// Copyright 2013 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.
// Package goobj implements reading of Go object files and archives.
//
// TODO(rsc): Decide where this package should live. (golang.org/issue/6932)
// TODO(rsc): Decide the appropriate integer types for various fields.
package goobj
import (
"bufio"
"bytes"
"cmd/internal/objabi"
"errors"
"fmt"
"io"
"os"
"strconv"
"strings"
)
// A Sym is a named symbol in an object file.
type Sym struct {
SymID // symbol identifier (name and version)
Kind objabi.SymKind // kind of symbol
DupOK bool // are duplicate definitions okay?
Size int64 // size of corresponding data
Type SymID // symbol for Go type information
Data Data // memory image of symbol
Reloc []Reloc // relocations to apply to Data
Func *Func // additional data for functions
}
// A SymID - the combination of Name and Version - uniquely identifies
// a symbol within a package.
type SymID struct {
// Name is the name of a symbol.
Name string
// Version is zero for symbols with global visibility.
// Symbols with only file visibility (such as file-level static
// declarations in C) have a non-zero version distinguishing
// a symbol in one file from a symbol of the same name
// in another file
Version int64
}
func (s SymID) String() string {
if s.Version == 0 {
return s.Name
}
return fmt.Sprintf("%s<%d>", s.Name, s.Version)
}
// A Data is a reference to data stored in an object file.
// It records the offset and size of the data, so that a client can
// read the data only if necessary.
type Data struct {
Offset int64
Size int64
}
// A Reloc describes a relocation applied to a memory image to refer
// to an address within a particular symbol.
type Reloc struct {
// The bytes at [Offset, Offset+Size) within the containing Sym
// should be updated to refer to the address Add bytes after the start
// of the symbol Sym.
Offset int64
Size int64
Sym SymID
Add int64
// The Type records the form of address expected in the bytes
// described by the previous fields: absolute, PC-relative, and so on.
// TODO(rsc): The interpretation of Type is not exposed by this package.
Type objabi.RelocType
}
// A Var describes a variable in a function stack frame: a declared
// local variable, an input argument, or an output result.
type Var struct {
// The combination of Name, Kind, and Offset uniquely
// identifies a variable in a function stack frame.
// Using fewer of these - in particular, using only Name - does not.
Name string // Name of variable.
Kind int64 // TODO(rsc): Define meaning.
Offset int64 // Frame offset. TODO(rsc): Define meaning.
Type SymID // Go type for variable.
}
// Func contains additional per-symbol information specific to functions.
type Func struct {
Args int64 // size in bytes of argument frame: inputs and outputs
Frame int64 // size in bytes of local variable frame
Leaf bool // function omits save of link register (ARM)
NoSplit bool // function omits stack split prologue
TopFrame bool // function is the top of the call stack
Var []Var // detail about local variables
PCSP Data // PC → SP offset map
PCFile Data // PC → file number map (index into File)
PCLine Data // PC → line number map
PCInline Data // PC → inline tree index map
PCData []Data // PC → runtime support data map
FuncData []FuncData // non-PC-specific runtime support data
File []string // paths indexed by PCFile
InlTree []InlinedCall
}
// TODO: Add PCData []byte and PCDataIter (similar to liblink).
// A FuncData is a single function-specific data value.
type FuncData struct {
Sym SymID // symbol holding data
Offset int64 // offset into symbol for funcdata pointer
}
// An InlinedCall is a node in an InlTree.
// See cmd/internal/obj.InlTree for details.
type InlinedCall struct {
Parent int64
File string
Line int64
Func SymID
ParentPC int64
}
// A Package is a parsed Go object file or archive defining a Go package.
type Package struct {
ImportPath string // import path denoting this package
Imports []string // packages imported by this package
SymRefs []SymID // list of symbol names and versions referred to by this pack
Syms []*Sym // symbols defined by this package
MaxVersion int64 // maximum Version in any SymID in Syms
Arch string // architecture
Native []*NativeReader // native object data (e.g. ELF)
}
type NativeReader struct {
Name string
io.ReaderAt
}
var (
archiveHeader = []byte("!<arch>\n")
archiveMagic = []byte("`\n")
goobjHeader = []byte("go objec") // truncated to size of archiveHeader
errCorruptArchive = errors.New("corrupt archive")
errTruncatedArchive = errors.New("truncated archive")
errCorruptObject = errors.New("corrupt object file")
errNotObject = errors.New("unrecognized object file format")
)
// An objReader is an object file reader.
type objReader struct {
p *Package
b *bufio.Reader
f *os.File
err error
offset int64
dataOffset int64
limit int64
tmp [256]byte
pkgprefix string
}
// init initializes r to read package p from f.
func (r *objReader) init(f *os.File, p *Package) {
r.f = f
r.p = p
r.offset, _ = f.Seek(0, io.SeekCurrent)
r.limit, _ = f.Seek(0, io.SeekEnd)
f.Seek(r.offset, io.SeekStart)
r.b = bufio.NewReader(f)
r.pkgprefix = objabi.PathToPrefix(p.ImportPath) + "."
}
// error records that an error occurred.
// It returns only the first error, so that an error
// caused by an earlier error does not discard information
// about the earlier error.
func (r *objReader) error(err error) error {
if r.err == nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
r.err = err
}
// panic("corrupt") // useful for debugging
return r.err
}
// peek returns the next n bytes without advancing the reader.
func (r *objReader) peek(n int) ([]byte, error) {
if r.err != nil {
return nil, r.err
}
if r.offset >= r.limit {
r.error(io.ErrUnexpectedEOF)
return nil, r.err
}
b, err := r.b.Peek(n)
if err != nil {
if err != bufio.ErrBufferFull {
r.error(err)
}
}
return b, err
}
// readByte reads and returns a byte from the input file.
// On I/O error or EOF, it records the error but returns byte 0.
// A sequence of 0 bytes will eventually terminate any
// parsing state in the object file. In particular, it ends the
// reading of a varint.
func (r *objReader) readByte() byte {
if r.err != nil {
return 0
}
if r.offset >= r.limit {
r.error(io.ErrUnexpectedEOF)
return 0
}
b, err := r.b.ReadByte()
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
r.error(err)
b = 0
} else {
r.offset++
}
return b
}
// read reads exactly len(b) bytes from the input file.
// If an error occurs, read returns the error but also
// records it, so it is safe for callers to ignore the result
// as long as delaying the report is not a problem.
func (r *objReader) readFull(b []byte) error {
if r.err != nil {
return r.err
}
if r.offset+int64(len(b)) > r.limit {
return r.error(io.ErrUnexpectedEOF)
}
n, err := io.ReadFull(r.b, b)
r.offset += int64(n)
if err != nil {
return r.error(err)
}
return nil
}
// readInt reads a zigzag varint from the input file.
func (r *objReader) readInt() int64 {
var u uint64
for shift := uint(0); ; shift += 7 {
if shift >= 64 {
r.error(errCorruptObject)
return 0
}
c := r.readByte()
u |= uint64(c&0x7F) << shift
if c&0x80 == 0 {
break
}
}
return int64(u>>1) ^ (int64(u) << 63 >> 63)
}
// readString reads a length-delimited string from the input file.
func (r *objReader) readString() string {
n := r.readInt()
buf := make([]byte, n)
r.readFull(buf)
return string(buf)
}
// readSymID reads a SymID from the input file.
func (r *objReader) readSymID() SymID {
i := r.readInt()
return r.p.SymRefs[i]
}
func (r *objReader) readRef() {
name, abiOrStatic := r.readString(), r.readInt()
// In a symbol name in an object file, "". denotes the
// prefix for the package in which the object file has been found.
// Expand it.
name = strings.ReplaceAll(name, `"".`, r.pkgprefix)
// The ABI field records either the ABI or -1 for static symbols.
//
// To distinguish different static symbols with the same name,
// we use the symbol "version". Version 0 corresponds to
// global symbols, and each file has a unique version > 0 for
// all of its static symbols. The version is incremented on
// each call to parseObject.
//
// For global symbols, we currently ignore the ABI.
//
// TODO(austin): Record the ABI in SymID. Since this is a
// public API, we'll have to keep Version as 0 and record the
// ABI in a new field (which differs from how the linker does
// this, but that's okay). Show the ABI in things like
// objdump.
var vers int64
if abiOrStatic == -1 {
// Static symbol
vers = r.p.MaxVersion
}
r.p.SymRefs = append(r.p.SymRefs, SymID{name, vers})
}
// readData reads a data reference from the input file.
func (r *objReader) readData() Data {
n := r.readInt()
d := Data{Offset: r.dataOffset, Size: n}
r.dataOffset += n
return d
}
// skip skips n bytes in the input.
func (r *objReader) skip(n int64) {
if n < 0 {
r.error(fmt.Errorf("debug/goobj: internal error: misuse of skip"))
}
if n < int64(len(r.tmp)) {
// Since the data is so small, a just reading from the buffered
// reader is better than flushing the buffer and seeking.
r.readFull(r.tmp[:n])
} else if n <= int64(r.b.Buffered()) {
// Even though the data is not small, it has already been read.
// Advance the buffer instead of seeking.
for n > int64(len(r.tmp)) {
r.readFull(r.tmp[:])
n -= int64(len(r.tmp))
}
r.readFull(r.tmp[:n])
} else {
// Seek, giving up buffered data.
_, err := r.f.Seek(r.offset+n, io.SeekStart)
if err != nil {
r.error(err)
}
r.offset += n
r.b.Reset(r.f)
}
}
// Parse parses an object file or archive from f,
// assuming that its import path is pkgpath.
func Parse(f *os.File, pkgpath string) (*Package, error) {
if pkgpath == "" {
pkgpath = `""`
}
p := new(Package)
p.ImportPath = pkgpath
var rd objReader
rd.init(f, p)
err := rd.readFull(rd.tmp[:8])
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
switch {
default:
return nil, errNotObject
case bytes.Equal(rd.tmp[:8], archiveHeader):
if err := rd.parseArchive(); err != nil {
return nil, err
}
case bytes.Equal(rd.tmp[:8], goobjHeader):
if err := rd.parseObject(goobjHeader); err != nil {
return nil, err
}
}
return p, nil
}
// trimSpace removes trailing spaces from b and returns the corresponding string.
// This effectively parses the form used in archive headers.
func trimSpace(b []byte) string {
return string(bytes.TrimRight(b, " "))
}
// parseArchive parses a Unix archive of Go object files.
func (r *objReader) parseArchive() error {
for r.offset < r.limit {
if err := r.readFull(r.tmp[:60]); err != nil {
return err
}
data := r.tmp[:60]
// Each file is preceded by this text header (slice indices in first column):
// 0:16 name
// 16:28 date
// 28:34 uid
// 34:40 gid
// 40:48 mode
// 48:58 size
// 58:60 magic - `\n
// We only care about name, size, and magic.
// The fields are space-padded on the right.
// The size is in decimal.
// The file data - size bytes - follows the header.
// Headers are 2-byte aligned, so if size is odd, an extra padding
// byte sits between the file data and the next header.
// The file data that follows is padded to an even number of bytes:
// if size is odd, an extra padding byte is inserted betw the next header.
if len(data) < 60 {
return errTruncatedArchive
}
if !bytes.Equal(data[58:60], archiveMagic) {
return errCorruptArchive
}
name := trimSpace(data[0:16])
size, err := strconv.ParseInt(trimSpace(data[48:58]), 10, 64)
if err != nil {
return errCorruptArchive
}
data = data[60:]
fsize := size + size&1
if fsize < 0 || fsize < size {
return errCorruptArchive
}
switch name {
case "__.PKGDEF":
r.skip(size)
default:
oldLimit := r.limit
r.limit = r.offset + size
p, err := r.peek(8)
if err != nil {
return err
}
if bytes.Equal(p, goobjHeader) {
if err := r.parseObject(nil); err != nil {
return fmt.Errorf("parsing archive member %q: %v", name, err)
}
} else {
r.p.Native = append(r.p.Native, &NativeReader{
Name: name,
ReaderAt: io.NewSectionReader(r.f, r.offset, size),
})
}
r.skip(r.limit - r.offset)
r.limit = oldLimit
}
if size&1 != 0 {
r.skip(1)
}
}
return nil
}
// parseObject parses a single Go object file.
// The prefix is the bytes already read from the file,
// typically in order to detect that this is an object file.
// The object file consists of a textual header ending in "\n!\n"
// and then the part we want to parse begins.
// The format of that part is defined in a comment at the top
// of src/liblink/objfile.c.
func (r *objReader) parseObject(prefix []byte) error {
r.p.MaxVersion++
h := make([]byte, 0, 256)
h = append(h, prefix...)
var c1, c2, c3 byte
for {
c1, c2, c3 = c2, c3, r.readByte()
h = append(h, c3)
// The new export format can contain 0 bytes.
// Don't consider them errors, only look for r.err != nil.
if r.err != nil {
return errCorruptObject
}
if c1 == '\n' && c2 == '!' && c3 == '\n' {
break
}
}
hs := strings.Fields(string(h))
if len(hs) >= 4 {
r.p.Arch = hs[3]
}
// TODO: extract OS + build ID if/when we need it
r.readFull(r.tmp[:8])
if !bytes.Equal(r.tmp[:8], []byte("\x00go112ld")) {
return r.error(errCorruptObject)
}
b := r.readByte()
if b != 1 {
return r.error(errCorruptObject)
}
// Direct package dependencies.
for {
s := r.readString()
if s == "" {
break
}
r.p.Imports = append(r.p.Imports, s)
}
r.p.SymRefs = []SymID{{"", 0}}
for {
if b := r.readByte(); b != 0xfe {
if b != 0xff {
return r.error(errCorruptObject)
}
break
}
r.readRef()
}
dataLength := r.readInt()
r.readInt() // n relocations - ignore
r.readInt() // n pcdata - ignore
r.readInt() // n autom - ignore
r.readInt() // n funcdata - ignore
r.readInt() // n files - ignore
r.dataOffset = r.offset
r.skip(dataLength)
// Symbols.
for {
if b := r.readByte(); b != 0xfe {
if b != 0xff {
return r.error(errCorruptObject)
}
break
}
typ := r.readByte()
s := &Sym{SymID: r.readSymID()}
r.p.Syms = append(r.p.Syms, s)
s.Kind = objabi.SymKind(typ)
flags := r.readInt()
s.DupOK = flags&1 != 0
s.Size = r.readInt()
s.Type = r.readSymID()
s.Data = r.readData()
s.Reloc = make([]Reloc, r.readInt())
for i := range s.Reloc {
rel := &s.Reloc[i]
rel.Offset = r.readInt()
rel.Size = r.readInt()
rel.Type = objabi.RelocType(r.readInt())
rel.Add = r.readInt()
rel.Sym = r.readSymID()
}
if s.Kind == objabi.STEXT {
f := new(Func)
s.Func = f
f.Args = r.readInt()
f.Frame = r.readInt()
flags := r.readInt()
f.Leaf = flags&(1<<0) != 0
f.TopFrame = flags&(1<<4) != 0
f.NoSplit = r.readInt() != 0
f.Var = make([]Var, r.readInt())
for i := range f.Var {
v := &f.Var[i]
v.Name = r.readSymID().Name
v.Offset = r.readInt()
v.Kind = r.readInt()
v.Type = r.readSymID()
}
f.PCSP = r.readData()
f.PCFile = r.readData()
f.PCLine = r.readData()
f.PCInline = r.readData()
f.PCData = make([]Data, r.readInt())
for i := range f.PCData {
f.PCData[i] = r.readData()
}
f.FuncData = make([]FuncData, r.readInt())
for i := range f.FuncData {
f.FuncData[i].Sym = r.readSymID()
}
for i := range f.FuncData {
f.FuncData[i].Offset = r.readInt() // TODO
}
f.File = make([]string, r.readInt())
for i := range f.File {
f.File[i] = r.readSymID().Name
}
f.InlTree = make([]InlinedCall, r.readInt())
for i := range f.InlTree {
f.InlTree[i].Parent = r.readInt()
f.InlTree[i].File = r.readSymID().Name
f.InlTree[i].Line = r.readInt()
f.InlTree[i].Func = r.readSymID()
f.InlTree[i].ParentPC = r.readInt()
}
}
}
r.readFull(r.tmp[:7])
if !bytes.Equal(r.tmp[:7], []byte("go112ld")) {
return r.error(errCorruptObject)
}
return nil
}
func (r *Reloc) String(insnOffset uint64) string {
delta := r.Offset - int64(insnOffset)
s := fmt.Sprintf("[%d:%d]%s", delta, delta+r.Size, r.Type)
if r.Sym.Name != "" {
if r.Add != 0 {
return fmt.Sprintf("%s:%s+%d", s, r.Sym.Name, r.Add)
}
return fmt.Sprintf("%s:%s", s, r.Sym.Name)
}
if r.Add != 0 {
return fmt.Sprintf("%s:%d", s, r.Add)
}
return s
}
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