// 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.
// Package macho implements access to Mach-O object files.
package macho
// High level access to low level data structures.
import (
"bytes"
"debug/dwarf"
"encoding/binary"
"fmt"
"io"
"os"
)
// A File represents an open Mach-O file.
type File struct {
FileHeader
ByteOrder binary.ByteOrder
Loads []Load
Sections []*Section
Symtab *Symtab
Dysymtab *Dysymtab
closer io.Closer
}
// A Load represents any Mach-O load command.
type Load interface {
Raw() []byte
}
// A LoadBytes is the uninterpreted bytes of a Mach-O load command.
type LoadBytes []byte
func (b LoadBytes) Raw() []byte { return b }
// A SegmentHeader is the header for a Mach-O 32-bit or 64-bit load segment command.
type SegmentHeader struct {
Cmd LoadCmd
Len uint32
Name string
Addr uint64
Memsz uint64
Offset uint64
Filesz uint64
Maxprot uint32
Prot uint32
Nsect uint32
Flag uint32
}
// A Segment represents a Mach-O 32-bit or 64-bit load segment command.
type Segment struct {
LoadBytes
SegmentHeader
// Embed ReaderAt for ReadAt method.
// Do not embed SectionReader directly
// to avoid having Read and Seek.
// If a client wants Read and Seek it must use
// Open() to avoid fighting over the seek offset
// with other clients.
io.ReaderAt
sr *io.SectionReader
}
// Data reads and returns the contents of the segment.
func (s *Segment) Data() ([]byte, error) {
dat := make([]byte, s.sr.Size())
n, err := s.sr.ReadAt(dat, 0)
if n == len(dat) {
err = nil
}
return dat[0:n], err
}
// Open returns a new ReadSeeker reading the segment.
func (s *Segment) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }
type SectionHeader struct {
Name string
Seg string
Addr uint64
Size uint64
Offset uint32
Align uint32
Reloff uint32
Nreloc uint32
Flags uint32
}
type Section struct {
SectionHeader
// Embed ReaderAt for ReadAt method.
// Do not embed SectionReader directly
// to avoid having Read and Seek.
// If a client wants Read and Seek it must use
// Open() to avoid fighting over the seek offset
// with other clients.
io.ReaderAt
sr *io.SectionReader
}
// Data reads and returns the contents of the Mach-O section.
func (s *Section) Data() ([]byte, error) {
dat := make([]byte, s.sr.Size())
n, err := s.sr.ReadAt(dat, 0)
if n == len(dat) {
err = nil
}
return dat[0:n], err
}
// Open returns a new ReadSeeker reading the Mach-O section.
func (s *Section) Open() io.ReadSeeker { return io.NewSectionReader(s.sr, 0, 1<<63-1) }
// A Dylib represents a Mach-O load dynamic library command.
type Dylib struct {
LoadBytes
Name string
Time uint32
CurrentVersion uint32
CompatVersion uint32
}
// A Symtab represents a Mach-O symbol table command.
type Symtab struct {
LoadBytes
SymtabCmd
Syms []Symbol
}
// A Dysymtab represents a Mach-O dynamic symbol table command.
type Dysymtab struct {
LoadBytes
DysymtabCmd
IndirectSyms []uint32 // indices into Symtab.Syms
}
/*
* Mach-O reader
*/
// FormatError is returned by some operations if the data does
// not have the correct format for an object file.
type FormatError struct {
off int64
msg string
val interface{}
}
func (e *FormatError) Error() string {
msg := e.msg
if e.val != nil {
msg += fmt.Sprintf(" '%v'", e.val)
}
msg += fmt.Sprintf(" in record at byte %#x", e.off)
return msg
}
// Open opens the named file using os.Open and prepares it for use as a Mach-O binary.
func Open(name string) (*File, error) {
f, err := os.Open(name)
if err != nil {
return nil, err
}
ff, err := NewFile(f)
if err != nil {
f.Close()
return nil, err
}
ff.closer = f
return ff, nil
}
// Close closes the File.
// If the File was created using NewFile directly instead of Open,
// Close has no effect.
func (f *File) Close() error {
var err error
if f.closer != nil {
err = f.closer.Close()
f.closer = nil
}
return err
}
// NewFile creates a new File for accessing a Mach-O binary in an underlying reader.
// The Mach-O binary is expected to start at position 0 in the ReaderAt.
func NewFile(r io.ReaderAt) (*File, error) {
f := new(File)
sr := io.NewSectionReader(r, 0, 1<<63-1)
// Read and decode Mach magic to determine byte order, size.
// Magic32 and Magic64 differ only in the bottom bit.
var ident [4]byte
if _, err := r.ReadAt(ident[0:], 0); err != nil {
return nil, err
}
be := binary.BigEndian.Uint32(ident[0:])
le := binary.LittleEndian.Uint32(ident[0:])
switch Magic32 &^ 1 {
case be &^ 1:
f.ByteOrder = binary.BigEndian
f.Magic = be
case le &^ 1:
f.ByteOrder = binary.LittleEndian
f.Magic = le
default:
return nil, &FormatError{0, "invalid magic number", nil}
}
// Read entire file header.
if err := binary.Read(sr, f.ByteOrder, &f.FileHeader); err != nil {
return nil, err
}
// Then load commands.
offset := int64(fileHeaderSize32)
if f.Magic == Magic64 {
offset = fileHeaderSize64
}
dat := make([]byte, f.Cmdsz)
if _, err := r.ReadAt(dat, offset); err != nil {
return nil, err
}
f.Loads = make([]Load, f.Ncmd)
bo := f.ByteOrder
for i := range f.Loads {
// Each load command begins with uint32 command and length.
if len(dat) < 8 {
return nil, &FormatError{offset, "command block too small", nil}
}
cmd, siz := LoadCmd(bo.Uint32(dat[0:4])), bo.Uint32(dat[4:8])
if siz < 8 || siz > uint32(len(dat)) {
return nil, &FormatError{offset, "invalid command block size", nil}
}
var cmddat []byte
cmddat, dat = dat[0:siz], dat[siz:]
offset += int64(siz)
var s *Segment
switch cmd {
default:
f.Loads[i] = LoadBytes(cmddat)
case LoadCmdDylib:
var hdr DylibCmd
b := bytes.NewReader(cmddat)
if err := binary.Read(b, bo, &hdr); err != nil {
return nil, err
}
l := new(Dylib)
if hdr.Name >= uint32(len(cmddat)) {
return nil, &FormatError{offset, "invalid name in dynamic library command", hdr.Name}
}
l.Name = cstring(cmddat[hdr.Name:])
l.Time = hdr.Time
l.CurrentVersion = hdr.CurrentVersion
l.CompatVersion = hdr.CompatVersion
l.LoadBytes = LoadBytes(cmddat)
f.Loads[i] = l
case LoadCmdSymtab:
var hdr SymtabCmd
b := bytes.NewReader(cmddat)
if err := binary.Read(b, bo, &hdr); err != nil {
return nil, err
}
strtab := make([]byte, hdr.Strsize)
if _, err := r.ReadAt(strtab, int64(hdr.Stroff)); err != nil {
return nil, err
}
var symsz int
if f.Magic == Magic64 {
symsz = 16
} else {
symsz = 12
}
symdat := make([]byte, int(hdr.Nsyms)*symsz)
if _, err := r.ReadAt(symdat, int64(hdr.Symoff)); err != nil {
return nil, err
}
st, err := f.parseSymtab(symdat, strtab, cmddat, &hdr, offset)
if err != nil {
return nil, err
}
f.Loads[i] = st
f.Symtab = st
case LoadCmdDysymtab:
var hdr DysymtabCmd
b := bytes.NewReader(cmddat)
if err := binary.Read(b, bo, &hdr); err != nil {
return nil, err
}
dat := make([]byte, hdr.Nindirectsyms*4)
if _, err := r.ReadAt(dat, int64(hdr.Indirectsymoff)); err != nil {
return nil, err
}
x := make([]uint32, hdr.Nindirectsyms)
if err := binary.Read(bytes.NewReader(dat), bo, x); err != nil {
return nil, err
}
st := new(Dysymtab)
st.LoadBytes = LoadBytes(cmddat)
st.DysymtabCmd = hdr
st.IndirectSyms = x
f.Loads[i] = st
f.Dysymtab = st
case LoadCmdSegment:
var seg32 Segment32
b := bytes.NewReader(cmddat)
if err := binary.Read(b, bo, &seg32); err != nil {
return nil, err
}
s = new(Segment)
s.LoadBytes = cmddat
s.Cmd = cmd
s.Len = siz
s.Name = cstring(seg32.Name[0:])
s.Addr = uint64(seg32.Addr)
s.Memsz = uint64(seg32.Memsz)
s.Offset = uint64(seg32.Offset)
s.Filesz = uint64(seg32.Filesz)
s.Maxprot = seg32.Maxprot
s.Prot = seg32.Prot
s.Nsect = seg32.Nsect
s.Flag = seg32.Flag
f.Loads[i] = s
for i := 0; i < int(s.Nsect); i++ {
var sh32 Section32
if err := binary.Read(b, bo, &sh32); err != nil {
return nil, err
}
sh := new(Section)
sh.Name = cstring(sh32.Name[0:])
sh.Seg = cstring(sh32.Seg[0:])
sh.Addr = uint64(sh32.Addr)
sh.Size = uint64(sh32.Size)
sh.Offset = sh32.Offset
sh.Align = sh32.Align
sh.Reloff = sh32.Reloff
sh.Nreloc = sh32.Nreloc
sh.Flags = sh32.Flags
f.pushSection(sh, r)
}
case LoadCmdSegment64:
var seg64 Segment64
b := bytes.NewReader(cmddat)
if err := binary.Read(b, bo, &seg64); err != nil {
return nil, err
}
s = new(Segment)
s.LoadBytes = cmddat
s.Cmd = cmd
s.Len = siz
s.Name = cstring(seg64.Name[0:])
s.Addr = seg64.Addr
s.Memsz = seg64.Memsz
s.Offset = seg64.Offset
s.Filesz = seg64.Filesz
s.Maxprot = seg64.Maxprot
s.Prot = seg64.Prot
s.Nsect = seg64.Nsect
s.Flag = seg64.Flag
f.Loads[i] = s
for i := 0; i < int(s.Nsect); i++ {
var sh64 Section64
if err := binary.Read(b, bo, &sh64); err != nil {
return nil, err
}
sh := new(Section)
sh.Name = cstring(sh64.Name[0:])
sh.Seg = cstring(sh64.Seg[0:])
sh.Addr = sh64.Addr
sh.Size = sh64.Size
sh.Offset = sh64.Offset
sh.Align = sh64.Align
sh.Reloff = sh64.Reloff
sh.Nreloc = sh64.Nreloc
sh.Flags = sh64.Flags
f.pushSection(sh, r)
}
}
if s != nil {
s.sr = io.NewSectionReader(r, int64(s.Offset), int64(s.Filesz))
s.ReaderAt = s.sr
}
}
return f, nil
}
func (f *File) parseSymtab(symdat, strtab, cmddat []byte, hdr *SymtabCmd, offset int64) (*Symtab, error) {
bo := f.ByteOrder
symtab := make([]Symbol, hdr.Nsyms)
b := bytes.NewReader(symdat)
for i := range symtab {
var n Nlist64
if f.Magic == Magic64 {
if err := binary.Read(b, bo, &n); err != nil {
return nil, err
}
} else {
var n32 Nlist32
if err := binary.Read(b, bo, &n32); err != nil {
return nil, err
}
n.Name = n32.Name
n.Type = n32.Type
n.Sect = n32.Sect
n.Desc = n32.Desc
n.Value = uint64(n32.Value)
}
sym := &symtab[i]
if n.Name >= uint32(len(strtab)) {
return nil, &FormatError{offset, "invalid name in symbol table", n.Name}
}
sym.Name = cstring(strtab[n.Name:])
sym.Type = n.Type
sym.Sect = n.Sect
sym.Desc = n.Desc
sym.Value = n.Value
}
st := new(Symtab)
st.LoadBytes = LoadBytes(cmddat)
st.Syms = symtab
return st, nil
}
func (f *File) pushSection(sh *Section, r io.ReaderAt) {
f.Sections = append(f.Sections, sh)
sh.sr = io.NewSectionReader(r, int64(sh.Offset), int64(sh.Size))
sh.ReaderAt = sh.sr
}
func cstring(b []byte) string {
var i int
for i = 0; i < len(b) && b[i] != 0; i++ {
}
return string(b[0:i])
}
// Segment returns the first Segment with the given name, or nil if no such segment exists.
func (f *File) Segment(name string) *Segment {
for _, l := range f.Loads {
if s, ok := l.(*Segment); ok && s.Name == name {
return s
}
}
return nil
}
// Section returns the first section with the given name, or nil if no such
// section exists.
func (f *File) Section(name string) *Section {
for _, s := range f.Sections {
if s.Name == name {
return s
}
}
return nil
}
// DWARF returns the DWARF debug information for the Mach-O file.
func (f *File) DWARF() (*dwarf.Data, error) {
// There are many other DWARF sections, but these
// are the ones the debug/dwarf package uses.
// Don't bother loading others.
var names = [...]string{"abbrev", "info", "line", "str"}
var dat [len(names)][]byte
for i, name := range names {
name = "__debug_" + name
s := f.Section(name)
if s == nil {
continue
}
b, err := s.Data()
if err != nil && uint64(len(b)) < s.Size {
return nil, err
}
dat[i] = b
}
abbrev, info, line, str := dat[0], dat[1], dat[2], dat[3]
return dwarf.New(abbrev, nil, nil, info, line, nil, nil, str)
}
// ImportedSymbols returns the names of all symbols
// referred to by the binary f that are expected to be
// satisfied by other libraries at dynamic load time.
func (f *File) ImportedSymbols() ([]string, error) {
if f.Dysymtab == nil || f.Symtab == nil {
return nil, &FormatError{0, "missing symbol table", nil}
}
st := f.Symtab
dt := f.Dysymtab
var all []string
for _, s := range st.Syms[dt.Iundefsym : dt.Iundefsym+dt.Nundefsym] {
all = append(all, s.Name)
}
return all, nil
}
// ImportedLibraries returns the paths of all libraries
// referred to by the binary f that are expected to be
// linked with the binary at dynamic link time.
func (f *File) ImportedLibraries() ([]string, error) {
var all []string
for _, l := range f.Loads {
if lib, ok := l.(*Dylib); ok {
all = append(all, lib.Name)
}
}
return all, nil
}