loader.go

}

// AttrTopFrame returns true for a function symbol that is an entry
// point, meaning that unwinders should stop when they hit this
// function.
func (l *Loader) AttrTopFrame(i Sym) bool {
	_, ok := l.attrTopFrame[i]
	return ok
}

// SetAttrTopFrame sets the "top frame" property for a symbol (see
// AttrTopFrame).
func (l *Loader) SetAttrTopFrame(i Sym, v bool) {
	if v {
		l.attrTopFrame[i] = struct{}{}
	} else {
		delete(l.attrTopFrame, i)
	}
}

// AttrSpecial returns true for a symbols that do not have their
// address (i.e. Value) computed by the usual mechanism of
// data.go:dodata() & data.go:address().
func (l *Loader) AttrSpecial(i Sym) bool {
	_, ok := l.attrSpecial[i]
	return ok
}

// SetAttrSpecial sets the "special" property for a symbol (see
// AttrSpecial).
func (l *Loader) SetAttrSpecial(i Sym, v bool) {
	if v {
		l.attrSpecial[i] = struct{}{}
	} else {
		delete(l.attrSpecial, i)
	}
}

// AttrCgoExportDynamic returns true for a symbol that has been
// specially marked via the "cgo_export_dynamic" compiler directive
// written by cgo (in response to //export directives in the source).
func (l *Loader) AttrCgoExportDynamic(i Sym) bool {
	_, ok := l.attrCgoExportDynamic[i]
	return ok
}

// SetAttrCgoExportDynamic sets the "cgo_export_dynamic" for a symbol
// (see AttrCgoExportDynamic).
func (l *Loader) SetAttrCgoExportDynamic(i Sym, v bool) {
	if v {
		l.attrCgoExportDynamic[i] = struct{}{}
	} else {
		delete(l.attrCgoExportDynamic, i)
	}
}

// AttrCgoExportStatic returns true for a symbol that has been
// specially marked via the "cgo_export_static" directive
// written by cgo.
func (l *Loader) AttrCgoExportStatic(i Sym) bool {
	_, ok := l.attrCgoExportStatic[i]
	return ok
}

// SetAttrCgoExportStatic sets the "cgo_export_static" for a symbol
// (see AttrCgoExportStatic).
func (l *Loader) SetAttrCgoExportStatic(i Sym, v bool) {
	if v {
		l.attrCgoExportStatic[i] = struct{}{}
	} else {
		delete(l.attrCgoExportStatic, i)
	}
}

// IsGeneratedSym returns true if a symbol's been previously marked as a
// generator symbol through the SetIsGeneratedSym. The functions for generator
// symbols are kept in the Link context.
func (l *Loader) IsGeneratedSym(i Sym) bool {
	_, ok := l.generatedSyms[i]
	return ok
}

// SetIsGeneratedSym marks symbols as generated symbols. Data shouldn't be
// stored in generated symbols, and a function is registered and called for
// each of these symbols.
func (l *Loader) SetIsGeneratedSym(i Sym, v bool) {
	if !l.IsExternal(i) {
		panic("only external symbols can be generated")
	}
	if v {
		l.generatedSyms[i] = struct{}{}
	} else {
		delete(l.generatedSyms, i)
	}
}

func (l *Loader) AttrCgoExport(i Sym) bool {
	return l.AttrCgoExportDynamic(i) || l.AttrCgoExportStatic(i)
}

// AttrReadOnly returns true for a symbol whose underlying data
// is stored via a read-only mmap.
func (l *Loader) AttrReadOnly(i Sym) bool {
	if v, ok := l.attrReadOnly[i]; ok {
		return v
	}
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		if pp.objidx != 0 {
			return l.objs[pp.objidx].r.ReadOnly()
		}
		return false
	}
	r, _ := l.toLocal(i)
	return r.ReadOnly()
}

// SetAttrReadOnly sets the "data is read only" property for a symbol
// (see AttrReadOnly).
func (l *Loader) SetAttrReadOnly(i Sym, v bool) {
	l.attrReadOnly[i] = v
}

// AttrSubSymbol returns true for symbols that are listed as a
// sub-symbol of some other outer symbol. The sub/outer mechanism is
// used when loading host objects (sections from the host object
// become regular linker symbols and symbols go on the Sub list of
// their section) and for constructing the global offset table when
// internally linking a dynamic executable.
//
// Note that in later stages of the linker, we set Outer(S) to some
// container symbol C, but don't set Sub(C). Thus we have two
// distinct scenarios:
//
// - Outer symbol covers the address ranges of its sub-symbols.
//   Outer.Sub is set in this case.
// - Outer symbol doesn't conver the address ranges. It is zero-sized
//   and doesn't have sub-symbols. In the case, the inner symbol is
//   not actually a "SubSymbol". (Tricky!)
//
// This method returns TRUE only for sub-symbols in the first scenario.
//
// FIXME: would be better to do away with this and have a better way
// to represent container symbols.

func (l *Loader) AttrSubSymbol(i Sym) bool {
	// we don't explicitly store this attribute any more -- return
	// a value based on the sub-symbol setting.
	o := l.OuterSym(i)
	if o == 0 {
		return false
	}
	return l.SubSym(o) != 0
}

// Note that we don't have a 'SetAttrSubSymbol' method in the loader;
// clients should instead use the AddInteriorSym method to establish
// containment relationships for host object symbols.

// Returns whether the i-th symbol has ReflectMethod attribute set.
func (l *Loader) IsReflectMethod(i Sym) bool {
	return l.SymAttr(i)&goobj2.SymFlagReflectMethod != 0
}

// Returns whether the i-th symbol is nosplit.
func (l *Loader) IsNoSplit(i Sym) bool {
	return l.SymAttr(i)&goobj2.SymFlagNoSplit != 0
}

// Returns whether this is a Go type symbol.
func (l *Loader) IsGoType(i Sym) bool {
	return l.SymAttr(i)&goobj2.SymFlagGoType != 0
}

// 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
}

// Return whether this is a trampoline of a deferreturn call.
func (l *Loader) IsDeferReturnTramp(i Sym) bool {
	return l.deferReturnTramp[i]
}

// Set that i is a trampoline of a deferreturn call.
func (l *Loader) SetIsDeferReturnTramp(i Sym, v bool) {
	l.deferReturnTramp[i] = v
}

// 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
}

// AddToSymValue adds to the value of the i-th symbol. i is the global index.
func (l *Loader) AddToSymValue(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)
}

// Returns the data of the i-th symbol in the output buffer.
func (l *Loader) OutData(i Sym) []byte {
	if int(i) < len(l.outdata) && l.outdata[i] != nil {
		return l.outdata[i]
	}
	return l.Data(i)
}

// SetOutData sets the position of the data of the i-th symbol in the output buffer.
// i is global index.
func (l *Loader) SetOutData(i Sym, data []byte) {
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		if pp != nil {
			pp.data = data
			return
		}
	}
	l.outdata[i] = data
}

// InitOutData initializes the slice used to store symbol output data.
func (l *Loader) InitOutData() {
	l.outdata = make([][]byte, l.extStart)
}

// SetExtRelocs sets the external relocations of the i-th symbol. i is global index.
func (l *Loader) SetExtRelocs(i Sym, relocs []ExtReloc) {
	l.extRelocs[i] = relocs
}

// InitExtRelocs initialize the slice used to store external relocations.
func (l *Loader) InitExtRelocs() {
	l.extRelocs = make([][]ExtReloc, l.NSym())
}

// SymAlign returns the alignment for a symbol.
func (l *Loader) SymAlign(i Sym) int32 {
	if int(i) >= len(l.align) {
		// align is extended lazily -- it the sym in question is
		// outside the range of the existing slice, then we assume its
		// alignment has not yet been set.
		return 0
	}
	// TODO: would it make sense to return an arch-specific
	// alignment depending on section type? E.g. STEXT => 32,
	// SDATA => 1, etc?
	abits := l.align[i]
	if abits == 0 {
		return 0
	}
	return int32(1 << (abits - 1))
}

// SetSymAlign sets the alignment for a symbol.
func (l *Loader) SetSymAlign(i Sym, align int32) {
	// Reject nonsense alignments.
	if align < 0 || align&(align-1) != 0 {
		panic("bad alignment value")
	}
	if int(i) >= len(l.align) {
		l.align = append(l.align, make([]uint8, l.NSym()-len(l.align))...)
	}
	if align == 0 {
		l.align[i] = 0
	}
	l.align[i] = uint8(bits.Len32(uint32(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]]
}

// SetSymSect 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
	}
}

// SymElfSym returns the ELF symbol index for a given loader
// symbol, assigned during ELF symtab generation.
func (l *Loader) SymElfSym(i Sym) int32 {
	return l.elfSym[i]
}

// SetSymElfSym sets the elf symbol index for a symbol.
func (l *Loader) SetSymElfSym(i Sym, es int32) {
	if i == 0 {
		panic("bad sym index")
	}
	if es == 0 {
		delete(l.elfSym, i)
	} else {
		l.elfSym[i] = es
	}
}

// SymLocalElfSym returns the "local" ELF symbol index for a given loader
// symbol, assigned during ELF symtab generation.
func (l *Loader) SymLocalElfSym(i Sym) int32 {
	return l.localElfSym[i]
}

// SetSymLocalElfSym sets the "local" elf symbol index for a symbol.
func (l *Loader) SetSymLocalElfSym(i Sym, es int32) {
	if i == 0 {
		panic("bad sym index")
	}
	if es == 0 {
		delete(l.localElfSym, i)
	} else {
		l.localElfSym[i] = es
	}
}

// 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
	}
}

// DynIdSyms returns the set of symbols for which dynID is set to an
// interesting (non-default) value. This is expected to be a fairly
// small set.
func (l *Loader) DynidSyms() []Sym {
	sl := make([]Sym, 0, len(l.dynid))
	for s := range l.dynid {
		sl = append(sl, s)
	}
	sort.Slice(sl, func(i, j int) bool { return sl[i] < sl[j] })
	return sl
}

// 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 {
	var r *oReader
	var auxs []goobj2.Aux
	if l.IsExternal(i) {
		pp := l.getPayload(i)
		r = l.objs[pp.objidx].r
		auxs = pp.auxs
	} else {
		var li uint32
		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.
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.SDWARFFCN {
				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
}

// AddInteriorSym sets up 'interior' as an interior symbol of
// container/payload symbol 'container'. An interior symbol does not
// itself have data, but gives a name to a subrange of the data in its
// container symbol. The container itself may or may not have a name.
// This method is intended primarily for use in the host object
// loaders, to capture the semantics of symbols and sections in an
// object file. When reading a host object file, we'll typically
// encounter a static section symbol (ex: ".text") containing content
// for a collection of functions, then a series of ELF (or macho, etc)
// symbol table entries each of which points into a sub-section
// (offset and length) of its corresponding container symbol. Within
// the go linker we create a loader.Sym for the container (which is
// expected to have the actual content/payload) and then a set of
// interior loader.Sym's that point into a portion of the container.
func (l *Loader) AddInteriorSym(container Sym, interior Sym) {
	// Container symbols are expected to have content/data.
	// NB: this restriction may turn out to be too strict (it's possible
	// to imagine a zero-sized container with an interior symbol pointing
	// into it); it's ok to relax or remove it if we counter an
	// oddball host object that triggers this.
	if l.SymSize(container) == 0 && len(l.Data(container)) == 0 {
		panic("unexpected empty container symbol")
	}
	// The interior symbols for a container are not expected to have
	// content/data or relocations.
	if len(l.Data(interior)) != 0 {
		panic("unexpected non-empty interior symbol")
	}
	// Interior symbol is expected to be in the symbol table.
	if l.AttrNotInSymbolTable(interior) {
		panic("interior symbol must be in symtab")
	}
	// Only a single level of containment is allowed.
	if l.OuterSym(container) != 0 {
		panic("outer has outer itself")
	}
	// Interior sym should not already have a sibling.
	if l.SubSym(interior) != 0 {
		panic("sub set for subsym")
	}
	// Interior sym should not already point at a container.
	if l.OuterSym(interior) != 0 {
		panic("outer already set for subsym")
	}
	l.sub[interior] = l.sub[container]
	l.sub[container] = interior
	l.outer[interior] = container
}

// 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]
}

// SetCarrierSym declares that 'c' is the carrier or container symbol
// for 's'. Carrier symbols are used in the linker to as a container
// for a collection of sub-symbols where the content of the
// sub-symbols is effectively concatenated to form the content of the
// carrier. The carrier is given a name in the output symbol table
// while the sub-symbol names are not. For example, the Go compiler
// emits named string symbols (type SGOSTRING) when compiling a
// package; after being deduplicated, these symbols are collected into
// a single unit by assigning them a new carrier symbol named
// "go.string.*" (which appears in the final symbol table for the
// output load module).
func (l *Loader) SetCarrierSym(s Sym, c Sym) {
	if c == 0 {
		panic("invalid carrier in SetCarrierSym")
	}
	if s == 0 {
		panic("invalid sub-symbol in SetCarrierSym")
	}
	// Carrier symbols are not expected to have content/data. It is
	// ok for them to have non-zero size (to allow for use of generator
	// symbols).
	if len(l.Data(c)) != 0 {
		panic("unexpected non-empty carrier symbol")
	}
	l.outer[s] = c
	// relocsym's foldSubSymbolOffset requires that we only
	// have a single level of containment-- enforce here.
	if l.outer[c] != 0 {
		panic("invalid nested carrier sym")
	}
}

// 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.attrUsedInIface = growBitmap(reqLen, l.attrUsedInIface)
	}
	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 uint32) 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,
	}
}

// ExtRelocs returns the external relocations of the i-th symbol.
func (l *Loader) ExtRelocs(i Sym) ExtRelocs {
	return ExtRelocs{l.Relocs(i), l.extRelocs[i]}
}

// ExtRelocs represents the set of external relocations of a symbol.
type ExtRelocs struct {
	rs Relocs
	es []ExtReloc
}

func (ers ExtRelocs) Count() int { return len(ers.es) }

func (ers ExtRelocs) At(j int) ExtRelocView {
	i := ers.es[j].Idx
	return ExtRelocView{ers.rs.At2(i), ers.es[j]}
}

// 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 {