GNU Assembler

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GNU Assembler
Stable release 2.20 / October 19, 2009; 136571315 ago
Platform Cross-platform

The GNU Assembler, commonly known as Gas, is the assembler used by the GNU Project. It is the default back-end of gcc. It is used to compile the GNU operating system and the Linux kernel, and various other software. It is a part of the GNU Binutils package.

Gas's executable is named after as, a Unix assembler. Gas is cross-platform, and both runs on and assembles for a number of different computer architectures. Released under the GNU General Public License, Gas is free software.


General syntax

The GNU Assembler has a general syntax that works for all of the supported architectures. The general syntax includes assembler directives and a method for commenting.

Assembler directives

The GNU Assembler uses assembler directives (also known as pseudo ops), which are keywords beginning with a period that behave similarly to preprocessor directives in the C programming language. While most of the available assembler directives are valid regardless of the target architecture, some directives are machine dependent.[1]


Gas uses the # symbol for a single-line comment.

For example:

    pop  %edx # this is a comment
# as well as this
    movl %edx,%eax


One source of criticism is the fact that on the x86 and x86-64 architecture it uses the AT&T assembler syntax, rather than the Intel syntax used in many other assemblers; however, since version 2.10[2], support for the Intel syntax via the .intel_syntax directive has been added.[3][4]

See also


External links

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