AS - the portable GNU assembler.
as [ -a
[ --defsym sym
] [-I dir
Target Alpha options:
Target ARC options:
Target ARM options:
Target CRIS options:
Target D10V options:
Target D30V options:
Target i386 options:
Target i960 options:
Target IA-64 options:
Target IP2K options:
Target M32C options:
Target M32R options:
Target M680X0 options:
Target M68HC11 options:
Target MCORE options:
Target MIPS options:
]] [-G num
] [ -mgp32
Target MMIX options:
Target PDP11 options:
Target picoJava options:
Target PowerPC options:
Target SPARC options:
Target TIC54X options:
[ -merrors-to-file <filename>
Target Z80 options:
Target Xtensa options:
[ --rename-section oldname
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
common with the others, including object file formats, most assembler
directives (often called pseudo-ops
) and assembler syntax.
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. 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 language 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
If you give as
no file names it attempts to read one input file from the
standard input, which is normally your terminal. You may have to
to tell as
there is no more program to assemble.
if you need to explicitly name the standard input file in your
If the source is empty, as
produces a small, empty object file.
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
assembling a flawed program; errors report a grave problem that stops the
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
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
see precisely what options it passes to each compilation pass, including the
- 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
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.
- Turn on listings, in any of a variety of ways:
- omit false conditionals
- omit debugging directives
- include high-level source
- include assembly
- include macro expansions
- omit forms processing
- include symbols
- 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
- Begin in alternate macro mode.
- Ignored. This option is accepted for script compatibility with calls to
- --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.
- "fast"---skip whitespace and comment preprocessing (assume
source is compiler output).
- 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.
- Generate stabs debugging information for each assembler line. This may
help debugging assembler code, if the debugger can handle it.
- 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.
- 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.
- Print a summary of the command line options and exit.
- Print a summary of all target specific options and exit.
- -I dir
- Add directory dir to the search list for ".include"
- Don't warn about signed overflow.
- Issue warnings when difference tables altered for long displacements.
- 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.
- Set the maximum width, in words, of the output data column for an
assembler listing to number.
- Set the maximum width, in words, of the output data column for
continuation lines in an assembler listing to number.
- Set the maximum width of an input source line, as displayed in a listing,
to number bytes.
- 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.
- 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.
- 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
- Print the maximum space (in bytes) and total time (in seconds) used by
- Remove local absolute symbols from the outgoing symbol table.
- Print the as version.
- Print the as version and exit.
- Suppress warning messages.
- Treat warnings as errors.
- Don't suppress warning messages or treat them as errors.
- 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.
- 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
- Specify which ARM processor variant is the target.
- Specify which ARM architecture variant is used by the target.
- Select which Floating Point architecture is the target.
- Select which floating point ABI is in use.
- 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.
- Specify that the code has been generated with interworking between Thumb
and ARM code in mind.
- 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.
- Optimize output by parallelizing instructions.
The following options are available when as is configured for a D30V processor.
- Optimize output by parallelizing instructions.
- Warn when nops are generated.
- 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
- -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
- Specify which variant of the 960 architecture is the target.
- Add code to collect statistics about branches taken.
- Do not alter compare-and-branch instructions for long displacements; error
The following options are available when as is configured for the Ubicom IP2K
- Specifies that the extended IP2022 instructions are allowed.
- 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.
- Assemble M32C instructions.
- Assemble M16C instructions (the default).
The following options are available when as is configured for the Renesas M32R
(formerly Mitsubishi M32R) series.
- 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
- --no-warn-explicit-parallel-conflicts or --Wnp
- Do not produce warning messages when questionable parallel constructs are
The following options are available when as is configured for the Motorola 68000
- 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 coprocessor 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
- -mpic | -mno-pic
- Generate position-independent (or position-dependent) code. The default is
- Enable all instruction set extensions. This is the default.
- Disable all instruction set extensions.
- -mextension | -mno-extension
- Enable (or disable) a particular instruction set extension.
- Enable the instruction set extensions supported by a particular CPU, and
disable all other extensions.
- Enable the instruction set extensions supported by a particular machine
model, and disable all other extensions.
The following options are available when as is configured for a picoJava
- Generate "big endian" format output.
- 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.
- Specify to use the 16-bit integer ABI.
- Specify to use the 32-bit integer ABI.
- Specify to use the 32-bit double ABI.
- Specify to use the 64-bit double ABI.
- 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
- Do not turn the direct addressing mode into extended addressing mode when
the instruction does not support direct addressing mode.
- Print the syntax of instruction in case of error.
- print the list of instructions with syntax and then exit.
- 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
- -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
- -xarch=v8plus | -xarch=v8plusa
- For compatibility with the Solaris v9 assembler. These options are
equivalent to -Av8plus and -Av8plusa, respectively.
- Warn when the assembler switches to another architecture.
The following options are available when as is configured for the 'c54x
- Enable extended addressing mode. All addresses and relocations will assume
extended addressing (usually 23 bits).
- 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.
- Generate "big endian" format output.
- Generate "little endian" format output.
- 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
- Generate code for a particular MIPS cpu.
- Schedule and tune for a particular MIPS cpu.
- Cause nops to be inserted if the read of the destination register of an
mfhi or mflo instruction occurs in the following two instructions.
- Cause stabs-style debugging output to go into an ECOFF-style .mdebug
section instead of the standard ELF .stabs sections.
- Control generation of ".pdr" sections.
- 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.
- 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.
- 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.
- Generate code for the MIPS-3D Application Specific Extension. This tells
the assembler to accept MIPS-3D instructions. -no-mips3d turns off
- Generate code for the MDMX Application Specific Extension. This tells the
assembler to accept MDMX instructions. -no-mdmx turns off this
- 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.
- 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.
- Generate code for the MT Application Specific Extension. This tells the
assembler to accept MT instructions. -mno-mt turns off this
- 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.
- 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
Eventually, this option will support more configurations, with more
fine-grained control over the assembler's behavior, and will be supported
for more processors.
- as ignores this option. It is accepted for compatibility with the
- 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.
- 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
- Enable or disable the JSRI to BSR transformation. By default this is
enabled. The command line option -nojsri2bsr can be used to disable
- Enable or disable the silicon filter behaviour. By default this is
disabled. The default can be overridden by the -sifilter command
- Alter jump instructions for long displacements.
- Select the cpu type on the target hardware. This controls which
instructions can be assembled.
- Assemble for a big endian target.
- 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
- --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
- --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. Otherwise, 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
- --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
- Assemble for Z80 processor.
- Assemble for R800 processor.
- Assemble undocumented Z80 instructions that also work on R800 without
- Assemble all undocumented Z80 instructions without warning.
- Issue a warning for undocumented Z80 instructions that also work on
- Issue a warning for undocumented Z80 instructions that do not work on
- Treat all undocumented instructions as errors.
- Treat undocumented Z80 instructions that do not work on R800 as
(1), and the Info entries for binutils
Copyright (c) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002, 2006, 2007
Free Software Foundation, Inc.
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 no Invariant Sections, 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