cmd/internal/macho: new package for handling mach-o files in toolchain

Currently the linker has some code handling and manipulating
Mach-O files. Specifically, it augments the debug/macho package
with file offset and length, so the content can be handled or
updated easily with the file.

Move this code to an internal package, so it can be used by other
part of the toolchain, e.g. buildid computation.

For #68678.

Cq-Include-Trybots: luci.golang.try:gotip-darwin-amd64_14,gotip-darwin-arm64_13
Change-Id: I2311af0a06441b7fd887ca5c6ed9e6fc44670a16
Reviewed-on: https://go-review.googlesource.com/c/go/+/618596
Reviewed-by: Than McIntosh <thanm@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 134 insertions, 0 deletions

diff --git a/src/cmd/internal/macho/macho.go b/src/cmd/internal/macho/macho.go
new file mode 100644
index 0000000000..ad29c32c50
--- /dev/null
+++ b/src/cmd/internal/macho/macho.go
@@ -0,0 +1,134 @@
+// Copyright 2024 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 provides functionalities to handle Mach-O
+// beyond the debug/macho package, for the toolchain.
+package macho
+
+import (
+	"debug/macho"
+	"encoding/binary"
+	"io"
+	"unsafe"
+)
+
+const (
+	LC_SEGMENT                  = 0x1
+	LC_SYMTAB                   = 0x2
+	LC_SYMSEG                   = 0x3
+	LC_THREAD                   = 0x4
+	LC_UNIXTHREAD               = 0x5
+	LC_LOADFVMLIB               = 0x6
+	LC_IDFVMLIB                 = 0x7
+	LC_IDENT                    = 0x8
+	LC_FVMFILE                  = 0x9
+	LC_PREPAGE                  = 0xa
+	LC_DYSYMTAB                 = 0xb
+	LC_LOAD_DYLIB               = 0xc
+	LC_ID_DYLIB                 = 0xd
+	LC_LOAD_DYLINKER            = 0xe
+	LC_ID_DYLINKER              = 0xf
+	LC_PREBOUND_DYLIB           = 0x10
+	LC_ROUTINES                 = 0x11
+	LC_SUB_FRAMEWORK            = 0x12
+	LC_SUB_UMBRELLA             = 0x13
+	LC_SUB_CLIENT               = 0x14
+	LC_SUB_LIBRARY              = 0x15
+	LC_TWOLEVEL_HINTS           = 0x16
+	LC_PREBIND_CKSUM            = 0x17
+	LC_LOAD_WEAK_DYLIB          = 0x80000018
+	LC_SEGMENT_64               = 0x19
+	LC_ROUTINES_64              = 0x1a
+	LC_UUID                     = 0x1b
+	LC_RPATH                    = 0x8000001c
+	LC_CODE_SIGNATURE           = 0x1d
+	LC_SEGMENT_SPLIT_INFO       = 0x1e
+	LC_REEXPORT_DYLIB           = 0x8000001f
+	LC_LAZY_LOAD_DYLIB          = 0x20
+	LC_ENCRYPTION_INFO          = 0x21
+	LC_DYLD_INFO                = 0x22
+	LC_DYLD_INFO_ONLY           = 0x80000022
+	LC_LOAD_UPWARD_DYLIB        = 0x80000023
+	LC_VERSION_MIN_MACOSX       = 0x24
+	LC_VERSION_MIN_IPHONEOS     = 0x25
+	LC_FUNCTION_STARTS          = 0x26
+	LC_DYLD_ENVIRONMENT         = 0x27
+	LC_MAIN                     = 0x80000028
+	LC_DATA_IN_CODE             = 0x29
+	LC_SOURCE_VERSION           = 0x2A
+	LC_DYLIB_CODE_SIGN_DRS      = 0x2B
+	LC_ENCRYPTION_INFO_64       = 0x2C
+	LC_LINKER_OPTION            = 0x2D
+	LC_LINKER_OPTIMIZATION_HINT = 0x2E
+	LC_VERSION_MIN_TVOS         = 0x2F
+	LC_VERSION_MIN_WATCHOS      = 0x30
+	LC_VERSION_NOTE             = 0x31
+	LC_BUILD_VERSION            = 0x32
+	LC_DYLD_EXPORTS_TRIE        = 0x80000033
+	LC_DYLD_CHAINED_FIXUPS      = 0x80000034
+)
+
+// LoadCmd is macho.LoadCmd with its length, which is also
+// the load command header in the Mach-O file.
+type LoadCmd struct {
+	Cmd macho.LoadCmd
+	Len uint32
+}
+
+type LoadCmdReader struct {
+	offset, next int64
+	f            io.ReadSeeker
+	order        binary.ByteOrder
+}
+
+func NewLoadCmdReader(f io.ReadSeeker, order binary.ByteOrder, nextOffset int64) LoadCmdReader {
+	return LoadCmdReader{next: nextOffset, f: f, order: order}
+}
+
+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) Offset() int64 { return r.offset }
+
+type LoadCmdUpdater struct {
+	LoadCmdReader
+}
+
+func NewLoadCmdUpdater(f io.ReadWriteSeeker, order binary.ByteOrder, nextOffset int64) LoadCmdUpdater {
+	return LoadCmdUpdater{NewLoadCmdReader(f, order, nextOffset)}
+}
+
+func (u LoadCmdUpdater) WriteAt(offset int64, data interface{}) error {
+	if _, err := u.f.Seek(u.offset+offset, 0); err != nil {
+		return err
+	}
+	return binary.Write(u.f.(io.Writer), u.order, data)
+}
+
+func FileHeaderSize(f *macho.File) int64 {
+	offset := int64(unsafe.Sizeof(f.FileHeader))
+	if is64bit := f.Magic == macho.Magic64; is64bit {
+		// mach_header_64 has one extra uint32.
+		offset += 4
+	}
+	return offset
+}