On Tue, Dec 13, 2022 at 11:16 AM Alejandro Colomar via Gcc
<gcc@gcc.gnu.org> 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.
GCC only warns during VRP which is only enabled at -O2:
<source>:8:12: warning: array subscript 6 is outside array bounds of
'char[5]' [-Warray-bounds=]
8 | p = buf + 6;
| ~~^~~~~~~~~
<source>:6:19: note: at offset 6 into object 'buf' of size 5
6 | char *p, buf[5];
| ^~~
Thanks,
Andrew
>
>
> >
> > $ 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/>
