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// 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"
)
var realdwarf, linkseg *macho.Segment
var dwarfstart, linkstart int64
var dwarfaddr int64
var linkoffset uint32
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() (cmd loadCmd, err error) {
r.offset = r.next
if _, err = r.f.Seek(r.offset, 0); err != nil {
return
}
if err = binary.Read(r.f, r.order, &cmd); err != nil {
return
}
r.next = r.offset + int64(cmd.Len)
return
}
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.
// machoCombineDwarf returns true and skips merging if the input executable is for iOS.
//
// With internal linking, DWARF is embedded into the executable, this lets us do the
// same for external linking.
// inexe is the path to the executable with no DWARF. It must have enough room in the macho
// header to add the DWARF sections. (Use ld's -headerpad option)
// 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, inexe, dsym, outexe string) (bool, error) {
exef, err := os.Open(inexe)
if err != nil {
return false, err
}
exem, err := macho.NewFile(exef)
if err != nil {
return false, err
}
cmdOffset := unsafe.Sizeof(exem.FileHeader)
is64bit := exem.Magic == macho.Magic64
if is64bit {
// mach_header_64 has one extra uint32.
cmdOffset += unsafe.Sizeof(exem.Magic)
}
// Check for LC_VERSION_MIN_IPHONEOS.
reader := loadCmdReader{next: int64(cmdOffset), f: exef, order: exem.ByteOrder}
for i := uint32(0); i < exem.Ncmd; i++ {
cmd, err := reader.Next()
if err != nil {
return false, err
}
if cmd.Cmd == LC_VERSION_MIN_IPHONEOS {
// The executable is for iOS, which doesn't support unmapped
// segments such as our __DWARF segment. Skip combining.
return true, nil
}
}
dwarff, err := os.Open(dsym)
if err != nil {
return false, err
}
outf, err := os.Create(outexe)
if err != nil {
return false, err
}
outf.Chmod(0755)
dwarfm, err := macho.NewFile(dwarff)
if err != nil {
return false, err
}
// 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 false, fmt.Errorf("missing __LINKEDIT segment")
}
if _, err = exef.Seek(0, 0); err != nil {
return false, err
}
if _, err := io.CopyN(outf, exef, int64(linkseg.Offset)); err != nil {
return false, err
}
realdwarf = dwarfm.Segment("__DWARF")
if realdwarf == nil {
return false, 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 false, 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 false, err
}
dwarfaddr = int64((linkseg.Addr + linkseg.Memsz + 1<<pageAlign - 1) &^ (1<<pageAlign - 1))
if _, err = dwarff.Seek(int64(realdwarf.Offset), 0); err != nil {
return false, 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 false, err
}
} else {
if _, err := io.CopyN(outf, dwarff, int64(realdwarf.Filesz)); err != nil {
return false, err
}
dwarfsize = realdwarf.Filesz
}
// And finally the linkedit section.
if _, err = exef.Seek(int64(linkseg.Offset), 0); err != nil {
return false, err
}
linkstart = machoCalcStart(linkseg.Offset, uint64(dwarfstart)+dwarfsize, pageAlign)
linkoffset = uint32(linkstart - int64(linkseg.Offset))
if _, err = outf.Seek(linkstart, 0); err != nil {
return false, err
}
if _, err := io.Copy(outf, exef); err != nil {
return false, err
}
// Now we need to update the headers.
textsect := exem.Section("__text")
if linkseg == nil {
return false, fmt.Errorf("missing __text section")
}
dwarfCmdOffset := int64(cmdOffset) + int64(exem.FileHeader.Cmdsz)
availablePadding := int64(textsect.Offset) - dwarfCmdOffset
if availablePadding < int64(realdwarf.Len) {
return false, 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(dwarfCmdOffset, 0); err != nil {
return false, err
}
if _, err := io.CopyN(outf, bytes.NewReader(realdwarf.Raw()), int64(realdwarf.Len)); err != nil {
return false, err
}
if _, err = outf.Seek(int64(unsafe.Offsetof(exem.FileHeader.Ncmd)), 0); err != nil {
return false, err
}
if err = binary.Write(outf, exem.ByteOrder, exem.Ncmd+1); err != nil {
return false, err
}
if err = binary.Write(outf, exem.ByteOrder, exem.Cmdsz+realdwarf.Len); err != nil {
return false, 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 false, err
}
switch cmd.Cmd {
case macho.LoadCmdSegment64:
err = machoUpdateSegment(reader, &macho.Segment64{}, &macho.Section64{})
case macho.LoadCmdSegment:
err = machoUpdateSegment(reader, &macho.Segment32{}, &macho.Section32{})
case LC_DYLD_INFO, LC_DYLD_INFO_ONLY:
err = machoUpdateLoadCommand(reader, &dyldInfoCmd{}, "RebaseOff", "BindOff", "WeakBindOff", "LazyBindOff", "ExportOff")
case macho.LoadCmdSymtab:
err = machoUpdateLoadCommand(reader, &macho.SymtabCmd{}, "Symoff", "Stroff")
case macho.LoadCmdDysymtab:
err = machoUpdateLoadCommand(reader, &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, &linkEditDataCmd{}, "DataOff")
case LC_ENCRYPTION_INFO, LC_ENCRYPTION_INFO_64:
err = machoUpdateLoadCommand(reader, &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)\n", int(cmd.Cmd), cmd.Cmd)
}
if err != nil {
return false, err
}
}
// Do the final update of the DWARF segment's load command.
return false, machoUpdateDwarfHeader(&reader, ctxt.BuildMode, compressedSects)
}
// 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 bytes []byte
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(len(bytes))
newSec.Addr = dwarfseg.Addr + uint64(len(bytes))
if compressed {
newSec.Name = "__z" + sect.Name[2:]
newSec.Size = uint64(len(contents))
}
sects = append(sects, &newSec)
bytes = append(bytes, contents...)
}
return sects, 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.Write([]byte("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 len(buf.Bytes()) >= 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, 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, any thing before that is fine.
if offset.Uint() < linkseg.Offset {
return nil
}
offset.SetUint(offset.Uint() + uint64(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), uint64(linkoffset), 0, nil)
}
func machoUpdateSections(r loadCmdReader, seg, sect reflect.Value, deltaOffset, deltaAddr 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 + deltaAddr)
}
} 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() + deltaAddr)
}
}
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, buildmode BuildMode, compressedSects []*macho.Section) 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))
segv.FieldByName("Addr").SetUint(uint64(dwarfaddr))
if compressedSects != nil {
var segSize uint64
for _, newSect := range compressedSects {
segSize += newSect.Size
}
segv.FieldByName("Filesz").SetUint(segSize)
segv.FieldByName("Memsz").SetUint(uint64(Rnd(int64(segSize), 1<<pageAlign)))
}
deltaOffset := uint64(dwarfstart) - realdwarf.Offset
deltaAddr := uint64(dwarfaddr) - realdwarf.Addr
// If we set Memsz to 0 (and might as well set Addr too),
// then the xnu kernel will bail out halfway through load_segment
// and not apply further sanity checks that we might fail in the future.
// We don't need the DWARF information actually available in memory.
// But if we do this for buildmode=c-shared then the user-space
// dynamic loader complains about memsz < filesz. Sigh.
if buildmode != BuildModeCShared {
segv.FieldByName("Addr").SetUint(0)
segv.FieldByName("Memsz").SetUint(0)
deltaAddr = 0
}
if err := r.WriteAt(0, seg); err != nil {
return err
}
return machoUpdateSections(*r, segv, reflect.ValueOf(sect), deltaOffset, deltaAddr, compressedSects)
}
func machoUpdateLoadCommand(r loadCmdReader, 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)
fieldval := field.Uint()
if fieldval >= linkseg.Offset {
field.SetUint(fieldval + uint64(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)
if (origAddr % align) == (newAddr % align) {
return int64(newAddr)
}
padding := (align - (newAddr % align))
padding += origAddr % align
return int64(padding + newAddr)
}