runtime: convert Stack to Go.

LGTM=khr
R=khr, josharian
CC=golang-codereviews
https://golang.org/cl/129510043

src/pkg/runtime/asm_386.s

@@ -860,6 +860,12 @@ TEXT runtime·getcallersp(SB), NOSPLIT, $0-4
 	MOVL	sp+0(FP), AX
 	RET
 
+// func gogetcallersp(p unsafe.Pointer) uintptr
+TEXT runtime·gogetcallersp(SB),NOSPLIT,$0-8
+	MOVL	p+0(FP),AX		// addr of first arg
+	MOVL	AX, ret+4(FP)
+	RET
+
 // int64 runtime·cputicks(void), so really
 // void runtime·cputicks(int64 *ticks)
 TEXT runtime·cputicks(SB),NOSPLIT,$0-4

src/pkg/runtime/asm_amd64.s

@@ -946,6 +946,12 @@ TEXT runtime·getcallersp(SB),NOSPLIT,$0-8
 	MOVQ	sp+0(FP), AX
 	RET
 
+// func gogetcallersp(p unsafe.Pointer) uintptr
+TEXT runtime·gogetcallersp(SB),NOSPLIT,$0-16
+	MOVQ	p+0(FP),AX		// addr of first arg
+	MOVQ	AX, ret+8(FP)
+	RET
+
 // int64 runtime·cputicks(void)
 TEXT runtime·cputicks(SB),NOSPLIT,$0-0
 	RDTSC

src/pkg/runtime/asm_amd64p32.s

@@ -747,6 +747,12 @@ TEXT runtime·getcallersp(SB),NOSPLIT,$0-8
 	MOVL	sp+0(FP), AX
 	RET
 
+// func gogetcallersp(p unsafe.Pointer) uintptr
+TEXT runtime·gogetcallersp(SB),NOSPLIT,$0-12
+	MOVL	p+0(FP),AX		// addr of first arg
+	MOVL	AX, ret+8(FP)
+	RET
+
 // int64 runtime·cputicks(void)
 TEXT runtime·cputicks(SB),NOSPLIT,$0-0
 	RDTSC

src/pkg/runtime/asm_arm.s

@@ -644,6 +644,13 @@ TEXT runtime·getcallersp(SB),NOSPLIT,$-4-4
 	MOVW	$-4(R0), R0
 	RET
 
+// func gogetcallersp(p unsafe.Pointer) uintptr
+TEXT runtime·gogetcallersp(SB),NOSPLIT,$-4-8
+	MOVW	0(FP), R0
+	MOVW	$-4(R0), R0
+	MOVW	R0, ret+4(FP)
+	RET
+
 TEXT runtime·emptyfunc(SB),0,$0-0
 	RET
 

src/pkg/runtime/debug.go

@@ -133,9 +133,3 @@ type BlockProfileRecord struct {
 	Cycles int64
 	StackRecord
 }
-
-// Stack formats a stack trace of the calling goroutine into buf
-// and returns the number of bytes written to buf.
-// If all is true, Stack formats stack traces of all other goroutines
-// into buf after the trace for the current goroutine.
-func Stack(buf []byte, all bool) int

src/pkg/runtime/mprof.go

@@ -141,6 +141,47 @@ func BlockProfile(p []BlockProfileRecord) (n int, ok bool) {
 	return
 }
 
+// Stack formats a stack trace of the calling goroutine into buf
+// and returns the number of bytes written to buf.
+// If all is true, Stack formats stack traces of all other goroutines
+// into buf after the trace for the current goroutine.
+func Stack(buf []byte, all bool) int {
+	sp := gogetcallersp(unsafe.Pointer(&buf))
+	pc := gogetcallerpc(unsafe.Pointer(&buf))
+	mp := acquirem()
+	gp := mp.curg
+	if all {
+		semacquire(&worldsema, false)
+		mp.gcing = 1
+		releasem(mp)
+		stoptheworld()
+		if mp != acquirem() {
+			gothrow("Stack: rescheduled")
+		}
+	}
+
+	n := 0
+	if len(buf) > 0 {
+		gp.writebuf = &buf[0]
+		gp.writenbuf = int32(len(buf))
+		traceback(pc, sp, 0, gp)
+		if all {
+			tracebackothers(gp)
+		}
+		n = len(buf) - int(gp.writenbuf)
+		gp.writebuf = nil
+		gp.writenbuf = 0
+	}
+
+	if all {
+		mp.gcing = 0
+		semrelease(&worldsema)
+		starttheworld()
+	}
+	releasem(mp)
+	return n
+}
+
 // ThreadCreateProfile returns n, the number of records in the thread creation profile.
 // If len(p) >= n, ThreadCreateProfile copies the profile into p and returns n, true.
 // If len(p) < n, ThreadCreateProfile does not change p and returns n, false.

src/pkg/runtime/mprof.goc

@@ -256,39 +256,6 @@ struct TRecord {
 	uintptr stk[32];
 };
 
-func Stack(b Slice, all bool) (n int) {
-	uintptr pc, sp;
-	
-	sp = runtime·getcallersp(&b);
-	pc = (uintptr)runtime·getcallerpc(&b);
-
-	if(all) {
-		runtime·semacquire(&runtime·worldsema, false);
-		g->m->gcing = 1;
-		runtime·stoptheworld();
-	}
-
-	if(b.len == 0)
-		n = 0;
-	else{
-		g->writebuf = (byte*)b.array;
-		g->writenbuf = b.len;
-		runtime·goroutineheader(g);
-		runtime·traceback(pc, sp, 0, g);
-		if(all)
-			runtime·tracebackothers(g);
-		n = b.len - g->writenbuf;
-		g->writebuf = nil;
-		g->writenbuf = 0;
-	}
-	
-	if(all) {
-		g->m->gcing = 0;
-		runtime·semrelease(&runtime·worldsema);
-		runtime·starttheworld();
-	}
-}
-
 static void
 saveg(uintptr pc, uintptr sp, G *gp, TRecord *r)
 {

src/pkg/runtime/stubs.go

@@ -18,6 +18,9 @@ const (
 //go:noescape
 func gogetcallerpc(p unsafe.Pointer) uintptr
 
+//go:noescape
+func gogetcallersp(p unsafe.Pointer) uintptr
+
 //go:noescape
 func racereadpc(addr unsafe.Pointer, callpc, pc uintptr)
 
@@ -212,3 +215,6 @@ func gonotetsleepg(n *note, t int64) {
 }
 
 func exitsyscall()
+
+func traceback(pc, sp, lr uintptr, gp *g)
+func tracebackothers(gp *g)