code: func (bu *Binutils) update(fn func(r *binrep)) {
  	r := &binrep{}
  	bu.mu.Lock()
  	defer bu.mu.Unlock()
  	if bu.rep == nil {
  		initTools(r, "")
  	} else {
  		*r = *bu.rep
  	}
  	fn(r)
  	bu.rep = r
  }
docs: // update modifies the rep for bu via the supplied function.