From: "H. Peter Anvin" <hpa@zytor.com>
To: Will Deacon <will.deacon@arm.com>, torvalds@linux-foundation.org
Cc: linux-kernel@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: Wed, 30 Apr 2014 14:22:19 -0700 [thread overview]
Message-ID: <5361698B.4060607@zytor.com> (raw)
In-Reply-To: <1398271972-15177-1-git-send-email-will.deacon@arm.com>
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))
next prev parent reply other threads:[~2014-04-30 21:22 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 [this message]
2014-05-01 9:04 ` Will Deacon
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