https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64735
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Bastiaan Jacques from comment #5) > (In reply to Jonathan Wakely from comment #3) > > i.e. it's not broken, it's missing, and that's by design. > > So is it the intention of the GCC developers that program writers targeting > such platforms simply avoid these facilities and use std::thread/mutex > instead? Or they could contribute an implementation that works for their target. The intention of the developers is that the feature should work correctly, and if that isn't possible with the current implementation for some target, then the feature should be disabled on that target. And that's what you see.