runtime/cgo: linux signal masking

Fixes #3314.
Fixes #3101 (again).

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5820047

src/pkg/runtime/cgo/gcc_linux_386.c

@@ -4,6 +4,7 @@
 
 #include <pthread.h>
 #include <string.h>
+#include <signal.h>
 #include "libcgo.h"
 
 static void *threadentry(void*);
@@ -26,10 +27,14 @@ void
 libcgo_sys_thread_start(ThreadStart *ts)
 {
 	pthread_attr_t attr;
+	sigset_t ign, oset;
 	pthread_t p;
 	size_t size;
 	int err;
 
+	sigfillset(&ign);
+	sigprocmask(SIG_SETMASK, &ign, &oset);
+
 	// Not sure why the memset is necessary here,
 	// but without it, we get a bogus stack size
 	// out of pthread_attr_getstacksize.  C'est la Linux.
@@ -39,6 +44,9 @@ libcgo_sys_thread_start(ThreadStart *ts)
 	pthread_attr_getstacksize(&attr, &size);
 	ts->g->stackguard = size;
 	err = pthread_create(&p, &attr, threadentry, ts);
+
+	sigprocmask(SIG_SETMASK, &oset, nil);
+
 	if (err != 0) {
 		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
 		abort();

src/pkg/runtime/cgo/gcc_linux_amd64.c

@@ -4,6 +4,7 @@
 
 #include <pthread.h>
 #include <string.h> // strerror
+#include <signal.h>
 #include "libcgo.h"
 
 static void* threadentry(void*);
@@ -26,14 +27,21 @@ void
 libcgo_sys_thread_start(ThreadStart *ts)
 {
 	pthread_attr_t attr;
+	sigset_t ign, oset;
 	pthread_t p;
 	size_t size;
 	int err;
 
+	sigfillset(&ign);
+	sigprocmask(SIG_SETMASK, &ign, &oset);
+
 	pthread_attr_init(&attr);
 	pthread_attr_getstacksize(&attr, &size);
 	ts->g->stackguard = size;
 	err = pthread_create(&p, &attr, threadentry, ts);
+
+	sigprocmask(SIG_SETMASK, &oset, nil);
+
 	if (err != 0) {
 		fprintf(stderr, "runtime/cgo: pthread_create failed: %s\n", strerror(err));
 		abort();