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cmd/link: code cleanup in macho_combine_dwarf.go

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- remove global variables
- add missing error checks
- add missing (*os.File).Close calls
- null-check text section correctly
- reduce some variable scopes
- use bytes.Buffer instead of appended slice
- reduce integer casting

Change-Id: I4f6899923d0b26627308beb5c5c3ee9e6c68c41d
Reviewed-on: https://go-review.googlesource.com/c/go/+/214657
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Tamir Duberstein 2020-01-14 10:43:55 -05:00 committed by Than McIntosh
parent ab7c174183
commit 494dd1dddc
1 changed files with 62 additions and 73 deletions
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135
src/cmd/link/internal/ld/macho_combine_dwarf.go
View File

@ -16,11 +16,6 @@ import (
"unsafe"
)
var realdwarf, linkseg *macho.Segment
var dwarfstart, linkstart int64
var dwarfaddr int64
var linkoffset uint32
const (
pageAlign = 12 // 4096 = 1 << 12
)
@ -59,16 +54,18 @@ type loadCmdReader struct {
order binary.ByteOrder
}
func (r *loadCmdReader) Next() (cmd loadCmd, err error) {
func (r *loadCmdReader) Next() (loadCmd, error) {
var cmd loadCmd
r.offset = r.next
if _, err = r.f.Seek(r.offset, 0); err != nil {
return
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
if err := binary.Read(r.f, r.order, &cmd); err != nil {
return cmd, err
}
r.next = r.offset + int64(cmd.Len)
return
return cmd, nil
}
func (r loadCmdReader) ReadAt(offset int64, data interface{}) error {
@ -100,33 +97,33 @@ func machoCombineDwarf(ctxt *Link, exef *os.File, exem *macho.File, dsym, outexe
return err
}
defer dwarff.Close()
outf, err := os.Create(outexe)
outf, err := os.OpenFile(outexe, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0755)
if err != nil {
return err
}
outf.Chmod(0755)
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")
linkseg := exem.Segment("__LINKEDIT")
if linkseg == nil {
return fmt.Errorf("missing __LINKEDIT segment")
}
if _, err = exef.Seek(0, 0); err != nil {
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")
realdwarf := dwarfm.Segment("__DWARF")
if realdwarf == nil {
return fmt.Errorf("missing __DWARF segment")
}
@ -141,13 +138,12 @@ func machoCombineDwarf(ctxt *Link, exef *os.File, exem *macho.File, dsym, outexe
// 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 {
dwarfstart := machoCalcStart(realdwarf.Offset, linkseg.Offset, pageAlign)
if _, err := outf.Seek(dwarfstart, 0); err != nil {
return err
}
dwarfaddr = int64((linkseg.Addr + linkseg.Memsz + 1<<pageAlign - 1) &^ (1<<pageAlign - 1))
if _, err = dwarff.Seek(int64(realdwarf.Offset), 0); err != nil {
if _, err := dwarff.Seek(int64(realdwarf.Offset), 0); err != nil {
return err
}
@ -167,12 +163,11 @@ func machoCombineDwarf(ctxt *Link, exef *os.File, exem *macho.File, dsym, outexe
}
// And finally the linkedit section.
if _, err = exef.Seek(int64(linkseg.Offset), 0); err != nil {
if _, err := exef.Seek(int64(linkseg.Offset), 0); err != nil {
return err
}
linkstart = machoCalcStart(linkseg.Offset, uint64(dwarfstart)+dwarfsize, pageAlign)
linkoffset = uint32(linkstart - int64(linkseg.Offset))
if _, err = outf.Seek(linkstart, 0); err != nil {
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 {
@ -181,36 +176,35 @@ func machoCombineDwarf(ctxt *Link, exef *os.File, exem *macho.File, dsym, outexe
// Now we need to update the headers.
textsect := exem.Section("__text")
if linkseg == nil {
if textsect == nil {
return fmt.Errorf("missing __text section")
}
cmdOffset := unsafe.Sizeof(exem.FileHeader)
is64bit := exem.Magic == macho.Magic64
if is64bit {
if is64bit := exem.Magic == macho.Magic64; is64bit {
// mach_header_64 has one extra uint32.
cmdOffset += unsafe.Sizeof(exem.Magic)
}
dwarfCmdOffset := int64(cmdOffset) + int64(exem.FileHeader.Cmdsz)
availablePadding := int64(textsect.Offset) - dwarfCmdOffset
if availablePadding < int64(realdwarf.Len) {
return fmt.Errorf("No room to add dwarf info. Need at least %d padding bytes, found %d", realdwarf.Len, availablePadding)
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(dwarfCmdOffset, 0); err != nil {
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 {
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 {
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 {
if err := binary.Write(outf, exem.ByteOrder, exem.Cmdsz+realdwarf.Len); err != nil {
return err
}
@ -220,32 +214,33 @@ func machoCombineDwarf(ctxt *Link, exef *os.File, exem *macho.File, dsym, outexe
if err != nil {
return err
}
linkoffset := uint64(linkstart) - linkseg.Offset
switch cmd.Cmd {
case macho.LoadCmdSegment64:
err = machoUpdateSegment(reader, &macho.Segment64{}, &macho.Section64{})
err = machoUpdateSegment(reader, linkseg, linkoffset, &macho.Segment64{}, &macho.Section64{})
case macho.LoadCmdSegment:
err = machoUpdateSegment(reader, &macho.Segment32{}, &macho.Section32{})
err = machoUpdateSegment(reader, linkseg, linkoffset, &macho.Segment32{}, &macho.Section32{})
case LC_DYLD_INFO, LC_DYLD_INFO_ONLY:
err = machoUpdateLoadCommand(reader, &dyldInfoCmd{}, "RebaseOff", "BindOff", "WeakBindOff", "LazyBindOff", "ExportOff")
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &dyldInfoCmd{}, "RebaseOff", "BindOff", "WeakBindOff", "LazyBindOff", "ExportOff")
case macho.LoadCmdSymtab:
err = machoUpdateLoadCommand(reader, &macho.SymtabCmd{}, "Symoff", "Stroff")
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &macho.SymtabCmd{}, "Symoff", "Stroff")
case macho.LoadCmdDysymtab:
err = machoUpdateLoadCommand(reader, &macho.DysymtabCmd{}, "Tocoffset", "Modtaboff", "Extrefsymoff", "Indirectsymoff", "Extreloff", "Locreloff")
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, &linkEditDataCmd{}, "DataOff")
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &linkEditDataCmd{}, "DataOff")
case LC_ENCRYPTION_INFO, LC_ENCRYPTION_INFO_64:
err = machoUpdateLoadCommand(reader, &encryptionInfoCmd{}, "CryptOff")
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)\n", int(cmd.Cmd), cmd.Cmd)
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)
return machoUpdateDwarfHeader(&reader, compressedSects, dwarfsize, dwarfstart, realdwarf)
}
// machoCompressSections tries to compress the DWARF segments in dwarfm,
@ -258,7 +253,7 @@ func machoCompressSections(ctxt *Link, dwarfm *macho.File) ([]*macho.Section, []
dwarfseg := dwarfm.Segment("__DWARF")
var sects []*macho.Section
var bytes []byte
var buf bytes.Buffer
for _, sect := range dwarfm.Sections {
if sect.Seg != "__DWARF" {
@ -283,22 +278,22 @@ func machoCompressSections(ctxt *Link, dwarfm *macho.File) ([]*macho.Section, []
}
newSec := *sect
newSec.Offset = uint32(dwarfseg.Offset) + uint32(len(bytes))
newSec.Addr = dwarfseg.Addr + uint64(len(bytes))
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)
bytes = append(bytes, contents...)
buf.Write(contents)
}
return sects, bytes, nil
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.Write([]byte("ZLIB"))
buf.WriteString("ZLIB")
var sizeBytes [8]byte
binary.BigEndian.PutUint64(sizeBytes[:], uint64(len(sectBytes)))
buf.Write(sizeBytes[:])
@ -310,7 +305,7 @@ func machoCompressSection(sectBytes []byte) (compressed bool, contents []byte, e
if err := z.Close(); err != nil {
return false, nil, err
}
if len(buf.Bytes()) >= len(sectBytes) {
if buf.Len() >= len(sectBytes) {
return false, sectBytes, nil
}
return true, buf.Bytes(), nil
@ -320,26 +315,26 @@ func machoCompressSection(sectBytes []byte) (compressed bool, contents []byte, e
// 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 {
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, any thing before that is fine.
// Only the linkedit segment moved, anything before that is fine.
if offset.Uint() < linkseg.Offset {
return nil
}
offset.SetUint(offset.Uint() + uint64(linkoffset))
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), uint64(linkoffset), 0, nil)
return machoUpdateSections(r, segValue, reflect.ValueOf(sect), linkoffset, nil)
}
func machoUpdateSections(r loadCmdReader, seg, sect reflect.Value, deltaOffset, deltaAddr uint64, compressedSects []*macho.Section) error {
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 {
@ -368,7 +363,7 @@ func machoUpdateSections(r loadCmdReader, seg, sect reflect.Value, deltaOffset,
offsetField.SetUint(uint64(cSect.Offset) + deltaOffset)
}
if cSect.Addr != 0 {
addrField.SetUint(cSect.Addr + deltaAddr)
addrField.SetUint(cSect.Addr)
}
} else {
if offsetField.Uint() != 0 {
@ -378,7 +373,7 @@ func machoUpdateSections(r loadCmdReader, seg, sect reflect.Value, deltaOffset,
reloffField.SetUint(reloffField.Uint() + deltaOffset)
}
if addrField.Uint() != 0 {
addrField.SetUint(addrField.Uint() + deltaAddr)
addrField.SetUint(addrField.Uint())
}
}
if err := r.WriteAt(sectOffset, sect.Interface()); err != nil {
@ -390,7 +385,7 @@ func machoUpdateSections(r loadCmdReader, seg, sect reflect.Value, deltaOffset,
}
// machoUpdateDwarfHeader updates the DWARF segment load command.
func machoUpdateDwarfHeader(r *loadCmdReader, compressedSects []*macho.Section, dwarfsize uint64) error {
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 {
@ -419,9 +414,6 @@ func machoUpdateDwarfHeader(r *loadCmdReader, compressedSects []*macho.Section,
segv.FieldByName("Filesz").SetUint(dwarfsize)
}
deltaOffset := uint64(dwarfstart) - realdwarf.Offset
deltaAddr := uint64(dwarfaddr) - realdwarf.Addr
// 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,
@ -435,15 +427,14 @@ func machoUpdateDwarfHeader(r *loadCmdReader, compressedSects []*macho.Section,
segv.FieldByName("Addr").SetUint(0)
segv.FieldByName("Memsz").SetUint(0)
segv.FieldByName("Prot").SetUint(0)
deltaAddr = 0
if err := r.WriteAt(0, seg); err != nil {
return err
}
return machoUpdateSections(*r, segv, reflect.ValueOf(sect), deltaOffset, deltaAddr, compressedSects)
return machoUpdateSections(*r, segv, reflect.ValueOf(sect), uint64(dwarfstart)-realdwarf.Offset, compressedSects)
}
func machoUpdateLoadCommand(r loadCmdReader, cmd interface{}, fields ...string) error {
func machoUpdateLoadCommand(r loadCmdReader, linkseg *macho.Segment, linkoffset uint64, cmd interface{}, fields ...string) error {
if err := r.ReadAt(0, cmd); err != nil {
return err
}
@ -451,9 +442,8 @@ func machoUpdateLoadCommand(r loadCmdReader, cmd interface{}, fields ...string)
for _, name := range fields {
field := value.FieldByName(name)
fieldval := field.Uint()
if fieldval >= linkseg.Offset {
field.SetUint(fieldval + uint64(linkoffset))
if fieldval := field.Uint(); fieldval >= linkseg.Offset {
field.SetUint(fieldval + linkoffset)
}
}
if err := r.WriteAt(0, cmd); err != nil {
@ -464,10 +454,9 @@ func machoUpdateLoadCommand(r loadCmdReader, cmd interface{}, fields ...string)
func machoCalcStart(origAddr, newAddr uint64, alignExp uint32) int64 {
align := uint64(1 << alignExp)
if (origAddr % align) == (newAddr % align) {
origMod, newMod := origAddr%align, newAddr%align
if origMod == newMod {
return int64(newAddr)
}
padding := (align - (newAddr % align))
padding += origAddr % align
return int64(padding + newAddr)
return int64(newAddr + align + origMod - newMod)
}