Currently setcontext for x86_64 restores the signal mask, even
though it is never saved anywhere. This means the signal mask
is often garbage after an unw_resume.
(changed in commit f8a15e9679)
It looks like this was a fix for the Gtest-resume-sig function -
testing if signal masks are restored across signal frames. The
root issue looks like that x86_64 only uses sigreturn for the exact
signal frame, and not for any decedant frames as well (as i64 does).
Instead, modify Gresume to use sigreturn if *any* frame on the stack
is a signal frame, so that we correct fixup the signal mask and any
sigaltstacks. The sigreturn os-specific functions are changed slightly
to copy in the saved ucontext structure if we are jumping farther
up the stack.
This should fix sigprocmask reported issues such as
https://github.com/dropbox/pyston/blob/master/libunwind_patches/0002-pyston-stop-x86_64-setcontext-restoring-uninitialize.patch
Tests pass on freebsd, linux
Mark frames which are unwound with the frame-chain walker or
syscall frame code, as non-interrupted. The return PC in the frame
points to the instruction after the call.
Insert static branch prediction predicates in useful places and avoid
unnecessary code in the hottest paths. Bypass unnecessary indirect
calls, in particular to access_mem(), when known to be safe.
