code: func (self *StateDB) AddPreimage(hash common.Hash, preimage []byte) {
  	if _, ok := self.preimages[hash]; !ok {
  		self.journal.append(addPreimageChange{hash: hash})
  		pi := make([]byte, len(preimage))
  		copy(pi, preimage)
  		self.preimages[hash] = pi
  	}
  }
docs: // AddPreimage records a SHA3 preimage seen by the VM.