cmd/compile, etc: use nameOff for rtype string

linux/amd64:
	cmd/go:   -8KB (basically nothing)

linux/amd64 PIE:
	cmd/go: -191KB (1.6%)
	jujud:  -1.5MB (1.9%)

Updates #6853
Fixes #15064

Change-Id: I0adbb95685e28be92e8548741df0e11daa0a9b5f
Reviewed-on: https://go-review.googlesource.com/21777Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -788,14 +788,21 @@ func typeptrdata(t *Type) int64 {
 	}
 }
 
-// tflag is documented in ../../../../reflect/type.go.
-const tflagUncommon = 1
-
-// commonType
-// ../../../../runtime/type.go:/commonType
+// tflag is documented in reflect/type.go.
+//
+// tflag values must be kept in sync with copies in:
+//	cmd/compile/internal/gc/reflect.go
+//	cmd/link/internal/ld/decodesym.go
+//	reflect/type.go
+//	runtime/type.go
+const (
+	tflagUncommon  = 1 << 0
+	tflagExtraStar = 1 << 1
+)
 
 var dcommontype_algarray *Sym
 
+// dcommontype dumps the contents of a reflect.rtype (runtime._type).
 func dcommontype(s *Sym, ot int, t *Type) int {
 	if ot != 0 {
 		Fatalf("dcommontype %d", ot)
@@ -836,7 +843,8 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 	//		kind          uint8
 	//		alg           *typeAlg
 	//		gcdata        *byte
-	//		string        *string
+	//		str           nameOff
+	//		_             int32
 	//	}
 	ot = duintptr(s, ot, uint64(t.Width))
 	ot = duintptr(s, ot, uint64(ptrdata))
@@ -847,6 +855,26 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 	if uncommonSize(t) != 0 {
 		tflag |= tflagUncommon
 	}
+
+	exported := false
+	p := Tconv(t, FmtLeft|FmtUnsigned)
+	// If we're writing out type T,
+	// we are very likely to write out type *T as well.
+	// Use the string "*T"[1:] for "T", so that the two
+	// share storage. This is a cheap way to reduce the
+	// amount of space taken up by reflect strings.
+	if !strings.HasPrefix(p, "*") {
+		p = "*" + p
+		tflag |= tflagExtraStar
+		if t.Sym != nil {
+			exported = exportname(t.Sym.Name)
+		}
+	} else {
+		if t.Elem() != nil && t.Elem().Sym != nil {
+			exported = exportname(t.Elem().Sym.Name)
+		}
+	}
+
 	ot = duint8(s, ot, tflag)
 
 	// runtime (and common sense) expects alignment to be a power of two.
@@ -882,21 +910,9 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 	}
 	ot = dsymptr(s, ot, gcsym, 0) // gcdata
 
-	p := Tconv(t, FmtLeft|FmtUnsigned)
-
-	// If we're writing out type T,
-	// we are very likely to write out type *T as well.
-	// Use the string "*T"[1:] for "T", so that the two
-	// share storage. This is a cheap way to reduce the
-	// amount of space taken up by reflect strings.
-	prefix := 0
-	if !strings.HasPrefix(p, "*") {
-		p = "*" + p
-		prefix = 1
-	}
-	_, symdata := stringsym(p) // string
-	ot = dsymptrLSym(Linksym(s), ot, symdata, prefix)
-	ot = duintxx(s, ot, uint64(len(p)-prefix), Widthint)
+	nsym := dname(p, "", nil, exported)
+	ot = dsymptrOffLSym(Linksym(s), ot, nsym, 0)
+	ot = duint32(s, ot, 0)
 
 	return ot
 }

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

@@ -1832,7 +1832,7 @@ func dodataSect(symn int, syms []*LSym) (result []*LSym, maxAlign int32) {
 		case obj.STYPELINK:
 			// Sort typelinks by the rtype.string field so the reflect
 			// package can binary search type links.
-			symsSort[i].name = string(decodetype_string(s.R[0].Sym))
+			symsSort[i].name = string(decodetype_str(s.R[0].Sym))
 		}
 	}
 

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

@@ -16,6 +16,18 @@ import (
 // ../../runtime/type.go, or more specifically, with what
 // ../gc/reflect.c stuffs in these.
 
+// tflag is documented in reflect/type.go.
+//
+// tflag values must be kept in sync with copies in:
+//	cmd/compile/internal/gc/reflect.go
+//	cmd/link/internal/ld/decodesym.go
+//	reflect/type.go
+//	runtime/type.go
+const (
+	tflagUncommon  = 1 << 0
+	tflagExtraStar = 1 << 1
+)
+
 func decode_reloc(s *LSym, off int32) *Reloc {
 	for i := range s.R {
 		if s.R[i].Off == off {
@@ -47,9 +59,9 @@ func decode_inuxi(p []byte, sz int) uint64 {
 	}
 }
 
-func commonsize() int      { return 6*SysArch.PtrSize + 8 } // runtime._type
-func structfieldSize() int { return 3 * SysArch.PtrSize }   // runtime.structfield
-func uncommonSize() int    { return 2 * SysArch.PtrSize }   // runtime.uncommontype
+func commonsize() int      { return 4*SysArch.PtrSize + 8 + 8 } // runtime._type
+func structfieldSize() int { return 3 * SysArch.PtrSize }       // runtime.structfield
+func uncommonSize() int    { return 2 * SysArch.PtrSize }       // runtime.uncommontype
 
 // Type.commonType.kind
 func decodetype_kind(s *LSym) uint8 {
@@ -73,7 +85,6 @@ func decodetype_ptrdata(s *LSym) int64 {
 
 // Type.commonType.tflag
 func decodetype_hasUncommon(s *LSym) bool {
-	const tflagUncommon = 1 // see ../../../../reflect/type.go:/^type.tflag
 	return s.P[2*SysArch.PtrSize+4]&tflagUncommon != 0
 }
 
@@ -211,16 +222,13 @@ func decodetype_structfieldarrayoff(s *LSym, i int) int {
 	return off
 }
 
-// decodetype_string returns the contents of an rtype's string field.
-func decodetype_string(s *LSym) []byte {
-	off := 4*SysArch.PtrSize + 8
-	strlen := int64(decode_inuxi(s.P[off+SysArch.PtrSize:], SysArch.IntSize))
-
-	r := decode_reloc(s, int32(off))
-	if r == nil {
-		return nil
+// decodetype_str returns the contents of an rtype's str field (a nameOff).
+func decodetype_str(s *LSym) string {
+	str := decodetype_name(s, 4*SysArch.PtrSize+8)
+	if s.P[2*SysArch.PtrSize+4]&tflagExtraStar != 0 {
+		return str[1:]
 	}
-	return r.Sym.P[r.Add : r.Add+strlen]
+	return str
 }
 
 // decodetype_name decodes the name from a reflect.name.
@@ -233,7 +241,6 @@ func decodetype_name(s *LSym, off int) string {
 	data := r.Sym.P
 	namelen := int(uint16(data[1]<<8) | uint16(data[2]))
 	return string(data[3 : 3+namelen])
-
 }
 
 func decodetype_structfieldname(s *LSym, i int) string {

src/reflect/all_test.go

@@ -4175,12 +4175,12 @@ func TestStructOfExportRules(t *testing.T) {
 		},
 		{
 			field:     StructField{Name: "", Type: TypeOf(ΦType{})},
-			mustPanic: true, // TODO(sbinet): creating a struct with UTF-8 fields not supported
+			mustPanic: false,
 			exported:  true,
 		},
 		{
 			field:     StructField{Name: "", Type: TypeOf(φType{})},
-			mustPanic: true, // TODO(sbinet): creating a struct with UTF-8 fields not supported
+			mustPanic: false,
 			exported:  false,
 		},
 		{
@@ -5674,6 +5674,42 @@ func TestNames(t *testing.T) {
 	}
 }
 
+func TestExported(t *testing.T) {
+	type ΦExported struct{}
+	type φUnexported struct{}
+	type BigP *big
+	type P int
+	type p *P
+	type P2 p
+	type p3 p
+
+	type exportTest struct {
+		v    interface{}
+		want bool
+	}
+	exportTests := []exportTest{
+		{D1{}, true},
+		{(*D1)(nil), true},
+		{big{}, false},
+		{(*big)(nil), false},
+		{(BigP)(nil), true},
+		{(*BigP)(nil), true},
+		{ΦExported{}, true},
+		{φUnexported{}, false},
+		{P(0), true},
+		{(p)(nil), false},
+		{(P2)(nil), true},
+		{(p3)(nil), false},
+	}
+
+	for i, test := range exportTests {
+		typ := TypeOf(test.v)
+		if got := IsExported(typ); got != test.want {
+			t.Errorf("%d: %s exported=%v, want %v", i, typ.Name(), got, test.want)
+		}
+	}
+}
+
 type embed struct {
 	EmbedWithUnexpMeth
 }

src/reflect/export_test.go

@@ -51,7 +51,7 @@ func TypeLinks() []string {
 		rodata := sections[i]
 		for _, off := range offs {
 			typ := (*rtype)(resolveTypeOff(unsafe.Pointer(rodata), off))
-			r = append(r, typ.string)
+			r = append(r, typ.String())
 		}
 	}
 	return r
@@ -103,3 +103,9 @@ type OtherPkgFields struct {
 	OtherExported   int
 	otherUnexported int
 }
+
+func IsExported(t Type) bool {
+	typ := t.(*rtype)
+	n := typ.nameOff(typ.str)
+	return n.isExported()
+}

src/reflect/type.go

@@ -242,6 +242,11 @@ const (
 
 // tflag is used by an rtype to signal what extra type information is
 // available in the memory directly following the rtype value.
+//
+// tflag values must be kept in sync with copies in:
+//	cmd/compile/internal/gc/reflect.go
+//	cmd/link/internal/ld/decodesym.go
+//	runtime/type.go
 type tflag uint8
 
 const (
@@ -256,7 +261,13 @@ const (
 	//		u uncommonType
 	//	}
 	//	u := &(*tUncommon)(unsafe.Pointer(t)).u
-	tflagUncommon tflag = 1
+	tflagUncommon tflag = 1 << 0
+
+	// tflagExtraStar means the name in the str field has an
+	// extraneous '*' prefix. This is because for most types T in
+	// a program, the type *T also exists and reusing the str data
+	// saves binary size.
+	tflagExtraStar tflag = 1 << 1
 )
 
 // rtype is the common implementation of most values.
@@ -273,7 +284,8 @@ type rtype struct {
 	kind       uint8    // enumeration for C
 	alg        *typeAlg // algorithm table
 	gcdata     *byte    // garbage collection data
-	string     string   // string form; unnecessary but undeniably useful
+	str        nameOff  // string form
+	_          int32    // unused; keeps rtype always a multiple of ptrSize
 }
 
 // a copy of runtime.typeAlg
@@ -420,6 +432,9 @@ type structType struct {
 // If the import path follows, then 4 bytes at the end of
 // the data form a nameOff. The import path is only set for concrete
 // methods that are defined in a different package than their type.
+//
+// If a name starts with "*", then the exported bit represents
+// whether the pointed to type is exported.
 type name struct {
 	bytes *byte
 }
@@ -724,7 +739,13 @@ func (t *rtype) uncommon() *uncommonType {
 	}
 }
 
-func (t *rtype) String() string { return t.string }
+func (t *rtype) String() string {
+	s := t.nameOff(t.str).name()
+	if t.tflag&tflagExtraStar != 0 {
+		return s[1:]
+	}
+	return s
+}
 
 func (t *rtype) Size() uintptr { return t.size }
 
@@ -833,33 +854,34 @@ func hasPrefix(s, prefix string) bool {
 }
 
 func (t *rtype) Name() string {
-	if hasPrefix(t.string, "map[") {
+	s := t.String()
+	if hasPrefix(s, "map[") {
 		return ""
 	}
-	if hasPrefix(t.string, "struct {") {
+	if hasPrefix(s, "struct {") {
 		return ""
 	}
-	if hasPrefix(t.string, "chan ") {
+	if hasPrefix(s, "chan ") {
 		return ""
 	}
-	if hasPrefix(t.string, "chan<-") {
+	if hasPrefix(s, "chan<-") {
 		return ""
 	}
-	if hasPrefix(t.string, "func(") {
+	if hasPrefix(s, "func(") {
 		return ""
 	}
-	switch t.string[0] {
+	switch s[0] {
 	case '[', '*', '<':
 		return ""
 	}
-	i := len(t.string) - 1
+	i := len(s) - 1
 	for i >= 0 {
-		if t.string[i] == '.' {
+		if s[i] == '.' {
 			break
 		}
 		i--
 	}
-	return t.string[i+1:]
+	return s[i+1:]
 }
 
 func (t *rtype) ChanDir() ChanDir {
@@ -1391,7 +1413,7 @@ func (t *rtype) ptrTo() *rtype {
 	}
 
 	// Look in known types.
-	s := "*" + t.string
+	s := "*" + t.String()
 	for _, tt := range typesByString(s) {
 		p = (*ptrType)(unsafe.Pointer(tt))
 		if p.elem == t {
@@ -1408,7 +1430,7 @@ func (t *rtype) ptrTo() *rtype {
 	prototype := *(**ptrType)(unsafe.Pointer(&iptr))
 	*p = *prototype
 
-	p.string = s
+	p.str = resolveReflectName(newName(s, "", "", false))
 
 	// For the type structures linked into the binary, the
 	// compiler provides a good hash of the string.
@@ -1645,7 +1667,7 @@ func haveIdenticalUnderlyingType(T, V *rtype) bool {
 //
 // and
 //
-//	t1.string < t2.string
+//	t1.String() < t2.String()
 //
 // Note that strings are not unique identifiers for types:
 // there can be more than one with a given string.
@@ -1669,12 +1691,12 @@ func typesByString(s string) []*rtype {
 		section := sections[offsI]
 
 		// We are looking for the first index i where the string becomes >= s.
-		// This is a copy of sort.Search, with f(h) replaced by (*typ[h].string >= s).
+		// This is a copy of sort.Search, with f(h) replaced by (*typ[h].String() >= s).
 		i, j := 0, len(offs)
 		for i < j {
 			h := i + (j-i)/2 // avoid overflow when computing h
 			// i ≤ h < j
-			if !(rtypeOff(section, offs[h]).string >= s) {
+			if !(rtypeOff(section, offs[h]).String() >= s) {
 				i = h + 1 // preserves f(i-1) == false
 			} else {
 				j = h // preserves f(j) == true
@@ -1687,7 +1709,7 @@ func typesByString(s string) []*rtype {
 		// to do a linear scan anyway.
 		for j := i; j < len(offs); j++ {
 			typ := rtypeOff(section, offs[j])
-			if typ.string != s {
+			if typ.String() != s {
 				break
 			}
 			ret = append(ret, typ)
@@ -1783,11 +1805,11 @@ func ChanOf(dir ChanDir, t Type) Type {
 		lookupCache.Unlock()
 		panic("reflect.ChanOf: invalid dir")
 	case SendDir:
-		s = "chan<- " + typ.string
+		s = "chan<- " + typ.String()
 	case RecvDir:
-		s = "<-chan " + typ.string
+		s = "<-chan " + typ.String()
 	case BothDir:
-		s = "chan " + typ.string
+		s = "chan " + typ.String()
 	}
 	for _, tt := range typesByString(s) {
 		ch := (*chanType)(unsafe.Pointer(tt))
@@ -1802,7 +1824,7 @@ func ChanOf(dir ChanDir, t Type) Type {
 	ch := new(chanType)
 	*ch = *prototype
 	ch.dir = uintptr(dir)
-	ch.string = s
+	ch.str = resolveReflectName(newName(s, "", "", false))
 	ch.hash = fnv1(typ.hash, 'c', byte(dir))
 	ch.elem = typ
 
@@ -1832,7 +1854,7 @@ func MapOf(key, elem Type) Type {
 	}
 
 	// Look in known types.
-	s := "map[" + ktyp.string + "]" + etyp.string
+	s := "map[" + ktyp.String() + "]" + etyp.String()
 	for _, tt := range typesByString(s) {
 		mt := (*mapType)(unsafe.Pointer(tt))
 		if mt.key == ktyp && mt.elem == etyp {
@@ -1844,7 +1866,7 @@ func MapOf(key, elem Type) Type {
 	var imap interface{} = (map[unsafe.Pointer]unsafe.Pointer)(nil)
 	mt := new(mapType)
 	*mt = **(**mapType)(unsafe.Pointer(&imap))
-	mt.string = s
+	mt.str = resolveReflectName(newName(s, "", "", false))
 	mt.hash = fnv1(etyp.hash, 'm', byte(ktyp.hash>>24), byte(ktyp.hash>>16), byte(ktyp.hash>>8), byte(ktyp.hash))
 	mt.key = ktyp
 	mt.elem = etyp
@@ -2002,7 +2024,7 @@ func FuncOf(in, out []Type, variadic bool) Type {
 	}
 
 	// Populate the remaining fields of ft and store in cache.
-	ft.string = str
+	ft.str = resolveReflectName(newName(str, "", "", false))
 	funcLookupCache.m[hash] = append(funcLookupCache.m[hash], &ft.rtype)
 
 	return &ft.rtype
@@ -2018,9 +2040,9 @@ func funcStr(ft *funcType) string {
 		}
 		if ft.IsVariadic() && i == int(ft.inCount)-1 {
 			repr = append(repr, "..."...)
-			repr = append(repr, (*sliceType)(unsafe.Pointer(t)).elem.string...)
+			repr = append(repr, (*sliceType)(unsafe.Pointer(t)).elem.String()...)
 		} else {
-			repr = append(repr, t.string...)
+			repr = append(repr, t.String()...)
 		}
 	}
 	repr = append(repr, ')')
@@ -2034,7 +2056,7 @@ func funcStr(ft *funcType) string {
 		if i > 0 {
 			repr = append(repr, ", "...)
 		}
-		repr = append(repr, t.string...)
+		repr = append(repr, t.String()...)
 	}
 	if len(out) > 1 {
 		repr = append(repr, ')')
@@ -2199,8 +2221,8 @@ func bucketOf(ktyp, etyp *rtype) *rtype {
 	b.ptrdata = ptrdata
 	b.kind = kind
 	b.gcdata = gcdata
-	s := "bucket(" + ktyp.string + "," + etyp.string + ")"
-	b.string = s
+	s := "bucket(" + ktyp.String() + "," + etyp.String() + ")"
+	b.str = resolveReflectName(newName(s, "", "", false))
 	return b
 }
 
@@ -2216,7 +2238,7 @@ func SliceOf(t Type) Type {
 	}
 
 	// Look in known types.
-	s := "[]" + typ.string
+	s := "[]" + typ.String()
 	for _, tt := range typesByString(s) {
 		slice := (*sliceType)(unsafe.Pointer(tt))
 		if slice.elem == typ {
@@ -2229,7 +2251,7 @@ func SliceOf(t Type) Type {
 	prototype := *(**sliceType)(unsafe.Pointer(&islice))
 	slice := new(sliceType)
 	*slice = *prototype
-	slice.string = s
+	slice.str = resolveReflectName(newName(s, "", "", false))
 	slice.hash = fnv1(typ.hash, '[')
 	slice.elem = typ
 
@@ -2337,11 +2359,11 @@ func StructOf(fields []StructField) Type {
 				// Embedded ** and *interface{} are illegal
 				elem := ft.Elem()
 				if k := elem.Kind(); k == Ptr || k == Interface {
-					panic("reflect.StructOf: illegal anonymous field type " + ft.string)
+					panic("reflect.StructOf: illegal anonymous field type " + ft.String())
 				}
 				name = elem.String()
 			} else {
-				name = ft.string
+				name = ft.String()
 			}
 			// TODO(sbinet) check for syntactically impossible type names?
 
@@ -2463,7 +2485,7 @@ func StructOf(fields []StructField) Type {
 
 		hash = fnv1(hash, byte(ft.hash>>24), byte(ft.hash>>16), byte(ft.hash>>8), byte(ft.hash))
 
-		repr = append(repr, (" " + ft.string)...)
+		repr = append(repr, (" " + ft.String())...)
 		if f.name.tagLen() > 0 {
 			hash = fnv1(hash, []byte(f.name.tag())...)
 			repr = append(repr, (" " + strconv.Quote(f.name.tag()))...)
@@ -2579,7 +2601,7 @@ func StructOf(fields []StructField) Type {
 		}
 	}
 
-	typ.string = str
+	typ.str = resolveReflectName(newName(str, "", "", false))
 	typ.hash = hash
 	typ.size = size
 	typ.align = typalign
@@ -2691,11 +2713,11 @@ func StructOf(fields []StructField) Type {
 func runtimeStructField(field StructField) structField {
 	exported := field.PkgPath == ""
 	if field.Name == "" {
-		t := field.Type
+		t := field.Type.(*rtype)
 		if t.Kind() == Ptr {
-			t = t.Elem()
+			t = t.Elem().(*rtype)
 		}
-		exported = isExported(t.Name())
+		exported = t.nameOff(t.str).isExported()
 	} else if exported {
 		b0 := field.Name[0]
 		if ('a' <= b0 && b0 <= 'z') || b0 == '_' {
@@ -2711,25 +2733,6 @@ func runtimeStructField(field StructField) structField {
 	}
 }
 
-func isExported(s string) bool {
-	if s == "" {
-		return false
-	}
-	// FIXME(sbinet): handle utf8/runes (see https://golang.org/issue/15064)
-	// TODO: turn rtype.string into a reflect.name type, and put the exported
-	//       bit on there which can be checked here with field.Type.(*rtype).string.isExported()
-	//       When done, remove the documented limitation of StructOf.
-	r := s[0]
-	switch {
-	case 'A' <= r && r <= 'Z':
-		return true
-	case r == '_' || 'a' <= r && r <= 'z':
-		return false
-	default:
-		panic("reflect.StructOf: creating a struct with UTF-8 fields is not supported yet")
-	}
-}
-
 // typeptrdata returns the length in bytes of the prefix of t
 // containing pointer data. Anything after this offset is scalar data.
 // keep in sync with ../cmd/compile/internal/gc/reflect.go
@@ -2779,7 +2782,7 @@ func ArrayOf(count int, elem Type) Type {
 	}
 
 	// Look in known types.
-	s := "[" + strconv.Itoa(count) + "]" + typ.string
+	s := "[" + strconv.Itoa(count) + "]" + typ.String()
 	for _, tt := range typesByString(s) {
 		array := (*arrayType)(unsafe.Pointer(tt))
 		if array.elem == typ {
@@ -2792,7 +2795,7 @@ func ArrayOf(count int, elem Type) Type {
 	prototype := *(**arrayType)(unsafe.Pointer(&iarray))
 	array := new(arrayType)
 	*array = *prototype
-	array.string = s
+	array.str = resolveReflectName(newName(s, "", "", false))
 	array.hash = fnv1(typ.hash, '[')
 	for n := uint32(count); n > 0; n >>= 8 {
 		array.hash = fnv1(array.hash, byte(n))
@@ -3046,11 +3049,11 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 
 	var s string
 	if rcvr != nil {
-		s = "methodargs(" + rcvr.string + ")(" + t.string + ")"
+		s = "methodargs(" + rcvr.String() + ")(" + t.String() + ")"
 	} else {
-		s = "funcargs(" + t.string + ")"
+		s = "funcargs(" + t.String() + ")"
 	}
-	x.string = s
+	x.str = resolveReflectName(newName(s, "", "", false))
 
 	// cache result for future callers
 	if layoutCache.m == nil {

src/runtime/alg.go

@@ -146,7 +146,7 @@ func interhash(p unsafe.Pointer, h uintptr) uintptr {
 	t := tab._type
 	fn := t.alg.hash
 	if fn == nil {
-		panic(errorString("hash of unhashable type " + t._string))
+		panic(errorString("hash of unhashable type " + t.string()))
 	}
 	if isDirectIface(t) {
 		return c1 * fn(unsafe.Pointer(&a.data), h^c0)
@@ -163,7 +163,7 @@ func nilinterhash(p unsafe.Pointer, h uintptr) uintptr {
 	}
 	fn := t.alg.hash
 	if fn == nil {
-		panic(errorString("hash of unhashable type " + t._string))
+		panic(errorString("hash of unhashable type " + t.string()))
 	}
 	if isDirectIface(t) {
 		return c1 * fn(unsafe.Pointer(&a.data), h^c0)
@@ -221,7 +221,7 @@ func efaceeq(x, y eface) bool {
 	}
 	eq := t.alg.equal
 	if eq == nil {
-		panic(errorString("comparing uncomparable type " + t._string))
+		panic(errorString("comparing uncomparable type " + t.string()))
 	}
 	if isDirectIface(t) {
 		return eq(noescape(unsafe.Pointer(&x.data)), noescape(unsafe.Pointer(&y.data)))
@@ -239,7 +239,7 @@ func ifaceeq(x, y iface) bool {
 	t := xtab._type
 	eq := t.alg.equal
 	if eq == nil {
-		panic(errorString("comparing uncomparable type " + t._string))
+		panic(errorString("comparing uncomparable type " + t.string()))
 	}
 	if isDirectIface(t) {
 		return eq(noescape(unsafe.Pointer(&x.data)), noescape(unsafe.Pointer(&y.data)))

src/runtime/error.go

@@ -67,7 +67,7 @@ type stringer interface {
 
 func typestring(x interface{}) string {
 	e := efaceOf(&x)
-	return e._type._string
+	return e._type.string()
 }
 
 // For calling from C.

src/runtime/heapdump.go

@@ -184,7 +184,7 @@ func dumptype(t *_type) {
 	dumpint(uint64(uintptr(unsafe.Pointer(t))))
 	dumpint(uint64(t.size))
 	if x := t.uncommon(); x == nil || x.pkgpath.name() == "" {
-		dumpstr(t._string)
+		dumpstr(t.string())
 	} else {
 		pkgpathstr := x.pkgpath.name()
 		pkgpath := stringStructOf(&pkgpathstr)

src/runtime/iface.go

@@ -38,7 +38,7 @@ func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
 			return nil
 		}
 		name := inter.typ.nameOff(inter.mhdr[0].name)
-		panic(&TypeAssertionError{"", typ._string, inter.typ._string, name.name()})
+		panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), name.name()})
 	}
 
 	h := itabhash(inter, typ)
@@ -128,7 +128,7 @@ func additab(m *itab, locked, canfail bool) {
 			if locked {
 				unlock(&ifaceLock)
 			}
-			panic(&TypeAssertionError{"", typ._string, inter.typ._string, iname})
+			panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), iname})
 		}
 		m.bad = 1
 		break
@@ -196,18 +196,18 @@ func convT2I(tab *itab, elem unsafe.Pointer, x unsafe.Pointer) (i iface) {
 func panicdottype(have, want, iface *_type) {
 	haveString := ""
 	if have != nil {
-		haveString = have._string
+		haveString = have.string()
 	}
-	panic(&TypeAssertionError{iface._string, haveString, want._string, ""})
+	panic(&TypeAssertionError{iface.string(), haveString, want.string(), ""})
 }
 
 func assertI2T(t *_type, i iface, r unsafe.Pointer) {
 	tab := i.tab
 	if tab == nil {
-		panic(&TypeAssertionError{"", "", t._string, ""})
+		panic(&TypeAssertionError{"", "", t.string(), ""})
 	}
 	if tab._type != t {
-		panic(&TypeAssertionError{tab.inter.typ._string, tab._type._string, t._string, ""})
+		panic(&TypeAssertionError{tab.inter.typ.string(), tab._type.string(), t.string(), ""})
 	}
 	if r != nil {
 		if isDirectIface(t) {
@@ -238,10 +238,10 @@ func assertI2T2(t *_type, i iface, r unsafe.Pointer) bool {
 
 func assertE2T(t *_type, e eface, r unsafe.Pointer) {
 	if e._type == nil {
-		panic(&TypeAssertionError{"", "", t._string, ""})
+		panic(&TypeAssertionError{"", "", t.string(), ""})
 	}
 	if e._type != t {
-		panic(&TypeAssertionError{"", e._type._string, t._string, ""})
+		panic(&TypeAssertionError{"", e._type.string(), t.string(), ""})
 	}
 	if r != nil {
 		if isDirectIface(t) {
@@ -285,7 +285,7 @@ func assertI2E(inter *interfacetype, i iface, r *eface) {
 	tab := i.tab
 	if tab == nil {
 		// explicit conversions require non-nil interface value.
-		panic(&TypeAssertionError{"", "", inter.typ._string, ""})
+		panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
 	}
 	r._type = tab._type
 	r.data = i.data
@@ -322,7 +322,7 @@ func assertI2I(inter *interfacetype, i iface, r *iface) {
 	tab := i.tab
 	if tab == nil {
 		// explicit conversions require non-nil interface value.
-		panic(&TypeAssertionError{"", "", inter.typ._string, ""})
+		panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
 	}
 	if tab.inter == inter {
 		r.tab = tab
@@ -361,7 +361,7 @@ func assertE2I(inter *interfacetype, e eface, r *iface) {
 	t := e._type
 	if t == nil {
 		// explicit conversions require non-nil interface value.
-		panic(&TypeAssertionError{"", "", inter.typ._string, ""})
+		panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
 	}
 	r.tab = getitab(inter, t, false)
 	r.data = e.data
@@ -402,7 +402,7 @@ func reflect_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
 func assertE2E(inter *interfacetype, e eface, r *eface) {
 	if e._type == nil {
 		// explicit conversions require non-nil interface value.
-		panic(&TypeAssertionError{"", "", inter.typ._string, ""})
+		panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
 	}
 	*r = e
 }

src/runtime/mbitmap.go

@@ -461,11 +461,11 @@ func typeBitsBulkBarrier(typ *_type, p, size uintptr) {
 		throw("runtime: typeBitsBulkBarrier without type")
 	}
 	if typ.size != size {
-		println("runtime: typeBitsBulkBarrier with type ", typ._string, " of size ", typ.size, " but memory size", size)
+		println("runtime: typeBitsBulkBarrier with type ", typ.string(), " of size ", typ.size, " but memory size", size)
 		throw("runtime: invalid typeBitsBulkBarrier")
 	}
 	if typ.kind&kindGCProg != 0 {
-		println("runtime: typeBitsBulkBarrier with type ", typ._string, " with GC prog")
+		println("runtime: typeBitsBulkBarrier with type ", typ.string(), " with GC prog")
 		throw("runtime: invalid typeBitsBulkBarrier")
 	}
 	if !writeBarrier.needed {
@@ -916,7 +916,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 	}
 	if nw == 0 {
 		// No pointers! Caller was supposed to check.
-		println("runtime: invalid type ", typ._string)
+		println("runtime: invalid type ", typ.string())
 		throw("heapBitsSetType: called with non-pointer type")
 		return
 	}
@@ -1100,7 +1100,7 @@ Phase4:
 	if doubleCheck {
 		end := heapBitsForAddr(x + size)
 		if typ.kind&kindGCProg == 0 && (hbitp != end.bitp || (w == nw+2) != (end.shift == 2)) {
-			println("ended at wrong bitmap byte for", typ._string, "x", dataSize/typ.size)
+			println("ended at wrong bitmap byte for", typ.string(), "x", dataSize/typ.size)
 			print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n")
 			print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n")
 			h0 := heapBitsForAddr(x)
@@ -1136,7 +1136,7 @@ Phase4:
 				}
 			}
 			if have != want {
-				println("mismatch writing bits for", typ._string, "x", dataSize/typ.size)
+				println("mismatch writing bits for", typ.string(), "x", dataSize/typ.size)
 				print("typ.size=", typ.size, " typ.ptrdata=", typ.ptrdata, " dataSize=", dataSize, " size=", size, "\n")
 				print("kindGCProg=", typ.kind&kindGCProg != 0, "\n")
 				print("w=", w, " nw=", nw, " b=", hex(b), " nb=", nb, " hb=", hex(hb), "\n")

src/runtime/mfinal.go

@@ -274,7 +274,7 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 		throw("runtime.SetFinalizer: first argument is nil")
 	}
 	if etyp.kind&kindMask != kindPtr {
-		throw("runtime.SetFinalizer: first argument is " + etyp._string + ", not pointer")
+		throw("runtime.SetFinalizer: first argument is " + etyp.string() + ", not pointer")
 	}
 	ot := (*ptrtype)(unsafe.Pointer(etyp))
 	if ot.elem == nil {
@@ -328,14 +328,14 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 	}
 
 	if ftyp.kind&kindMask != kindFunc {
-		throw("runtime.SetFinalizer: second argument is " + ftyp._string + ", not a function")
+		throw("runtime.SetFinalizer: second argument is " + ftyp.string() + ", not a function")
 	}
 	ft := (*functype)(unsafe.Pointer(ftyp))
 	if ft.dotdotdot() {
-		throw("runtime.SetFinalizer: cannot pass " + etyp._string + " to finalizer " + ftyp._string + " because dotdotdot")
+		throw("runtime.SetFinalizer: cannot pass " + etyp.string() + " to finalizer " + ftyp.string() + " because dotdotdot")
 	}
 	if ft.dotdotdot() || ft.inCount != 1 {
-		throw("runtime.SetFinalizer: cannot pass " + etyp._string + " to finalizer " + ftyp._string)
+		throw("runtime.SetFinalizer: cannot pass " + etyp.string() + " to finalizer " + ftyp.string())
 	}
 	fint := ft.in()[0]
 	switch {
@@ -358,7 +358,7 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 			goto okarg
 		}
 	}
-	throw("runtime.SetFinalizer: cannot pass " + etyp._string + " to finalizer " + ftyp._string)
+	throw("runtime.SetFinalizer: cannot pass " + etyp.string() + " to finalizer " + ftyp.string())
 okarg:
 	// compute size needed for return parameters
 	nret := uintptr(0)

src/runtime/mprof.go

@@ -624,7 +624,7 @@ func tracealloc(p unsafe.Pointer, size uintptr, typ *_type) {
 	if typ == nil {
 		print("tracealloc(", p, ", ", hex(size), ")\n")
 	} else {
-		print("tracealloc(", p, ", ", hex(size), ", ", typ._string, ")\n")
+		print("tracealloc(", p, ", ", hex(size), ", ", typ.string(), ")\n")
 	}
 	if gp.m.curg == nil || gp == gp.m.curg {
 		goroutineheader(gp)

src/runtime/type.go

@@ -8,10 +8,18 @@ package runtime
 
 import "unsafe"
 
-// tflag is documented in ../reflect/type.go.
+// tflag is documented in reflect/type.go.
+//
+// tflag values must be kept in sync with copies in:
+//	cmd/compile/internal/gc/reflect.go
+//	cmd/link/internal/ld/decodesym.go
+//	reflect/type.go
 type tflag uint8
 
-const tflagUncommon tflag = 1
+const (
+	tflagUncommon  tflag = 1 << 0
+	tflagExtraStar tflag = 1 << 1
+)
 
 // Needs to be in sync with ../cmd/compile/internal/ld/decodesym.go:/^func.commonsize,
 // ../cmd/compile/internal/gc/reflect.go:/^func.dcommontype and
@@ -28,8 +36,17 @@ type _type struct {
 	// gcdata stores the GC type data for the garbage collector.
 	// If the KindGCProg bit is set in kind, gcdata is a GC program.
 	// Otherwise it is a ptrmask bitmap. See mbitmap.go for details.
-	gcdata  *byte
-	_string string
+	gcdata *byte
+	str    nameOff
+	_      int32
+}
+
+func (t *_type) string() string {
+	s := t.nameOff(t.str).name()
+	if t.tflag&tflagExtraStar != 0 {
+		return s[1:]
+	}
+	return s
 }
 
 func (t *_type) uncommon() *uncommontype {
@@ -99,33 +116,34 @@ func hasPrefix(s, prefix string) bool {
 }
 
 func (t *_type) name() string {
-	if hasPrefix(t._string, "map[") {
+	s := t.string()
+	if hasPrefix(s, "map[") {
 		return ""
 	}
-	if hasPrefix(t._string, "struct {") {
+	if hasPrefix(s, "struct {") {
 		return ""
 	}
-	if hasPrefix(t._string, "chan ") {
+	if hasPrefix(s, "chan ") {
 		return ""
 	}
-	if hasPrefix(t._string, "chan<-") {
+	if hasPrefix(s, "chan<-") {
 		return ""
 	}
-	if hasPrefix(t._string, "func(") {
+	if hasPrefix(s, "func(") {
 		return ""
 	}
-	switch t._string[0] {
+	switch s[0] {
 	case '[', '*', '<':
 		return ""
 	}
-	i := len(t._string) - 1
+	i := len(s) - 1
 	for i >= 0 {
-		if t._string[i] == '.' {
+		if s[i] == '.' {
 			break
 		}
 		i--
 	}
-	return t._string[i+1:]
+	return s[i+1:]
 }
 
 // reflectOffs holds type offsets defined at run time by the reflect package.
@@ -497,7 +515,7 @@ func typesEqual(t, v *_type) bool {
 	if kind != v.kind&kindMask {
 		return false
 	}
-	if t._string != v._string {
+	if t.string() != v.string() {
 		return false
 	}
 	ut := t.uncommon()