On Wed, Nov 18, 2020 at 01:11:27PM -0600, Segher Boessenkool wrote: > Calling this via a different declared function type is undefined > behaviour, but that is independent of how the function is *defined*. > Your program can make ducks appear from your nose even if that function > is never called, if you do that. Just don't do UB, not even once! Ah, see, here I think we disagree. UB is a flaw of the spec, but the real world often has very sane behaviour there (sometimes also very much not). In this particular instance the behaviour is UB because the C spec doesn't want to pin down the calling convention, which is something I can understand. But once you combine the C spec with the ABI(s) at hand, there really isn't two ways about it. This has to work, under the premise that the ABI defines a caller cleanup calling convention. So in the view that the compiler is a glorified assembler, I'll take UB every day if it means I can get the thing to do what I want it to. Obviously in the interest of co-operation and longer term viability, it would be nice if we can agree on the behaviour and get a language extention covering it. Note that we have a fairly extensive tradition of defining away UB with language extentions, -fno-strict-overflow, -fno-strict-aliasing, -fno-delete-null-pointer-checks etc..
