https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66848
--- Comment #4 from Jack Howarth <howarth.at.gcc at gmail dot com> --- The gctest hang backtraces as... # lldb ./gctest (lldb) target create "./gctest" Current executable set to './gctest' (x86_64). (lldb) r Process 35911 launched: './gctest' (x86_64) Switched to incremental mode Emulating dirty bits with mprotect/signals thread_get_state failed in forward_exception Process 35911 stopped * thread #2: tid = 0x20d116, 0x00007fff8e6c4076 libsystem_kernel.dylib`__pthread_kill + 10, stop reason = signal SIGABRT frame #0: 0x00007fff8e6c4076 libsystem_kernel.dylib`__pthread_kill + 10 libsystem_kernel.dylib`__pthread_kill: -> 0x7fff8e6c4076 <+10>: jae 0x7fff8e6c4080 ; <+20> 0x7fff8e6c4078 <+12>: movq %rax, %rdi 0x7fff8e6c407b <+15>: jmp 0x7fff8e6bf0df ; cerror_nocancel 0x7fff8e6c4080 <+20>: retq (lldb) bt * thread #2: tid = 0x20d116, 0x00007fff8e6c4076 libsystem_kernel.dylib`__pthread_kill + 10, stop reason = signal SIGABRT * frame #0: 0x00007fff8e6c4076 libsystem_kernel.dylib`__pthread_kill + 10 frame #1: 0x00007fff9e61163d libsystem_pthread.dylib`pthread_kill + 90 frame #2: 0x00007fff95d5783b libsystem_c.dylib`abort + 129 frame #3: 0x0000000100022e29 libgcjgc.1.dylib`GC_abort(msg=<unavailable>) + 57 at misc.c:1081 (lldb)