Re: [Xen-devel] [PATCH] libxc-x86-64-fixes.patch

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Arun Sharma wrote:

> +#ifdef __i386__
>     __asm__ __volatile__ ("pushl %%ebx; cpuid; popl %%ebx" 
> 			  : "=a" (eax), "=c" (ecx) 
> 			  : "0" (1) 
> 			  : "dx");
> +#elif defined __x86_64__
> +    __asm__ __volatile__ ("pushq %%rbx; cpuid; popq %%rbx"
> +                          : "=a" (eax), "=c" (ecx)
> +                          : "0" (1)
> +                          : "dx");
> +#endif
> +
>  
Does this mean the ebx-clobbering bug in gcc 3.4 also exists on x86-64 
(except it clobbers rbx instead)?
I really hate to see this end up a permanent part of the tree...  
perhaps we should add a Linux style cpuid() function:
static inline void cpuid(int op, int *eax, int *ebx, int *ecx, int *edx)
{
   int ax, bx, cx, dx;

#if defined __i386__ || defined __x86_64__
   __asm__("cpuid"
       : "=a" (ax),
         "=b" (bx),
         "=c" (cx),
         "=d" (dx)
       : "0" (op));
#else
#error cpuid not defined on current architecture
#endif

   if (eax) *eax = ax;
   if (ebx) *ebx = bx;
   if (ecx) *ecx = cx
   if (edx) *edx = dx;
}

This should take care of the ebx clobbering bug while also resulting in 
more shared code.
Just a thought.

Regards,
Anthony Liguori

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