runtime: fix memory leaks due to defers

fn can clearly hold a closure in memory.
argp/pc point into stack and so can hold
in memory a block that was previously
a large stack serment.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/10784043

src/pkg/runtime/panic.c

@@ -104,11 +104,15 @@ popdefer(void)
 static void
 freedefer(Defer *d)
 {
+	int32 total;
+
 	if(d->special) {
 		if(d->free)
 			runtime·free(d);
 	} else {
-		runtime·memclr((byte*)d->args, d->siz);
+		// Wipe out any possible pointers in argp/pc/fn/args.
+		total = sizeof(*d) + ROUND(d->siz, sizeof(uintptr)) - sizeof(d->args);
+		runtime·memclr((byte*)d, total);
 	}
 }
 

test/deferfin.go

+// run
+
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test that defers do not prevent garbage collection.
+
+package main
+
+import (
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+var sink func()
+
+func main() {
+	// Does not work on 32-bits due to partially conservative GC.
+	// Try to enable when we have fully precise GC.
+	if runtime.GOARCH != "amd64" {
+		return
+	}
+	N := 10
+	count := int32(N)
+	var wg sync.WaitGroup
+	wg.Add(N)
+	for i := 0; i < N; i++ {
+		go func() {
+			defer wg.Done()
+			v := new(int)
+			f := func() {
+				if *v != 0 {
+					panic("oops")
+				}
+			}
+			if *v != 0 {
+				// let the compiler think f escapes
+				sink = f
+			}
+			runtime.SetFinalizer(v, func(p *int) {
+				atomic.AddInt32(&count, -1)
+			})
+			defer f()
+		}()
+	}
+	wg.Wait()
+	for i := 0; i < 3; i++ {
+		time.Sleep(10 * time.Millisecond)
+		runtime.GC()
+	}
+	if count != 0 {
+		println(count, "out of", N, "finalizer are not called")
+		panic("not all finalizers are called")
+	}
+}
+