Source file src/cmd/compile/internal/reflectdata/reflect.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package reflectdata
     6  
     7  import (
     8  	"encoding/binary"
     9  	"fmt"
    10  	"internal/abi"
    11  	"slices"
    12  	"sort"
    13  	"strings"
    14  	"sync"
    15  
    16  	"cmd/compile/internal/base"
    17  	"cmd/compile/internal/bitvec"
    18  	"cmd/compile/internal/compare"
    19  	"cmd/compile/internal/ir"
    20  	"cmd/compile/internal/objw"
    21  	"cmd/compile/internal/rttype"
    22  	"cmd/compile/internal/staticdata"
    23  	"cmd/compile/internal/typebits"
    24  	"cmd/compile/internal/typecheck"
    25  	"cmd/compile/internal/types"
    26  	"cmd/internal/obj"
    27  	"cmd/internal/objabi"
    28  	"cmd/internal/src"
    29  )
    30  
    31  type ptabEntry struct {
    32  	s *types.Sym
    33  	t *types.Type
    34  }
    35  
    36  // runtime interface and reflection data structures
    37  var (
    38  	// protects signatset and signatslice
    39  	signatmu sync.Mutex
    40  	// Tracking which types need runtime type descriptor
    41  	signatset = make(map[*types.Type]struct{})
    42  	// Queue of types wait to be generated runtime type descriptor
    43  	signatslice []typeAndStr
    44  
    45  	gcsymmu  sync.Mutex // protects gcsymset and gcsymslice
    46  	gcsymset = make(map[*types.Type]struct{})
    47  )
    48  
    49  type typeSig struct {
    50  	name  *types.Sym
    51  	isym  *obj.LSym
    52  	tsym  *obj.LSym
    53  	type_ *types.Type
    54  	mtype *types.Type
    55  }
    56  
    57  func commonSize() int { return int(rttype.Type.Size()) } // Sizeof(runtime._type{})
    58  
    59  func uncommonSize(t *types.Type) int { // Sizeof(runtime.uncommontype{})
    60  	if t.Sym() == nil && len(methods(t)) == 0 {
    61  		return 0
    62  	}
    63  	return int(rttype.UncommonType.Size())
    64  }
    65  
    66  func makefield(name string, t *types.Type) *types.Field {
    67  	sym := (*types.Pkg)(nil).Lookup(name)
    68  	return types.NewField(src.NoXPos, sym, t)
    69  }
    70  
    71  // methods returns the methods of the non-interface type t, sorted by name.
    72  // Generates stub functions as needed.
    73  func methods(t *types.Type) []*typeSig {
    74  	if t.HasShape() {
    75  		// Shape types have no methods.
    76  		return nil
    77  	}
    78  	// method type
    79  	mt := types.ReceiverBaseType(t)
    80  
    81  	if mt == nil {
    82  		return nil
    83  	}
    84  	typecheck.CalcMethods(mt)
    85  
    86  	// make list of methods for t,
    87  	// generating code if necessary.
    88  	var ms []*typeSig
    89  	for _, f := range mt.AllMethods() {
    90  		if f.Sym == nil {
    91  			base.Fatalf("method with no sym on %v", mt)
    92  		}
    93  		if !f.IsMethod() {
    94  			base.Fatalf("non-method on %v method %v %v", mt, f.Sym, f)
    95  		}
    96  		if f.Type.Recv() == nil {
    97  			base.Fatalf("receiver with no type on %v method %v %v", mt, f.Sym, f)
    98  		}
    99  		if f.Nointerface() && !t.IsFullyInstantiated() {
   100  			// Skip creating method wrappers if f is nointerface. But, if
   101  			// t is an instantiated type, we still have to call
   102  			// methodWrapper, because methodWrapper generates the actual
   103  			// generic method on the type as well.
   104  			continue
   105  		}
   106  
   107  		// get receiver type for this particular method.
   108  		// if pointer receiver but non-pointer t and
   109  		// this is not an embedded pointer inside a struct,
   110  		// method does not apply.
   111  		if !types.IsMethodApplicable(t, f) {
   112  			continue
   113  		}
   114  
   115  		sig := &typeSig{
   116  			name:  f.Sym,
   117  			isym:  methodWrapper(t, f, true),
   118  			tsym:  methodWrapper(t, f, false),
   119  			type_: typecheck.NewMethodType(f.Type, t),
   120  			mtype: typecheck.NewMethodType(f.Type, nil),
   121  		}
   122  		if f.Nointerface() {
   123  			// In the case of a nointerface method on an instantiated
   124  			// type, don't actually append the typeSig.
   125  			continue
   126  		}
   127  		ms = append(ms, sig)
   128  	}
   129  
   130  	return ms
   131  }
   132  
   133  // imethods returns the methods of the interface type t, sorted by name.
   134  func imethods(t *types.Type) []*typeSig {
   135  	var methods []*typeSig
   136  	for _, f := range t.AllMethods() {
   137  		if f.Type.Kind() != types.TFUNC || f.Sym == nil {
   138  			continue
   139  		}
   140  		if f.Sym.IsBlank() {
   141  			base.Fatalf("unexpected blank symbol in interface method set")
   142  		}
   143  		if n := len(methods); n > 0 {
   144  			last := methods[n-1]
   145  			if types.CompareSyms(last.name, f.Sym) >= 0 {
   146  				base.Fatalf("sigcmp vs sortinter %v %v", last.name, f.Sym)
   147  			}
   148  		}
   149  
   150  		sig := &typeSig{
   151  			name:  f.Sym,
   152  			mtype: f.Type,
   153  			type_: typecheck.NewMethodType(f.Type, nil),
   154  		}
   155  		methods = append(methods, sig)
   156  
   157  		// NOTE(rsc): Perhaps an oversight that
   158  		// IfaceType.Method is not in the reflect data.
   159  		// Generate the method body, so that compiled
   160  		// code can refer to it.
   161  		methodWrapper(t, f, false)
   162  	}
   163  
   164  	return methods
   165  }
   166  
   167  func dimportpath(p *types.Pkg) {
   168  	if p.Pathsym != nil {
   169  		return
   170  	}
   171  
   172  	if p == types.LocalPkg && base.Ctxt.Pkgpath == "" {
   173  		panic("missing pkgpath")
   174  	}
   175  
   176  	// If we are compiling the runtime package, there are two runtime packages around
   177  	// -- localpkg and Pkgs.Runtime. We don't want to produce import path symbols for
   178  	// both of them, so just produce one for localpkg.
   179  	if base.Ctxt.Pkgpath == "runtime" && p == ir.Pkgs.Runtime {
   180  		return
   181  	}
   182  
   183  	s := base.Ctxt.Lookup("type:.importpath." + p.Prefix + ".")
   184  	ot := dnameData(s, 0, p.Path, "", nil, false, false)
   185  	objw.Global(s, int32(ot), obj.DUPOK|obj.RODATA)
   186  	s.Set(obj.AttrContentAddressable, true)
   187  	p.Pathsym = s
   188  }
   189  
   190  func dgopkgpath(c rttype.Cursor, pkg *types.Pkg) {
   191  	c = c.Field("Bytes")
   192  	if pkg == nil {
   193  		c.WritePtr(nil)
   194  		return
   195  	}
   196  
   197  	dimportpath(pkg)
   198  	c.WritePtr(pkg.Pathsym)
   199  }
   200  
   201  // dgopkgpathOff writes an offset relocation to the pkg path symbol to c.
   202  func dgopkgpathOff(c rttype.Cursor, pkg *types.Pkg) {
   203  	if pkg == nil {
   204  		c.WriteInt32(0)
   205  		return
   206  	}
   207  
   208  	dimportpath(pkg)
   209  	c.WriteSymPtrOff(pkg.Pathsym, false)
   210  }
   211  
   212  // dnameField dumps a reflect.name for a struct field.
   213  func dnameField(c rttype.Cursor, spkg *types.Pkg, ft *types.Field) {
   214  	if !types.IsExported(ft.Sym.Name) && ft.Sym.Pkg != spkg {
   215  		base.Fatalf("package mismatch for %v", ft.Sym)
   216  	}
   217  	nsym := dname(ft.Sym.Name, ft.Note, nil, types.IsExported(ft.Sym.Name), ft.Embedded != 0)
   218  	c.Field("Bytes").WritePtr(nsym)
   219  }
   220  
   221  // dnameData writes the contents of a reflect.name into s at offset ot.
   222  func dnameData(s *obj.LSym, ot int, name, tag string, pkg *types.Pkg, exported, embedded bool) int {
   223  	if len(name) >= 1<<29 {
   224  		base.Fatalf("name too long: %d %s...", len(name), name[:1024])
   225  	}
   226  	if len(tag) >= 1<<29 {
   227  		base.Fatalf("tag too long: %d %s...", len(tag), tag[:1024])
   228  	}
   229  	var nameLen [binary.MaxVarintLen64]byte
   230  	nameLenLen := binary.PutUvarint(nameLen[:], uint64(len(name)))
   231  	var tagLen [binary.MaxVarintLen64]byte
   232  	tagLenLen := binary.PutUvarint(tagLen[:], uint64(len(tag)))
   233  
   234  	// Encode name and tag. See reflect/type.go for details.
   235  	var bits byte
   236  	l := 1 + nameLenLen + len(name)
   237  	if exported {
   238  		bits |= 1 << 0
   239  	}
   240  	if len(tag) > 0 {
   241  		l += tagLenLen + len(tag)
   242  		bits |= 1 << 1
   243  	}
   244  	if pkg != nil {
   245  		bits |= 1 << 2
   246  	}
   247  	if embedded {
   248  		bits |= 1 << 3
   249  	}
   250  	b := make([]byte, l)
   251  	b[0] = bits
   252  	copy(b[1:], nameLen[:nameLenLen])
   253  	copy(b[1+nameLenLen:], name)
   254  	if len(tag) > 0 {
   255  		tb := b[1+nameLenLen+len(name):]
   256  		copy(tb, tagLen[:tagLenLen])
   257  		copy(tb[tagLenLen:], tag)
   258  	}
   259  
   260  	ot = int(s.WriteBytes(base.Ctxt, int64(ot), b))
   261  
   262  	if pkg != nil {
   263  		c := rttype.NewCursor(s, int64(ot), types.Types[types.TUINT32])
   264  		dgopkgpathOff(c, pkg)
   265  		ot += 4
   266  	}
   267  
   268  	return ot
   269  }
   270  
   271  var dnameCount int
   272  
   273  // dname creates a reflect.name for a struct field or method.
   274  func dname(name, tag string, pkg *types.Pkg, exported, embedded bool) *obj.LSym {
   275  	// Write out data as "type:." to signal two things to the
   276  	// linker, first that when dynamically linking, the symbol
   277  	// should be moved to a relro section, and second that the
   278  	// contents should not be decoded as a type.
   279  	sname := "type:.namedata."
   280  	if pkg == nil {
   281  		// In the common case, share data with other packages.
   282  		if name == "" {
   283  			if exported {
   284  				sname += "-noname-exported." + tag
   285  			} else {
   286  				sname += "-noname-unexported." + tag
   287  			}
   288  		} else {
   289  			if exported {
   290  				sname += name + "." + tag
   291  			} else {
   292  				sname += name + "-" + tag
   293  			}
   294  		}
   295  	} else {
   296  		// TODO(mdempsky): We should be able to share these too (except
   297  		// maybe when dynamic linking).
   298  		sname = fmt.Sprintf("%s%s.%d", sname, types.LocalPkg.Prefix, dnameCount)
   299  		dnameCount++
   300  	}
   301  	if embedded {
   302  		sname += ".embedded"
   303  	}
   304  	s := base.Ctxt.Lookup(sname)
   305  	if len(s.P) > 0 {
   306  		return s
   307  	}
   308  	ot := dnameData(s, 0, name, tag, pkg, exported, embedded)
   309  	objw.Global(s, int32(ot), obj.DUPOK|obj.RODATA)
   310  	s.Set(obj.AttrContentAddressable, true)
   311  	return s
   312  }
   313  
   314  // dextratype dumps the fields of a runtime.uncommontype.
   315  // dataAdd is the offset in bytes after the header where the
   316  // backing array of the []method field should be written.
   317  func dextratype(lsym *obj.LSym, off int64, t *types.Type, dataAdd int) {
   318  	m := methods(t)
   319  	if t.Sym() == nil && len(m) == 0 {
   320  		base.Fatalf("extra requested of type with no extra info %v", t)
   321  	}
   322  	noff := types.RoundUp(off, int64(types.PtrSize))
   323  	if noff != off {
   324  		base.Fatalf("unexpected alignment in dextratype for %v", t)
   325  	}
   326  
   327  	for _, a := range m {
   328  		writeType(a.type_)
   329  	}
   330  
   331  	c := rttype.NewCursor(lsym, off, rttype.UncommonType)
   332  	dgopkgpathOff(c.Field("PkgPath"), typePkg(t))
   333  
   334  	dataAdd += uncommonSize(t)
   335  	mcount := len(m)
   336  	if mcount != int(uint16(mcount)) {
   337  		base.Fatalf("too many methods on %v: %d", t, mcount)
   338  	}
   339  	xcount := sort.Search(mcount, func(i int) bool { return !types.IsExported(m[i].name.Name) })
   340  	if dataAdd != int(uint32(dataAdd)) {
   341  		base.Fatalf("methods are too far away on %v: %d", t, dataAdd)
   342  	}
   343  
   344  	c.Field("Mcount").WriteUint16(uint16(mcount))
   345  	c.Field("Xcount").WriteUint16(uint16(xcount))
   346  	c.Field("Moff").WriteUint32(uint32(dataAdd))
   347  	// Note: there is an unused uint32 field here.
   348  
   349  	// Write the backing array for the []method field.
   350  	array := rttype.NewArrayCursor(lsym, off+int64(dataAdd), rttype.Method, mcount)
   351  	for i, a := range m {
   352  		exported := types.IsExported(a.name.Name)
   353  		var pkg *types.Pkg
   354  		if !exported && a.name.Pkg != typePkg(t) {
   355  			pkg = a.name.Pkg
   356  		}
   357  		nsym := dname(a.name.Name, "", pkg, exported, false)
   358  
   359  		e := array.Elem(i)
   360  		e.Field("Name").WriteSymPtrOff(nsym, false)
   361  		dmethodptrOff(e.Field("Mtyp"), writeType(a.mtype))
   362  		dmethodptrOff(e.Field("Ifn"), a.isym)
   363  		dmethodptrOff(e.Field("Tfn"), a.tsym)
   364  	}
   365  }
   366  
   367  func typePkg(t *types.Type) *types.Pkg {
   368  	tsym := t.Sym()
   369  	if tsym == nil {
   370  		switch t.Kind() {
   371  		case types.TARRAY, types.TSLICE, types.TPTR, types.TCHAN:
   372  			if t.Elem() != nil {
   373  				tsym = t.Elem().Sym()
   374  			}
   375  		}
   376  	}
   377  	if tsym != nil && tsym.Pkg != types.BuiltinPkg {
   378  		return tsym.Pkg
   379  	}
   380  	return nil
   381  }
   382  
   383  func dmethodptrOff(c rttype.Cursor, x *obj.LSym) {
   384  	c.WriteInt32(0)
   385  	c.Reloc(obj.Reloc{Type: objabi.R_METHODOFF, Sym: x})
   386  }
   387  
   388  var kinds = []abi.Kind{
   389  	types.TINT:        abi.Int,
   390  	types.TUINT:       abi.Uint,
   391  	types.TINT8:       abi.Int8,
   392  	types.TUINT8:      abi.Uint8,
   393  	types.TINT16:      abi.Int16,
   394  	types.TUINT16:     abi.Uint16,
   395  	types.TINT32:      abi.Int32,
   396  	types.TUINT32:     abi.Uint32,
   397  	types.TINT64:      abi.Int64,
   398  	types.TUINT64:     abi.Uint64,
   399  	types.TUINTPTR:    abi.Uintptr,
   400  	types.TFLOAT32:    abi.Float32,
   401  	types.TFLOAT64:    abi.Float64,
   402  	types.TBOOL:       abi.Bool,
   403  	types.TSTRING:     abi.String,
   404  	types.TPTR:        abi.Pointer,
   405  	types.TSTRUCT:     abi.Struct,
   406  	types.TINTER:      abi.Interface,
   407  	types.TCHAN:       abi.Chan,
   408  	types.TMAP:        abi.Map,
   409  	types.TARRAY:      abi.Array,
   410  	types.TSLICE:      abi.Slice,
   411  	types.TFUNC:       abi.Func,
   412  	types.TCOMPLEX64:  abi.Complex64,
   413  	types.TCOMPLEX128: abi.Complex128,
   414  	types.TUNSAFEPTR:  abi.UnsafePointer,
   415  }
   416  
   417  func ABIKindOfType(t *types.Type) abi.Kind {
   418  	return kinds[t.Kind()]
   419  }
   420  
   421  var (
   422  	memhashvarlen  *obj.LSym
   423  	memequalvarlen *obj.LSym
   424  )
   425  
   426  // dcommontype dumps the contents of a reflect.rtype (runtime._type) to c.
   427  func dcommontype(c rttype.Cursor, t *types.Type) {
   428  	types.CalcSize(t)
   429  	eqfunc := geneq(t)
   430  
   431  	sptrWeak := true
   432  	var sptr *obj.LSym
   433  	if !t.IsPtr() || t.IsPtrElem() {
   434  		tptr := types.NewPtr(t)
   435  		if t.Sym() != nil || methods(tptr) != nil {
   436  			sptrWeak = false
   437  		}
   438  		sptr = writeType(tptr)
   439  	}
   440  
   441  	gcsym, onDemand, ptrdata := dgcsym(t, true, true)
   442  	if !onDemand {
   443  		delete(gcsymset, t)
   444  	}
   445  
   446  	// ../../../../reflect/type.go:/^type.rtype
   447  	// actual type structure
   448  	//	type rtype struct {
   449  	//		size          uintptr
   450  	//		ptrdata       uintptr
   451  	//		hash          uint32
   452  	//		tflag         tflag
   453  	//		align         uint8
   454  	//		fieldAlign    uint8
   455  	//		kind          uint8
   456  	//		equal         func(unsafe.Pointer, unsafe.Pointer) bool
   457  	//		gcdata        *byte
   458  	//		str           nameOff
   459  	//		ptrToThis     typeOff
   460  	//	}
   461  	c.Field("Size_").WriteUintptr(uint64(t.Size()))
   462  	c.Field("PtrBytes").WriteUintptr(uint64(ptrdata))
   463  	c.Field("Hash").WriteUint32(types.TypeHash(t))
   464  
   465  	var tflag abi.TFlag
   466  	if uncommonSize(t) != 0 {
   467  		tflag |= abi.TFlagUncommon
   468  	}
   469  	if t.Sym() != nil && t.Sym().Name != "" {
   470  		tflag |= abi.TFlagNamed
   471  	}
   472  	if compare.IsRegularMemory(t) {
   473  		tflag |= abi.TFlagRegularMemory
   474  	}
   475  	if onDemand {
   476  		tflag |= abi.TFlagGCMaskOnDemand
   477  	}
   478  
   479  	exported := false
   480  	p := t.NameString()
   481  	// If we're writing out type T,
   482  	// we are very likely to write out type *T as well.
   483  	// Use the string "*T"[1:] for "T", so that the two
   484  	// share storage. This is a cheap way to reduce the
   485  	// amount of space taken up by reflect strings.
   486  	if !strings.HasPrefix(p, "*") {
   487  		p = "*" + p
   488  		tflag |= abi.TFlagExtraStar
   489  		if t.Sym() != nil {
   490  			exported = types.IsExported(t.Sym().Name)
   491  		}
   492  	} else {
   493  		if t.Elem() != nil && t.Elem().Sym() != nil {
   494  			exported = types.IsExported(t.Elem().Sym().Name)
   495  		}
   496  	}
   497  	if types.IsDirectIface(t) {
   498  		tflag |= abi.TFlagDirectIface
   499  	}
   500  
   501  	if tflag != abi.TFlag(uint8(tflag)) {
   502  		// this should optimize away completely
   503  		panic("Unexpected change in size of abi.TFlag")
   504  	}
   505  	c.Field("TFlag").WriteUint8(uint8(tflag))
   506  
   507  	// runtime (and common sense) expects alignment to be a power of two.
   508  	i := int(uint8(t.Alignment()))
   509  
   510  	if i == 0 {
   511  		i = 1
   512  	}
   513  	if i&(i-1) != 0 {
   514  		base.Fatalf("invalid alignment %d for %v", uint8(t.Alignment()), t)
   515  	}
   516  	c.Field("Align_").WriteUint8(uint8(t.Alignment()))
   517  	c.Field("FieldAlign_").WriteUint8(uint8(t.Alignment()))
   518  
   519  	c.Field("Kind_").WriteUint8(uint8(ABIKindOfType(t)))
   520  
   521  	c.Field("Equal").WritePtr(eqfunc)
   522  	c.Field("GCData").WritePtr(gcsym)
   523  
   524  	nsym := dname(p, "", nil, exported, false)
   525  	c.Field("Str").WriteSymPtrOff(nsym, false)
   526  	c.Field("PtrToThis").WriteSymPtrOff(sptr, sptrWeak)
   527  }
   528  
   529  // TrackSym returns the symbol for tracking use of field/method f, assumed
   530  // to be a member of struct/interface type t.
   531  func TrackSym(t *types.Type, f *types.Field) *obj.LSym {
   532  	return base.PkgLinksym("go:track", t.LinkString()+"."+f.Sym.Name, obj.ABI0)
   533  }
   534  
   535  func TypeSymPrefix(prefix string, t *types.Type) *types.Sym {
   536  	p := prefix + "." + t.LinkString()
   537  	s := types.TypeSymLookup(p)
   538  
   539  	// This function is for looking up type-related generated functions
   540  	// (e.g. eq and hash). Make sure they are indeed generated.
   541  	signatmu.Lock()
   542  	NeedRuntimeType(t)
   543  	signatmu.Unlock()
   544  
   545  	//print("algsym: %s -> %+S\n", p, s);
   546  
   547  	return s
   548  }
   549  
   550  func TypeSym(t *types.Type) *types.Sym {
   551  	if t == nil || (t.IsPtr() && t.Elem() == nil) || t.IsUntyped() {
   552  		base.Fatalf("TypeSym %v", t)
   553  	}
   554  	if t.Kind() == types.TFUNC && t.Recv() != nil {
   555  		base.Fatalf("misuse of method type: %v", t)
   556  	}
   557  	s := types.TypeSym(t)
   558  	signatmu.Lock()
   559  	NeedRuntimeType(t)
   560  	signatmu.Unlock()
   561  	return s
   562  }
   563  
   564  func TypeLinksymPrefix(prefix string, t *types.Type) *obj.LSym {
   565  	return TypeSymPrefix(prefix, t).Linksym()
   566  }
   567  
   568  func TypeLinksymLookup(name string) *obj.LSym {
   569  	return types.TypeSymLookup(name).Linksym()
   570  }
   571  
   572  func TypeLinksym(t *types.Type) *obj.LSym {
   573  	lsym := TypeSym(t).Linksym()
   574  	signatmu.Lock()
   575  	if lsym.Extra == nil {
   576  		ti := lsym.NewTypeInfo()
   577  		ti.Type = t
   578  	}
   579  	signatmu.Unlock()
   580  	return lsym
   581  }
   582  
   583  // TypePtrAt returns an expression that evaluates to the
   584  // *runtime._type value for t.
   585  func TypePtrAt(pos src.XPos, t *types.Type) *ir.AddrExpr {
   586  	return typecheck.LinksymAddr(pos, TypeLinksym(t), types.Types[types.TUINT8])
   587  }
   588  
   589  // ITabLsym returns the LSym representing the itab for concrete type typ implementing
   590  // interface iface. A dummy tab will be created in the unusual case where typ doesn't
   591  // implement iface. Normally, this wouldn't happen, because the typechecker would
   592  // have reported a compile-time error. This situation can only happen when the
   593  // destination type of a type assert or a type in a type switch is parameterized, so
   594  // it may sometimes, but not always, be a type that can't implement the specified
   595  // interface.
   596  func ITabLsym(typ, iface *types.Type) *obj.LSym {
   597  	return itabLsym(typ, iface, true)
   598  }
   599  
   600  func itabLsym(typ, iface *types.Type, allowNonImplement bool) *obj.LSym {
   601  	s, existed := ir.Pkgs.Itab.LookupOK(typ.LinkString() + "," + iface.LinkString())
   602  	lsym := s.Linksym()
   603  	signatmu.Lock()
   604  	if lsym.Extra == nil {
   605  		ii := lsym.NewItabInfo()
   606  		ii.Type = typ
   607  	}
   608  	signatmu.Unlock()
   609  
   610  	if !existed {
   611  		writeITab(lsym, typ, iface, allowNonImplement)
   612  	}
   613  	return lsym
   614  }
   615  
   616  // ITabAddrAt returns an expression that evaluates to the
   617  // *runtime.itab value for concrete type typ implementing interface
   618  // iface.
   619  func ITabAddrAt(pos src.XPos, typ, iface *types.Type) *ir.AddrExpr {
   620  	lsym := itabLsym(typ, iface, false)
   621  	return typecheck.LinksymAddr(pos, lsym, types.Types[types.TUINT8])
   622  }
   623  
   624  // needkeyupdate reports whether map updates with t as a key
   625  // need the key to be updated.
   626  func needkeyupdate(t *types.Type) bool {
   627  	switch t.Kind() {
   628  	case types.TBOOL, types.TINT, types.TUINT, types.TINT8, types.TUINT8, types.TINT16, types.TUINT16, types.TINT32, types.TUINT32,
   629  		types.TINT64, types.TUINT64, types.TUINTPTR, types.TPTR, types.TUNSAFEPTR, types.TCHAN:
   630  		return false
   631  
   632  	case types.TFLOAT32, types.TFLOAT64, types.TCOMPLEX64, types.TCOMPLEX128, // floats and complex can be +0/-0
   633  		types.TINTER,
   634  		types.TSTRING: // strings might have smaller backing stores
   635  		return true
   636  
   637  	case types.TARRAY:
   638  		return needkeyupdate(t.Elem())
   639  
   640  	case types.TSTRUCT:
   641  		for _, t1 := range t.Fields() {
   642  			if needkeyupdate(t1.Type) {
   643  				return true
   644  			}
   645  		}
   646  		return false
   647  
   648  	default:
   649  		base.Fatalf("bad type for map key: %v", t)
   650  		return true
   651  	}
   652  }
   653  
   654  // hashMightPanic reports whether the hash of a map key of type t might panic.
   655  func hashMightPanic(t *types.Type) bool {
   656  	switch t.Kind() {
   657  	case types.TINTER:
   658  		return true
   659  
   660  	case types.TARRAY:
   661  		return hashMightPanic(t.Elem())
   662  
   663  	case types.TSTRUCT:
   664  		for _, t1 := range t.Fields() {
   665  			if hashMightPanic(t1.Type) {
   666  				return true
   667  			}
   668  		}
   669  		return false
   670  
   671  	default:
   672  		return false
   673  	}
   674  }
   675  
   676  // formalType replaces predeclared aliases with real types.
   677  // They've been separate internally to make error messages
   678  // better, but we have to merge them in the reflect tables.
   679  func formalType(t *types.Type) *types.Type {
   680  	switch t {
   681  	case types.AnyType, types.ByteType, types.RuneType:
   682  		return types.Types[t.Kind()]
   683  	}
   684  	return t
   685  }
   686  
   687  func writeType(t *types.Type) *obj.LSym {
   688  	t = formalType(t)
   689  	if t.IsUntyped() {
   690  		base.Fatalf("writeType %v", t)
   691  	}
   692  
   693  	s := types.TypeSym(t)
   694  	lsym := s.Linksym()
   695  
   696  	// special case (look for runtime below):
   697  	// when compiling package runtime,
   698  	// emit the type structures for int, float, etc.
   699  	tbase := t
   700  	if t.IsPtr() && t.Sym() == nil && t.Elem().Sym() != nil {
   701  		tbase = t.Elem()
   702  	}
   703  	if tbase.Kind() == types.TFORW {
   704  		base.Fatalf("unresolved defined type: %v", tbase)
   705  	}
   706  
   707  	// This is a fake type we generated for our builtin pseudo-runtime
   708  	// package. We'll emit a description for the real type while
   709  	// compiling package runtime, so we don't need or want to emit one
   710  	// from this fake type.
   711  	if sym := tbase.Sym(); sym != nil && sym.Pkg == ir.Pkgs.Runtime {
   712  		return lsym
   713  	}
   714  
   715  	if s.Siggen() {
   716  		return lsym
   717  	}
   718  	s.SetSiggen(true)
   719  
   720  	if !tbase.HasShape() {
   721  		TypeLinksym(t) // ensure lsym.Extra is set
   722  	}
   723  
   724  	if !NeedEmit(tbase) {
   725  		if i := typecheck.BaseTypeIndex(t); i >= 0 {
   726  			lsym.Pkg = tbase.Sym().Pkg.Prefix
   727  			lsym.SymIdx = int32(i)
   728  			lsym.Set(obj.AttrIndexed, true)
   729  		}
   730  
   731  		// TODO(mdempsky): Investigate whether this still happens.
   732  		// If we know we don't need to emit code for a type,
   733  		// we should have a link-symbol index for it.
   734  		// See also TODO in NeedEmit.
   735  		return lsym
   736  	}
   737  
   738  	// Type layout                          Written by               Marker
   739  	// +--------------------------------+                            - 0
   740  	// | abi/internal.Type              |   dcommontype
   741  	// +--------------------------------+                            - A
   742  	// | additional type-dependent      |   code in the switch below
   743  	// | fields, e.g.                   |
   744  	// | abi/internal.ArrayType.Len     |
   745  	// +--------------------------------+                            - B
   746  	// | internal/abi.UncommonType      |   dextratype
   747  	// | This section is optional,      |
   748  	// | if type has a name or methods  |
   749  	// +--------------------------------+                            - C
   750  	// | variable-length data           |   code in the switch below
   751  	// | referenced by                  |
   752  	// | type-dependent fields, e.g.    |
   753  	// | abi/internal.StructType.Fields |
   754  	// | dataAdd = size of this section |
   755  	// +--------------------------------+                            - D
   756  	// | method list, if any            |   dextratype
   757  	// +--------------------------------+                            - E
   758  
   759  	// runtime.moduleTypelinks is aware of this type layout,
   760  	// and must be changed if the layout change.
   761  
   762  	// UncommonType section is included if we have a name or a method.
   763  	extra := t.Sym() != nil || len(methods(t)) != 0
   764  
   765  	// Decide the underlying type of the descriptor, and remember
   766  	// the size we need for variable-length data.
   767  	var rt *types.Type
   768  	dataAdd := 0
   769  	switch t.Kind() {
   770  	default:
   771  		rt = rttype.Type
   772  	case types.TARRAY:
   773  		rt = rttype.ArrayType
   774  	case types.TSLICE:
   775  		rt = rttype.SliceType
   776  	case types.TCHAN:
   777  		rt = rttype.ChanType
   778  	case types.TFUNC:
   779  		rt = rttype.FuncType
   780  		dataAdd = (t.NumRecvs() + t.NumParams() + t.NumResults()) * types.PtrSize
   781  	case types.TINTER:
   782  		rt = rttype.InterfaceType
   783  		dataAdd = len(imethods(t)) * int(rttype.IMethod.Size())
   784  	case types.TMAP:
   785  		rt = rttype.MapType
   786  	case types.TPTR:
   787  		rt = rttype.PtrType
   788  		// TODO: use rttype.Type for Elem() is ANY?
   789  	case types.TSTRUCT:
   790  		rt = rttype.StructType
   791  		dataAdd = t.NumFields() * int(rttype.StructField.Size())
   792  	}
   793  
   794  	// Compute offsets of each section.
   795  	B := rt.Size()
   796  	C := B
   797  	if extra {
   798  		C = B + rttype.UncommonType.Size()
   799  	}
   800  	D := C + int64(dataAdd)
   801  	E := D + int64(len(methods(t)))*rttype.Method.Size()
   802  
   803  	// Write the runtime._type
   804  	c := rttype.NewCursor(lsym, 0, rt)
   805  	if rt == rttype.Type {
   806  		dcommontype(c, t)
   807  	} else {
   808  		dcommontype(c.Field("Type"), t)
   809  	}
   810  
   811  	// Write additional type-specific data
   812  	// (Both the fixed size and variable-sized sections.)
   813  	switch t.Kind() {
   814  	case types.TARRAY:
   815  		// internal/abi.ArrayType
   816  		s1 := writeType(t.Elem())
   817  		t2 := types.NewSlice(t.Elem())
   818  		s2 := writeType(t2)
   819  		c.Field("Elem").WritePtr(s1)
   820  		c.Field("Slice").WritePtr(s2)
   821  		c.Field("Len").WriteUintptr(uint64(t.NumElem()))
   822  
   823  	case types.TSLICE:
   824  		// internal/abi.SliceType
   825  		s1 := writeType(t.Elem())
   826  		c.Field("Elem").WritePtr(s1)
   827  
   828  	case types.TCHAN:
   829  		// internal/abi.ChanType
   830  		s1 := writeType(t.Elem())
   831  		c.Field("Elem").WritePtr(s1)
   832  		c.Field("Dir").WriteInt(int64(t.ChanDir()))
   833  
   834  	case types.TFUNC:
   835  		// internal/abi.FuncType
   836  		for _, t1 := range t.RecvParamsResults() {
   837  			writeType(t1.Type)
   838  		}
   839  		inCount := t.NumRecvs() + t.NumParams()
   840  		outCount := t.NumResults()
   841  		if t.IsVariadic() {
   842  			outCount |= 1 << 15
   843  		}
   844  
   845  		c.Field("InCount").WriteUint16(uint16(inCount))
   846  		c.Field("OutCount").WriteUint16(uint16(outCount))
   847  
   848  		// Array of rtype pointers follows funcType.
   849  		typs := t.RecvParamsResults()
   850  		array := rttype.NewArrayCursor(lsym, C, types.Types[types.TUNSAFEPTR], len(typs))
   851  		for i, t1 := range typs {
   852  			array.Elem(i).WritePtr(writeType(t1.Type))
   853  		}
   854  
   855  	case types.TINTER:
   856  		// internal/abi.InterfaceType
   857  		m := imethods(t)
   858  		n := len(m)
   859  		for _, a := range m {
   860  			writeType(a.type_)
   861  		}
   862  
   863  		var tpkg *types.Pkg
   864  		if t.Sym() != nil && t != types.Types[t.Kind()] && t != types.ErrorType {
   865  			tpkg = t.Sym().Pkg
   866  		}
   867  		dgopkgpath(c.Field("PkgPath"), tpkg)
   868  		c.Field("Methods").WriteSlice(lsym, C, int64(n), int64(n))
   869  
   870  		array := rttype.NewArrayCursor(lsym, C, rttype.IMethod, n)
   871  		for i, a := range m {
   872  			exported := types.IsExported(a.name.Name)
   873  			var pkg *types.Pkg
   874  			if !exported && a.name.Pkg != tpkg {
   875  				pkg = a.name.Pkg
   876  			}
   877  			nsym := dname(a.name.Name, "", pkg, exported, false)
   878  
   879  			e := array.Elem(i)
   880  			e.Field("Name").WriteSymPtrOff(nsym, false)
   881  			e.Field("Typ").WriteSymPtrOff(writeType(a.type_), false)
   882  		}
   883  
   884  	case types.TMAP:
   885  		writeMapType(t, lsym, c)
   886  
   887  	case types.TPTR:
   888  		// internal/abi.PtrType
   889  		if t.Elem().Kind() == types.TANY {
   890  			base.Fatalf("bad pointer base type")
   891  		}
   892  
   893  		s1 := writeType(t.Elem())
   894  		c.Field("Elem").WritePtr(s1)
   895  
   896  	case types.TSTRUCT:
   897  		// internal/abi.StructType
   898  		fields := t.Fields()
   899  		for _, t1 := range fields {
   900  			writeType(t1.Type)
   901  		}
   902  
   903  		// All non-exported struct field names within a struct
   904  		// type must originate from a single package. By
   905  		// identifying and recording that package within the
   906  		// struct type descriptor, we can omit that
   907  		// information from the field descriptors.
   908  		var spkg *types.Pkg
   909  		for _, f := range fields {
   910  			if !types.IsExported(f.Sym.Name) {
   911  				spkg = f.Sym.Pkg
   912  				break
   913  			}
   914  		}
   915  
   916  		dgopkgpath(c.Field("PkgPath"), spkg)
   917  		c.Field("Fields").WriteSlice(lsym, C, int64(len(fields)), int64(len(fields)))
   918  
   919  		array := rttype.NewArrayCursor(lsym, C, rttype.StructField, len(fields))
   920  		for i, f := range fields {
   921  			e := array.Elem(i)
   922  			dnameField(e.Field("Name"), spkg, f)
   923  			e.Field("Typ").WritePtr(writeType(f.Type))
   924  			e.Field("Offset").WriteUintptr(uint64(f.Offset))
   925  		}
   926  	}
   927  
   928  	// Write the extra info, if any.
   929  	if extra {
   930  		dextratype(lsym, B, t, dataAdd)
   931  	}
   932  
   933  	// Note: DUPOK is required to ensure that we don't end up with more
   934  	// than one type descriptor for a given type, if the type descriptor
   935  	// can be defined in multiple packages, that is, unnamed types,
   936  	// instantiated types and shape types.
   937  	dupok := 0
   938  	if tbase.Sym() == nil || tbase.IsFullyInstantiated() || tbase.HasShape() {
   939  		dupok = obj.DUPOK
   940  	}
   941  
   942  	objw.Global(lsym, int32(E), int16(dupok|obj.RODATA))
   943  
   944  	// The linker will leave a table of all the typelinks for
   945  	// types in the binary, so the runtime can find them.
   946  	//
   947  	// When buildmode=shared, all types are in typelinks so the
   948  	// runtime can deduplicate type pointers.
   949  	keep := base.Ctxt.Flag_dynlink
   950  	if !keep && t.Sym() == nil {
   951  		// For an unnamed type, we only need the link if the type can
   952  		// be created at run time by reflect.PointerTo and similar
   953  		// functions. If the type exists in the program, those
   954  		// functions must return the existing type structure rather
   955  		// than creating a new one.
   956  		switch t.Kind() {
   957  		case types.TPTR, types.TARRAY, types.TCHAN, types.TFUNC, types.TMAP, types.TSLICE, types.TSTRUCT:
   958  			keep = true
   959  		}
   960  	}
   961  	// Do not put Noalg types in typelinks.  See issue #22605.
   962  	if types.TypeHasNoAlg(t) {
   963  		keep = false
   964  	}
   965  	lsym.Set(obj.AttrMakeTypelink, keep)
   966  
   967  	return lsym
   968  }
   969  
   970  // InterfaceMethodOffset returns the offset of the i-th method in the interface
   971  // type descriptor, ityp.
   972  func InterfaceMethodOffset(ityp *types.Type, i int64) int64 {
   973  	// interface type descriptor layout is struct {
   974  	//   _type        // commonSize
   975  	//   pkgpath      // 1 word
   976  	//   []imethod    // 3 words (pointing to [...]imethod below)
   977  	//   uncommontype // uncommonSize
   978  	//   [...]imethod
   979  	// }
   980  	// The size of imethod is 8.
   981  	return int64(commonSize()+4*types.PtrSize+uncommonSize(ityp)) + i*8
   982  }
   983  
   984  // NeedRuntimeType ensures that a runtime type descriptor is emitted for t.
   985  func NeedRuntimeType(t *types.Type) {
   986  	if _, ok := signatset[t]; !ok {
   987  		signatset[t] = struct{}{}
   988  		signatslice = append(signatslice, typeAndStr{t: t, short: types.TypeSymName(t), regular: t.String()})
   989  	}
   990  }
   991  
   992  func WriteRuntimeTypes() {
   993  	// Process signatslice. Use a loop, as writeType adds
   994  	// entries to signatslice while it is being processed.
   995  	for len(signatslice) > 0 {
   996  		signats := signatslice
   997  		// Sort for reproducible builds.
   998  		slices.SortFunc(signats, typesStrCmp)
   999  		for _, ts := range signats {
  1000  			t := ts.t
  1001  			writeType(t)
  1002  			if t.Sym() != nil {
  1003  				writeType(types.NewPtr(t))
  1004  			}
  1005  		}
  1006  		signatslice = signatslice[len(signats):]
  1007  	}
  1008  }
  1009  
  1010  func WriteGCSymbols() {
  1011  	// Emit GC data symbols.
  1012  	gcsyms := make([]typeAndStr, 0, len(gcsymset))
  1013  	for t := range gcsymset {
  1014  		gcsyms = append(gcsyms, typeAndStr{t: t, short: types.TypeSymName(t), regular: t.String()})
  1015  	}
  1016  	slices.SortFunc(gcsyms, typesStrCmp)
  1017  	for _, ts := range gcsyms {
  1018  		dgcsym(ts.t, true, false)
  1019  	}
  1020  }
  1021  
  1022  // writeITab writes the itab for concrete type typ implementing interface iface. If
  1023  // allowNonImplement is true, allow the case where typ does not implement iface, and just
  1024  // create a dummy itab with zeroed-out method entries.
  1025  func writeITab(lsym *obj.LSym, typ, iface *types.Type, allowNonImplement bool) {
  1026  	// TODO(mdempsky): Fix methodWrapper, geneq, and genhash (and maybe
  1027  	// others) to stop clobbering these.
  1028  	oldpos, oldfn := base.Pos, ir.CurFunc
  1029  	defer func() { base.Pos, ir.CurFunc = oldpos, oldfn }()
  1030  
  1031  	if typ == nil || (typ.IsPtr() && typ.Elem() == nil) || typ.IsUntyped() || iface == nil || !iface.IsInterface() || iface.IsEmptyInterface() {
  1032  		base.Fatalf("writeITab(%v, %v)", typ, iface)
  1033  	}
  1034  
  1035  	sigs := iface.AllMethods()
  1036  	entries := make([]*obj.LSym, 0, len(sigs))
  1037  
  1038  	// both sigs and methods are sorted by name,
  1039  	// so we can find the intersection in a single pass
  1040  	for _, m := range methods(typ) {
  1041  		if m.name == sigs[0].Sym {
  1042  			entries = append(entries, m.isym)
  1043  			if m.isym == nil {
  1044  				panic("NO ISYM")
  1045  			}
  1046  			sigs = sigs[1:]
  1047  			if len(sigs) == 0 {
  1048  				break
  1049  			}
  1050  		}
  1051  	}
  1052  	completeItab := len(sigs) == 0
  1053  	if !allowNonImplement && !completeItab {
  1054  		base.Fatalf("incomplete itab")
  1055  	}
  1056  
  1057  	// dump empty itab symbol into i.sym
  1058  	// type itab struct {
  1059  	//   inter  *interfacetype
  1060  	//   _type  *_type
  1061  	//   hash   uint32 // copy of _type.hash. Used for type switches.
  1062  	//   _      [4]byte
  1063  	//   fun    [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter.
  1064  	// }
  1065  	c := rttype.NewCursor(lsym, 0, rttype.ITab)
  1066  	c.Field("Inter").WritePtr(writeType(iface))
  1067  	c.Field("Type").WritePtr(writeType(typ))
  1068  	c.Field("Hash").WriteUint32(types.TypeHash(typ)) // copy of type hash
  1069  
  1070  	var delta int64
  1071  	c = c.Field("Fun")
  1072  	if !completeItab {
  1073  		// If typ doesn't implement iface, make method entries be zero.
  1074  		c.Elem(0).WriteUintptr(0)
  1075  	} else {
  1076  		var a rttype.ArrayCursor
  1077  		a, delta = c.ModifyArray(len(entries))
  1078  		for i, fn := range entries {
  1079  			a.Elem(i).WritePtrWeak(fn) // method pointer for each method
  1080  		}
  1081  	}
  1082  	// Nothing writes static itabs, so they are read only.
  1083  	objw.Global(lsym, int32(rttype.ITab.Size()+delta), int16(obj.DUPOK|obj.RODATA))
  1084  	lsym.Set(obj.AttrContentAddressable, true)
  1085  }
  1086  
  1087  func WritePluginTable() {
  1088  	ptabs := typecheck.Target.PluginExports
  1089  	if len(ptabs) == 0 {
  1090  		return
  1091  	}
  1092  
  1093  	lsym := base.Ctxt.Lookup("go:plugin.tabs")
  1094  	ot := 0
  1095  	for _, p := range ptabs {
  1096  		// Dump ptab symbol into go.pluginsym package.
  1097  		//
  1098  		// type ptab struct {
  1099  		//	name nameOff
  1100  		//	typ  typeOff // pointer to symbol
  1101  		// }
  1102  		nsym := dname(p.Sym().Name, "", nil, true, false)
  1103  		t := p.Type()
  1104  		if p.Class != ir.PFUNC {
  1105  			t = types.NewPtr(t)
  1106  		}
  1107  		tsym := writeType(t)
  1108  		ot = objw.SymPtrOff(lsym, ot, nsym)
  1109  		ot = objw.SymPtrOff(lsym, ot, tsym)
  1110  		// Plugin exports symbols as interfaces. Mark their types
  1111  		// as UsedInIface.
  1112  		tsym.Set(obj.AttrUsedInIface, true)
  1113  	}
  1114  	objw.Global(lsym, int32(ot), int16(obj.RODATA))
  1115  
  1116  	lsym = base.Ctxt.Lookup("go:plugin.exports")
  1117  	ot = 0
  1118  	for _, p := range ptabs {
  1119  		ot = objw.SymPtr(lsym, ot, p.Linksym(), 0)
  1120  	}
  1121  	objw.Global(lsym, int32(ot), int16(obj.RODATA))
  1122  }
  1123  
  1124  // writtenByWriteBasicTypes reports whether typ is written by WriteBasicTypes.
  1125  // WriteBasicTypes always writes pointer types; any pointer has been stripped off typ already.
  1126  func writtenByWriteBasicTypes(typ *types.Type) bool {
  1127  	if typ.Sym() == nil && typ.Kind() == types.TFUNC {
  1128  		// func(error) string
  1129  		if typ.NumRecvs() == 0 &&
  1130  			typ.NumParams() == 1 && typ.NumResults() == 1 &&
  1131  			typ.Param(0).Type == types.ErrorType &&
  1132  			typ.Result(0).Type == types.Types[types.TSTRING] {
  1133  			return true
  1134  		}
  1135  	}
  1136  
  1137  	// Now we have left the basic types plus any and error, plus slices of them.
  1138  	// Strip the slice.
  1139  	if typ.Sym() == nil && typ.IsSlice() {
  1140  		typ = typ.Elem()
  1141  	}
  1142  
  1143  	// Basic types.
  1144  	sym := typ.Sym()
  1145  	if sym != nil && (sym.Pkg == types.BuiltinPkg || sym.Pkg == types.UnsafePkg) {
  1146  		return true
  1147  	}
  1148  	// any or error
  1149  	return (sym == nil && typ.IsEmptyInterface()) || typ == types.ErrorType
  1150  }
  1151  
  1152  func WriteBasicTypes() {
  1153  	// do basic types if compiling package runtime.
  1154  	// they have to be in at least one package,
  1155  	// and runtime is always loaded implicitly,
  1156  	// so this is as good as any.
  1157  	// another possible choice would be package main,
  1158  	// but using runtime means fewer copies in object files.
  1159  	// The code here needs to be in sync with writtenByWriteBasicTypes above.
  1160  	if base.Ctxt.Pkgpath != "runtime" {
  1161  		return
  1162  	}
  1163  
  1164  	// Note: always write NewPtr(t) because NeedEmit's caller strips the pointer.
  1165  	var list []*types.Type
  1166  	for i := types.Kind(1); i <= types.TBOOL; i++ {
  1167  		list = append(list, types.Types[i])
  1168  	}
  1169  	list = append(list,
  1170  		types.Types[types.TSTRING],
  1171  		types.Types[types.TUNSAFEPTR],
  1172  		types.AnyType,
  1173  		types.ErrorType)
  1174  	for _, t := range list {
  1175  		writeType(types.NewPtr(t))
  1176  		writeType(types.NewPtr(types.NewSlice(t)))
  1177  	}
  1178  
  1179  	// emit type for func(error) string,
  1180  	// which is the type of an auto-generated wrapper.
  1181  	writeType(types.NewPtr(types.NewSignature(nil, []*types.Field{
  1182  		types.NewField(base.Pos, nil, types.ErrorType),
  1183  	}, []*types.Field{
  1184  		types.NewField(base.Pos, nil, types.Types[types.TSTRING]),
  1185  	})))
  1186  }
  1187  
  1188  type typeAndStr struct {
  1189  	t       *types.Type
  1190  	short   string // "short" here means TypeSymName
  1191  	regular string
  1192  }
  1193  
  1194  func typesStrCmp(a, b typeAndStr) int {
  1195  	// put named types before unnamed types
  1196  	if a.t.Sym() != nil && b.t.Sym() == nil {
  1197  		return -1
  1198  	}
  1199  	if a.t.Sym() == nil && b.t.Sym() != nil {
  1200  		return +1
  1201  	}
  1202  
  1203  	if r := strings.Compare(a.short, b.short); r != 0 {
  1204  		return r
  1205  	}
  1206  	// When the only difference between the types is whether
  1207  	// they refer to byte or uint8, such as **byte vs **uint8,
  1208  	// the types' NameStrings can be identical.
  1209  	// To preserve deterministic sort ordering, sort these by String().
  1210  	//
  1211  	// TODO(mdempsky): This all seems suspect. Using LinkString would
  1212  	// avoid naming collisions, and there shouldn't be a reason to care
  1213  	// about "byte" vs "uint8": they share the same runtime type
  1214  	// descriptor anyway.
  1215  	if r := strings.Compare(a.regular, b.regular); r != 0 {
  1216  		return r
  1217  	}
  1218  	// Identical anonymous interfaces defined in different locations
  1219  	// will be equal for the above checks, but different in DWARF output.
  1220  	// Sort by source position to ensure deterministic order.
  1221  	// See issues 27013 and 30202.
  1222  	if a.t.Kind() == types.TINTER && len(a.t.AllMethods()) > 0 {
  1223  		if a.t.AllMethods()[0].Pos.Before(b.t.AllMethods()[0].Pos) {
  1224  			return -1
  1225  		}
  1226  		return +1
  1227  	}
  1228  	return 0
  1229  }
  1230  
  1231  // GCSym returns a data symbol containing GC information for type t.
  1232  // GC information is always a bitmask, never a gc program.
  1233  // GCSym may be called in concurrent backend, so it does not emit the symbol
  1234  // content.
  1235  func GCSym(t *types.Type, onDemandAllowed bool) (lsym *obj.LSym, ptrdata int64) {
  1236  	// Record that we need to emit the GC symbol.
  1237  	gcsymmu.Lock()
  1238  	if _, ok := gcsymset[t]; !ok {
  1239  		gcsymset[t] = struct{}{}
  1240  	}
  1241  	gcsymmu.Unlock()
  1242  
  1243  	lsym, _, ptrdata = dgcsym(t, false, onDemandAllowed)
  1244  	return
  1245  }
  1246  
  1247  // dgcsym returns a data symbol containing GC information for type t, along
  1248  // with a boolean reporting whether the gc mask should be computed on demand
  1249  // at runtime, and the ptrdata field to record in the reflect type information.
  1250  // When write is true, it writes the symbol data.
  1251  func dgcsym(t *types.Type, write, onDemandAllowed bool) (lsym *obj.LSym, onDemand bool, ptrdata int64) {
  1252  	ptrdata = types.PtrDataSize(t)
  1253  	if !onDemandAllowed || ptrdata/int64(types.PtrSize) <= abi.MaxPtrmaskBytes*8 {
  1254  		lsym = dgcptrmask(t, write)
  1255  		return
  1256  	}
  1257  
  1258  	onDemand = true
  1259  	lsym = dgcptrmaskOnDemand(t, write)
  1260  	return
  1261  }
  1262  
  1263  // dgcptrmask emits and returns the symbol containing a pointer mask for type t.
  1264  func dgcptrmask(t *types.Type, write bool) *obj.LSym {
  1265  	// Bytes we need for the ptrmask.
  1266  	n := (types.PtrDataSize(t)/int64(types.PtrSize) + 7) / 8
  1267  	// Runtime wants ptrmasks padded to a multiple of uintptr in size.
  1268  	n = (n + int64(types.PtrSize) - 1) &^ (int64(types.PtrSize) - 1)
  1269  	ptrmask := make([]byte, n)
  1270  	fillptrmask(t, ptrmask)
  1271  	p := fmt.Sprintf("runtime.gcbits.%x", ptrmask)
  1272  
  1273  	lsym := base.Ctxt.Lookup(p)
  1274  	if write && !lsym.OnList() {
  1275  		for i, x := range ptrmask {
  1276  			objw.Uint8(lsym, i, x)
  1277  		}
  1278  		objw.Global(lsym, int32(len(ptrmask)), obj.DUPOK|obj.RODATA|obj.LOCAL)
  1279  		lsym.Set(obj.AttrContentAddressable, true)
  1280  	}
  1281  	return lsym
  1282  }
  1283  
  1284  // fillptrmask fills in ptrmask with 1s corresponding to the
  1285  // word offsets in t that hold pointers.
  1286  // ptrmask is assumed to fit at least types.PtrDataSize(t)/PtrSize bits.
  1287  func fillptrmask(t *types.Type, ptrmask []byte) {
  1288  	if !t.HasPointers() {
  1289  		return
  1290  	}
  1291  
  1292  	vec := bitvec.New(8 * int32(len(ptrmask)))
  1293  	typebits.Set(t, 0, vec)
  1294  
  1295  	nptr := types.PtrDataSize(t) / int64(types.PtrSize)
  1296  	for i := int64(0); i < nptr; i++ {
  1297  		if vec.Get(int32(i)) {
  1298  			ptrmask[i/8] |= 1 << (uint(i) % 8)
  1299  		}
  1300  	}
  1301  }
  1302  
  1303  // dgcptrmaskOnDemand emits and returns the symbol that should be referenced by
  1304  // the GCData field of a type, for large types.
  1305  func dgcptrmaskOnDemand(t *types.Type, write bool) *obj.LSym {
  1306  	lsym := TypeLinksymPrefix(".gcmask", t)
  1307  	if write && !lsym.OnList() {
  1308  		// Note: contains a pointer, but a pointer to a
  1309  		// persistentalloc allocation. Starts with nil.
  1310  		objw.Uintptr(lsym, 0, 0)
  1311  		objw.Global(lsym, int32(types.PtrSize), obj.DUPOK|obj.NOPTR|obj.LOCAL) // TODO:bss?
  1312  	}
  1313  	return lsym
  1314  }
  1315  
  1316  // ZeroAddr returns the address of a symbol with at least
  1317  // size bytes of zeros.
  1318  func ZeroAddr(size int64) ir.Node {
  1319  	if size >= 1<<31 {
  1320  		base.Fatalf("map elem too big %d", size)
  1321  	}
  1322  	if ZeroSize < size {
  1323  		ZeroSize = size
  1324  	}
  1325  	lsym := base.PkgLinksym("go:map", "zero", obj.ABI0)
  1326  	x := ir.NewLinksymExpr(base.Pos, lsym, types.Types[types.TUINT8])
  1327  	return typecheck.Expr(typecheck.NodAddr(x))
  1328  }
  1329  
  1330  // NeedEmit reports whether typ is a type that we need to emit code
  1331  // for (e.g., runtime type descriptors, method wrappers).
  1332  func NeedEmit(typ *types.Type) bool {
  1333  	// TODO(mdempsky): Export data should keep track of which anonymous
  1334  	// and instantiated types were emitted, so at least downstream
  1335  	// packages can skip re-emitting them.
  1336  	//
  1337  	// Perhaps we can just generalize the linker-symbol indexing to
  1338  	// track the index of arbitrary types, not just defined types, and
  1339  	// use its presence to detect this. The same idea would work for
  1340  	// instantiated generic functions too.
  1341  
  1342  	switch sym := typ.Sym(); {
  1343  	case writtenByWriteBasicTypes(typ):
  1344  		return base.Ctxt.Pkgpath == "runtime"
  1345  
  1346  	case sym == nil:
  1347  		// Anonymous type; possibly never seen before or ever again.
  1348  		// Need to emit to be safe (however, see TODO above).
  1349  		return true
  1350  
  1351  	case sym.Pkg == types.LocalPkg:
  1352  		// Local defined type; our responsibility.
  1353  		return true
  1354  
  1355  	case typ.IsFullyInstantiated():
  1356  		// Instantiated type; possibly instantiated with unique type arguments.
  1357  		// Need to emit to be safe (however, see TODO above).
  1358  		return true
  1359  
  1360  	case typ.HasShape():
  1361  		// Shape type; need to emit even though it lives in the .shape package.
  1362  		// TODO: make sure the linker deduplicates them (see dupok in writeType above).
  1363  		return true
  1364  
  1365  	default:
  1366  		// Should have been emitted by an imported package.
  1367  		return false
  1368  	}
  1369  }
  1370  
  1371  // Generate a wrapper function to convert from
  1372  // a receiver of type T to a receiver of type U.
  1373  // That is,
  1374  //
  1375  //	func (t T) M() {
  1376  //		...
  1377  //	}
  1378  //
  1379  // already exists; this function generates
  1380  //
  1381  //	func (u U) M() {
  1382  //		u.M()
  1383  //	}
  1384  //
  1385  // where the types T and U are such that u.M() is valid
  1386  // and calls the T.M method.
  1387  // The resulting function is for use in method tables.
  1388  //
  1389  //	rcvr - U
  1390  //	method - M func (t T)(), a TFIELD type struct
  1391  //
  1392  // Also wraps methods on instantiated generic types for use in itab entries.
  1393  // For an instantiated generic type G[int], we generate wrappers like:
  1394  // G[int] pointer shaped:
  1395  //
  1396  //	func (x G[int]) f(arg) {
  1397  //		.inst.G[int].f(dictionary, x, arg)
  1398  //	}
  1399  //
  1400  // G[int] not pointer shaped:
  1401  //
  1402  //	func (x *G[int]) f(arg) {
  1403  //		.inst.G[int].f(dictionary, *x, arg)
  1404  //	}
  1405  //
  1406  // These wrappers are always fully stenciled.
  1407  func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSym {
  1408  	if forItab && !types.IsDirectIface(rcvr) {
  1409  		rcvr = rcvr.PtrTo()
  1410  	}
  1411  
  1412  	newnam := ir.MethodSym(rcvr, method.Sym)
  1413  	lsym := newnam.Linksym()
  1414  
  1415  	// Unified IR creates its own wrappers.
  1416  	return lsym
  1417  }
  1418  
  1419  var ZeroSize int64
  1420  
  1421  // MarkTypeUsedInInterface marks that type t is converted to an interface.
  1422  // This information is used in the linker in dead method elimination.
  1423  func MarkTypeUsedInInterface(t *types.Type, from *obj.LSym) {
  1424  	if t.HasShape() {
  1425  		// Shape types shouldn't be put in interfaces, so we shouldn't ever get here.
  1426  		base.Fatalf("shape types have no methods %+v", t)
  1427  	}
  1428  	MarkTypeSymUsedInInterface(TypeLinksym(t), from)
  1429  }
  1430  func MarkTypeSymUsedInInterface(tsym *obj.LSym, from *obj.LSym) {
  1431  	// Emit a marker relocation. The linker will know the type is converted
  1432  	// to an interface if "from" is reachable.
  1433  	from.AddRel(base.Ctxt, obj.Reloc{Type: objabi.R_USEIFACE, Sym: tsym})
  1434  }
  1435  
  1436  // MarkUsedIfaceMethod marks that an interface method is used in the current
  1437  // function. n is OCALLINTER node.
  1438  func MarkUsedIfaceMethod(n *ir.CallExpr) {
  1439  	// skip unnamed functions (func _())
  1440  	if ir.CurFunc.LSym == nil {
  1441  		return
  1442  	}
  1443  	dot := n.Fun.(*ir.SelectorExpr)
  1444  	ityp := dot.X.Type()
  1445  	if ityp.HasShape() {
  1446  		// Here we're calling a method on a generic interface. Something like:
  1447  		//
  1448  		// type I[T any] interface { foo() T }
  1449  		// func f[T any](x I[T]) {
  1450  		//     ... = x.foo()
  1451  		// }
  1452  		// f[int](...)
  1453  		// f[string](...)
  1454  		//
  1455  		// In this case, in f we're calling foo on a generic interface.
  1456  		// Which method could that be? Normally we could match the method
  1457  		// both by name and by type. But in this case we don't really know
  1458  		// the type of the method we're calling. It could be func()int
  1459  		// or func()string. So we match on just the function name, instead
  1460  		// of both the name and the type used for the non-generic case below.
  1461  		// TODO: instantiations at least know the shape of the instantiated
  1462  		// type, and the linker could do more complicated matching using
  1463  		// some sort of fuzzy shape matching. For now, only use the name
  1464  		// of the method for matching.
  1465  		ir.CurFunc.LSym.AddRel(base.Ctxt, obj.Reloc{
  1466  			Type: objabi.R_USENAMEDMETHOD,
  1467  			Sym:  staticdata.StringSymNoCommon(dot.Sel.Name),
  1468  		})
  1469  		return
  1470  	}
  1471  
  1472  	// dot.Offset() is the method index * PtrSize (the offset of code pointer in itab).
  1473  	midx := dot.Offset() / int64(types.PtrSize)
  1474  	ir.CurFunc.LSym.AddRel(base.Ctxt, obj.Reloc{
  1475  		Type: objabi.R_USEIFACEMETHOD,
  1476  		Sym:  TypeLinksym(ityp),
  1477  		Add:  InterfaceMethodOffset(ityp, midx),
  1478  	})
  1479  }
  1480  

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