Re: [PATCH] 1/5 more-asm-cleanup

[Zachary Amsden <zach@vmware.com>]

Please explain why this is a reject after looking at the cpuid macro.  
It changed recently.  Note 0 -> %ecx.

Would you prefer that I call cpuid_count and pass an explicit zero 
parameter for ecx?


/*
* Generic CPUID function
* clear %ecx since some cpus (Cyrix MII) do not set or clear %ecx
* resulting in stale register contents being returned.
*/
static inline void cpuid(unsigned int op, unsigned int *eax, unsigned 
int *ebx, unsigned int *ecx, unsigned int *edx)
{
       __asm__("cpuid"
               : "=a" (*eax),
                 "=b" (*ebx),
                 "=c" (*ecx),
                 "=d" (*edx)
               : "0" (op), "c"(0));
}


H. Peter Anvin wrote:

> zach@vmware.com wrote:
>
> > Some more assembler cleanups I noticed along the way.
>
>
> > Index: linux-2.6.13/arch/i386/kernel/cpu/intel.c
> > ===================================================================
> > --- linux-2.6.13.orig/arch/i386/kernel/cpu/intel.c    2005-08-03 
> > 15:18:18.000000000 -0700
> > +++ linux-2.6.13/arch/i386/kernel/cpu/intel.c    2005-08-03 
> > 15:19:39.000000000 -0700
> > @@ -82,16 +82,12 @@
> >   */
> >  static int __devinit num_cpu_cores(struct cpuinfo_x86 *c)
> >  {
> > -    unsigned int eax;
> > +    unsigned int eax, ebx, ecx, edx;
> >  
> >      if (c->cpuid_level < 4)
> >          return 1;
> >  
> > -    __asm__("cpuid"
> > -        : "=a" (eax)
> > -        : "0" (4), "c" (0)
> > -        : "bx", "dx");
> > -
> > +    cpuid(4, &eax, &ebx, &ecx, &edx);
> >      if (eax & 0x1f)
> >          return ((eax >> 26) + 1);
>
>
> Reject!  This is a bogus patch; Intel's CPUID level 4 has a 
> nonstandard dependency on ECX (idiots...) and therefore this needs 
> special handling.
>
>     -hpa

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/