src/debug/gosym/pclntab.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 /*
  * Line tables
  */

 package gosym

 import (
 	"bytes"
 	"encoding/binary"
 	"sort"
 	"sync"
 )

 // version of the pclntab
 type version int

 const (
 	verUnknown version = iota
 	ver11
 	ver12
 	ver116
 	ver118
 	ver120
 )

 // A LineTable is a data structure mapping program counters to line numbers.
 //
 // In Go 1.1 and earlier, each function (represented by a [Func]) had its own LineTable,
 // and the line number corresponded to a numbering of all source lines in the
 // program, across all files. That absolute line number would then have to be
 // converted separately to a file name and line number within the file.
 //
 // In Go 1.2, the format of the data changed so that there is a single LineTable
 // for the entire program, shared by all Funcs, and there are no absolute line
 // numbers, just line numbers within specific files.
 //
 // For the most part, LineTable's methods should be treated as an internal
 // detail of the package; callers should use the methods on [Table] instead.
 type LineTable struct {
 	Data []byte
 	PC   uint64
 	Line int

 	// This mutex is used to keep parsing of pclntab synchronous.
 	mu sync.Mutex

 	// Contains the version of the pclntab section.
 	version version

 	// Go 1.2/1.16/1.18 state
 	binary      binary.ByteOrder
 	quantum     uint32
 	ptrsize     uint32
 	textStart   uint64 // address of runtime.text symbol (1.18+)
 	funcnametab []byte
 	cutab       []byte
 	funcdata    []byte
 	functab     []byte
 	nfunctab    uint32
 	filetab     []byte
 	pctab       []byte // points to the pctables.
 	nfiletab    uint32
 	funcNames   map[uint32]string // cache the function names
 	strings     map[uint32]string // interned substrings of Data, keyed by offset
 	// fileMap varies depending on the version of the object file.
 	// For ver12, it maps the name to the index in the file table.
 	// For ver116, it maps the name to the offset in filetab.
 	fileMap map[string]uint32
 }

 // NOTE(rsc): This is wrong for GOARCH=arm, which uses a quantum of 4,
 // but we have no idea whether we're using arm or not. This only
 // matters in the old (pre-Go 1.2) symbol table format, so it's not worth
 // fixing.
 const oldQuantum = 1

 func (t *LineTable) parse(targetPC uint64, targetLine int) (b []byte, pc uint64, line int) {
 	// The PC/line table can be thought of as a sequence of
 	//  <pc update>* <line update>
 	// batches. Each update batch results in a (pc, line) pair,
 	// where line applies to every PC from pc up to but not
 	// including the pc of the next pair.
 	//
 	// Here we process each update individually, which simplifies
 	// the code, but makes the corner cases more confusing.
 	b, pc, line = t.Data, t.PC, t.Line
 	for pc <= targetPC && line != targetLine && len(b) > 0 {
 		code := b[0]
 		b = b[1:]
 		switch {
 		case code == 0:
 			if len(b) < 4 {
 				b = b[0:0]
 				break
 			}
 			val := binary.BigEndian.Uint32(b)
 			b = b[4:]
 			line += int(val)
 		case code <= 64:
 			line += int(code)
 		case code <= 128:
 			line -= int(code - 64)
 		default:
 			pc += oldQuantum * uint64(code-128)
 			continue
 		}
 		pc += oldQuantum
 	}
 	return b, pc, line
 }

 func (t *LineTable) slice(pc uint64) *LineTable {
 	data, pc, line := t.parse(pc, -1)
 	return &LineTable{Data: data, PC: pc, Line: line}
 }

 // PCToLine returns the line number for the given program counter.
 //
 // Deprecated: Use Table's PCToLine method instead.
 func (t *LineTable) PCToLine(pc uint64) int {
 	if t.isGo12() {
 		return t.go12PCToLine(pc)
 	}
 	_, _, line := t.parse(pc, -1)
 	return line
 }

 // LineToPC returns the program counter for the given line number,
 // considering only program counters before maxpc.
 //
 // Deprecated: Use Table's LineToPC method instead.
 func (t *LineTable) LineToPC(line int, maxpc uint64) uint64 {
 	if t.isGo12() {
 		return 0
 	}
 	_, pc, line1 := t.parse(maxpc, line)
 	if line1 != line {
 		return 0
 	}
 	// Subtract quantum from PC to account for post-line increment
 	return pc - oldQuantum
 }

 // NewLineTable returns a new PC/line table
 // corresponding to the encoded data.
 // Text must be the start address of the
 // corresponding text segment.
 func NewLineTable(data []byte, text uint64) *LineTable {
 	return &LineTable{Data: data, PC: text, Line: 0, funcNames: make(map[uint32]string), strings: make(map[uint32]string)}
 }

 // Go 1.2 symbol table format.
 // See golang.org/s/go12symtab.
 //
 // A general note about the methods here: rather than try to avoid
 // index out of bounds errors, we trust Go to detect them, and then
 // we recover from the panics and treat them as indicative of a malformed
 // or incomplete table.
 //
 // The methods called by symtab.go, which begin with "go12" prefixes,
 // are expected to have that recovery logic.

 // isGo12 reports whether this is a Go 1.2 (or later) symbol table.
 func (t *LineTable) isGo12() bool {
 	t.parsePclnTab()
 	return t.version >= ver12
 }

 const (
 	go12magic  = 0xfffffffb
 	go116magic = 0xfffffffa
 	go118magic = 0xfffffff0
 	go120magic = 0xfffffff1
 )

 // uintptr returns the pointer-sized value encoded at b.
 // The pointer size is dictated by the table being read.
 func (t *LineTable) uintptr(b []byte) uint64 {
 	if t.ptrsize == 4 {
 		return uint64(t.binary.Uint32(b))
 	}
 	return t.binary.Uint64(b)
 }

 // parsePclnTab parses the pclntab, setting the version.
 func (t *LineTable) parsePclnTab() {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 	if t.version != verUnknown {
 		return
 	}

 	// Note that during this function, setting the version is the last thing we do.
 	// If we set the version too early, and parsing failed (likely as a panic on
 	// slice lookups), we'd have a mistaken version.
 	//
 	// Error paths through this code will default the version to 1.1.
 	t.version = ver11

 	if !disableRecover {
 		defer func() {
 			// If we panic parsing, assume it's a Go 1.1 pclntab.
 			recover()
 		}()
 	}

 	// Check header: 4-byte magic, two zeros, pc quantum, pointer size.
 	if len(t.Data) < 16 || t.Data[4] != 0 || t.Data[5] != 0 ||
 		(t.Data[6] != 1 && t.Data[6] != 2 && t.Data[6] != 4) || // pc quantum
 		(t.Data[7] != 4 && t.Data[7] != 8) { // pointer size
 		return
 	}

 	var possibleVersion version
 	leMagic := binary.LittleEndian.Uint32(t.Data)
 	beMagic := binary.BigEndian.Uint32(t.Data)
 	switch {
 	case leMagic == go12magic:
 		t.binary, possibleVersion = binary.LittleEndian, ver12
 	case beMagic == go12magic:
 		t.binary, possibleVersion = binary.BigEndian, ver12
 	case leMagic == go116magic:
 		t.binary, possibleVersion = binary.LittleEndian, ver116
 	case beMagic == go116magic:
 		t.binary, possibleVersion = binary.BigEndian, ver116
 	case leMagic == go118magic:
 		t.binary, possibleVersion = binary.LittleEndian, ver118
 	case beMagic == go118magic:
 		t.binary, possibleVersion = binary.BigEndian, ver118
 	case leMagic == go120magic:
 		t.binary, possibleVersion = binary.LittleEndian, ver120
 	case beMagic == go120magic:
 		t.binary, possibleVersion = binary.BigEndian, ver120
 	default:
 		return
 	}
 	t.version = possibleVersion

 	// quantum and ptrSize are the same between 1.2, 1.16, and 1.18
 	t.quantum = uint32(t.Data[6])
 	t.ptrsize = uint32(t.Data[7])

 	offset := func(word uint32) uint64 {
 		return t.uintptr(t.Data[8+word*t.ptrsize:])
 	}
 	data := func(word uint32) []byte {
 		return t.Data[offset(word):]
 	}

 	switch possibleVersion {
 	case ver118, ver120:
 		t.nfunctab = uint32(offset(0))
 		t.nfiletab = uint32(offset(1))
 		t.textStart = t.PC // use the start PC instead of reading from the table, which may be unrelocated
 		t.funcnametab = data(3)
 		t.cutab = data(4)
 		t.filetab = data(5)
 		t.pctab = data(6)
 		t.funcdata = data(7)
 		t.functab = data(7)
 		functabsize := (int(t.nfunctab)*2 + 1) * t.functabFieldSize()
 		t.functab = t.functab[:functabsize]
 	case ver116:
 		t.nfunctab = uint32(offset(0))
 		t.nfiletab = uint32(offset(1))
 		t.funcnametab = data(2)
 		t.cutab = data(3)
 		t.filetab = data(4)
 		t.pctab = data(5)
 		t.funcdata = data(6)
 		t.functab = data(6)
 		functabsize := (int(t.nfunctab)*2 + 1) * t.functabFieldSize()
 		t.functab = t.functab[:functabsize]
 	case ver12:
 		t.nfunctab = uint32(t.uintptr(t.Data[8:]))
 		t.funcdata = t.Data
 		t.funcnametab = t.Data
 		t.functab = t.Data[8+t.ptrsize:]
 		t.pctab = t.Data
 		functabsize := (int(t.nfunctab)*2 + 1) * t.functabFieldSize()
 		fileoff := t.binary.Uint32(t.functab[functabsize:])
 		t.functab = t.functab[:functabsize]
 		t.filetab = t.Data[fileoff:]
 		t.nfiletab = t.binary.Uint32(t.filetab)
 		t.filetab = t.filetab[:t.nfiletab*4]
 	default:
 		panic("unreachable")
 	}
 }

 // go12Funcs returns a slice of Funcs derived from the Go 1.2+ pcln table.
 func (t *LineTable) go12Funcs() []Func {
 	// Assume it is malformed and return nil on error.
 	if !disableRecover {
 		defer func() {
 			recover()
 		}()
 	}

 	ft := t.funcTab()
 	funcs := make([]Func, ft.Count())
 	syms := make([]Sym, len(funcs))
 	for i := range funcs {
 		f := &funcs[i]
 		f.Entry = ft.pc(i)
 		f.End = ft.pc(i + 1)
 		info := t.funcData(uint32(i))
 		f.LineTable = t
 		f.FrameSize = int(info.deferreturn())
 		syms[i] = Sym{
 			Value:     f.Entry,
 			Type:      'T',
 			Name:      t.funcName(info.nameOff()),
 			GoType:    0,
 			Func:      f,
 			goVersion: t.version,
 		}
 		f.Sym = &syms[i]
 	}
 	return funcs
 }

 // findFunc returns the funcData corresponding to the given program counter.
 func (t *LineTable) findFunc(pc uint64) funcData {
 	ft := t.funcTab()
 	if pc < ft.pc(0) || pc >= ft.pc(ft.Count()) {
 		return funcData{}
 	}
 	idx := sort.Search(int(t.nfunctab), func(i int) bool {
 		return ft.pc(i) > pc
 	})
 	idx--
 	return t.funcData(uint32(idx))
 }

 // readvarint reads, removes, and returns a varint from *pp.
 func (t *LineTable) readvarint(pp *[]byte) uint32 {
 	var v, shift uint32
 	p := *pp
 	for shift = 0; ; shift += 7 {
 		b := p[0]
 		p = p[1:]
 		v |= (uint32(b) & 0x7F) << shift
 		if b&0x80 == 0 {
 			break
 		}
 	}
 	*pp = p
 	return v
 }

 // funcName returns the name of the function found at off.
 func (t *LineTable) funcName(off uint32) string {
 	if s, ok := t.funcNames[off]; ok {
 		return s
 	}
 	i := bytes.IndexByte(t.funcnametab[off:], 0)
 	s := string(t.funcnametab[off : off+uint32(i)])
 	t.funcNames[off] = s
 	return s
 }

 // stringFrom returns a Go string found at off from a position.
 func (t *LineTable) stringFrom(arr []byte, off uint32) string {
 	if s, ok := t.strings[off]; ok {
 		return s
 	}
 	i := bytes.IndexByte(arr[off:], 0)
 	s := string(arr[off : off+uint32(i)])
 	t.strings[off] = s
 	return s
 }

 // string returns a Go string found at off.
 func (t *LineTable) string(off uint32) string {
 	return t.stringFrom(t.funcdata, off)
 }

 // functabFieldSize returns the size in bytes of a single functab field.
 func (t *LineTable) functabFieldSize() int {
 	if t.version >= ver118 {
 		return 4
 	}
 	return int(t.ptrsize)
 }

 // funcTab returns t's funcTab.
 func (t *LineTable) funcTab() funcTab {
 	return funcTab{LineTable: t, sz: t.functabFieldSize()}
 }

 // funcTab is memory corresponding to a slice of functab structs, followed by an invalid PC.
 // A functab struct is a PC and a func offset.
 type funcTab struct {
 	*LineTable
 	sz int // cached result of t.functabFieldSize
 }

 // Count returns the number of func entries in f.
 func (f funcTab) Count() int {
 	return int(f.nfunctab)
 }

 // pc returns the PC of the i'th func in f.
 func (f funcTab) pc(i int) uint64 {
 	u := f.uint(f.functab[2*i*f.sz:])
 	if f.version >= ver118 {
 		u += f.textStart
 	}
 	return u
 }

 // funcOff returns the funcdata offset of the i'th func in f.
 func (f funcTab) funcOff(i int) uint64 {
 	return f.uint(f.functab[(2*i+1)*f.sz:])
 }

 // uint returns the uint stored at b.
 func (f funcTab) uint(b []byte) uint64 {
 	if f.sz == 4 {
 		return uint64(f.binary.Uint32(b))
 	}
 	return f.binary.Uint64(b)
 }

 // funcData is memory corresponding to an _func struct.
 type funcData struct {
 	t    *LineTable // LineTable this data is a part of
 	data []byte     // raw memory for the function
 }

 // funcData returns the ith funcData in t.functab.
 func (t *LineTable) funcData(i uint32) funcData {
 	data := t.funcdata[t.funcTab().funcOff(int(i)):]
 	return funcData{t: t, data: data}
 }

 // IsZero reports whether f is the zero value.
 func (f funcData) IsZero() bool {
 	return f.t == nil && f.data == nil
 }

 // entryPC returns the func's entry PC.
 func (f *funcData) entryPC() uint64 {
 	// In Go 1.18, the first field of _func changed
 	// from a uintptr entry PC to a uint32 entry offset.
 	if f.t.version >= ver118 {
 		// TODO: support multiple text sections.
 		// See runtime/symtab.go:(*moduledata).textAddr.
 		return uint64(f.t.binary.Uint32(f.data)) + f.t.textStart
 	}
 	return f.t.uintptr(f.data)
 }

 func (f funcData) nameOff() uint32     { return f.field(1) }
 func (f funcData) deferreturn() uint32 { return f.field(3) }
 func (f funcData) pcfile() uint32      { return f.field(5) }
 func (f funcData) pcln() uint32        { return f.field(6) }
 func (f funcData) cuOffset() uint32    { return f.field(8) }

 // field returns the nth field of the _func struct.
 // It panics if n == 0 or n > 9; for n == 0, call f.entryPC.
 // Most callers should use a named field accessor (just above).
 func (f funcData) field(n uint32) uint32 {
 	if n == 0 || n > 9 {
 		panic("bad funcdata field")
 	}
 	// In Go 1.18, the first field of _func changed
 	// from a uintptr entry PC to a uint32 entry offset.
 	sz0 := f.t.ptrsize
 	if f.t.version >= ver118 {
 		sz0 = 4
 	}
 	off := sz0 + (n-1)*4 // subsequent fields are 4 bytes each
 	data := f.data[off:]
 	return f.t.binary.Uint32(data)
 }

 // step advances to the next pc, value pair in the encoded table.
 func (t *LineTable) step(p *[]byte, pc *uint64, val *int32, first bool) bool {
 	uvdelta := t.readvarint(p)
 	if uvdelta == 0 && !first {
 		return false
 	}
 	if uvdelta&1 != 0 {
 		uvdelta = ^(uvdelta >> 1)
 	} else {
 		uvdelta >>= 1
 	}
 	vdelta := int32(uvdelta)
 	pcdelta := t.readvarint(p) * t.quantum
 	*pc += uint64(pcdelta)
 	*val += vdelta
 	return true
 }

 // pcvalue reports the value associated with the target pc.
 // off is the offset to the beginning of the pc-value table,
 // and entry is the start PC for the corresponding function.
 func (t *LineTable) pcvalue(off uint32, entry, targetpc uint64) int32 {
 	p := t.pctab[off:]

 	val := int32(-1)
 	pc := entry
 	for t.step(&p, &pc, &val, pc == entry) {
 		if targetpc < pc {
 			return val
 		}
 	}
 	return -1
 }

 // findFileLine scans one function in the binary looking for a
 // program counter in the given file on the given line.
 // It does so by running the pc-value tables mapping program counter
 // to file number. Since most functions come from a single file, these
 // are usually short and quick to scan. If a file match is found, then the
 // code goes to the expense of looking for a simultaneous line number match.
 func (t *LineTable) findFileLine(entry uint64, filetab, linetab uint32, filenum, line int32, cutab []byte) uint64 {
 	if filetab == 0 || linetab == 0 {
 		return 0
 	}

 	fp := t.pctab[filetab:]
 	fl := t.pctab[linetab:]
 	fileVal := int32(-1)
 	filePC := entry
 	lineVal := int32(-1)
 	linePC := entry
 	fileStartPC := filePC
 	for t.step(&fp, &filePC, &fileVal, filePC == entry) {
 		fileIndex := fileVal
 		if t.version == ver116 || t.version == ver118 || t.version == ver120 {
 			fileIndex = int32(t.binary.Uint32(cutab[fileVal*4:]))
 		}
 		if fileIndex == filenum && fileStartPC < filePC {
 			// fileIndex is in effect starting at fileStartPC up to
 			// but not including filePC, and it's the file we want.
 			// Run the PC table looking for a matching line number
 			// or until we reach filePC.
 			lineStartPC := linePC
 			for linePC < filePC && t.step(&fl, &linePC, &lineVal, linePC == entry) {
 				// lineVal is in effect until linePC, and lineStartPC < filePC.
 				if lineVal == line {
 					if fileStartPC <= lineStartPC {
 						return lineStartPC
 					}
 					if fileStartPC < linePC {
 						return fileStartPC
 					}
 				}
 				lineStartPC = linePC
 			}
 		}
 		fileStartPC = filePC
 	}
 	return 0
 }

 // go12PCToLine maps program counter to line number for the Go 1.2+ pcln table.
 func (t *LineTable) go12PCToLine(pc uint64) (line int) {
 	defer func() {
 		if !disableRecover && recover() != nil {
 			line = -1
 		}
 	}()

 	f := t.findFunc(pc)
 	if f.IsZero() {
 		return -1
 	}
 	entry := f.entryPC()
 	linetab := f.pcln()
 	return int(t.pcvalue(linetab, entry, pc))
 }

 // go12PCToFile maps program counter to file name for the Go 1.2+ pcln table.
 func (t *LineTable) go12PCToFile(pc uint64) (file string) {
 	defer func() {
 		if !disableRecover && recover() != nil {
 			file = ""
 		}
 	}()

 	f := t.findFunc(pc)
 	if f.IsZero() {
 		return ""
 	}
 	entry := f.entryPC()
 	filetab := f.pcfile()
 	fno := t.pcvalue(filetab, entry, pc)
 	if t.version == ver12 {
 		if fno <= 0 {
 			return ""
 		}
 		return t.string(t.binary.Uint32(t.filetab[4*fno:]))
 	}
 	// Go ≥ 1.16
 	if fno < 0 { // 0 is valid for ≥ 1.16
 		return ""
 	}
 	cuoff := f.cuOffset()
 	if fnoff := t.binary.Uint32(t.cutab[(cuoff+uint32(fno))*4:]); fnoff != ^uint32(0) {
 		return t.stringFrom(t.filetab, fnoff)
 	}
 	return ""
 }

 // go12LineToPC maps a (file, line) pair to a program counter for the Go 1.2+ pcln table.
 func (t *LineTable) go12LineToPC(file string, line int) (pc uint64) {
 	defer func() {
 		if !disableRecover && recover() != nil {
 			pc = 0
 		}
 	}()

 	t.initFileMap()
 	filenum, ok := t.fileMap[file]
 	if !ok {
 		return 0
 	}

 	// Scan all functions.
 	// If this turns out to be a bottleneck, we could build a map[int32][]int32
 	// mapping file number to a list of functions with code from that file.
 	var cutab []byte
 	for i := uint32(0); i < t.nfunctab; i++ {
 		f := t.funcData(i)
 		entry := f.entryPC()
 		filetab := f.pcfile()
 		linetab := f.pcln()
 		if t.version == ver116 || t.version == ver118 || t.version == ver120 {
 			if f.cuOffset() == ^uint32(0) {
 				// skip functions without compilation unit (not real function, or linker generated)
 				continue
 			}
 			cutab = t.cutab[f.cuOffset()*4:]
 		}
 		pc := t.findFileLine(entry, filetab, linetab, int32(filenum), int32(line), cutab)
 		if pc != 0 {
 			return pc
 		}
 	}
 	return 0
 }

 // initFileMap initializes the map from file name to file number.
 func (t *LineTable) initFileMap() {
 	t.mu.Lock()
 	defer t.mu.Unlock()

 	if t.fileMap != nil {
 		return
 	}
 	m := make(map[string]uint32)

 	if t.version == ver12 {
 		for i := uint32(1); i < t.nfiletab; i++ {
 			s := t.string(t.binary.Uint32(t.filetab[4*i:]))
 			m[s] = i
 		}
 	} else {
 		var pos uint32
 		for i := uint32(0); i < t.nfiletab; i++ {
 			s := t.stringFrom(t.filetab, pos)
 			m[s] = pos
 			pos += uint32(len(s) + 1)
 		}
 	}
 	t.fileMap = m
 }

 // go12MapFiles adds to m a key for every file in the Go 1.2 LineTable.
 // Every key maps to obj. That's not a very interesting map, but it provides
 // a way for callers to obtain the list of files in the program.
 func (t *LineTable) go12MapFiles(m map[string]*Obj, obj *Obj) {
 	if !disableRecover {
 		defer func() {
 			recover()
 		}()
 	}

 	t.initFileMap()
 	for file := range t.fileMap {
 		m[file] = obj
 	}
 }

 // disableRecover causes this package not to swallow panics.
 // This is useful when making changes.
 const disableRecover = false
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	/*
	* Line tables
	*/

	package gosym

	import (
	"bytes"
	"encoding/binary"
	"sort"
	"sync"
	)

	// version of the pclntab
	type version int

	const (
	verUnknown version = iota
	ver11
	ver12
	ver116
	ver118
	ver120
	)

	// A LineTable is a data structure mapping program counters to line numbers.
	//
	// In Go 1.1 and earlier, each function (represented by a [Func]) had its own LineTable,
	// and the line number corresponded to a numbering of all source lines in the
	// program, across all files. That absolute line number would then have to be
	// converted separately to a file name and line number within the file.
	//
	// In Go 1.2, the format of the data changed so that there is a single LineTable
	// for the entire program, shared by all Funcs, and there are no absolute line
	// numbers, just line numbers within specific files.
	//
	// For the most part, LineTable's methods should be treated as an internal
	// detail of the package; callers should use the methods on [Table] instead.
	type LineTable struct {
	Data []byte
	PC uint64
	Line int

	// This mutex is used to keep parsing of pclntab synchronous.
	mu sync.Mutex

	// Contains the version of the pclntab section.
	version version

	// Go 1.2/1.16/1.18 state
	binary binary.ByteOrder
	quantum uint32
	ptrsize uint32
	textStart uint64 // address of runtime.text symbol (1.18+)
	funcnametab []byte
	cutab []byte
	funcdata []byte
	functab []byte
	nfunctab uint32
	filetab []byte
	pctab []byte // points to the pctables.
	nfiletab uint32
	funcNames map[uint32]string // cache the function names
	strings map[uint32]string // interned substrings of Data, keyed by offset
	// fileMap varies depending on the version of the object file.
	// For ver12, it maps the name to the index in the file table.
	// For ver116, it maps the name to the offset in filetab.
	fileMap map[string]uint32
	}

	// NOTE(rsc): This is wrong for GOARCH=arm, which uses a quantum of 4,
	// but we have no idea whether we're using arm or not. This only
	// matters in the old (pre-Go 1.2) symbol table format, so it's not worth
	// fixing.
	const oldQuantum = 1

	func (t *LineTable) parse(targetPC uint64, targetLine int) (b []byte, pc uint64, line int) {
	// The PC/line table can be thought of as a sequence of
	// <pc update>* <line update>
	// batches. Each update batch results in a (pc, line) pair,
	// where line applies to every PC from pc up to but not
	// including the pc of the next pair.
	//
	// Here we process each update individually, which simplifies
	// the code, but makes the corner cases more confusing.
	b, pc, line = t.Data, t.PC, t.Line
	for pc <= targetPC && line != targetLine && len(b) > 0 {
	code := b[0]
	b = b[1:]
	switch {
	case code == 0:
	if len(b) < 4 {
	b = b[0:0]
	break
	}
	val := binary.BigEndian.Uint32(b)
	b = b[4:]
	line += int(val)
	case code <= 64:
	line += int(code)
	case code <= 128:
	line -= int(code - 64)
	default:
	pc += oldQuantum * uint64(code-128)
	continue
	}
	pc += oldQuantum
	}
	return b, pc, line
	}

	func (t LineTable) slice(pc uint64) LineTable {
	data, pc, line := t.parse(pc, -1)
	return &LineTable{Data: data, PC: pc, Line: line}
	}

	// PCToLine returns the line number for the given program counter.
	//
	// Deprecated: Use Table's PCToLine method instead.
	func (t *LineTable) PCToLine(pc uint64) int {
	if t.isGo12() {
	return t.go12PCToLine(pc)
	}
	_, _, line := t.parse(pc, -1)
	return line
	}

	// LineToPC returns the program counter for the given line number,
	// considering only program counters before maxpc.
	//
	// Deprecated: Use Table's LineToPC method instead.
	func (t *LineTable) LineToPC(line int, maxpc uint64) uint64 {
	if t.isGo12() {
	return 0
	}
	_, pc, line1 := t.parse(maxpc, line)
	if line1 != line {
	return 0
	}
	// Subtract quantum from PC to account for post-line increment
	return pc - oldQuantum
	}

	// NewLineTable returns a new PC/line table
	// corresponding to the encoded data.
	// Text must be the start address of the
	// corresponding text segment.
	func NewLineTable(data []byte, text uint64) *LineTable {
	return &LineTable{Data: data, PC: text, Line: 0, funcNames: make(map[uint32]string), strings: make(map[uint32]string)}
	}

	// Go 1.2 symbol table format.
	// See golang.org/s/go12symtab.
	//
	// A general note about the methods here: rather than try to avoid
	// index out of bounds errors, we trust Go to detect them, and then
	// we recover from the panics and treat them as indicative of a malformed
	// or incomplete table.
	//
	// The methods called by symtab.go, which begin with "go12" prefixes,
	// are expected to have that recovery logic.

	// isGo12 reports whether this is a Go 1.2 (or later) symbol table.
	func (t *LineTable) isGo12() bool {
	t.parsePclnTab()
	return t.version >= ver12
	}

	const (
	go12magic = 0xfffffffb
	go116magic = 0xfffffffa
	go118magic = 0xfffffff0
	go120magic = 0xfffffff1
	)

	// uintptr returns the pointer-sized value encoded at b.
	// The pointer size is dictated by the table being read.
	func (t *LineTable) uintptr(b []byte) uint64 {
	if t.ptrsize == 4 {
	return uint64(t.binary.Uint32(b))
	}
	return t.binary.Uint64(b)
	}

	// parsePclnTab parses the pclntab, setting the version.
	func (t *LineTable) parsePclnTab() {
	t.mu.Lock()
	defer t.mu.Unlock()
	if t.version != verUnknown {
	return
	}

	// Note that during this function, setting the version is the last thing we do.
	// If we set the version too early, and parsing failed (likely as a panic on
	// slice lookups), we'd have a mistaken version.
	//
	// Error paths through this code will default the version to 1.1.
	t.version = ver11

	if !disableRecover {
	defer func() {
	// If we panic parsing, assume it's a Go 1.1 pclntab.
	recover()
	}()
	}

	// Check header: 4-byte magic, two zeros, pc quantum, pointer size.
	if len(t.Data) < 16 \|\| t.Data[4] != 0 \|\| t.Data[5] != 0 \|\|
	(t.Data[6] != 1 && t.Data[6] != 2 && t.Data[6] != 4) \|\| // pc quantum
	(t.Data[7] != 4 && t.Data[7] != 8) { // pointer size
	return
	}

	var possibleVersion version
	leMagic := binary.LittleEndian.Uint32(t.Data)
	beMagic := binary.BigEndian.Uint32(t.Data)
	switch {
	case leMagic == go12magic:
	t.binary, possibleVersion = binary.LittleEndian, ver12
	case beMagic == go12magic:
	t.binary, possibleVersion = binary.BigEndian, ver12
	case leMagic == go116magic:
	t.binary, possibleVersion = binary.LittleEndian, ver116
	case beMagic == go116magic:
	t.binary, possibleVersion = binary.BigEndian, ver116
	case leMagic == go118magic:
	t.binary, possibleVersion = binary.LittleEndian, ver118
	case beMagic == go118magic:
	t.binary, possibleVersion = binary.BigEndian, ver118
	case leMagic == go120magic:
	t.binary, possibleVersion = binary.LittleEndian, ver120
	case beMagic == go120magic:
	t.binary, possibleVersion = binary.BigEndian, ver120
	default:
	return
	}
	t.version = possibleVersion

	// quantum and ptrSize are the same between 1.2, 1.16, and 1.18
	t.quantum = uint32(t.Data[6])
	t.ptrsize = uint32(t.Data[7])

	offset := func(word uint32) uint64 {
	return t.uintptr(t.Data[8+word*t.ptrsize:])
	}
	data := func(word uint32) []byte {
	return t.Data[offset(word):]
	}

	switch possibleVersion {
	case ver118, ver120:
	t.nfunctab = uint32(offset(0))
	t.nfiletab = uint32(offset(1))
	t.textStart = t.PC // use the start PC instead of reading from the table, which may be unrelocated
	t.funcnametab = data(3)
	t.cutab = data(4)
	t.filetab = data(5)
	t.pctab = data(6)
	t.funcdata = data(7)
	t.functab = data(7)
	functabsize := (int(t.nfunctab)2 + 1) t.functabFieldSize()
	t.functab = t.functab[:functabsize]
	case ver116:
	t.nfunctab = uint32(offset(0))
	t.nfiletab = uint32(offset(1))
	t.funcnametab = data(2)
	t.cutab = data(3)
	t.filetab = data(4)
	t.pctab = data(5)
	t.funcdata = data(6)
	t.functab = data(6)
	functabsize := (int(t.nfunctab)2 + 1) t.functabFieldSize()
	t.functab = t.functab[:functabsize]
	case ver12:
	t.nfunctab = uint32(t.uintptr(t.Data[8:]))
	t.funcdata = t.Data
	t.funcnametab = t.Data
	t.functab = t.Data[8+t.ptrsize:]
	t.pctab = t.Data
	functabsize := (int(t.nfunctab)2 + 1) t.functabFieldSize()
	fileoff := t.binary.Uint32(t.functab[functabsize:])
	t.functab = t.functab[:functabsize]
	t.filetab = t.Data[fileoff:]
	t.nfiletab = t.binary.Uint32(t.filetab)
	t.filetab = t.filetab[:t.nfiletab*4]
	default:
	panic("unreachable")
	}
	}

	// go12Funcs returns a slice of Funcs derived from the Go 1.2+ pcln table.
	func (t *LineTable) go12Funcs() []Func {
	// Assume it is malformed and return nil on error.
	if !disableRecover {
	defer func() {
	recover()
	}()
	}

	ft := t.funcTab()
	funcs := make([]Func, ft.Count())
	syms := make([]Sym, len(funcs))
	for i := range funcs {
	f := &funcs[i]
	f.Entry = ft.pc(i)
	f.End = ft.pc(i + 1)
	info := t.funcData(uint32(i))
	f.LineTable = t
	f.FrameSize = int(info.deferreturn())
	syms[i] = Sym{
	Value: f.Entry,
	Type: 'T',
	Name: t.funcName(info.nameOff()),
	GoType: 0,
	Func: f,
	goVersion: t.version,
	}
	f.Sym = &syms[i]
	}
	return funcs
	}

	// findFunc returns the funcData corresponding to the given program counter.
	func (t *LineTable) findFunc(pc uint64) funcData {
	ft := t.funcTab()
	if pc < ft.pc(0) \|\| pc >= ft.pc(ft.Count()) {
	return funcData{}
	}
	idx := sort.Search(int(t.nfunctab), func(i int) bool {
	return ft.pc(i) > pc
	})
	idx--
	return t.funcData(uint32(idx))
	}

	// readvarint reads, removes, and returns a varint from *pp.
	func (t LineTable) readvarint(pp []byte) uint32 {
	var v, shift uint32
	p := *pp
	for shift = 0; ; shift += 7 {
	b := p[0]
	p = p[1:]
	v \|= (uint32(b) & 0x7F) << shift
	if b&0x80 == 0 {
	break
	}
	}
	*pp = p
	return v
	}

	// funcName returns the name of the function found at off.
	func (t *LineTable) funcName(off uint32) string {
	if s, ok := t.funcNames[off]; ok {
	return s
	}
	i := bytes.IndexByte(t.funcnametab[off:], 0)
	s := string(t.funcnametab[off : off+uint32(i)])
	t.funcNames[off] = s
	return s
	}

	// stringFrom returns a Go string found at off from a position.
	func (t *LineTable) stringFrom(arr []byte, off uint32) string {
	if s, ok := t.strings[off]; ok {
	return s
	}
	i := bytes.IndexByte(arr[off:], 0)
	s := string(arr[off : off+uint32(i)])
	t.strings[off] = s
	return s
	}

	// string returns a Go string found at off.
	func (t *LineTable) string(off uint32) string {
	return t.stringFrom(t.funcdata, off)
	}

	// functabFieldSize returns the size in bytes of a single functab field.
	func (t *LineTable) functabFieldSize() int {
	if t.version >= ver118 {
	return 4
	}
	return int(t.ptrsize)
	}

	// funcTab returns t's funcTab.
	func (t *LineTable) funcTab() funcTab {
	return funcTab{LineTable: t, sz: t.functabFieldSize()}
	}

	// funcTab is memory corresponding to a slice of functab structs, followed by an invalid PC.
	// A functab struct is a PC and a func offset.
	type funcTab struct {
	*LineTable
	sz int // cached result of t.functabFieldSize
	}

	// Count returns the number of func entries in f.
	func (f funcTab) Count() int {
	return int(f.nfunctab)
	}

	// pc returns the PC of the i'th func in f.
	func (f funcTab) pc(i int) uint64 {
	u := f.uint(f.functab[2if.sz:])
	if f.version >= ver118 {
	u += f.textStart
	}
	return u
	}

	// funcOff returns the funcdata offset of the i'th func in f.
	func (f funcTab) funcOff(i int) uint64 {
	return f.uint(f.functab[(2i+1)f.sz:])
	}

	// uint returns the uint stored at b.
	func (f funcTab) uint(b []byte) uint64 {
	if f.sz == 4 {
	return uint64(f.binary.Uint32(b))
	}
	return f.binary.Uint64(b)
	}

	// funcData is memory corresponding to an _func struct.
	type funcData struct {
	t *LineTable // LineTable this data is a part of
	data []byte // raw memory for the function
	}

	// funcData returns the ith funcData in t.functab.
	func (t *LineTable) funcData(i uint32) funcData {
	data := t.funcdata[t.funcTab().funcOff(int(i)):]
	return funcData{t: t, data: data}
	}

	// IsZero reports whether f is the zero value.
	func (f funcData) IsZero() bool {
	return f.t == nil && f.data == nil
	}

	// entryPC returns the func's entry PC.
	func (f *funcData) entryPC() uint64 {
	// In Go 1.18, the first field of _func changed
	// from a uintptr entry PC to a uint32 entry offset.
	if f.t.version >= ver118 {
	// TODO: support multiple text sections.
	// See runtime/symtab.go:(*moduledata).textAddr.
	return uint64(f.t.binary.Uint32(f.data)) + f.t.textStart
	}
	return f.t.uintptr(f.data)
	}

	func (f funcData) nameOff() uint32 { return f.field(1) }
	func (f funcData) deferreturn() uint32 { return f.field(3) }
	func (f funcData) pcfile() uint32 { return f.field(5) }
	func (f funcData) pcln() uint32 { return f.field(6) }
	func (f funcData) cuOffset() uint32 { return f.field(8) }

	// field returns the nth field of the _func struct.
	// It panics if n == 0 or n > 9; for n == 0, call f.entryPC.
	// Most callers should use a named field accessor (just above).
	func (f funcData) field(n uint32) uint32 {
	if n == 0 \|\| n > 9 {
	panic("bad funcdata field")
	}
	// In Go 1.18, the first field of _func changed
	// from a uintptr entry PC to a uint32 entry offset.
	sz0 := f.t.ptrsize
	if f.t.version >= ver118 {
	sz0 = 4
	}
	off := sz0 + (n-1)*4 // subsequent fields are 4 bytes each
	data := f.data[off:]
	return f.t.binary.Uint32(data)
	}

	// step advances to the next pc, value pair in the encoded table.
	func (t LineTable) step(p []byte, pc uint64, val int32, first bool) bool {
	uvdelta := t.readvarint(p)
	if uvdelta == 0 && !first {
	return false
	}
	if uvdelta&1 != 0 {
	uvdelta = ^(uvdelta >> 1)
	} else {
	uvdelta >>= 1
	}
	vdelta := int32(uvdelta)
	pcdelta := t.readvarint(p) * t.quantum
	*pc += uint64(pcdelta)
	*val += vdelta
	return true
	}

	// pcvalue reports the value associated with the target pc.
	// off is the offset to the beginning of the pc-value table,
	// and entry is the start PC for the corresponding function.
	func (t *LineTable) pcvalue(off uint32, entry, targetpc uint64) int32 {
	p := t.pctab[off:]

	val := int32(-1)
	pc := entry
	for t.step(&p, &pc, &val, pc == entry) {
	if targetpc < pc {
	return val
	}
	}
	return -1
	}

	// findFileLine scans one function in the binary looking for a
	// program counter in the given file on the given line.
	// It does so by running the pc-value tables mapping program counter
	// to file number. Since most functions come from a single file, these
	// are usually short and quick to scan. If a file match is found, then the
	// code goes to the expense of looking for a simultaneous line number match.
	func (t *LineTable) findFileLine(entry uint64, filetab, linetab uint32, filenum, line int32, cutab []byte) uint64 {
	if filetab == 0 \|\| linetab == 0 {
	return 0
	}

	fp := t.pctab[filetab:]
	fl := t.pctab[linetab:]
	fileVal := int32(-1)
	filePC := entry
	lineVal := int32(-1)
	linePC := entry
	fileStartPC := filePC
	for t.step(&fp, &filePC, &fileVal, filePC == entry) {
	fileIndex := fileVal
	if t.version == ver116 \|\| t.version == ver118 \|\| t.version == ver120 {
	fileIndex = int32(t.binary.Uint32(cutab[fileVal*4:]))
	}
	if fileIndex == filenum && fileStartPC < filePC {
	// fileIndex is in effect starting at fileStartPC up to
	// but not including filePC, and it's the file we want.
	// Run the PC table looking for a matching line number
	// or until we reach filePC.
	lineStartPC := linePC
	for linePC < filePC && t.step(&fl, &linePC, &lineVal, linePC == entry) {
	// lineVal is in effect until linePC, and lineStartPC < filePC.
	if lineVal == line {
	if fileStartPC <= lineStartPC {
	return lineStartPC
	}
	if fileStartPC < linePC {
	return fileStartPC
	}
	}
	lineStartPC = linePC
	}
	}
	fileStartPC = filePC
	}
	return 0
	}

	// go12PCToLine maps program counter to line number for the Go 1.2+ pcln table.
	func (t *LineTable) go12PCToLine(pc uint64) (line int) {
	defer func() {
	if !disableRecover && recover() != nil {
	line = -1
	}
	}()

	f := t.findFunc(pc)
	if f.IsZero() {
	return -1
	}
	entry := f.entryPC()
	linetab := f.pcln()
	return int(t.pcvalue(linetab, entry, pc))
	}

	// go12PCToFile maps program counter to file name for the Go 1.2+ pcln table.
	func (t *LineTable) go12PCToFile(pc uint64) (file string) {
	defer func() {
	if !disableRecover && recover() != nil {
	file = ""
	}
	}()

	f := t.findFunc(pc)
	if f.IsZero() {
	return ""
	}
	entry := f.entryPC()
	filetab := f.pcfile()
	fno := t.pcvalue(filetab, entry, pc)
	if t.version == ver12 {
	if fno <= 0 {
	return ""
	}
	return t.string(t.binary.Uint32(t.filetab[4*fno:]))
	}
	// Go ≥ 1.16
	if fno < 0 { // 0 is valid for ≥ 1.16
	return ""
	}
	cuoff := f.cuOffset()
	if fnoff := t.binary.Uint32(t.cutab[(cuoff+uint32(fno))*4:]); fnoff != ^uint32(0) {
	return t.stringFrom(t.filetab, fnoff)
	}
	return ""
	}

	// go12LineToPC maps a (file, line) pair to a program counter for the Go 1.2+ pcln table.
	func (t *LineTable) go12LineToPC(file string, line int) (pc uint64) {
	defer func() {
	if !disableRecover && recover() != nil {
	pc = 0
	}
	}()

	t.initFileMap()
	filenum, ok := t.fileMap[file]
	if !ok {
	return 0
	}

	// Scan all functions.
	// If this turns out to be a bottleneck, we could build a map[int32][]int32
	// mapping file number to a list of functions with code from that file.
	var cutab []byte
	for i := uint32(0); i < t.nfunctab; i++ {
	f := t.funcData(i)
	entry := f.entryPC()
	filetab := f.pcfile()
	linetab := f.pcln()
	if t.version == ver116 \|\| t.version == ver118 \|\| t.version == ver120 {
	if f.cuOffset() == ^uint32(0) {
	// skip functions without compilation unit (not real function, or linker generated)
	continue
	}
	cutab = t.cutab[f.cuOffset()*4:]
	}
	pc := t.findFileLine(entry, filetab, linetab, int32(filenum), int32(line), cutab)
	if pc != 0 {
	return pc
	}
	}
	return 0
	}

	// initFileMap initializes the map from file name to file number.
	func (t *LineTable) initFileMap() {
	t.mu.Lock()
	defer t.mu.Unlock()

	if t.fileMap != nil {
	return
	}
	m := make(map[string]uint32)

	if t.version == ver12 {
	for i := uint32(1); i < t.nfiletab; i++ {
	s := t.string(t.binary.Uint32(t.filetab[4*i:]))
	m[s] = i
	}
	} else {
	var pos uint32
	for i := uint32(0); i < t.nfiletab; i++ {
	s := t.stringFrom(t.filetab, pos)
	m[s] = pos
	pos += uint32(len(s) + 1)
	}
	}
	t.fileMap = m
	}

	// go12MapFiles adds to m a key for every file in the Go 1.2 LineTable.
	// Every key maps to obj. That's not a very interesting map, but it provides
	// a way for callers to obtain the list of files in the program.
	func (t LineTable) go12MapFiles(m map[string]Obj, obj *Obj) {
	if !disableRecover {
	defer func() {
	recover()
	}()
	}

	t.initFileMap()
	for file := range t.fileMap {
	m[file] = obj
	}
	}

	// disableRecover causes this package not to swallow panics.
	// This is useful when making changes.
	const disableRecover = false