sighook: Always re-raise faults on macOSHEADmain

macOS always fills in si_code for SIG{BUS,ILL,SEGV} as if it were a real
hardware fault, so returning from the handler is not guaranteed to re-
trigger the signal.

Fixes: aecdabb ("sighook: Return instead of re-raising for faults")
Link: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/2386463/4/util/posix/signals_test.cc
Link: https://github.com/chromium/crashpad/commit/e0d8a0aa01ac176804077f1f128ccc894c098f79

2 files changed, 11 insertions, 0 deletions

diff --git a/src/sighook.c b/src/sighook.c
index 6fd4c86..e74bb78 100644
--- a/src/sighook.c
+++ b/src/sighook.c
@@ -452,9 +452,16 @@ static void sigdispatch(int sig, siginfo_t *info, void *context) {
 	// to die "correctly" (e.g. with a core dump pointing at the faulting
 	// instruction, not reraise()).
 	if (is_fault(info)) {
+		// On macOS, we cannot reliably distinguish between faults and
+		// asynchronous signals.  For example, pkill -SEGV bfs will
+		// result in si_code == SEGV_ACCERR.  So we always re-raise the
+		// signal, because just returning would cause us to ignore
+		// asynchronous SIG{BUS,ILL,SEGV}.
+#if !__APPLE__
 		if (signal(sig, SIG_DFL) != SIG_ERR) {
 			return;
 		}
+#endif
 		reraise(sig);
 	}
 
diff --git a/tests/sighook.c b/tests/sighook.c
index 3a715e6..ba1c424 100644
--- a/tests/sighook.c
+++ b/tests/sighook.c
@@ -216,5 +216,9 @@ void check_sighook(void) {
 	check_sigexit(SIGINT);
 	check_sigexit(SIGQUIT);
 	check_sigexit(SIGPIPE);
+
+	// macOS cannot distinguish between sync and async SIG{BUS,ILL,SEGV}
+#if !__APPLE__
 	check_sigexit(SIGSEGV);
+#endif
 }