[PATCH 2/3] Fold __builtin_memchr (version 2)

Wilco Dijkstra Wilco.Dijkstra@arm.com
Mon Oct 10 11:28:00 GMT 2016


Martin Liška <mliska@suse.cz> wrote:
> On 10/07/2016 01:21 PM, Wilco Dijkstra wrote:
>
> > I believe target_char_cast is incorrect if the host/target chars are not identical
> > (depending on how constant strings are created there may be signed/unsigned
> > mismatches too). I recently added target_char_cst_p to gimple-fold.c to avoid
> > char representation mismatches, so it would be better to use that instead.
>
> Thank you for the predicate, I'm going to use it.
>
> I have one additional question whether also c_getstr should be guarded
> with a similar guard? Or is it always safe to grab a char* by TREE_STRING_POINTER
> and use it by a host string functions (strcmp, ...)?

Yes I guess that one is incorrect too. I can't find the internal implementation of tree strings,
but it may well be that GCC just doesn't support any mismatches in host/target character
size. In any case an explicit check won't do any harm as it isn't possible to use host string
functions if there is a mismatch in character size.

Another thing, what happens with:

memchr ("abc", 225, 1000000000);

It seems your new code will call memchr with the given size (and potentially crash) rather
than report the obvious bug and set a consistent return value that doesn't rely on reading
random memory on the host.

Wilco





More information about the Gcc-patches mailing list