runtime: Permit default behaviour of SIGTSTP, SIGTTIN, SIGTTOU.

Fixes #3037.

R=rsc, minux.ma, r, rsc
CC=golang-dev
https://golang.org/cl/5674072

src/pkg/runtime/runtime.h

diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 48f6b3e..910f00c 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -268,9 +268,10 @@
 enum
 {
 	SigNotify = 1<<0,	// let signal.Notify have signal, even if from kernel
-	SigKill = 1<<1,  // if signal.Notify doesn't take it, exit quietly
-	SigThrow = 1<<2,  // if signal.Notify doesn't take it, exit loudly
-	SigPanic = 1<<3,  // if the signal is from the kernel, panic
+	SigKill = 1<<1,		// if signal.Notify doesn't take it, exit quietly
+	SigThrow = 1<<2,	// if signal.Notify doesn't take it, exit loudly
+	SigPanic = 1<<3,	// if the signal is from the kernel, panic
+	SigDefault = 1<<4,	// if the signal isn't explicitly requested, don't monitor it
 };
 
 // NOTE(rsc): keep in sync with extern.go:/type.Func.
@@ -501,6 +502,7 @@
 String	runtime·gostringnocopy(byte*);
 String	runtime·gostringw(uint16*);
 void	runtime·initsig(void);
+void	runtime·sigenable(uint32 sig);
 int32	runtime·gotraceback(void);
 void	runtime·goroutineheader(G*);
 void	runtime·traceback(uint8 *pc, uint8 *sp, uint8 *lr, G* gp);

src/pkg/runtime/signal_plan9_386.c

diff --git a/src/pkg/runtime/signal_plan9_386.c b/src/pkg/runtime/signal_plan9_386.c
index c0b759c..996ce8b 100644
--- a/src/pkg/runtime/signal_plan9_386.c
+++ b/src/pkg/runtime/signal_plan9_386.c
@@ -11,6 +11,11 @@
 }
 
 void
+runtime·sigenable(uint32 sig)
+{
+}
+
+void
 runtime·resetcpuprofiler(int32 hz)
 {
 	// TODO: Enable profiling interrupts.

src/pkg/runtime/signal_unix.c

diff --git a/src/pkg/runtime/signal_unix.c b/src/pkg/runtime/signal_unix.c
index 14ce141..1370841 100644
--- a/src/pkg/runtime/signal_unix.c
+++ b/src/pkg/runtime/signal_unix.c
@@ -27,9 +27,27 @@
 	// First call: basic setup.
 	for(i = 0; i<NSIG; i++) {
 		t = &runtime·sigtab[i];
-		if(t->flags == 0)
+		if((t->flags == 0) || (t->flags & SigDefault))
 			continue;
-		runtime·setsig(i, runtime·sighandler, 1);
+		runtime·setsig(i, runtime·sighandler, true);
+	}
+}
+
+void
+runtime·sigenable(uint32 sig)
+{
+	int32 i;
+	SigTab *t;
+
+	for(i = 0; i<NSIG; i++) {
+		// ~0 means all signals.
+		if(~sig == 0 || i == sig) {
+			t = &runtime·sigtab[i];
+			if(t->flags & SigDefault) {
+				runtime·setsig(i, runtime·sighandler, true);
+				t->flags &= ~SigDefault;  // make this idempotent
+			}
+		}
 	}
 }
 

src/pkg/runtime/signal_windows_386.c

diff --git a/src/pkg/runtime/signal_windows_386.c b/src/pkg/runtime/signal_windows_386.c
index 0efa8c0..7b3492f 100644
--- a/src/pkg/runtime/signal_windows_386.c
+++ b/src/pkg/runtime/signal_windows_386.c
@@ -81,6 +81,11 @@
 }
 
 void
+runtime·sigenable(uint32 sig)
+{
+}
+
+void
 runtime·dosigprof(Context *r, G *gp)
 {
 	runtime·sigprof((uint8*)r->Eip, (uint8*)r->Esp, nil, gp);

src/pkg/runtime/signal_windows_amd64.c

diff --git a/src/pkg/runtime/signal_windows_amd64.c b/src/pkg/runtime/signal_windows_amd64.c
index 3db89e6..e5e20fa 100644
--- a/src/pkg/runtime/signal_windows_amd64.c
+++ b/src/pkg/runtime/signal_windows_amd64.c
@@ -88,6 +88,11 @@
 }
 
 void
+runtime·sigenable(uint32 sig)
+{
+}
+
+void
 runtime·dosigprof(Context *r, G *gp)
 {
 	runtime·sigprof((uint8*)r->Rip, (uint8*)r->Rsp, nil, gp);

src/pkg/runtime/signals_darwin.h

diff --git a/src/pkg/runtime/signals_darwin.h b/src/pkg/runtime/signals_darwin.h
index 4ff08bc..229b585 100644
--- a/src/pkg/runtime/signals_darwin.h
+++ b/src/pkg/runtime/signals_darwin.h
@@ -6,6 +6,7 @@
 #define K SigKill
 #define T SigThrow
 #define P SigPanic
+#define D SigDefault
 
 SigTab runtime·sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
@@ -26,11 +27,11 @@
 	/* 15 */	N+K, "SIGTERM: termination",
 	/* 16 */	N, "SIGURG: urgent condition on socket",
 	/* 17 */	0, "SIGSTOP: stop",
-	/* 18 */	N, "SIGTSTP: keyboard stop",
+	/* 18 */	N+D, "SIGTSTP: keyboard stop",
 	/* 19 */	0, "SIGCONT: continue after stop",
 	/* 20 */	N, "SIGCHLD: child status has changed",
-	/* 21 */	N, "SIGTTIN: background read from tty",
-	/* 22 */	N, "SIGTTOU: background write to tty",
+	/* 21 */	N+D, "SIGTTIN: background read from tty",
+	/* 22 */	N+D, "SIGTTOU: background write to tty",
 	/* 23 */	N, "SIGIO: i/o now possible",
 	/* 24 */	N, "SIGXCPU: cpu limit exceeded",
 	/* 25 */	N, "SIGXFSZ: file size limit exceeded",
@@ -46,3 +47,4 @@
 #undef K
 #undef T
 #undef P
+#undef D

src/pkg/runtime/signals_freebsd.h

diff --git a/src/pkg/runtime/signals_freebsd.h b/src/pkg/runtime/signals_freebsd.h
index 6a15017..4d27e05 100644
--- a/src/pkg/runtime/signals_freebsd.h
+++ b/src/pkg/runtime/signals_freebsd.h
@@ -6,6 +6,7 @@
 #define K SigKill
 #define T SigThrow
 #define P SigPanic
+#define D SigDefault
 
 SigTab runtime·sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
@@ -26,11 +27,11 @@
 	/* 15 */	N+K, "SIGTERM: termination",
 	/* 16 */	N, "SIGURG: urgent condition on socket",
 	/* 17 */	0, "SIGSTOP: stop",
-	/* 18 */	N, "SIGTSTP: keyboard stop",
+	/* 18 */	N+D, "SIGTSTP: keyboard stop",
 	/* 19 */	0, "SIGCONT: continue after stop",
 	/* 20 */	N, "SIGCHLD: child status has changed",
-	/* 21 */	N, "SIGTTIN: background read from tty",
-	/* 22 */	N, "SIGTTOU: background write to tty",
+	/* 21 */	N+D, "SIGTTIN: background read from tty",
+	/* 22 */	N+D, "SIGTTOU: background write to tty",
 	/* 23 */	N, "SIGIO: i/o now possible",
 	/* 24 */	N, "SIGXCPU: cpu limit exceeded",
 	/* 25 */	N, "SIGXFSZ: file size limit exceeded",
@@ -47,3 +48,4 @@
 #undef K
 #undef T
 #undef P
+#undef D

src/pkg/runtime/signals_linux.h

diff --git a/src/pkg/runtime/signals_linux.h b/src/pkg/runtime/signals_linux.h
index 1df063a..345a6c5 100644
--- a/src/pkg/runtime/signals_linux.h
+++ b/src/pkg/runtime/signals_linux.h
@@ -6,6 +6,7 @@
 #define K SigKill
 #define T SigThrow
 #define P SigPanic
+#define D SigDefault
 
 SigTab runtime·sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
@@ -28,9 +29,9 @@
 	/* 17 */	N, "SIGCHLD: child status has changed",
 	/* 18 */	0, "SIGCONT: continue",
 	/* 19 */	0, "SIGSTOP: stop, unblockable",
-	/* 20 */	N, "SIGTSTP: keyboard stop",
-	/* 21 */	N, "SIGTTIN: background read from tty",
-	/* 22 */	N, "SIGTTOU: background write to tty",
+	/* 20 */	N+D, "SIGTSTP: keyboard stop",
+	/* 21 */	N+D, "SIGTTIN: background read from tty",
+	/* 22 */	N+D, "SIGTTOU: background write to tty",
 	/* 23 */	N, "SIGURG: urgent condition on socket",
 	/* 24 */	N, "SIGXCPU: cpu limit exceeded",
 	/* 25 */	N, "SIGXFSZ: file size limit exceeded",
@@ -79,3 +80,4 @@
 #undef K
 #undef T
 #undef P
+#undef D

src/pkg/runtime/signals_netbsd.h

diff --git a/src/pkg/runtime/signals_netbsd.h b/src/pkg/runtime/signals_netbsd.h
index 6a15017..4d27e05 100644
--- a/src/pkg/runtime/signals_netbsd.h
+++ b/src/pkg/runtime/signals_netbsd.h
@@ -6,6 +6,7 @@
 #define K SigKill
 #define T SigThrow
 #define P SigPanic
+#define D SigDefault
 
 SigTab runtime·sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
@@ -26,11 +27,11 @@
 	/* 15 */	N+K, "SIGTERM: termination",
 	/* 16 */	N, "SIGURG: urgent condition on socket",
 	/* 17 */	0, "SIGSTOP: stop",
-	/* 18 */	N, "SIGTSTP: keyboard stop",
+	/* 18 */	N+D, "SIGTSTP: keyboard stop",
 	/* 19 */	0, "SIGCONT: continue after stop",
 	/* 20 */	N, "SIGCHLD: child status has changed",
-	/* 21 */	N, "SIGTTIN: background read from tty",
-	/* 22 */	N, "SIGTTOU: background write to tty",
+	/* 21 */	N+D, "SIGTTIN: background read from tty",
+	/* 22 */	N+D, "SIGTTOU: background write to tty",
 	/* 23 */	N, "SIGIO: i/o now possible",
 	/* 24 */	N, "SIGXCPU: cpu limit exceeded",
 	/* 25 */	N, "SIGXFSZ: file size limit exceeded",
@@ -47,3 +48,4 @@
 #undef K
 #undef T
 #undef P
+#undef D

src/pkg/runtime/signals_openbsd.h

diff --git a/src/pkg/runtime/signals_openbsd.h b/src/pkg/runtime/signals_openbsd.h
index 6a15017..4d27e05 100644
--- a/src/pkg/runtime/signals_openbsd.h
+++ b/src/pkg/runtime/signals_openbsd.h
@@ -6,6 +6,7 @@
 #define K SigKill
 #define T SigThrow
 #define P SigPanic
+#define D SigDefault
 
 SigTab runtime·sigtab[] = {
 	/* 0 */	0, "SIGNONE: no trap",
@@ -26,11 +27,11 @@
 	/* 15 */	N+K, "SIGTERM: termination",
 	/* 16 */	N, "SIGURG: urgent condition on socket",
 	/* 17 */	0, "SIGSTOP: stop",
-	/* 18 */	N, "SIGTSTP: keyboard stop",
+	/* 18 */	N+D, "SIGTSTP: keyboard stop",
 	/* 19 */	0, "SIGCONT: continue after stop",
 	/* 20 */	N, "SIGCHLD: child status has changed",
-	/* 21 */	N, "SIGTTIN: background read from tty",
-	/* 22 */	N, "SIGTTOU: background write to tty",
+	/* 21 */	N+D, "SIGTTIN: background read from tty",
+	/* 22 */	N+D, "SIGTTOU: background write to tty",
 	/* 23 */	N, "SIGIO: i/o now possible",
 	/* 24 */	N, "SIGXCPU: cpu limit exceeded",
 	/* 25 */	N, "SIGXFSZ: file size limit exceeded",
@@ -47,3 +48,4 @@
 #undef K
 #undef T
 #undef P
+#undef D

src/pkg/runtime/sigqueue.goc

diff --git a/src/pkg/runtime/sigqueue.goc b/src/pkg/runtime/sigqueue.goc
index 02b5755..b49fdba 100644
--- a/src/pkg/runtime/sigqueue.goc
+++ b/src/pkg/runtime/sigqueue.goc
@@ -140,10 +140,12 @@
 		// Special case: want everything.
 		for(i=0; i<nelem(sig.wanted); i++)
 			sig.wanted[i] = ~(uint32)0;
+		runtime·sigenable(s);
 		return;
 	}
 
 	if(s >= nelem(sig.wanted)*32)
 		return;
 	sig.wanted[s/32] |= 1U<<(s&31);
+	runtime·sigenable(s);
 }