When scanning the registers+stack for an SGEN collection, we do not currently scan the FPU registers on Darwin for ARM64.
We do scan XMM registers on Darwin for Intel ( https://github.com/mono/mono/pull/4127 ). We do not have proof that FPU needs to be scanned on Darwin for ARM64, however, since Clang has been spotted using XMM registers to accelerate memcpys on Darwin/Intel32 and Darwin/Intel64, and GCC has been spotted using the FPU registers for register spilling on Linux/ARM, it is very plausible Clang is using the FPU registers on ARM64 and we just haven't caught it yet.
Because this creates high risk for hard-to-spot bugs it should be fixed for C9.
Did you apply the intel darwin fix to arm?
C9 is now closed. We'll move this bug to the next scheduled milestone, "15.1". We'll continue working on these issues, and will attempt to resolve them ASAP.
15.1 is shipping C9, I think this should be bumped to 15.3
Or rather I mean 15.1 is shipping Mono 4.8.
Moving back to Ludovic to find someone to work on it.