godwarf: handle unsupported types gracefully (#2106)

Backport https://go-review.googlesource.com/c/go/+/158797 from upstream.

Fixes #2101

pkg/dwarf/godwarf/type.go

@@ -513,6 +513,22 @@ func (t *ChanType) stringIntl(recCheck recCheck) string {
 	return "chan " + t.ElemType.String()
 }
 
+// An UnsupportedType is a placeholder returned in situations where we
+// encounter a type that isn't supported.
+type UnsupportedType struct {
+	CommonType
+	Tag dwarf.Tag
+}
+
+func (t *UnsupportedType) stringIntl(recCheck) string {
+	if t.Name != "" {
+		return t.Name
+	}
+	return fmt.Sprintf("(unsupported type %s)", t.Tag.String())
+}
+
+func (t *UnsupportedType) String() string { return t.stringIntl(nil) }
+
 // Type reads the type at off in the DWARF ``info'' section.
 func ReadType(d *dwarf.Data, index int, off dwarf.Offset, typeCache map[dwarf.Offset]Type) (Type, error) {
 	typ, err := readType(d, "info", d.Reader(), off, typeCache, nil)
@@ -1008,6 +1024,16 @@ func readType(d *dwarf.Data, name string, r *dwarf.Reader, off dwarf.Offset, typ
 		typ = t
 		typeCache[off] = t
 		t.Name, _ = e.Val(dwarf.AttrName).(string)
+
+	default:
+		// This is some other type DIE that we're currently not
+		// equipped to handle. Return an abstract "unsupported type"
+		// object in such cases.
+		t := new(UnsupportedType)
+		typ = t
+		typeCache[off] = t
+		t.Tag = e.Tag
+		t.Name, _ = e.Val(dwarf.AttrName).(string)
 	}
 
 	if err != nil {

pkg/proc/dwarf_expr_test.go

@@ -323,3 +323,17 @@ func TestIssue1636_InlineWithoutOrigin(t *testing.T) {
 	dwb.TagClose()
 	fakeBinaryInfo(t, dwb)
 }
+
+func TestUnsupportedType(t *testing.T) {
+	// Tests that reading an unsupported type does not cause an error
+	dwb := dwarfbuilder.New()
+	dwb.AddCompileUnit("main", 0x0)
+	off := dwb.TagOpen(dwarf.TagReferenceType, "blah")
+	dwb.TagClose()
+	dwb.TagClose()
+	_, dw := fakeBinaryInfo(t, dwb)
+	_, err := godwarf.ReadType(dw, 0, off, make(map[dwarf.Offset]godwarf.Type))
+	if err != nil {
+		t.Errorf("unexpected error reading unsupported type: %#v", err)
+	}
+}