blob: 6bd730dc0bb8ff631463323fc45d8b4d84f53d99 [file] [log] [blame]
// Copyright 2014 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
import (
// A FatFile is a Mach-O universal binary that contains at least one architecture.
type FatFile struct {
Magic uint32
Arches []FatArch
closer io.Closer
// A FatArchHeader represents a fat header for a specific image architecture.
type FatArchHeader struct {
Cpu Cpu
SubCpu uint32
Offset uint32
Size uint32
Align uint32
const fatArchHeaderSize = 5 * 4
// A FatArch is a Mach-O File inside a FatFile.
type FatArch struct {
// ErrNotFat is returned from NewFatFile or OpenFat when the file is not a
// universal binary but may be a thin binary, based on its magic number.
var ErrNotFat = &FormatError{0, "not a fat Mach-O file", nil}
// NewFatFile creates a new FatFile for accessing all the Mach-O images in a
// universal binary. The Mach-O binary is expected to start at position 0 in
// the ReaderAt.
func NewFatFile(r io.ReaderAt) (*FatFile, error) {
var ff FatFile
sr := io.NewSectionReader(r, 0, 1<<63-1)
// Read the fat_header struct, which is always in big endian.
// Start with the magic number.
err := binary.Read(sr, binary.BigEndian, &ff.Magic)
if err != nil {
return nil, &FormatError{0, "error reading magic number", nil}
} else if ff.Magic != MagicFat {
// See if this is a Mach-O file via its magic number. The magic
// must be converted to little endian first though.
var buf [4]byte
binary.BigEndian.PutUint32(buf[:], ff.Magic)
leMagic := binary.LittleEndian.Uint32(buf[:])
if leMagic == Magic32 || leMagic == Magic64 {
return nil, ErrNotFat
} else {
return nil, &FormatError{0, "invalid magic number", nil}
offset := int64(4)
// Read the number of FatArchHeaders that come after the fat_header.
var narch uint32
err = binary.Read(sr, binary.BigEndian, &narch)
if err != nil {
return nil, &FormatError{offset, "invalid fat_header", nil}
offset += 4
if narch < 1 {
return nil, &FormatError{offset, "file contains no images", nil}
// Combine the Cpu and SubCpu (both uint32) into a uint64 to make sure
// there are not duplicate architectures.
seenArches := make(map[uint64]bool, narch)
// Make sure that all images are for the same MH_ type.
var machoType Type
// Following the fat_header comes narch fat_arch structs that index
// Mach-O images further in the file.
ff.Arches = make([]FatArch, narch)
for i := uint32(0); i < narch; i++ {
fa := &ff.Arches[i]
err = binary.Read(sr, binary.BigEndian, &fa.FatArchHeader)
if err != nil {
return nil, &FormatError{offset, "invalid fat_arch header", nil}
offset += fatArchHeaderSize
fr := io.NewSectionReader(r, int64(fa.Offset), int64(fa.Size))
fa.File, err = NewFile(fr)
if err != nil {
return nil, err
// Make sure the architecture for this image is not duplicate.
seenArch := (uint64(fa.Cpu) << 32) | uint64(fa.SubCpu)
if o, k := seenArches[seenArch]; o || k {
return nil, &FormatError{offset, fmt.Sprintf("duplicate architecture cpu=%v, subcpu=%#x", fa.Cpu, fa.SubCpu), nil}
seenArches[seenArch] = true
// Make sure the Mach-O type matches that of the first image.
if i == 0 {
machoType = fa.Type
} else {
if fa.Type != machoType {
return nil, &FormatError{offset, fmt.Sprintf("Mach-O type for architecture #%d (type=%#x) does not match first (type=%#x)", i, fa.Type, machoType), nil}
return &ff, nil
// OpenFat opens the named file using os.Open and prepares it for use as a Mach-O
// universal binary.
func OpenFat(name string) (*FatFile, error) {
f, err := os.Open(name)
if err != nil {
return nil, err
ff, err := NewFatFile(f)
if err != nil {
return nil, err
ff.closer = f
return ff, nil
func (ff *FatFile) Close() error {
var err error
if ff.closer != nil {
err = ff.closer.Close()
ff.closer = nil
return err