Re: [BUG] missing warning for pointer arithmetic out of bounds

[David Malcolm <dmalcolm@redhat.com>]

On Tue, 2022-12-13 at 20:15 +0100, Alejandro Colomar via Gcc wrote:
> 
> 
> On 12/13/22 20:08, Alejandro Colomar wrote:
> > Hi!
> > 
> > For the following program:
> > 
> > 
> >      $ cat buf.c
> >      #include <stdio.h>
> > 
> >      int main(void)
> >      {
> >          char *p, buf[5];
> > 
> >          p = buf + 6;
> >          printf("%p\n", p);
> >      }
> > 
> > 
> > There are no warnings in gcc, as I would expect:
> 
> I just re-read my text, and it is ambiguous.  I meant that I expect
> warnings.

Yeah, it would be good to warn about such code.

Looking in bugzilla, I see:
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81172
which seems to talk about this issue, but that bug was closed as
resolved on 2020-04-13; I'm not sure what happened here.

Dave


> 
> 
> > 
> >      $ gcc -Wall -Wextra buf.c -O0
> > 
> > Clang does warn, however:
> > 
> >      $ clang -Weverything -Wall -Wextra buf.c -O0
> >      buf.c:8:17: warning: format specifies type 'void *' but the
> > argument has 
> > type 'char *' [-Wformat-pedantic]
> >          printf("%p\n", p);
> >                  ~~     ^
> >                  %s
> >      buf.c:7:6: warning: the pointer incremented by 6 refers past
> > the end of the 
> > array (that contains 5 elements) [-Warray-bounds-pointer-
> > arithmetic]
> >          p = buf + 6;
> >              ^     ~
> >      buf.c:5:2: note: array 'buf' declared here
> >          char *p, buf[5];
> >          ^
> >      2 warnings generated.
> > 
> > Cheers,
> > 
> > Alex
> > 
> > 
> 
> -- 
> <http://www.alejandro-colomar.es/>