Initial Proposal: Cronos v1.2 Network Upgrade

[lezzokafka]

Authors and Credit

Cronos Team and Community

Status

DRAFT

Proposal

Dear community members, we are pleased to propose the scheduled v1.2 Cronos mainnet upgrade. The Cronos Mainnet version v1.2 introduces improvements to backward compatibility and RPC improvements.

The tentative upgrade block height is set to 13520000 which is expected around
7 AM GMT on the 17th of April 2024 (3 PM HKT/SGT).

This proposes a breaking network upgrade for the Cronos Chain mainnet "cronosmainnet_25-1". This implies that validators and full nodes must upgrade their cronosd binary from the current version v1.1.* to the latest v1.2 binary at block height 13520000, the block countdown timer can be found here.

What is this upgrade about?

The Cronos v1.2 upgrade focuses on two major goals:

1. Provide backward compatibility for Dapps using block.prevrandao or block.difficulty in their contracts

In the Titan upgrade, we have implemented Ethereum's "Shanghai" upgrade as part of Cronos' roadmap of Ethereum compatibility. This introduced a breaking change for some smart contracts deployed on Cronos, which were utilizing the block.difficulty and/or block.prevrandao expressions in their smart contracts:

• Before the Titan upgrade:
  These expressions returned a meaningless constant value on Cronos (not a random number).

• After the Titan upgrade:
  The block.prevrandao opcode does not exist and these expressions were returning an error at execution.

In the v1.2 upgrade, the opcode associated with block.difficulty and/or block.prevrandao (which are interchangeable depending on the Solidity version) returns a constant value again. This fixes the behavior of legacy smart contracts without impacting new ones.

As a reminder, this constant value is meaningless and smart contract developers should not use these expressions in their smart contracts going forward, especially as a source of randomness. Depending on future evolutions of go-ethereum and Solidity, it is possible that block.difficulty and/or block.prevrandao may become inoperative again in the future.

2. RPC for querying legacy EVM parameters

As described in this pull request, v1.2 includes:

• New feature: support added for new EVM types and parameters.
• Bug fix: an RPC issue was addressed by adding a parameter key table in EVM for previous upgrades.

This v1.2 upgrade supports RPC querying for blocks generated in previous versions of Cronos.

Testing

The proposed upgrades and changes have been tested on both internal testnets and the Cronos testnet (currently at v1.2.0-rc1) to ensure the achievement of expected outcomes.

Action required

Node hosts must apply the new v1.2 binary at the upgrade height; otherwise, the node will stop operating;

DO NOT upgrade your node before the upgrade block height, as the new binary is incompatible before the upgrade height.

References:

Pull request for legacy PRC quering
Pull request for prevrando opcode supports