runtime: don't forward SIGPIPE on macOS

macOS and iOS deliver SIGPIPE signals to the main thread and not
the thread that raised it by writing to a closed socket or pipe.

SIGPIPE signals can be suppressed for sockets with the SO_NOSIGPIPE
option, but there is no similar option for pipes. We have no other
choice but to never forward SIGPIPE on macOS.

This is a fixup of reverted CL 188297.

Fixes #33384

Change-Id: I09b258b078857ad3b22025bc2902d1b12d2afd92
Reviewed-on: https://go-review.googlesource.com/c/go/+/191785
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcarchive/carchive_test.go

@@ -282,7 +282,13 @@ func TestEarlySignalHandler(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if out, err := exec.Command(bin[0], bin[1:]...).CombinedOutput(); err != nil {
+	darwin := "0"
+	if runtime.GOOS == "darwin" {
+		darwin = "1"
+	}
+	cmd = exec.Command(bin[0], append(bin[1:], darwin)...)
+
+	if out, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("%s", out)
 		t.Fatal(err)
 	}
@@ -320,12 +326,15 @@ func TestSignalForwarding(t *testing.T) {
 	t.Logf("%s", out)
 	expectSignal(t, err, syscall.SIGSEGV)
 
+	// SIGPIPE is never forwarded on darwin. See golang.org/issue/33384.
+	if runtime.GOOS != "darwin" {
 		// Test SIGPIPE forwarding
 		cmd = exec.Command(bin[0], append(bin[1:], "3")...)
 
 		out, err = cmd.CombinedOutput()
 		t.Logf("%s", out)
 		expectSignal(t, err, syscall.SIGPIPE)
+	}
 }
 
 func TestSignalForwardingExternal(t *testing.T) {
@@ -744,11 +753,20 @@ func TestCompileWithoutShared(t *testing.T) {
 	}
 	defer os.Remove(exe)
 
+	binArgs := append(cmdToRun(exe), "1")
+	t.Log(binArgs)
+	out, err = exec.Command(binArgs[0], binArgs[1:]...).CombinedOutput()
+	t.Logf("%s", out)
+	expectSignal(t, err, syscall.SIGSEGV)
+
+	// SIGPIPE is never forwarded on darwin. See golang.org/issue/33384.
+	if runtime.GOOS != "darwin" {
 		binArgs := append(cmdToRun(exe), "3")
 		t.Log(binArgs)
 		out, err = exec.Command(binArgs[0], binArgs[1:]...).CombinedOutput()
 		t.Logf("%s", out)
 		expectSignal(t, err, syscall.SIGPIPE)
+	}
 }
 
 // Test that installing a second time recreates the header files.

misc/cgo/testcarchive/testdata/main2.c

@@ -123,8 +123,12 @@ int main(int argc, char** argv) {
 	sigset_t mask;
 	int i;
 	struct timespec ts;
+	int darwin;
+
+	darwin = atoi(argv[1]);
+
+	verbose = argc > 2;
 
-	verbose = argc > 1;
 	setvbuf(stdout, NULL, _IONBF, 0);
 
 	// Call setsid so that we can use kill(0, SIGIO) below.
@@ -186,6 +190,8 @@ int main(int argc, char** argv) {
 		printf("provoking SIGPIPE\n");
 	}
 
+	// SIGPIPE is never forwarded on Darwin, see golang.org/issue/33384.
+	if (!darwin) {
 		GoRaiseSIGPIPE();
 
 		if (verbose) {
@@ -204,6 +210,7 @@ int main(int argc, char** argv) {
 				exit(EXIT_FAILURE);
 			}
 		}
+	}
 
 	if (verbose) {
 		printf("calling setjmp\n");

misc/cgo/testcarchive/testdata/main3.c

@@ -12,6 +12,7 @@
 #include <time.h>
 #include <sched.h>
 #include <unistd.h>
+#include <pthread.h>
 
 #include "libgo3.h"
 
@@ -51,11 +52,18 @@ static void init() {
 	}
 }
 
+static void *provokeSIGPIPE(void *arg) {
+	ProvokeSIGPIPE();
+	return NULL;
+}
+
 int main(int argc, char** argv) {
 	int verbose;
 	struct sigaction sa;
 	int i;
 	struct timespec ts;
+	int res;
+	pthread_t tid;
 
 	verbose = argc > 2;
 	setvbuf(stdout, NULL, _IONBF, 0);
@@ -68,6 +76,19 @@ int main(int argc, char** argv) {
 	// a non-default SIGPIPE handler before the runtime initializes.
 	ProvokeSIGPIPE();
 
+	// Test that SIGPIPE on a non-main thread is also handled by Go.
+	res = pthread_create(&tid, NULL, provokeSIGPIPE, NULL);
+	if (res != 0) {
+		fprintf(stderr, "pthread_create: %s\n", strerror(res));
+		exit(EXIT_FAILURE);
+	}
+
+	res = pthread_join(tid, NULL);
+	if (res != 0) {
+		fprintf(stderr, "pthread_join: %s\n", strerror(res));
+		exit(EXIT_FAILURE);
+	}
+
 	if (verbose) {
 		printf("calling sigaction\n");
 	}

src/runtime/signal_unix.go

@@ -636,6 +636,13 @@ func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
 		return true
 	}
 
+	// This function and its caller sigtrampgo assumes SIGPIPE is delivered on the
+	// originating thread. This property does not hold on macOS (golang.org/issue/33384),
+	// so we have no choice but to ignore SIGPIPE.
+	if GOOS == "darwin" && sig == _SIGPIPE {
+		return true
+	}
+
 	// If there is no handler to forward to, no need to forward.
 	if fwdFn == _SIG_DFL {
 		return false