blob: 9d9f916b8eac911994d100158332b5e35af66d8f [file] [log] [blame]
// Copyright 2015 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 ld
import (
"bytes"
"compress/zlib"
"debug/macho"
"encoding/binary"
"fmt"
"io"
"os"
"reflect"
"unsafe"
)
const (
pageAlign = 12 // 4096 = 1 << 12
)
type loadCmd struct {
Cmd macho.LoadCmd
Len uint32
}
type dyldInfoCmd struct {
Cmd macho.LoadCmd
Len uint32
RebaseOff, RebaseLen uint32
BindOff, BindLen uint32
WeakBindOff, WeakBindLen uint32
LazyBindOff, LazyBindLen uint32
ExportOff, ExportLen uint32
}
type linkEditDataCmd struct {
Cmd macho.LoadCmd
Len uint32
DataOff, DataLen uint32
}
type encryptionInfoCmd struct {
Cmd macho.LoadCmd
Len uint32
CryptOff, CryptLen uint32
CryptId uint32
}
type loadCmdReader struct {
offset, next int64
f *os.File
order binary.ByteOrder
}
func (r *loadCmdReader) Next() (loadCmd, error) {
var cmd loadCmd
r.offset = r.next
if _, err := r.f.Seek(r.offset, 0); err != nil {
return cmd, err
}
if err := binary.Read(r.f, r.order, &cmd); err != nil {
return cmd, err
}
r.next = r.offset + int64(cmd.Len)
return cmd, nil
}
func (r loadCmdReader) ReadAt(offset int64, data interface{}) error {
if _, err := r.f.Seek(r.offset+offset, 0); err != nil {
return err
}
return binary.Read(r.f, r.order, data)
}
func (r loadCmdReader) WriteAt(offset int64, data interface{}) error {
if _, err := r.f.Seek(r.offset+offset, 0); err != nil {
return err
}
return binary.Write(r.f, r.order, data)
}
// machoCombineDwarf merges dwarf info generated by dsymutil into a macho executable.
//
// With internal linking, DWARF is embedded into the executable, this lets us do the
// same for external linking.
// exef is the file of the executable with no DWARF. It must have enough room in the macho
// header to add the DWARF sections. (Use ld's -headerpad option)
// exem is the macho representation of exef.
// dsym is the path to the macho file containing DWARF from dsymutil.
// outexe is the path where the combined executable should be saved.
func machoCombineDwarf(ctxt *Link, exef *os.File, exem *macho.File, dsym, outexe string) error {
dwarff, err := os.Open(dsym)
if err != nil {
return err
}
defer dwarff.Close()
outf, err := os.OpenFile(outexe, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0755)
if err != nil {
return err
}
defer outf.Close()
dwarfm, err := macho.NewFile(dwarff)
if err != nil {
return err
}
defer dwarfm.Close()
// The string table needs to be the last thing in the file
// for code signing to work. So we'll need to move the
// linkedit section, but all the others can be copied directly.
linkseg := exem.Segment("__LINKEDIT")
if linkseg == nil {
return fmt.Errorf("missing __LINKEDIT segment")
}
if _, err := exef.Seek(0, 0); err != nil {
return err
}
if _, err := io.CopyN(outf, exef, int64(linkseg.Offset)); err != nil {
return err
}
realdwarf := dwarfm.Segment("__DWARF")
if realdwarf == nil {
return fmt.Errorf("missing __DWARF segment")
}
// Try to compress the DWARF sections. This includes some Apple
// proprietary sections like __apple_types.
compressedSects, compressedBytes, err := machoCompressSections(ctxt, dwarfm)
if err != nil {
return err
}
// Now copy the dwarf data into the output.
// Kernel requires all loaded segments to be page-aligned in the file,
// even though we mark this one as being 0 bytes of virtual address space.
dwarfstart := machoCalcStart(realdwarf.Offset, linkseg.Offset, pageAlign)
if _, err := outf.Seek(dwarfstart, 0); err != nil {
return err
}
if _, err := dwarff.Seek(int64(realdwarf.Offset), 0); err != nil {
return err
}
// Write out the compressed sections, or the originals if we gave up
// on compressing them.
var dwarfsize uint64
if compressedBytes != nil {
dwarfsize = uint64(len(compressedBytes))
if _, err := outf.Write(compressedBytes); err != nil {
return err
}
} else {
if _, err := io.CopyN(outf, dwarff, int64(realdwarf.Filesz)); err != nil {
return err
}
dwarfsize = realdwarf.Filesz
}
// And finally the linkedit section.
if _, err := exef.Seek(int64(linkseg.Offset), 0); err != nil {
return err
}
linkstart := machoCalcStart(linkseg.Offset, uint64(dwarfstart)+dwarfsize, pageAlign)
if _, err := outf.Seek(linkstart, 0); err != nil {
return err
}
if _, err := io.Copy(outf, exef); err != nil {
return err
}
// Now we need to update the headers.
textsect := exem.Section("__text")
if textsect == nil {
return fmt.Errorf("missing __text section")
}
cmdOffset := unsafe.Sizeof(exem.FileHeader)
if is64bit := exem.Magic == macho.Magic64; is64bit {
// mach_header_64 has one extra uint32.
cmdOffset += unsafe.Sizeof(exem.Magic)
}
dwarfCmdOffset := uint32(cmdOffset) + exem.FileHeader.Cmdsz
availablePadding := textsect.Offset - dwarfCmdOffset
if availablePadding < realdwarf.Len {
return fmt.Errorf("no room to add dwarf info. Need at least %d padding bytes, found %d", realdwarf.Len, availablePadding)
}
// First, copy the dwarf load command into the header. It will be
// updated later with new offsets and lengths as necessary.
if _, err := outf.Seek(int64(dwarfCmdOffset), 0); err != nil {
return err
}
if _, err := io.CopyN(outf, bytes.NewReader(realdwarf.Raw()), int64(realdwarf.Len)); err != nil {
return err
}
if _, err := outf.Seek(int64(unsafe.Offsetof(exem.FileHeader.Ncmd)), 0); err != nil {
return err
}
if err := binary.Write(outf, exem.ByteOrder, exem.Ncmd+1); err != nil {
return err
}
if err := binary.Write(outf, exem.ByteOrder, exem.Cmdsz+realdwarf.Len); err != nil {
return err
}
reader := loadCmdReader{next: int64(cmdOffset), f: outf, order: exem.ByteOrder}
for i := uint32(0); i < exem.Ncmd; i++ {
cmd, err := reader.Next()
if err != nil {
return err
}
linkoffset := uint64(linkstart) - linkseg.Offset
switch cmd.Cmd {
case macho.LoadCmdSegment64:
err = machoUpdateSegment(reader, linkseg, linkoffset, &macho.Segment64{}, &macho.Section64{})
case macho.LoadCmdSegment:
err = machoUpdateSegment(reader, linkseg, linkoffset, &macho.Segment32{}, &macho.Section32{})
case LC_DYLD_INFO, LC_DYLD_INFO_ONLY:
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &dyldInfoCmd{}, "RebaseOff", "BindOff", "WeakBindOff", "LazyBindOff", "ExportOff")
case macho.LoadCmdSymtab:
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &macho.SymtabCmd{}, "Symoff", "Stroff")
case macho.LoadCmdDysymtab:
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &macho.DysymtabCmd{}, "Tocoffset", "Modtaboff", "Extrefsymoff", "Indirectsymoff", "Extreloff", "Locreloff")
case LC_CODE_SIGNATURE, LC_SEGMENT_SPLIT_INFO, LC_FUNCTION_STARTS, LC_DATA_IN_CODE, LC_DYLIB_CODE_SIGN_DRS:
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &linkEditDataCmd{}, "DataOff")
case LC_ENCRYPTION_INFO, LC_ENCRYPTION_INFO_64:
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &encryptionInfoCmd{}, "CryptOff")
case macho.LoadCmdDylib, macho.LoadCmdThread, macho.LoadCmdUnixThread, LC_PREBOUND_DYLIB, LC_UUID, LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS, LC_SOURCE_VERSION, LC_MAIN, LC_LOAD_DYLINKER, LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB, LC_RPATH, LC_ID_DYLIB, LC_SYMSEG, LC_LOADFVMLIB, LC_IDFVMLIB, LC_IDENT, LC_FVMFILE, LC_PREPAGE, LC_ID_DYLINKER, LC_ROUTINES, LC_SUB_FRAMEWORK, LC_SUB_UMBRELLA, LC_SUB_CLIENT, LC_SUB_LIBRARY, LC_TWOLEVEL_HINTS, LC_PREBIND_CKSUM, LC_ROUTINES_64, LC_LAZY_LOAD_DYLIB, LC_LOAD_UPWARD_DYLIB, LC_DYLD_ENVIRONMENT, LC_LINKER_OPTION, LC_LINKER_OPTIMIZATION_HINT, LC_VERSION_MIN_TVOS, LC_VERSION_MIN_WATCHOS, LC_VERSION_NOTE, LC_BUILD_VERSION:
// Nothing to update
default:
err = fmt.Errorf("unknown load command 0x%x (%s)", int(cmd.Cmd), cmd.Cmd)
}
if err != nil {
return err
}
}
// Do the final update of the DWARF segment's load command.
return machoUpdateDwarfHeader(&reader, compressedSects, dwarfsize, dwarfstart, realdwarf)
}
// machoCompressSections tries to compress the DWARF segments in dwarfm,
// returning the updated sections and segment contents, nils if the sections
// weren't compressed, or an error if there was a problem reading dwarfm.
func machoCompressSections(ctxt *Link, dwarfm *macho.File) ([]*macho.Section, []byte, error) {
if !ctxt.compressDWARF {
return nil, nil, nil
}
dwarfseg := dwarfm.Segment("__DWARF")
var sects []*macho.Section
var buf bytes.Buffer
for _, sect := range dwarfm.Sections {
if sect.Seg != "__DWARF" {
continue
}
// As of writing, there are no relocations in dsymutil's output
// so there's no point in worrying about them. Bail out if that
// changes.
if sect.Nreloc != 0 {
return nil, nil, nil
}
data, err := sect.Data()
if err != nil {
return nil, nil, err
}
compressed, contents, err := machoCompressSection(data)
if err != nil {
return nil, nil, err
}
newSec := *sect
newSec.Offset = uint32(dwarfseg.Offset) + uint32(buf.Len())
newSec.Addr = dwarfseg.Addr + uint64(buf.Len())
if compressed {
newSec.Name = "__z" + sect.Name[2:]
newSec.Size = uint64(len(contents))
}
sects = append(sects, &newSec)
buf.Write(contents)
}
return sects, buf.Bytes(), nil
}
// machoCompressSection compresses secBytes if it results in less data.
func machoCompressSection(sectBytes []byte) (compressed bool, contents []byte, err error) {
var buf bytes.Buffer
buf.WriteString("ZLIB")
var sizeBytes [8]byte
binary.BigEndian.PutUint64(sizeBytes[:], uint64(len(sectBytes)))
buf.Write(sizeBytes[:])
z := zlib.NewWriter(&buf)
if _, err := z.Write(sectBytes); err != nil {
return false, nil, err
}
if err := z.Close(); err != nil {
return false, nil, err
}
if buf.Len() >= len(sectBytes) {
return false, sectBytes, nil
}
return true, buf.Bytes(), nil
}
// machoUpdateSegment updates the load command for a moved segment.
// Only the linkedit segment should move, and it should have 0 sections.
// seg should be a macho.Segment32 or macho.Segment64 as appropriate.
// sect should be a macho.Section32 or macho.Section64 as appropriate.
func machoUpdateSegment(r loadCmdReader, linkseg *macho.Segment, linkoffset uint64, seg, sect interface{}) error {
if err := r.ReadAt(0, seg); err != nil {
return err
}
segValue := reflect.ValueOf(seg)
offset := reflect.Indirect(segValue).FieldByName("Offset")
// Only the linkedit segment moved, anything before that is fine.
if offset.Uint() < linkseg.Offset {
return nil
}
offset.SetUint(offset.Uint() + linkoffset)
if err := r.WriteAt(0, seg); err != nil {
return err
}
// There shouldn't be any sections, but just to make sure...
return machoUpdateSections(r, segValue, reflect.ValueOf(sect), linkoffset, nil)
}
func machoUpdateSections(r loadCmdReader, seg, sect reflect.Value, deltaOffset uint64, compressedSects []*macho.Section) error {
iseg := reflect.Indirect(seg)
nsect := iseg.FieldByName("Nsect").Uint()
if nsect == 0 {
return nil
}
sectOffset := int64(iseg.Type().Size())
isect := reflect.Indirect(sect)
offsetField := isect.FieldByName("Offset")
reloffField := isect.FieldByName("Reloff")
addrField := isect.FieldByName("Addr")
nameField := isect.FieldByName("Name")
sizeField := isect.FieldByName("Size")
sectSize := int64(isect.Type().Size())
for i := uint64(0); i < nsect; i++ {
if err := r.ReadAt(sectOffset, sect.Interface()); err != nil {
return err
}
if compressedSects != nil {
cSect := compressedSects[i]
var name [16]byte
copy(name[:], []byte(cSect.Name))
nameField.Set(reflect.ValueOf(name))
sizeField.SetUint(cSect.Size)
if cSect.Offset != 0 {
offsetField.SetUint(uint64(cSect.Offset) + deltaOffset)
}
if cSect.Addr != 0 {
addrField.SetUint(cSect.Addr)
}
} else {
if offsetField.Uint() != 0 {
offsetField.SetUint(offsetField.Uint() + deltaOffset)
}
if reloffField.Uint() != 0 {
reloffField.SetUint(reloffField.Uint() + deltaOffset)
}
if addrField.Uint() != 0 {
addrField.SetUint(addrField.Uint())
}
}
if err := r.WriteAt(sectOffset, sect.Interface()); err != nil {
return err
}
sectOffset += sectSize
}
return nil
}
// machoUpdateDwarfHeader updates the DWARF segment load command.
func machoUpdateDwarfHeader(r *loadCmdReader, compressedSects []*macho.Section, dwarfsize uint64, dwarfstart int64, realdwarf *macho.Segment) error {
var seg, sect interface{}
cmd, err := r.Next()
if err != nil {
return err
}
if cmd.Cmd == macho.LoadCmdSegment64 {
seg = new(macho.Segment64)
sect = new(macho.Section64)
} else {
seg = new(macho.Segment32)
sect = new(macho.Section32)
}
if err := r.ReadAt(0, seg); err != nil {
return err
}
segv := reflect.ValueOf(seg).Elem()
segv.FieldByName("Offset").SetUint(uint64(dwarfstart))
if compressedSects != nil {
var segSize uint64
for _, newSect := range compressedSects {
segSize += newSect.Size
}
segv.FieldByName("Filesz").SetUint(segSize)
} else {
segv.FieldByName("Filesz").SetUint(dwarfsize)
}
// We want the DWARF segment to be considered non-loadable, so
// force vmaddr and vmsize to zero. In addition, set the initial
// protection to zero so as to make the dynamic loader happy,
// since otherwise it may complain that that the vm size and file
// size don't match for the segment. See issues 21647 and 32673
// for more context. Also useful to refer to the Apple dynamic
// loader source, specifically ImageLoaderMachO::sniffLoadCommands
// in ImageLoaderMachO.cpp (various versions can be found online, see
// https://opensource.apple.com/source/dyld/dyld-519.2.2/src/ImageLoaderMachO.cpp.auto.html
// as one example).
segv.FieldByName("Addr").SetUint(0)
segv.FieldByName("Memsz").SetUint(0)
segv.FieldByName("Prot").SetUint(0)
if err := r.WriteAt(0, seg); err != nil {
return err
}
return machoUpdateSections(*r, segv, reflect.ValueOf(sect), uint64(dwarfstart)-realdwarf.Offset, compressedSects)
}
func machoUpdateLoadCommand(r loadCmdReader, linkseg *macho.Segment, linkoffset uint64, cmd interface{}, fields ...string) error {
if err := r.ReadAt(0, cmd); err != nil {
return err
}
value := reflect.Indirect(reflect.ValueOf(cmd))
for _, name := range fields {
field := value.FieldByName(name)
if fieldval := field.Uint(); fieldval >= linkseg.Offset {
field.SetUint(fieldval + linkoffset)
}
}
if err := r.WriteAt(0, cmd); err != nil {
return err
}
return nil
}
func machoCalcStart(origAddr, newAddr uint64, alignExp uint32) int64 {
align := uint64(1 << alignExp)
origMod, newMod := origAddr%align, newAddr%align
if origMod == newMod {
return int64(newAddr)
}
return int64(newAddr + align + origMod - newMod)
}