From: Ingo Molnar <mingo@kernel.org>
To: zhong jiang <zhongjiang@huawei.com>
Cc: akpm@linux-foundation.org, tglx@linutronix.de, mingo@redhat.com,
minchan@kernel.org, mhocko@suse.com, hpa@zytor.com,
x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] futex: avoid undefined behaviour when shift exponent is negative
Date: Wed, 21 Jun 2017 18:40:36 +0200 [thread overview]
Message-ID: <20170621164036.4findvvz7jj4cvqo@gmail.com> (raw)
In-Reply-To: <1498045437-7675-1-git-send-email-zhongjiang@huawei.com>
* zhong jiang <zhongjiang@huawei.com> wrote:
> when shift expoment is negative, left shift alway zero. therefore, we
> modify the logic to avoid the warining.
>
> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
> ---
> arch/x86/include/asm/futex.h | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
> index b4c1f54..2425fca 100644
> --- a/arch/x86/include/asm/futex.h
> +++ b/arch/x86/include/asm/futex.h
> @@ -49,8 +49,12 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
> int cmparg = (encoded_op << 20) >> 20;
> int oldval = 0, ret, tem;
>
> - if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
> - oparg = 1 << oparg;
> + if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
> + if (oparg >= 0)
> + oparg = 1 << oparg;
> + else
> + oparg = 0;
> + }
Could we avoid all these complications by using an unsigned type?
Thanks,
Ingo
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next prev parent reply other threads:[~2017-06-21 16:40 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-21 11:43 [PATCH] futex: avoid undefined behaviour when shift exponent is negative zhong jiang
2017-06-21 16:40 ` Ingo Molnar [this message]
2017-06-28 4:35 ` zhong jiang
2017-06-28 21:43 ` hpa
2017-06-29 2:12 ` zhong jiang
2017-06-29 4:29 ` hpa
2017-06-29 5:57 ` zhong jiang
2017-06-28 22:13 ` Thomas Gleixner
2017-06-29 1:54 ` zhong jiang
2017-06-29 6:33 ` Thomas Gleixner
2017-06-29 7:04 ` zhong jiang
2017-08-25 5:21 ` zhong jiang
2017-08-25 21:13 ` Thomas Gleixner
2017-08-26 2:51 ` zhong jiang
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