Added basic support for arm64

src/macho/Constants.go

@@ -9,6 +9,11 @@ const (
 	CPU_ARM_64 CPU = CPU_ARM | 0x01000000
 )
 
+const (
+	CPU_SUBTYPE_ARM64_ALL  = 0
+	CPU_SUBTYPE_X86_64_ALL = 3
+)
+
 type Prot uint32
 
 const (

src/macho/MachO.go

@@ -28,13 +28,24 @@ func Write(writer io.Writer, code []byte, data []byte) {
 	var (
 		codeStart, codePadding = fs.Align(HeaderEnd, config.Align)
 		dataStart, dataPadding = fs.Align(codeStart+len(code), config.Align)
+		arch                   CPU
+		microArch              uint32
 	)
 
+	switch config.TargetArch {
+	case config.ARM:
+		arch = CPU_ARM_64
+		microArch = CPU_SUBTYPE_ARM64_ALL | 0x80000000
+	case config.X86:
+		arch = CPU_X86_64
+		microArch = CPU_SUBTYPE_X86_64_ALL | 0x80000000
+	}
+
 	m := &MachO{
 		Header: Header{
 			Magic:             0xFEEDFACF,
-			Architecture:      CPU_X86_64,
-			MicroArchitecture: 3 | 0x80000000,
+			Architecture:      arch,
+			MicroArchitecture: microArch,
 			Type:              TypeExecute,
 			NumCommands:       4,
 			SizeCommands:      SizeCommands,