x86: do not allow to optimize flag_is_changeable_p() (rev. 2)

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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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

...

This commit is contained in:

Krzysztof Helt 2008-09-30 23:17:51 +02:00 • committed by Ingo Molnar

parent e2ce07c804

commit 94f6bac105

1 changed files with 19 additions and 12 deletions

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31

arch/x86/kernel/cpu/common.c

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