go/src/runtime/type.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Runtime type representation.

package runtime

import "unsafe"

// 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 << 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
// ../reflect/type.go:/^type.rtype.
type _type struct {
	size       uintptr
	ptrdata    uintptr // size of memory prefix holding all pointers
	hash       uint32
	tflag      tflag
	align      uint8
	fieldalign uint8
	kind       uint8
	alg        *typeAlg
	// 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
	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 {
	if t.tflag&tflagUncommon == 0 {
		return nil
	}
	switch t.kind & kindMask {
	case kindStruct:
		type u struct {
			structtype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindPtr:
		type u struct {
			ptrtype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindFunc:
		type u struct {
			functype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindSlice:
		type u struct {
			slicetype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindArray:
		type u struct {
			arraytype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindChan:
		type u struct {
			chantype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindMap:
		type u struct {
			maptype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	case kindInterface:
		type u struct {
			interfacetype
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	default:
		type u struct {
			_type
			u uncommontype
		}
		return &(*u)(unsafe.Pointer(t)).u
	}
}

func hasPrefix(s, prefix string) bool {
	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
}

func (t *_type) name() string {
	s := t.string()
	if hasPrefix(s, "map[") {
		return ""
	}
	if hasPrefix(s, "struct {") {
		return ""
	}
	if hasPrefix(s, "chan ") {
		return ""
	}
	if hasPrefix(s, "chan<-") {
		return ""
	}
	if hasPrefix(s, "func(") {
		return ""
	}
	switch s[0] {
	case '[', '*', '<':
		return ""
	}
	i := len(s) - 1
	for i >= 0 {
		if s[i] == '.' {
			break
		}
		i--
	}
	return s[i+1:]
}

// reflectOffs holds type offsets defined at run time by the reflect package.
//
// When a type is defined at run time, its *rtype data lives on the heap.
// There are a wide range of possible addresses the heap may use, that
// may not be representable as a 32-bit offset. Moreover the GC may
// one day start moving heap memory, in which case there is no stable
// offset that can be defined.
//
// To provide stable offsets, we add pin *rtype objects in a global map
// and treat the offset as an identifier. We use negative offsets that
// do not overlap with any compile-time module offsets.
//
// Entries are created by reflect.addReflectOff.
var reflectOffs struct {
	lock mutex
	next int32
	m    map[int32]unsafe.Pointer
	minv map[unsafe.Pointer]int32
}

func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
	if off == 0 {
		return name{}
	}
	base := uintptr(ptrInModule)
	var md *moduledata
	for next := &firstmoduledata; next != nil; next = next.next {
		if base >= next.types && base < next.etypes {
			md = next
			break
		}
	}
	if md == nil {
		lock(&reflectOffs.lock)
		res, found := reflectOffs.m[int32(off)]
		unlock(&reflectOffs.lock)
		if !found {
			println("runtime: nameOff", hex(off), "base", hex(base), "not in ranges:")
			for next := &firstmoduledata; next != nil; next = next.next {
				println("\ttypes", hex(next.types), "etypes", hex(next.etypes))
			}
			throw("runtime: name offset base pointer out of range")
		}
		return name{(*byte)(res)}
	}
	res := md.types + uintptr(off)
	if res > md.etypes {
		println("runtime: nameOff", hex(off), "out of range", hex(md.types), "-", hex(md.etypes))
		throw("runtime: name offset out of range")
	}
	return name{(*byte)(unsafe.Pointer(res))}
}

func (t *_type) nameOff(off nameOff) name {
	return resolveNameOff(unsafe.Pointer(t), off)
}

func (t *_type) typeOff(off typeOff) *_type {
	if off == 0 {
		return nil
	}
	base := uintptr(unsafe.Pointer(t))
	var md *moduledata
	for next := &firstmoduledata; next != nil; next = next.next {
		if base >= next.types && base < next.etypes {
			md = next
			break
		}
	}
	if md == nil {
		lock(&reflectOffs.lock)
		res := reflectOffs.m[int32(off)]
		unlock(&reflectOffs.lock)
		if res == nil {
			println("runtime: typeOff", hex(off), "base", hex(base), "not in ranges:")
			for next := &firstmoduledata; next != nil; next = next.next {
				println("\ttypes", hex(next.types), "etypes", hex(next.etypes))
			}
			throw("runtime: type offset base pointer out of range")
		}
		return (*_type)(res)
	}
	if t := md.typemap[off]; t != nil {
		return t
	}
	res := md.types + uintptr(off)
	if res > md.etypes {
		println("runtime: typeOff", hex(off), "out of range", hex(md.types), "-", hex(md.etypes))
		throw("runtime: type offset out of range")
	}
	return (*_type)(unsafe.Pointer(res))
}

func (t *_type) textOff(off textOff) unsafe.Pointer {
	base := uintptr(unsafe.Pointer(t))
	var md *moduledata
	for next := &firstmoduledata; next != nil; next = next.next {
		if base >= next.types && base < next.etypes {
			md = next
			break
		}
	}
	if md == nil {
		lock(&reflectOffs.lock)
		res := reflectOffs.m[int32(off)]
		unlock(&reflectOffs.lock)
		if res == nil {
			println("runtime: textOff", hex(off), "base", hex(base), "not in ranges:")
			for next := &firstmoduledata; next != nil; next = next.next {
				println("\ttypes", hex(next.types), "etypes", hex(next.etypes))
			}
			throw("runtime: text offset base pointer out of range")
		}
		return res
	}
	res := md.text + uintptr(off)
	if res > md.etext {
		println("runtime: textOff", hex(off), "out of range", hex(md.text), "-", hex(md.etext))
		throw("runtime: text offset out of range")
	}
	return unsafe.Pointer(res)
}

func (t *functype) in() []*_type {
	// See funcType in reflect/type.go for details on data layout.
	uadd := uintptr(unsafe.Sizeof(functype{}))
	if t.typ.tflag&tflagUncommon != 0 {
		uadd += unsafe.Sizeof(uncommontype{})
	}
	return (*[1 << 20]*_type)(add(unsafe.Pointer(t), uadd))[:t.inCount]
}

func (t *functype) out() []*_type {
	// See funcType in reflect/type.go for details on data layout.
	uadd := uintptr(unsafe.Sizeof(functype{}))
	if t.typ.tflag&tflagUncommon != 0 {
		uadd += unsafe.Sizeof(uncommontype{})
	}
	outCount := t.outCount & (1<<15 - 1)
	return (*[1 << 20]*_type)(add(unsafe.Pointer(t), uadd))[t.inCount : t.inCount+outCount]
}

func (t *functype) dotdotdot() bool {
	return t.outCount&(1<<15) != 0
}

type nameOff int32
type typeOff int32
type textOff int32

type method struct {
	name nameOff
	mtyp typeOff
	ifn  textOff
	tfn  textOff
}

type uncommontype struct {
	pkgpath name
	mcount  uint16 // number of methods
	moff    uint16 // offset from this uncommontype to [mcount]method
}

type imethod struct {
	name nameOff
	ityp typeOff
}

type interfacetype struct {
	typ     _type
	pkgpath name
	mhdr    []imethod
}

type maptype struct {
	typ           _type
	key           *_type
	elem          *_type
	bucket        *_type // internal type representing a hash bucket
	hmap          *_type // internal type representing a hmap
	keysize       uint8  // size of key slot
	indirectkey   bool   // store ptr to key instead of key itself
	valuesize     uint8  // size of value slot
	indirectvalue bool   // store ptr to value instead of value itself
	bucketsize    uint16 // size of bucket
	reflexivekey  bool   // true if k==k for all keys
	needkeyupdate bool   // true if we need to update key on an overwrite
}

type arraytype struct {
	typ   _type
	elem  *_type
	slice *_type
	len   uintptr
}

type chantype struct {
	typ  _type
	elem *_type
	dir  uintptr
}

type slicetype struct {
	typ  _type
	elem *_type
}

type functype struct {
	typ      _type
	inCount  uint16
	outCount uint16
}

type ptrtype struct {
	typ  _type
	elem *_type
}

type structfield struct {
	name   name
	typ    *_type
	offset uintptr
}

type structtype struct {
	typ     _type
	pkgPath name
	fields  []structfield
}

// name is an encoded type name with optional extra data.
// See reflect/type.go for details.
type name struct {
	bytes *byte
}

func (n name) data(off int) *byte {
	return (*byte)(add(unsafe.Pointer(n.bytes), uintptr(off)))
}

func (n name) isExported() bool {
	return (*n.bytes)&(1<<0) != 0
}

func (n name) nameLen() int {
	return int(uint16(*n.data(1))<<8 | uint16(*n.data(2)))
}

func (n name) tagLen() int {
	if *n.data(0)&(1<<1) == 0 {
		return 0
	}
	off := 3 + n.nameLen()
	return int(uint16(*n.data(off))<<8 | uint16(*n.data(off + 1)))
}

func (n name) name() (s string) {
	if n.bytes == nil {
		return ""
	}
	nl := n.nameLen()
	if nl == 0 {
		return ""
	}
	hdr := (*stringStruct)(unsafe.Pointer(&s))
	hdr.str = unsafe.Pointer(n.data(3))
	hdr.len = nl
	return s
}

func (n name) tag() (s string) {
	tl := n.tagLen()
	if tl == 0 {
		return ""
	}
	nl := n.nameLen()
	hdr := (*stringStruct)(unsafe.Pointer(&s))
	hdr.str = unsafe.Pointer(n.data(3 + nl + 2))
	hdr.len = tl
	return s
}

func (n name) pkgPath() string {
	if n.bytes == nil || *n.data(0)&(1<<2) == 0 {
		return ""
	}
	off := 3 + n.nameLen()
	if tl := n.tagLen(); tl > 0 {
		off += 2 + tl
	}
	var nameOff nameOff
	copy((*[4]byte)(unsafe.Pointer(&nameOff))[:], (*[4]byte)(unsafe.Pointer(n.data(off)))[:])
	pkgPathName := resolveNameOff(unsafe.Pointer(n.bytes), nameOff)
	return pkgPathName.name()
}

// typelinksinit scans the types from extra modules and builds the
// moduledata typemap used to de-duplicate type pointers.
func typelinksinit() {
	if firstmoduledata.next == nil {
		return
	}
	typehash := make(map[uint32][]*_type)

	modules := []*moduledata{}
	for md := &firstmoduledata; md != nil; md = md.next {
		modules = append(modules, md)
	}
	prev, modules := modules[len(modules)-1], modules[:len(modules)-1]
	for len(modules) > 0 {
		// Collect types from the previous module into typehash.
	collect:
		for _, tl := range prev.typelinks {
			var t *_type
			if prev.typemap == nil {
				t = (*_type)(unsafe.Pointer(prev.types + uintptr(tl)))
			} else {
				t = prev.typemap[typeOff(tl)]
			}
			// Add to typehash if not seen before.
			tlist := typehash[t.hash]
			for _, tcur := range tlist {
				if tcur == t {
					continue collect
				}
			}
			typehash[t.hash] = append(tlist, t)
		}

		// If any of this module's typelinks match a type from a
		// prior module, prefer that prior type by adding the offset
		// to this module's typemap.
		md := modules[len(modules)-1]
		md.typemap = make(map[typeOff]*_type, len(md.typelinks))
		for _, tl := range md.typelinks {
			t := (*_type)(unsafe.Pointer(md.types + uintptr(tl)))
			for _, candidate := range typehash[t.hash] {
				if typesEqual(t, candidate) {
					t = candidate
					break
				}
			}
			md.typemap[typeOff(tl)] = t
		}

		prev, modules = md, modules[:len(modules)-1]
	}
}

// typesEqual reports whether two types are equal.
//
// Everywhere in the runtime and reflect packages, it is assumed that
// there is exactly one *_type per Go type, so that pointer equality
// can be used to test if types are equal. There is one place that
// breaks this assumption: buildmode=shared. In this case a type can
// appear as two different pieces of memory. This is hidden from the
// runtime and reflect package by the per-module typemap built in
// typelinksinit. It uses typesEqual to map types from later modules
// back into earlier ones.
//
// Only typelinksinit needs this function.
func typesEqual(t, v *_type) bool {
	if t == v {
		return true
	}
	kind := t.kind & kindMask
	if kind != v.kind&kindMask {
		return false
	}
	if t.string() != v.string() {
		return false
	}
	ut := t.uncommon()
	uv := v.uncommon()
	if ut != nil || uv != nil {
		if ut == nil || uv == nil {
			return false
		}
		if ut.pkgpath.name() != uv.pkgpath.name() {
			return false
		}
	}
	if kindBool <= kind && kind <= kindComplex128 {
		return true
	}
	switch kind {
	case kindString, kindUnsafePointer:
		return true
	case kindArray:
		at := (*arraytype)(unsafe.Pointer(t))
		av := (*arraytype)(unsafe.Pointer(v))
		return typesEqual(at.elem, av.elem) && at.len == av.len
	case kindChan:
		ct := (*chantype)(unsafe.Pointer(t))
		cv := (*chantype)(unsafe.Pointer(v))
		return ct.dir == cv.dir && typesEqual(ct.elem, cv.elem)
	case kindFunc:
		ft := (*functype)(unsafe.Pointer(t))
		fv := (*functype)(unsafe.Pointer(v))
		if ft.outCount != fv.outCount || ft.inCount != fv.inCount {
			return false
		}
		tin, vin := ft.in(), fv.in()
		for i := 0; i < len(tin); i++ {
			if !typesEqual(tin[i], vin[i]) {
				return false
			}
		}
		tout, vout := ft.out(), fv.out()
		for i := 0; i < len(tout); i++ {
			if !typesEqual(tout[i], vout[i]) {
				return false
			}
		}
		return true
	case kindInterface:
		it := (*interfacetype)(unsafe.Pointer(t))
		iv := (*interfacetype)(unsafe.Pointer(v))
		if it.pkgpath.name() != iv.pkgpath.name() {
			return false
		}
		if len(it.mhdr) != len(iv.mhdr) {
			return false
		}
		for i := range it.mhdr {
			tm := &it.mhdr[i]
			vm := &iv.mhdr[i]
			tname := it.typ.nameOff(tm.name)
			vname := iv.typ.nameOff(vm.name)
			if tname.name() != vname.name() {
				return false
			}
			if tname.pkgPath() != vname.pkgPath() {
				return false
			}
			if !typesEqual(it.typ.typeOff(tm.ityp), iv.typ.typeOff(vm.ityp)) {
				return false
			}
		}
		return true
	case kindMap:
		mt := (*maptype)(unsafe.Pointer(t))
		mv := (*maptype)(unsafe.Pointer(v))
		return typesEqual(mt.key, mv.key) && typesEqual(mt.elem, mv.elem)
	case kindPtr:
		pt := (*ptrtype)(unsafe.Pointer(t))
		pv := (*ptrtype)(unsafe.Pointer(v))
		return typesEqual(pt.elem, pv.elem)
	case kindSlice:
		st := (*slicetype)(unsafe.Pointer(t))
		sv := (*slicetype)(unsafe.Pointer(v))
		return typesEqual(st.elem, sv.elem)
	case kindStruct:
		st := (*structtype)(unsafe.Pointer(t))
		sv := (*structtype)(unsafe.Pointer(v))
		if len(st.fields) != len(sv.fields) {
			return false
		}
		for i := range st.fields {
			tf := &st.fields[i]
			vf := &sv.fields[i]
			if tf.name.name() != vf.name.name() {
				return false
			}
			if tf.name.pkgPath() != vf.name.pkgPath() {
				return false
			}
			if !typesEqual(tf.typ, vf.typ) {
				return false
			}
			if tf.name.tag() != vf.name.tag() {
				return false
			}
			if tf.offset != vf.offset {
				return false
			}
		}
		return true
	default:
		println("runtime: impossible type kind", kind)
		throw("runtime: impossible type kind")
		return false
	}
}