On Thu, Dec 01, 2022 at 07:18:15PM -0800, Eric Biggers wrote: > On Thu, Dec 01, 2022 at 05:04:14PM -0800, Kees Cook wrote: > > GCC 12 appears to perform constant propagation incompletely(?) and can > > no longer notice that "len" is always 0 when "data" is NULL. Expand the > > check to avoid warnings about memcpy() having a NULL argument: > > Is there a gcc option to turn off the "memcpy with NULL and len=0 is undefined > behavior" thing? It's basically a bug in the C standard. It's not undefined -- it's just pedantic. __builtin_memcpy is defined internally to GCC with __attribute__((nonnull (1, 2))), and since it can find a path from an always-NULL argument, it warns. I think it's a dumb limitation, given that "zero size to/from NULL" is perfectly valid. -- Kees Cook
