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8.13.1 Options

The i386 version of as has a few machine dependent options:

--32 | --64
Select the word size, either 32 bits or 64 bits. Selecting 32-bit implies Intel i386 architecture, while 64-bit implies AMD x86-64 architecture.

These options are only available with the ELF object file format, and require that the necessary BFD support has been included (on a 32-bit platform you have to add –enable-64-bit-bfd to configure enable 64-bit usage and use x86-64 as target platform).

By default, x86 GAS replaces multiple nop instructions used for alignment within code sections with multi-byte nop instructions such as leal 0(%esi,1),%esi. This switch disables the optimization.

On SVR4-derived platforms, the character `/' is treated as a comment character, which means that it cannot be used in expressions. The `--divide' option turns `/' into a normal character. This does not disable `/' at the beginning of a line starting a comment, or affect using `#' for starting a comment.

This option specifies an instruction set architecture for generating instructions. The following architectures are recognized: i8086, i186, i286, i386, i486, i586, i686, pentium, pentiumpro, pentiumii, pentiumiii, pentium4, prescott, nocona, core, core2, k6, k6_2, athlon, sledgehammer, opteron, k8, generic32 and generic64.

This option only affects instructions generated by the assembler. The .arch directive will take precedent.

This option specifies a processor to optimize for. When used in conjunction with the -march option, only instructions of the processor specified by the -march option will be generated.

Valid CPU values are identical to -march=CPU.