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 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