Scroll Upgrades

As the team continues to progress on Scroll’s roadmap, we will be upgrading the Scroll network to include new features and improvements.

The following contracts are used to initiate upgrades and execute upgrades after the two-week timelock period:

February 2024 Bridge Upgrade

Overview

To reduce bridging costs, we implemented several gas optimizations on our bridge and rollup contract suite. The optimization techniques used include the following:

• We will now use constants to store some companion contract addresses, instead of using storage variables. This is possible since these values should (almost) never change. With this change we can save on a few storage load operations.
• We updated the intrinsic gas estimation in L1MessageQueue to use a simple upper bound instead of an exact calculation. The two results will be similar for most bridge transactions but the new implementation is significantly cheaper.
• We merged two contracts L1MessageQueue and L2GasPriceOracle to save on call costs from one contract to the other.

Timeline

• Scroll Sepolia:
  • Network Upgrade: January 19, 2024
• Scroll Mainnet:
  • Upgrade Initiation: February 7, 2024
  • Timelock Completion & Upgrade: February 21, 2024

Technical Details

Code Changes

• Bridge Cost Optimization
• Audit Fixes
• Previously deployed version (commit ff380141a8cbcc214dc65f17ffa44faf4be646b6)
• Version deployed (commit 6030927680a92d0285c2c13e6bb27ed27d1f32d1)

Audits

• OpenZeppelin

List of Changes

Changes to L1 contracts:

• In ScrollChain, change messageQueue and verifier to immutable.
• In L1ScrollMessenger, change counterpart, rollup, and messageQueue to immutable.
• In all token gateways, change counterpart, router, and messenger to immutable.
• Merge L1MessageQueue and L2GasPriceOracle into a single contract L1MessageQueueWithGasPriceOracle (deployed on the same address as the previous L1MessageQueue). In this contract we also change messenger and scrollChain to immutable, and simplify calculateIntrinsicGasFee.

Changes to L2 contracts:

• In L2ScrollMessenger, change counterpart to immutable.
• In all token gateways, change counterpart, router, and messenger to immutable.

Contracts affected:

• L1: L1MessageQueue, L2GasPriceOracle, ScrollChain, L1WETHGateway, L1StandardERC20Gateway, L1GatewayRouter, L1ScrollMessenger, L1CustomERC20Gateway, L1ERC721Gateway, L1ERC1155Gateway.
• L2: L2ScrollMessenger, L2WETHGateway, L2StandardERC20Gateway, L2GatewayRouter, L2CustomERC20Gateway, L2ERC721Gateway, L2ERC1155Gateway.

Compatibility

Sequencer and follower nodes (l2geth)

Operators running an l2geth node do not need to upgrade. The changes in this upgrade will not affect l2geth.

Dapps and indexers

Dapps and indexers (and similar off-chain infrastructure) that query contracts or rely on contract interfaces would, in most cases, not need to be changed. The majority of the contract changes are internal and/or backward compatible.

If your application depends on L2GasPriceOracle to monitor how Scroll keeps track of the L2 gas price on L1, from the upgrade block number you will need to start monitoring L1MessageQueueWithGasPriceOracle.

The original gas price oracle contract will be deprecated: it will no longer be updated or used by the Scroll bridge.

• Ethereum:
  • L2GasPriceOracle: 0x987e300fDfb06093859358522a79098848C33852
  • L1MessageQueueWithGasPriceOracle: 0x0d7E906BD9cAFa154b048cFa766Cc1E54E39AF9B
• Sepolia:
  • L2GasPriceOracle: 0x247969F4fad93a33d4826046bc3eAE0D36BdE548
  • L1MessageQueueWithGasPriceOracle: 0xF0B2293F5D834eAe920c6974D50957A1732de763