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 for use by the linker
. 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 (version 2),
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 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.
--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
This option is accepted but has no effect on the TARGET family.
-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
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
Specify what processor is the target. The default is
defined by the configuration option when building the assembler.
--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
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
-mips32
-mips64
Generate code for a particular MIPS Instruction Set Architecture level.
-mips1 corresponds to the R2000 and R3000 processors,
-mips2 to the R6000 processor, and -mips3 to the R4000
processor.
-mips5, -mips32, and -mips64 correspond
to generic MIPS V, MIPS32, and MIPS64 ISA
processors, respectively.
-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.
-mcpu=CPU
Generate code for a particular MIPS cpu. It is exactly equivalent to
-mcpu, except that there are more value of cpu
understood.
--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.
SEE ALSO
gcc(1), ld(1), and the Info entries for binutils and ld.
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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''.