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Date: Mon, 29 Sep 2008 11:17:34 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Krzysztof Helt <krzysztof.h1@poczta.fm>
CC: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Yinghai Lu <yhlu.kernel@gmail.com>
Subject: Re: [PATCH] x86: do not allow to optimize flag_is_changeable_p()
References: <20080929200603.dcdc5b71.krzysztof.h1@poczta.fm>
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Krzysztof Helt 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 but
> it is not detected due to the gcc optimization.
> Thus the ARR registers (mtrr like) are not detected
> on such a cpu.
> 

I suspect we should also out-of-line this function.  It's actually 
relatively sizable and certainly there is no point in inlining it.

	-hpa