debug/macho: parse relocations

Fixes #21957

Change-Id: I69ef9e257aa2b7b6c4fc4c115e99f8a7f93d8d9c
Reviewed-on: https://go-review.googlesource.com/65150Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/debug/macho/file.go

@@ -94,8 +94,23 @@ type SectionHeader struct {
 	Flags  uint32
 }
 
+// A Reloc represents a Mach-O relocation.
+type Reloc struct {
+	Addr  uint32
+	Value uint32
+	// when Scattered == false && Extern == true, Value is the symbol number.
+	// when Scattered == false && Extern == false, Value is the section number.
+	// when Scattered == true, Value is the value that this reloc refers to.
+	Type      uint8
+	Len       uint8 // 0=byte, 1=word, 2=long, 3=quad
+	Pcrel     bool
+	Extern    bool // valid if Scattered == false
+	Scattered bool
+}
+
 type Section struct {
 	SectionHeader
+	Relocs []Reloc
 
 	// Embed ReaderAt for ReadAt method.
 	// Do not embed SectionReader directly
@@ -377,7 +392,9 @@ func NewFile(r io.ReaderAt) (*File, error) {
 				sh.Reloff = sh32.Reloff
 				sh.Nreloc = sh32.Nreloc
 				sh.Flags = sh32.Flags
-				f.pushSection(sh, r)
+				if err := f.pushSection(sh, r); err != nil {
+					return nil, err
+				}
 			}
 
 		case LoadCmdSegment64:
@@ -415,7 +432,9 @@ func NewFile(r io.ReaderAt) (*File, error) {
 				sh.Reloff = sh64.Reloff
 				sh.Nreloc = sh64.Nreloc
 				sh.Flags = sh64.Flags
-				f.pushSection(sh, r)
+				if err := f.pushSection(sh, r); err != nil {
+					return nil, err
+				}
 			}
 		}
 		if s != nil {
@@ -463,10 +482,65 @@ func (f *File) parseSymtab(symdat, strtab, cmddat []byte, hdr *SymtabCmd, offset
 	return st, nil
 }
 
-func (f *File) pushSection(sh *Section, r io.ReaderAt) {
+type relocInfo struct {
+	Addr   uint32
+	Symnum uint32
+}
+
+func (f *File) pushSection(sh *Section, r io.ReaderAt) error {
 	f.Sections = append(f.Sections, sh)
 	sh.sr = io.NewSectionReader(r, int64(sh.Offset), int64(sh.Size))
 	sh.ReaderAt = sh.sr
+
+	if sh.Nreloc > 0 {
+		reldat := make([]byte, int(sh.Nreloc)*8)
+		if _, err := r.ReadAt(reldat, int64(sh.Reloff)); err != nil {
+			return err
+		}
+		b := bytes.NewReader(reldat)
+
+		bo := f.ByteOrder
+
+		sh.Relocs = make([]Reloc, sh.Nreloc)
+		for i := range sh.Relocs {
+			rel := &sh.Relocs[i]
+
+			var ri relocInfo
+			if err := binary.Read(b, bo, &ri); err != nil {
+				return err
+			}
+
+			if ri.Addr&(1<<31) != 0 { // scattered
+				rel.Addr = ri.Addr & (1<<24 - 1)
+				rel.Type = uint8((ri.Addr >> 24) & (1<<4 - 1))
+				rel.Len = uint8((ri.Addr >> 28) & (1<<2 - 1))
+				rel.Pcrel = ri.Addr&(1<<30) != 0
+				rel.Value = ri.Symnum
+				rel.Scattered = true
+			} else {
+				switch bo {
+				case binary.LittleEndian:
+					rel.Addr = ri.Addr
+					rel.Value = ri.Symnum & (1<<24 - 1)
+					rel.Pcrel = ri.Symnum&(1<<24) != 0
+					rel.Len = uint8((ri.Symnum >> 25) & (1<<2 - 1))
+					rel.Extern = ri.Symnum&(1<<27) != 0
+					rel.Type = uint8((ri.Symnum >> 28) & (1<<4 - 1))
+				case binary.BigEndian:
+					rel.Addr = ri.Addr
+					rel.Value = ri.Symnum >> 8
+					rel.Pcrel = ri.Symnum&(1<<7) != 0
+					rel.Len = uint8((ri.Symnum >> 5) & (1<<2 - 1))
+					rel.Extern = ri.Symnum&(1<<4) != 0
+					rel.Type = uint8(ri.Symnum & (1<<4 - 1))
+				default:
+					panic("unreachable")
+				}
+			}
+		}
+	}
+
+	return nil
 }
 
 func cstring(b []byte) string {

src/debug/macho/file_test.go

@@ -10,10 +10,11 @@ import (
 )
 
 type fileTest struct {
-	file     string
-	hdr      FileHeader
-	loads    []interface{}
-	sections []*SectionHeader
+	file        string
+	hdr         FileHeader
+	loads       []interface{}
+	sections    []*SectionHeader
+	relocations map[string][]Reloc
 }
 
 var fileTests = []fileTest{
@@ -41,6 +42,7 @@ var fileTests = []fileTest{
 			{"__dyld", "__DATA", 0x2014, 0x1c, 0x1014, 0x2, 0x0, 0x0, 0x0},
 			{"__jump_table", "__IMPORT", 0x3000, 0xa, 0x2000, 0x6, 0x0, 0x0, 0x4000008},
 		},
+		nil,
 	},
 	{
 		"testdata/gcc-amd64-darwin-exec",
@@ -68,6 +70,7 @@ var fileTests = []fileTest{
 			{"__dyld", "__DATA", 0x100001020, 0x38, 0x1020, 0x3, 0x0, 0x0, 0x0},
 			{"__la_symbol_ptr", "__DATA", 0x100001058, 0x10, 0x1058, 0x2, 0x0, 0x0, 0x7},
 		},
+		nil,
 	},
 	{
 		"testdata/gcc-amd64-darwin-exec-debug",
@@ -95,6 +98,7 @@ var fileTests = []fileTest{
 			{"__debug_pubnames", "__DWARF", 0x100002141, 0x1b, 0x1141, 0x0, 0x0, 0x0, 0x0},
 			{"__debug_str", "__DWARF", 0x10000215c, 0x60, 0x115c, 0x0, 0x0, 0x0, 0x0},
 		},
+		nil,
 	},
 	{
 		"testdata/clang-386-darwin-exec-with-rpath",
@@ -118,6 +122,7 @@ var fileTests = []fileTest{
 			nil, // LC_DATA_IN_CODE
 		},
 		nil,
+		nil,
 	},
 	{
 		"testdata/clang-amd64-darwin-exec-with-rpath",
@@ -141,6 +146,78 @@ var fileTests = []fileTest{
 			nil, // LC_DATA_IN_CODE
 		},
 		nil,
+		nil,
+	},
+	{
+		"testdata/clang-386-darwin.obj",
+		FileHeader{0xfeedface, Cpu386, 0x3, 0x1, 0x4, 0x138, 0x2000},
+		nil,
+		nil,
+		map[string][]Reloc{
+			"__text": []Reloc{
+				{
+					Addr:      0x1d,
+					Type:      uint8(GENERIC_RELOC_VANILLA),
+					Len:       2,
+					Pcrel:     true,
+					Extern:    true,
+					Value:     1,
+					Scattered: false,
+				},
+				{
+					Addr:      0xe,
+					Type:      uint8(GENERIC_RELOC_LOCAL_SECTDIFF),
+					Len:       2,
+					Pcrel:     false,
+					Value:     0x2d,
+					Scattered: true,
+				},
+				{
+					Addr:      0x0,
+					Type:      uint8(GENERIC_RELOC_PAIR),
+					Len:       2,
+					Pcrel:     false,
+					Value:     0xb,
+					Scattered: true,
+				},
+			},
+		},
+	},
+	{
+		"testdata/clang-amd64-darwin.obj",
+		FileHeader{0xfeedfacf, CpuAmd64, 0x3, 0x1, 0x4, 0x200, 0x2000},
+		nil,
+		nil,
+		map[string][]Reloc{
+			"__text": []Reloc{
+				{
+					Addr:   0x19,
+					Type:   uint8(X86_64_RELOC_BRANCH),
+					Len:    2,
+					Pcrel:  true,
+					Extern: true,
+					Value:  1,
+				},
+				{
+					Addr:   0xb,
+					Type:   uint8(X86_64_RELOC_SIGNED),
+					Len:    2,
+					Pcrel:  true,
+					Extern: false,
+					Value:  2,
+				},
+			},
+			"__compact_unwind": []Reloc{
+				{
+					Addr:   0x0,
+					Type:   uint8(X86_64_RELOC_UNSIGNED),
+					Len:    3,
+					Pcrel:  false,
+					Extern: false,
+					Value:  1,
+				},
+			},
+		},
 	},
 }
 
@@ -157,42 +234,44 @@ func TestOpen(t *testing.T) {
 			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.loads) {
-				break
-			}
-
-			want := tt.loads[i]
-			if want == nil {
-				continue
-			}
-
-			switch l := l.(type) {
-			case *Segment:
-				have := &l.SegmentHeader
-				if !reflect.DeepEqual(have, want) {
-					t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want)
+		if tt.loads != nil {
+			for i, l := range f.Loads {
+				if i >= len(tt.loads) {
+					break
 				}
-			case *Dylib:
-				have := l
-				have.LoadBytes = nil
-				if !reflect.DeepEqual(have, want) {
-					t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want)
+
+				want := tt.loads[i]
+				if want == nil {
+					continue
 				}
-			case *Rpath:
-				have := l
-				have.LoadBytes = nil
-				if !reflect.DeepEqual(have, want) {
-					t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want)
+
+				switch l := l.(type) {
+				case *Segment:
+					have := &l.SegmentHeader
+					if !reflect.DeepEqual(have, want) {
+						t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want)
+					}
+				case *Dylib:
+					have := l
+					have.LoadBytes = nil
+					if !reflect.DeepEqual(have, want) {
+						t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want)
+					}
+				case *Rpath:
+					have := l
+					have.LoadBytes = nil
+					if !reflect.DeepEqual(have, want) {
+						t.Errorf("open %s, segment %d:\n\thave %#v\n\twant %#v\n", tt.file, i, have, want)
+					}
+				default:
+					t.Errorf("open %s, section %d: unknown load command\n\thave %#v\n\twant %#v\n", tt.file, i, l, want)
 				}
-			default:
-				t.Errorf("open %s, section %d: unknown load command\n\thave %#v\n\twant %#v\n", tt.file, i, l, want)
 			}
-		}
-		tn := len(tt.loads)
-		fn := len(f.Loads)
-		if tn != fn {
-			t.Errorf("open %s: len(Loads) = %d, want %d", tt.file, fn, tn)
+			tn := len(tt.loads)
+			fn := len(f.Loads)
+			if tn != fn {
+				t.Errorf("open %s: len(Loads) = %d, want %d", tt.file, fn, tn)
+			}
 		}
 
 		if tt.sections != nil {
@@ -206,12 +285,22 @@ func TestOpen(t *testing.T) {
 					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)
+			tn := len(tt.sections)
+			fn := len(f.Sections)
 			if tn != fn {
 				t.Errorf("open %s: len(Sections) = %d, want %d", tt.file, fn, tn)
 			}
 		}
+
+		if tt.relocations != nil {
+			for i, sh := range f.Sections {
+				have := sh.Relocs
+				want := tt.relocations[sh.Name]
+				if !reflect.DeepEqual(have, want) {
+					t.Errorf("open %s, relocations in section %d (%s):\n\thave %#v\n\twant %#v\n", tt.file, i, sh.Name, have, want)
+				}
+			}
+		}
 	}
 }