On June 27, 2017 9:35:10 PM PDT, zhong jiang <zhongjiang@xxxxxxxxxx> wrote:
>Hi, Ingo
>
>Thank you for the comment.
>On 2017/6/22 0:40, Ingo Molnar wrote:
>> * zhong jiang <zhongjiang@xxxxxxxxxx> 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@xxxxxxxxxx>
>>> ---
>>> 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?
>I think it is not feasible. a negative shift exponent is likely
>existence and reasonable.
> as the above case, oparg is a negative is common.
>
> I think it can be avoided by following change.
>
>diff --git a/arch/x86/include/asm/futex.h
>b/arch/x86/include/asm/futex.h
>index b4c1f54..3205e86 100644
>--- a/arch/x86/include/asm/futex.h
>+++ b/arch/x86/include/asm/futex.h
>@@ -50,7 +50,7 @@ static inline int futex_atomic_op_inuser(int
>encoded_op, u32 __user *uaddr)
> int oldval = 0, ret, tem;
>
> if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
>- oparg = 1 << oparg;
>+ oparg = safe_shift(1, oparg);
>
> if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
> return -EFAULT;
>diff --git a/drivers/video/fbdev/core/fbmem.c
>b/drivers/video/fbdev/core/fbmem.c
>index 069fe79..b4edda3 100644
>--- a/drivers/video/fbdev/core/fbmem.c
>+++ b/drivers/video/fbdev/core/fbmem.c
>@@ -190,11 +190,6 @@ char* fb_get_buffer_offset(struct fb_info *info,
>struct fb_pixmap *buf, u32 size
>
> #ifdef CONFIG_LOGO
>
>-static inline unsigned safe_shift(unsigned d, int n)
>-{
>- return n < 0 ? d >> -n : d << n;
>-}
>-
> static void fb_set_logocmap(struct fb_info *info,
> const struct linux_logo *logo)
> {
>diff --git a/include/linux/kernel.h b/include/linux/kernel.h
>index d043ada..f3b8856 100644
>--- a/include/linux/kernel.h
>+++ b/include/linux/kernel.h
>@@ -841,6 +841,10 @@ static inline void ftrace_dump(enum
>ftrace_dump_mode oops_dump_mode) { }
> */
> #define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
>
>+static inline unsigned safe_shift(unsigned d, int n)
>+{
>+ return n < 0 ? d >> -n : d << n;
>+}
>
>Thansk
>zhongjiang
>
>> Thanks,
>>
>> Ingo
>>
>> .
>>
What makes it reasonable? It is totally ill-defined and doesn't do anything useful now?
--
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