runtime: fix finalizer iterator

It could only handle one finalizer before it raised an out-of-bounds error.

Fixes issue #9172

Change-Id: Ibb4d0c8aff2d78a1396e248c7129a631176ab427
Reviewed-on: https://go-review.googlesource.com/1201Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/debug/heapdump_test.go

@@ -31,3 +31,40 @@ func TestWriteHeapDumpNonempty(t *testing.T) {
 		t.Fatalf("Heap dump size %d bytes, expected at least %d bytes", size, minSize)
 	}
 }
+
+
+type Obj struct {
+       x, y int
+}
+
+func objfin(x *Obj) {
+       println("finalized", x)
+}
+
+func TestWriteHeapDumpFinalizers(t *testing.T) {
+	if runtime.GOOS == "nacl" {
+		t.Skip("WriteHeapDump is not available on NaCl.")
+	}
+	f, err := ioutil.TempFile("", "heapdumptest")
+	if err != nil {
+		t.Fatalf("TempFile failed: %v", err)
+	}
+	defer os.Remove(f.Name())
+	defer f.Close()
+
+	// bug 9172: WriteHeapDump couldn't handle more than one finalizer
+	println("allocating objects")
+	x := &Obj{}
+	runtime.SetFinalizer(x, objfin)
+	y := &Obj{}
+	runtime.SetFinalizer(y, objfin)
+
+	// Trigger collection of x and y, queueing of their finalizers.
+	println("starting gc")
+	runtime.GC()
+
+	// Make sure WriteHeapDump doesn't fail with multiple queued finalizers.
+	println("starting dump")
+	WriteHeapDump(f.Fd())
+	println("done dump")
+}

src/runtime/malloc2.go

@@ -476,8 +476,8 @@ type finblock struct {
 	alllink *finblock
 	next    *finblock
 	cnt     int32
-	cap     int32
-	fin     [1]finalizer
+	_       int32
+	fin     [(_FinBlockSize-2*ptrSize-2*4)/unsafe.Sizeof(finalizer{})]finalizer
 }
 
 // Information from the compiler about the layout of stack frames.

src/runtime/mgc.go

@@ -1093,10 +1093,9 @@ var finalizer1 = [...]byte{
 
 func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot *ptrtype) {
 	lock(&finlock)
-	if finq == nil || finq.cnt == finq.cap {
+	if finq == nil || finq.cnt == int32(len(finq.fin)) {
 		if finc == nil {
 			finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gc_sys))
-			finc.cap = int32((_FinBlockSize-unsafe.Sizeof(finblock{}))/unsafe.Sizeof(finalizer{}) + 1)
 			finc.alllink = allfin
 			allfin = finc
 			if finptrmask[0] == 0 {
@@ -1121,7 +1120,7 @@ func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot
 		block.next = finq
 		finq = block
 	}
-	f := (*finalizer)(add(unsafe.Pointer(&finq.fin[0]), uintptr(finq.cnt)*unsafe.Sizeof(finq.fin[0])))
+	f := &finq.fin[finq.cnt]
 	finq.cnt++
 	f.fn = fn
 	f.nret = nret