runtime: introduce, use funcPC to convert Go func to PC

This removes the ** unsafe hack.

Real bug fixed at chan.go:101.

LGTM=dave, r, iant
R=golang-codereviews, dave, r, iant
CC=dvyukov, golang-codereviews, khr
https://codereview.appspot.com/140870044

9 files changed, 33 insertions, 72 deletions

diff --git a/src/pkg/runtime/chan.go b/src/pkg/runtime/chan.go
index 77df16939..91ade4d37 100644
--- a/src/pkg/runtime/chan.go
+++ b/src/pkg/runtime/chan.go
@@ -82,9 +82,7 @@ func chansend1(t *chantype, c *hchan, elem unsafe.Pointer) {
  */
 func chansend(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 	if raceenabled {
-		fn := chansend
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		raceReadObjectPC(t.elem, ep, callerpc, pc)
+		raceReadObjectPC(t.elem, ep, callerpc, funcPC(chansend))
 	}
 
 	if c == nil {
@@ -100,9 +98,7 @@ func chansend(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uin
 	}
 
 	if raceenabled {
-		fn := chansend
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(c), pc, callerpc)
+		racereadpc(unsafe.Pointer(c), callerpc, funcPC(chansend))
 	}
 
 	// Fast path: check for failed non-blocking operation without acquiring the lock.
@@ -269,9 +265,7 @@ func closechan(c *hchan) {
 
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&c))
-		fn := closechan
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racewritepc(unsafe.Pointer(c), callerpc, pc)
+		racewritepc(unsafe.Pointer(c), callerpc, funcPC(closechan))
 		racerelease(unsafe.Pointer(c))
 	}
 
diff --git a/src/pkg/runtime/cpuprof.go b/src/pkg/runtime/cpuprof.go
index 540c78de8..b397eafbe 100644
--- a/src/pkg/runtime/cpuprof.go
+++ b/src/pkg/runtime/cpuprof.go
@@ -289,8 +289,7 @@ func (p *cpuProfile) flushlog() bool {
 	log := &p.log[p.toggle]
 	q := uintptr(0)
 	if p.lost > 0 {
-		f := lostProfileData
-		lostPC := **(**uintptr)(unsafe.Pointer(&f))
+		lostPC := funcPC(lostProfileData)
 		log[0] = p.lost
 		log[1] = 1
 		log[2] = lostPC
diff --git a/src/pkg/runtime/export_test.go b/src/pkg/runtime/export_test.go
index 5579449c4..cce9afbef 100644
--- a/src/pkg/runtime/export_test.go
+++ b/src/pkg/runtime/export_test.go
@@ -86,7 +86,7 @@ func ParForSetup(desc *ParFor, nthr, n uint32, ctx *byte, wait bool, body func(*
 	mp := acquirem()
 	mp.ptrarg[0] = unsafe.Pointer(desc)
 	mp.ptrarg[1] = unsafe.Pointer(ctx)
-	mp.ptrarg[2] = **(**unsafe.Pointer)(unsafe.Pointer(&body))
+	mp.ptrarg[2] = unsafe.Pointer(funcPC(body)) // TODO(rsc): Should be a scalar.
 	mp.scalararg[0] = uintptr(nthr)
 	mp.scalararg[1] = uintptr(n)
 	mp.scalararg[2] = 0
diff --git a/src/pkg/runtime/hashmap.go b/src/pkg/runtime/hashmap.go
index 1bdceab8b..55287f6ff 100644
--- a/src/pkg/runtime/hashmap.go
+++ b/src/pkg/runtime/hashmap.go
@@ -235,8 +235,7 @@ func makemap(t *maptype, hint int64) *hmap {
 func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess1
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
+		pc := funcPC(mapaccess1)
 		racereadpc(unsafe.Pointer(h), callerpc, pc)
 		raceReadObjectPC(t.key, key, callerpc, pc)
 	}
@@ -284,8 +283,7 @@ func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
 func mapaccess2(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, bool) {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess2
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
+		pc := funcPC(mapaccess2)
 		racereadpc(unsafe.Pointer(h), callerpc, pc)
 		raceReadObjectPC(t.key, key, callerpc, pc)
 	}
@@ -379,8 +377,7 @@ func mapassign1(t *maptype, h *hmap, key unsafe.Pointer, val unsafe.Pointer) {
 	}
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapassign1
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
+		pc := funcPC(mapassign1)
 		racewritepc(unsafe.Pointer(h), callerpc, pc)
 		raceReadObjectPC(t.key, key, callerpc, pc)
 		raceReadObjectPC(t.elem, val, callerpc, pc)
@@ -488,8 +485,7 @@ again:
 func mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapdelete
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
+		pc := funcPC(mapdelete)
 		racewritepc(unsafe.Pointer(h), callerpc, pc)
 		raceReadObjectPC(t.key, key, callerpc, pc)
 	}
@@ -545,9 +541,7 @@ func mapiterinit(t *maptype, h *hmap, it *hiter) {
 
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapiterinit
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiterinit))
 	}
 
 	if h == nil || h.count == 0 {
@@ -591,9 +585,7 @@ func mapiternext(it *hiter) {
 	h := it.h
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&it))
-		fn := mapiternext
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiternext))
 	}
 	t := it.t
 	bucket := it.bucket
@@ -942,9 +934,7 @@ func reflect_maplen(h *hmap) int {
 	}
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&h))
-		fn := reflect_maplen
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
 	}
 	return h.count
 }
diff --git a/src/pkg/runtime/hashmap_fast.go b/src/pkg/runtime/hashmap_fast.go
index 7059e22a0..8e21e02d6 100644
--- a/src/pkg/runtime/hashmap_fast.go
+++ b/src/pkg/runtime/hashmap_fast.go
@@ -11,9 +11,7 @@ import (
 func mapaccess1_fast32(t *maptype, h *hmap, key uint32) unsafe.Pointer {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess1_fast32
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapaccess1_fast32))
 	}
 	if h == nil || h.count == 0 {
 		return unsafe.Pointer(t.elem.zero)
@@ -55,9 +53,7 @@ func mapaccess1_fast32(t *maptype, h *hmap, key uint32) unsafe.Pointer {
 func mapaccess2_fast32(t *maptype, h *hmap, key uint32) (unsafe.Pointer, bool) {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess2_fast32
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapaccess2_fast32))
 	}
 	if h == nil || h.count == 0 {
 		return unsafe.Pointer(t.elem.zero), false
@@ -99,9 +95,7 @@ func mapaccess2_fast32(t *maptype, h *hmap, key uint32) (unsafe.Pointer, bool) {
 func mapaccess1_fast64(t *maptype, h *hmap, key uint64) unsafe.Pointer {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess1_fast64
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapaccess1_fast64))
 	}
 	if h == nil || h.count == 0 {
 		return unsafe.Pointer(t.elem.zero)
@@ -143,9 +137,7 @@ func mapaccess1_fast64(t *maptype, h *hmap, key uint64) unsafe.Pointer {
 func mapaccess2_fast64(t *maptype, h *hmap, key uint64) (unsafe.Pointer, bool) {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess2_fast64
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapaccess2_fast64))
 	}
 	if h == nil || h.count == 0 {
 		return unsafe.Pointer(t.elem.zero), false
@@ -187,9 +179,7 @@ func mapaccess2_fast64(t *maptype, h *hmap, key uint64) (unsafe.Pointer, bool) {
 func mapaccess1_faststr(t *maptype, h *hmap, ky string) unsafe.Pointer {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess1_faststr
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapaccess1_faststr))
 	}
 	if h == nil || h.count == 0 {
 		return unsafe.Pointer(t.elem.zero)
@@ -291,9 +281,7 @@ dohash:
 func mapaccess2_faststr(t *maptype, h *hmap, ky string) (unsafe.Pointer, bool) {
 	if raceenabled && h != nil {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := mapaccess2_faststr
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapaccess2_faststr))
 	}
 	if h == nil || h.count == 0 {
 		return unsafe.Pointer(t.elem.zero), false
diff --git a/src/pkg/runtime/proc.go b/src/pkg/runtime/proc.go
index d47503e23..a36b931b8 100644
--- a/src/pkg/runtime/proc.go
+++ b/src/pkg/runtime/proc.go
@@ -110,3 +110,9 @@ func releaseSudog(s *sudog) {
 	s.next = c.sudogcache
 	c.sudogcache = s
 }
+
+// funcPC returns the entry PC of the function f.
+// It assumes that f is a func value. Otherwise the behavior is undefined.
+func funcPC(f interface{}) uintptr {
+	return **(**uintptr)(add(unsafe.Pointer(&f), ptrSize))
+}
diff --git a/src/pkg/runtime/select.go b/src/pkg/runtime/select.go
index dbe0543bf..6d2531e7f 100644
--- a/src/pkg/runtime/select.go
+++ b/src/pkg/runtime/select.go
@@ -13,17 +13,10 @@ const (
 )
 
 var (
-	chansendpc uintptr
-	chanrecvpc uintptr
+	chansendpc = funcPC(chansend)
+	chanrecvpc = funcPC(chanrecv)
 )
 
-func init() {
-	f := chansend
-	chansendpc = **(**uintptr)(unsafe.Pointer(&f))
-	g := chanrecv
-	chanrecvpc = **(**uintptr)(unsafe.Pointer(&g))
-}
-
 func selectsize(size uintptr) uintptr {
 	selsize := unsafe.Sizeof(_select{}) +
 		(size-1)*unsafe.Sizeof(_select{}.scase[0]) +
@@ -286,7 +279,6 @@ func selectgoImpl(sel *_select) (uintptr, uint16) {
 		k      *scase
 		sglist *sudog
 		sgnext *sudog
-		fn     func(*g, *_select) bool
 	)
 
 loop:
@@ -371,8 +363,7 @@ loop:
 
 	// wait for someone to wake us up
 	gp.param = nil
-	fn = selparkcommit
-	gopark(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), unsafe.Pointer(sel), "select")
+	gopark(unsafe.Pointer(funcPC(selparkcommit)), unsafe.Pointer(sel), "select")
 
 	// someone woke us up
 	sellock(sel)
diff --git a/src/pkg/runtime/slice.go b/src/pkg/runtime/slice.go
index c282125b4..68a225a50 100644
--- a/src/pkg/runtime/slice.go
+++ b/src/pkg/runtime/slice.go
@@ -48,9 +48,7 @@ func growslice(t *slicetype, old sliceStruct, n int64) sliceStruct {
 
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&t))
-		fn := growslice
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
-		racereadrangepc(old.array, old.len*int(t.elem.size), callerpc, pc)
+		racereadrangepc(old.array, old.len*int(t.elem.size), callerpc, funcPC(growslice))
 	}
 
 	et := t.elem
@@ -105,8 +103,7 @@ func slicecopy(to sliceStruct, fm sliceStruct, width uintptr) int {
 
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&to))
-		fn := slicecopy
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
+		pc := funcPC(slicecopy)
 		racewriterangepc(to.array, n*int(width), callerpc, pc)
 		racereadrangepc(fm.array, n*int(width), callerpc, pc)
 	}
@@ -133,8 +130,7 @@ func slicestringcopy(to []byte, fm string) int {
 
 	if raceenabled {
 		callerpc := getcallerpc(unsafe.Pointer(&to))
-		fn := slicestringcopy
-		pc := **(**uintptr)(unsafe.Pointer(&fn))
+		pc := funcPC(slicestringcopy)
 		racewriterangepc(unsafe.Pointer(&to[0]), n, callerpc, pc)
 	}
 
diff --git a/src/pkg/runtime/string.go b/src/pkg/runtime/string.go
index e9ea926df..1cefad967 100644
--- a/src/pkg/runtime/string.go
+++ b/src/pkg/runtime/string.go
@@ -61,11 +61,10 @@ func concatstring5(a [5]string) string {
 
 func slicebytetostring(b []byte) string {
 	if raceenabled && len(b) > 0 {
-		fn := slicebytetostring
 		racereadrangepc(unsafe.Pointer(&b[0]),
 			len(b),
 			getcallerpc(unsafe.Pointer(&b)),
-			**(**uintptr)(unsafe.Pointer(&fn)))
+			funcPC(slicebytetostring))
 	}
 	s, c := rawstring(len(b))
 	copy(c, b)
@@ -82,11 +81,10 @@ func slicebytetostringtmp(b []byte) string {
 	// m is a string-keyed map and k is a []byte.
 
 	if raceenabled && len(b) > 0 {
-		fn := slicebytetostringtmp
 		racereadrangepc(unsafe.Pointer(&b[0]),
 			len(b),
 			getcallerpc(unsafe.Pointer(&b)),
-			**(**uintptr)(unsafe.Pointer(&fn)))
+			funcPC(slicebytetostringtmp))
 	}
 	return *(*string)(unsafe.Pointer(&b))
 }
@@ -120,11 +118,10 @@ func stringtoslicerune(s string) []rune {
 
 func slicerunetostring(a []rune) string {
 	if raceenabled && len(a) > 0 {
-		fn := slicerunetostring
 		racereadrangepc(unsafe.Pointer(&a[0]),
 			len(a)*int(unsafe.Sizeof(a[0])),
 			getcallerpc(unsafe.Pointer(&a)),
-			**(**uintptr)(unsafe.Pointer(&fn)))
+			funcPC(slicerunetostring))
 	}
 	var dum [4]byte
 	size1 := 0