numatop: %{optflags} fail the 32bit build

[Dridi Boukelmoune]

On Thu, Sep 12, 2013 at 5:39 PM, Dave Jones <davej at redhat.com> wrote:
> 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

On my ubuntu machine at work, I have this:

$ ls /dev/cpu/
microcode

Also, wouldn't it be a problem on a chrooted environment ?

And during my tests I've noticed that numatop calls cpuid once for
each core on my laptop. It should discard the affinity problem,
shouldn't it ?

Tanks again for your help, it's been very interesting for me !

Dridi

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