On Thu, Jul 13, 2017 at 12:25 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote:
> > Anyway this seems like a clang bug to me. If I specify RSP as an input > register then the compiler shouldn't overwrite it first. For that > matter it has no reason to overwrite it if it's an output register > either. > It's certainly a difference in behavior between clang and gcc. My question is whether this particular construct is really a "supported" (or, at least, reasonably guaranteed) way of forcing gcc to create a stack frame if none exists. or whether it is something that "just happens to work". If someone could explain the rationale behind *why* this works the way that it does on gcc that might help convince the clang people that this is actually a bug rather than just a piece of undefined behavior which gcc and clang happen to handle differently.
