src/cmd/internal/obj/objfile.go - go - Git at Google

 // Copyright 2013 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.

 // Writing Go object files.

 package obj

 import (
 	"bytes"
 	"cmd/internal/bio"
 	"cmd/internal/goobj"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"crypto/sha1"
 	"encoding/binary"
 	"fmt"
 	"io"
 	"log"
 	"os"
 	"path/filepath"
 	"sort"
 	"strings"
 )

 // Entry point of writing new object file.
 func WriteObjFile(ctxt *Link, b *bio.Writer) {

 	debugAsmEmit(ctxt)

 	genFuncInfoSyms(ctxt)

 	w := writer{
 		Writer:  goobj.NewWriter(b),
 		ctxt:    ctxt,
 		pkgpath: objabi.PathToPrefix(ctxt.Pkgpath),
 	}

 	start := b.Offset()
 	w.init()

 	// Header
 	// We just reserve the space. We'll fill in the offsets later.
 	flags := uint32(0)
 	if ctxt.Flag_shared {
 		flags |= goobj.ObjFlagShared
 	}
 	if w.pkgpath == "" {
 		flags |= goobj.ObjFlagNeedNameExpansion
 	}
 	if ctxt.IsAsm {
 		flags |= goobj.ObjFlagFromAssembly
 	}
 	h := goobj.Header{
 		Magic:       goobj.Magic,
 		Fingerprint: ctxt.Fingerprint,
 		Flags:       flags,
 	}
 	h.Write(w.Writer)

 	// String table
 	w.StringTable()

 	// Autolib
 	h.Offsets[goobj.BlkAutolib] = w.Offset()
 	for i := range ctxt.Imports {
 		ctxt.Imports[i].Write(w.Writer)
 	}

 	// Package references
 	h.Offsets[goobj.BlkPkgIdx] = w.Offset()
 	for _, pkg := range w.pkglist {
 		w.StringRef(pkg)
 	}

 	// File table (for DWARF and pcln generation).
 	h.Offsets[goobj.BlkFile] = w.Offset()
 	for _, f := range ctxt.PosTable.FileTable() {
 		w.StringRef(filepath.ToSlash(f))
 	}

 	// Symbol definitions
 	h.Offsets[goobj.BlkSymdef] = w.Offset()
 	for _, s := range ctxt.defs {
 		w.Sym(s)
 	}

 	// Short hashed symbol definitions
 	h.Offsets[goobj.BlkHashed64def] = w.Offset()
 	for _, s := range ctxt.hashed64defs {
 		w.Sym(s)
 	}

 	// Hashed symbol definitions
 	h.Offsets[goobj.BlkHasheddef] = w.Offset()
 	for _, s := range ctxt.hasheddefs {
 		w.Sym(s)
 	}

 	// Non-pkg symbol definitions
 	h.Offsets[goobj.BlkNonpkgdef] = w.Offset()
 	for _, s := range ctxt.nonpkgdefs {
 		w.Sym(s)
 	}

 	// Non-pkg symbol references
 	h.Offsets[goobj.BlkNonpkgref] = w.Offset()
 	for _, s := range ctxt.nonpkgrefs {
 		w.Sym(s)
 	}

 	// Referenced package symbol flags
 	h.Offsets[goobj.BlkRefFlags] = w.Offset()
 	w.refFlags()

 	// Hashes
 	h.Offsets[goobj.BlkHash64] = w.Offset()
 	for _, s := range ctxt.hashed64defs {
 		w.Hash64(s)
 	}
 	h.Offsets[goobj.BlkHash] = w.Offset()
 	for _, s := range ctxt.hasheddefs {
 		w.Hash(s)
 	}
 	// TODO: hashedrefs unused/unsupported for now

 	// Reloc indexes
 	h.Offsets[goobj.BlkRelocIdx] = w.Offset()
 	nreloc := uint32(0)
 	lists := [][]*LSym{ctxt.defs, ctxt.hashed64defs, ctxt.hasheddefs, ctxt.nonpkgdefs}
 	for _, list := range lists {
 		for _, s := range list {
 			w.Uint32(nreloc)
 			nreloc += uint32(len(s.R))
 		}
 	}
 	w.Uint32(nreloc)

 	// Symbol Info indexes
 	h.Offsets[goobj.BlkAuxIdx] = w.Offset()
 	naux := uint32(0)
 	for _, list := range lists {
 		for _, s := range list {
 			w.Uint32(naux)
 			naux += uint32(nAuxSym(s))
 		}
 	}
 	w.Uint32(naux)

 	// Data indexes
 	h.Offsets[goobj.BlkDataIdx] = w.Offset()
 	dataOff := int64(0)
 	for _, list := range lists {
 		for _, s := range list {
 			w.Uint32(uint32(dataOff))
 			dataOff += int64(len(s.P))
 			if file := s.File(); file != nil {
 				dataOff += int64(file.Size)
 			}
 		}
 	}
 	if int64(uint32(dataOff)) != dataOff {
 		log.Fatalf("data too large")
 	}
 	w.Uint32(uint32(dataOff))

 	// Relocs
 	h.Offsets[goobj.BlkReloc] = w.Offset()
 	for _, list := range lists {
 		for _, s := range list {
 			for i := range s.R {
 				w.Reloc(&s.R[i])
 			}
 		}
 	}

 	// Aux symbol info
 	h.Offsets[goobj.BlkAux] = w.Offset()
 	for _, list := range lists {
 		for _, s := range list {
 			w.Aux(s)
 		}
 	}

 	// Data
 	h.Offsets[goobj.BlkData] = w.Offset()
 	for _, list := range lists {
 		for _, s := range list {
 			w.Bytes(s.P)
 			if file := s.File(); file != nil {
 				w.writeFile(ctxt, file)
 			}
 		}
 	}

 	// Pcdata
 	h.Offsets[goobj.BlkPcdata] = w.Offset()
 	for _, s := range ctxt.Text { // iteration order must match genFuncInfoSyms
 		// Because of the phase order, it's possible that we try to write an invalid
 		// object file, and the Pcln variables haven't been filled in. As such, we
 		// need to check that Pcsp exists, and assume the other pcln variables exist
 		// as well. Tests like test/fixedbugs/issue22200.go demonstrate this issue.
 		if fn := s.Func(); fn != nil && fn.Pcln.Pcsp != nil {
 			pc := &fn.Pcln
 			w.Bytes(pc.Pcsp.P)
 			w.Bytes(pc.Pcfile.P)
 			w.Bytes(pc.Pcline.P)
 			w.Bytes(pc.Pcinline.P)
 			for i := range pc.Pcdata {
 				w.Bytes(pc.Pcdata[i].P)
 			}
 		}
 	}

 	// Blocks used only by tools (objdump, nm).

 	// Referenced symbol names from other packages
 	h.Offsets[goobj.BlkRefName] = w.Offset()
 	w.refNames()

 	h.Offsets[goobj.BlkEnd] = w.Offset()

 	// Fix up block offsets in the header
 	end := start + int64(w.Offset())
 	b.MustSeek(start, 0)
 	h.Write(w.Writer)
 	b.MustSeek(end, 0)
 }

 type writer struct {
 	*goobj.Writer
 	filebuf []byte
 	ctxt    *Link
 	pkgpath string   // the package import path (escaped), "" if unknown
 	pkglist []string // list of packages referenced, indexed by ctxt.pkgIdx
 }

 // prepare package index list
 func (w *writer) init() {
 	w.pkglist = make([]string, len(w.ctxt.pkgIdx)+1)
 	w.pkglist[0] = "" // dummy invalid package for index 0
 	for pkg, i := range w.ctxt.pkgIdx {
 		w.pkglist[i] = pkg
 	}
 }

 func (w *writer) writeFile(ctxt *Link, file *FileInfo) {
 	f, err := os.Open(file.Name)
 	if err != nil {
 		ctxt.Diag("%v", err)
 		return
 	}
 	defer f.Close()
 	if w.filebuf == nil {
 		w.filebuf = make([]byte, 1024)
 	}
 	buf := w.filebuf
 	written := int64(0)
 	for {
 		n, err := f.Read(buf)
 		w.Bytes(buf[:n])
 		written += int64(n)
 		if err == io.EOF {
 			break
 		}
 		if err != nil {
 			ctxt.Diag("%v", err)
 			return
 		}
 	}
 	if written != file.Size {
 		ctxt.Diag("copy %s: unexpected length %d != %d", file.Name, written, file.Size)
 	}
 }

 func (w *writer) StringTable() {
 	w.AddString("")
 	for _, p := range w.ctxt.Imports {
 		w.AddString(p.Pkg)
 	}
 	for _, pkg := range w.pkglist {
 		w.AddString(pkg)
 	}
 	w.ctxt.traverseSyms(traverseAll, func(s *LSym) {
 		// TODO: this includes references of indexed symbols from other packages,
 		// for which the linker doesn't need the name. Consider moving them to
 		// a separate block (for tools only).
 		if w.pkgpath != "" {
 			s.Name = strings.Replace(s.Name, "\"\".", w.pkgpath+".", -1)
 		}
 		// Don't put names of builtins into the string table (to save
 		// space).
 		if s.PkgIdx == goobj.PkgIdxBuiltin {
 			return
 		}
 		w.AddString(s.Name)
 	})

 	// All filenames are in the postable.
 	for _, f := range w.ctxt.PosTable.FileTable() {
 		w.AddString(filepath.ToSlash(f))
 	}
 }

 // cutoff is the maximum data section size permitted by the linker
 // (see issue #9862).
 const cutoff = int64(2e9) // 2 GB (or so; looks better in errors than 2^31)

 func (w *writer) Sym(s *LSym) {
 	abi := uint16(s.ABI())
 	if s.Static() {
 		abi = goobj.SymABIstatic
 	}
 	flag := uint8(0)
 	if s.DuplicateOK() {
 		flag |= goobj.SymFlagDupok
 	}
 	if s.Local() {
 		flag |= goobj.SymFlagLocal
 	}
 	if s.MakeTypelink() {
 		flag |= goobj.SymFlagTypelink
 	}
 	if s.Leaf() {
 		flag |= goobj.SymFlagLeaf
 	}
 	if s.NoSplit() {
 		flag |= goobj.SymFlagNoSplit
 	}
 	if s.ReflectMethod() {
 		flag |= goobj.SymFlagReflectMethod
 	}
 	if strings.HasPrefix(s.Name, "type.") && s.Name[5] != '.' && s.Type == objabi.SRODATA {
 		flag |= goobj.SymFlagGoType
 	}
 	flag2 := uint8(0)
 	if s.UsedInIface() {
 		flag2 |= goobj.SymFlagUsedInIface
 	}
 	if strings.HasPrefix(s.Name, "go.itab.") && s.Type == objabi.SRODATA {
 		flag2 |= goobj.SymFlagItab
 	}
 	name := s.Name
 	if strings.HasPrefix(name, "gofile..") {
 		name = filepath.ToSlash(name)
 	}
 	var align uint32
 	if fn := s.Func(); fn != nil {
 		align = uint32(fn.Align)
 	}
 	if s.ContentAddressable() {
 		// We generally assume data symbols are natually aligned,
 		// except for strings. If we dedup a string symbol and a
 		// non-string symbol with the same content, we should keep
 		// the largest alignment.
 		// TODO: maybe the compiler could set the alignment for all
 		// data symbols more carefully.
 		if s.Size != 0 && !strings.HasPrefix(s.Name, "go.string.") {
 			switch {
 			case w.ctxt.Arch.PtrSize == 8 && s.Size%8 == 0:
 				align = 8
 			case s.Size%4 == 0:
 				align = 4
 			case s.Size%2 == 0:
 				align = 2
 			}
 			// don't bother setting align to 1.
 		}
 	}
 	if s.Size > cutoff {
 		w.ctxt.Diag("%s: symbol too large (%d bytes > %d bytes)", s.Name, s.Size, cutoff)
 	}
 	var o goobj.Sym
 	o.SetName(name, w.Writer)
 	o.SetABI(abi)
 	o.SetType(uint8(s.Type))
 	o.SetFlag(flag)
 	o.SetFlag2(flag2)
 	o.SetSiz(uint32(s.Size))
 	o.SetAlign(align)
 	o.Write(w.Writer)
 }

 func (w *writer) Hash64(s *LSym) {
 	if !s.ContentAddressable() || len(s.R) != 0 {
 		panic("Hash of non-content-addresable symbol")
 	}
 	b := contentHash64(s)
 	w.Bytes(b[:])
 }

 func (w *writer) Hash(s *LSym) {
 	if !s.ContentAddressable() {
 		panic("Hash of non-content-addresable symbol")
 	}
 	b := w.contentHash(s)
 	w.Bytes(b[:])
 }

 func contentHash64(s *LSym) goobj.Hash64Type {
 	var b goobj.Hash64Type
 	copy(b[:], s.P)
 	return b
 }

 // Compute the content hash for a content-addressable symbol.
 // We build a content hash based on its content and relocations.
 // Depending on the category of the referenced symbol, we choose
 // different hash algorithms such that the hash is globally
 // consistent.
 // - For referenced content-addressable symbol, its content hash
 //   is globally consistent.
 // - For package symbol and builtin symbol, its local index is
 //   globally consistent.
 // - For non-package symbol, its fully-expanded name is globally
 //   consistent. For now, we require we know the current package
 //   path so we can always expand symbol names. (Otherwise,
 //   symbols with relocations are not considered hashable.)
 //
 // For now, we assume there is no circular dependencies among
 // hashed symbols.
 func (w *writer) contentHash(s *LSym) goobj.HashType {
 	h := sha1.New()
 	var tmp [14]byte

 	// Include the size of the symbol in the hash.
 	// This preserves the length of symbols, preventing the following two symbols
 	// from hashing the same:
 	//
 	//    [2]int{1,2} ≠ [10]int{1,2,0,0,0...}
 	//
 	// In this case, if the smaller symbol is alive, the larger is not kept unless
 	// needed.
 	binary.LittleEndian.PutUint64(tmp[:8], uint64(s.Size))
 	h.Write(tmp[:8])

 	// Don't dedup type symbols with others, as they are in a different
 	// section.
 	if strings.HasPrefix(s.Name, "type.") {
 		h.Write([]byte{'T'})
 	} else {
 		h.Write([]byte{0})
 	}
 	// The compiler trims trailing zeros _sometimes_. We just do
 	// it always.
 	h.Write(bytes.TrimRight(s.P, "\x00"))
 	for i := range s.R {
 		r := &s.R[i]
 		binary.LittleEndian.PutUint32(tmp[:4], uint32(r.Off))
 		tmp[4] = r.Siz
 		tmp[5] = uint8(r.Type)
 		binary.LittleEndian.PutUint64(tmp[6:14], uint64(r.Add))
 		h.Write(tmp[:])
 		rs := r.Sym
 		switch rs.PkgIdx {
 		case goobj.PkgIdxHashed64:
 			h.Write([]byte{0})
 			t := contentHash64(rs)
 			h.Write(t[:])
 		case goobj.PkgIdxHashed:
 			h.Write([]byte{1})
 			t := w.contentHash(rs)
 			h.Write(t[:])
 		case goobj.PkgIdxNone:
 			h.Write([]byte{2})
 			io.WriteString(h, rs.Name) // name is already expanded at this point
 		case goobj.PkgIdxBuiltin:
 			h.Write([]byte{3})
 			binary.LittleEndian.PutUint32(tmp[:4], uint32(rs.SymIdx))
 			h.Write(tmp[:4])
 		case goobj.PkgIdxSelf:
 			io.WriteString(h, w.pkgpath)
 			binary.LittleEndian.PutUint32(tmp[:4], uint32(rs.SymIdx))
 			h.Write(tmp[:4])
 		default:
 			io.WriteString(h, rs.Pkg)
 			binary.LittleEndian.PutUint32(tmp[:4], uint32(rs.SymIdx))
 			h.Write(tmp[:4])
 		}
 	}
 	var b goobj.HashType
 	copy(b[:], h.Sum(nil))
 	return b
 }

 func makeSymRef(s *LSym) goobj.SymRef {
 	if s == nil {
 		return goobj.SymRef{}
 	}
 	if s.PkgIdx == 0 || !s.Indexed() {
 		fmt.Printf("unindexed symbol reference: %v\n", s)
 		panic("unindexed symbol reference")
 	}
 	return goobj.SymRef{PkgIdx: uint32(s.PkgIdx), SymIdx: uint32(s.SymIdx)}
 }

 func (w *writer) Reloc(r *Reloc) {
 	var o goobj.Reloc
 	o.SetOff(r.Off)
 	o.SetSiz(r.Siz)
 	o.SetType(uint8(r.Type))
 	o.SetAdd(r.Add)
 	o.SetSym(makeSymRef(r.Sym))
 	o.Write(w.Writer)
 }

 func (w *writer) aux1(typ uint8, rs *LSym) {
 	var o goobj.Aux
 	o.SetType(typ)
 	o.SetSym(makeSymRef(rs))
 	o.Write(w.Writer)
 }

 func (w *writer) Aux(s *LSym) {
 	if s.Gotype != nil {
 		w.aux1(goobj.AuxGotype, s.Gotype)
 	}
 	if fn := s.Func(); fn != nil {
 		w.aux1(goobj.AuxFuncInfo, fn.FuncInfoSym)

 		for _, d := range fn.Pcln.Funcdata {
 			w.aux1(goobj.AuxFuncdata, d)
 		}

 		if fn.dwarfInfoSym != nil && fn.dwarfInfoSym.Size != 0 {
 			w.aux1(goobj.AuxDwarfInfo, fn.dwarfInfoSym)
 		}
 		if fn.dwarfLocSym != nil && fn.dwarfLocSym.Size != 0 {
 			w.aux1(goobj.AuxDwarfLoc, fn.dwarfLocSym)
 		}
 		if fn.dwarfRangesSym != nil && fn.dwarfRangesSym.Size != 0 {
 			w.aux1(goobj.AuxDwarfRanges, fn.dwarfRangesSym)
 		}
 		if fn.dwarfDebugLinesSym != nil && fn.dwarfDebugLinesSym.Size != 0 {
 			w.aux1(goobj.AuxDwarfLines, fn.dwarfDebugLinesSym)
 		}
 		if fn.Pcln.Pcsp != nil && fn.Pcln.Pcsp.Size != 0 {
 			w.aux1(goobj.AuxPcsp, fn.Pcln.Pcsp)
 		}
 		if fn.Pcln.Pcfile != nil && fn.Pcln.Pcfile.Size != 0 {
 			w.aux1(goobj.AuxPcfile, fn.Pcln.Pcfile)
 		}
 		if fn.Pcln.Pcline != nil && fn.Pcln.Pcline.Size != 0 {
 			w.aux1(goobj.AuxPcline, fn.Pcln.Pcline)
 		}
 		if fn.Pcln.Pcinline != nil && fn.Pcln.Pcinline.Size != 0 {
 			w.aux1(goobj.AuxPcinline, fn.Pcln.Pcinline)
 		}
 		for _, pcSym := range fn.Pcln.Pcdata {
 			w.aux1(goobj.AuxPcdata, pcSym)
 		}

 	}
 }

 // Emits flags of referenced indexed symbols.
 func (w *writer) refFlags() {
 	seen := make(map[*LSym]bool)
 	w.ctxt.traverseSyms(traverseRefs, func(rs *LSym) { // only traverse refs, not auxs, as tools don't need auxs
 		switch rs.PkgIdx {
 		case goobj.PkgIdxNone, goobj.PkgIdxHashed64, goobj.PkgIdxHashed, goobj.PkgIdxBuiltin, goobj.PkgIdxSelf: // not an external indexed reference
 			return
 		case goobj.PkgIdxInvalid:
 			panic("unindexed symbol reference")
 		}
 		if seen[rs] {
 			return
 		}
 		seen[rs] = true
 		symref := makeSymRef(rs)
 		flag2 := uint8(0)
 		if rs.UsedInIface() {
 			flag2 |= goobj.SymFlagUsedInIface
 		}
 		if flag2 == 0 {
 			return // no need to write zero flags
 		}
 		var o goobj.RefFlags
 		o.SetSym(symref)
 		o.SetFlag2(flag2)
 		o.Write(w.Writer)
 	})
 }

 // Emits names of referenced indexed symbols, used by tools (objdump, nm)
 // only.
 func (w *writer) refNames() {
 	seen := make(map[*LSym]bool)
 	w.ctxt.traverseSyms(traverseRefs, func(rs *LSym) { // only traverse refs, not auxs, as tools don't need auxs
 		switch rs.PkgIdx {
 		case goobj.PkgIdxNone, goobj.PkgIdxHashed64, goobj.PkgIdxHashed, goobj.PkgIdxBuiltin, goobj.PkgIdxSelf: // not an external indexed reference
 			return
 		case goobj.PkgIdxInvalid:
 			panic("unindexed symbol reference")
 		}
 		if seen[rs] {
 			return
 		}
 		seen[rs] = true
 		symref := makeSymRef(rs)
 		var o goobj.RefName
 		o.SetSym(symref)
 		o.SetName(rs.Name, w.Writer)
 		o.Write(w.Writer)
 	})
 	// TODO: output in sorted order?
 	// Currently tools (cmd/internal/goobj package) doesn't use mmap,
 	// and it just read it into a map in memory upfront. If it uses
 	// mmap, if the output is sorted, it probably could avoid reading
 	// into memory and just do lookups in the mmap'd object file.
 }

 // return the number of aux symbols s have.
 func nAuxSym(s *LSym) int {
 	n := 0
 	if s.Gotype != nil {
 		n++
 	}
 	if fn := s.Func(); fn != nil {
 		// FuncInfo is an aux symbol, each Funcdata is an aux symbol
 		n += 1 + len(fn.Pcln.Funcdata)
 		if fn.dwarfInfoSym != nil && fn.dwarfInfoSym.Size != 0 {
 			n++
 		}
 		if fn.dwarfLocSym != nil && fn.dwarfLocSym.Size != 0 {
 			n++
 		}
 		if fn.dwarfRangesSym != nil && fn.dwarfRangesSym.Size != 0 {
 			n++
 		}
 		if fn.dwarfDebugLinesSym != nil && fn.dwarfDebugLinesSym.Size != 0 {
 			n++
 		}
 		if fn.Pcln.Pcsp != nil && fn.Pcln.Pcsp.Size != 0 {
 			n++
 		}
 		if fn.Pcln.Pcfile != nil && fn.Pcln.Pcfile.Size != 0 {
 			n++
 		}
 		if fn.Pcln.Pcline != nil && fn.Pcln.Pcline.Size != 0 {
 			n++
 		}
 		if fn.Pcln.Pcinline != nil && fn.Pcln.Pcinline.Size != 0 {
 			n++
 		}
 		n += len(fn.Pcln.Pcdata)
 	}
 	return n
 }

 // generate symbols for FuncInfo.
 func genFuncInfoSyms(ctxt *Link) {
 	infosyms := make([]*LSym, 0, len(ctxt.Text))
 	hashedsyms := make([]*LSym, 0, 4*len(ctxt.Text))
 	preparePcSym := func(s *LSym) *LSym {
 		if s == nil {
 			return s
 		}
 		s.PkgIdx = goobj.PkgIdxHashed
 		s.SymIdx = int32(len(hashedsyms) + len(ctxt.hasheddefs))
 		s.Set(AttrIndexed, true)
 		hashedsyms = append(hashedsyms, s)
 		return s
 	}
 	var b bytes.Buffer
 	symidx := int32(len(ctxt.defs))
 	for _, s := range ctxt.Text {
 		fn := s.Func()
 		if fn == nil {
 			continue
 		}
 		o := goobj.FuncInfo{
 			Args:     uint32(fn.Args),
 			Locals:   uint32(fn.Locals),
 			FuncID:   fn.FuncID,
 			FuncFlag: fn.FuncFlag,
 		}
 		pc := &fn.Pcln
 		o.Pcsp = makeSymRef(preparePcSym(pc.Pcsp))
 		o.Pcfile = makeSymRef(preparePcSym(pc.Pcfile))
 		o.Pcline = makeSymRef(preparePcSym(pc.Pcline))
 		o.Pcinline = makeSymRef(preparePcSym(pc.Pcinline))
 		o.Pcdata = make([]goobj.SymRef, len(pc.Pcdata))
 		for i, pcSym := range pc.Pcdata {
 			o.Pcdata[i] = makeSymRef(preparePcSym(pcSym))
 		}
 		o.Funcdataoff = make([]uint32, len(pc.Funcdataoff))
 		for i, x := range pc.Funcdataoff {
 			o.Funcdataoff[i] = uint32(x)
 		}
 		i := 0
 		o.File = make([]goobj.CUFileIndex, len(pc.UsedFiles))
 		for f := range pc.UsedFiles {
 			o.File[i] = f
 			i++
 		}
 		sort.Slice(o.File, func(i, j int) bool { return o.File[i] < o.File[j] })
 		o.InlTree = make([]goobj.InlTreeNode, len(pc.InlTree.nodes))
 		for i, inl := range pc.InlTree.nodes {
 			f, l := getFileIndexAndLine(ctxt, inl.Pos)
 			o.InlTree[i] = goobj.InlTreeNode{
 				Parent:   int32(inl.Parent),
 				File:     goobj.CUFileIndex(f),
 				Line:     l,
 				Func:     makeSymRef(inl.Func),
 				ParentPC: inl.ParentPC,
 			}
 		}

 		o.Write(&b)
 		isym := &LSym{
 			Type:   objabi.SDATA, // for now, I don't think it matters
 			PkgIdx: goobj.PkgIdxSelf,
 			SymIdx: symidx,
 			P:      append([]byte(nil), b.Bytes()...),
 		}
 		isym.Set(AttrIndexed, true)
 		symidx++
 		infosyms = append(infosyms, isym)
 		fn.FuncInfoSym = isym
 		b.Reset()

 		dwsyms := []*LSym{fn.dwarfRangesSym, fn.dwarfLocSym, fn.dwarfDebugLinesSym, fn.dwarfInfoSym}
 		for _, s := range dwsyms {
 			if s == nil || s.Size == 0 {
 				continue
 			}
 			s.PkgIdx = goobj.PkgIdxSelf
 			s.SymIdx = symidx
 			s.Set(AttrIndexed, true)
 			symidx++
 			infosyms = append(infosyms, s)
 		}
 	}
 	ctxt.defs = append(ctxt.defs, infosyms...)
 	ctxt.hasheddefs = append(ctxt.hasheddefs, hashedsyms...)
 }

 func writeAuxSymDebug(ctxt *Link, par *LSym, aux *LSym) {
 	// Most aux symbols (ex: funcdata) are not interesting--
 	// pick out just the DWARF ones for now.
 	if aux.Type != objabi.SDWARFLOC &&
 		aux.Type != objabi.SDWARFFCN &&
 		aux.Type != objabi.SDWARFABSFCN &&
 		aux.Type != objabi.SDWARFLINES &&
 		aux.Type != objabi.SDWARFRANGE {
 		return
 	}
 	ctxt.writeSymDebugNamed(aux, "aux for "+par.Name)
 }

 func debugAsmEmit(ctxt *Link) {
 	if ctxt.Debugasm > 0 {
 		ctxt.traverseSyms(traverseDefs, ctxt.writeSymDebug)
 		if ctxt.Debugasm > 1 {
 			fn := func(par *LSym, aux *LSym) {
 				writeAuxSymDebug(ctxt, par, aux)
 			}
 			ctxt.traverseAuxSyms(traverseAux, fn)
 		}
 	}
 }

 func (ctxt *Link) writeSymDebug(s *LSym) {
 	ctxt.writeSymDebugNamed(s, s.Name)
 }

 func (ctxt *Link) writeSymDebugNamed(s *LSym, name string) {
 	ver := ""
 	if ctxt.Debugasm > 1 {
 		ver = fmt.Sprintf("<%d>", s.ABI())
 	}
 	fmt.Fprintf(ctxt.Bso, "%s%s ", name, ver)
 	if s.Type != 0 {
 		fmt.Fprintf(ctxt.Bso, "%v ", s.Type)
 	}
 	if s.Static() {
 		fmt.Fprint(ctxt.Bso, "static ")
 	}
 	if s.DuplicateOK() {
 		fmt.Fprintf(ctxt.Bso, "dupok ")
 	}
 	if s.CFunc() {
 		fmt.Fprintf(ctxt.Bso, "cfunc ")
 	}
 	if s.NoSplit() {
 		fmt.Fprintf(ctxt.Bso, "nosplit ")
 	}
 	if s.Func() != nil && s.Func().FuncFlag&objabi.FuncFlag_TOPFRAME != 0 {
 		fmt.Fprintf(ctxt.Bso, "topframe ")
 	}
 	fmt.Fprintf(ctxt.Bso, "size=%d", s.Size)
 	if s.Type == objabi.STEXT {
 		fn := s.Func()
 		fmt.Fprintf(ctxt.Bso, " args=%#x locals=%#x funcid=%#x", uint64(fn.Args), uint64(fn.Locals), uint64(fn.FuncID))
 		if s.Leaf() {
 			fmt.Fprintf(ctxt.Bso, " leaf")
 		}
 	}
 	fmt.Fprintf(ctxt.Bso, "\n")
 	if s.Type == objabi.STEXT {
 		for p := s.Func().Text; p != nil; p = p.Link {
 			fmt.Fprintf(ctxt.Bso, "\t%#04x ", uint(int(p.Pc)))
 			if ctxt.Debugasm > 1 {
 				io.WriteString(ctxt.Bso, p.String())
 			} else {
 				p.InnermostString(ctxt.Bso)
 			}
 			fmt.Fprintln(ctxt.Bso)
 		}
 	}
 	for i := 0; i < len(s.P); i += 16 {
 		fmt.Fprintf(ctxt.Bso, "\t%#04x", uint(i))
 		j := i
 		for ; j < i+16 && j < len(s.P); j++ {
 			fmt.Fprintf(ctxt.Bso, " %02x", s.P[j])
 		}
 		for ; j < i+16; j++ {
 			fmt.Fprintf(ctxt.Bso, "   ")
 		}
 		fmt.Fprintf(ctxt.Bso, "  ")
 		for j = i; j < i+16 && j < len(s.P); j++ {
 			c := int(s.P[j])
 			b := byte('.')
 			if ' ' <= c && c <= 0x7e {
 				b = byte(c)
 			}
 			ctxt.Bso.WriteByte(b)
 		}

 		fmt.Fprintf(ctxt.Bso, "\n")
 	}

 	sort.Sort(relocByOff(s.R)) // generate stable output
 	for _, r := range s.R {
 		name := ""
 		ver := ""
 		if r.Sym != nil {
 			name = r.Sym.Name
 			if ctxt.Debugasm > 1 {
 				ver = fmt.Sprintf("<%d>", r.Sym.ABI())
 			}
 		} else if r.Type == objabi.R_TLS_LE {
 			name = "TLS"
 		}
 		if ctxt.Arch.InFamily(sys.ARM, sys.PPC64) {
 			fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s%s+%x\n", int(r.Off), r.Siz, r.Type, name, ver, uint64(r.Add))
 		} else {
 			fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s%s+%d\n", int(r.Off), r.Siz, r.Type, name, ver, r.Add)
 		}
 	}
 }

 // relocByOff sorts relocations by their offsets.
 type relocByOff []Reloc

 func (x relocByOff) Len() int           { return len(x) }
 func (x relocByOff) Less(i, j int) bool { return x[i].Off < x[j].Off }
 func (x relocByOff) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
	// Copyright 2013 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.

	// Writing Go object files.

	package obj

	import (
	"bytes"
	"cmd/internal/bio"
	"cmd/internal/goobj"
	"cmd/internal/objabi"
	"cmd/internal/sys"
	"crypto/sha1"
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strings"
	)

	// Entry point of writing new object file.
	func WriteObjFile(ctxt Link, b bio.Writer) {

	debugAsmEmit(ctxt)

	genFuncInfoSyms(ctxt)

	w := writer{
	Writer: goobj.NewWriter(b),
	ctxt: ctxt,
	pkgpath: objabi.PathToPrefix(ctxt.Pkgpath),
	}

	start := b.Offset()
	w.init()

	// Header
	// We just reserve the space. We'll fill in the offsets later.
	flags := uint32(0)
	if ctxt.Flag_shared {
	flags \|= goobj.ObjFlagShared
	}
	if w.pkgpath == "" {
	flags \|= goobj.ObjFlagNeedNameExpansion
	}
	if ctxt.IsAsm {
	flags \|= goobj.ObjFlagFromAssembly
	}
	h := goobj.Header{
	Magic: goobj.Magic,
	Fingerprint: ctxt.Fingerprint,
	Flags: flags,
	}
	h.Write(w.Writer)

	// String table
	w.StringTable()

	// Autolib
	h.Offsets[goobj.BlkAutolib] = w.Offset()
	for i := range ctxt.Imports {
	ctxt.Imports[i].Write(w.Writer)
	}

	// Package references
	h.Offsets[goobj.BlkPkgIdx] = w.Offset()
	for _, pkg := range w.pkglist {
	w.StringRef(pkg)
	}

	// File table (for DWARF and pcln generation).
	h.Offsets[goobj.BlkFile] = w.Offset()
	for _, f := range ctxt.PosTable.FileTable() {
	w.StringRef(filepath.ToSlash(f))
	}

	// Symbol definitions
	h.Offsets[goobj.BlkSymdef] = w.Offset()
	for _, s := range ctxt.defs {
	w.Sym(s)
	}

	// Short hashed symbol definitions
	h.Offsets[goobj.BlkHashed64def] = w.Offset()
	for _, s := range ctxt.hashed64defs {
	w.Sym(s)
	}

	// Hashed symbol definitions
	h.Offsets[goobj.BlkHasheddef] = w.Offset()
	for _, s := range ctxt.hasheddefs {
	w.Sym(s)
	}

	// Non-pkg symbol definitions
	h.Offsets[goobj.BlkNonpkgdef] = w.Offset()
	for _, s := range ctxt.nonpkgdefs {
	w.Sym(s)
	}

	// Non-pkg symbol references
	h.Offsets[goobj.BlkNonpkgref] = w.Offset()
	for _, s := range ctxt.nonpkgrefs {
	w.Sym(s)
	}

	// Referenced package symbol flags
	h.Offsets[goobj.BlkRefFlags] = w.Offset()
	w.refFlags()

	// Hashes
	h.Offsets[goobj.BlkHash64] = w.Offset()
	for _, s := range ctxt.hashed64defs {
	w.Hash64(s)
	}
	h.Offsets[goobj.BlkHash] = w.Offset()
	for _, s := range ctxt.hasheddefs {
	w.Hash(s)
	}
	// TODO: hashedrefs unused/unsupported for now

	// Reloc indexes
	h.Offsets[goobj.BlkRelocIdx] = w.Offset()
	nreloc := uint32(0)
	lists := [][]*LSym{ctxt.defs, ctxt.hashed64defs, ctxt.hasheddefs, ctxt.nonpkgdefs}
	for _, list := range lists {
	for _, s := range list {
	w.Uint32(nreloc)
	nreloc += uint32(len(s.R))
	}
	}
	w.Uint32(nreloc)

	// Symbol Info indexes
	h.Offsets[goobj.BlkAuxIdx] = w.Offset()
	naux := uint32(0)
	for _, list := range lists {
	for _, s := range list {
	w.Uint32(naux)
	naux += uint32(nAuxSym(s))
	}
	}
	w.Uint32(naux)

	// Data indexes
	h.Offsets[goobj.BlkDataIdx] = w.Offset()
	dataOff := int64(0)
	for _, list := range lists {
	for _, s := range list {
	w.Uint32(uint32(dataOff))
	dataOff += int64(len(s.P))
	if file := s.File(); file != nil {
	dataOff += int64(file.Size)
	}
	}
	}
	if int64(uint32(dataOff)) != dataOff {
	log.Fatalf("data too large")
	}
	w.Uint32(uint32(dataOff))

	// Relocs
	h.Offsets[goobj.BlkReloc] = w.Offset()
	for _, list := range lists {
	for _, s := range list {
	for i := range s.R {
	w.Reloc(&s.R[i])
	}
	}
	}

	// Aux symbol info
	h.Offsets[goobj.BlkAux] = w.Offset()
	for _, list := range lists {
	for _, s := range list {
	w.Aux(s)
	}
	}

	// Data
	h.Offsets[goobj.BlkData] = w.Offset()
	for _, list := range lists {
	for _, s := range list {
	w.Bytes(s.P)
	if file := s.File(); file != nil {
	w.writeFile(ctxt, file)
	}
	}
	}

	// Pcdata
	h.Offsets[goobj.BlkPcdata] = w.Offset()
	for _, s := range ctxt.Text { // iteration order must match genFuncInfoSyms
	// Because of the phase order, it's possible that we try to write an invalid
	// object file, and the Pcln variables haven't been filled in. As such, we
	// need to check that Pcsp exists, and assume the other pcln variables exist
	// as well. Tests like test/fixedbugs/issue22200.go demonstrate this issue.
	if fn := s.Func(); fn != nil && fn.Pcln.Pcsp != nil {
	pc := &fn.Pcln
	w.Bytes(pc.Pcsp.P)
	w.Bytes(pc.Pcfile.P)
	w.Bytes(pc.Pcline.P)
	w.Bytes(pc.Pcinline.P)
	for i := range pc.Pcdata {
	w.Bytes(pc.Pcdata[i].P)
	}
	}
	}

	// Blocks used only by tools (objdump, nm).

	// Referenced symbol names from other packages
	h.Offsets[goobj.BlkRefName] = w.Offset()
	w.refNames()

	h.Offsets[goobj.BlkEnd] = w.Offset()

	// Fix up block offsets in the header
	end := start + int64(w.Offset())
	b.MustSeek(start, 0)
	h.Write(w.Writer)
	b.MustSeek(end, 0)
	}

	type writer struct {
	*goobj.Writer
	filebuf []byte
	ctxt *Link
	pkgpath string // the package import path (escaped), "" if unknown
	pkglist []string // list of packages referenced, indexed by ctxt.pkgIdx
	}

	// prepare package index list
	func (w *writer) init() {
	w.pkglist = make([]string, len(w.ctxt.pkgIdx)+1)
	w.pkglist[0] = "" // dummy invalid package for index 0
	for pkg, i := range w.ctxt.pkgIdx {
	w.pkglist[i] = pkg
	}
	}

	func (w writer) writeFile(ctxt Link, file *FileInfo) {
	f, err := os.Open(file.Name)
	if err != nil {
	ctxt.Diag("%v", err)
	return
	}
	defer f.Close()
	if w.filebuf == nil {
	w.filebuf = make([]byte, 1024)
	}
	buf := w.filebuf
	written := int64(0)
	for {
	n, err := f.Read(buf)
	w.Bytes(buf[:n])
	written += int64(n)
	if err == io.EOF {
	break
	}
	if err != nil {
	ctxt.Diag("%v", err)
	return
	}
	}
	if written != file.Size {
	ctxt.Diag("copy %s: unexpected length %d != %d", file.Name, written, file.Size)
	}
	}

	func (w *writer) StringTable() {
	w.AddString("")
	for _, p := range w.ctxt.Imports {
	w.AddString(p.Pkg)
	}
	for _, pkg := range w.pkglist {
	w.AddString(pkg)
	}
	w.ctxt.traverseSyms(traverseAll, func(s *LSym) {
	// TODO: this includes references of indexed symbols from other packages,
	// for which the linker doesn't need the name. Consider moving them to
	// a separate block (for tools only).
	if w.pkgpath != "" {
	s.Name = strings.Replace(s.Name, "\"\".", w.pkgpath+".", -1)
	}
	// Don't put names of builtins into the string table (to save
	// space).
	if s.PkgIdx == goobj.PkgIdxBuiltin {
	return
	}
	w.AddString(s.Name)
	})

	// All filenames are in the postable.
	for _, f := range w.ctxt.PosTable.FileTable() {
	w.AddString(filepath.ToSlash(f))
	}
	}

	// cutoff is the maximum data section size permitted by the linker
	// (see issue #9862).
	const cutoff = int64(2e9) // 2 GB (or so; looks better in errors than 2^31)

	func (w writer) Sym(s LSym) {
	abi := uint16(s.ABI())
	if s.Static() {
	abi = goobj.SymABIstatic
	}
	flag := uint8(0)
	if s.DuplicateOK() {
	flag \|= goobj.SymFlagDupok
	}
	if s.Local() {
	flag \|= goobj.SymFlagLocal
	}
	if s.MakeTypelink() {
	flag \|= goobj.SymFlagTypelink
	}
	if s.Leaf() {
	flag \|= goobj.SymFlagLeaf
	}
	if s.NoSplit() {
	flag \|= goobj.SymFlagNoSplit
	}
	if s.ReflectMethod() {
	flag \|= goobj.SymFlagReflectMethod
	}
	if strings.HasPrefix(s.Name, "type.") && s.Name[5] != '.' && s.Type == objabi.SRODATA {
	flag \|= goobj.SymFlagGoType
	}
	flag2 := uint8(0)
	if s.UsedInIface() {
	flag2 \|= goobj.SymFlagUsedInIface
	}
	if strings.HasPrefix(s.Name, "go.itab.") && s.Type == objabi.SRODATA {
	flag2 \|= goobj.SymFlagItab
	}
	name := s.Name
	if strings.HasPrefix(name, "gofile..") {
	name = filepath.ToSlash(name)
	}
	var align uint32
	if fn := s.Func(); fn != nil {
	align = uint32(fn.Align)
	}
	if s.ContentAddressable() {
	// We generally assume data symbols are natually aligned,
	// except for strings. If we dedup a string symbol and a
	// non-string symbol with the same content, we should keep
	// the largest alignment.
	// TODO: maybe the compiler could set the alignment for all
	// data symbols more carefully.
	if s.Size != 0 && !strings.HasPrefix(s.Name, "go.string.") {
	switch {
	case w.ctxt.Arch.PtrSize == 8 && s.Size%8 == 0:
	align = 8
	case s.Size%4 == 0:
	align = 4
	case s.Size%2 == 0:
	align = 2
	}
	// don't bother setting align to 1.
	}
	}
	if s.Size > cutoff {
	w.ctxt.Diag("%s: symbol too large (%d bytes > %d bytes)", s.Name, s.Size, cutoff)
	}
	var o goobj.Sym
	o.SetName(name, w.Writer)
	o.SetABI(abi)
	o.SetType(uint8(s.Type))
	o.SetFlag(flag)
	o.SetFlag2(flag2)
	o.SetSiz(uint32(s.Size))
	o.SetAlign(align)
	o.Write(w.Writer)
	}

	func (w writer) Hash64(s LSym) {
	if !s.ContentAddressable() \|\| len(s.R) != 0 {
	panic("Hash of non-content-addresable symbol")
	}
	b := contentHash64(s)
	w.Bytes(b[:])
	}

	func (w writer) Hash(s LSym) {
	if !s.ContentAddressable() {
	panic("Hash of non-content-addresable symbol")
	}
	b := w.contentHash(s)
	w.Bytes(b[:])
	}

	func contentHash64(s *LSym) goobj.Hash64Type {
	var b goobj.Hash64Type
	copy(b[:], s.P)
	return b
	}

	// Compute the content hash for a content-addressable symbol.
	// We build a content hash based on its content and relocations.
	// Depending on the category of the referenced symbol, we choose
	// different hash algorithms such that the hash is globally
	// consistent.
	// - For referenced content-addressable symbol, its content hash
	// is globally consistent.
	// - For package symbol and builtin symbol, its local index is
	// globally consistent.
	// - For non-package symbol, its fully-expanded name is globally
	// consistent. For now, we require we know the current package
	// path so we can always expand symbol names. (Otherwise,
	// symbols with relocations are not considered hashable.)
	//
	// For now, we assume there is no circular dependencies among
	// hashed symbols.
	func (w writer) contentHash(s LSym) goobj.HashType {
	h := sha1.New()
	var tmp [14]byte

	// Include the size of the symbol in the hash.
	// This preserves the length of symbols, preventing the following two symbols
	// from hashing the same:
	//
	// [2]int{1,2} ≠ [10]int{1,2,0,0,0...}
	//
	// In this case, if the smaller symbol is alive, the larger is not kept unless
	// needed.
	binary.LittleEndian.PutUint64(tmp[:8], uint64(s.Size))
	h.Write(tmp[:8])

	// Don't dedup type symbols with others, as they are in a different
	// section.
	if strings.HasPrefix(s.Name, "type.") {
	h.Write([]byte{'T'})
	} else {
	h.Write([]byte{0})
	}
	// The compiler trims trailing zeros _sometimes_. We just do
	// it always.
	h.Write(bytes.TrimRight(s.P, "\x00"))
	for i := range s.R {
	r := &s.R[i]
	binary.LittleEndian.PutUint32(tmp[:4], uint32(r.Off))
	tmp[4] = r.Siz
	tmp[5] = uint8(r.Type)
	binary.LittleEndian.PutUint64(tmp[6:14], uint64(r.Add))
	h.Write(tmp[:])
	rs := r.Sym
	switch rs.PkgIdx {
	case goobj.PkgIdxHashed64:
	h.Write([]byte{0})
	t := contentHash64(rs)
	h.Write(t[:])
	case goobj.PkgIdxHashed:
	h.Write([]byte{1})
	t := w.contentHash(rs)
	h.Write(t[:])
	case goobj.PkgIdxNone:
	h.Write([]byte{2})
	io.WriteString(h, rs.Name) // name is already expanded at this point
	case goobj.PkgIdxBuiltin:
	h.Write([]byte{3})
	binary.LittleEndian.PutUint32(tmp[:4], uint32(rs.SymIdx))
	h.Write(tmp[:4])
	case goobj.PkgIdxSelf:
	io.WriteString(h, w.pkgpath)
	binary.LittleEndian.PutUint32(tmp[:4], uint32(rs.SymIdx))
	h.Write(tmp[:4])
	default:
	io.WriteString(h, rs.Pkg)
	binary.LittleEndian.PutUint32(tmp[:4], uint32(rs.SymIdx))
	h.Write(tmp[:4])
	}
	}
	var b goobj.HashType
	copy(b[:], h.Sum(nil))
	return b
	}

	func makeSymRef(s *LSym) goobj.SymRef {
	if s == nil {
	return goobj.SymRef{}
	}
	if s.PkgIdx == 0 \|\| !s.Indexed() {
	fmt.Printf("unindexed symbol reference: %v\n", s)
	panic("unindexed symbol reference")
	}
	return goobj.SymRef{PkgIdx: uint32(s.PkgIdx), SymIdx: uint32(s.SymIdx)}
	}

	func (w writer) Reloc(r Reloc) {
	var o goobj.Reloc
	o.SetOff(r.Off)
	o.SetSiz(r.Siz)
	o.SetType(uint8(r.Type))
	o.SetAdd(r.Add)
	o.SetSym(makeSymRef(r.Sym))
	o.Write(w.Writer)
	}

	func (w writer) aux1(typ uint8, rs LSym) {
	var o goobj.Aux
	o.SetType(typ)
	o.SetSym(makeSymRef(rs))
	o.Write(w.Writer)
	}

	func (w writer) Aux(s LSym) {
	if s.Gotype != nil {
	w.aux1(goobj.AuxGotype, s.Gotype)
	}
	if fn := s.Func(); fn != nil {
	w.aux1(goobj.AuxFuncInfo, fn.FuncInfoSym)

	for _, d := range fn.Pcln.Funcdata {
	w.aux1(goobj.AuxFuncdata, d)
	}

	if fn.dwarfInfoSym != nil && fn.dwarfInfoSym.Size != 0 {
	w.aux1(goobj.AuxDwarfInfo, fn.dwarfInfoSym)
	}
	if fn.dwarfLocSym != nil && fn.dwarfLocSym.Size != 0 {
	w.aux1(goobj.AuxDwarfLoc, fn.dwarfLocSym)
	}
	if fn.dwarfRangesSym != nil && fn.dwarfRangesSym.Size != 0 {
	w.aux1(goobj.AuxDwarfRanges, fn.dwarfRangesSym)
	}
	if fn.dwarfDebugLinesSym != nil && fn.dwarfDebugLinesSym.Size != 0 {
	w.aux1(goobj.AuxDwarfLines, fn.dwarfDebugLinesSym)
	}
	if fn.Pcln.Pcsp != nil && fn.Pcln.Pcsp.Size != 0 {
	w.aux1(goobj.AuxPcsp, fn.Pcln.Pcsp)
	}
	if fn.Pcln.Pcfile != nil && fn.Pcln.Pcfile.Size != 0 {
	w.aux1(goobj.AuxPcfile, fn.Pcln.Pcfile)
	}
	if fn.Pcln.Pcline != nil && fn.Pcln.Pcline.Size != 0 {
	w.aux1(goobj.AuxPcline, fn.Pcln.Pcline)
	}
	if fn.Pcln.Pcinline != nil && fn.Pcln.Pcinline.Size != 0 {
	w.aux1(goobj.AuxPcinline, fn.Pcln.Pcinline)
	}
	for _, pcSym := range fn.Pcln.Pcdata {
	w.aux1(goobj.AuxPcdata, pcSym)
	}

	}
	}

	// Emits flags of referenced indexed symbols.
	func (w *writer) refFlags() {
	seen := make(map[*LSym]bool)
	w.ctxt.traverseSyms(traverseRefs, func(rs *LSym) { // only traverse refs, not auxs, as tools don't need auxs
	switch rs.PkgIdx {
	case goobj.PkgIdxNone, goobj.PkgIdxHashed64, goobj.PkgIdxHashed, goobj.PkgIdxBuiltin, goobj.PkgIdxSelf: // not an external indexed reference
	return
	case goobj.PkgIdxInvalid:
	panic("unindexed symbol reference")
	}
	if seen[rs] {
	return
	}
	seen[rs] = true
	symref := makeSymRef(rs)
	flag2 := uint8(0)
	if rs.UsedInIface() {
	flag2 \|= goobj.SymFlagUsedInIface
	}
	if flag2 == 0 {
	return // no need to write zero flags
	}
	var o goobj.RefFlags
	o.SetSym(symref)
	o.SetFlag2(flag2)
	o.Write(w.Writer)
	})
	}

	// Emits names of referenced indexed symbols, used by tools (objdump, nm)
	// only.
	func (w *writer) refNames() {
	seen := make(map[*LSym]bool)
	w.ctxt.traverseSyms(traverseRefs, func(rs *LSym) { // only traverse refs, not auxs, as tools don't need auxs
	switch rs.PkgIdx {
	case goobj.PkgIdxNone, goobj.PkgIdxHashed64, goobj.PkgIdxHashed, goobj.PkgIdxBuiltin, goobj.PkgIdxSelf: // not an external indexed reference
	return
	case goobj.PkgIdxInvalid:
	panic("unindexed symbol reference")
	}
	if seen[rs] {
	return
	}
	seen[rs] = true
	symref := makeSymRef(rs)
	var o goobj.RefName
	o.SetSym(symref)
	o.SetName(rs.Name, w.Writer)
	o.Write(w.Writer)
	})
	// TODO: output in sorted order?
	// Currently tools (cmd/internal/goobj package) doesn't use mmap,
	// and it just read it into a map in memory upfront. If it uses
	// mmap, if the output is sorted, it probably could avoid reading
	// into memory and just do lookups in the mmap'd object file.
	}

	// return the number of aux symbols s have.
	func nAuxSym(s *LSym) int {
	n := 0
	if s.Gotype != nil {
	n++
	}
	if fn := s.Func(); fn != nil {
	// FuncInfo is an aux symbol, each Funcdata is an aux symbol
	n += 1 + len(fn.Pcln.Funcdata)
	if fn.dwarfInfoSym != nil && fn.dwarfInfoSym.Size != 0 {
	n++
	}
	if fn.dwarfLocSym != nil && fn.dwarfLocSym.Size != 0 {
	n++
	}
	if fn.dwarfRangesSym != nil && fn.dwarfRangesSym.Size != 0 {
	n++
	}
	if fn.dwarfDebugLinesSym != nil && fn.dwarfDebugLinesSym.Size != 0 {
	n++
	}
	if fn.Pcln.Pcsp != nil && fn.Pcln.Pcsp.Size != 0 {
	n++
	}
	if fn.Pcln.Pcfile != nil && fn.Pcln.Pcfile.Size != 0 {
	n++
	}
	if fn.Pcln.Pcline != nil && fn.Pcln.Pcline.Size != 0 {
	n++
	}
	if fn.Pcln.Pcinline != nil && fn.Pcln.Pcinline.Size != 0 {
	n++
	}
	n += len(fn.Pcln.Pcdata)
	}
	return n
	}

	// generate symbols for FuncInfo.
	func genFuncInfoSyms(ctxt *Link) {
	infosyms := make([]*LSym, 0, len(ctxt.Text))
	hashedsyms := make([]LSym, 0, 4len(ctxt.Text))
	preparePcSym := func(s LSym) LSym {
	if s == nil {
	return s
	}
	s.PkgIdx = goobj.PkgIdxHashed
	s.SymIdx = int32(len(hashedsyms) + len(ctxt.hasheddefs))
	s.Set(AttrIndexed, true)
	hashedsyms = append(hashedsyms, s)
	return s
	}
	var b bytes.Buffer
	symidx := int32(len(ctxt.defs))
	for _, s := range ctxt.Text {
	fn := s.Func()
	if fn == nil {
	continue
	}
	o := goobj.FuncInfo{
	Args: uint32(fn.Args),
	Locals: uint32(fn.Locals),
	FuncID: fn.FuncID,
	FuncFlag: fn.FuncFlag,
	}
	pc := &fn.Pcln
	o.Pcsp = makeSymRef(preparePcSym(pc.Pcsp))
	o.Pcfile = makeSymRef(preparePcSym(pc.Pcfile))
	o.Pcline = makeSymRef(preparePcSym(pc.Pcline))
	o.Pcinline = makeSymRef(preparePcSym(pc.Pcinline))
	o.Pcdata = make([]goobj.SymRef, len(pc.Pcdata))
	for i, pcSym := range pc.Pcdata {
	o.Pcdata[i] = makeSymRef(preparePcSym(pcSym))
	}
	o.Funcdataoff = make([]uint32, len(pc.Funcdataoff))
	for i, x := range pc.Funcdataoff {
	o.Funcdataoff[i] = uint32(x)
	}
	i := 0
	o.File = make([]goobj.CUFileIndex, len(pc.UsedFiles))
	for f := range pc.UsedFiles {
	o.File[i] = f
	i++
	}
	sort.Slice(o.File, func(i, j int) bool { return o.File[i] < o.File[j] })
	o.InlTree = make([]goobj.InlTreeNode, len(pc.InlTree.nodes))
	for i, inl := range pc.InlTree.nodes {
	f, l := getFileIndexAndLine(ctxt, inl.Pos)
	o.InlTree[i] = goobj.InlTreeNode{
	Parent: int32(inl.Parent),
	File: goobj.CUFileIndex(f),
	Line: l,
	Func: makeSymRef(inl.Func),
	ParentPC: inl.ParentPC,
	}
	}

	o.Write(&b)
	isym := &LSym{
	Type: objabi.SDATA, // for now, I don't think it matters
	PkgIdx: goobj.PkgIdxSelf,
	SymIdx: symidx,
	P: append([]byte(nil), b.Bytes()...),
	}
	isym.Set(AttrIndexed, true)
	symidx++
	infosyms = append(infosyms, isym)
	fn.FuncInfoSym = isym
	b.Reset()

	dwsyms := []*LSym{fn.dwarfRangesSym, fn.dwarfLocSym, fn.dwarfDebugLinesSym, fn.dwarfInfoSym}
	for _, s := range dwsyms {
	if s == nil \|\| s.Size == 0 {
	continue
	}
	s.PkgIdx = goobj.PkgIdxSelf
	s.SymIdx = symidx
	s.Set(AttrIndexed, true)
	symidx++
	infosyms = append(infosyms, s)
	}
	}
	ctxt.defs = append(ctxt.defs, infosyms...)
	ctxt.hasheddefs = append(ctxt.hasheddefs, hashedsyms...)
	}

	func writeAuxSymDebug(ctxt Link, par LSym, aux *LSym) {
	// Most aux symbols (ex: funcdata) are not interesting--
	// pick out just the DWARF ones for now.
	if aux.Type != objabi.SDWARFLOC &&
	aux.Type != objabi.SDWARFFCN &&
	aux.Type != objabi.SDWARFABSFCN &&
	aux.Type != objabi.SDWARFLINES &&
	aux.Type != objabi.SDWARFRANGE {
	return
	}
	ctxt.writeSymDebugNamed(aux, "aux for "+par.Name)
	}

	func debugAsmEmit(ctxt *Link) {
	if ctxt.Debugasm > 0 {
	ctxt.traverseSyms(traverseDefs, ctxt.writeSymDebug)
	if ctxt.Debugasm > 1 {
	fn := func(par LSym, aux LSym) {
	writeAuxSymDebug(ctxt, par, aux)
	}
	ctxt.traverseAuxSyms(traverseAux, fn)
	}
	}
	}

	func (ctxt Link) writeSymDebug(s LSym) {
	ctxt.writeSymDebugNamed(s, s.Name)
	}

	func (ctxt Link) writeSymDebugNamed(s LSym, name string) {
	ver := ""
	if ctxt.Debugasm > 1 {
	ver = fmt.Sprintf("<%d>", s.ABI())
	}
	fmt.Fprintf(ctxt.Bso, "%s%s ", name, ver)
	if s.Type != 0 {
	fmt.Fprintf(ctxt.Bso, "%v ", s.Type)
	}
	if s.Static() {
	fmt.Fprint(ctxt.Bso, "static ")
	}
	if s.DuplicateOK() {
	fmt.Fprintf(ctxt.Bso, "dupok ")
	}
	if s.CFunc() {
	fmt.Fprintf(ctxt.Bso, "cfunc ")
	}
	if s.NoSplit() {
	fmt.Fprintf(ctxt.Bso, "nosplit ")
	}
	if s.Func() != nil && s.Func().FuncFlag&objabi.FuncFlag_TOPFRAME != 0 {
	fmt.Fprintf(ctxt.Bso, "topframe ")
	}
	fmt.Fprintf(ctxt.Bso, "size=%d", s.Size)
	if s.Type == objabi.STEXT {
	fn := s.Func()
	fmt.Fprintf(ctxt.Bso, " args=%#x locals=%#x funcid=%#x", uint64(fn.Args), uint64(fn.Locals), uint64(fn.FuncID))
	if s.Leaf() {
	fmt.Fprintf(ctxt.Bso, " leaf")
	}
	}
	fmt.Fprintf(ctxt.Bso, "\n")
	if s.Type == objabi.STEXT {
	for p := s.Func().Text; p != nil; p = p.Link {
	fmt.Fprintf(ctxt.Bso, "\t%#04x ", uint(int(p.Pc)))
	if ctxt.Debugasm > 1 {
	io.WriteString(ctxt.Bso, p.String())
	} else {
	p.InnermostString(ctxt.Bso)
	}
	fmt.Fprintln(ctxt.Bso)
	}
	}
	for i := 0; i < len(s.P); i += 16 {
	fmt.Fprintf(ctxt.Bso, "\t%#04x", uint(i))
	j := i
	for ; j < i+16 && j < len(s.P); j++ {
	fmt.Fprintf(ctxt.Bso, " %02x", s.P[j])
	}
	for ; j < i+16; j++ {
	fmt.Fprintf(ctxt.Bso, " ")
	}
	fmt.Fprintf(ctxt.Bso, " ")
	for j = i; j < i+16 && j < len(s.P); j++ {
	c := int(s.P[j])
	b := byte('.')
	if ' ' <= c && c <= 0x7e {
	b = byte(c)
	}
	ctxt.Bso.WriteByte(b)
	}

	fmt.Fprintf(ctxt.Bso, "\n")
	}

	sort.Sort(relocByOff(s.R)) // generate stable output
	for _, r := range s.R {
	name := ""
	ver := ""
	if r.Sym != nil {
	name = r.Sym.Name
	if ctxt.Debugasm > 1 {
	ver = fmt.Sprintf("<%d>", r.Sym.ABI())
	}
	} else if r.Type == objabi.R_TLS_LE {
	name = "TLS"
	}
	if ctxt.Arch.InFamily(sys.ARM, sys.PPC64) {
	fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s%s+%x\n", int(r.Off), r.Siz, r.Type, name, ver, uint64(r.Add))
	} else {
	fmt.Fprintf(ctxt.Bso, "\trel %d+%d t=%d %s%s+%d\n", int(r.Off), r.Siz, r.Type, name, ver, r.Add)
	}
	}
	}

	// relocByOff sorts relocations by their offsets.
	type relocByOff []Reloc

	func (x relocByOff) Len() int { return len(x) }
	func (x relocByOff) Less(i, j int) bool { return x[i].Off < x[j].Off }
	func (x relocByOff) Swap(i, j int) { x[i], x[j] = x[j], x[i] }