linux-kernel - Re: current git kernel crashes UML system during boot

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Message-ID: <20100530150214.GA1565@liondog.tnic>
Date:	Sun, 30 May 2010 17:02:14 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Toralf Förster <toralf.foerster@....de>,
	Borislav Petkov <borislav.petkov@....com>,
	"H. Peter Anvin" <hpa@...or.com>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: current git kernel crashes UML system during boot

From: Geert Uytterhoeven <geert@...ux-m68k.org>
Date: Sun, May 30, 2010 at 01:57:05PM +0200

> On Sun, May 30, 2010 at 13:39, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > 2010/5/27 Toralf Förster <toralf.foerster@....de>:
> >> I bisected it to this :
> 
> > After fixing the missing/superfluous slab inclusion issues, I bisected
> > it further to
> >
> > commit d61931d89be506372d01a90d1755f6d0a9fafe2d
> > Author: Borislav Petkov <borislav.petkov@....com>
> > Date:   Fri Mar 5 17:34:46 2010 +0100
> >
> >    x86: Add optimized popcnt variants
> >
> >    Add support for the hardware version of the Hamming weight function,
> >    popcnt, present in CPUs which advertize it under CPUID, Function
> >    0x0000_0001_ECX[23]. On CPUs which don't support it, we fallback to the
> >    default lib/hweight.c sw versions.
> >
> >    A synthetic benchmark comparing popcnt with __sw_hweight64 showed almost
> >    a 3x speedup on a F10h machine.
> >
> >    Signed-off-by: Borislav Petkov <borislav.petkov@....com>
> >    LKML-Reference: <20100318112015.GC11152@...ab>
> >    Signed-off-by: H. Peter Anvin <hpa@...or.com>
> >
> > I reverted that commit on top of current mainline (and fixed up the
> > conflicts), and now
> > it boots again.
> 
> I tried adding
> 
> config ARCH_HWEIGHT_CFLAGS
>         string
>         default "-fcall-saved-ecx -fcall-saved-edx" if !64_BIT
>         default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx
> -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10
> -fcall-saved-r11" if 64_BIT
> 
> to arch/um/Kconfig.x86. Now it got a bit further, but it still crashes:

Ok, this is a kinda stab in the dark but from what I could decypher
from the include hell, one possible fix should be if UML didn't include
<arch/x86/include/asm/arch_hweight.h> but use the software hweight
version only.

Can you guys check whether the following fixes the issue?

Thanks.

--
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 545776e..c9dad12 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -444,7 +444,11 @@ static inline int fls(int x)
 
 #define ARCH_HAS_FAST_MULTIPLIER 1
 
+#ifdef CONFIG_UML
+#include <asm-generic/bitops/arch_hweight.h>
+#else
 #include <asm/arch_hweight.h>
+#endif
 
 #include <asm-generic/bitops/const_hweight.h>
 

-- 
Regards/Gruss,
    Boris.
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