GNU as − the portable GNU assembler.


as [−a[dhlns]=file]] [−D] [−−defsym SYM=VAL] [−f] [−−gstabs] [−I path] [−K] [−L] [−M | −−mri] [−o objfile] [−R] [−−traditional−format] [−v] [−w] [−− | files...]

i960-only options:
[−ACA|−ACA_A|−ACB|−ACC|−AKA|−AKB|−AKC|−AMC] [−b] [−no-relax]

m680x0-only options:
[−l] [−mc68000|−mc68010|−mc68020]


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.

For information on the syntax and pseudo-ops used by GNU as, see ‘as’ entry in info (or the manual Using as: The GNU Assembler).

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 the native assembler would. 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.)

If as is given 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.

as may write warnings and error messages to the standard error file (usually your terminal). This should not happen when as is run automatically by a compiler. Warnings report an assumption made so that as could keep assembling a flawed program; errors report a grave problem that stops the assembly.



Turn on assembly listings. There are various suboptions. d omits debugging directives. h includes the high level source code; this is only available if the source file can be found, and the code was compiled with −g. l includes an assembly listing. n omits forms processing. s includes a symbol listing. = file sets the listing file name; this must be the last suboption. The default suboptions are hls.


This option is accepted only for script compatibility with calls to other assemblers; it has no effect on as.

−−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.


‘‘fast’’--skip preprocessing (assume source is compiler output).

−I path

Add path to the search list for .include directives.


Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it.


Issue warnings when difference tables altered for long displacements.


Keep (in symbol table) local symbols, starting with ‘L

−M, −−mri

Assemble in MRI compatibility mode.

−o objfile

Name the object-file output from as


Fold data section into text section


Use same format as native assembler, when possible.


Announce as version

−W, −−no-warn

Suppress warning messages.


Consider warnings to be fatal.


Just warn on warnings.

−− | files...

Source files to assemble, or standard input (−−)


(When configured for Intel 960.) Specify which variant of the 960 architecture is the target.


(When configured for Intel 960.) Add code to collect statistics about branches taken.


(When configured for Intel 960.) Do not alter compare-and-branch instructions for long displacements; error if necessary.


(When configured for Motorola 68000).

Shorten references to undefined symbols, to one word instead of two.


(When configured for Motorola 68000).
Specify what processor in the 68000 family is the target (default 68020)

Options may be in any order, and may be before, after, or between file names. The order of file names is significant.

−−’ (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.

The ‘−o’ option expects exactly one file name to follow. 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


as’ entry in info; Using as: The GNU Assembler; gcc(1), ld(1).


Copyright (c) 1991, 1992 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be included in translations approved by the Free Software Foundation instead of in the original English.