Re: i686 repository

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On Tuesday 09 March 2004 16:49, nyook wrote:
> Colin Charles wrote:
> > On Wed, 2004-03-10 at 00:25, Phil Hannent wrote:
> >>Does anyone know of a repository that has i686 binaries compiled for
> >> fedora?
> >
> > They are all i686 optimised.
>
> I see. Does that mean that although the files are labeled i386 they are
> compiled for i386 "under the hood"?

See the difference between the -march and -mcpu from the gcc man page:

 -mcpu=cpu-type
           Tune to cpu-type everything applicable about the generated code,
           except for the ABI and the set of available instructions.  The
           choices for cpu-type are i386, i486, i586, i686, pentium, pentium-
           mmx, pentiumpro, pentium2, pentium3, pentium4, k6, k6-2, k6-3,
           athlon, athlon-tbird, athlon-4, athlon-xp, athlon-mp, winchip-c6,
           winchip2 and c3.

           While picking a specific cpu-type will schedule things appropri-
           ately for that particular chip, the compiler will not generate any
           code that does not run on the i386 without the -march=cpu-type
           option being used.  i586 is equivalent to pentium and i686 is
           equivalent to pentiumpro.  k6 and athlon are the AMD chips as
           opposed to the Intel ones.

       -march=cpu-type
           Generate instructions for the machine type cpu-type.  The choices
           for cpu-type are the same as for -mcpu.  Moreover, specifying
           -march=cpu-type implies -mcpu=cpu-type.

So, if you compile a package with -march=i386 -mcpu=i686 (which is the default 
for RedHat/Fedora) the code will still run on a i586 system but it will be 
actually optimized for i686.


Mihai




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