From Linux Man Pages
AS - the portable GNU assembler.
SYNOPSIS
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 Alpha options:
[-mcpu]
[-mdebug | -no-mdebug]
[-relax] [-g] [-Gsize]
[-F] [-32addr]
Target ARC options:
[-marc[5|6|7|8]]
[-EB|-EL]
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 CRIS options:
[--underscore | --no-underscore]
[--pic] [-N]
[--emulation=criself | --emulation=crisaout]
[--march=v0_v10 | --march=v10 | --march=v32 | --march=common_v10_v32]
Target D10V options:
[-O]
Target D30V options:
[-O|-n|-N]
Target i386 options:
[--32|--64] [-n]
[-march=CPU] [-mtune=CPU]
Target i960 options:
[-ACA|-ACA_A|-ACB|-ACC|-AKA|-AKB|
-AKC|-AMC]
[-b] [-no-relax]
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 IP2K options:
[-mip2022|-mip2022ext]
Target M32C options:
[-m32c|-m16c]
Target M32R options:
[--m32rx|--[no-]warn-explicit-parallel-conflicts|
--W[n]p]
Target M680X0 options:
[-l] [-m68000|-m68010|-m68020|...]
Target M68HC11 options:
[-m68hc11|-m68hc12|-m68hcs12]
[-mshort|-mlong]
[-mshort-double|-mlong-double]
[--force-long-branches] [--short-branches]
[--strict-direct-mode] [--print-insn-syntax]
[--print-opcodes] [--generate-example]
Target MCORE options:
[-jsri2bsr] [-sifilter] [-relax]
[-mcpu=[210|340]]
Target MIPS options:
[-nocpp] [-EL] [-EB] [-O[optimization level]]
[-g[debug level]] [-G num] [-KPIC] [-call_shared]
[-non_shared] [-xgot]
[-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]
[-mmt] [-mno-mt]
[-mdebug] [-no-mdebug]
[-mpdr] [-mno-pdr]
Target MMIX options:
[--fixed-special-register-names] [--globalize-symbols]
[--gnu-syntax] [--relax] [--no-predefined-symbols]
[--no-expand] [--no-merge-gregs] [-x]
[--linker-allocated-gregs]
Target PDP11 options:
[-mpic|-mno-pic] [-mall] [-mno-extensions]
[-mextension|-mno-extension]
[-mcpu] [-mmachine]
Target picoJava options:
[-mb|-me]
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]
Target TIC54X options:
[-mcpu=54[123589]|-mcpu=54[56]lp] [-mfar-mode|-mf]
[-merrors-to-file <filename>|-me <filename>]
Target Z80 options:
[-z80] [-r800]
[ -ignore-undocumented-instructions] [-Wnud]
[ -ignore-unportable-instructions] [-Wnup]
[ -warn-undocumented-instructions] [-Wud]
[ -warn-unportable-instructions] [-Wup]
[ -forbid-undocumented-instructions] [-Fud]
[ -forbid-unportable-instructions] [-Fup]
Target Xtensa options:
[--[no-]text-section-literals] [--[no-]absolute-literals]
[--[no-]target-align] [--[no-]longcalls]
[--[no-]transform]
[--rename-section oldname=newname]
DESCRIPTION
GNU as is really a family of assemblers. If you use (or have used) the GNU assembler on one architecture, you
should find a fairly similar environment when you use it on another architecture. Each version has much in com-
mon with the others, including object file formats, most assembler directives (often called pseudo-ops) and
assembler syntax.
as is primarily intended to assemble the output of the GNU C compiler "gcc" for use by the linker "ld". Never-
theless, we've tried to make as assemble correctly everything that other assemblers for the same machine would
assemble. Any exceptions are documented explicitly. This doesn't mean as always uses the same syntax as another
assembler for the same architecture; for example, we know of several incompatible versions of 680x0 assembly lan-
guage syntax.
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.
as may write warnings and error messages to the standard error file (usually your terminal). This should not
happen when a compiler runs as automatically. Warnings report an assumption made so that as could keep assem-
bling a flawed program; errors report a grave problem that stops the assembly.
If you are invoking as via the GNU C compiler, you can use the -Wa option to pass arguments through to the assem-
bler. 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 pre-
cisely what options it passes to each compilation pass, including the assembler.)
OPTIONS
@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 sur-
rounding 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.
-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.
-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 assem-
bling 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 Issue warnings when difference tables altered for long displacements.
-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.
--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. Cur-
rently 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.
The following options are available when as is configured for an ARC processor.
-marc[5|6|7|8]
This option selects the core processor variant.
-EB | -EL
Select either big-endian (-EB) or little-endian (-EL) output.
The following options are available when as is configured for the ARM processor family.
-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.
See the info pages for documentation of the CRIS-specific options.
The following options are available when as is configured for a D10V processor.
-O Optimize output by parallelizing instructions.
The following options are available when as is configured for a D30V processor.
-O Optimize output by parallelizing instructions.
-n Warn when nops are generated.
-N Warn when a nop after a 32-bit multiply instruction is generated.
The following options are available when as is configured for the Intel 80960 processor.
-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
Specify which variant of the 960 architecture is the target.
-b Add code to collect statistics about branches taken.
-no-relax
Do not alter compare-and-branch instructions for long displacements; error if necessary.
The following options are available when as is configured for the Ubicom IP2K series.
-mip2022ext
Specifies that the extended IP2022 instructions are allowed.
-mip2022
Restores the default behaviour, which restricts the permitted instructions to just the basic IP2022 ones.
The following options are available when as is configured for the Renesas M32C and M16C processors.
-m32c
Assemble M32C instructions.
-m16c
Assemble M16C instructions (the default).
The following options are available when as is configured for the Renesas M32R (formerly Mitsubishi M32R) series.
--m32rx
Specify which processor in the M32R family is the target. The default is normally the M32R, but this option
changes it to the M32RX.
--warn-explicit-parallel-conflicts or --Wp
Produce warning messages when questionable parallel constructs are encountered.
--no-warn-explicit-parallel-conflicts or --Wnp
Do not produce warning messages when questionable parallel constructs are encountered.
The following options are available when as is configured for the Motorola 68000 series.
-l Shorten references to undefined symbols, to one word instead of two.
-m68000 | -m68008 | -m68010 | -m68020 | -m68030
| -m68040 | -m68060 | -m68302 | -m68331 | -m68332
| -m68333 | -m68340 | -mcpu32 | -m5200
Specify what processor in the 68000 family is the target. The default is normally the 68020, but this can be
changed at configuration time.
-m68881 | -m68882 | -mno-68881 | -mno-68882
The target machine does (or does not) have a floating-point coprocessor. The default is to assume a copro-
cessor for 68020, 68030, and cpu32. Although the basic 68000 is not compatible with the 68881, a combination
of the two can be specified, since it's possible to do emulation of the coprocessor instructions with the
main processor.
-m68851 | -mno-68851
The target machine does (or does not) have a memory-management unit coprocessor. The default is to assume an
MMU for 68020 and up.
For details about the PDP-11 machine dependent features options, see PDP-11-Options.
-mpic | -mno-pic
Generate position-independent (or position-dependent) code. The default is -mpic.
-mall
-mall-extensions
Enable all instruction set extensions. This is the default.
-mno-extensions
Disable all instruction set extensions.
-mextension | -mno-extension
Enable (or disable) a particular instruction set extension.
-mcpu
Enable the instruction set extensions supported by a particular CPU, and disable all other extensions.
-mmachine
Enable the instruction set extensions supported by a particular machine model, and disable all other exten-
sions.
The following options are available when as is configured for a picoJava processor.
-mb Generate "big endian" format output.
-ml Generate "little endian" format output.
The following options are available when as is configured for the Motorola 68HC11 or 68HC12 series.
-m68hc11 | -m68hc12 | -m68hcs12
Specify what processor is the target. The default is defined by the configuration option when building the
assembler.
-mshort
Specify to use the 16-bit integer ABI.
-mlong
Specify to use the 32-bit integer ABI.
-mshort-double
Specify to use the 32-bit double ABI.
-mlong-double
Specify to use the 64-bit double ABI.
--force-long-branches
Relative branches are turned into absolute ones. This concerns conditional branches, unconditional branches
and branches to a sub routine.
-S | --short-branches
Do not turn relative branches into absolute ones when the offset is out of range.
--strict-direct-mode
Do not turn the direct addressing mode into extended addressing mode when the instruction does not support
direct addressing mode.
--print-insn-syntax
Print the syntax of instruction in case of error.
--print-opcodes
print the list of instructions with syntax and then exit.
--generate-example
print an example of instruction for each possible instruction and then exit. This option is only useful for
testing as.
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 the 'c54x architecture.
-mfar-mode
Enable extended addressing mode. All addresses and relocations will assume extended addressing (usually 23
bits).
-mcpu=CPU_VERSION
Sets the CPU version being compiled for.
-merrors-to-file FILENAME
Redirect error output to a file, for broken systems which don't support such behaviour in the shell.
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 reg-
isters 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 instruc-
tions. -no-mdmx turns off this option.
-mdsp
-mno-dsp
Generate code for the DSP Application Specific Extension. This tells the assembler to accept DSP instruc-
tions. -mno-dsp 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 load-
ing 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 for-
mat (choosing between ELF and ECOFF only), handling of pseudo-opcodes which may generate debugging informa-
tion 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 endi-
anness 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 endian-
ness 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 configura-
tion 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 syn-
onyms) 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.
The following options are available when as is configured for an MCore processor.
-jsri2bsr
-nojsri2bsr
Enable or disable the JSRI to BSR transformation. By default this is enabled. The command line option
-nojsri2bsr can be used to disable it.
-sifilter
-nosifilter
Enable or disable the silicon filter behaviour. By default this is disabled. The default can be overridden
by the -sifilter command line option.
-relax
Alter jump instructions for long displacements.
-mcpu=[210|340]
Select the cpu type on the target hardware. This controls which instructions can be assembled.
-EB Assemble for a big endian target.
-EL Assemble for a little endian target.
See the info pages for documentation of the MMIX-specific options.
The following options are available when as is configured for an Xtensa processor.
--text-section-literals | --no-text-section-literals
With --text-section-literals, literal pools are interspersed in the text section. The default is
--no-text-section-literals, which places literals in a separate section in the output file. These options
only affect literals referenced via PC-relative "L32R" instructions; literals for absolute mode "L32R"
instructions are handled separately.
--absolute-literals | --no-absolute-literals
Indicate to the assembler whether "L32R" instructions use absolute or PC-relative addressing. The default is
to assume absolute addressing if the Xtensa processor includes the absolute "L32R" addressing option. Other-
wise, only the PC-relative "L32R" mode can be used.
--target-align | --no-target-align
Enable or disable automatic alignment to reduce branch penalties at the expense of some code density. The
default is --target-align.
--longcalls | --no-longcalls
Enable or disable transformation of call instructions to allow calls across a greater range of addresses.
The default is --no-longcalls.
--transform | --no-transform
Enable or disable all assembler transformations of Xtensa instructions. The default is --transform;
--no-transform should be used only in the rare cases when the instructions must be exactly as specified in
the assembly source.
The following options are available when as is configured for a Z80 family processor.
-z80
Assemble for Z80 processor.
-r800
Assemble for R800 processor.
-ignore-undocumented-instructions
-Wnud
Assemble undocumented Z80 instructions that also work on R800 without warning.
-ignore-unportable-instructions
-Wnup
Assemble all undocumented Z80 instructions without warning.
-warn-undocumented-instructions
-Wud
Issue a warning for undocumented Z80 instructions that also work on R800.
-warn-unportable-instructions
-Wup
Issue a warning for undocumented Z80 instructions that do not work on R800.
-forbid-undocumented-instructions
-Fud
Treat all undocumented instructions as errors.
-forbid-unportable-instructions
-Fup
Treat undocumented Z80 instructions that do not work on R800 as errors.
RELATED
gcc(1), ld(1), and the Info entries for binutils and ld.
COPYRIGHT
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002, 2006 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documenta-
tion License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sec-
tions, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section
entitled "GNU Free Documentation License".
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