Updated Mach-O format to use LC_MAIN

docs/macho.md

@@ -2,7 +2,8 @@
 
 ## Notes
 
-MacOS requires including the headers in the __TEXT segment.
+- Headers must be included in the __TEXT segment.
+- Load command size must be divisible by 8.
 
 ## Links
 

src/macho/Constants.go

@@ -2,6 +2,6 @@ package macho
 
 const (
 	BaseAddress  = 0x1000000
-	SizeCommands = Segment64Size*3 + ThreadSize
+	SizeCommands = Segment64Size*4 + DyldInfoCommandSize + MainSize + DylinkerCommandSize + len(LinkerString) + DylibCommandSize + len(LibSystemString)
 	HeaderEnd    = HeaderSize + SizeCommands
 )

src/macho/DyldInfoCommand.go

@@ -0,0 +1,19 @@
+package macho
+
+const DyldInfoCommandSize = 48
+
+// DyldInfoCommand contains the file offsets and sizes that dyld needs to load the image.
+type DyldInfoCommand struct {
+	LoadCommand
+	Length         uint32
+	RebaseOffset   uint32
+	RebaseSize     uint32
+	BindOffset     uint32
+	BindSize       uint32
+	WeakBindOffset uint32
+	WeakBindSize   uint32
+	LazyBindOffset uint32
+	LazyBindSize   uint32
+	ExportOffset   uint32
+	ExportSize     uint32
+}

src/macho/DylibCommand.go

@@ -0,0 +1,16 @@
+package macho
+
+const (
+	DylibCommandSize = 24
+	LibSystemString  = "/usr/lib/libSystem.B.dylib\000\000\000\000\000\000"
+)
+
+// DylibCommand is added for each shared library.
+type DylibCommand struct {
+	LoadCommand
+	Length               uint32
+	Name                 uint32
+	TimeStamp            uint32
+	CurrentVersion       uint32
+	CompatibilityVersion uint32
+}

src/macho/DylinkerCommand.go

@@ -0,0 +1,13 @@
+package macho
+
+const (
+	DylinkerCommandSize = 12
+	LinkerString        = "/usr/lib/dyld\000\000\000\000\000\000\000"
+)
+
+// DylinkerCommand is needed if the program uses a dynamic linker.
+type DylinkerCommand struct {
+	LoadCommand
+	Length uint32
+	Name   uint32
+}

src/macho/LoadCommand.go

@@ -8,7 +8,7 @@ const (
 	LcThread             LoadCommand = 0x4
 	LcUnixthread         LoadCommand = 0x5
 	LcDysymtab           LoadCommand = 0xB
-	LcDylib              LoadCommand = 0xC
+	LcLoadDylib          LoadCommand = 0xC
 	LcIdDylib            LoadCommand = 0xD
 	LcLoadDylinker       LoadCommand = 0xE
 	LcIdDylinker         LoadCommand = 0xF

src/macho/MachO.go

@@ -11,19 +11,23 @@ import (
 // MachO is the executable format used on MacOS.
 type MachO struct {
 	Header
-	PageZero   Segment64
+	PageZero        Segment64
-	CodeHeader Segment64
+	CodeHeader      Segment64
-	DataHeader Segment64
+	DataHeader      Segment64
-	UnixThread Thread
+	ImportsHeader   Segment64
+	MainHeader      Main
+	InfoHeader      DyldInfoCommand
+	LinkerHeader    DylinkerCommand
+	LibSystemHeader DylibCommand
 }
 
 // Write writes the Mach-O format to the given writer.
 func Write(writer io.WriteSeeker, b *build.Build, codeBytes []byte, dataBytes []byte) {
-	x := exe.New(HeaderEnd, b.FileAlign(), b.MemoryAlign(), b.Congruent(), codeBytes, dataBytes)
+	x := exe.New(HeaderEnd, b.FileAlign(), b.MemoryAlign(), b.Congruent(), codeBytes, dataBytes, nil)
 	code := x.Sections[0]
 	data := x.Sections[1]
+	imports := x.Sections[2]
 	arch, microArch := Arch(b.Arch)
-	entryPoint := BaseAddress + code.MemoryOffset
 
 	m := &MachO{
 		Header: Header{
@@ -31,8 +35,8 @@ func Write(writer io.WriteSeeker, b *build.Build, codeBytes []byte, dataBytes []
 			Architecture:      arch,
 			MicroArchitecture: microArch,
 			Type:              TypeExecute,
-			NumCommands:       4,
+			NumCommands:       8,
-			SizeCommands:      SizeCommands,
+			SizeCommands:      uint32(SizeCommands),
 			Flags:             FlagNoUndefs | FlagPIE | FlagNoHeapExecution,
 			Reserved:          0,
 		},
@@ -65,7 +69,7 @@ func Write(writer io.WriteSeeker, b *build.Build, codeBytes []byte, dataBytes []
 		DataHeader: Segment64{
 			LoadCommand:  LcSegment64,
 			Length:       Segment64Size,
-			Name:         [16]byte{'_', '_', 'D', 'A', 'T', 'A'},
+			Name:         [16]byte{'_', '_', 'D', 'A', 'T', 'A', '_', 'C', 'O', 'N', 'S', 'T'},
 			Address:      uint64(BaseAddress + data.MemoryOffset),
 			SizeInMemory: uint64(len(data.Bytes)),
 			Offset:       uint64(data.FileOffset),
@@ -75,34 +79,40 @@ func Write(writer io.WriteSeeker, b *build.Build, codeBytes []byte, dataBytes []
 			MaxProt:      ProtReadable,
 			InitProt:     ProtReadable,
 		},
-		UnixThread: Thread{
+		ImportsHeader: Segment64{
-			LoadCommand: LcUnixthread,
+			LoadCommand:  LcSegment64,
-			Len:         ThreadSize,
+			Length:       Segment64Size,
-			Type:        0x4,
+			Name:         [16]byte{'_', '_', 'L', 'I', 'N', 'K', 'E', 'D', 'I', 'T'},
-			Data: [43]uint32{
+			Address:      uint64(BaseAddress + imports.MemoryOffset),
-				42,
+			SizeInMemory: uint64(len(imports.Bytes)),
-				0, 0,
+			Offset:       uint64(imports.FileOffset),
-				0, 0,
+			SizeInFile:   uint64(len(imports.Bytes)),
-				0, 0,
+			NumSections:  0,
-				0, 0,
+			Flag:         0,
-				0, 0,
+			MaxProt:      ProtReadable,
-				0, 0,
+			InitProt:     ProtReadable,
-				0, 0,
+		},
-				0, 0,
+		MainHeader: Main{
-				0, 0,
+			LoadCommand:     LcMain,
-				0, 0,
+			Length:          MainSize,
-				0, 0,
+			EntryFileOffset: uint64(code.MemoryOffset),
-				0, 0,
+			StackSize:       0,
-				0, 0,
+		},
-				0, 0,
+		InfoHeader: DyldInfoCommand{
-				0, 0,
+			LoadCommand:  LcDyldInfoOnly,
-				0, 0,
+			Length:       DyldInfoCommandSize,
-				uint32(entryPoint), 0,
+			RebaseOffset: uint32(imports.FileOffset),
-				0, 0,
+			RebaseSize:   uint32(len(imports.Bytes)),
-				0, 0,
+		},
-				0, 0,
+		LinkerHeader: DylinkerCommand{
-				0, 0,
+			LoadCommand: LcLoadDylinker,
-			},
+			Length:      uint32(DylinkerCommandSize + len(LinkerString)),
+			Name:        DylinkerCommandSize,
+		},
+		LibSystemHeader: DylibCommand{
+			LoadCommand: LcLoadDylib,
+			Length:      uint32(DylibCommandSize + len(LibSystemString)),
+			Name:        DylibCommandSize,
 		},
 	}
 
@@ -110,9 +120,17 @@ func Write(writer io.WriteSeeker, b *build.Build, codeBytes []byte, dataBytes []
 	binary.Write(writer, binary.LittleEndian, &m.PageZero)
 	binary.Write(writer, binary.LittleEndian, &m.CodeHeader)
 	binary.Write(writer, binary.LittleEndian, &m.DataHeader)
-	binary.Write(writer, binary.LittleEndian, &m.UnixThread)
+	binary.Write(writer, binary.LittleEndian, &m.ImportsHeader)
+	binary.Write(writer, binary.LittleEndian, &m.MainHeader)
+	binary.Write(writer, binary.LittleEndian, &m.InfoHeader)
+	binary.Write(writer, binary.LittleEndian, &m.LinkerHeader)
+	writer.Write([]byte(LinkerString))
+	binary.Write(writer, binary.LittleEndian, &m.LibSystemHeader)
+	writer.Write([]byte(LibSystemString))
 	writer.Seek(int64(code.Padding), io.SeekCurrent)
 	writer.Write(code.Bytes)
 	writer.Seek(int64(data.Padding), io.SeekCurrent)
 	writer.Write(data.Bytes)
+	writer.Seek(int64(imports.Padding), io.SeekCurrent)
+	writer.Write(imports.Bytes)
 }

src/macho/Main.go

@@ -0,0 +1,11 @@
+package macho
+
+const MainSize = 24
+
+// Main is the structure of the LC_MAIN load command.
+type Main struct {
+	LoadCommand
+	Length          uint32
+	EntryFileOffset uint64
+	StackSize       uint64
+}