[dpdk-dev] [PATCH] net/avf/base: fix shifting 32 bits signed variable 31 times
Ferruh Yigit
ferruh.yigit at intel.com
Mon Nov 5 15:30:47 CET 2018
On 10/31/2018 3:34 AM, Zhao1, Wei wrote:
>
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ferruh Yigit
>> Sent: Sunday, October 28, 2018 11:52 AM
>> To: Wu, Jingjing <jingjing.wu at intel.com>; Lu, Wenzhuo
>> <wenzhuo.lu at intel.com>
>> Cc: dev at dpdk.org; Yigit, Ferruh <ferruh.yigit at intel.com>; stable at dpdk.org
>> Subject: [dpdk-dev] [PATCH] net/avf/base: fix shifting 32 bits signed variable
>> 31 times
>>
>> Fixes: e5b2a9e957e7 ("net/avf/base: add base code for avf PMD")
>> Cc: stable at dpdk.org
>>
>> Signed-off-by: Ferruh Yigit <ferruh.yigit at intel.com>
>> ---
>> drivers/net/avf/base/avf_register.h | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/avf/base/avf_register.h
>> b/drivers/net/avf/base/avf_register.h
>> index ba5a9f3fa..adb989583 100644
>> --- a/drivers/net/avf/base/avf_register.h
>> +++ b/drivers/net/avf/base/avf_register.h
>> @@ -76,7 +76,7 @@ POSSIBILITY OF SUCH DAMAGE.
>> #define AVF_ARQLEN1_ARQCRIT_SHIFT 30
>> #define AVF_ARQLEN1_ARQCRIT_MASK AVF_MASK(0x1,
>> AVF_ARQLEN1_ARQCRIT_SHIFT)
>> #define AVF_ARQLEN1_ARQENABLE_SHIFT 31
>> -#define AVF_ARQLEN1_ARQENABLE_MASK AVF_MASK(0x1,
>> AVF_ARQLEN1_ARQENABLE_SHIFT)
>> +#define AVF_ARQLEN1_ARQENABLE_MASK AVF_MASK(0x1U,
>> +AVF_ARQLEN1_ARQENABLE_SHIFT)
>> #define AVF_ARQT1 0x00007000 /* Reset: EMPR */
>> #define AVF_ARQT1_ARQT_SHIFT 0
>> #define AVF_ARQT1_ARQT_MASK AVF_MASK(0x3FF,
>> AVF_ARQT1_ARQT_SHIFT) @@ -99,7 +99,7 @@ POSSIBILITY OF SUCH
>> DAMAGE.
>> #define AVF_ATQLEN1_ATQCRIT_SHIFT 30
>> #define AVF_ATQLEN1_ATQCRIT_MASK AVF_MASK(0x1,
>> AVF_ATQLEN1_ATQCRIT_SHIFT)
>> #define AVF_ATQLEN1_ATQENABLE_SHIFT 31
>> -#define AVF_ATQLEN1_ATQENABLE_MASK AVF_MASK(0x1,
>> AVF_ATQLEN1_ATQENABLE_SHIFT)
>> +#define AVF_ATQLEN1_ATQENABLE_MASK AVF_MASK(0x1U,
>> +AVF_ATQLEN1_ATQENABLE_SHIFT)
>> #define AVF_ATQT1 0x00008400 /* Reset: EMPR */
>> #define AVF_ATQT1_ATQT_SHIFT 0
>> #define AVF_ATQT1_ATQT_MASK AVF_MASK(0x3FF,
>> AVF_ATQT1_ATQT_SHIFT)
>> --
>> 2.17.2
>
> I have test this code change with a small function to observe the difference.
> Reviewed-by: Wei Zhao <wei.zhao1 at intel.com>
>
> #define AVF_ARQLEN1_ARQENABLE_SHIFT 31
> #define AVF_MASK(mask, shift) (mask << shift)
> #define AVF_ARQLEN1_ARQENABLE_MASK1 AVF_MASK(0x1, AVF_ARQLEN1_ARQENABLE_SHIFT)
> #define AVF_ARQLEN1_ARQENABLE_MASK2 AVF_MASK(0x1U, AVF_ARQLEN1_ARQENABLE_SHIFT)
>
> void main(int argc,char **argv)
> {
> signed int a=1;
>
> printf("Hello Linux\n");
> printf("%x,=%x\n",AVF_ARQLEN1_ARQENABLE_MASK1,AVF_ARQLEN1_ARQENABLE_MASK2);
> printf("a=%x\n",a<<31);
>
> }
I guess you are tying to say there is no difference, output of your code is:
Hello Linux
80000000,=80000000
a=80000000
Let's have a little addition to your program,
#include <stdio.h>
#define AVF_ARQLEN1_ARQENABLE_SHIFT 31
#define AVF_MASK(mask, shift) (mask << shift)
#define AVF_ARQLEN1_ARQENABLE_MASK1 AVF_MASK(0x1, AVF_ARQLEN1_ARQENABLE_SHIFT)
#define AVF_ARQLEN1_ARQENABLE_MASK2 AVF_MASK(0x1U, AVF_ARQLEN1_ARQENABLE_SHIFT)
#define AVF_MASK2(mask, shift) (mask >> shift)
#define AVF_ARQLEN1_ARQENABLE_MASK11 AVF_MASK2(AVF_ARQLEN1_ARQENABLE_MASK1, 30)
#define AVF_ARQLEN1_ARQENABLE_MASK22 AVF_MASK2(AVF_ARQLEN1_ARQENABLE_MASK2, 30)
void main(int argc,char **argv)
{
signed int a=1;
printf("Hello Linux\n");
printf("%x,=%x\n", AVF_ARQLEN1_ARQENABLE_MASK1,
AVF_ARQLEN1_ARQENABLE_MASK2);
printf("%x,=%x\n", AVF_ARQLEN1_ARQENABLE_MASK11,
AVF_ARQLEN1_ARQENABLE_MASK22);
printf("a=%x\n", a<<31);
}
Will results same for second line? Both does ((1 << 31) >> 30).
'1' is promoted to signed int by default and cppcheck complains that shifting
signed variable 31 times is undefined behaviour, and here intention is not
really have the 1 as signed integer, so better to fix it.
Thanks,
ferruh
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