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
>
> .
>
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