fix signature size/alignment computation

gotypes/signature.go

@@ -64,15 +64,21 @@ func (s *Signature) init() {
 	p := s.sig.Params()
 	r := s.sig.Results()
 
-	// Compute offsets of parameters and return values.
+	// Compute parameter offsets.
 	vs := tuplevars(p)
-	vs = append(vs, tuplevars(r)...)
 	vs = append(vs, types.NewParam(token.NoPos, nil, "sentinel", types.Typ[types.Uint64]))
-	offsets := Sizes.Offsetsof(vs)
+	paramsoffsets := Sizes.Offsetsof(vs)
+	paramssize := paramsoffsets[p.Len()]
+	s.params = newTuple(p, paramsoffsets, paramssize, "arg")
 
-	// Build components for them.
-	s.params = newTuple(p, offsets, "arg")
-	s.results = newTuple(r, offsets[p.Len():], "ret")
+	// Result offsets.
+	vs = tuplevars(r)
+	resultsoffsets := Sizes.Offsetsof(vs)
+	for i := range resultsoffsets {
+		resultsoffsets[i] += paramssize
+	}
+	resultssize := Sizes.Sizeof(types.NewStruct(vs, nil))
+	s.results = newTuple(r, resultsoffsets, resultssize, "ret")
 }
 
 type Tuple struct {
@@ -81,10 +87,10 @@ type Tuple struct {
 	size       int
 }
 
-func newTuple(t *types.Tuple, offsets []int64, defaultprefix string) *Tuple {
+func newTuple(t *types.Tuple, offsets []int64, size int64, defaultprefix string) *Tuple {
 	tuple := &Tuple{
 		byname: map[string]Component{},
-		size:   int(offsets[t.Len()] - offsets[0]),
+		size:   int(size),
 	}
 	for i := 0; i < t.Len(); i++ {
 		v := t.At(i)

gotypes/signature_test.go

@@ -93,3 +93,23 @@ func TypesTuplesEqual(a, b *types.Tuple) bool {
 func TypesVarsEqual(a, b *types.Var) bool {
 	return a.Name() == b.Name() && types.Identical(a.Type(), b.Type())
 }
+
+func TestSignatureSizes(t *testing.T) {
+	cases := []struct {
+		Expr    string
+		ArgSize int
+	}{
+		{"func()", 0},
+		{"func(uint64) uint64", 16},
+		{"func([7]byte) byte", 9},
+	}
+	for _, c := range cases {
+		s, err := ParseSignature(c.Expr)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if s.Bytes() != c.ArgSize {
+			t.Errorf("%s: size %d expected %d", s, s.Bytes(), c.ArgSize)
+		}
+	}
+}