runtime: fix FreeBSD signal handling around thread creation

Ignore signals while we are spawning a new thread. Previously, a
signal arriving just before runtime.minit setting up the signal
handler triggers a "double fault" in signal trampolining.
Fixes #3017.

R=rsc, mikioh.mikioh, minux.ma, adg
CC=golang-dev
https://golang.org/cl/5684060

src/pkg/runtime/cgo/gcc_freebsd_386.c

@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+#include <sys/types.h>
+#include <sys/signalvar.h>
 #include <pthread.h>
+#include <signal.h>
 #include "libcgo.h"
 
 static void* threadentry(void*);
@@ -25,14 +28,21 @@ 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();

src/pkg/runtime/cgo/gcc_freebsd_amd64.c

@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+#include <sys/types.h>
+#include <sys/signalvar.h>
 #include <pthread.h>
+#include <signal.h>
 #include "libcgo.h"
 
 static void* threadentry(void*);
@@ -25,14 +28,22 @@ 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();

src/pkg/runtime/os_freebsd.h

@@ -7,6 +7,7 @@ void	runtime·sigpanic(void);
 void	runtime·sigaltstack(Sigaltstack*, Sigaltstack*);
 struct	sigaction;
 void	runtime·sigaction(int32, struct sigaction*, struct sigaction*);
+void	runtime·sigprocmask(Sigset *, Sigset *);
 void	runtime·setsig(int32, void(*)(int32, Siginfo*, void*, G*), bool);
 void	runtiem·setitimerval(int32, Itimerval*, Itimerval*);
 void	runtime·setitimer(int32, Itimerval*, Itimerval*);

src/pkg/runtime/sys_freebsd_386.s

@@ -304,4 +304,17 @@ TEXT runtime·osyield(SB),7,$-4
 	INT	$0x80
 	RET
 
+TEXT runtime·sigprocmask(SB),7,$16
+	MOVL	$0, 0(SP)		// syscall gap
+	MOVL	$3, 4(SP)		// arg 1 - how (SIG_SETMASK)
+	MOVL	args+0(FP), AX
+	MOVL	AX, 8(SP)		// arg 2 - set
+	MOVL	args+4(FP), AX
+	MOVL	AX, 12(SP)		// arg 3 - oset
+	MOVL	$340, AX		// sys_sigprocmask
+	INT	$0x80
+	JAE	2(PC)
+	CALL	runtime·notok(SB)
+	RET
+
 GLOBL runtime·tlsoffset(SB),$4

src/pkg/runtime/sys_freebsd_amd64.s

@@ -233,3 +233,13 @@ TEXT runtime·osyield(SB),7,$-4
 	MOVL	$331, AX		// sys_sched_yield
 	SYSCALL
 	RET
+
+TEXT runtime·sigprocmask(SB),7,$0
+	MOVL	$3, DI			// arg 1 - how (SIG_SETMASK)
+	MOVQ	8(SP), SI		// arg 2 - set
+	MOVQ	16(SP), DX		// arg 3 - oset
+	MOVL	$340, AX		// sys_sigprocmask
+	SYSCALL
+	JAE	2(PC)
+	CALL	runtime·notok(SB)
+	RET

src/pkg/runtime/thread_freebsd.c

@@ -13,6 +13,9 @@ extern int32 runtime·sys_umtx_op(uint32*, int32, uint32, void*, void*);
 #define	CTL_HW	6
 #define	HW_NCPU	3
 
+static Sigset sigset_all = { ~(uint32)0, ~(uint32)0, ~(uint32)0, ~(uint32)0, };
+static Sigset sigset_none = { 0, 0, 0, 0, };
+
 static int32
 getncpu(void)
 {
@@ -77,6 +80,7 @@ void
 runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 {
 	ThrParam param;
+	Sigset oset;
 
 	USED(fn);	// thr_start assumes fn == mstart
 	USED(g);	// thr_start assumes g == m->g0
@@ -86,6 +90,7 @@ runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 			stk, m, g, fn, m->id, m->tls[0], &m);
 	}
 
+	runtime·sigprocmask(&sigset_all, &oset);
 	runtime·memclr((byte*)&param, sizeof param);
 
 	param.start_func = runtime·thr_start;
@@ -100,6 +105,7 @@ runtime·newosproc(M *m, G *g, void *stk, void (*fn)(void))
 	m->tls[0] = m->id;	// so 386 asm can find it
 
 	runtime·thr_new(&param, sizeof param);
+	runtime·sigprocmask(&oset, nil);
 }
 
 void
@@ -121,6 +127,7 @@ runtime·minit(void)
 	// Initialize signal handling
 	m->gsignal = runtime·malg(32*1024);
 	runtime·signalstack(m->gsignal->stackguard - StackGuard, 32*1024);
+	runtime·sigprocmask(&sigset_none, nil);
 }
 
 void