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Message-ID: <48C55CEC.1080900@kernel.org>
Date: Mon, 08 Sep 2008 10:12:12 -0700
From: "H. Peter Anvin" <hpa@kernel.org>
Organization: Linux Kernel Organization, Inc.
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andi Kleen <andi@firstfloor.org>, linux@sandersweb.net,
       linux-kernel@vger.kernel.org, the arch/x86 maintainers <x86@kernel.org>,
       Andi Kleen <andi-suse@firstfloor.org>
Subject: Re: [BUG] x86 kenel won't boot under Virtual PC
References: <200809071922.32974.linux@sandersweb.net> <48C48467.40703@zytor.com> <200809072249.17280.linux@sandersweb.net> <48C4A46B.90705@zytor.com> <alpine.LFD.1.10.0809080805240.3117@nehalem.linux-foundation.org> <20080908154535.GL26079@one.firstfloor.org> <48C54839.8050304@zytor.com> <alpine.LFD.1.10.0809080857450.3117@nehalem.linux-foundation.org> <48C54F1B.8040604@zytor.com> <alpine.LFD.1.10.0809080916550.3117@nehalem.linux-foundation.org> <20080908170029.GP26079@one.firstfloor.org> <alpine.LFD.1.10.0809081000490.3117@nehalem.linux-foundation.org> <48C55C0A.7070203@zytor.com>
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H. Peter Anvin wrote:
> 
> Yes, it does:
> 
>   /* We need to decide which NOP sequence to use for 32bit and
>      64bit. When -mtune= is used:
> 
>      1. For PROCESSOR_I386, PROCESSOR_I486, PROCESSOR_PENTIUM and
>      PROCESSOR_GENERIC32, f32_patt will be used.
>      2. For PROCESSOR_PENTIUMPRO, PROCESSOR_PENTIUM4, PROCESSOR_NOCONA,
>      PROCESSOR_CORE, PROCESSOR_CORE2, and PROCESSOR_GENERIC64,
>      alt_long_patt will be used.
>      3. For PROCESSOR_ATHLON, PROCESSOR_K6, PROCESSOR_K8 and
>      PROCESSOR_AMDFAM10, alt_short_patt will be used.
> 
>      When -mtune= isn't used, alt_long_patt will be used if
>      cpu_arch_isa_flags has Cpu686. Otherwise, f32_patt will
>      be used.
> 
> "alt_long_patt" uses NOPL and its variants.
> 

I should point out that the code above is from binutils (gas), not from 
gcc.  It is entirely possible that doing something like
"-mtune=core2 -Wa,-mtune=generic" might actually work, but I have not 
dug through the gcc code proper to figure out if that (a) would work, 
and (b) will remain the case...

	-hpa