The upstream issue with discussion about Arm support is https://github.com/mozilla/rr/issues/1373 https://github.com/mozilla/rr/issues/1373 -- the underlying pr

The upstream issue with discussion about Arm support is https://github.com/mozilla/rr/issues/1373 https://github.com/mozilla/rr/issues/1373 -- the underlying problem is that rr's design assumes that if you execute N instructions you'll always deterministically end up in the same place. In architectures which implement atomics via a load-linked/store-conditional loop (including Alpha, Arm, MIPS, PPC,...) this isn't true, because differences at the OS level (eg timing of other interrupts or process scheduling) could cause an ll/sc loop to loop round more often. It's not clear how this could be addressed, because it's pretty deeply baked into rr's design.