https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105708
--- Comment #5 from Keno Fischer <keno at juliacomputing dot com> --- Yes, rr cannot record ll/sc. I'm happy to go into depth here, but this is not really an aarch64 issue. rr doesn't work on ppc64le either for this reason. The introduction of lse has made rr feasible on aarch64, and there has been a substantial effort to get to this point where rr is working on the architecture. We're now working through the distribution issues, where this cropped up (as mentioned, we didn't notice earlier, because the initialization is not deterministic). For the moment, we're telling downstream users to avoid manual use of ll/sc in programs that they want to record under rr. Obviously this is a significant effort, but for many people it's worth it, because rr is a critical tool. Perhaps in future hardware iterations, we'll get the ability to fault on stxr abort or similar, which would allow rr to support ll/sc, but until then we need to make due with what we have. The issue here is that `-moutline-atomics` now introduces extra ll/sc instructions even in software where the implementer was careful to avoid manual uses of ll/sc and in particular also in system libraries like libc and rtld that the user may have little control over. Of course we can keep telling people to build their distribution images with `-march=armv8.3-a -mno-outline-atomics` and avoid this issue or have them patch libgcc downstream, but that really seems to defeat the point of `-moutline-atomics`, which was exactly to avoid this kind of split.
