Re: different asm code
Hendrik Visage <[email protected]> Mon, 18 Feb 2013 17:22:32 +0200
| Newsgroups | org.kernel.vger.linux-assembly |
|---|---|
| Message-ID | <CADtGFvkFR_rGnC18Z+yYFObtVOAQPXo1KrrNfT1_kOb-3Zg4XQ@mail.gmail.com> |
On Mon, Feb 18, 2013 at 7:06 AM, horseriver <[email protected]> wrote: > hi:) > > I have compiled a .S file ,using command gcc -c x.S -o x. > Then I use objdump to look up its asm code, even find that some code is not the > same as that .S file , more important is , some code in origin .S file has disappear . > > what is about the reason ? If it is due to version , why some code chould get lost after compile? Give examples please. There are several "similar"/equivalent code/instructions that the assembler could chose from. Ie. to zero a register, you could 1) mov REGISTER,0 2) xor REGISTER, REGISTER 3) mv REGISTER,g0 (on a SPARC where g0 is always zero)