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

[Anthony Liguori <aliguori@us.ibm.com>]

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