runtime: implement getcontext and sigprocmask for netbsd

Implement getcontext and sigprocmask for NetBSD - these will soon be
used by the thread handling code.

Also fix netbsd/386 signal handling - there is no sigreturn, just
return so that we hit the trampoline.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6215049

src/pkg/runtime/os_netbsd.h

@@ -5,17 +5,22 @@
 #define SIG_DFL ((void*)0)
 #define SIG_IGN ((void*)1)
 
+#define SIG_BLOCK 1
+#define SIG_UNBLOCK 2
+#define SIG_SETMASK 3
+
 struct sigaction;
 
-void	runtime·sigpanic(void);
-void	runtime·sigaltstack(Sigaltstack*, Sigaltstack*);
-void	runtime·sigaction(int32, struct sigaction*, struct sigaction*);
+void	runtime·raisesigpipe(void);
 void	runtime·setsig(int32, void(*)(int32, Siginfo*, void*, G*), bool);
 void	runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp);
+void	runtime·sigpanic(void);
+
+void	runtime·sigaction(int32, struct sigaction*, struct sigaction*);
+void	runtime·sigaltstack(Sigaltstack*, Sigaltstack*);
 void	runtime·setitimer(int32, Itimerval*, Itimerval*);
+void	runtime·sigprocmask(int32, Sigset*, Sigset*);
 int32	runtime·sysctl(uint32*, uint32, byte*, uintptr*, byte*, uintptr);
 
-void	runtime·raisesigpipe(void);
-
 #define	NSIG 33
 #define	SI_USER	0

src/pkg/runtime/sys_netbsd_386.s

@@ -122,12 +122,26 @@ TEXT runtime·nanotime(SB),7,$32
 	IMULL	$1000, BX
 	ADDL	BX, AX
 	ADCL	$0, DX
-	
+
 	MOVL	ret+0(FP), DI
 	MOVL	AX, 0(DI)
 	MOVL	DX, 4(DI)
 	RET
 
+TEXT runtime·getcontext(SB),7,$-4
+	MOVL	$307, AX		// sys_getcontext
+	INT	$0x80
+	JAE	2(PC)
+	MOVL	$0xf1, 0xf1		// crash
+	RET
+
+TEXT runtime·sigprocmask(SB),7,$-4
+	MOVL	$293, AX		// sys_sigprocmask
+	INT	$0x80
+	JAE	2(PC)
+	MOVL	$0xf1, 0xf1		// crash
+	RET
+
 TEXT runtime·sigreturn_tramp(SB),7,$0
 	LEAL	140(SP), AX		// Load address of ucontext
 	MOVL	AX, 4(SP)
@@ -166,7 +180,7 @@ TEXT runtime·sigtramp(SB),7,$44
 	// save g
 	MOVL	g(CX), DI
 	MOVL	DI, 20(SP)
-	
+
 	// g = m->gsignal
 	MOVL	m_gsignal(BX), BX
 	MOVL	BX, g(CX)
@@ -186,14 +200,6 @@ TEXT runtime·sigtramp(SB),7,$44
 	get_tls(CX)
 	MOVL	20(SP), BX
 	MOVL	BX, g(CX)
-	
-	// call sigreturn
-	MOVL	context+8(FP), AX
-	MOVL	$0, 0(SP)		// syscall gap
-	MOVL	AX, 4(SP)		// arg 1 - sigcontext
-	MOVL	$103, AX		// sys_sigreturn
-	INT	$0x80
-	MOVL	$0xf1, 0xf1		// crash
 	RET
 
 // int32 rfork_thread(int32 flags, void *stack, M *m, G *g, void (*fn)(void));
@@ -255,7 +261,7 @@ TEXT runtime·rfork_thread(SB),7,$8
 	CALL	runtime·settls(SB)
 	POPL	AX
 	POPAL
-	
+
 	// Now segment is established.  Initialize m, g.
 	get_tls(AX)
 	MOVL	DX, g(AX)

src/pkg/runtime/sys_netbsd_amd64.s

@@ -163,6 +163,24 @@ TEXT runtime·nanotime(SB),7,$32
 	ADDQ	DX, AX
 	RET
 
+TEXT runtime·getcontext(SB),7,$-8
+	MOVQ	8(SP), DI		// arg 1 - context
+	MOVL	$307, AX		// sys_getcontext
+	SYSCALL
+	JCC	2(PC)
+	MOVL	$0xf1, 0xf1		// crash
+	RET
+
+TEXT runtime·sigprocmask(SB),7,$0
+	MOVL	8(SP), DI		// arg 1 - how
+	MOVQ	16(SP), SI		// arg 2 - set
+	MOVQ	24(SP), DX		// arg 3 - oset
+	MOVL	$293, AX		// sys_sigprocmask
+	SYSCALL
+	JCC	2(PC)
+	MOVL	$0xf1, 0xf1		// crash
+	RET
+
 TEXT runtime·sigreturn_tramp(SB),7,$-8
 	MOVQ	R15, DI			// Load address of ucontext
 	MOVQ	$308, AX		// sys_setcontext
@@ -186,7 +204,7 @@ TEXT runtime·sigaction(SB),7,$-8
 
 TEXT runtime·sigtramp(SB),7,$64
 	get_tls(BX)
-	
+
 	// check that m exists
 	MOVQ	m(BX), BP
 	CMPQ	BP, $0
@@ -196,16 +214,16 @@ TEXT runtime·sigtramp(SB),7,$64
 	// save g
 	MOVQ	g(BX), R10
 	MOVQ	R10, 40(SP)
-	
+
 	// g = m->signal
 	MOVQ	m_gsignal(BP), BP
 	MOVQ	BP, g(BX)
-	
+
 	MOVQ	DI, 0(SP)
 	MOVQ	SI, 8(SP)
 	MOVQ	DX, 16(SP)
 	MOVQ	R10, 24(SP)
-	
+
 	CALL	runtime·sighandler(SB)
 
 	// restore g