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    SubjectRe: current git kernel crashes UML system during boot
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    On Sun, May 30, 2010 at 17:02, Borislav Petkov <bp@alien8.de> wrote:
    > From: Geert Uytterhoeven <geert@linux-m68k.org>
    > Date: Sun, May 30, 2010 at 01:57:05PM +0200
    >
    >> On Sun, May 30, 2010 at 13:39, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
    >> > 2010/5/27 Toralf Förster <toralf.foerster@gmx.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@amd.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@amd.com>
    >> >    LKML-Reference: <20100318112015.GC11152@aftab>
    >> >    Signed-off-by: H. Peter Anvin <hpa@zytor.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?

    Works, thanks!

    BTW, if you want to check yourself:

    make ARCH=um defconfig
    make ACH=um
    ./linux

    If it panics because it cannot mount the root file system, it works.

    > 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>

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds
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