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

		t.Errorf("WriteAt(-10) = %v, %v; want 0, ...%q...", n, err, wantsub)
	}
}

// Verify that WriteAt doesn't work in append mode.
func TestWriteAtInAppendMode(t *testing.T) {
	defer chtmpdir(t)()
	f, err := OpenFile("write_at_in_append_mode.txt", O_APPEND|O_CREATE, 0666)
	if err != nil {
		t.Fatalf("OpenFile: %v", err)
	}
	defer f.Close()

	_, err = f.WriteAt([]byte(""), 1)

		var tmp [8]byte
		mf.ByteOrder.PutUint32(tmp[:4], uint32(sz))
		_, err = f.WriteAt(tmp[:4], csCmdOff+12)
		if err != nil {
			return err
		}

		// Uodate the __LINKEDIT segment.
		segSz := sigOff + sz - int64(linkeditSeg.Offset)
		mf.ByteOrder.PutUint64(tmp[:8], uint64(segSz))
		_, err = f.WriteAt(tmp[:8], int64(linkeditOff)+int64(unsafe.Offsetof(macho.Segment64{}.Memsz)))
		if err != nil {

	}
	n, err = lw.w.Write(p)
	lw.remain -= n
	return n, err
}

func TestMarshalWriteErrors(t *testing.T) {
	var buf bytes.Buffer
	const writeCap = 1024
	w := &limitedBytesWriter{&buf, writeCap}
	enc := NewEncoder(w)
	var err error
	var i int
	const n = 4000
	for i = 1; i <= n; i++ {
		err = enc.Encode(&Passenger{
			Name:   []string{"Alice", "Bob"},

		// Rewriting the file failed.

		if n == 0 {
			// Original file unchanged.
			os.Remove(bakname)
			return err
		}

		// Try to restore the original contents.

		no, erro := fout.WriteAt(orig, 0)
		if erro != nil {
			// That failed too.
			restoreFail(erro)
			return err
		}

		if no < n {
			// Original file is shorter. Truncate.
			if erro = fout.Truncate(int64(no)); erro != nil {

	}
	defer func() {
		if closeErr := hf.Close(); err == nil && closeErr != nil {
			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.

	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) {

		{"Seeker", Type, 0},
		{"StringWriter", Type, 12},
		{"TeeReader", Func, 0},
		{"WriteCloser", Type, 0},
		{"WriteSeeker", Type, 0},
		{"WriteString", Func, 0},
		{"Writer", Type, 0},
		{"WriterAt", Type, 0},
		{"WriterTo", Type, 0},
	},
	"io/fs": {
		{"(*PathError).Error", Method, 16},
		{"(*PathError).Timeout", Method, 16},
		{"(*PathError).Unwrap", Method, 16},