Messages in this thread |  | | Date | Wed, 21 Jun 2017 18:40:36 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] futex: avoid undefined behaviour when shift exponent is negative |
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* 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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