runtime: convert lfstack to Go

It is called from Go only in tests.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/125610043

src/pkg/runtime/export_test.go

@@ -6,6 +6,8 @@
 
 package runtime
 
+import "unsafe"
+
 var Fadd64 = fadd64
 var Fsub64 = fsub64
 var Fmul64 = fmul64
@@ -31,11 +33,28 @@ type LFNode struct {
 	Pushcnt uintptr
 }
 
-func lfstackpush_go(head *uint64, node *LFNode)
-func lfstackpop_go(head *uint64) *LFNode
+var (
+	lfstackpush_m,
+	lfstackpop_m mFunction
+)
+
+func LFStackPush(head *uint64, node *LFNode) {
+	mp := acquirem()
+	mp.ptrarg[0] = unsafe.Pointer(head)
+	mp.ptrarg[1] = unsafe.Pointer(node)
+	onM(&lfstackpush_m)
+	releasem(mp)
+}
 
-var LFStackPush = lfstackpush_go
-var LFStackPop = lfstackpop_go
+func LFStackPop(head *uint64) *LFNode {
+	mp := acquirem()
+	mp.ptrarg[0] = unsafe.Pointer(head)
+	onM(&lfstackpop_m)
+	node := (*LFNode)(unsafe.Pointer(mp.ptrarg[0]))
+	mp.ptrarg[0] = nil
+	releasem(mp)
+	return node
+}
 
 type ParFor struct {
 	body    *byte

src/pkg/runtime/lfstack.goc → src/pkg/runtime/lfstack.c

@@ -3,8 +3,8 @@
 // license that can be found in the LICENSE file.
 
 // Lock-free stack.
+// The following code runs only on g0 stack.
 
-package runtime
 #include "runtime.h"
 #include "arch_GOARCH.h"
 
@@ -72,10 +72,16 @@ runtime·lfstackpop(uint64 *head)
 	}
 }
 
-func lfstackpush_go(head *uint64, node *LFNode) {
-	runtime·lfstackpush(head, node);
+void
+runtime·lfstackpush_m(void)
+{
+	runtime·lfstackpush(g->m->ptrarg[0], g->m->ptrarg[1]);
+	g->m->ptrarg[0] = nil;
+	g->m->ptrarg[1] = nil;
 }
 
-func lfstackpop_go(head *uint64) (node *LFNode) {
-	node = runtime·lfstackpop(head);
+void
+runtime·lfstackpop_m(void)
+{
+	g->m->ptrarg[0] = runtime·lfstackpop(g->m->ptrarg[0]);
 }