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 common 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". 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 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 assembling 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 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.)
OPTIONS
-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.
-D
Ignored. This option is accepted for script compatibility with calls to
other assemblers.
--defsymsym=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).
--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.
--gdwarf2
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.
-Idir
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. On traditional a.out systems
these start with L, but different systems have different local
label prefixes.
--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.
-oobjfile
Name the object-file output from asobjfile.
-R
Fold the data section into the text section.
--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.
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 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 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 @ref{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 extensions.
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-branchs
Relative branches are turned into absolute ones. This concerns
conditional branches, unconditional branches and branches to a
sub routine.
-S | --short-branchs
Do not turn relative branchs 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-fileFILENAME
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.
-Gnum
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.
-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.
--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.
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.
--density | --no-density
Enable or disable use of instructions from the Xtensa code density
option. This is enabled by default when the Xtensa processor supports
the code density option.
--relax | --no-relax
Enable or disable instruction relaxation. This is enabled by default.
Note: In the current implementation, these options also control whether
assembler optimizations are performed, making these options equivalent
to --generics and --no-generics.
--generics | --no-generics
Enable or disable all assembler transformations of Xtensa instructions.
The default is --generics;
--no-generics should be used only in the rare cases when the
instructions must be exactly as specified in the assembly source.
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.
--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.
SEE ALSO
gcc(1), ld(1), and the Info entries for binutils and ld.
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 License''.
