x86_64: Use sigprocmask from signal frames

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 f8a15e9679e59872ca2)

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

1 files changed, 2 insertions, 6 deletions

diff --git a/tests/Gtest-resume-sig.c b/tests/Gtest-resume-sig.c
index 147ecd03..846bba9f 100644
--- a/tests/Gtest-resume-sig.c
+++ b/tests/Gtest-resume-sig.c
@@ -74,7 +74,7 @@ handler (int sig)
 #endif
 {
   unw_word_t ip;
-  sigset_t mask, oldmask;
+  sigset_t mask;
   unw_context_t uc;
   unw_cursor_t c;
   char foo;
@@ -95,17 +95,13 @@ handler (int sig)
 
       sigemptyset (&mask);
       sigaddset (&mask, SIGUSR2);
-      sigprocmask (SIG_BLOCK, &mask, &oldmask);
+      sigprocmask (SIG_BLOCK, &mask, NULL);
       kill (getpid (), SIGUSR2);	/* pend SIGUSR2 */
 
       signal (SIGUSR1, SIG_IGN);
 
       if ((ret = unw_getcontext (&uc)) < 0)
 	panic ("unw_getcontext() failed: ret=%d\n", ret);
-#if UNW_TARGET_X86_64
-      /* unw_getcontext() doesn't save signal mask to avoid a syscall */
-      uc.uc_sigmask = oldmask; 
-#endif
       if ((ret = unw_init_local (&c, &uc)) < 0)
 	panic ("unw_init_local() failed: ret=%d\n", ret);