[Bug sanitizer/105405] missed buffer-overflow in -O0

["marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105405

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #5)
> j[5][1].h is 36 after the end of a array, that is definitely too far.

Yes. Just a small note that clang emits there a bit bigger red-zone:

=>0x0000801c50a0: 00 00 00 00 00 00 00 00 f9 f9 f9 f9 f9[f9]f9 f9
  0x0000801c50b0: 04 f9 f9 f9 00 00 00 00 00 00 00 00 00 00 00 00

and thus catches that.

> Red zone can be 16 bytes or even less in certain cases (e.g. in the PR105396
> case it is 12 bytes in between d and b variables).
> ASan mostly protects against buffer overflows, something accesses the last
> byte of a variable, then the byte after it, ... (or similarly the first byte
> of a variable, then the byte before it, ...).
> -fsanitize=undefined on the other side includes the bounds sanitizer that
> verifies array indexes by comparing them against the number of elements the
> array has.

gcc-11 pr105405.c -fsanitize=undefined && ./a.out
pr105405.c:10:13: runtime error: index 1 out of bounds for type 'a [1]'