GNU as [Command]

GNU as [Command]

Command GNU as

GNU as — The portable GNU assembler


as [ –a | –al | -as ][–D ][–f ][–I path ][–K ][–L ][–o objfile ][–R ][–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 680×0 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 filenames, it attempts to read one input file from the as standard input, which is normally your terminal. You may have to type Ctrl-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.


–a|–al|–as: Turn on assembly listings; –al, listing only, –as, symbols only, -a, everything.
–D: This option is accepted only for script compatibility with calls to other assemblers; it has no effect on as.
–f: “Fast”–skip preprocessing (assume source is compiler output).
–I\path: Add path to the search list for .include directives.
–K: Issue warnings when difference tables altered for long displacements.
–L: Keep (in symbol table) local symbols, starting with L.
–o\objfile: Name the object-file output from as.
–R: Fold data section into text section.
–v: Announce as version.
–W: Suppress warning messages.
––\|\files… Source files to assemble, or standard input (––).
–Avar: (When configured for Intel 960.) Specify which variant of the 960 architecture is the target.
–b: (When configured for Intel 960.) Add code to collect statistics about branches taken.
–no-relax: (When configured for Intel 960.) Do not alter compare-and-branch instructions for long displacements; error if necessary.
–l: (When configured for Motorola 68000.) Shorten references to undefined symbols to one word instead of two.
–mc68000|–mc68010|–mc68020: (When configured for Motorola 68000.) Specify which processor in the 68000 family is the target (default 68020).

Options may be in any order, and may be before, after, or between filenames. The order of filenames is significant.
The double hyphens command (—) 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 hyphen followed by one or more letters; the case of the letter is important. All options are optional.
The –o option expects exactly one filename to follow. The filename 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

See also

as entry in info

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