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(as.info)GNU Assembler

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The GNU Assembler
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   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 (Note: Machine Dependencies).  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.

   Unlike older assemblers, `as' is designed to assemble a source
program in one pass of the source file.  This has a subtle impact on the
`.org' directive (Note: `.org'.).