On Wed, Sep 11, 2013 at 08:46:33AM +0200, Florian Weimer wrote:
> This is the offending function:
>
> void
> cpuid(unsigned int *eax, unsigned int *ebx, unsigned int *ecx,
> unsigned int *edx)
> {
> __asm volatile
> ("cpuid\n\t"
> : "=a" (*eax),
> "=b" (*ebx),
> "=c" (*ecx),
> "=d" (*edx)
> : "a" (*eax));
> }
>
> The cryptic GCC error message (inconsistent operand constraints in
> an ‘asm’) refers to the fact that in PIC mode (which is activated
> by the hardening flags), %ebx is a reserved register.
>
> This version should work in 32 bit mode, and only in 32 bit mode:
>
> void
> cpuid(unsigned int *eax, unsigned int *ebx, unsigned int *ecx,
> unsigned int *edx)
> {
> __asm volatile
> ("push %%ebx\n\t"
> "cpuid\n\t"
> "mov %%ebx, (%1)\n\t"
> "pop %%ebx"
> : "=a" (*eax),
> "=S" (ebx),
> "=c" (*ecx),
> "=d" (*edx)
> : "0" (*eax));
> }
>
> I have not actually tested this. There are other solutions
> floating around, but they are clearly incorrect and produce wrong
> code.
A better fix would be to rip all this out, and use reads from
/dev/cpu/*/cpuid, which is arch agnostic, and also takes care of cpu affinity problems.
Dave
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