runtime: fix exit status when killed by signal

Previously, when a program died because of a SIGHUP, SIGINT, or SIGTERM
signal it would exit with status 2.  This CL fixes the runtime to exit
with a status indicating that the program was killed by a signal.

Change-Id: Ic2982a2562857edfdccaf68856e0e4df532af136
Reviewed-on: https://go-review.googlesource.com/18156Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/runtime/crash_unix_test.go

@@ -133,3 +133,21 @@ func loop(i int, c chan bool) {
 	}
 }
 `
+
+func TestSignalExitStatus(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	exe, err := buildTestProg(t, "testprog")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = testEnv(exec.Command(exe, "SignalExitStatus")).Run()
+	if err == nil {
+		t.Error("test program succeeded unexpectedly")
+	} else if ee, ok := err.(*exec.ExitError); !ok {
+		t.Errorf("error (%v) has type %T; expected exec.ExitError", err, err)
+	} else if ws, ok := ee.Sys().(syscall.WaitStatus); !ok {
+		t.Errorf("error.Sys (%v) has type %T; expected syscall.WaitStatus", ee.Sys(), ee.Sys())
+	} else if !ws.Signaled() || ws.Signal() != syscall.SIGTERM {
+		t.Errorf("got %v; expected SIGTERM", ee)
+	}
+}

src/runtime/os_nacl.go

@@ -45,6 +45,10 @@ func os_sigpipe() {
 	throw("too many writes on closed pipe")
 }
 
+func dieFromSignal(sig int32) {
+	exit(2)
+}
+
 func sigpanic() {
 	g := getg()
 	if !canpanic(g) {

src/runtime/signal1_unix.go

@@ -142,8 +142,18 @@ func sigpipe() {
 	if sigsend(_SIGPIPE) {
 		return
 	}
-	setsig(_SIGPIPE, _SIG_DFL, false)
-	raise(_SIGPIPE)
+	dieFromSignal(_SIGPIPE)
+}
+
+// dieFromSignal kills the program with a signal.
+// This provides the expected exit status for the shell.
+// This is only called with fatal signals expected to kill the process.
+func dieFromSignal(sig int32) {
+	setsig(sig, _SIG_DFL, false)
+	updatesigmask(sigmask{})
+	raise(sig)
+	// That should have killed us; call exit just in case.
+	exit(2)
 }
 
 // raisebadsignal is called when a signal is received on a non-Go
@@ -196,9 +206,7 @@ func crash() {
 		}
 	}
 
-	updatesigmask(sigmask{})
-	setsig(_SIGABRT, _SIG_DFL, false)
-	raise(_SIGABRT)
+	dieFromSignal(_SIGABRT)
 }
 
 // ensureSigM starts one global, sleeping thread to make sure at least one thread

src/runtime/signal_386.go

@@ -108,7 +108,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	if flags&_SigKill != 0 {
-		exit(2)
+		dieFromSignal(int32(sig))
 	}
 
 	if flags&_SigThrow == 0 {

src/runtime/signal_amd64x.go

@@ -140,7 +140,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	if flags&_SigKill != 0 {
-		exit(2)
+		dieFromSignal(int32(sig))
 	}
 
 	if flags&_SigThrow == 0 {

src/runtime/signal_arm.go

@@ -100,7 +100,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	if flags&_SigKill != 0 {
-		exit(2)
+		dieFromSignal(int32(sig))
 	}
 
 	if flags&_SigThrow == 0 {

src/runtime/signal_arm64.go

@@ -116,7 +116,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	if flags&_SigKill != 0 {
-		exit(2)
+		dieFromSignal(int32(sig))
 	}
 
 	if flags&_SigThrow == 0 {

src/runtime/signal_mips64x.go

@@ -118,7 +118,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	if flags&_SigKill != 0 {
-		exit(2)
+		dieFromSignal(int32(sig))
 	}
 
 	if flags&_SigThrow == 0 {

src/runtime/signal_ppc64x.go

@@ -122,7 +122,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	}
 
 	if flags&_SigKill != 0 {
-		exit(2)
+		dieFromSignal(int32(sig))
 	}
 
 	if flags&_SigThrow == 0 {

src/runtime/testdata/testprog/signal.go

+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !windows,!plan9,!nacl
+
+package main
+
+import "syscall"
+
+func init() {
+	register("SignalExitStatus", SignalExitStatus)
+}
+
+func SignalExitStatus() {
+	syscall.Kill(syscall.Getpid(), syscall.SIGTERM)
+}