loader.go

func (l *Loader) IsGoType(i Sym) bool {
	return l.SymAttr(i)&goobj2.SymFlagGoType != 0
}

// Returns whether this is a "go.itablink.*" symbol.
func (l *Loader) IsItabLink(i Sym) bool {
	if _, ok := l.itablink[i]; ok {
		return true
	}
	return false
}

// growValues grows the slice used to store symbol values.
func (l *Loader) growValues(reqLen int) {
	curLen := len(l.values)
	if reqLen > curLen {
		l.values = append(l.values, make([]int64, reqLen+1-curLen)...)
	}
}

// SymValue returns the value of the i-th symbol. i is global index.
func (l *Loader) SymValue(i Sym) int64 {
	return l.values[i]
}

// SetSymValue sets the value of the i-th symbol. i is global index.
func (l *Loader) SetSymValue(i Sym, val int64) {
	l.values[i] = val
}

// Returns the symbol content of the i-th symbol. i is global index.
func (l *Loader) Data(i Sym) []byte {
	if l.IsExternal(i) {
		if s := l.Syms[i]; s != nil {
			return s.P
		}
		pp := l.getPayload(i)
		if pp != nil {
			return pp.data
		}
		return nil
	}
	r, li := l.toLocal(i)
	return r.Data(li)
}

// SymAlign returns the alignment for a symbol.
func (l *Loader) SymAlign(i Sym) int32 {
	// If an alignment has been recorded, return that.
	if align, ok := l.align[i]; ok {
		return align
	}
	// TODO: would it make sense to return an arch-specific
	// alignment depending on section type? E.g. STEXT => 32,
	// SDATA => 1, etc?
	return 0
}

// SetSymAlign sets the alignment for a symbol.
func (l *Loader) SetSymAlign(i Sym, align int32) {
	// reject bad synbols
	if i > l.max || i == 0 {
		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 > l.max || 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 > l.max || 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 > l.max || i == 0 {
		panic("bad symbol index in SetExtname")
	}
	if value == "" {
		delete(l.extname, i)
	} else {
		l.extname[i] = value
	}
}

// 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 > l.max || 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)
}

// 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)
	for i := 0; i < naux; i++ {
		a := goobj2.Aux{}
		a.Read(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) {
	if l.Syms[outer] != nil {
		panic("not implemented for sym.Symbol based syms")
	}
	// 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 {
	sym := l.Syms[i]
	if sym != nil && sym.Outer != nil {
		outer := sym.Outer
		return l.Lookup(outer.Name, int(outer.Version))
	}
	// 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 {
	sym := l.Syms[i]
	if sym != nil && sym.Sub != nil {
		sub := sym.Sub
		return l.Lookup(sub.Name, int(sub.Version))
	}
	// 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)
	}
	// These are indexed by external symbol offset (e.g. i - l.extStart)
	if l.extStart == 0 {
		return
	}
	extReqLen := reqLen - int(l.extStart)
	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 s := relocs.l.Syms[relocs.extIdx]; s != nil {
		rel := s.R[j]
		return Reloc{
			Off:  rel.Off,
			Size: rel.Siz,
			Type: rel.Type,
			Add:  rel.Add,
			Sym:  relocs.l.Lookup(rel.Sym.Name, int(rel.Sym.Version)),
		}
	}
	if relocs.extIdx != 0 {
		pp := relocs.l.getPayload(relocs.extIdx)
		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 {
	if relocs.Count == 0 {
		return dst[:0]
	}

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

	if s := relocs.l.Syms[relocs.extIdx]; s != nil {
		for i := 0; i < relocs.Count; i++ {
			erel := &s.R[i]
			rel := Reloc{
				Off:  erel.Off,
				Size: erel.Siz,
				Type: erel.Type,
				Add:  erel.Add,
				Sym:  relocs.l.Lookup(erel.Sym.Name, int(erel.Sym.Version)),
			}
			dst = append(dst, rel)
		}
		return dst
	}

	if relocs.extIdx != 0 {
		pp := relocs.l.getPayload(relocs.extIdx)
		dst = append(dst, pp.relocs...)
		return dst
	}

	off := relocs.r.RelocOff(relocs.li, 0)
	for i := 0; i < relocs.Count; i++ {
		rel := goobj2.Reloc{}
		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 {
	if l.IsExternal(i) {
		if s := l.Syms[i]; s != nil {
			return Relocs{Count: len(s.R), l: l, extIdx: i}
		}
		pp := l.getPayload(i)
		if pp != nil {
			return Relocs{Count: len(pp.relocs), l: l, extIdx: i}
		}
		return 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 {
	return Relocs{
		Count: r.NReloc(li),
		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 }

// Preload a package: add autolibs, add symbols to the symbol table.
// Does not read symbol data yet.
func (l *Loader) Preload(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *sym.Library, unit *sym.CompilationUnit, length int64, pn string, 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) + "."
	or := &oReader{r, unit, localSymVersion, r.Flags(), pkgprefix, nil}

	// 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)
	}

	istart := l.addObj(lib.Pkg, or)

	ndef := r.NSym()
	nnonpkgdef := r.NNonpkgdef()
	for i, n := 0, ndef+nnonpkgdef; i < n; i++ {
		osym := goobj2.Sym{}
		osym.Read(r, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", pkgprefix, -1)
		if name == "" {
			continue // don't add unnamed aux symbol
		}
		v := abiToVer(osym.ABI, localSymVersion)
		dupok := osym.Dupok()
		added := l.AddSym(name, v, istart+Sym(i), or, dupok, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)])
		if added && strings.HasPrefix(name, "go.itablink.") {
			l.itablink[istart+Sym(i)] = struct{}{}
		}
		if added && 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] = istart + Sym(i)
			}
		}
	}

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

// Make sure referenced symbols are added. Most of them should already be added.
// This should only be needed for referenced external symbols.
func (l *Loader) LoadRefs(arch *sys.Arch, syms *sym.Symbols) {
	for _, o := range l.objs[1:] {
		loadObjRefs(l, o.r, arch, syms)
	}
}

func loadObjRefs(l *Loader, r *oReader, arch *sys.Arch, 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)
		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, l.max-l.extStart+1)
	for i := l.extStart; i <= l.max; i++ {
		if s := l.Syms[i]; s != nil {
			s.Attr.Set(sym.AttrReachable, l.attrReachable.has(i))
			continue
		}
		if i != l.getOverwrite(i) {
			continue
		}
		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.
		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[i-l.extStart]
		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]
		}

		// 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)

		// Copy data
		s.P = pp.data

		// Convert outer/sub relationships
		if outer, ok := l.outer[i]; ok {
			s.Outer = l.Syms[outer]
		}
		if sub, ok := l.sub[i]; ok {
			s.Sub = l.Syms[sub]
		}

		// Preprocess symbol and set reachability and onlist.
		preprocess(arch, s)
		s.Attr.Set(sym.AttrReachable, l.attrReachable.has(i))
		s.Attr.Set(sym.AttrOnList, l.attrOnList.has(i))

		// Set sub-symbol attribute. FIXME: would be better
		// to do away with this and just use l.OuterSymbol() != 0
		// elsewhere within the linker.
		s.Attr.Set(sym.AttrSubSymbol, s.Outer != nil)

		// Copy over dynimplib, dynimpvers, extname.
		if l.SymExtname(i) != "" {
			s.SetExtname(l.SymExtname(i))
		}
		if l.SymDynimplib(i) != "" {
			s.SetDynimplib(l.SymDynimplib(i))
		}
		if l.SymDynimpvers(i) != "" {
			s.SetDynimpvers(l.SymDynimpvers(i))
		}
	}

	// 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 := l.extStart; i <= l.max; i++ {
		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
				}
			}
		}
	}
}

// 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) {
	// Nil out overwritten symbols.
	// Overwritten Go symbols aren't a problem (as they're lazy loaded), but
	// symbols loaded from host object loaders are fully loaded, and we might
	// have multiple symbols with the same name. This loop nils them out.
	for oldI := range l.overwrite {
		l.Syms[oldI] = nil
	}

	// 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
		}
		if s.Name != "" && s.Version >= 0 {
			syms.Add(s)
		} else {
			syms.Allsym = append(syms.Allsym, s)
		}
		if s.Version < 0 {
			s.Version = int16(anonVerReplacement)
		}
	}
}

// allocSym allocates a new symbol backing.
func (l *Loader) allocSym(name string, version int) *sym.Symbol {
	batch := l.symBatch
	if len(batch) == 0 {
		batch = make([]sym.Symbol, 1000)
	}
	s := &batch[0]
	l.symBatch = batch[1:]

	s.Dynid = -1
	s.Name = name
	s.Version = int16(version)

	return s
}

// installSym sets the underlying sym.Symbol for the specified sym index.
func (l *Loader) installSym(i Sym, s *sym.Symbol) {
	if s == nil {
		panic("installSym nil symbol")
	}
	if l.Syms[i] != nil {
		panic("sym already present in installSym")
	}
	l.Syms[i] = s
}

// addNewSym adds a new sym.Symbol to the i-th index in the list of symbols.
func (l *Loader) addNewSym(i Sym, name string, ver int, unit *sym.CompilationUnit, t sym.SymKind) *sym.Symbol {
	s := l.allocSym(name, ver)
	if s.Type != 0 && s.Type != sym.SXREF {
		fmt.Println("symbol already processed:", unit.Lib, i, s)
		panic("symbol already processed")
	}
	if t == sym.SBSS && (s.Type == sym.SRODATA || s.Type == sym.SNOPTRBSS) {
		t = s.Type
	}
	s.Type = t
	s.Unit = unit
	l.growSyms(int(i))
	l.installSym(i, s)
	return s
}

// loadObjSyms creates sym.Symbol objects for the live Syms in the
// object corresponding to object reader "r". Return value is the
// number of sym.Reloc entries required for all the new symbols.
func loadObjSyms(l *Loader, syms *sym.Symbols, r *oReader) int {
	istart := l.startIndex(r)
	nr := 0

	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
		// If it's been previously loaded in host object loading, we don't need to do it again.
		if s := l.Syms[istart+Sym(i)]; s != nil {
			// Mark symbol as reachable as it wasn't marked as such before.
			s.Attr.Set(sym.AttrReachable, l.attrReachable.has(istart+Sym(i)))
			nr += r.NReloc(i)
			continue
		}
		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
		if name == "" {
			continue
		}
		ver := abiToVer(osym.ABI, r.version)
		if osym.ABI != goobj2.SymABIstatic && l.symsByName[ver][name] != istart+Sym(i) {
			continue
		}

		t := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)]
		if t == sym.SXREF {
			log.Fatalf("bad sxref")
		}
		if t == 0 {
			log.Fatalf("missing type for %s in %s", name, r.unit.Lib)
		}
		if !l.attrReachable.has(istart+Sym(i)) && !(t == sym.SRODATA && strings.HasPrefix(name, "type.")) && name != "runtime.addmoduledata" && name != "runtime.lastmoduledatap" {
			// No need to load unreachable symbols.
			// XXX some type symbol's content may be needed in DWARF code, but they are not marked.
			// XXX reference to runtime.addmoduledata may be generated later by the linker in plugin mode.
			continue
		}

		s := l.addNewSym(istart+Sym(i), name, ver, r.unit, t)
		s.Attr.Set(sym.AttrReachable, l.attrReachable.has(istart+Sym(i)))
		nr += r.NReloc(i)
	}
	return nr
}

// funcInfoSym records the sym.Symbol for a function, along with a copy
// of the corresponding goobj2.Sym and the index of its FuncInfo aux sym.
// We use this to delay populating FuncInfo until we can batch-allocate
// slices for their sub-objects.
type funcInfoSym struct {
	s    *sym.Symbol // sym.Symbol for a live function
	osym goobj2.Sym  // object file symbol data for that function
	isym int         // global symbol index of FuncInfo aux sym for func
}

// funcAllocInfo records totals/counts for all functions in an objfile;
// used to help with bulk allocation of sym.Symbol sub-objects.
type funcAllocInfo struct {
	symPtr  uint32 // number of *sym.Symbol's needed in file slices
	inlCall uint32 // number of sym.InlinedCall's needed in inltree slices
	pcData  uint32 // number of sym.Pcdata's needed in pdata slices
	fdOff   uint32 // number of int64's needed in all Funcdataoff slices
}

// loadSymbol loads a single symbol by name.
// NB: This function does NOT set the symbol as reachable.
func (l *Loader) loadSymbol(name string, version int) *sym.Symbol {
	global := l.Lookup(name, version)

	// If we're already loaded, bail.
	if global != 0 && int(global) < len(l.Syms) && l.Syms[global] != nil {
		return l.Syms[global]
	}

	// Read the symbol.
	r, i := l.toLocal(global)
	istart := l.startIndex(r)

	osym := goobj2.Sym{}
	osym.Read(r.Reader, r.SymOff(int(i)))
	if l.symsByName[version][name] != istart+Sym(i) {
		return nil
	}

	return l.addNewSym(istart+Sym(i), name, version, r.unit, sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)])
}

// LookupOrCreate looks up a symbol by name, and creates one if not found.
// Either way, it will also create a sym.Symbol for it, if not already.
// This should only be called when interacting with parts of the linker
// that still works on sym.Symbols (i.e. internal cgo linking, for now).
func (l *Loader) LookupOrCreate(name string, version int) *sym.Symbol {
	i := l.Lookup(name, version)
	if i != 0 {
		// symbol exists
		if int(i) < len(l.Syms) && l.Syms[i] != nil {
			return l.Syms[i]
		}
		if l.IsExternal(i) {
			panic("Can't load an external symbol.")
		}
		return l.loadSymbol(name, version)
	}
	i = l.AddExtSym(name, version)
	s := l.allocSym(name, version)
	l.Syms[i] = s
	return s
}

// cloneToExternal takes the existing object file symbol (symIdx)
// and creates a new external symbol that is a clone with respect
// to name, version, type, relocations, etc. The idea here is that
// if the linker decides it wants to update the contents of a
// symbol originally discovered as part of an object file, it's
// easier to do this if we make the updates to a new and similarly
// named external copy of that symbol.
func (l *Loader) cloneToExternal(symIdx Sym) Sym {
	if l.IsExternal(symIdx) {
		panic("sym is already external, no need for clone")
	}

	// Read the particulars from object.
	osym := goobj2.Sym{}
	r, li := l.toLocal(symIdx)
	osym.Read(r.Reader, r.SymOff(li))
	sname := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
	sver := abiToVer(osym.ABI, r.version)
	skind := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type)]

	// Create new symbol, update version and kind.
	ns := l.newExtSym(sname, sver)
	pp := &l.payloads[ns-l.extStart]
	pp.kind = skind
	pp.ver = sver
	pp.size = int64(osym.Siz)

	// If this is a def, then copy the guts. We expect this case
	// to be very rare (one case it may come up is with -X).
	if li < (r.NSym() + r.NNonpkgdef()) {

		// Copy relocations
		relocs := l.Relocs(symIdx)
		pp.relocs = relocs.ReadAll(nil)

		// Copy data
		pp.data = r.Data(li)

		// Copy read-only attr
		if r.ReadOnly() {
			l.attrReadOnly[ns] = true
		}
	}

	// If we're overriding a data symbol, collect the associated
	// Gotype, so as to propagate it to the new symbol.
	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:
			pp.gotype = l.resolve(r, a.Sym)
		default:
			log.Fatalf("internal error: cloneToExternal applied to %s symbol %s with non-gotype aux data %d", skind.String(), sname, a.Type)
		}
	}

	// Fix up the lookup tables if the symbol in question was
	// present in the lookup tables. At the moment it only makes
	// sense to do this sort of clone/update for symbols that are
	// in the symbol table (as opposed to anonymous symbols);
	// issue an error if we can't look up the original symbol.
	if sver >= sym.SymVerStatic {
		s, ok := l.extStaticSyms[nameVer{sname, sver}]
		if !ok || s != symIdx {
			panic("lookup failed for clone of non-external static symbol")
		}
		l.extStaticSyms[nameVer{sname, sver}] = ns
	} else {
		s, ok := l.symsByName[sver][sname]
		if !ok || s != symIdx {
			panic("lookup failed for clone of non-external symbol")
		}
		l.symsByName[sver][sname] = ns
	}

	// Add an overwrite entry (in case there are relocations against
	// the old symbol).
	l.overwrite[symIdx] = ns

	// FIXME: copy other attributes? reachable is the main one, and we
	// don't expect it to be set at this point.

	return ns
}

// CreateExtSym creates a new external symbol with the specified name
// without adding it to any lookup tables, returning a Sym index for it.
func (l *Loader) CreateExtSym(name string) Sym {
	// Assign a new unique negative version -- this is to mark the
	// symbol so that it can be skipped when ExtractSymbols is adding
	// ext syms to the sym.Symbols hash.
	l.anonVersion--
	return l.newExtSym(name, l.anonVersion)
}

// Create creates a symbol with the specified name, returning a
// sym.Symbol object for it. This method is intended for static/hidden
// symbols discovered while loading host objects. We can see more than
// one instance of a given static symbol with the same name/version,
// so we can't add them to the lookup tables "as is". Instead assign
// them fictitious (unique) versions, starting at -1 and decreasing by
// one for each newly created symbol, and record them in the
// extStaticSyms hash.
func (l *Loader) Create(name string) *sym.Symbol {
	i := l.max + 1
	l.max++
	if l.extStart == 0 {
		l.extStart = i
	}

	// Assign a new unique negative version -- this is to mark the
	// symbol so that it can be skipped when ExtractSymbols is adding
	// ext syms to the sym.Symbols hash.
	l.anonVersion--
	ver := l.anonVersion
	l.growSyms(int(i))
	s := l.allocSym(name, ver)
	l.installSym(i, s)
	l.extStaticSyms[nameVer{name, ver}] = i

	return s
}

func loadObjFull(l *Loader, r *oReader) {
	lib := r.unit.Lib
	istart := l.startIndex(r)

	resolveSymRef := func(s goobj2.SymRef) *sym.Symbol {
		i := l.resolve(r, s)
		return l.Syms[i]
	}

	funcs := []funcInfoSym{}
	fdsyms := []*sym.Symbol{}
	var funcAllocCounts funcAllocInfo
	pcdataBase := r.PcdataBase()
	rslice := []Reloc{}
	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
		osym := goobj2.Sym{}
		osym.Read(r.Reader, r.SymOff(i))
		name := strings.Replace(osym.Name, "\"\".", r.pkgprefix, -1)
		if name == "" {
			continue
		}
		ver := abiToVer(osym.ABI, r.version)
		dupok := osym.Dupok()