[CentOS-devel] Re: CentOS-5 on i586

Manuel Tuthill Manuel at Nebula-IT.co.uk
Mon Apr 7 18:06:42 UTC 2008

> It looks like the Geode is i586 but with cmov functionality.
> It strikes me as odd that AMD would build a 586 processor with cmov
> instructions, but also build a 686 class without that instruction set.
> Makes
> me wonder if it was an engineering snafu that was too costly to fix for
> the
> quantity they expected to sell.

Wow, that seems very odd. cmov was only part of the i686 instruction set so
this still wouldn't work with a native i686 distribution right?

BTW it was VIA not AMD who made the "engineering snafu" on the VIA C3 class
chips. Rather than being a "snafu" they interpreted the IA32 specifications
a little to literary, the CMOV is an optional instruction, but as fair as I
understand if it's optional it shouldn't be used at all (since there is no
guarantee that it will be available to all i686 cpu's) but since every other
i686 class cpu had the instruction when they were doing GCC it got left.

The GCC devs are not happy with you for pointing this out, they kindly point
you to the C3 tag for building reasons, when you explain this doesn't help
as really it's the vendors who should be building correctly and not blindly
for i686 they said well i686 means Pentiumpro and everyone can go jump.
(Personally I'm just waiting for an embedded Pentiumpro to come out that
excludes the CMOV and is perfectly valid) 

It still affects the C3 as fair as I can tell, they are still being sold but
they have been superseded by the C7.

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