[PATCH] string/stratcliff.c: Replace int with size_t [BZ #21982]

[Stefan Liebler]

On 08/22/2017 02:43 PM, H.J. Lu wrote:
> On Tue, Aug 22, 2017 at 5:07 AM, Stefan Liebler <stli@linux.vnet.ibm.com> wrote:
>> On 08/22/2017 01:05 AM, H.J. Lu wrote:
>>>
>>> On Mon, Aug 21, 2017 at 8:41 AM, Stefan Liebler <stli@linux.vnet.ibm.com>
>>> wrote:
>>>>
>>>> On 08/21/2017 04:53 PM, H.J. Lu wrote:
>>>>>
>>>>>
>>>>> On Mon, Aug 21, 2017 at 6:48 AM, Stefan Liebler
>>>>> <stli@linux.vnet.ibm.com>
>>>>> wrote:
>>>>>>
>>>>>>
>>>>>> On 08/20/2017 07:17 PM, H.J. Lu wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Fix GCC 7 errors when string/stratcliff.c is compiled with -O3:
>>>>>>>
>>>>>>> stratcliff.c: In function ‘do_test’:
>>>>>>> cc1: error: assuming signed overflow does not occur when assuming that
>>>>>>> (X
>>>>>>> - c) <= X is always true [-Werror=strict-overflow]
>>>>>>>
>>>>>>> OK for master?
>>>>>>>
>>>>>>> H.J.
>>>>>>> ---
>>>>>>>            [BZ #21982]
>>>>>>>            * string/stratcliff.c (do_test): Declare size, nchars,
>>>>>>> inner,
>>>>>>>            middle and outer with size_t instead of int.  Repleace %d
>>>>>>> with
>>>>>>>            %Zd in printf.
>>>>>>> ---
>>>>>>>      string/stratcliff.c | 72
>>>>>>> ++++++++++++++++++++++++++---------------------------
>>>>>>>      1 file changed, 36 insertions(+), 36 deletions(-)
>>>>>>>
>>>>>>> diff --git a/string/stratcliff.c b/string/stratcliff.c
>>>>>>> index e28b0c5058..ae780379cb 100644
>>>>>>> --- a/string/stratcliff.c
>>>>>>> +++ b/string/stratcliff.c
>>>>>>> @@ -58,8 +58,8 @@
>>>>>>>      int
>>>>>>>      do_test (void)
>>>>>>>      {
>>>>>>> -  int size = sysconf (_SC_PAGESIZE);
>>>>>>> -  int nchars = size / sizeof (CHAR);
>>>>>>> +  size_t size = sysconf (_SC_PAGESIZE);
>>>>>>> +  size_t nchars = size / sizeof (CHAR);
>>>>>>>        CHAR *adr;
>>>>>>>        CHAR *dest;
>>>>>>>        int result = 0;
>>>>>>> @@ -80,7 +80,7 @@ do_test (void)
>>>>>>>          }
>>>>>>>        else
>>>>>>>          {
>>>>>>> -      int inner, middle, outer;
>>>>>>> +      size_t inner, middle, outer;
>>>>>>>
>>>>>>>            mprotect (adr, size, PROT_NONE);
>>>>>>>            mprotect (adr + 2 * nchars, size, PROT_NONE);
>>>>>>> @@ -101,7 +101,7 @@ do_test (void)
>>>>>>>
>>>>>>>                  if (STRLEN (&adr[outer]) != (size_t) (inner - outer))
>>>>>>>                    {
>>>>>>> -                 printf ("%s flunked for outer = %d, inner = %d\n",
>>>>>>> +                 printf ("%s flunked for outer = %Zd, inner = %Zd\n",
>>>>>>>                              STRINGIFY (STRLEN), outer, inner);
>>>>>>>                      result = 1;
>>>>>>>                    }
>>>>>>>                    {
>>>>>>> -                 printf ("%s flunked for outer = %d, middle = %d\n",
>>>>>>> +                 printf ("%s flunked for outer = %Zd, middle =
>>>>>>> %Zd\n",
>>>>>>>                              STRINGIFY (rawmemchr), outer, middle);
>>>>>>>                      result = 1;
>>>>>>>                    }
>>>>>>> Hi H.J. Lu,
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> I've applied your patch and the warnings does not occur anymore on
>>>>>> s390.
>>>>>
>>>>>
>>>>>
>>>>> Great.
>>>>>
>>>>>> The outer loops of the string tests are all using the following:
>>>>>> size_t nchars, outer;
>>>>>> for (outer = nchars - 1; outer >= MAX (0, nchars - 128); --outer)
>>>>>>
>>>>>> I think we can assume, that nchars is always > 128 as it is derived by
>>>>>> the
>>>>>> pagesize.
>>>>>> But if nchars would be equal to 128, this would result in an infinite
>>>>>> loop
>>>>>> (outer >= 0)?
>>>>>> If nchars would be less than 128, the tests would be skipped.
>>>>>>
>>>>>> Should we add a check that nchars > 128 at the beginning and replace
>>>>>> the
>>>>>> "MAX (0, nchars - 128)" with only "nchars - 128"?
>>>>>
>>>>>
>>>>>
>>>>> This is a separate issue beyond BZ #21982.
>>>>>
>>>>>
>>>> Your patch is introducing this behaviour.
>>>> Before your patch, nchars and outer was an int and the for-loop-condition
>>>> "outer >= MAX (0, nchars - 128)" does not lead to an infinite loop or to
>>>> skipping the test if nchars <= 128.
>>>>
>>>
>>> How about this patch?
>>>
>> This solves the cases if nchars < 128.
>> But if nchars == 128, then the condition of the for-loop is "size_t outer >=
>> 0", which is always true.
>>
>> Could we check once if nchars > 128 and exit the test with an error if
>> nchars is <= 128?
>> Are there architectures where the page size is < 4096?
>> Or where wchar_t > 4byte?
>>
> 
> Here is the updated patch.  I added
> 
>   if (outer == 0)
>     break;
> 
> at the end of loop.
> 

Okay. This fixes the case nchars == 128.
I've retested this patch on s390x with gcc 7 -O3 and the warnings does 
not occur anymore.

Thanks.
Stefan