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Alternative Scheme of Precompiled Contract Versioning for Hard Fork

Number: ella-2018-0001
Title: Alternative Scheme of Precompiled Contract Versioning for Hard Fork
Author: Wei Tang <hi@that.world>
Status: Proposed
Type: Standards Track
Layer: Consensus
Discussion: https://github.com/ellaism/specs/issues/5
Created: 2018-01-02

Motivation

This defines a scheme for precompiled contract versioning as an alternative for the precompiled contract handling defined in ella-2017-0001. This adds certain complexity. However, it has the advantage that it makes effect of precompiled contracts to be visible on the state trie and might to simplify future virtual machine design.

Specification

Even with ella-2017-0001 applied, the effect of precompiled contracts are hidden in the state trie. As an alternative, however, we can make it visiable. We do this by having a separate set of account versions for precompiled contracts.

We define precompiled contract deployment system transactions. This type of transaction is in the same category of block reward system transactions and it is not recorded in a block's transactions set. Precompiled contract deployment system transactions are only valid for a particular block number, and for a particular address. Not having this system transaction is also invalid. Once executed, this type of transaction deploys a precompiled contract with a given account version starting from 10001. It inherits the current account balance, set the code hash to to the empty code hash, stroage to the empty storage, and set the given account version. To transit to this scheme, we use the following backward-compatible method.

  • The account version 0 inherits the old behavior. When contracts with account version 0 calls address from 0x1 to 0x4, instead of refering to the actual account, it executes a pre-defined code together with a message call transaction.
  • With the hard fork that we transit to use the new account versioning scheme, issue four precompiled contract deployment system transactions to address 0x1 to 0x4 with account version number 0x10001 to 0x10004. This will create account 0x1 to 0x4 if not exist, and the deployment transaction will then only change the account version.
  • From this point, no matter which account version the VM is executing, the behavior of precompiled contracts are defined by version 0x10001 to 0x10004 and will remain the same.