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

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

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.


-- 
H.J.