loader.go

		su := l.MakeSymbolUpdater(s)
		su.SetType(sym.SRODATA)
		su.SetLocal(true)
		switch name[:5] {
		case "$f32.":
			if uint64(uint32(x)) != x {
				log.Panicf("$-symbol %s too large: %d", name, x)
			}
			su.AddUint32(arch, uint32(x))
		case "$f64.", "$i64.":
			su.AddUint64(arch, x)
		default:
			log.Panicf("unrecognized $-symbol: %s", name)
		}
	}
}

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

		// Copy relocations
		if needReloc {
			batch := l.relocBatch
			s.R = batch[:len(pp.relocs):len(pp.relocs)]
			l.relocBatch = batch[len(pp.relocs):]
			relocs := l.Relocs(i)
			l.convertRelocations(i, &relocs, s, false)
		}

		// Copy data
		s.P = pp.data

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

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

	// 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.
	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
				}
			}
		}
	}
}

// ResolveABIAlias given a symbol returns the ABI alias target of that
// symbol. If the sym in question is not an alias, the sym itself is
// returned.
func (l *Loader) ResolveABIAlias(s Sym) Sym {
	if l.SymType(s) != sym.SABIALIAS {
		return s
	}
	relocs := l.Relocs(s)
	target := relocs.At2(0).Sym()
	if l.SymType(target) == sym.SABIALIAS {
		panic(fmt.Sprintf("ABI alias %s references another ABI alias %s", l.SymName(s), l.SymName(target)))
	}
	return target
}

// 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. The parameter
// anonVerReplacement specifies a version number for any new anonymous
// symbols encountered on the list, when creating sym.Symbols for them
// (or zero if we don't expect to encounter any new anon symbols). 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 we may wipe out some information when copying
// back.

func (l *Loader) PropagateLoaderChangesToSymbols(toconvert []Sym, anonVerReplacement int) []*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.
	for _, cand := range toconvert {

		sn := l.SymName(cand)
		sv := l.SymVersion(cand)
		st := l.SymType(cand)
		if sv < 0 {
			if anonVerReplacement == 0 {
				panic("expected valid anon version replacement")
			}
			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 = l.SymLookup(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.
		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)
		if len(s.R) != relocs.Count() {
			s.R = make([]sym.Reloc, relocs.Count())
		}
		l.convertRelocations(cand, &relocs, 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) {
	// 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.Version < 0 {
			s.Version = int16(anonVerReplacement)
		}
	}

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

// 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
	s.SymIdx = sym.LoaderSym(i)
}

// 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
	l.growSyms(int(i))
	l.installSym(i, s)
	return s
}

// TopLevelSym tests a symbol (by name and kind) to determine whether
// the symbol first class sym (participating in the link) or is an
// anonymous aux or sub-symbol containing some sub-part or payload of
// another symbol.
func (l *Loader) TopLevelSym(s Sym) bool {
	return topLevelSym(l.RawSymName(s), l.SymType(s))
}

// topLevelSym tests a symbol name and kind to determine whether
// the symbol first class sym (participating in the link) or is an
// anonymous aux or sub-symbol containing some sub-part or payload of
// another symbol.
func topLevelSym(sname string, skind sym.SymKind) bool {
	if sname != "" {
		return true
	}
	switch skind {
	case sym.SDWARFINFO, sym.SDWARFRANGE, sym.SDWARFLOC, sym.SDWARFLINES, sym.SGOFUNC:
		return true
	default:
		return false
	}
}

// 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 {
	nr := 0
	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
		gi := r.syms[i]
		if r2, i2 := l.toLocal(gi); r2 != r || i2 != i {
			continue // come from a different object
		}
		osym := r.Sym(i)
		name := strings.Replace(osym.Name(r.Reader), "\"\".", r.pkgprefix, -1)
		t := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type())]

		// Skip non-dwarf anonymous symbols (e.g. funcdata),
		// since they will never be turned into sym.Symbols.
		if !topLevelSym(name, t) {
			continue
		}
		ver := abiToVer(osym.ABI(), r.version)
		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(gi) && name != "runtime.addmoduledata" && name != "runtime.lastmoduledatap" {
			// No need to load unreachable symbols.
			// XXX reference to runtime.addmoduledata may be generated later by the linker in plugin mode.
			continue
		}

		l.addNewSym(gi, name, ver, r.unit, t)
		nr += r.NReloc(i)
	}
	return nr
}

// cloneToExternal takes the existing object file symbol (symIdx)
// and creates a new external symbol payload 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 an external symbol
// payload.
// XXX maybe rename? makeExtPayload?
func (l *Loader) cloneToExternal(symIdx Sym) {
	if l.IsExternal(symIdx) {
		panic("sym is already external, no need for clone")
	}
	l.growSyms(int(symIdx))

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

	// Create new symbol, update version and kind.
	pi := l.newPayload(sname, sver)
	pp := l.payloads[pi]
	pp.kind = skind
	pp.ver = sver
	pp.size = int64(osym.Siz())
	pp.objidx = r.objidx

	// 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 = make([]goobj2.Reloc, relocs.Count())
		pp.reltypes = make([]objabi.RelocType, relocs.Count())
		for i := range pp.relocs {
			// Copy the relocs slice.
			// Convert local reference to global reference.
			rel := relocs.At2(i)
			pp.relocs[i].Set(rel.Off(), rel.Siz(), 0, rel.Add(), goobj2.SymRef{PkgIdx: 0, SymIdx: uint32(rel.Sym())})
			pp.reltypes[i] = rel.Type()
		}

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

	// If we're overriding a data symbol, collect the associated
	// Gotype, so as to propagate it to the new symbol.
	auxs := r.Auxs(li)
	pp.auxs = auxs
loop:
	for j := range auxs {
		a := &auxs[j]
		switch a.Type() {
		case goobj2.AuxGotype:
			pp.gotype = l.resolve(r, a.Sym())
			break loop
		default:
			// nothing to do
		}
	}

	// Install new payload to global index space.
	// (This needs to happen at the end, as the accessors above
	// need to access the old symbol content.)
	l.objSyms[symIdx] = objSym{l.extReader, pi}
	l.extReader.syms = append(l.extReader.syms, symIdx)
}

// Copy the payload of symbol src to dst. Both src and dst must be external
// symbols.
// The intended use case is that when building/linking against a shared library,
// where we do symbol name mangling, the Go object file may have reference to
// the original symbol name whereas the shared library provides a symbol with
// the mangled name. When we do mangling, we copy payload of mangled to original.
func (l *Loader) CopySym(src, dst Sym) {
	if !l.IsExternal(dst) {
		panic("dst is not external") //l.newExtSym(l.SymName(dst), l.SymVersion(dst))
	}
	if !l.IsExternal(src) {
		panic("src is not external") //l.cloneToExternal(src)
	}
	l.payloads[l.extIndex(dst)] = l.payloads[l.extIndex(src)]
	l.SetSymPkg(dst, l.SymPkg(src))
	// TODO: other attributes?
}

// CopyAttributes copies over all of the attributes of symbol 'src' to
// symbol 'dst'.
func (l *Loader) CopyAttributes(src Sym, dst Sym) {
	l.SetAttrReachable(dst, l.AttrReachable(src))
	l.SetAttrOnList(dst, l.AttrOnList(src))
	l.SetAttrLocal(dst, l.AttrLocal(src))
	l.SetAttrNotInSymbolTable(dst, l.AttrNotInSymbolTable(src))
	if l.IsExternal(dst) {
		l.SetAttrVisibilityHidden(dst, l.AttrVisibilityHidden(src))
		l.SetAttrDuplicateOK(dst, l.AttrDuplicateOK(src))
		l.SetAttrShared(dst, l.AttrShared(src))
		l.SetAttrExternal(dst, l.AttrExternal(src))
	} else {
		// Some attributes are modifiable only for external symbols.
		// In such cases, don't try to transfer over the attribute
		// from the source even if there is a clash. This comes up
		// when copying attributes from a dupOK ABI wrapper symbol to
		// the real target symbol (which may not be marked dupOK).
	}
	l.SetAttrTopFrame(dst, l.AttrTopFrame(src))
	l.SetAttrSpecial(dst, l.AttrSpecial(src))
	l.SetAttrCgoExportDynamic(dst, l.AttrCgoExportDynamic(src))
	l.SetAttrCgoExportStatic(dst, l.AttrCgoExportStatic(src))
	l.SetAttrReadOnly(dst, l.AttrReadOnly(src))
}

// migrateAttributes copies over all of the attributes of symbol 'src' to
// sym.Symbol 'dst'.
func (l *Loader) migrateAttributes(src Sym, dst *sym.Symbol) {
	dst.Value = l.SymValue(src)
	dst.Align = l.SymAlign(src)
	dst.Sect = l.SymSect(src)

	dst.Attr.Set(sym.AttrReachable, l.AttrReachable(src))
	dst.Attr.Set(sym.AttrOnList, l.AttrOnList(src))
	dst.Attr.Set(sym.AttrLocal, l.AttrLocal(src))
	dst.Attr.Set(sym.AttrNotInSymbolTable, l.AttrNotInSymbolTable(src))
	dst.Attr.Set(sym.AttrNoSplit, l.IsNoSplit(src))
	dst.Attr.Set(sym.AttrVisibilityHidden, l.AttrVisibilityHidden(src))
	dst.Attr.Set(sym.AttrDuplicateOK, l.AttrDuplicateOK(src))
	dst.Attr.Set(sym.AttrShared, l.AttrShared(src))
	dst.Attr.Set(sym.AttrExternal, l.AttrExternal(src))
	dst.Attr.Set(sym.AttrTopFrame, l.AttrTopFrame(src))
	dst.Attr.Set(sym.AttrSpecial, l.AttrSpecial(src))
	dst.Attr.Set(sym.AttrCgoExportDynamic, l.AttrCgoExportDynamic(src))
	dst.Attr.Set(sym.AttrCgoExportStatic, l.AttrCgoExportStatic(src))
	dst.Attr.Set(sym.AttrReadOnly, l.AttrReadOnly(src))

	// Convert outer relationship
	if outer, ok := l.outer[src]; ok {
		dst.Outer = l.Syms[outer]
	}

	// Set sub-symbol attribute. See the comment on the AttrSubSymbol
	// method for more on this, there is some tricky stuff here.
	dst.Attr.Set(sym.AttrSubSymbol, l.outer[src] != 0 && l.sub[l.outer[src]] != 0)

	// Copy over dynimplib, dynimpvers, extname.
	if name, ok := l.extname[src]; ok {
		dst.SetExtname(name)
	}
	if l.SymDynimplib(src) != "" {
		dst.SetDynimplib(l.SymDynimplib(src))
	}
	if l.SymDynimpvers(src) != "" {
		dst.SetDynimpvers(l.SymDynimpvers(src))
	}

	// Copy ELF type if set.
	if et, ok := l.elfType[src]; ok {
		dst.SetElfType(et)
	}

	// Copy pe objects values if set.
	if plt, ok := l.plt[src]; ok {
		dst.SetPlt(plt)
	}
	if got, ok := l.got[src]; ok {
		dst.SetGot(got)
	}

	// Copy dynid
	if dynid, ok := l.dynid[src]; ok {
		dst.Dynid = dynid
	}
}

// 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, ver int) Sym {
	return l.newExtSym(name, ver)
}

// CreateStaticSym creates a new static symbol with the specified name
// without adding it to any lookup tables, returning a Sym index for it.
func (l *Loader) CreateStaticSym(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)
}

func loadObjFull(l *Loader, r *oReader, needReloc bool) {
	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
		// A symbol may be a dup or overwritten. In this case, its
		// content will actually be provided by a different object
		// (to which its global index points). Skip those symbols.
		gi := l.toGlobal(r, i)
		if r2, i2 := l.toLocal(gi); r2 != r || i2 != i {
			continue
		}
		s := l.Syms[gi]
		if s == nil {
			continue
		}

		l.migrateAttributes(gi, s)
		// Be careful not to overwrite attributes set by the linker.
		// Don't use the attributes from the object file.

		osym := r.Sym(i)
		size := osym.Siz()

		// Symbol data
		s.P = l.OutData(gi)

		// Relocs
		if needReloc {
			relocs := l.relocs(r, i)
			batch := l.relocBatch
			s.R = batch[:relocs.Count():relocs.Count()]
			l.relocBatch = batch[relocs.Count():]
			l.convertRelocations(gi, &relocs, s, false)
		}

		// Aux symbol info
		auxs := r.Auxs(i)
		for j := range auxs {
			a := &auxs[j]
			switch a.Type() {
			case goobj2.AuxFuncInfo, goobj2.AuxFuncdata, goobj2.AuxGotype:
				// already handled
			case goobj2.AuxDwarfInfo, goobj2.AuxDwarfLoc, goobj2.AuxDwarfRanges, goobj2.AuxDwarfLines:
				// ignored for now
			default:
				panic("unknown aux type")
			}
		}

		if s.Size < int64(size) {
			s.Size = int64(size)
		}
	}
}

// convertRelocations takes a vector of loader.Reloc relocations and
// translates them into an equivalent set of sym.Reloc relocations on
// the symbol "dst", performing fixups along the way for ABI aliases,
// etc. It is assumed that the caller has pre-allocated the dst symbol
// relocations slice. If 'strict' is set, then this method will
// panic if it finds a relocation targeting a nil symbol.
func (l *Loader) convertRelocations(symIdx Sym, src *Relocs, dst *sym.Symbol, strict bool) {
	for j := range dst.R {
		r := src.At2(j)
		rs := r.Sym()
		sz := r.Siz()
		rt := r.Type()
		if rt == objabi.R_METHODOFF {
			if l.attrReachable.Has(rs) {
				rt = objabi.R_ADDROFF
			} else {
				sz = 0
				rs = 0
			}
		}
		if rt == objabi.R_WEAKADDROFF && !l.attrReachable.Has(rs) {
			rs = 0
			sz = 0
		}
		if rs != 0 && l.Syms[rs] != nil && l.Syms[rs].Type == sym.SABIALIAS {
			rsrelocs := l.Relocs(rs)
			rs = rsrelocs.At2(0).Sym()
		}
		if strict && rs != 0 && l.Syms[rs] == nil && rt != objabi.R_USETYPE {
			panic("nil reloc target in convertRelocations")
		}
		dst.R[j] = sym.Reloc{
			Off:  r.Off(),
			Siz:  sz,
			Type: rt,
			Add:  r.Add(),
			Sym:  l.Syms[rs],
		}
		if rv := l.RelocVariant(symIdx, j); rv != 0 {
			dst.R[j].InitExt()
			dst.R[j].Variant = rv
		}
	}
}

// relocId is essentially a <S,R> tuple identifying the Rth
// relocation of symbol S.
type relocId struct {
	sym  Sym
	ridx int
}

// SetRelocVariant sets the 'variant' property of a relocation on
// some specific symbol.
func (l *Loader) SetRelocVariant(s Sym, ri int, v sym.RelocVariant) {
	// sanity check
	if relocs := l.Relocs(s); ri >= relocs.Count() {
		panic("invalid relocation ID")
	}
	if l.relocVariant == nil {
		l.relocVariant = make(map[relocId]sym.RelocVariant)
	}
	if v != 0 {
		l.relocVariant[relocId{s, ri}] = v
	} else {
		delete(l.relocVariant, relocId{s, ri})
	}
}

// RelocVariant returns the 'variant' property of a relocation on
// some specific symbol.
func (l *Loader) RelocVariant(s Sym, ri int) sym.RelocVariant {
	return l.relocVariant[relocId{s, ri}]
}

// UndefinedRelocTargets iterates through the global symbol index
// space, looking for symbols with relocations targeting undefined
// references. The linker's loadlib method uses this to determine if
// there are unresolved references to functions in system libraries
// (for example, libgcc.a), presumably due to CGO code. Return
// value is a list of loader.Sym's corresponding to the undefined
// cross-refs. The "limit" param controls the maximum number of
// results returned; if "limit" is -1, then all undefs are returned.
func (l *Loader) UndefinedRelocTargets(limit int) []Sym {
	result := []Sym{}
	for si := Sym(1); si < Sym(len(l.objSyms)); si++ {
		relocs := l.Relocs(si)
		for ri := 0; ri < relocs.Count(); ri++ {
			r := relocs.At2(ri)
			rs := r.Sym()
			if rs != 0 && l.SymType(rs) == sym.SXREF && l.RawSymName(rs) != ".got" {
				result = append(result, rs)
				if limit != -1 && len(result) >= limit {
					break
				}
			}
		}
	}
	return result
}

// AssignTextSymbolOrder populates the Textp2 slices within each
// library and compilation unit, insuring that packages are laid down
// in dependency order (internal first, then everything else). Return value
// is a slice of all text syms.
func (l *Loader) AssignTextSymbolOrder(libs []*sym.Library, intlibs []bool, extsyms []Sym) []Sym {

	// Library Textp2 lists should be empty at this point.
	for _, lib := range libs {
		if len(lib.Textp2) != 0 {
			panic("expected empty Textp2 slice for library")
		}
		if len(lib.DupTextSyms2) != 0 {
			panic("expected empty DupTextSyms2 slice for library")
		}
	}

	// Used to record which dupok symbol we've assigned to a unit.
	// Can't use the onlist attribute here because it will need to
	// clear for the later assignment of the sym.Symbol to a unit.
	// NB: we can convert to using onList once we no longer have to
	// call the regular addToTextp.
	assignedToUnit := MakeBitmap(l.NSym() + 1)

	// Start off textp2 with reachable external syms.
	textp2 := []Sym{}
	for _, sym := range extsyms {
		if !l.attrReachable.Has(sym) {
			continue
		}
		textp2 = append(textp2, sym)
	}

	// Walk through all text symbols from Go object files and append
	// them to their corresponding library's textp2 list.
	for _, o := range l.objs[1:] {
		r := o.r
		lib := r.unit.Lib
		for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
			gi := l.toGlobal(r, i)
			if !l.attrReachable.Has(gi) {
				continue
			}
			osym := r.Sym(i)
			st := sym.AbiSymKindToSymKind[objabi.SymKind(osym.Type())]
			if st != sym.STEXT {
				continue
			}
			dupok := osym.Dupok()
			if r2, i2 := l.toLocal(gi); r2 != r || i2 != i {
				// A dupok text symbol is resolved to another package.
				// We still need to record its presence in the current
				// package, as the trampoline pass expects packages
				// are laid out in dependency order.
				lib.DupTextSyms2 = append(lib.DupTextSyms2, sym.LoaderSym(gi))
				continue // symbol in different object
			}
			if dupok {
				lib.DupTextSyms2 = append(lib.DupTextSyms2, sym.LoaderSym(gi))
				continue
			}

			lib.Textp2 = append(lib.Textp2, sym.LoaderSym(gi))
		}
	}

	// Now assemble global textp, and assign text symbols to units.
	for _, doInternal := range [2]bool{true, false} {
		for idx, lib := range libs {
			if intlibs[idx] != doInternal {
				continue
			}
			lists := [2][]sym.LoaderSym{lib.Textp2, lib.DupTextSyms2}
			for i, list := range lists {
				for _, s := range list {
					sym := Sym(s)
					if l.attrReachable.Has(sym) && !assignedToUnit.Has(sym) {
						textp2 = append(textp2, sym)
						unit := l.SymUnit(sym)
						if unit != nil {
							unit.Textp2 = append(unit.Textp2, s)
							assignedToUnit.Set(sym)
						}
						// Dupok symbols may be defined in multiple packages; the
						// associated package for a dupok sym is chosen sort of
						// arbitrarily (the first containing package that the linker
						// loads). Canonicalizes its Pkg to the package with which
						// it will be laid down in text.
						if i == 1 /* DupTextSyms2 */ && l.SymPkg(sym) != lib.Pkg {
							l.SetSymPkg(sym, lib.Pkg)
						}
					}
				}
			}
			lib.Textp2 = nil
			lib.DupTextSyms2 = nil
		}
	}

	return textp2
}

// ErrorReporter is a helper class for reporting errors.
type ErrorReporter struct {
	ldr              *Loader
	AfterErrorAction func()
}

// Errorf method logs an error message.
//
// After each error, the error actions function will be invoked; this
// will either terminate the link immediately (if -h option given)
// or it will keep a count and exit if more than 20 errors have been printed.
//
// Logging an error means that on exit cmd/link will delete any
// output file and return a non-zero error code.
//
func (reporter *ErrorReporter) Errorf(s Sym, format string, args ...interface{}) {
	if s != 0 && reporter.ldr.SymName(s) != "" {
		format = reporter.ldr.SymName(s) + ": " + format
	} else {
		format = fmt.Sprintf("sym %d: %s", s, format)
	}
	format += "\n"
	fmt.Fprintf(os.Stderr, format, args...)
	reporter.AfterErrorAction()
}

// GetErrorReporter returns the loader's associated error reporter.
func (l *Loader) GetErrorReporter() *ErrorReporter {
	return l.errorReporter
}

// Errorf method logs an error message. See ErrorReporter.Errorf for details.
func (l *Loader) Errorf(s Sym, format string, args ...interface{}) {
	l.errorReporter.Errorf(s, format, args...)
}

// For debugging.
func (l *Loader) Dump() {
	fmt.Println("objs")
	for _, obj := range l.objs {
		if obj.r != nil {
			fmt.Println(obj.i, obj.r.unit.Lib)
		}
	}
	fmt.Println("extStart:", l.extStart)
	fmt.Println("Nsyms:", len(l.objSyms))
	fmt.Println("syms")
	for i := Sym(1); i < Sym(len(l.objSyms)); i++ {
		pi := interface{}("")
		if l.IsExternal(i) {
			pi = fmt.Sprintf("<ext %d>", l.extIndex(i))
		}
		var s *sym.Symbol
		if int(i) < len(l.Syms) {
			s = l.Syms[i]
		}
		if s != nil {
			fmt.Println(i, s, s.Type, pi)
		} else {
			fmt.Println(i, l.SymName(i), "<not loaded>", pi)
		}
	}
	fmt.Println("symsByName")
	for name, i := range l.symsByName[0] {
		fmt.Println(i, name, 0)
	}
	for name, i := range l.symsByName[1] {
		fmt.Println(i, name, 1)
	}
	fmt.Println("payloads:")
	for i := range l.payloads {
		pp := l.payloads[i]
		fmt.Println(i, pp.name, pp.ver, pp.kind)
	}
}