cmd/link,compile: Provide size for func types

They are currently not given a size, which makes the DWARF reader
very confused. Particularly things like [4]func() get a size of -4, not 32.

Fixes #21097

Change-Id: I01e754134d82fbbe6567e3c7847a4843792a3776
Reviewed-on: https://go-review.googlesource.com/55551Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/dwarf/dwarf.go

@@ -467,6 +467,7 @@ var abbrevs = [DW_NABRV]dwAbbrev{
 		DW_CHILDREN_yes,
 		[]dwAttrForm{
 			{DW_AT_name, DW_FORM_string},
+			{DW_AT_byte_size, DW_FORM_udata},
 			// {DW_AT_type,	DW_FORM_ref_addr},
 			{DW_AT_go_kind, DW_FORM_data1},
 		},

src/cmd/link/internal/ld/dwarf.go

@@ -430,6 +430,7 @@ func newtype(ctxt *Link, gotype *Symbol) *dwarf.DWDie {
 
 	case objabi.KindFunc:
 		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_FUNCTYPE, name, 0)
+		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
 		dotypedef(ctxt, &dwtypes, name, die)
 		newrefattr(die, dwarf.DW_AT_type, mustFind(ctxt, "void"))
 		nfields := decodetypeFuncInCount(ctxt.Arch, gotype)

src/cmd/link/internal/ld/dwarf_test.go

@@ -192,3 +192,46 @@ func findMembers(rdr *dwarf.Reader) (map[string]bool, error) {
 	}
 	return memberEmbedded, nil
 }
+
+func TestSizes(t *testing.T) {
+	// DWARF sizes should never be -1.
+	// See issue #21097
+	const prog = `
+package main
+var x func()
+var y [4]func()
+func main() {
+	x = nil
+	y[0] = nil
+}
+`
+	dir, err := ioutil.TempDir("", "TestSizes")
+	if err != nil {
+		t.Fatalf("could not create directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+	f := gobuild(t, dir, prog)
+	defer f.Close()
+	d, err := f.DWARF()
+	if err != nil {
+		t.Fatalf("error reading DWARF: %v", err)
+	}
+	rdr := d.Reader()
+	for entry, err := rdr.Next(); entry != nil; entry, err = rdr.Next() {
+		if err != nil {
+			t.Fatalf("error reading DWARF: %v", err)
+		}
+		switch entry.Tag {
+		case dwarf.TagArrayType, dwarf.TagPointerType, dwarf.TagStructType, dwarf.TagBaseType, dwarf.TagSubroutineType, dwarf.TagTypedef:
+		default:
+			continue
+		}
+		typ, err := d.Type(entry.Offset)
+		if err != nil {
+			t.Fatalf("can't read type: %v", err)
+		}
+		if typ.Size() < 0 {
+			t.Errorf("subzero size %s %s %T", typ, entry.Tag, typ)
+		}
+	}
+}