loader.go

// Returns whether this symbol should be included in typelink.
func (l *Loader) IsTypelink(i Sym) bool {
	return l.SymAttr(i)&goobj2.SymFlagTypelink != 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) {
		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 >= Sym(len(l.objSyms)) || 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
	}
}

// SymValue returns the section of the i-th symbol. i is global index.
func (l *Loader) SymSect(i Sym) *sym.Section {
	if int(i) >= len(l.symSects) {
		// symSects is extended lazily -- it the sym in question is
		// outside the range of the existing slice, then we assume its
		// section has not yet been set.
		return nil
	}
	return l.sects[l.symSects[i]]
}

// SetSymValue sets the section of the i-th symbol. i is global index.
func (l *Loader) SetSymSect(i Sym, sect *sym.Section) {
	if int(i) >= len(l.symSects) {
		l.symSects = append(l.symSects, make([]uint16, l.NSym()-len(l.symSects))...)
	}
	l.symSects[i] = sect.Index
}

// growSects grows the slice used to store symbol sections.
func (l *Loader) growSects(reqLen int) {
	curLen := len(l.symSects)
	if reqLen > curLen {
		l.symSects = append(l.symSects, make([]uint16, reqLen+1-curLen)...)
	}
}

// NewSection creates a new (output) section.
func (l *Loader) NewSection() *sym.Section {
	sect := new(sym.Section)
	idx := len(l.sects)
	if idx != int(uint16(idx)) {
		panic("too many sections created")
	}
	sect.Index = uint16(idx)
	l.sects = append(l.sects, sect)
	return sect
}

// 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 {
	if s, ok := l.extname[i]; ok {
		return s
	}
	return l.SymName(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
	}
}

// SymPlt returns the plt value for pe symbols.
func (l *Loader) SymPlt(s Sym) int32 {
	if v, ok := l.plt[s]; ok {
		return v
	}
	return -1
}

// 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 == -1 {
		delete(l.plt, i)
	} else {
		l.plt[i] = v
	}
}

// SymGot returns the got value for pe symbols.
func (l *Loader) SymGot(s Sym) int32 {
	if v, ok := l.got[s]; ok {
		return v
	}
	return -1
}

// 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 SetGot")
	}
	if v == -1 {
		delete(l.got, i)
	} else {
		l.got[i] = v
	}
}

// SymDynid returns the "dynid" property for the specified symbol.
func (l *Loader) SymDynid(i Sym) int32 {
	if s, ok := l.dynid[i]; ok {
		return s
	}
	return -1
}

// SetSymDynid sets the "dynid" property for a symbol.
func (l *Loader) SetSymDynid(i Sym, val int32) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetSymDynid")
	}
	if val == -1 {
		delete(l.dynid, i)
	} else {
		l.dynid[i] = val
	}
}

// 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)
	auxs := r.Auxs(li)
	for j := range auxs {
		a := &auxs[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
}

// SymPkg returns the package where 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
// shared library), will hold the library name.
// NOTE: this correspondes to sym.Symbol.File field.
func (l *Loader) SymPkg(i Sym) string {
	if f, ok := l.symPkg[i]; ok {
		return f
	}
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		if pp.objidx != 0 {
			r := l.objs[pp.objidx].r
			return r.unit.Lib.Pkg
		}
		return ""
	}
	r, _ := l.toLocal(i)
	return r.unit.Lib.Pkg
}

// SetSymPkg sets the package/library for a symbol. This is
// needed mainly for external symbols, specifically those imported
// from shared libraries.
func (l *Loader) SetSymPkg(i Sym, pkg string) {
	// reject bad symbols
	if i >= Sym(len(l.objSyms)) || i == 0 {
		panic("bad symbol index in SetSymPkg")
	}
	l.symPkg[i] = pkg
}

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

// SetSymLocalentry sets the "local entry" 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 SetSymLocalentry")
	}
	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 "handle" to the j-th aux symbol of the i-th symbol.
func (l *Loader) Aux2(i Sym, j int) Aux2 {
	if l.IsExternal(i) {
		return Aux2{}
	}
	r, li := l.toLocal(i)
	if j >= r.NAux(li) {
		return Aux2{}
	}
	return Aux2{r.Aux(li, j), r, l}
}

// 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
	}
	r, li := l.toLocal(fnSymIdx)
	auxs := r.Auxs(li)
	for i := range auxs {
		a := &auxs[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
}

// 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]
}

// SetOuterSym sets the outer symbol of i to o (without setting
// sub symbols).
func (l *Loader) SetOuterSym(i Sym, o Sym) {
	if o != 0 {
		l.outer[i] = o
	} else {
		delete(l.outer, 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)
	}
}

func (relocs *Relocs) Count() int { return len(relocs.rs) }

// At2 returns the j-th reloc for a global symbol.
func (relocs *Relocs) At2(j int) Reloc2 {
	if relocs.l.isExtReader(relocs.r) {
		pp := relocs.l.payloads[relocs.li]
		return Reloc2{&relocs.rs[j], relocs.r, relocs.l, pp.reltypes[j]}
	}
	return Reloc2{&relocs.rs[j], relocs.r, relocs.l, 0}
}

// 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 rs []goobj2.Reloc
	if l.isExtReader(r) {
		pp := l.payloads[li]
		rs = pp.relocs
	} else {
		rs = r.Relocs(li)
	}
	return Relocs{
		rs: rs,
		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
	auxs    []goobj2.Aux
	lengths goobj2.FuncInfoLengths
}

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

func (fi *FuncInfo) Args() int {
	return int((*goobj2.FuncInfo)(nil).ReadArgs(fi.data))
}

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))
}

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

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

// Preload has to be called prior to invoking the various methods
// below related to pcdata, funcdataoff, files, and inltree nodes.
func (fi *FuncInfo) Preload() {
	fi.lengths = (*goobj2.FuncInfo)(nil).ReadFuncInfoLengths(fi.data)
}

func (fi *FuncInfo) Pcinline() []byte {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	pcinl, end := (*goobj2.FuncInfo)(nil).ReadPcinline(fi.data, fi.lengths.PcdataOff)
	return fi.r.BytesAt(fi.r.PcdataBase()+pcinl, int(end-pcinl))
}

func (fi *FuncInfo) NumPcdata() uint32 {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	return fi.lengths.NumPcdata
}

func (fi *FuncInfo) Pcdata(k int) []byte {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	pcdat, end := (*goobj2.FuncInfo)(nil).ReadPcdata(fi.data, fi.lengths.PcdataOff, uint32(k))
	return fi.r.BytesAt(fi.r.PcdataBase()+pcdat, int(end-pcdat))
}

func (fi *FuncInfo) NumFuncdataoff() uint32 {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	return fi.lengths.NumFuncdataoff
}

func (fi *FuncInfo) Funcdataoff(k int) int64 {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	return (*goobj2.FuncInfo)(nil).ReadFuncdataoff(fi.data, fi.lengths.FuncdataoffOff, uint32(k))
}

func (fi *FuncInfo) Funcdata(syms []Sym) []Sym {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	if int(fi.lengths.NumFuncdataoff) > cap(syms) {
		syms = make([]Sym, 0, fi.lengths.NumFuncdataoff)
	} else {
		syms = syms[:0]
	}
	for j := range fi.auxs {
		a := &fi.auxs[j]
		if a.Type() == goobj2.AuxFuncdata {
			syms = append(syms, fi.l.resolve(fi.r, a.Sym()))
		}
	}
	return syms
}

func (fi *FuncInfo) NumFile() uint32 {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	return fi.lengths.NumFile
}

func (fi *FuncInfo) File(k int) Sym {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	sr := (*goobj2.FuncInfo)(nil).ReadFile(fi.data, fi.lengths.FileOff, uint32(k))
	return fi.l.resolve(fi.r, sr)
}

type InlTreeNode struct {
	Parent   int32
	File     Sym
	Line     int32
	Func     Sym
	ParentPC int32
}

func (fi *FuncInfo) NumInlTree() uint32 {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	return fi.lengths.NumInlTree
}

func (fi *FuncInfo) InlTree(k int) InlTreeNode {
	if !fi.lengths.Initialized {
		panic("need to call Preload first")
	}
	node := (*goobj2.FuncInfo)(nil).ReadInlTree(fi.data, fi.lengths.InlTreeOff, uint32(k))
	return InlTreeNode{
		Parent:   node.Parent,
		File:     fi.l.resolve(fi.r, node.File),
		Line:     node.Line,
		Func:     fi.l.resolve(fi.r, node.Func),
		ParentPC: node.ParentPC,
	}
}

func (l *Loader) FuncInfo(i Sym) FuncInfo {
	var r *oReader
	var auxs []goobj2.Aux
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		if pp.objidx == 0 {
			return FuncInfo{}
		}
		r = l.objs[pp.objidx].r
		auxs = pp.auxs
	} else {
		var li int
		r, li = l.toLocal(i)
		auxs = r.Auxs(li)
	}
	for j := range auxs {
		a := &auxs[j]
		if a.Type() == goobj2.AuxFuncInfo {
			b := r.Data(int(a.Sym().SymIdx))
			return FuncInfo{l, r, b, auxs, goobj2.FuncInfoLengths{}}
		}
	}
	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 {
		if len(roObject) >= 8 && bytes.Equal(roObject[:8], []byte("\x00go114ld")) {
			log.Fatalf("found object file %s in old format, but -go115newobj is true\nset -go115newobj consistently in all -gcflags, -asmflags, and -ldflags", f.File().Name())
		}
		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 := r.Sym(i)
		name := strings.Replace(osym.Name(r.Reader), "\"\".", 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 osym.Local() {
			l.SetAttrLocal(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)
		}
		if a := osym.Align(); a != 0 {
			l.SetSymAlign(gi, int32(a))
		}
	}
}

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

func loadObjRefs(l *Loader, r *oReader, arch *sys.Arch) {
	ndef := r.NSym() + r.NNonpkgdef()
	for i, n := 0, r.NNonpkgref(); i < n; i++ {
		osym := r.Sym(ndef + i)
		name := strings.Replace(osym.Name(r.Reader), "\"\".", r.pkgprefix, -1)
		v := abiToVer(osym.ABI(), r.version)
		r.syms[ndef+i] = l.LookupOrCreateSym(name, v)
		gi := r.syms[ndef+i]
		if osym.Local() {
			l.SetAttrLocal(gi, true)
		}
		l.preprocess(arch, gi, name)
	}
}

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
}

// preprocess looks for integer/floating point constant symbols whose
// content is encoded into the symbol name, and promotes them into
// real symbols with RODATA type and a payload that matches the
// encoded content.
func (l *Loader) preprocess(arch *sys.Arch, s Sym, name string) {
	if name != "" && name[0] == '$' && len(name) > 5 && l.SymType(s) == 0 && len(l.Data(s)) == 0 {
		x, err := strconv.ParseUint(name[5:], 16, 64)
		if err != nil {
			log.Panicf("failed to parse $-symbol %s: %v", name, err)
		}
		su := l.MakeSymbolUpdater(s)
		su.SetType(sym.SRODATA)
		su.SetLocal(true)
		switch name[:5] {
		case "$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) {
	// 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
	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
		if pp.gotype != 0 {
			s.Gotype = l.Syms[pp.gotype]
		}
		if f, ok := l.symPkg[i]; ok {
			s.File = f
		} else if pp.objidx != 0 {
			s.File = l.objs[pp.objidx].r.unit.Lib.Pkg
		}

		// Copy relocations
		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)
	}

	// 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)