code: func newAddr2LinerNM(cmd, file string, base uint64) (*addr2LinerNM, error) {
  	if cmd == "" {
  		cmd = defaultNM
  	}
  	var b bytes.Buffer
  	c := exec.Command(cmd, "-n", file)
  	c.Stdout = &b
  	if err := c.Run(); err != nil {
  		return nil, err
  	}
  	return parseAddr2LinerNM(base, &b)
  }
docs: //  newAddr2LinerNM starts the given nm command reporting information about the
  // given executable file. If file is a shared library, base should be
  // the address at which it was mapped in the program under
  // consideration.