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
