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

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Aug 22, 2017 at 7:56 AM, Stefan Liebler <stli@linux.vnet.ibm.com> wrote:
> 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.

I am checking it in shortly.

Thanks.

-- 
H.J.