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

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

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?

Bye
Stefan