loader.go

		panic("bad symbol index in SetSymAlign")
	}
	// Reject nonsense alignments.
	// TODO: do we need this?
	if align < 0 {
		panic("bad alignment value")
	}
	if align == 0 {
		delete(l.align, i)
	} else {
		// Alignment should be a power of 2.
		if bits.OnesCount32(uint32(align)) != 1 {
			panic("bad alignment value")
		}
		l.align[i] = align
	}
}

// SymDynImplib returns the "dynimplib" attribute for the specified
// symbol, making up a portion of the info for a symbol specified
// on a "cgo_import_dynamic" compiler directive.
func (l *Loader) SymDynimplib(i Sym) string {
	return l.dynimplib[i]
}

// SetSymDynimplib sets the "dynimplib" attribute for a symbol.
func (l *Loader) SetSymDynimplib(i Sym, value string) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetDynimplib")
	}
	if value == "" {
		delete(l.dynimplib, i)
	} else {
		l.dynimplib[i] = value
	}
}

// SymDynimpvers returns the "dynimpvers" attribute for the specified
// symbol, making up a portion of the info for a symbol specified
// on a "cgo_import_dynamic" compiler directive.
func (l *Loader) SymDynimpvers(i Sym) string {
	return l.dynimpvers[i]
}

// SetSymDynimpvers sets the "dynimpvers" attribute for a symbol.
func (l *Loader) SetSymDynimpvers(i Sym, value string) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetDynimpvers")
	}
	if value == "" {
		delete(l.dynimpvers, i)
	} else {
		l.dynimpvers[i] = value
	}
}

// SymExtname returns the "extname" value for the specified
// symbol.
func (l *Loader) SymExtname(i Sym) string {
	return l.extname[i]
}

// SetSymExtname sets the  "extname" attribute for a symbol.
func (l *Loader) SetSymExtname(i Sym, value string) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetExtname")
	}
	if value == "" {
		delete(l.extname, i)
	} else {
		l.extname[i] = value
	}
}

// SymElfType returns the previously recorded ELF type for a symbol
// (used only for symbols read from shared libraries by ldshlibsyms).
// It is not set for symbols defined by the packages being linked or
// by symbols read by ldelf (and so is left as elf.STT_NOTYPE).
func (l *Loader) SymElfType(i Sym) elf.SymType {
	if et, ok := l.elfType[i]; ok {
		return et
	}
	return elf.STT_NOTYPE
}

// SetSymElfType sets the elf type attribute for a symbol.
func (l *Loader) SetSymElfType(i Sym, et elf.SymType) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetSymElfType")
	}
	if et == elf.STT_NOTYPE {
		delete(l.elfType, i)
	} else {
		l.elfType[i] = et
	}
}

// SetPlt sets the plt value for pe symbols.
func (l *Loader) SetPlt(i Sym, v int32) {
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol for SetPlt")
	}
	if v == 0 {
		delete(l.plt, i)
	} else {
		l.plt[i] = v
	}
}

// SetGot sets the got value for pe symbols.
func (l *Loader) SetGot(i Sym, v int32) {
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol for SetPlt")
	}
	if v == 0 {
		delete(l.got, i)
	} else {
		l.got[i] = v
	}
}

// SymGoType returns the 'Gotype' property for a given symbol (set by
// the Go compiler for variable symbols). This version relies on
// reading aux symbols for the target sym -- it could be that a faster
// approach would be to check for gotype during preload and copy the
// results in to a map (might want to try this at some point and see
// if it helps speed things up).
func (l *Loader) SymGoType(i Sym) Sym {
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		return pp.gotype
	}
	r, li := l.toLocal(i)
	naux := r.NAux(li)
	for j := 0; j < naux; j++ {
		a := goobj2.Aux{}
		a.Read(r.Reader, r.AuxOff(li, j))
		switch a.Type {
		case goobj2.AuxGotype:
			return l.resolve(r, a.Sym)
		}
	}
	return 0
}

// SymUnit returns the compilation unit for a given symbol (which will
// typically be nil for external or linker-manufactured symbols).
func (l *Loader) SymUnit(i Sym) *sym.CompilationUnit {
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		if pp.objidx != 0 {
			r := l.objs[pp.objidx].r
			return r.unit
		}
		return nil
	}
	r, _ := l.toLocal(i)
	return r.unit
}

// SymFile returns the file for a symbol, which is normally the
// package the symbol came from (for regular compiler-generated Go
// symbols), but in the case of building with "-linkshared" (when a
// symbol is read from a a shared library), will hold the library
// name.
func (l *Loader) SymFile(i Sym) string {
	if l.IsExternal(i) {
		if f, ok := l.symFile[i]; ok {
			return f
		}
		pp := l.getPayload(i)
		if pp.objidx != 0 {
			r := l.objs[pp.objidx].r
			return r.unit.Lib.File
		}
		return ""
	}
	r, _ := l.toLocal(i)
	return r.unit.Lib.File
}

// SetSymFile sets the file attribute for a symbol. This is
// needed mainly for external symbols, specifically those imported
// from shared libraries.
func (l *Loader) SetSymFile(i Sym, file string) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetSymFile")
	}
	if !l.IsExternal(i) {
		panic("can't set file for non-external sym")
	}
	l.symFile[i] = file
}

// SymLocalentry returns the "local entry" value for the specified
// symbol.
func (l *Loader) SymLocalentry(i Sym) uint8 {
	return l.localentry[i]
}

// SetSymExtname sets the "extname" attribute for a symbol.
func (l *Loader) SetSymLocalentry(i Sym, value uint8) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetExtname")
	}
	if value == 0 {
		delete(l.localentry, i)
	} else {
		l.localentry[i] = value
	}
}

// Returns the number of aux symbols given a global index.
func (l *Loader) NAux(i Sym) int {
	if l.IsExternal(i) {
		return 0
	}
	r, li := l.toLocal(i)
	return r.NAux(li)
}

// Returns the referred symbol of the j-th aux symbol of the i-th
// symbol.
func (l *Loader) AuxSym(i Sym, j int) Sym {
	if l.IsExternal(i) {
		return 0
	}
	r, li := l.toLocal(i)
	a := goobj2.Aux{}
	a.Read(r.Reader, r.AuxOff(li, j))
	return l.resolve(r, a.Sym)
}

// GetFuncDwarfAuxSyms collects and returns the auxiliary DWARF
// symbols associated with a given function symbol.  Prior to the
// introduction of the loader, this was done purely using name
// lookups, e.f. for function with name XYZ we would then look up
// go.info.XYZ, etc.
// FIXME: once all of dwarfgen is converted over to the loader,
// it would save some space to make these aux symbols nameless.
func (l *Loader) GetFuncDwarfAuxSyms(fnSymIdx Sym) (auxDwarfInfo, auxDwarfLoc, auxDwarfRanges, auxDwarfLines Sym) {
	if l.SymType(fnSymIdx) != sym.STEXT {
		log.Fatalf("error: non-function sym %d/%s t=%s passed to GetFuncDwarfAuxSyms", fnSymIdx, l.SymName(fnSymIdx), l.SymType(fnSymIdx).String())
	}
	if l.IsExternal(fnSymIdx) {
		// Current expectation is that any external function will
		// not have auxsyms.
		return
	}
	naux := l.NAux(fnSymIdx)
	if naux == 0 {
		return
	}
	r, li := l.toLocal(fnSymIdx)
	for i := 0; i < naux; i++ {
		a := goobj2.Aux{}
		a.Read(r.Reader, r.AuxOff(li, i))
		switch a.Type {
		case goobj2.AuxDwarfInfo:
			auxDwarfInfo = l.resolve(r, a.Sym)
			if l.SymType(auxDwarfInfo) != sym.SDWARFINFO {
				panic("aux dwarf info sym with wrong type")
			}
		case goobj2.AuxDwarfLoc:
			auxDwarfLoc = l.resolve(r, a.Sym)
			if l.SymType(auxDwarfLoc) != sym.SDWARFLOC {
				panic("aux dwarf loc sym with wrong type")
			}
		case goobj2.AuxDwarfRanges:
			auxDwarfRanges = l.resolve(r, a.Sym)
			if l.SymType(auxDwarfRanges) != sym.SDWARFRANGE {
				panic("aux dwarf ranges sym with wrong type")
			}
		case goobj2.AuxDwarfLines:
			auxDwarfLines = l.resolve(r, a.Sym)
			if l.SymType(auxDwarfLines) != sym.SDWARFLINES {
				panic("aux dwarf lines sym with wrong type")
			}
		}
	}
	return
}

// ReadAuxSyms reads the aux symbol ids for the specified symbol into the
// slice passed as a parameter. If the slice capacity is not large enough, a new
// larger slice will be allocated. Final slice is returned.
func (l *Loader) ReadAuxSyms(symIdx Sym, dst []Sym) []Sym {
	if l.IsExternal(symIdx) {
		return dst[:0]
	}
	naux := l.NAux(symIdx)
	if naux == 0 {
		return dst[:0]
	}

	if cap(dst) < naux {
		dst = make([]Sym, naux)
	}
	dst = dst[:0]

	r, li := l.toLocal(symIdx)
	a := goobj2.Aux{}
	for i := 0; i < naux; i++ {
		a.ReadSym(r.Reader, r.AuxOff(li, i))
		dst = append(dst, l.resolve(r, a.Sym))
	}

	return dst
}

// PrependSub prepends 'sub' onto the sub list for outer symbol 'outer'.
// Will panic if 'sub' already has an outer sym or sub sym.
// FIXME: should this be instead a method on SymbolBuilder?
func (l *Loader) PrependSub(outer Sym, sub Sym) {
	// NB: this presupposes that an outer sym can't be a sub symbol of
	// some other outer-outer sym (I'm assuming this is true, but I
	// haven't tested exhaustively).
	if l.OuterSym(outer) != 0 {
		panic("outer has outer itself")
	}
	if l.SubSym(sub) != 0 {
		panic("sub set for subsym")
	}
	if l.OuterSym(sub) != 0 {
		panic("outer already set for subsym")
	}
	l.sub[sub] = l.sub[outer]
	l.sub[outer] = sub
	l.outer[sub] = outer
}

// OuterSym gets the outer symbol for host object loaded symbols.
func (l *Loader) OuterSym(i Sym) Sym {
	// FIXME: add check for isExternal?
	return l.outer[i]
}

// SubSym gets the subsymbol for host object loaded symbols.
func (l *Loader) SubSym(i Sym) Sym {
	// NB: note -- no check for l.isExternal(), since I am pretty sure
	// that later phases in the linker set subsym for "type." syms
	return l.sub[i]
}

// Initialize Reachable bitmap and its siblings for running deadcode pass.
func (l *Loader) InitReachable() {
	l.growAttrBitmaps(l.NSym() + 1)
}

type symWithVal struct {
	s Sym
	v int64
}
type bySymValue []symWithVal

func (s bySymValue) Len() int           { return len(s) }
func (s bySymValue) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s bySymValue) Less(i, j int) bool { return s[i].v < s[j].v }

// SortSub walks through the sub-symbols for 's' and sorts them
// in place by increasing value. Return value is the new
// sub symbol for the specified outer symbol.
func (l *Loader) SortSub(s Sym) Sym {

	if s == 0 || l.sub[s] == 0 {
		return s
	}

	// Sort symbols using a slice first. Use a stable sort on the off
	// chance that there's more than once symbol with the same value,
	// so as to preserve reproducible builds.
	sl := []symWithVal{}
	for ss := l.sub[s]; ss != 0; ss = l.sub[ss] {
		sl = append(sl, symWithVal{s: ss, v: l.SymValue(ss)})
	}
	sort.Stable(bySymValue(sl))

	// Then apply any changes needed to the sub map.
	ns := Sym(0)
	for i := len(sl) - 1; i >= 0; i-- {
		s := sl[i].s
		l.sub[s] = ns
		ns = s
	}

	// Update sub for outer symbol, then return
	l.sub[s] = sl[0].s
	return sl[0].s
}

// Insure that reachable bitmap and its siblings have enough size.
func (l *Loader) growAttrBitmaps(reqLen int) {
	if reqLen > l.attrReachable.Len() {
		// These are indexed by global symbol
		l.attrReachable = growBitmap(reqLen, l.attrReachable)
		l.attrOnList = growBitmap(reqLen, l.attrOnList)
		l.attrLocal = growBitmap(reqLen, l.attrLocal)
		l.attrNotInSymbolTable = growBitmap(reqLen, l.attrNotInSymbolTable)
	}
	l.growExtAttrBitmaps()
}

func (l *Loader) growExtAttrBitmaps() {
	// These are indexed by external symbol index (e.g. l.extIndex(i))
	extReqLen := len(l.payloads)
	if extReqLen > l.attrVisibilityHidden.Len() {
		l.attrVisibilityHidden = growBitmap(extReqLen, l.attrVisibilityHidden)
		l.attrDuplicateOK = growBitmap(extReqLen, l.attrDuplicateOK)
		l.attrShared = growBitmap(extReqLen, l.attrShared)
		l.attrExternal = growBitmap(extReqLen, l.attrExternal)
	}
}

// At method returns the j-th reloc for a global symbol.
func (relocs *Relocs) At(j int) Reloc {
	if relocs.l.isExtReader(relocs.r) {
		pp := relocs.l.payloads[relocs.li]
		return pp.relocs[j]
	}
	rel := goobj2.Reloc{}
	rel.Read(relocs.r.Reader, relocs.r.RelocOff(relocs.li, j))
	target := relocs.l.resolve(relocs.r, rel.Sym)
	return Reloc{
		Off:  rel.Off,
		Size: rel.Siz,
		Type: objabi.RelocType(rel.Type),
		Add:  rel.Add,
		Sym:  target,
	}
}

// ReadAll method reads all relocations for a symbol into the
// specified slice. If the slice capacity is not large enough, a new
// larger slice will be allocated. Final slice is returned.
func (relocs *Relocs) ReadAll(dst []Reloc) []Reloc {
	return relocs.readAll(dst, false)
}

// ReadSyms method reads all relocation target symbols and reloc types
// for a symbol into the specified slice. It is like ReadAll but only
// fill in the Sym and Type fields.
func (relocs *Relocs) ReadSyms(dst []Reloc) []Reloc {
	return relocs.readAll(dst, true)
}

func (relocs *Relocs) readAll(dst []Reloc, onlySymType bool) []Reloc {
	if relocs.Count == 0 {
		return dst[:0]
	}

	if cap(dst) < relocs.Count {
		dst = make([]Reloc, relocs.Count)
	}
	dst = dst[:0]

	if relocs.l.isExtReader(relocs.r) {
		pp := relocs.l.payloads[relocs.li]
		dst = append(dst, pp.relocs...)
		return dst
	}

	off := relocs.r.RelocOff(relocs.li, 0)
	rel := goobj2.Reloc{}
	for i := 0; i < relocs.Count; i++ {
		if onlySymType {
			rel.ReadSymType(relocs.r.Reader, off)
		} else {
			rel.Read(relocs.r.Reader, off)
		}
		off += uint32(rel.Size())
		target := relocs.l.resolve(relocs.r, rel.Sym)
		dst = append(dst, Reloc{
			Off:  rel.Off,
			Size: rel.Siz,
			Type: objabi.RelocType(rel.Type),
			Add:  rel.Add,
			Sym:  target,
		})
	}
	return dst
}

// Relocs returns a Relocs object for the given global sym.
func (l *Loader) Relocs(i Sym) Relocs {
	r, li := l.toLocal(i)
	if r == nil {
		panic(fmt.Sprintf("trying to get oreader for invalid sym %d\n\n", i))
	}
	return l.relocs(r, li)
}

// Relocs returns a Relocs object given a local sym index and reader.
func (l *Loader) relocs(r *oReader, li int) Relocs {
	var n int
	if l.isExtReader(r) {
		pp := l.payloads[li]
		n = len(pp.relocs)
	} else {
		n = r.NReloc(li)
	}
	return Relocs{
		Count: n,
		li:    li,
		r:     r,
		l:     l,
	}
}

// RelocByOff implements sort.Interface for sorting relocations by offset.

type RelocByOff []Reloc

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

// FuncInfo provides hooks to access goobj2.FuncInfo in the objects.
type FuncInfo struct {
	l    *Loader
	r    *oReader
	data []byte
}

func (fi *FuncInfo) Valid() bool { return fi.r != nil }

func (fi *FuncInfo) Locals() int {
	return int((*goobj2.FuncInfo)(nil).ReadLocals(fi.data))
}

func (fi *FuncInfo) Pcsp() []byte {
	pcsp, end := (*goobj2.FuncInfo)(nil).ReadPcsp(fi.data)
	return fi.r.BytesAt(fi.r.PcdataBase()+pcsp, int(end-pcsp))
}

// TODO: more accessors.

func (l *Loader) FuncInfo(i Sym) FuncInfo {
	if l.IsExternal(i) {
		return FuncInfo{}
	}
	r, li := l.toLocal(i)
	n := r.NAux(li)
	for j := 0; j < n; j++ {
		a := goobj2.Aux{}
		a.Read(r.Reader, r.AuxOff(li, j))
		if a.Type == goobj2.AuxFuncInfo {
			b := r.Data(int(a.Sym.SymIdx))
			return FuncInfo{l, r, b}
		}
	}
	return FuncInfo{}
}

// Preload a package: add autolibs, add defined package symbols to the symbol table.
// Does not add non-package symbols yet, which will be done in LoadNonpkgSyms.
// Does not read symbol data.
func (l *Loader) Preload(syms *sym.Symbols, f *bio.Reader, lib *sym.Library, unit *sym.CompilationUnit, length int64, flags int) {
	roObject, readonly, err := f.Slice(uint64(length))
	if err != nil {
		log.Fatal("cannot read object file:", err)
	}
	r := goobj2.NewReaderFromBytes(roObject, readonly)
	if r == nil {
		panic("cannot read object file")
	}
	localSymVersion := syms.IncVersion()
	pkgprefix := objabi.PathToPrefix(lib.Pkg) + "."
	ndef := r.NSym()
	nnonpkgdef := r.NNonpkgdef()
	or := &oReader{r, unit, localSymVersion, r.Flags(), pkgprefix, make([]Sym, ndef+nnonpkgdef+r.NNonpkgref()), ndef, uint32(len(l.objs))}

	// Autolib
	lib.ImportStrings = append(lib.ImportStrings, r.Autolib()...)

	// DWARF file table
	nfile := r.NDwarfFile()
	unit.DWARFFileTable = make([]string, nfile)
	for i := range unit.DWARFFileTable {
		unit.DWARFFileTable[i] = r.DwarfFile(i)
	}

	l.addObj(lib.Pkg, or)
	l.preloadSyms(or, pkgDef)

	// The caller expects us consuming all the data
	f.MustSeek(length, os.SEEK_CUR)
}

// Preload symbols of given kind from an object.
func (l *Loader) preloadSyms(r *oReader, kind int) {
	ndef := r.NSym()
	nnonpkgdef := r.NNonpkgdef()
	var start, end int
	switch kind {
	case pkgDef:
		start = 0
		end = ndef
	case nonPkgDef:
		start = ndef
		end = ndef + nnonpkgdef
	default:
		panic("preloadSyms: bad kind")
	}
	l.growSyms(len(l.objSyms) + end - start)
	l.growAttrBitmaps(len(l.objSyms) + end - start)
	for i := start; i < end; i++ {
		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
		v := abiToVer(osym.ABI, r.version)
		dupok := osym.Dupok()
		gi, added := l.AddSym(name, v, r, i, kind, dupok, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)])
		r.syms[i] = gi
		if !added {
			continue
		}
		if osym.TopFrame() {
			l.SetAttrTopFrame(gi, true)
		}
		if strings.HasPrefix(name, "go.itablink.") {
			l.itablink[gi] = struct{}{}
		}
		if strings.HasPrefix(name, "runtime.") {
			if bi := goobj2.BuiltinIdx(name, v); bi != -1 {
				// This is a definition of a builtin symbol. Record where it is.
				l.builtinSyms[bi] = gi
			}
		}
		if strings.HasPrefix(name, "go.string.") ||
			strings.HasPrefix(name, "gclocals·") ||
			strings.HasPrefix(name, "runtime.gcbits.") {
			l.SetAttrNotInSymbolTable(gi, true)
		}
	}
}

// Add non-package symbols and references to external symbols (which are always
// named).
func (l *Loader) LoadNonpkgSyms(syms *sym.Symbols) {
	for _, o := range l.objs[1:] {
		l.preloadSyms(o.r, nonPkgDef)
	}
	for _, o := range l.objs[1:] {
		loadObjRefs(l, o.r, syms)
	}
}

func loadObjRefs(l *Loader, r *oReader, syms *sym.Symbols) {
	ndef := r.NSym() + r.NNonpkgdef()
	for i, n := 0, r.NNonpkgref(); i < n; i++ {
		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(ndef+i))
		name := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
		v := abiToVer(osym.ABI, r.version)
		r.syms[ndef+i] = l.AddExtSym(name, v)
	}
}

func abiToVer(abi uint16, localSymVersion int) int {
	var v int
	if abi == goobj2.SymABIstatic {
		// Static
		v = localSymVersion
	} else if abiver := sym.ABIToVersion(obj.ABI(abi)); abiver != -1 {
		// Note that data symbols are "ABI0", which maps to version 0.
		v = abiver
	} else {
		log.Fatalf("invalid symbol ABI: %d", abi)
	}
	return v
}

func preprocess(arch *sys.Arch, s *sym.Symbol) {
	if s.Name != "" && s.Name[0] == '$' && len(s.Name) > 5 && s.Type == 0 && len(s.P) == 0 {
		x, err := strconv.ParseUint(s.Name[5:], 16, 64)
		if err != nil {
			log.Panicf("failed to parse $-symbol %s: %v", s.Name, err)
		}
		s.Type = sym.SRODATA
		s.Attr |= sym.AttrLocal
		switch s.Name[:5] {
		case "$f32.":
			if uint64(uint32(x)) != x {
				log.Panicf("$-symbol %s too large: %d", s.Name, x)
			}
			s.AddUint32(arch, uint32(x))
		case "$f64.", "$i64.":
			s.AddUint64(arch, x)
		default:
			log.Panicf("unrecognized $-symbol: %s", s.Name)
		}
	}
}

// Load full contents.
func (l *Loader) LoadFull(arch *sys.Arch, syms *sym.Symbols) {
	// create all Symbols first.
	l.growSyms(l.NSym())

	nr := 0 // total number of sym.Reloc's we'll need
	for _, o := range l.objs[1:] {
		nr += loadObjSyms(l, syms, o.r)
	}

	// Make a first pass through the external symbols, making
	// sure that each external symbol has a non-nil entry in
	// l.Syms (note that relocations and symbol content will
	// be copied in a later loop).
	toConvert := make([]Sym, 0, len(l.payloads))
	for _, i := range l.extReader.syms {
		sname := l.RawSymName(i)
		if !l.attrReachable.Has(i) && !strings.HasPrefix(sname, "gofile..") { // XXX file symbols are used but not marked
			continue
		}
		pp := l.getPayload(i)
		nr += len(pp.relocs)
		// create and install the sym.Symbol here so that l.Syms will
		// be fully populated when we do relocation processing and
		// outer/sub processing below. Note that once we do this,
		// we'll need to get at the payload for a symbol with direct
		// reference to l.payloads[] as opposed to calling l.getPayload().
		s := l.allocSym(sname, 0)
		l.installSym(i, s)
		toConvert = append(toConvert, i)
	}

	// allocate a single large slab of relocations for all live symbols
	l.relocBatch = make([]sym.Reloc, nr)

	// convert payload-based external symbols into sym.Symbol-based
	for _, i := range toConvert {

		// Copy kind/size/value etc.
		pp := l.payloads[l.extIndex(i)]
		s := l.Syms[i]
		s.Version = int16(pp.ver)
		s.Type = pp.kind
		s.Size = pp.size
		s.Value = l.SymValue(i)
		if pp.gotype != 0 {
			s.Gotype = l.Syms[pp.gotype]
		}
		s.Value = l.values[i]
		if f, ok := l.symFile[i]; ok {
			s.File = f
		} else if pp.objidx != 0 {
			s.File = l.objs[pp.objidx].r.unit.Lib.File
		}

		// Copy relocations
		batch := l.relocBatch
		s.R = batch[:len(pp.relocs):len(pp.relocs)]
		l.relocBatch = batch[len(pp.relocs):]
		l.convertRelocations(pp.relocs, s, false)

		// Copy data
		s.P = pp.data

		// Transfer over attributes.
		l.migrateAttributes(i, s)

		// Preprocess symbol. May set 'AttrLocal'.
		preprocess(arch, s)
	}

	// load contents of defined symbols
	for _, o := range l.objs[1:] {
		loadObjFull(l, o.r)
	}

	// Note: resolution of ABI aliases is now also handled in
	// loader.convertRelocations, so once the host object loaders move
	// completely to loader.Sym, we can remove the code below.

	// Resolve ABI aliases for external symbols. This is only
	// needed for internal cgo linking.
	// (The old code does this in deadcode, but deadcode2 doesn't
	// do this.)
	for _, i := range l.extReader.syms {
		if s := l.Syms[i]; s != nil && s.Attr.Reachable() {
			for ri := range s.R {
				r := &s.R[ri]
				if r.Sym != nil && r.Sym.Type == sym.SABIALIAS {
					r.Sym = r.Sym.R[0].Sym
				}
			}
		}
	}
}

// PropagateSymbolChangesBackToLoader is a temporary shim function
// that copies over a given sym.Symbol into the equivalent representation
// in the loader world. The intent is to enable converting a given
// linker phase/pass from dealing with sym.Symbol's to a modernized
// pass that works with loader.Sym, in cases where the "loader.Sym
// wavefront" has not yet reached the pass in question. For such work
// the recipe is to first call PropagateSymbolChangesBackToLoader(),
// then exexute the pass working with the loader, then call
// PropagateLoaderChangesToSymbols to copy the changes made by the
// pass back to the sym.Symbol world.
func (l *Loader) PropagateSymbolChangesBackToLoader() {

	// For the moment we only copy symbol values, and we don't touch
	// any new sym.Symbols created since loadlibfull() was run. This
	// seems to be what's needed for DWARF gen.
	for i := Sym(1); i < Sym(len(l.objSyms)); i++ {
		s := l.Syms[i]
		if s != nil {
			if s.Value != l.SymValue(i) {
				l.SetSymValue(i, s.Value)
			}
		}
	}
}

// PropagateLoaderChangesToSymbols is a temporary shim function that
// takes a list of loader.Sym symbols and works to copy their contents
// and attributes over to a corresponding sym.Symbol. See the
// PropagateSymbolChangesBackToLoader header comment for more info.
//
// WARNING: this function is brittle and depends heavily on loader
// implementation. A key problem with doing this is that as things
// stand at the moment, some sym.Symbol contents/attributes are
// populated only when converting from loader.Sym to sym.Symbol
// in loadlibfull, meaning if we may wipe out some information
// when copying back.

func (l *Loader) PropagateLoaderChangesToSymbols(toconvert []Sym, syms *sym.Symbols) []*sym.Symbol {

	result := []*sym.Symbol{}
	relocfixup := []Sym{}

	// Note: this loop needs to allow for the possibility that we may
	// see "new" symbols on the 'toconvert' list that come from object
	// files (for example, DWARF location lists), as opposed to just
	// newly manufactured symbols (ex: DWARF section symbols such as
	// ".debug_info").  This means that we have to be careful not to
	// stomp on sym.Symbol attributes/content that was set up in
	// in loadlibfull().

	// Also note that in order for the relocation fixup to work, we
	// have to do this in two passes -- one pass to create the symbols,
	// and then a second fix up the relocations once all necessary
	// sym.Symbols are created.

	// First pass, symbol creation and symbol data fixup.
	anonVerReplacement := syms.IncVersion()
	rslice := []Reloc{}
	for _, cand := range toconvert {

		sn := l.SymName(cand)
		sv := l.SymVersion(cand)
		st := l.SymType(cand)
		if sv < 0 {
			sv = anonVerReplacement
		}

		s := l.Syms[cand]

		isnew := false
		if sn == "" {
			// Don't install anonymous symbols in the lookup tab.
			if s == nil {
				s = l.allocSym(sn, sv)
				l.installSym(cand, s)
			}
			isnew = true
		} else {
			if s != nil {
				// Already have a symbol for this -- it must be
				// something that was previously processed by
				// loadObjFull. Note that the symbol in question may
				// or may not be in the name lookup map.
			} else {
				isnew = true
				s = syms.Lookup(sn, sv)
			}
		}
		result = append(result, s)

		// Always copy these from new to old.
		s.Value = l.SymValue(cand)
		s.Type = st

		// If the data for a symbol has increased in size, make sure
		// we bring the new content across.
		relfix := isnew
		if isnew || len(l.Data(cand)) > len(s.P) {
			s.P = l.Data(cand)
			s.Size = int64(len(s.P))
			relfix = true
		}

		// For 'new' symbols, copy other content (such as Gotype,
		// sym file, relocations, etc).
		if isnew {
			if gt := l.SymGoType(cand); gt != 0 {
				s.Gotype = l.Syms[gt]
			}
			if f, ok := l.symFile[cand]; ok {
				s.File = f
			} else {
				r, _ := l.toLocal(cand)
				if r != nil && r != l.extReader {
					s.File = l.SymFile(cand)
				}
			}
		}

		// If this symbol has any DWARF file relocations, we need to
		// make sure that the relocations are copied back over, since
		// DWARF-gen alters the offset values for these relocs. Also:
		// if this is an info symbol and it refers to a previously
		// unseen range/loc symbol, we'll need to fix up relocations
		// for it as well.
		relocs := l.Relocs(cand)
		rslice = relocs.ReadSyms(rslice)
		for ri := range rslice {
			if rslice[ri].Type == objabi.R_DWARFFILEREF {
				relfix = true
				break
			}
			if st != sym.SDWARFINFO {
				continue
			}
			rst := l.SymType(rslice[ri].Sym)
			if rst == sym.SDWARFRANGE || rst == sym.SDWARFLOC {
				relfix = true
				break
			}
		}

		if relfix {
			relocfixup = append(relocfixup, cand)
		}

		// If new symbol, call a helper to migrate attributes.
		// Otherwise touch only not-in-symbol-table, since there are
		// some attrs that are only set up at the point where we
		// convert loader.Sym to sym.Symbol.
		if isnew {
			l.migrateAttributes(cand, s)
		} else {
			if l.AttrNotInSymbolTable(cand) {
				s.Attr.Set(sym.AttrNotInSymbolTable, true)
			}
		}
	}

	// Second pass to fix up relocations.
	for _, cand := range relocfixup {
		s := l.Syms[cand]
		relocs := l.Relocs(cand)
		rslice = relocs.ReadAll(rslice)
		s.R = make([]sym.Reloc, len(rslice))
		l.convertRelocations(rslice, s, true)
	}

	return result
}

// ExtractSymbols grabs the symbols out of the loader for work that hasn't been
// ported to the new symbol type.
func (l *Loader) ExtractSymbols(syms *sym.Symbols, rp map[*sym.Symbol]*sym.Symbol) {
	// Add symbols to the ctxt.Syms lookup table. This explicitly skips things
	// created via loader.Create (marked with versions less than zero), since
	// if we tried to add these we'd wind up with collisions. We do, however,
	// add these symbols to the list of global symbols so that other future
	// steps (like pclntab generation) can find these symbols if neceassary.
	// Along the way, update the version from the negative anon version to
	// something larger than sym.SymVerStatic (needed so that
	// sym.symbol.IsFileLocal() works properly).
	anonVerReplacement := syms.IncVersion()
	for _, s := range l.Syms {
		if s == nil {
			continue
		}
		syms.Allsym = append(syms.Allsym, s) // XXX still add to Allsym for now, as there are code looping through Allsym
		if s.Version < 0 {
			s.Version = int16(anonVerReplacement)
		}
	}

	for i, s := range l.Reachparent {
		if i == 0 {
			continue
		}
		rp[l.Syms[i]] = l.Syms[s]
	}

	// Provide lookup functions for sym.Symbols.
	syms.Lookup = func(name string, ver int) *sym.Symbol {
		i := l.LookupOrCreateSym(name, ver)
		if s := l.Syms[i]; s != nil {