Le mardi 09 août 2011 à 05:10 +0200, Eric Dumazet a écrit :
> Le dimanche 07 août 2011 à 18:30 +0900, Akinobu Mita a écrit :
> > The check_bytes() function is used by slub debugging. It returns a pointer
> > to the first unmatching byte for a character in the given memory area.
> >
> > If the character for matching byte is greater than 0x80, check_bytes()
> > doesn't work. Becuase 64-bit pattern is generated as below.
> >
> > value64 = value | value << 8 | value << 16 | value << 24;
> > value64 = value64 | value64 << 32;
> >
> > The integer promotions are performed and sign-extended as the type of value
> > is u8. The upper 32 bits of value64 is 0xffffffff in the first line, and
> > the second line has no effect.
> >
> > This fixes the 64-bit pattern generation.
> >
> > Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
> > Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > Cc: Matt Mackall <mpm@xxxxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > ---
> > mm/slub.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index eb5a8f9..5695f92 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -701,7 +701,7 @@ static u8 *check_bytes(u8 *start, u8 value, unsigned int bytes)
> > return check_bytes8(start, value, bytes);
> >
> > value64 = value | value << 8 | value << 16 | value << 24;
> > - value64 = value64 | value64 << 32;
> > + value64 = (value64 & 0xffffffff) | value64 << 32;
> > prefix = 8 - ((unsigned long)start) % 8;
> >
> > if (prefix) {
>
> Still buggy I am afraid. Could we use the following ?
>
>
> value64 = value;
> value64 |= value64 << 8;
> value64 |= value64 << 16;
> value64 |= value64 << 32;
>
>
Well, 'buggy' was not well chosen.
Another possibility would be to use a multiply if arch has a fast
multiplier...
value64 = value;
#if defined(ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
value64 *= 0x0101010101010101;
#elif defined(ARCH_HAS_FAST_MULTIPLIER)
value64 *= 0x01010101;
value64 |= value64 << 32;
#else
value64 |= value64 << 8;
value64 |= value64 << 16;
value64 |= value64 << 32;
#endif
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