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

[Stefan Liebler]

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.