Re: [Qemu-devel] 0.9.0 and svn don't build with -march=pentium2 etc.; was: Latest SVN fails to build on Fedora Core 6 (same with 0.9.0)

[Sunil Amitkumar Janki]

Thomas Orgis wrote:
> Am Thu, 22 Mar 2007 21:13:00 +0100
> schrieb Sunil Amitkumar Janki <address@hidden>: 
>
>   
> > I have seen this error as well when building with i686/pentium3/athlon
> > optimisations. As I am doing a course on x86 assembly programming
> > at the moment I can tell you that it suffers from register starvation
> > and the message tells you that there aren't enough registers left.
> >     
>
> Yeah, that's the message... what I wonder is this is to be expected.
> Does SSE steal or add registers?
> -march=pentium-mmx -m3dnow
> seems to work, though. Is it just a coincidence that gcc optimizattion
> uses some registers with high march (and SSE) that it didn't use with lower 
> march?
> I'm wondering if it's the code that is just lucky to compile with some
> march settings and not so lucky with others or if it's a gcc bug or
> whatever...
>
>
> Thomas.
>
>
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>
>   
The reason I build it with "-march=i486" is because Pentium optimisations
are really only meant for real Intel Pentium (MMX) and not for AMD K6 
(I/II/II).

You would probably be better off using "-march=k6-* -m3dnow -mmx" for
an Athlon. I have seen my Athlon slowing to a grind with a Pentium kernel
instead of an i486 or Athlon kernel.

I do not understand enough of QEMU yet, but I have checked out CVS and
am reading through its source. When I understand more I hope we can fix
this long-standing annoyance.

Do you have a 64-bit  X86 processor running 64-bit software? It doesn't
seem to suffer from this same problem. I am testing on an AMD Athlon 64
X2 (AM2) now and QEMU works with "-march=opteron" and of course KVM.

Sunil.