On Linux, when alternate signal stack is used with thread cancellation, _Unwind_Resume fails when it tries to unwind shadow stack from signal handler on alternate signal stack. The issue is that signal handler on alternate signal stack uses a separate shadow stack and we must switch to the original shadow stack to unwind it. But frame count will be wrong in this case. For thread cancellation, there is no need to unwind shadow stack since it will long jump back and exit.
One possibility is 1. Add _URC_NO_REASON_CANCEL. 2. unwind_stop in libpthread returns _URC_NO_REASON_CANCEL. 3. _Unwind_ForcedUnwind_Phase2 sets frames to 1 for _URC_NO_REASON_CANCEL BTW, I opened: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85086 -- H.J.
