cmd/link: rewrite some code without using reflection
In Mach-O DWARF combining, some code was written using reflection,
so it could support both 32-bit and 64-bit Mach-O files without
duplicating code. We no longer support 32-bit darwin platforms
now. 32-bit support can go. Rewrite it with direct field access,
for 64-bit only.
Change-Id: If1338c3cd37cecf603f4df0c6eb0c890eaebfe5f
Reviewed-on: https://go-review.googlesource.com/c/go/+/253557
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/src/cmd/link/internal/ld/macho_combine_dwarf.go b/src/cmd/link/internal/ld/macho_combine_dwarf.go
index 9d9f916..e43aeb1 100644
--- a/src/cmd/link/internal/ld/macho_combine_dwarf.go
+++ b/src/cmd/link/internal/ld/macho_combine_dwarf.go
@@ -217,9 +217,9 @@
linkoffset := uint64(linkstart) - linkseg.Offset
switch cmd.Cmd {
case macho.LoadCmdSegment64:
- err = machoUpdateSegment(reader, linkseg, linkoffset, &macho.Segment64{}, &macho.Section64{})
+ err = machoUpdateSegment(reader, linkseg, linkoffset)
case macho.LoadCmdSegment:
- err = machoUpdateSegment(reader, linkseg, linkoffset, &macho.Segment32{}, &macho.Section32{})
+ panic("unexpected 32-bit segment")
case LC_DYLD_INFO, LC_DYLD_INFO_ONLY:
err = machoUpdateLoadCommand(reader, linkseg, linkoffset, &dyldInfoCmd{}, "RebaseOff", "BindOff", "WeakBindOff", "LazyBindOff", "ExportOff")
case macho.LoadCmdSymtab:
@@ -313,70 +313,56 @@
// 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 {
+func machoUpdateSegment(r loadCmdReader, linkseg *macho.Segment, linkoffset uint64) error {
+ var seg macho.Segment64
+ 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 {
+ if seg.Offset < linkseg.Offset {
return nil
}
- offset.SetUint(offset.Uint() + linkoffset)
- if err := r.WriteAt(0, seg); err != nil {
+ seg.Offset += 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)
+ return machoUpdateSections(r, &seg, 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()
+func machoUpdateSections(r loadCmdReader, seg *macho.Segment64, deltaOffset uint64, compressedSects []*macho.Section) error {
+ nsect := seg.Nsect
if nsect == 0 {
return nil
}
- sectOffset := int64(iseg.Type().Size())
+ sectOffset := int64(unsafe.Sizeof(*seg))
- 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 {
+ var sect macho.Section64
+ sectSize := int64(unsafe.Sizeof(sect))
+ for i := uint32(0); i < nsect; i++ {
+ if err := r.ReadAt(sectOffset, §); 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)
+ copy(sect.Name[:], cSect.Name)
+ sect.Size = cSect.Size
if cSect.Offset != 0 {
- offsetField.SetUint(uint64(cSect.Offset) + deltaOffset)
+ sect.Offset = cSect.Offset + uint32(deltaOffset)
}
if cSect.Addr != 0 {
- addrField.SetUint(cSect.Addr)
+ sect.Addr = cSect.Addr
}
} else {
- if offsetField.Uint() != 0 {
- offsetField.SetUint(offsetField.Uint() + deltaOffset)
+ if sect.Offset != 0 {
+ sect.Offset += uint32(deltaOffset)
}
- if reloffField.Uint() != 0 {
- reloffField.SetUint(reloffField.Uint() + deltaOffset)
- }
- if addrField.Uint() != 0 {
- addrField.SetUint(addrField.Uint())
+ if sect.Reloff != 0 {
+ sect.Reloff += uint32(deltaOffset)
}
}
- if err := r.WriteAt(sectOffset, sect.Interface()); err != nil {
+ if err := r.WriteAt(sectOffset, §); err != nil {
return err
}
sectOffset += sectSize
@@ -386,32 +372,27 @@
// 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 cmd.Cmd != macho.LoadCmdSegment64 {
+ panic("not a Segment64")
}
- if err := r.ReadAt(0, seg); err != nil {
+ var seg macho.Segment64
+ if err := r.ReadAt(0, &seg); err != nil {
return err
}
- segv := reflect.ValueOf(seg).Elem()
- segv.FieldByName("Offset").SetUint(uint64(dwarfstart))
+ seg.Offset = uint64(dwarfstart)
if compressedSects != nil {
var segSize uint64
for _, newSect := range compressedSects {
segSize += newSect.Size
}
- segv.FieldByName("Filesz").SetUint(segSize)
+ seg.Filesz = segSize
} else {
- segv.FieldByName("Filesz").SetUint(dwarfsize)
+ seg.Filesz = dwarfsize
}
// We want the DWARF segment to be considered non-loadable, so
@@ -424,14 +405,14 @@
// 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)
+ seg.Addr = 0
+ seg.Memsz = 0
+ seg.Prot = 0
- if err := r.WriteAt(0, seg); err != nil {
+ if err := r.WriteAt(0, &seg); err != nil {
return err
}
- return machoUpdateSections(*r, segv, reflect.ValueOf(sect), uint64(dwarfstart)-realdwarf.Offset, compressedSects)
+ return machoUpdateSections(*r, &seg, uint64(dwarfstart)-realdwarf.Offset, compressedSects)
}
func machoUpdateLoadCommand(r loadCmdReader, linkseg *macho.Segment, linkoffset uint64, cmd interface{}, fields ...string) error {
