runtime: implement SysUnused for openbsd

R=golang-dev, minux.ma
CC=golang-dev
https://golang.org/cl/6854079

src/pkg/runtime/defs_openbsd.go

@@ -34,6 +34,8 @@ const (
 	MAP_PRIVATE = C.MAP_PRIVATE
 	MAP_FIXED   = C.MAP_FIXED
 
+	MADV_FREE = C.MADV_FREE
+
 	SA_SIGINFO = C.SA_SIGINFO
 	SA_RESTART = C.SA_RESTART
 	SA_ONSTACK = C.SA_ONSTACK

src/pkg/runtime/defs_openbsd_386.h

@@ -12,6 +12,8 @@ enum {
 	MAP_PRIVATE	= 0x2,
 	MAP_FIXED	= 0x10,
 
+	MADV_FREE	= 0x6,
+
 	SA_SIGINFO	= 0x40,
 	SA_RESTART	= 0x2,
 	SA_ONSTACK	= 0x1,

src/pkg/runtime/defs_openbsd_amd64.h

@@ -12,6 +12,8 @@ enum {
 	MAP_PRIVATE	= 0x2,
 	MAP_FIXED	= 0x10,
 
+	MADV_FREE	= 0x6,
+
 	SA_SIGINFO	= 0x40,
 	SA_RESTART	= 0x2,
 	SA_ONSTACK	= 0x1,

src/pkg/runtime/mem_openbsd.c

@@ -28,9 +28,7 @@ runtime·SysAlloc(uintptr n)
 void
 runtime·SysUnused(void *v, uintptr n)
 {
-	USED(v);
-	USED(n);
-	// TODO(rsc): call madvise MADV_DONTNEED
+	runtime·madvise(v, n, MADV_FREE);
 }
 
 void

src/pkg/runtime/sys_openbsd_386.s

@@ -84,6 +84,13 @@ TEXT runtime·munmap(SB),7,$-4
 	MOVL	$0xf1, 0xf1		// crash
 	RET
 
+TEXT runtime·madvise(SB),7,$-4
+	MOVL	$75, AX			// sys_madvise
+	INT	$0x80
+	JAE	2(PC)
+	MOVL	$0xf1, 0xf1		// crash
+	RET
+
 TEXT runtime·setitimer(SB),7,$-4
 	MOVL	$83, AX
 	INT	$0x80

src/pkg/runtime/sys_openbsd_amd64.s

@@ -236,6 +236,16 @@ TEXT runtime·munmap(SB),7,$0
 	MOVL	$0xf1, 0xf1		// crash
 	RET
 
+TEXT runtime·madvise(SB),7,$0
+	MOVQ	addr+0(FP), DI		// arg 1 - addr
+	MOVQ	len+8(FP), SI		// arg 2 - len
+	MOVQ	behav+16(FP), DX	// arg 3 - behav
+	MOVQ	$75, AX			// sys_madvise
+	SYSCALL
+	JCC	2(PC)
+	MOVL	$0xf1, 0xf1		// crash
+	RET
+
 TEXT runtime·sigaltstack(SB),7,$-8
 	MOVQ	new+8(SP), DI		// arg 1 - nss
 	MOVQ	old+16(SP), SI		// arg 2 - oss