and should be used even if interworking is not going to be performed.
The presence of this directive also implies
.thumb
This directive is not neccessary when generating EABI objects. On these targets the encoding is implicit when generating Thumb code.
| |
.thumb_set | |
This performs the equivalent of a
.set
directive in that it creates a symbol which is an alias for another symbol
(possibly not yet defined). This directive also has the added property in
that it marks the aliased symbol as being a thumb function entry point, in
the same way that the
.thumb_func
directive does.
| |
.ltorg |
This directive causes the current contents of the literal pool to be dumped
into the current section (which is assumed to be the .text section) at the
current location (aligned to a word boundary).
GAS
maintains a separate literal pool for each section and each sub-section. The
.ltorg
directive will only affect the literal pool of the current section and sub-section.
At the end of assembly all remaining, un-empty literal pools will automatically
be dumped.
Note - older versions of GAS would dump the current literal pool any time a section change occurred. This is no longer done, since it prevents accurate control of the placement of literal pools.
|
.pool |
This is a synonym for .ltorg.
|
.unwind_fnstart | |
Marks the start of a function with an unwind table entry.
| |
.unwind_fnend | |
Marks the end of a function with an unwind table entry. The unwind index table
entry is created when this directive is processed.
If no personality routine has been specified then standard personality routine 0 or 1 will be used, depending on the number of unwind opcodes required.
| |
.cantunwind | |
Prevents unwinding through the current function. No personality routine or
exception table data is required or permitted.
| |
.personality name | |
Sets the personality routine for the current function to
name.
| |
.personalityindex index | |
Sets the personality routine for the current function to the EABI standard
routine number
index
| |
.handlerdata | |
Marks the end of the current function, and the start of the exception table
entry for that function. Anything between this directive and the
.fnend
directive will be added to the exception table entry.
Must be preceded by a .personality or .personalityindex directive.
| |
.save reglist | |
Generate unwinder annotations to restore the registers in
reglist.
The format of
reglist
is the same as the corresponding store-multiple instruction.
.save {r4, r5, r6, lr} stmfd sp!, {r4, r5, r6, lr} .save f4, 2 sfmfd f4, 2, [sp]! .save {d8, d9, d10} fstmdx sp!, {d8, d9, d10} .save {wr10, wr11} wstrd wr11, [sp, #-8]! wstrd wr10, [sp, #-8]! or .save wr11 wstrd wr11, [sp, #-8]! .save wr10 wstrd wr10, [sp, #-8]!
| |
.vsave vfp-reglist | |
Generate unwinder annotations to restore the VFP registers in
vfp-reglist
using FLDMD. Also works for VFPv3 registers that are to be restored using
VLDM. The format of
vfp-reglist
is the same as the corresponding store-multiple instruction.
.vsave {d8, d9, d10} fstmdd sp!, {d8, d9, d10} .vsave {d15, d16, d17} vstm sp!, {d15, d16, d17} Since FLDMX and FSTMX are now deprecated, this directive should be used in favour of .save for saving VFP registers for ARMv6 and above.
| |
.pad # count | |
Generate unwinder annotations for a stack adjustment of
count
bytes. A positive value indicates the function prologue allocated stack space
by decrementing the stack pointer.
| |
.movsp reg [, # offset] | |
Tell the unwinder that
reg
contains an offset from the current stack pointer. If
offset
is not specified then it is assumed to be zero.
| |
.setfp fpreg, spreg [, # offset] | |
Make all unwinder annotations relaive to a frame pointer. Without this the
unwinder will use offsets from the stack pointer.
The syntax of this directive is the same as the sub or mov instruction used to set the frame pointer. spreg must be either sp or mentioned in a previous .movsp directive.
amp;.movsp ip mov ip, sp amp;... amp;.setfp fp, ip, #4 sub fp, ip, #4
| |
.raw offset, byte1, ... | |
Insert one of more arbitary unwind opcode bytes, which are known to adjust
the stack pointer by
offset
bytes.
For example .unwind_raw 4, 0xb1, 0x01 is equivalent to .save {r0}
| |
.cpu name | |
Select the target processor. Valid values for
name
are the same as for the
[-mcpu]
commandline option.
| |
.arch name | |
Select the target architecture. Valid values for
name
are the same as for the
[-march]
commandline option.
| |
.object_arch name | |
Override the architecture recorded in the EABI object attribute section. Valid
values for
name
are the same as for the
.arch
directive. Typically this is useful when code uses runtime detection of CPU
features.
| |
.fpu name | |
Select the floating point unit to assemble for. Valid values for
name
are the same as for the
[-mfpu]
commandline option.
| |
.eabi_attribute tag, value | |
Set the EABI object attribute number
tag
to
value.
The value is either a
number,
string,
or
number, string
depending on the tag.
| |
NOP |
nop This pseudo op will always evaluate to a legal ARM instruction that does nothing. Currently it will evaluate to MOV r0, r0.
|
LDR |
ldr <register> , = <expression> If expression evaluates to a numeric constant then a MOV or MVN instruction will be used in place of the LDR instruction, if the constant can be generated by either of these instructions. Otherwise the constant will be placed into the nearest literal pool (if it not already there) and a PC relative LDR instruction will be generated.
|
ADR |
adr <register> <label> This instruction will load the address of label into the indicated register. The instruction will evaluate to a PC relative ADD or SUB instruction depending upon where the label is located. If the label is out of range, or if it is not defined in the same file (and section) as the ADR instruction, then an error will be generated. This instruction will not make use of the literal pool.
|
ADRL |
adrl <register> <label> This instruction will load the address of label into the indicated register. The instruction will evaluate to one or two PC relative ADD or SUB instructions depending upon where the label is located. If a second instruction is not needed a NOP instruction will be generated in its place, so that this instruction is always 8 bytes long. If the label is out of range, or if it is not defined in the same file (and section) as the ADRL instruction, then an error will be generated. This instruction will not make use of the literal pool.
|
$a |
At the start of a region of code containing ARM instructions.
|
$t |
At the start of a region of code containing THUMB instructions.
|
$d |
At the start of a region of data.
|
--32 | --64 | |
Select the word size, either 32 bits or 64 bits. Selecting 32-bit implies
Intel i386 architecture, while 64-bit implies AMD x86-64 architecture.
These options are only available with the ELF object file format, and require that the necessary BFD support has been included (on a 32-bit platform you have to add --enable-64-bit-bfd to configure enable 64-bit usage and use x86-64 as target platform).
| |
-n |
By default, x86 GAS replaces multiple nop instructions used for alignment
within code sections with multi-byte nop instructions such as leal 0(%esi,1),%esi.
This switch disables the optimization.
|
--divide | |
On SVR4-derived platforms, the character
/
is treated as a comment character, which means that it cannot be used in expressions.
The
--divide
option turns
/
into a normal character. This does not disable
/
at the beginning of a line starting a comment, or affect using
#
for starting a comment.
| |
-march= CPU | |
This option specifies an instruction set architecture for generating instructions.
The following architectures are recognized:
i8086,
i186,
i286,
i386,
i486,
i586,
i686,
pentium,
pentiumpro,
pentiumii,
pentiumiii,
pentium4,
prescott,
nocona,
core,
core2,
k6,
k6_2,
athlon,
sledgehammer,
opteron,
k8,
generic32
and
generic64.
This option only affects instructions generated by the assembler. The .arch directive will take precedent.
| |
-mtune= CPU | |
This option specifies a processor to optimize for. When used in conjunction
with the
[-march]
option, only instructions of the processor specified by the
[-march]
option will be generated.
Valid CPU values are identical to [-march= CPU].
| |
Almost all instructions have the same names in AT&T and Intel format. There are a few exceptions. The sign extend and zero extend instructions need two sizes to specify them. They need a size to sign/zero extend from and a size to zero extend to. This is accomplished by using two instruction mnemonic suffixes in AT&T syntax. Base names for sign extend and zero extend are movs... and movz... in AT&T syntax ( movsx and movzx in Intel syntax). The instruction mnemonic suffixes are tacked on to this base name, the from suffix before the to suffix. Thus, movsbl %al, %edx is AT&T syntax for “move sign extend from %al to %edx.” Possible suffixes, thus, are bl (from byte to long), bw (from byte to word), wl (from word to long), bq (from byte to quadruple word), wq (from word to quadruple word), and lq (from long to quadruple word).
The Intel-syntax conversion instructions
are called cbtw, cwtl, cwtd, cltd, cltq, and cqto in AT&T naming. as accepts either naming for these instructions.
Far call/jump instructions are lcall and ljmp in AT&T syntax, but are call far and jump far in Intel convention.
The AMD x86-64 architecture extends the register set by:
repne scas %es:(%edi),%al
You may also place prefixes on the lines immediately preceding the instruction, but this circumvents checks that as does with prefixes, and will not work with all prefixes.
Here is a list of instruction prefixes:
addr32 jmpl *(%ebx)
You may write the rex prefixes directly. The rex64xyz instruction emits rex prefix with all the bits set. By omitting the 64, x, y or z you may write other prefixes as well. Normally, there is no need to write the prefixes explicitly, since gas will automatically generate them based on the instruction operands.
section:[base + index*scale + disp]
is translated into the AT&T syntax
section:disp(base, index, scale)
where base and index are the optional 32-bit base and index registers, disp is the optional displacement, and scale, taking the values 1, 2, 4, and 8, multiplies index to calculate the address of the operand. If no scale is specified, scale is taken to be 1. section specifies the optional section register for the memory operand, and may override the default section register (see a 80386 manual for section register defaults). Note that section overrides in AT&T syntax must be preceded by a %. If you specify a section override which coincides with the default section register, as does not output any section register override prefixes to assemble the given instruction. Thus, section overrides can be specified to emphasize which section register is used for a given memory operand.
Here are some examples of Intel and AT&T style memory references:
AT&T:-4(%ebp), Intel:[ebp - 4] | |
base
is
%ebp;
disp
is
-4.
section
is missing, and the default section is used (
%ss
for addressing with
%ebp
as the base register).
index,
scale
are both missing.
| |
AT&T:foo(,%eax,4), Intel:[foo + eax*4] | |
index
is
%eax
(scaled by a
scale
4);
disp
is
foo.
All other fields are missing. The section register here defaults to
%ds.
| |
AT&T:foo(,1); Intel[foo] | |
This uses the value pointed to by
foo
as a memory operand. Note that
base
and
index
are both missing, but there is only
one
,.
This is a syntactic exception.
| |
AT&T:%gs:foo; Intelgs:foo | |
This selects the contents of the variable foo with section register section being %gs. | |
Absolute (as opposed to PC relative) call and jump operands must be prefixed with *. If no * is specified, as always chooses PC relative addressing for jump/call labels.
Any instruction that has a memory operand, but no register operand, must specify its size (byte, word, long, or quadruple) with an instruction mnemonic suffix ( b, w, l or q, respectively).
The x86-64 architecture adds an RIP (instruction pointer relative) addressing. This addressing mode is specified by using rip as a base register. Only constant offsets are valid. For example:
AT&T:1234(%rip), Intel:[rip + 1234] | |
Points to the address 1234 bytes past the end of the current instruction.
| |
AT&T:symbol(%rip), Intel:[rip + symbol] | |
Points to the symbol in RIP relative way, this is shorter than the default absolute addressing. | |
Other addressing modes remain unchanged in x86-64 architecture, except registers used are 64-bit instead of 32-bit.
Note that the jcxz, jecxz, loop, loopz, loope, loopnz and loopne instructions only come in byte displacements, so that if you use these instructions ( gcc does not use them) you may get an error message (and incorrect code). The AT&T 80386 assembler tries to get around this problem by expanding jcxz foo to
jcxz cx_zero jmp cx_nonzero cx_zero: jmp foo cx_nonzero:
Register to register operations should not use instruction mnemonic suffixes. fstl %st, %st(1) will give a warning, and be assembled as if you wrote fst %st, %st(1), since all register to register operations use 80-bit floating point operands. (Contrast this with fstl %st, mem, which converts %st from 80-bit to 64-bit floating point format, then stores the result in the 4 byte location mem)
Currently, as does not support Intel's floating point SIMD, Katmai (KNI).
The eight 64-bit MMX operands, also used by 3DNow!, are called %mm0, %mm1, amp;... %mm7. They contain eight 8-bit integers, four 16-bit integers, two 32-bit integers, one 64-bit integer, or two 32-bit floating point values. The MMX registers cannot be used at the same time as the floating point stack.
See Intel and AMD documentation, keeping in mind that the operand order in instructions is reversed from the Intel syntax.
.code16gcc provides experimental support for generating 16-bit code from gcc, and differs from .code16 in that call, ret, enter, leave, push, pop, pusha, popa, pushf, and popf instructions default to 32-bit size. This is so that the stack pointer is manipulated in the same way over function calls, allowing access to function parameters at the same stack offsets as in 32-bit mode. .code16gcc also automatically adds address size prefixes where necessary to use the 32-bit addressing modes that gcc generates.
The code which as generates in 16-bit mode will not necessarily run on a 16-bit pre-80386 processor. To write code that runs on such a processor, you must refrain from using any 32-bit constructs which require as to output address or operand size prefixes.
Note that writing 16-bit code instructions by explicitly specifying a prefix or an instruction mnemonic suffix within a 32-bit code section generates different machine instructions than those generated for a 16-bit code segment. In a 32-bit code section, the following code generates the machine opcode bytes 66 6a 04, which pushes the value 4 onto the stack, decrementing %esp by 2.
pushw $4
The same code in a 16-bit code section would generate the machine opcode bytes 6a 04 (i.e., without the operand size prefix), which is correct since the processor default operand size is assumed to be 16 bits in a 16-bit code section.
For example
fsub %st,%st(3)results in %st(3) being updated to %st - %st(3) rather than the expected %st(3) - %st. This happens with all the non-commutative arithmetic floating point operations with two register operands where the source register is %st and the destination register is %st(i).
i8086 i186 i286 i386 i486 i586 i686 pentium pentiumpro pentiumii pentiumiii pentium4 prescott nocona core core2 amdfam10 k6 athlon sledgehammer k8 amp;.mmx .sse .sse2 .sse3 amp;.ssse3 .sse4.1 .sse4.2 .sse4 amp;.sse4a .3dnow .3dnowa .padlock amp;.pacifica .svme .abm
Apart from the warning, there are only two other effects on as operation; Firstly, if you specify a CPU other than i486, then shift by one instructions such as sarl $1, %eax will automatically use a two byte opcode sequence. The larger three byte opcode sequence is used on the 486 (and when no architecture is specified) because it executes faster on the 486. Note that you can explicitly request the two byte opcode by writing sarl %eax. Secondly, if you specify i8086, i186, or i286, and .code16 or .code16gcc then byte offset conditional jumps will be promoted when necessary to a two instruction sequence consisting of a conditional jump of the opposite sense around an unconditional jump to the target.
Following the CPU architecture (but not a sub-architecture, which are those starting with a dot), you may specify jumps or nojumps to control automatic promotion of conditional jumps. jumps is the default, and enables jump promotion; All external jumps will be of the long variety, and file-local jumps will be promoted as necessary. (see Section "i386-Jumps") nojumps leaves external conditional jumps as byte offset jumps, and warns about file-local conditional jumps that as promotes. Unconditional jumps are treated as for jumps.
For example
.arch i8086,nojumps
We have added a two operand form of imul when the first operand is an immediate mode expression and the second operand is a register. This is just a shorthand, so that, multiplying %eax by 69, for example, can be done with imul $69, %eax rather than imul $69, %eax, %eax.
-mconstant-gp | |
This option instructs the assembler to mark the resulting object file as using
the “constant GP” model. With this model, it is assumed that the entire program
uses a single global pointer (GP) value. Note that this option does not in
any fashion affect the machine code emitted by the assembler. All it does
is turn on the EF_IA_64_CONS_GP flag in the ELF file header.
| |
-mauto-pic | |
This option instructs the assembler to mark the resulting object file as using
the “constant GP without function descriptor” data model. This model is like
the “constant GP” model, except that it additionally does away with function
descriptors. What this means is that the address of a function refers directly
to the function's code entry-point. Normally, such an address would refer
to a function descriptor, which contains both the code entry-point and the
GP-value needed by the function. Note that this option does not in any fashion
affect the machine code emitted by the assembler. All it does is turn on the
EF_IA_64_NOFUNCDESC_CONS_GP flag in the ELF file header.
| |
-milp32
-milp64 -mlp64 -mp64 | |
These options select the data model. The assembler defaults to
-mlp64
(LP64 data model).
| |
-mle
-mbe | |
These options select the byte order. The
-mle
option selects little-endian byte order (default) and
-mbe
selects big-endian byte order. Note that IA-64 machine code always uses little-endian
byte order.
| |
-mtune=itanium1
-mtune=itanium2 | |
Tune for a particular IA-64 CPU,
itanium1
or
itanium2.
The default is
itanium2.
| |
-munwind-check=warning
-munwind-check=error | |
These options control what the assembler will do when performing consistency
checks on unwind directives.
-munwind-check=warning
will make the assembler issue a warning when an unwind directive check fails.
This is the default.
-munwind-check=error
will make the assembler issue an error when an unwind directive check fails.
| |
-mhint.b=ok
-mhint.b=warning -mhint.b=error | |
These options control what the assembler will do when the
hint.b
instruction is used.
-mhint.b=ok
will make the assembler accept
hint.b.
-mint.b=warning
will make the assembler issue a warning when
hint.b
is used.
-mhint.b=error
will make the assembler treat
hint.b
as an error, which is the default.
| |
-x
-xexplicit | |
These options turn on dependency violation checking.
| |
-xauto | |
This option instructs the assembler to automatically insert stop bits where
necessary to remove dependency violations. This is the default mode.
| |
-xnone | |
This option turns off dependency violation checking.
| |
-xdebug | |
This turns on debug output intended to help tracking down bugs in the dependency
violation checker.
| |
-xdebugn | |
This is a shortcut for -xnone -xdebug.
| |
-xdebugx | |
This is a shortcut for -xexplicit -xdebug.
| |
Special Characters
// is the line comment token.
; can be used instead of a newline to separate statements.
Register Names
The 128 integer registers are referred to as r n. The 128 floating-point registers are referred to as f n. The 128 application registers are referred to as ar n. The 128 control registers are referred to as cr n. The 64 one-bit predicate registers are referred to as p n. The 8 branch registers are referred to as b n. In addition, the assembler defines a number of aliases: gp ( r1), sp ( r12), rp ( b0), ret0 ( r8), ret1 ( r9), ret2 ( r10), ret3 ( r9), farg n ( f8+ n), and fret n ( f8+ n).
For convenience, the assembler also defines aliases for all named application and control registers. For example, ar.bsp refers to the register backing store pointer ( ar17). Similarly, cr.eoi refers to the end-of-interrupt register ( cr67).
IA-64 Processor-Status-Register (PSR) Bit Names
The assembler defines bit masks for each of the bits in the IA-64 processor status register. For example, psr.ic corresponds to a value of 0x2000. These masks are primarily intended for use with the ssm / sum and rsm / rum instructions, but they can be used anywhere else where an integer constant is expected.
-G num | |
This option sets the largest size of an object that can be referenced implicitly
with the
gp
register. It is only accepted for targets that use ecoff format. The default
value is 8.
| |
-EB
-EL | |
Any mips configuration of
as
can select big-endian or little-endian output at run time (unlike the other
GNU development tools, which must be configured for one or the other). Use
-EB
to select big-endian output, and
-EL
for little-endian.
| |
-KPIC |
Generate SVR4-style PIC. This option tells the assembler to generate SVR4-style
position-independent macro expansions. It also tells the assembler to mark
the output file as PIC.
|
-mvxworks-pic | |
Generate VxWorks PIC. This option tells the assembler to generate VxWorks-style
position-independent macro expansions.
| |
-mips1
-mips2 -mips3 -mips4 -mips5 -mips32 -mips32r2 -mips64 -mips64r2 | |
Generate code for a particular MIPS Instruction Set Architecture level.
-mips1
corresponds to the r2000 and r3000 processors,
-mips2
to the r6000 processor,
-mips3
to the r4000 processor, and
-mips4
to the r8000 and r10000 processors.
-mips5,
-mips32,
-mips32r2,
-mips64,
and
-mips64r2
correspond to generic MIPS V, MIPS32, MIPS32 Release 2, MIPS64, and MIPS64
Release 2 ISA processors, respectively. You can also switch instruction sets
during the assembly; see MIPS ISA, Directives to override the ISA level.
| |
-mgp32
-mfp32 | |
Some macros have different expansions for 32-bit and 64-bit registers. The
register sizes are normally inferred from the ISA and ABI, but these flags
force a certain group of registers to be treated as 32 bits wide at all times.
-mgp32
controls the size of general-purpose registers and
-mfp32
controls the size of floating-point registers.
The .set gp=32 and .set fp=32 directives allow the size of registers to be changed for parts of an object. The default value is restored by .set gp=default and .set fp=default. On some MIPS variants there is a 32-bit mode flag; when this flag is set, 64-bit instructions generate a trap. Also, some 32-bit OSes only save the 32-bit registers on a context switch, so it is essential never to use the 64-bit registers.
| |
-mgp64
-mfp64 | |
Assume that 64-bit registers are available. This is provided in the interests
of symmetry with
-mgp32
and
-mfp32.
The .set gp=64 and .set fp=64 directives allow the size of registers to be changed for parts of an object. The default value is restored by .set gp=default and .set fp=default.
| |
-mips16
-no-mips16 | |
Generate code for the MIPS 16 processor. This is equivalent to putting
.set mips16
at the start of the assembly file.
-no-mips16
turns off this option.
| |
-msmartmips
-mno-smartmips | |
Enables the SmartMIPS extensions to the MIPS32 instruction set, which provides
a number of new instructions which target smartcard and cryptographic applications.
This is equivalent to putting
.set smartmips
at the start of the assembly file.
-mno-smartmips
turns off this option.
| |
-mips3d
-no-mips3d | |
Generate code for the MIPS-3D Application Specific Extension. This tells the
assembler to accept MIPS-3D instructions.
-no-mips3d
turns off this option.
| |
-mdmx
-no-mdmx | |
Generate code for the MDMX Application Specific Extension. This tells the
assembler to accept MDMX instructions.
-no-mdmx
turns off this option.
| |
-mdsp
-mno-dsp | |
Generate code for the DSP Release 1 Application Specific Extension. This tells
the assembler to accept DSP Release 1 instructions.
-mno-dsp
turns off this option.
| |
-mdspr2
-mno-dspr2 | |
Generate code for the DSP Release 2 Application Specific Extension. This option
implies -mdsp. This tells the assembler to accept DSP Release 2 instructions.
-mno-dspr2
turns off this option.
| |
-mmt
-mno-mt | |
Generate code for the MT Application Specific Extension. This tells the assembler
to accept MT instructions.
-mno-mt
turns off this option.
| |
-mfix7000
-mno-fix7000 | |
Cause nops to be inserted if the read of the destination register of an mfhi
or mflo instruction occurs in the following two instructions.
| |
-mfix-vr4120
-no-mfix-vr4120 | |
Insert nops to work around certain VR4120 errata. This option is intended
to be used on GCC-generated code: it is not designed to catch all problems
in hand-written assembler code.
| |
-mfix-vr4130
-no-mfix-vr4130 | |
Insert nops to work around the VR4130
mflo
/
mfhi
errata.
| |
-m4010
-no-m4010 | |
Generate code for the LSI r4010 chip. This tells the assembler to accept the
r4010 specific instructions (
addciu,
ffc,
etc.), and to not schedule
nop
instructions around accesses to the
HI
and
LO
registers.
-no-m4010
turns off this option.
| |
-m4650
-no-m4650 | |
Generate code for the MIPS r4650 chip. This tells the assembler to accept
the
mad
and
madu
instruction, and to not schedule
nop
instructions around accesses to the
HI
and
LO
registers.
-no-m4650
turns off this option.
| |
-m3900
-no-m3900 -m4100 -no-m4100 | |
For each option
-m nnnn,
generate code for the MIPS r
nnnn
chip. This tells the assembler to accept instructions specific to that chip,
and to schedule for that chip's hazards.
| |
-march= cpu | |
Generate code for a particular MIPS cpu. It is exactly equivalent to
-m cpu,
except that there are more value of
cpu
understood. Valid
cpu
value are:
" 2000, 3000, 3900, 4000, 4010, 4100, 4111, vr4120, vr4130, vr4181, 4300, 4400, 4600, 4650, 5000, rm5200, rm5230, rm5231, rm5261, rm5721, vr5400, vr5500, 6000, rm7000, 8000, rm9000, 10000, 12000, 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, m4k, m4kp, 24kc, 24kf, 24kx, 24kec, 24kef, 24kex, 34kc, 34kf, 34kx, 74kc, 74kf, 74kx, 5kc, 5kf, 20kc, 25kf, sb1, sb1a "
| |
-mtune= cpu | |
Schedule and tune for a particular MIPS cpu. Valid
cpu
values are identical to
-march= cpu.
| |
-mabi= abi | |
Record which ABI the source code uses. The recognized arguments are:
32,
n32,
o64,
64
and
eabi.
| |
-msym32
-mno-sym32 | |
Equivalent to adding
.set sym32
or
.set nosym32
to the beginning of the assembler input.See Section
"MIPS symbol sizes".
| |
-nocpp | |
This option is ignored. It is accepted for command-line compatibility with
other assemblers, which use it to turn off C style preprocessing. With GNU
as,
there is no need for
-nocpp,
because the GNU assembler itself never runs the C preprocessor.
| |
--construct-floats
--no-construct-floats | |
The
--no-construct-floats
option disables the construction of double width floating point constants
by loading the two halves of the value into the two single width floating
point registers that make up the double width register. This feature is useful
if the processor support the FR bit in its status register, and this bit is
known (by the programmer) to be set. This bit prevents the aliasing of the
double width register by the single width registers.
By default --construct-floats is selected, allowing construction of these floating point constants.
| |
--trap
--no-break | |
as
automatically macro expands certain division and multiplication instructions
to check for overflow and division by zero. This option causes
as
to generate code to take a trap exception rather than a break exception when
an error is detected. The trap instructions are only supported at Instruction
Set Architecture level 2 and higher.
| |
--break
--no-trap | |
Generate code to take a break exception rather than a trap exception when
an error is detected. This is the default.
| |
-mpdr
-mno-pdr | |
Control generation of
.pdr
sections. Off by default on IRIX, on elsewhere.
| |
-mshared
-mno-shared | |
When generating code using the Unix calling conventions (selected by -KPIC or -mcall_shared), gas will normally generate code which can go into a shared library. The -mno-shared option tells gas to generate code which uses the calling convention, but can not go into a shared library. The resulting code is slightly more efficient. This option only affects the handling of the .cpload and .cpsetup pseudo-ops. | |
When assembling for ecoff, the assembler uses the $gp ( $28) register to form the address of a “small object”. Any object in the .sdata or .sbss sections is considered “small” in this sense. For external objects, or for objects in the .bss section, you can use the gcc -G option to control the size of objects addressed via $gp; the default value is 8, meaning that a reference to any object eight bytes or smaller uses $gp. Passing -G 0 to as prevents it from using the $gp register on the basis of object size (but the assembler uses $gp for objects in .sdata or sbss in any case). The size of an object in the .bss section is set by the .comm or .lcomm directive that defines it. The size of an external object may be set with the .extern directive. For example, .extern sym,4 declares that the object at sym is 4 bytes in length, whie leaving sym otherwise undefined.
Using small ecoff objects requires linker support, and assumes that the $gp register is correctly initialized (normally done automatically by the startup code). mips ecoff assembly code must not modify the $gp register.
lui $4,%highest(sym) lui $1,%hi(sym) daddiu $4,$4,%higher(sym) daddiu $1,$1,%lo(sym) dsll32 $4,$4,0 daddu $4,$4,$1
whereas the 32-bit expansion is simply:
lui $4,%hi(sym) daddiu $4,$4,%lo(sym)
n64 code is sometimes constructed in such a way that all symbolic constants are known to have 32-bit values, and in such cases, it's preferable to use the 32-bit expansion instead of the 64-bit expansion.
You can use the .set sym32 directive to tell the assembler that, from this point on, all expressions of the form symbol or symbol + offset have 32-bit values. For example:
amp;.set sym32 dla $4,sym lw $4,sym+16 sw $4,sym+0x8000($4)
will cause the assembler to treat sym, sym+16 and sym+0x8000 as 32-bit values. The handling of non-symbolic addresses is not affected.
The directive .set nosym32 ends a .set sym32 block and reverts to the normal behavior. It is also possible to change the symbol size using the command-line options [-msym32] and [-mno-sym32].
These options and directives are always accepted, but at present, they have no effect for anything other than n64.
The .set arch= cpu directive provides even finer control. It changes the effective CPU target and allows the assembler to use instructions specific to a particular CPU. All CPUs supported by the -march command line option are also selectable by this directive. The original value is restored by .set arch=default.
The directive .set mips16 puts the assembler into MIPS 16 mode, in which it will assemble instructions for the MIPS 16 processor. Use .set nomips16 to return to normal 32 bit mode.
Traditional mips assemblers do not support this directive.
This directive is only meaningful when in MIPS 16 mode. Traditional mips assemblers do not support this directive.
These directives can be useful inside an macro which must change an option such as the ISA level or instruction reordering but does not want to change the state of the code which invoked the macro.
Traditional mips assemblers do not support these directives.
The directive .set smartmips makes the assembler accept instructions from the SmartMIPS Application Specific Extension to the MIPS32 isa from that point on in the assembly. The .set nosmartmips directive prevents SmartMIPS instructions from being accepted.
The directive .set mdmx makes the assembler accept instructions from the MDMX Application Specific Extension from that point on in the assembly. The .set nomdmx directive prevents MDMX instructions from being accepted.
The directive .set dsp makes the assembler accept instructions from the DSP Release 1 Application Specific Extension from that point on in the assembly. The .set nodsp directive prevents DSP Release 1 instructions from being accepted.
The directive .set dspr2 makes the assembler accept instructions from the DSP Release 2 Application Specific Extension from that point on in the assembly. This dirctive implies .set dsp. The .set nodspr2 directive prevents DSP Release 2 instructions from being accepted.
The directive .set mt makes the assembler accept instructions from the MT Application Specific Extension from that point on in the assembly. The .set nomt directive prevents MT instructions from being accepted.
Traditional mips assemblers do not support these directives.
The following table lists all available PowerPC options.
-mpwrx | -mpwr2 | |
Generate code for POWER/2 (RIOS2).
| |
-mpwr |
Generate code for POWER (RIOS1)
|
-m601 |
Generate code for PowerPC 601.
|
-mppc, -mppc32, -m603, -m604 | |
Generate code for PowerPC 603/604.
| |
-m403, -m405 | |
Generate code for PowerPC 403/405.
| |
-m440 |
Generate code for PowerPC 440. BookE and some 405 instructions.
|
-m7400, -m7410, -m7450, -m7455 | |
Generate code for PowerPC 7400/7410/7450/7455.
| |
-mppc64, -m620 | |
Generate code for PowerPC 620/625/630.
| |
-me500, -me500x2 | |
Generate code for Motorola e500 core complex.
| |
-mspe |
Generate code for Motorola SPE instructions.
|
-mppc64bridge | |
Generate code for PowerPC 64, including bridge insns.
| |
-mbooke64 | |
Generate code for 64-bit BookE.
| |
-mbooke, mbooke32 | |
Generate code for 32-bit BookE.
| |
-me300 | |
Generate code for PowerPC e300 family.
| |
-maltivec | |
Generate code for processors with AltiVec instructions.
| |
-mpower4 | |
Generate code for Power4 architecture.
| |
-mpower5 | |
Generate code for Power5 architecture.
| |
-mpower6 | |
Generate code for Power6 architecture.
| |
-mcell | |
Generate code for Cell Broadband Engine architecture.
| |
-mcom |
Generate code Power/PowerPC common instructions.
|
-many |
Generate code for any architecture (PWR/PWRX/PPC).
|
-mregnames | |
Allow symbolic names for registers.
| |
-mno-regnames | |
Do not allow symbolic names for registers.
| |
-mrelocatable | |
Support for GCC's -mrelocatable option.
| |
-mrelocatable-lib | |
Support for GCC's -mrelocatable-lib option.
| |
-memb |
Set PPC_EMB bit in ELF flags.
|
-mlittle, -mlittle-endian | |
Generate code for a little endian machine.
| |
-mbig, -mbig-endian | |
Generate code for a big endian machine.
| |
-msolaris | |
Generate code for Solaris.
| |
-mno-solaris | |
Do not generate code for Solaris. | |
.machine string | |
This directive allows you to change the machine for which code is generated. string may be any of the -m cpu selection options (without the -m) enclosed in double quotes, push, or pop. .machine push saves the currently selected cpu, which may be restored with .machine pop. | |
By default, as assumes the core instruction set (SPARC v6), but “bumps” the architecture level as needed: it switches to successively higher architectures as it encounters instructions that only exist in the higher levels.
If not configured for SPARC v9 ( sparc64-*-*) GAS will not bump passed sparclite by default, an option must be passed to enable the v9 instructions.
GAS treats sparclite as being compatible with v8, unless an architecture is explicitly requested. SPARC v9 is always incompatible with sparclite.
-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite
-Av8plus | -Av8plusa | -Av9 | -Av9a | |
Use one of the
-A
options to select one of the SPARC architectures explicitly. If you select
an architecture explicitly,
as
reports a fatal error if it encounters an instruction or feature requiring
an incompatible or higher level.
-Av8plus and -Av8plusa select a 32 bit environment. -Av9 and -Av9a select a 64 bit environment and are not available unless GAS is explicitly configured with 64 bit environment support. -Av8plusa and -Av9a enable the SPARC V9 instruction set with UltraSPARC extensions.
| |
-xarch=v8plus | -xarch=v8plusa | |
For compatibility with the Solaris v9 assembler. These options are equivalent
to -Av8plus and -Av8plusa, respectively.
| |
-bump |
Warn whenever it is necessary to switch to another level. If an architecture
level is explicitly requested, GAS will not issue warnings until that level
is reached, and will then bump the level as required (except between incompatible
levels).
|
-32 | -64 | |
Select the word size, either 32 bits or 64 bits. These options are only available with the ELF object file format, and require that the necessary BFD support has been included. | |
You can use the --enforce-aligned-data option to make SPARC GAS also issue an error about misaligned data, just as the SunOS and Solaris assemblers do.
The --enforce-aligned-data option is not the default because gcc issues misaligned data pseudo-ops when it initializes certain packed data structures (structures defined using the packed attribute). You may have to assemble with GAS in order to initialize packed data structures in your own code.
.align |
This must be followed by the desired alignment in bytes.
|
.common | |
This must be followed by a symbol name, a positive number, and
bss.
This behaves somewhat like
.comm,
but the syntax is different.
| |
.half |
This is functionally identical to
.short.
|
.nword |
On the Sparc, the
.nword
directive produces native word sized value, ie. if assembling with -32 it
is equivalent to
.word,
if assembling with -64 it is equivalent to
.xword.
|
.proc |
This directive is ignored. Any text following it on the same line is also
ignored.
|
.register | |
This directive declares use of a global application or system register. It
must be followed by a register name %g2, %g3, %g6 or %g7, comma and the symbol
name for that register. If symbol name is
#scratch,
it is a scratch register, if it is
#ignore,
it just suppresses any errors about using undeclared global register, but
does not emit any information about it into the object file. This can be useful
e.g. if you save the register before use and restore it after.
| |
.reserve | |
This must be followed by a symbol name, a positive number, and
bss.
This behaves somewhat like
.lcomm,
but the syntax is different.
| |
.seg |
This must be followed by
text,
data,
or
data1.
It behaves like
.text,
.data,
or
.data 1.
|
.skip |
This is functionally identical to the
.space
directive.
|
.word |
On the Sparc, the
.word
directive produces 32 bit values, instead of the 16 bit values it produces
on many other machines.
|
.xword | On the Sparc V9 processor, the .xword directive produces 64 bit values. |
Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of as work better. Bug reports are your contribution to the maintenance of as.
In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.
You can find contact information for many support companies and individuals in the file etc/SERVICE in the GNU Emacs distribution.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of a symbol you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the assembler into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug if it is new to us. Therefore, always write your bug reports on the assumption that the bug has not been reported previously.
Sometimes people give a few sketchy facts and ask, “Does this ring a bell?” This cannot help us fix a bug, so it is basically useless. We respond by asking for enough details to enable us to investigate. You might as well expedite matters by sending them to begin with.
To enable us to fix the bug, you should include all these things:
Without this, we will not know whether there is any point in looking for the bug in the current version of as.
If we were to try to guess the arguments, we would probably guess wrong and then we might not encounter the bug.
Of course, if the bug is that as gets a fatal signal, then we will certainly notice it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of as is out of sync, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and ours would not. If you told us to expect a crash, then when ours fails to crash, we would know that the bug was not happening for us. If you had not told us to expect a crash, then we would not be able to draw any conclusion from our observations.
The line numbers in our development sources will not match those in your sources. Your line numbers would convey no useful information to us.
Here are some things that are not necessary:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. We recommend that you save your time for something else.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience for us. Errors in the output will be easier to spot, running under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug anyway and send us the entire test case you used.
A patch for the bug does help us if it is a good one. But do not omit the necessary information, such as the test case, on the assumption that a patch is all we need. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.
Sometimes with a program as complicated as as it is very hard to construct an example that will make the program follow a certain path through the code. If you do not send us the example, we will not be able to construct one, so we will not be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should be an improvement, we will not install it. A test case will help us to understand.
Such guesses are usually wrong. Even we cannot guess right about such things without first using the debugger to find the facts.
Dean Elsner wrote the original GNU assembler for the VAX.
Jay Fenlason maintained GAS for a while, adding support for GDB-specific debug information and the 68k series machines, most of the preprocessing pass, and extensive changes in messages.c, input-file.c, write.c.
K. Richard Pixley maintained GAS for a while, adding various enhancements and many bug fixes, including merging support for several processors, breaking GAS up to handle multiple object file format back ends (including heavy rewrite, testing, an integration of the coff and b.out back ends), adding configuration including heavy testing and verification of cross assemblers and file splits and renaming, converted GAS to strictly ANSI C including full prototypes, added support for m680[34]0 and cpu32, did considerable work on i960 including a COFF port (including considerable amounts of reverse engineering), a SPARC opcode file rewrite, DECstation, rs6000, and hp300hpux host ports, updated “know” assertions and made them work, much other reorganization, cleanup, and lint.
Ken Raeburn wrote the high-level BFD interface code to replace most of the code in format-specific I/O modules.
The original VMS support was contributed by David L. Kashtan. Eric Youngdale has done much work with it since.
The Intel 80386 machine description was written by Eliot Dresselhaus.
Minh Tran-Le at IntelliCorp contributed some AIX 386 support.
The Motorola 88k machine description was contributed by Devon Bowen of Buffalo University and Torbjorn Granlund of the Swedish Institute of Computer Science.
Keith Knowles at the Open Software Foundation wrote the original MIPS back end ( tc-mips.c, tc-mips.h), and contributed Rose format support (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to support a.out format.
Support for the Zilog Z8k and Renesas H8/300 processors (tc-z8k, tc-h8300), and IEEE 695 object file format (obj-ieee), was written by Steve Chamberlain of CyGNUs Support. Steve also modified the COFF back end to use BFD for some low-level operations, for use with the H8/300 and AMD 29k targets.
John Gilmore built the AMD 29000 support, added .include support, and simplified the configuration of which versions accept which directives. He updated the 68k machine description so that Motorola's opcodes always produced fixed-size instructions (e.g., jsr), while synthetic instructions remained shrinkable ( jbsr). John fixed many bugs, including true tested cross-compilation support, and one bug in relaxation that took a week and required the proverbial one-bit fix.
Ian Lance Taylor of CyGNUs Support merged the Motorola and MIT syntax for the 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix), added support for MIPS ECOFF and ELF targets, wrote the initial RS/6000 and PowerPC assembler, and made a few other minor patches.
Steve Chamberlain made GAS able to generate listings.
Hewlett-Packard contributed support for the HP9000/300.
Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM) along with a fairly extensive HPPA testsuite (for both SOM and ELF object formats). This work was supported by both the Center for Software Science at the University of Utah and CyGNUs Support.
Support for ELF format files has been worked on by Mark Eichin of CyGNUs Support (original, incomplete implementation for SPARC), Pete Hoogenboom and Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open Software Foundation (i386 mainly), and Ken Raeburn of CyGNUs Support (sparc, and some initial 64-bit support).
Linas Vepstas added GAS support for the ESA/390 “IBM 370” architecture.
Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD support for openVMS/Alpha.
Timothy Wall, Michael Hayes, and Greg Smart contributed to the various tic* flavors.
David Heine, Sterling Augustine, Bob Wilson and John Ruttenberg from Tensilica, Inc. added support for Xtensa processors.
Several engineers at CyGNUs Support have also provided many small bug fixes and configuration enhancements.
Many others have contributed large or small bugfixes and enhancements. If you have contributed significant work and are not mentioned on this list, and want to be, let us know. Some of the history has been lost; we are not intentionally leaving anyone out.
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
The purpose of this License is to make a manual, textbook, or other written document “free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you.”
A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.
A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License.
The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License.
A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent. A copy that is not “Transparent” is called “Opaque.”
Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML designed for human modification. Opaque formats include PostScript, PDF, proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML produced by some word processors for output purposes only.
The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.
You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission. B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has less than five). C. State on the Title page the name of the publisher of the Modified Version, as the publisher. D. Preserve all the copyright notices of the Document. E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices. F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below. G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice. H. Include an unaltered copy of this License. I. Preserve the section entitled “History”, and its title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence. J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission. K. In any section entitled “Acknowledgements” or “Dedications”, preserve the section's title, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein. L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles. M. Delete any section entitled “Endorsements.” Such a section may not be included in the Modified Version. N. Do not retitle any existing section as “Endorsements” or to conflict in title with any Invariant Section.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections entitled “History” in the various original documents, forming one section entitled “History”; likewise combine any sections entitled “Acknowledgements”, and any sections entitled “Dedications.” You must delete all sections entitled “Endorsements.”
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an “aggregate”, and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around the whole aggregate.
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list. A copy of the license is included in the section entitled "GNU Free Documentation License."
If you have no Invariant Sections, write “with no Invariant Sections” instead of saying which ones are invariant. If you have no Front-Cover Texts, write “no Front-Cover Texts” instead of “Front-Cover Texts being list ”; likewise for Back-Cover Texts.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
AS (7) | 2015-03-02 |
Main index | Section 7 | Options |
Please direct any comments about this manual page service to Ben Bullock. Privacy policy.
“ | Modern Unix impedes progress in computer science, wastes billions of dollars, and destroys the common sense of many who seriously use it. | ” |
— The Unix Haters' handbook |