diff --git a/src/pkg/debug/macho/Makefile b/src/pkg/debug/macho/Makefile
new file mode 100644
index 00000000000..1a88c73778a
--- /dev/null
+++ b/src/pkg/debug/macho/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 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.
+
+include $(GOROOT)/src/Make.$(GOARCH)
+
+TARG=debug/macho
+GOFILES=\
+	macho.go\
+	file.go\
+
+include $(GOROOT)/src/Make.pkg
diff --git a/src/pkg/debug/macho/file.go b/src/pkg/debug/macho/file.go
new file mode 100644
index 00000000000..fee02fb27aa
--- /dev/null
+++ b/src/pkg/debug/macho/file.go
@@ -0,0 +1,374 @@
+// Copyright 2009 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 implements access to Mach-O object files, as defined by
+// http://developer.apple.com/mac/library/documentation/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html.
+package macho
+
+// High level access to low level data structures.
+
+import (
+	"bytes";
+	"debug/binary";
+	"debug/dwarf";
+	"fmt";
+	"io";
+	"os";
+)
+
+// A File represents an open Mach-O file.
+type File struct {
+	FileHeader;
+	ByteOrder binary.ByteOrder;
+	Loads []Load;
+	Sections []*Section;
+
+	closer io.Closer;
+}
+
+// A Load represents any Mach-O load command.
+type Load interface {
+	Raw() []byte
+}
+
+// A LoadBytes is the uninterpreted bytes of a Mach-O load command.
+type LoadBytes []byte
+
+func (b LoadBytes) Raw() []byte {
+	return b
+}
+
+// A SegmentHeader is the header for a Mach-O 32-bit or 64-bit load segment command.
+type SegmentHeader struct {
+	Cmd LoadCmd;
+	Len uint32;
+	Name string;
+	Addr uint64;
+	Memsz uint64;
+	Offset uint64;
+	Filesz uint64;
+	Maxprot uint32;
+	Prot uint32;
+	Nsect uint32;
+	Flag uint32;
+}
+
+// A Segment represents a Mach-O 32-bit or 64-bit load segment command.
+type Segment struct {
+	LoadBytes;
+	SegmentHeader;
+
+	// Embed ReaderAt for ReadAt method.
+	// Do not embed SectionReader directly
+	// to avoid having Read and Seek.
+	// If a client wants Read and Seek it must use
+	// Open() to avoid fighting over the seek offset
+	// with other clients.
+	io.ReaderAt;
+	sr *io.SectionReader;
+}
+
+// Data reads and returns the contents of the segment.
+func (s *Segment) Data() ([]byte, os.Error) {
+	dat := make([]byte, s.sr.Size());
+	n, err := s.sr.ReadAt(dat, 0);
+	return dat[0:n], err;
+}
+
+// Open returns a new ReadSeeker reading the segment.
+func (s *Segment) Open() io.ReadSeeker {
+	return io.NewSectionReader(s.sr, 0, 1<<63 - 1);
+}
+
+type SectionHeader struct {
+	Name	string;
+	Seg	string;
+	Addr	uint64;
+	Size	uint64;
+	Offset	uint32;
+	Align	uint32;
+	Reloff	uint32;
+	Nreloc	uint32;
+	Flags	uint32;
+}
+
+type Section struct {
+	SectionHeader;
+
+	// Embed ReaderAt for ReadAt method.
+	// Do not embed SectionReader directly
+	// to avoid having Read and Seek.
+	// If a client wants Read and Seek it must use
+	// Open() to avoid fighting over the seek offset
+	// with other clients.
+	io.ReaderAt;
+	sr *io.SectionReader;
+}
+
+// Data reads and returns the contents of the Mach-O section.
+func (s *Section) Data() ([]byte, os.Error) {
+	dat := make([]byte, s.sr.Size());
+	n, err := s.sr.ReadAt(dat, 0);
+	return dat[0:n], err;
+}
+
+// Open returns a new ReadSeeker reading the Mach-O section.
+func (s *Section) Open() io.ReadSeeker {
+	return io.NewSectionReader(s.sr, 0, 1<<63 - 1);
+}
+
+
+/*
+ * Mach-O reader
+ */
+
+type FormatError struct {
+	off int64;
+	msg string;
+	val interface{};
+}
+
+func (e *FormatError) String() string {
+	msg := e.msg;
+	if e.val != nil {
+		msg += fmt.Sprintf(" '%v' ", e.val);
+	}
+	msg += fmt.Sprintf("in record at byte %#x", e.off);
+	return msg;
+}
+
+// Open opens the named file using os.Open and prepares it for use as a Mach-O binary.
+func Open(name string) (*File, os.Error) {
+	f, err := os.Open(name, os.O_RDONLY, 0);
+	if err != nil {
+		return nil, err;
+	}
+	ff, err := NewFile(f);
+	if err != nil {
+		f.Close();
+		return nil, err;
+	}
+	ff.closer = f;
+	return ff, nil;
+}
+
+// Close closes the File.
+// If the File was created using NewFile directly instead of Open,
+// Close has no effect.
+func (f *File) Close() os.Error {
+	var err os.Error;
+	if f.closer != nil {
+		err = f.closer.Close();
+		f.closer = nil;
+	}
+	return err;
+}
+
+// NewFile creates a new File for acecssing a Mach-O binary in an underlying reader.
+// The Mach-O binary is expected to start at position 0 in the ReaderAt.
+func NewFile(r io.ReaderAt) (*File, os.Error) {
+	f := new(File);
+	sr := io.NewSectionReader(r, 0, 1<<63 - 1);
+
+	// Read and decode Mach magic to determine byte order, size.
+	// Magic32 and Magic64 differ only in the bottom bit.
+	var ident [4]uint8;
+	if _, err := r.ReadAt(&ident, 0); err != nil {
+		return nil, err;
+	}
+	be := binary.BigEndian.Uint32(&ident);
+	le := binary.LittleEndian.Uint32(&ident);
+	switch Magic32&^1 {
+	case be&^1:
+		f.ByteOrder = binary.BigEndian;
+		f.Magic = be;
+	case le&^1:
+		f.ByteOrder = binary.LittleEndian;
+		f.Magic = le;
+	}
+
+	// Read entire file header.
+	if err := binary.Read(sr, f.ByteOrder, &f.FileHeader); err != nil {
+		return nil, err;
+	}
+
+	// Then load commands.
+	offset := int64(fileHeaderSize32);
+	if f.Magic == Magic64 {
+		offset = fileHeaderSize64;
+	}
+	dat := make([]byte, f.Cmdsz);
+	if _, err := r.ReadAt(dat, offset); err != nil {
+		return nil, err;
+	}
+	f.Loads = make([]Load, f.Ncmd);
+	bo := f.ByteOrder;
+	for i := range f.Loads {
+		// Each load command begins with uint32 command and length.
+		if len(dat) < 8 {
+			return nil, &FormatError{offset, "command block too small", nil};
+		}
+		cmd, siz := LoadCmd(bo.Uint32(dat[0:4])), bo.Uint32(dat[4:8]);
+		if siz < 8 || siz > uint32(len(dat)) {
+			return nil, &FormatError{offset, "invalid command block size", nil};
+		}
+		var cmddat []byte;
+		cmddat, dat = dat[0:siz], dat[siz:len(dat)];
+		offset += int64(siz);
+		var s *Segment;
+		switch cmd {
+		default:
+			f.Loads[i] = LoadBytes(cmddat);
+
+		case LoadCmdSegment:
+			var seg32 Segment32;
+			b := bytes.NewBuffer(cmddat);
+			if err := binary.Read(b, bo, &seg32); err != nil {
+				return nil, err;
+			}
+			s = new(Segment);
+			s.LoadBytes = cmddat;
+			s.Cmd = cmd;
+			s.Len = siz;
+			s.Name = cstring(&seg32.Name);
+			s.Addr = uint64(seg32.Addr);
+			s.Memsz = uint64(seg32.Memsz);
+			s.Offset = uint64(seg32.Offset);
+			s.Filesz = uint64(seg32.Filesz);
+			s.Maxprot = seg32.Maxprot;
+			s.Prot = seg32.Prot;
+			s.Nsect = seg32.Nsect;
+			s.Flag = seg32.Flag;
+			f.Loads[i] = s;
+			for i := 0; i < int(s.Nsect); i++ {
+				var sh32 Section32;
+				if err := binary.Read(b, bo, &sh32); err != nil {
+					return nil, err;
+				}
+				sh := new(Section);
+				sh.Name = cstring(&sh32.Name);
+				sh.Seg = cstring(&sh32.Seg);
+				sh.Addr = uint64(sh32.Addr);
+				sh.Size = uint64(sh32.Size);
+				sh.Offset = sh32.Offset;
+				sh.Align = sh32.Align;
+				sh.Reloff = sh32.Reloff;
+				sh.Nreloc = sh32.Nreloc;
+				sh.Flags = sh32.Flags;
+				f.pushSection(sh, r);
+			}
+
+		case LoadCmdSegment64:
+			var seg64 Segment64;
+			b := bytes.NewBuffer(cmddat);
+			if err := binary.Read(b, bo, &seg64); err != nil {
+				return nil, err;
+			}
+			s = new(Segment);
+			s.LoadBytes = cmddat;
+			s.Cmd = cmd;
+			s.Len = siz;
+			s.Name = cstring(&seg64.Name);
+			s.Addr = seg64.Addr;
+			s.Memsz = seg64.Memsz;
+			s.Offset = seg64.Offset;
+			s.Filesz = seg64.Filesz;
+			s.Maxprot = seg64.Maxprot;
+			s.Prot = seg64.Prot;
+			s.Nsect = seg64.Nsect;
+			s.Flag = seg64.Flag;
+			f.Loads[i] = s;
+			for i := 0; i < int(s.Nsect); i++ {
+				var sh64 Section64;
+				if err := binary.Read(b, bo, &sh64); err != nil {
+					return nil, err;
+				}
+				sh := new(Section);
+				sh.Name = cstring(&sh64.Name);
+				sh.Seg = cstring(&sh64.Seg);
+				sh.Addr = sh64.Addr;
+				sh.Size = sh64.Size;
+				sh.Offset = sh64.Offset;
+				sh.Align = sh64.Align;
+				sh.Reloff = sh64.Reloff;
+				sh.Nreloc = sh64.Nreloc;
+				sh.Flags = sh64.Flags;
+				f.pushSection(sh, r);
+			}
+		}
+		if s != nil {
+			s.sr = io.NewSectionReader(r, int64(s.Offset), int64(s.Filesz));
+			s.ReaderAt = s.sr;
+		}
+	}
+	return f, nil;
+}
+
+func (f *File) pushSection(sh *Section, r io.ReaderAt) {
+	n := len(f.Sections);
+	if n >= cap(f.Sections) {
+		m := (n+1)*2;
+		new := make([]*Section, n, m);
+		for i, sh := range f.Sections {
+			new[i] = sh;
+		}
+		f.Sections = new;
+	}
+	f.Sections = f.Sections[0:n+1];
+	f.Sections[n] = sh;
+	sh.sr = io.NewSectionReader(r, int64(sh.Offset), int64(sh.Size));
+	sh.ReaderAt = sh.sr;
+}
+
+func cstring(b []byte) string {
+	var i int;
+	for i=0; i<len(b) && b[i] != 0; i++ {
+	}
+	return string(b[0:i]);
+}
+
+// Segment returns the first Segment with the given name, or nil if no such segment exists.
+func (f *File) Segment(name string) *Segment {
+	for _, l := range f.Loads {
+		if s, ok := l.(*Segment); ok && s.Name == name {
+			return s;
+		}
+	}
+	return nil;
+}
+
+// Section returns the first section with the given name, or nil if no such
+// section exists.
+func (f *File) Section(name string) *Section {
+	for _, s := range f.Sections {
+		if s.Name == name {
+			return s;
+		}
+	}
+	return nil;
+}
+
+// DWARF returns the DWARF debug information for the Mach-O file.
+func (f *File) DWARF() (*dwarf.Data, os.Error) {
+	// There are many other DWARF sections, but these
+	// are the required ones, and the debug/dwarf package
+	// does not use the others, so don't bother loading them.
+	var names = [...]string{"abbrev", "info", "str"};
+	var dat [len(names)][]byte;
+	for i, name := range names {
+		name = "__debug_" + name;
+		s := f.Section(name);
+		if s == nil {
+			return nil, os.NewError("missing Mach-O section " + name);
+		}
+		b, err := s.Data();
+		if err != nil && uint64(len(b)) < s.Size {
+			return nil, err;
+		}
+		dat[i] = b;
+	}
+
+	abbrev, info, str := dat[0], dat[1], dat[2];
+	return dwarf.New(abbrev, nil, nil, info, nil, nil, nil, str);
+}
diff --git a/src/pkg/debug/macho/file_test.go b/src/pkg/debug/macho/file_test.go
new file mode 100644
index 00000000000..69b87575f20
--- /dev/null
+++ b/src/pkg/debug/macho/file_test.go
@@ -0,0 +1,159 @@
+// Copyright 2009 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
+
+import (
+	"reflect";
+	"testing";
+)
+
+type fileTest struct {
+	file string;
+	hdr FileHeader;
+	segments []*SegmentHeader;
+	sections []*SectionHeader;
+}
+
+var fileTests = []fileTest {
+	fileTest{
+		"testdata/gcc-386-darwin-exec",
+		FileHeader{0xfeedface, Cpu386, 0x3, 0x2, 0xc, 0x3c0, 0x85},
+		[]*SegmentHeader{
+			&SegmentHeader{LoadCmdSegment, 0x38, "__PAGEZERO", 0x0, 0x1000, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
+			&SegmentHeader{LoadCmdSegment, 0xc0, "__TEXT", 0x1000, 0x1000, 0x0, 0x1000, 0x7, 0x5, 0x2, 0x0},
+			&SegmentHeader{LoadCmdSegment, 0xc0, "__DATA", 0x2000, 0x1000, 0x1000, 0x1000, 0x7, 0x3, 0x2, 0x0},
+			&SegmentHeader{LoadCmdSegment, 0x7c, "__IMPORT", 0x3000, 0x1000, 0x2000, 0x1000, 0x7, 0x7, 0x1, 0x0},
+			&SegmentHeader{LoadCmdSegment, 0x38, "__LINKEDIT", 0x4000, 0x1000, 0x3000, 0x12c, 0x7, 0x1, 0x0, 0x0},
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+		},
+		[]*SectionHeader{
+			&SectionHeader{"__text", "__TEXT", 0x1f68, 0x88, 0xf68, 0x2, 0x0, 0x0, 0x80000400},
+			&SectionHeader{"__cstring", "__TEXT", 0x1ff0, 0xd, 0xff0, 0x0, 0x0, 0x0, 0x2},
+			&SectionHeader{"__data", "__DATA", 0x2000, 0x14, 0x1000, 0x2, 0x0, 0x0, 0x0},
+			&SectionHeader{"__dyld", "__DATA", 0x2014, 0x1c, 0x1014, 0x2, 0x0, 0x0, 0x0},
+			&SectionHeader{"__jump_table", "__IMPORT", 0x3000, 0xa, 0x2000, 0x6, 0x0, 0x0, 0x4000008},
+		},
+	},
+	fileTest{
+		"testdata/gcc-amd64-darwin-exec",
+		FileHeader{0xfeedfacf, CpuAmd64, 0x80000003, 0x2, 0xb, 0x568, 0x85},
+		[]*SegmentHeader{
+			&SegmentHeader{LoadCmdSegment64, 0x48, "__PAGEZERO", 0x0, 0x100000000, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
+			&SegmentHeader{LoadCmdSegment64, 0x1d8, "__TEXT", 0x100000000, 0x1000, 0x0, 0x1000, 0x7, 0x5, 0x5, 0x0},
+			&SegmentHeader{LoadCmdSegment64, 0x138, "__DATA", 0x100001000, 0x1000, 0x1000, 0x1000, 0x7, 0x3, 0x3, 0x0},
+			&SegmentHeader{LoadCmdSegment64, 0x48, "__LINKEDIT", 0x100002000, 0x1000, 0x2000, 0x140, 0x7, 0x1, 0x0, 0x0},
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+		},
+		[]*SectionHeader{
+			&SectionHeader{"__text", "__TEXT", 0x100000f14, 0x6d, 0xf14, 0x2, 0x0, 0x0, 0x80000400},
+			&SectionHeader{"__symbol_stub1", "__TEXT", 0x100000f81, 0xc, 0xf81, 0x0, 0x0, 0x0, 0x80000408},
+			&SectionHeader{"__stub_helper", "__TEXT", 0x100000f90, 0x18, 0xf90, 0x2, 0x0, 0x0, 0x0},
+			&SectionHeader{"__cstring", "__TEXT", 0x100000fa8, 0xd, 0xfa8, 0x0, 0x0, 0x0, 0x2},
+			&SectionHeader{"__eh_frame", "__TEXT", 0x100000fb8, 0x48, 0xfb8, 0x3, 0x0, 0x0, 0x6000000b},
+			&SectionHeader{"__data", "__DATA", 0x100001000, 0x1c, 0x1000, 0x3, 0x0, 0x0, 0x0},
+			&SectionHeader{"__dyld", "__DATA", 0x100001020, 0x38, 0x1020, 0x3, 0x0, 0x0, 0x0},
+			&SectionHeader{"__la_symbol_ptr", "__DATA", 0x100001058, 0x10, 0x1058, 0x2, 0x0, 0x0, 0x7},
+		},
+	},
+	fileTest{
+		"testdata/gcc-amd64-darwin-exec-debug",
+		FileHeader{0xfeedfacf, CpuAmd64, 0x80000003, 0xa, 0x4, 0x5a0, 0},
+		[]*SegmentHeader{
+			nil,
+			&SegmentHeader{LoadCmdSegment64, 0x1d8, "__TEXT", 0x100000000, 0x1000, 0x0, 0x0, 0x7, 0x5, 0x5, 0x0},
+			&SegmentHeader{LoadCmdSegment64, 0x138, "__DATA", 0x100001000, 0x1000, 0x0, 0x0, 0x7, 0x3, 0x3, 0x0},
+			&SegmentHeader{LoadCmdSegment64, 0x278, "__DWARF", 0x100002000, 0x1000, 0x1000, 0x1bc, 0x7, 0x3, 0x7, 0x0},
+		},
+		[]*SectionHeader{
+			&SectionHeader{"__text", "__TEXT", 0x100000f14, 0x0, 0x0, 0x2, 0x0, 0x0, 0x80000400},
+			&SectionHeader{"__symbol_stub1", "__TEXT", 0x100000f81, 0x0, 0x0, 0x0, 0x0, 0x0, 0x80000408},
+			&SectionHeader{"__stub_helper", "__TEXT", 0x100000f90, 0x0, 0x0, 0x2, 0x0, 0x0, 0x0},
+			&SectionHeader{"__cstring", "__TEXT", 0x100000fa8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2},
+			&SectionHeader{"__eh_frame", "__TEXT", 0x100000fb8, 0x0, 0x0, 0x3, 0x0, 0x0, 0x6000000b},
+			&SectionHeader{"__data", "__DATA", 0x100001000, 0x0, 0x0, 0x3, 0x0, 0x0, 0x0},
+			&SectionHeader{"__dyld", "__DATA", 0x100001020, 0x0, 0x0, 0x3, 0x0, 0x0, 0x0},
+			&SectionHeader{"__la_symbol_ptr", "__DATA", 0x100001058, 0x0, 0x0, 0x2, 0x0, 0x0, 0x7},
+			&SectionHeader{"__debug_abbrev", "__DWARF", 0x100002000, 0x36, 0x1000, 0x0, 0x0, 0x0, 0x0},
+			&SectionHeader{"__debug_aranges", "__DWARF", 0x100002036, 0x30, 0x1036, 0x0, 0x0, 0x0, 0x0},
+			&SectionHeader{"__debug_frame", "__DWARF", 0x100002066, 0x40, 0x1066, 0x0, 0x0, 0x0, 0x0},
+			&SectionHeader{"__debug_info", "__DWARF", 0x1000020a6, 0x54, 0x10a6, 0x0, 0x0, 0x0, 0x0},
+			&SectionHeader{"__debug_line", "__DWARF", 0x1000020fa, 0x47, 0x10fa, 0x0, 0x0, 0x0, 0x0},
+			&SectionHeader{"__debug_pubnames", "__DWARF", 0x100002141, 0x1b, 0x1141, 0x0, 0x0, 0x0, 0x0},
+			&SectionHeader{"__debug_str", "__DWARF", 0x10000215c, 0x60, 0x115c, 0x0, 0x0, 0x0, 0x0},
+		},
+	},
+}
+
+func TestOpen(t *testing.T) {
+	for i := range fileTests {
+		tt := &fileTests[i];
+
+		f, err := Open(tt.file);
+		if err != nil {
+			t.Error(err);
+			continue;
+		}
+		if !reflect.DeepEqual(f.FileHeader, tt.hdr) {
+			t.Errorf("open %s:\n\thave %#v\n\twant %#v\n", tt.file, f.FileHeader, tt.hdr);
+			continue;
+		}
+		for i, l := range f.Loads {
+			if i >= len(tt.segments) {
+				break;
+			}
+			sh := tt.segments[i];
+			s, ok := l.(*Segment);
+			if sh == nil {
+				if ok {
+					t.Errorf("open %s, section %d: skipping %#v\n", tt.file, i, &s.SegmentHeader);
+				}
+				continue;
+			}
+			if !ok {
+				t.Errorf("open %s, section %d: not *Segment\n", tt.file, i);
+				continue;
+			}
+			have := &s.SegmentHeader;
+			want := sh;
+			if !reflect.DeepEqual(have, want) {
+				t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want);
+			}
+		}
+		tn := len(tt.segments);
+		fn := len(f.Loads);
+		if tn != fn {
+			t.Errorf("open %s: len(Loads) = %d, want %d", tt.file, fn, tn);
+		}
+
+		for i, sh := range f.Sections {
+			if i >= len(tt.sections) {
+				break;
+			}
+			have := &sh.SectionHeader;
+			want := tt.sections[i];
+			if !reflect.DeepEqual(have, want) {
+				t.Errorf("open %s, section %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want);
+			}
+		}
+		tn = len(tt.sections);
+		fn = len(f.Sections);
+		if tn != fn {
+			t.Errorf("open %s: len(Sections) = %d, want %d", tt.file, fn, tn);
+		}
+
+	}
+}
diff --git a/src/pkg/debug/macho/macho.go b/src/pkg/debug/macho/macho.go
new file mode 100644
index 00000000000..78f2d7fc3b9
--- /dev/null
+++ b/src/pkg/debug/macho/macho.go
@@ -0,0 +1,230 @@
+// Copyright 2009 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.
+
+// Mach-O header data structures
+// http://developer.apple.com/mac/library/documentation/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html
+
+package macho
+
+import "strconv"
+
+// A FileHeader represents a Mach-O file header.
+type FileHeader struct {
+	Magic	uint32;
+	Cpu	Cpu;
+	SubCpu	uint32;
+	Type	Type;
+	Ncmd	uint32;
+	Cmdsz	uint32;
+	Flags	uint32;
+}
+const (
+	fileHeaderSize32 = 7*4;
+	fileHeaderSize64 = 8*4;
+)
+
+const (
+	Magic32 uint32 = 0xfeedface;
+	Magic64 uint32 = 0xfeedfacf;
+)
+
+// A Type is a Mach-O file type, either an object or an executable.
+type Type uint32
+const (
+	TypeObj Type = 1;
+	TypeExec Type = 2;
+)
+
+// A Cpu is a Mach-O cpu type.
+type Cpu uint32
+const (
+	Cpu386 Cpu = 7;
+	CpuAmd64 Cpu = Cpu386 + 1<<24;
+)
+
+var cpuStrings = []intName {
+	intName{ uint32(Cpu386), "Cpu386" },
+	intName{ uint32(CpuAmd64), "CpuAmd64" },
+}
+func (i Cpu) String() string {
+	return stringName(uint32(i), cpuStrings, false)
+}
+func (i Cpu) GoString() string {
+	return stringName(uint32(i), cpuStrings, true)
+}
+
+// A LoadCmd is a Mach-O load command.
+type LoadCmd uint32;
+const (
+	LoadCmdSegment LoadCmd = 1;
+	LoadCmdSegment64 LoadCmd = 25;
+	LoadCmdThread LoadCmd = 4;
+	LoadCmdUnixThread LoadCmd = 5;	// thread+stack
+)
+var cmdStrings = []intName {
+	intName{ uint32(LoadCmdSegment), "LoadCmdSegment" },
+	intName{ uint32(LoadCmdSegment64), "LoadCmdSegment64" },
+	intName{ uint32(LoadCmdThread), "LoadCmdThread" },
+	intName{ uint32(LoadCmdUnixThread), "LoadCmdUnixThread" },
+}
+func (i LoadCmd) String() string {
+	return stringName(uint32(i), cmdStrings, false)
+}
+func (i LoadCmd) GoString() string {
+	return stringName(uint32(i), cmdStrings, true)
+}
+
+// A Segment64 is a 64-bit Mach-O segment load command.
+type Segment64 struct {
+	Cmd	LoadCmd;
+	Len	uint32;
+	Name	[16]byte;
+	Addr	uint64;
+	Memsz	uint64;
+	Offset	uint64;
+	Filesz	uint64;
+	Maxprot	uint32;
+	Prot	uint32;
+	Nsect	uint32;
+	Flag	uint32;
+}
+
+// A Segment32 is a 32-bit Mach-O segment load command.
+type Segment32 struct {
+	Cmd	LoadCmd;
+	Len	uint32;
+	Name	[16]byte;
+	Addr	uint32;
+	Memsz	uint32;
+	Offset	uint32;
+	Filesz	uint32;
+	Maxprot	uint32;
+	Prot	uint32;
+	Nsect	uint32;
+	Flag	uint32;
+}
+
+// A Section32 is a 32-bit Mach-O section header.
+type Section32 struct {
+	Name	[16]byte;
+	Seg		[16]byte;
+	Addr	uint32;
+	Size	uint32;
+	Offset	uint32;
+	Align	uint32;
+	Reloff	uint32;
+	Nreloc	uint32;
+	Flags	uint32;
+	Reserve1	uint32;
+	Reserve2	uint32;
+}
+
+// A Section32 is a 64-bit Mach-O section header.
+type Section64 struct {
+	Name	[16]byte;
+	Seg		[16]byte;
+	Addr	uint64;
+	Size	uint64;
+	Offset	uint32;
+	Align	uint32;
+	Reloff	uint32;
+	Nreloc	uint32;
+	Flags	uint32;
+	Reserve1	uint32;
+	Reserve2	uint32;
+	Reserve3	uint32;
+}
+
+// A Thread is a Mach-O thread state command.
+type Thread struct {
+	Cmd	LoadCmd;
+	Len	uint32;
+	Type	uint32;
+	Data	[]uint32;
+}
+
+// Regs386 is the Mach-O 386 register structure.
+type Regs386 struct {
+	AX	uint32;
+	BX	uint32;
+	CX	uint32;
+	DX	uint32;
+	DI	uint32;
+	SI	uint32;
+	BP	uint32;
+	SP	uint32;
+	SS	uint32;
+	FLAGS	uint32;
+	IP	uint32;
+	CS	uint32;
+	DS	uint32;
+	ES	uint32;
+	FS	uint32;
+	GS	uint32;
+}
+
+// RegsAMD64 is the Mach-O AMD64 register structure.
+type RegsAMD64 struct {
+	AX	uint64;
+	BX	uint64;
+	CX	uint64;
+	DX	uint64;
+	DI	uint64;
+	SI	uint64;
+	BP	uint64;
+	SP	uint64;
+	R8	uint64;
+	R9	uint64;
+	R10	uint64;
+	R11	uint64;
+	R12	uint64;
+	R13	uint64;
+	R14	uint64;
+	R15	uint64;
+	IP	uint64;
+	FLAGS	uint64;
+	CS	uint64;
+	FS	uint64;
+	GS	uint64;
+}
+
+type intName struct {
+	i uint32;
+	s string;
+}
+
+func stringName(i uint32, names []intName, goSyntax bool) string {
+	for _, n := range names {
+		if n.i == i {
+			if goSyntax {
+				return "macho." + n.s
+			}
+			return n.s
+		}
+	}
+	return strconv.Uitoa64(uint64(i))
+}
+
+func flagName(i uint32, names []intName, goSyntax bool) string {
+	s := "";
+	for _, n := range names {
+		if n.i & i == n.i {
+			if len(s) > 0 {
+				s += "+";
+			}
+			if goSyntax {
+				s += "macho.";
+			}
+			s += n.s;
+			i -= n.i;
+		}
+	}
+	if len(s) == 0 {
+		return "0x" + strconv.Uitob64(uint64(i), 16)
+	}
+	if i != 0 {
+		s += "+0x" + strconv.Uitob64(uint64(i), 16)
+	}
+	return s
+}
diff --git a/src/pkg/debug/macho/testdata/gcc-386-darwin-exec b/src/pkg/debug/macho/testdata/gcc-386-darwin-exec
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diff --git a/src/pkg/debug/macho/testdata/gcc-amd64-darwin-exec b/src/pkg/debug/macho/testdata/gcc-amd64-darwin-exec
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diff --git a/src/pkg/debug/macho/testdata/gcc-amd64-darwin-exec-debug b/src/pkg/debug/macho/testdata/gcc-amd64-darwin-exec-debug
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