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

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

On 08/21/2017 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.