On 11/24/2016 12:47 AM, Jakub Jelinek wrote:
On Wed, Nov 23, 2016 at 02:27:05PM -0700, Jeff Law wrote:
I believe we should be warning on trying to allocation 0 bytes of memory via
malloc, realloc or alloca, with the exception of a non-builtin alloca with
no return value, but I think we've covered that elsewhere and Martin's code
will DTRT more by accident than design.
But we aren't going to warn on all places which might call alloca at runtime
with 0 arguments, you would need runtime instrumentation for that (like
ubsan). You are going to warn about explicit cases and random subset of the
other ones where the user is just unlucky enough that the compiler threaded
some jumps etc. For the explicit ptr = alloca (0) it is easy to get rid of
it, for the implicit one one has to pessimize code if they want to avoid the
warning.
No, it's a compile-time warning when the 0 size argument can be exposed.
It's not unlike many other warnings in GCC.
jeff
