[Xen-devel] Re: [RFC, PATCH 12/24] i386 Vmi processor header

[Zachary Amsden <zach@xxxxxxxxxx>]

Chuck Ebbert wrote:
> > +/* Some CPUID calls want 'count' to be placed in ecx */
> > +static inline void cpuid_count(int op, int count, int *eax, int *ebx, int *ecx,
> > +             int *edx)
> > +{
> > +     asm volatile(""::"c"(count));
> > +     vmi_cpuid(op, eax, ebx, ecx, edx);
> > +}
> >     
> You can't assume those last two statements will stay together.
> >From the gcc 4.0.2 info file:
>   
I know.  I've abused this a bit.  When we originally wrote the cpuid 
call, there were no ecx dependencies on cpuid.  Never got around to 
fixing it properly.
>   
> > <...> you can't expect a sequence of volatile `asm' instructions
> > to remain perfectly consecutive.  If you want consecutive output, use a
> > single `asm'.
> >     
> Maybe you could make vmi_cpuid always take a 'count' param, then just make cpuid
> do:
>
>         vmi_cpuid(op, 0, eax, ebx, ecx, edx);
>
> and cpuid_count do:
>
>         vmi_cpuid(op, count, eax, ebx, ecx, edx);
>   
That is the proper fix.  I'll put that in the next round.

> (And sorry about trimming the cc: but I'm reading from a digest and that list
> is too long to enter manually.)
>   
N.P.

Thanks for looking at my code,
Zach

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