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// 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, with the exact
// value stored in the 'runtime.text' symbol.
// This value may differ from the start
// address of the text segment if
// binary was built with cgo enabled.
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