linux-kernel - Re: [PATCH] x86, hweight: Fix UML boot crash

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Message-ID: <4C02D408.1030306@zytor.com>
Date:	Sun, 30 May 2010 14:09:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Borislav Petkov <borislav.petkov@....com>,
	Toralf Förster <toralf.foerster@....de>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
CC:	Jeff Dike <jdike@...toit.com>
Subject: Re: [PATCH] x86, hweight: Fix UML boot crash

On 05/30/2010 01:17 PM, Borislav Petkov wrote:
>>> This bothers me, because it really feels like something is fundamentally
>>> broken in UML tryingto track the upstream architecture, and this is just
>>> a bandage.
>>
>> First of all, scratch that patch. It is indeed dumb idea to sprinkle UML
>> special cases in x86 just because they include it.
>>
>> Which begs the question why _is_ UML sucking in x86 stuff and can anyone
>> provide us with some sensible reasons? Because if there aren't any, it
>> is their includes that should be fixed. Let me see what I can do to
>> redirect hweight stuff properly...
> 
> Ok, AFAICT UML is sucking in the includes of the sub-architecture the
> UML "guest" is running on. See below¹ for the whole gcc string make
> executes. Among the switches is
> 
> "-I/home/boris/kernel/linux-2.6/arch/x86/include"
> 
> so there will be no untangling today. Instead, we could do another
> bandaid which is confined to UML include space only and redirect
> arch_hweight.h includes to the generic ones. Check this out, it seems to
> work here:
> 

That looks better to me, although I'm still wondering why UML can't
stomach the register-saving tricks... it is not at all "obvious" why
that can't be done.

Perhaps we can get Jeff to comment on this?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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