Messages in this thread |  | | | Date | Wed, 1 Oct 2008 09:11:38 +0200 | | From | Ingo Molnar <> | | Subject | Re: [PATCH] x86: do not allow to optimize flag_is_changeable_p() (rev. 2) | |
* Krzysztof Helt <krzysztof.h1@wp.pl> wrote:
> From: Krzysztof Helt <krzysztof.h1@wp.pl>
>
> The flag_is_changeable_p() is used by
> has_cpuid_p() which can return different results
> in the code sequence below:
>
> if (!have_cpuid_p())
> identify_cpu_without_cpuid(c);
>
> /* cyrix could have cpuid enabled via c_identify()*/
> if (!have_cpuid_p())
> return;
>
> Otherwise, the gcc 3.4.6 optimizes these two calls
> into one which make the code not working correctly.
>
> Cyrix cpus have the CPUID instruction enabled before
> the second call to the have_cpuid_p() but
> it is not detected due to the gcc optimization.
> Thus the ARR registers (mtrr like) are not detected
> on such a cpu.
>
> Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
applied to tip/x86/core, thanks Krzysztof!
Ingo
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