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

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Message-ID: <4C02B020.2040103@zytor.com>
Date:	Sun, 30 May 2010 11:36:16 -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
Subject: Re: [PATCH] x86, hweight: Fix UML boot crash

On 05/30/2010 10:03 AM, Borislav Petkov wrote:
> Obviously UML cannot stomach callee reg-saving trickery
> introduced with d61931d89be506372d01a90d1755f6d0a9fafe2d (x86:
> Add optimized popcnt variants) and oopses during boot:
> http://marc.info/?l=linux-kernel&m=127522065202435&w=2
> 
> Go ahead and fall back to the software hweight* routines on UML.

I actually don't understand why UML can't stomach that... it would work
exactly the same in userspace as in kernel space.  The only thing that I
can think of is if UML overrides the CFLAGS including the per-file
CFLAGS, but that would seem to cause all kinds of other issues.

I would also be a lot happier if this was handled in
<asm/arch_hweight.h> than in <asm/bitops.h>.  Finally, if UML really
can't handle this, then ARCH_HWEIGHT_CFLAGS should be disabled on UML.

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.

	-hpa

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

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