runtime: fix syscalls for netbsd

Use correct syscall numbers and arguments for NetBSD.
Provide a trampoline for signal returns (using signal API 3).

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6209048

src/pkg/runtime/sys_netbsd_386.s

@@ -128,8 +128,27 @@ TEXT runtime·nanotime(SB),7,$32
 	MOVL	DX, 4(DI)
 	RET
 
-TEXT runtime·sigaction(SB),7,$-4
-	MOVL	$46, AX			// sys_sigaction
+TEXT runtime·sigreturn_tramp(SB),7,$0
+	LEAL	140(SP), AX		// Load address of ucontext
+	MOVL	AX, 4(SP)
+	MOVL	$308, AX		// sys_setcontext
+	INT	$0x80
+	MOVL	$-1, 4(SP)		// Something failed...
+	MOVL	$1, AX			// sys_exit
+	INT	$0x80
+
+TEXT runtime·sigaction(SB),7,$24
+	LEAL	arg0+0(FP), SI
+	LEAL	4(SP), DI
+	CLD
+	MOVSL				// arg 1 - sig
+	MOVSL				// arg 2 - act
+	MOVSL				// arg 3 - oact
+	LEAL	runtime·sigreturn_tramp(SB), AX
+	STOSL				// arg 4 - tramp
+	MOVL	$3, AX
+	STOSL				// arg 5 - vers
+	MOVL	$340, AX		// sys___sigaction_sigtramp
 	INT	$0x80
 	JAE	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
@@ -259,7 +278,7 @@ TEXT runtime·rfork_thread(SB),7,$8
 	RET
 
 TEXT runtime·sigaltstack(SB),7,$-8
-	MOVL	$288, AX		// sys_sigaltstack
+	MOVL	$281, AX		// sys___sigaltstack14
 	MOVL	new+4(SP), BX
 	MOVL	old+8(SP), CX
 	INT	$0x80
@@ -281,7 +300,7 @@ TEXT runtime·settls(SB),7,$16
 	ADDL	$8, CX
 	MOVL	CX, 0(CX)
 	MOVL	$0, 0(SP)		// syscall gap
-	MOVL	$9, 4(SP)		// I386_SET_GSBASE (machine/sysarch.h)
+	MOVL	$16, 4(SP)		// X86_SET_GSBASE (x86/sysarch.h)
 	MOVL	CX, 8(SP)		// pointer to base
 	MOVL	$165, AX		// sys_sysarch
 	INT	$0x80

src/pkg/runtime/sys_netbsd_amd64.s

@@ -163,11 +163,23 @@ TEXT runtime·nanotime(SB),7,$32
 	ADDQ	DX, AX
 	RET
 
+TEXT runtime·sigreturn_tramp(SB),7,$-8
+	MOVQ	R15, DI			// Load address of ucontext
+	MOVQ	$308, AX		// sys_setcontext
+	SYSCALL
+	MOVQ	$-1, DI			// Something failed...
+	MOVL	$1, AX			// sys_exit
+	SYSCALL
+
 TEXT runtime·sigaction(SB),7,$-8
 	MOVL	8(SP), DI		// arg 1 - signum
 	MOVQ	16(SP), SI		// arg 2 - nsa
 	MOVQ	24(SP), DX		// arg 3 - osa
-	MOVL	$46, AX
+					// arg 4 - tramp
+	LEAQ	runtime·sigreturn_tramp(SB), R10
+	MOVQ	$3, R8			// arg 5 - version
+	MOVL	$340, AX		// sys___sigaction_sigtramp
+
 	SYSCALL
 	JCC	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
@@ -232,7 +244,7 @@ TEXT runtime·munmap(SB),7,$0
 TEXT runtime·sigaltstack(SB),7,$-8
 	MOVQ	new+8(SP), DI		// arg 1 - nss
 	MOVQ	old+16(SP), SI		// arg 2 - oss
-	MOVQ	$288, AX		// sys_sigaltstack
+	MOVQ	$281, AX		// sys___sigaltstack14
 	SYSCALL
 	JCC	2(PC)
 	MOVL	$0xf1, 0xf1  // crash
@@ -244,7 +256,7 @@ TEXT runtime·settls(SB),7,$8
 	ADDQ	$16, DI
 	MOVQ	DI, 0(SP)
 	MOVQ	SP, SI
-	MOVQ	$12, DI			// AMD64_SET_FSBASE (machine/sysarch.h)
+	MOVQ	$17, DI			// X86_64_SET_FSBASE (x86/sysarch.h)
 	MOVQ	$165, AX		// sys_sysarch
 	SYSCALL
 	JCC	2(PC)