On Wed, Oct 30 2013, Bruce Cran wrote:
> It seems there's a bug in the x86_64 version of do_cpuid() that causes fio
> to segfault when built with clang at lower optimization levels:
>
> static inline void do_cpuid(unsigned int *eax, unsigned int *ebx,
> unsigned int *ecx, unsigned int *edx)
> {
> asm volatile("cpuid"
> : "=a" (*eax), "=b" (*ebx), "=r" (*ecx), "=d" (*edx)
> : "0" (*eax), "2" (*ecx)
> : "memory");
> }
>
> via Tijl Coosemans:
>
> Should be: "=c" (*ecx)
>
> But you can also use the '+' modifier and remove the input operands:
>
> : "+a" (*eax), "=b" (*ebx), "+c" (*ecx), "=d" (*edx)
> :
> : "memory"
+a/+c doesn't work, but =c will do the trick.
--
Jens Axboe
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