return err
		}
		if cmd.Cmd == LC_UUID {
			var u uuidCmd
			if err := reader.ReadAt(0, &u); err != nil {
				return err
			}
			copy(u.Uuid[:], uuidFromGoBuildId(*flagBuildid))
			if err := reader.WriteAt(0, &u); err != nil {
				return err
			}
			break
		}
	}

	// We're done
	return nil

// hide the WriteTo method of that other type.
type noWriteTo struct{}

// WriteTo hides another WriteTo method.
// It should never be called.
func (noWriteTo) WriteTo(io.Writer) (int64, error) {
	panic("can't happen")
}

// fileWithoutWriteTo implements all the methods of *File other
// than WriteTo. This is used to permit WriteTo to call io.Copy
// without leading to a recursive call to WriteTo.

	for _, tc := range [...]struct {
		Name string
		r    Reader
	}{
		{"not a WriterTo", Reader(nil)},
		{"a WriterTo", struct {
			Reader
			WriterTo
		}{}},
	} {
		nc := NopCloser(tc.r)

		_, expected := tc.r.(WriterTo)
		_, got := nc.(WriterTo)
		if expected != got {
			t.Errorf("NopCloser incorrectly forwards WriterTo for %s, got %t want %t", tc.Name, got, expected)
		}
	}
}

			out.Write32(s.prot2)
			out.Write32(s.nsect)
			out.Write32(s.flag)
		} else {
			out.Write32(LC_SEGMENT)
			out.Write32(56 + 68*s.nsect)
			out.WriteStringN(s.name, 16)
			out.Write32(uint32(s.vaddr))
			out.Write32(uint32(s.vsize))
			out.Write32(uint32(s.fileoffset))
			out.Write32(uint32(s.filesize))
			out.Write32(s.prot1)
			out.Write32(s.prot2)
			out.Write32(s.nsect)
			out.Write32(s.flag)
		}

		return nil, err
	}

	// Establish file header and initial data area if not already present.
	if info.Size() < minFileLen {
		if _, err := f.WriteAt(hdr, 0); err != nil {
			return nil, err
		}
		// Write zeros at the end of the file to extend it to minFileLen.
		if _, err := f.WriteAt(m.zero[:], int64(minFileLen-len(m.zero))); err != nil {
			return nil, err
		}
		info, err = f.Stat()
		if err != nil {
			return nil, err

	}
	b[len(b)-1] = '\n'
	n, err := Stdout.Write(b)
	if err != nil {
		t.Fatalf("Write to os.Stdout failed: %v", err)
	}
	if n != len(b) {
		t.Errorf("Write to os.Stdout should return %d; got %d", len(b), n)
	}
	n, err = Stderr.Write(b)
	if err != nil {
		t.Fatalf("Write to os.Stderr failed: %v", err)
	}
	if n != len(b) {
		t.Errorf("Write to os.Stderr should return %d; got %d", len(b), n)
	}

	for i := range w.buffer {
		delete(w.buffer, i)
	}
	w.wg.Wait()
	return err
}

type writerAt struct {
	w      *io.PipeWriter
	r      *io.PipeReader
	wg     *sync.WaitGroup
	buffer map[int64][]byte
	err    error

	nextOffset int64
	m          sync.Mutex
}

func (w *writerAt) WriteAt(b []byte, offset int64) (n int, err error) {
	w.m.Lock()
	defer w.m.Unlock()

	fmt.Fprintf(r.getState().err, format, args...)
}

// Write emits a slice to the reporter's output stream.
//
// Any error is returned to the caller, and does not otherwise affect the
// reporter's exit code.
func (r *reporter) Write(p []byte) (int, error) {
	return r.getState().out.Write(p)
}

// Report emits a non-nil error to the reporter's error stream,

			err = closeErr
		}
	}()
	if err := hf.Truncate(int64(len(hash))); err != nil {
		return err
	}
	if _, err := hf.WriteAt([]byte(hash), 0); err != nil {
		return err
	}
	return nil
}

// makeDirsReadOnly makes a best-effort attempt to remove write permissions for dir
// and its transitive contents.
func makeDirsReadOnly(dir string) {
	type pathMode struct {
		path string

	if cap(buf) < len(buf)+20 {
		b := make([]byte, len(buf), 20+cap(buf)*2)
		copy(b, buf)
		buf = b
	}
	writeAt := len(buf)
	buf = buf[0 : len(buf)+ctxt.Arch.PtrSize]
	writePtr(ctxt, buf[writeAt:], word)
	return buf
}

// Write a pointer-sized uint to the beginning of buf.
func writePtr(ctxt *obj.Link, buf []byte, word uint64) {
	switch ctxt.Arch.PtrSize {
	case 4: