From: Will Deacon <will.deacon@arm.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
Victor Kamensky <victor.kamensky@linaro.org>
Subject: Re: [PATCH] word-at-a-time: avoid undefined behaviour in zero_bytemask macro
Date: Thu, 1 May 2014 10:04:39 +0100 [thread overview]
Message-ID: <20140501090438.GA30166@arm.com> (raw)
In-Reply-To: <5361698B.4060607@zytor.com>
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
prev parent reply other threads:[~2014-05-01 9:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-23 16:52 [PATCH] word-at-a-time: avoid undefined behaviour in zero_bytemask macro Will Deacon
2014-04-30 21:22 ` H. Peter Anvin
2014-05-01 9:04 ` Will Deacon [this message]
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