// 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"
"sync"
)
// 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
// Go 1.2 state
mu sync.Mutex
go12 int // is this in Go 1.2 format? -1 no, 0 unknown, 1 yes
binary binary.ByteOrder
quantum uint32
ptrsize uint32
functab []byte
nfunctab uint32
filetab []byte
nfiletab uint32
fileMap map[string]uint32
strings map[uint32]string // interned substrings of Data, keyed by offset
}
// 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.
// Callers should 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.
// Callers should 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, 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.go12Init()
return t.go12 == 1
}
const go12magic = 0xfffffffb
// 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)
}
// go12init initializes the Go 1.2 metadata if t is a Go 1.2 symbol table.
func (t *LineTable) go12Init() {
t.mu.Lock()
defer t.mu.Unlock()
if t.go12 != 0 {
return
}
defer func() {
// If we panic parsing, assume it's not a Go 1.2 symbol table.
recover()
}()
// Check header: 4-byte magic, two zeros, pc quantum, pointer size.
t.go12 = -1 // not Go 1.2 until proven otherwise
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
}
switch uint32(go12magic) {
case binary.LittleEndian.Uint32(t.Data):
t.binary = binary.LittleEndian
case binary.BigEndian.Uint32(t.Data):
t.binary = binary.BigEndian
default:
return
}
t.quantum = uint32(t.Data[6])
t.ptrsize = uint32(t.Data[7])
t.nfunctab = uint32(t.uintptr(t.Data[8:]))
t.functab = t.Data[8+t.ptrsize:]
functabsize := t.nfunctab*2*t.ptrsize + t.ptrsize
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]
t.go12 = 1 // so far so good
}
// 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.
defer func() {
recover()
}()
n := len(t.functab) / int(t.ptrsize) / 2
funcs := make([]Func, n)
for i := range funcs {
f := &funcs[i]
f.Entry = t.uintptr(t.functab[2*i*int(t.ptrsize):])
f.End = t.uintptr(t.functab[(2*i+2)*int(t.ptrsize):])
info := t.Data[t.uintptr(t.functab[(2*i+1)*int(t.ptrsize):]):]
f.LineTable = t
f.FrameSize = int(t.binary.Uint32(info[t.ptrsize+2*4:]))
f.Sym = &Sym{
Value: f.Entry,
Type: 'T',
Name: t.string(t.binary.Uint32(info[t.ptrsize:])),
GoType: 0,
Func: f,
}
}
return funcs
}
// findFunc returns the func corresponding to the given program counter.
func (t *LineTable) findFunc(pc uint64) []byte {
if pc < t.uintptr(t.functab) || pc >= t.uintptr(t.functab[len(t.functab)-int(t.ptrsize):]) {
return nil
}
// The function table is a list of 2*nfunctab+1 uintptrs,
// alternating program counters and offsets to func structures.
f := t.functab
nf := t.nfunctab
for nf > 0 {
m := nf / 2
fm := f[2*t.ptrsize*m:]
if t.uintptr(fm) <= pc && pc < t.uintptr(fm[2*t.ptrsize:]) {
return t.Data[t.uintptr(fm[t.ptrsize:]):]
} else if pc < t.uintptr(fm) {
nf = m
} else {
f = f[(m+1)*2*t.ptrsize:]
nf -= m + 1
}
}
return nil
}
// 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
}
// string returns a Go string found at off.
func (t *LineTable) string(off uint32) string {
if s, ok := t.strings[off]; ok {
return s
}
i := bytes.IndexByte(t.Data[off:], 0)
s := string(t.Data[off : off+uint32(i)])
t.strings[off] = s
return s
}
// 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.Data[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) uint64 {
if filetab == 0 || linetab == 0 {
return 0
}
fp := t.Data[filetab:]
fl := t.Data[linetab:]
fileVal := int32(-1)
filePC := entry
lineVal := int32(-1)
linePC := entry
fileStartPC := filePC
for t.step(&fp, &filePC, &fileVal, filePC == entry) {
if fileVal == filenum && fileStartPC < filePC {
// fileVal 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 recover() != nil {
line = -1
}
}()
f := t.findFunc(pc)
if f == nil {
return -1
}
entry := t.uintptr(f)
linetab := t.binary.Uint32(f[t.ptrsize+5*4:])
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 recover() != nil {
file = ""
}
}()
f := t.findFunc(pc)
if f == nil {
return ""
}
entry := t.uintptr(f)
filetab := t.binary.Uint32(f[t.ptrsize+4*4:])
fno := t.pcvalue(filetab, entry, pc)
if fno <= 0 {
return ""
}
return t.string(t.binary.Uint32(t.filetab[4*fno:]))
}
// 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 recover() != nil {
pc = 0
}
}()
t.initFileMap()
filenum := t.fileMap[file]
if filenum == 0 {
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.
for i := uint32(0); i < t.nfunctab; i++ {
f := t.Data[t.uintptr(t.functab[2*t.ptrsize*i+t.ptrsize:]):]
entry := t.uintptr(f)
filetab := t.binary.Uint32(f[t.ptrsize+4*4:])
linetab := t.binary.Uint32(f[t.ptrsize+5*4:])
pc := t.findFileLine(entry, filetab, linetab, int32(filenum), int32(line))
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)
for i := uint32(1); i < t.nfiletab; i++ {
s := t.string(t.binary.Uint32(t.filetab[4*i:]))
m[s] = i
}
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) {
defer func() {
recover()
}()
t.initFileMap()
for file := range t.fileMap {
m[file] = obj
}
}