Messages in this thread | | | Date | Thu, 1 May 2014 10:04:39 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] word-at-a-time: avoid undefined behaviour in zero_bytemask macro |
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Hi Peter,
On Wed, Apr 30, 2014 at 10:22:19PM +0100, H. Peter Anvin wrote: > On 04/23/2014 09:52 AM, Will Deacon wrote: > > diff --git a/include/asm-generic/word-at-a-time.h b/include/asm-generic/word-at-a-time.h > > index d3909effd725..d96deb443f18 100644 > > --- a/include/asm-generic/word-at-a-time.h > > +++ b/include/asm-generic/word-at-a-time.h > > @@ -50,11 +50,7 @@ static inline bool has_zero(unsigned long val, unsigned long *data, const struct > > } > > > > #ifndef zero_bytemask > > -#ifdef CONFIG_64BIT > > -#define zero_bytemask(mask) (~0ul << fls64(mask)) > > -#else > > -#define zero_bytemask(mask) (~0ul << fls(mask)) > > -#endif /* CONFIG_64BIT */ > > -#endif /* zero_bytemask */ > > +#define zero_bytemask(mask) (~0ul << __fls(mask) << 1) > > +#endif > > > > #endif /* _ASM_WORD_AT_A_TIME_H */ > > > > Why not: > > #define zero_bytemask(mask) (~1ul << __fls(mask))
Yup, that'll work too -- it produces an identical disassembly for arm64.
Will
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