diff --git a/src/cmd/internal/objfile/disasm.go b/src/cmd/internal/objfile/disasm.go
new file mode 100644
index 0000000000000000000000000000000000000000..7982faa47c12d2bd9a8cb5d44cfe53bde8551dd9
--- /dev/null
+++ b/src/cmd/internal/objfile/disasm.go
@@ -0,0 +1,243 @@
+package objfile
+
+import (
+ "bufio"
+ "debug/gosym"
+ "encoding/binary"
+ "fmt"
+ "io"
+ "regexp"
+ "sort"
+ "strings"
+ "text/tabwriter"
+
+ "cmd/internal/rsc.io/arm/armasm"
+ "cmd/internal/rsc.io/x86/x86asm"
+)
+
+// Disasm is a disassembler for a given File.
+type Disasm struct {
+ syms []Sym
+ pcln *gosym.Table
+ text []byte
+ textStart uint64
+ textEnd uint64
+ goarch string
+ disasm disasmFunc
+ byteOrder binary.ByteOrder
+}
+
+// Disasm returns a disassembler for the file f.
+func (f *File) Disasm() (*Disasm, error) {
+ syms, err := f.Symbols()
+ if err != nil {
+ return nil, err
+ }
+
+ pcln, err := f.PCLineTable()
+ if err != nil {
+ return nil, err
+ }
+
+ textStart, textBytes, err := f.Text()
+ if err != nil {
+ return nil, err
+ }
+
+ goarch := f.GOARCH()
+ disasm := disasms[goarch]
+ byteOrder := byteOrders[goarch]
+ if disasm == nil || byteOrder == nil {
+ return nil, fmt.Errorf("unsupported architecture")
+ }
+
+ // Filter out section symbols, overwriting syms in place.
+ keep := syms[:0]
+ for _, sym := range syms {
+ switch sym.Name {
+ case "runtime.text", "text", "_text", "runtime.etext", "etext", "_etext":
+ // drop
+ default:
+ keep = append(keep, sym)
+ }
+ }
+ syms = keep
+ d := &Disasm{
+ syms: syms,
+ pcln: pcln,
+ text: textBytes,
+ textStart: textStart,
+ textEnd: textStart + uint64(len(textBytes)),
+ goarch: goarch,
+ disasm: disasm,
+ byteOrder: byteOrder,
+ }
+
+ return d, nil
+}
+
+// lookup finds the symbol name containing addr.
+func (d *Disasm) lookup(addr uint64) (name string, base uint64) {
+ i := sort.Search(len(d.syms), func(i int) bool { return addr < d.syms[i].Addr })
+ if i > 0 {
+ s := d.syms[i-1]
+ if s.Addr != 0 && s.Addr <= addr && addr < s.Addr+uint64(s.Size) {
+ return s.Name, s.Addr
+ }
+ }
+ return "", 0
+}
+
+// base returns the final element in the path.
+// It works on both Windows and Unix paths.
+func base(path string) string {
+ path = path[strings.LastIndex(path, "/")+1:]
+ path = path[strings.LastIndex(path, `\`)+1:]
+ return path
+}
+
+// Print prints a disassembly of the file to w.
+// If filter is non-nil, the disassembly only includes functions with names matching filter.
+// The disassembly only includes functions that overlap the range [start, end).
+func (d *Disasm) Print(w io.Writer, filter *regexp.Regexp, start, end uint64) {
+ if start < d.textStart {
+ start = d.textStart
+ }
+ if end > d.textEnd {
+ end = d.textEnd
+ }
+ printed := false
+ bw := bufio.NewWriter(w)
+ for _, sym := range d.syms {
+ symStart := sym.Addr
+ symEnd := sym.Addr + uint64(sym.Size)
+ if sym.Code != 'T' && sym.Code != 't' ||
+ symStart < d.textStart ||
+ symEnd <= start || end <= symStart ||
+ filter != nil && !filter.MatchString(sym.Name) {
+ continue
+ }
+ if printed {
+ fmt.Fprintf(bw, "\n")
+ }
+ printed = true
+
+ file, _, _ := d.pcln.PCToLine(sym.Addr)
+ fmt.Fprintf(bw, "TEXT %s(SB) %s\n", sym.Name, file)
+
+ tw := tabwriter.NewWriter(bw, 1, 8, 1, '\t', 0)
+ if symEnd > end {
+ symEnd = end
+ }
+ code := d.text[:end-d.textStart]
+ d.Decode(symStart, symEnd, func(pc, size uint64, file string, line int, text string) {
+ i := pc - d.textStart
+ fmt.Fprintf(tw, "\t%s:%d\t%#x\t", base(file), line, pc)
+ if size%4 != 0 || d.goarch == "386" || d.goarch == "amd64" {
+ // Print instruction as bytes.
+ fmt.Fprintf(tw, "%x", code[i:i+size])
+ } else {
+ // Print instruction as 32-bit words.
+ for j := uint64(0); j < size; j += 4 {
+ if j > 0 {
+ fmt.Fprintf(tw, " ")
+ }
+ fmt.Fprintf(tw, "%08x", d.byteOrder.Uint32(code[i+j:]))
+ }
+ }
+ fmt.Fprintf(tw, "\t%s\n", text)
+ })
+ tw.Flush()
+ }
+ bw.Flush()
+}
+
+// Decode disassembles the text segment range [start, end), calling f for each instruction.
+func (d *Disasm) Decode(start, end uint64, f func(pc, size uint64, file string, line int, text string)) {
+ if start < d.textStart {
+ start = d.textStart
+ }
+ if end > d.textEnd {
+ end = d.textEnd
+ }
+ code := d.text[:end-d.textStart]
+ lookup := d.lookup
+ for pc := start; pc < end; {
+ i := pc - d.textStart
+ text, size := d.disasm(code[i:], pc, lookup)
+ file, line, _ := d.pcln.PCToLine(pc)
+ f(pc, uint64(size), file, line, text)
+ pc += uint64(size)
+ }
+}
+
+type lookupFunc func(addr uint64) (sym string, base uint64)
+type disasmFunc func(code []byte, pc uint64, lookup lookupFunc) (text string, size int)
+
+func disasm_386(code []byte, pc uint64, lookup lookupFunc) (string, int) {
+ return disasm_x86(code, pc, lookup, 32)
+}
+
+func disasm_amd64(code []byte, pc uint64, lookup lookupFunc) (string, int) {
+ return disasm_x86(code, pc, lookup, 64)
+}
+
+func disasm_x86(code []byte, pc uint64, lookup lookupFunc, arch int) (string, int) {
+ inst, err := x86asm.Decode(code, 64)
+ var text string
+ size := inst.Len
+ if err != nil || size == 0 || inst.Op == 0 {
+ size = 1
+ text = "?"
+ } else {
+ text = x86asm.Plan9Syntax(inst, pc, lookup)
+ }
+ return text, size
+}
+
+type textReader struct {
+ code []byte
+ pc uint64
+}
+
+func (r textReader) ReadAt(data []byte, off int64) (n int, err error) {
+ if off < 0 || uint64(off) < r.pc {
+ return 0, io.EOF
+ }
+ d := uint64(off) - r.pc
+ if d >= uint64(len(r.code)) {
+ return 0, io.EOF
+ }
+ n = copy(data, r.code[d:])
+ if n < len(data) {
+ err = io.ErrUnexpectedEOF
+ }
+ return
+}
+
+func disasm_arm(code []byte, pc uint64, lookup lookupFunc) (string, int) {
+ inst, err := armasm.Decode(code, armasm.ModeARM)
+ var text string
+ size := inst.Len
+ if err != nil || size == 0 || inst.Op == 0 {
+ size = 4
+ text = "?"
+ } else {
+ text = armasm.Plan9Syntax(inst, pc, lookup, textReader{code, pc})
+ }
+ return text, size
+}
+
+var disasms = map[string]disasmFunc{
+ "386": disasm_386,
+ "amd64": disasm_amd64,
+ "arm": disasm_arm,
+}
+
+var byteOrders = map[string]binary.ByteOrder{
+ "386": binary.LittleEndian,
+ "amd64": binary.LittleEndian,
+ "arm": binary.LittleEndian,
+ "power64": binary.BigEndian,
+ "power64le": binary.LittleEndian,
+}