Scroll introduced l1sload as a component of our Keystore infrastructure.  However, it is a generalized infrastructure solution that can be leveraged for use cases beyond the Keystore.

What is L1SLOAD?

L1SLOAD is a new precompile built into Scroll.  It allows L2 smart contracts to read data from Ethereum L1 smart contract storage in a trustless manner without requiring Merkle Inclusion Proofs (MIP).  It introduces 2 significant benefits:

• Reduces coding complexity for devs. Implementing MIP requires substantial effort and lines of code. With l1Sload, devs only need to make a simple call to the precompile.
• Reduced gas cost for users. Executing MIP on-chain is expensive due to hashing operations, data storage/retrieval, tree traversal, etc., and it will require fees on both L1 and L2. On the other hand, gas cost for l1Sload is relatively low and incurred only on L2.

We’ve created a Rollup Improvement Proposal to encourage the L2 community to implement this functionality across rollups. See https://ethereum-magicians.org/t/rip-7728-l1sload-precompile/20388 if interested.

How to use it?

Demos:

• https://www.levelup.xyz/content/l1sload-guide-read-arrays-mappings-structs
• https://www.levelup.xyz/content/l1sload-guide-read-the-l1-state-from-l2
• https://dev.to/filosofiacodigoen/how-to-use-l1sload-the-keystores-backbone-25ah
• ‣ (⚠️ Uses previous version of spec)
• https://github.com/5afe/safe-scroll-keystore (⚠️ Uses previous version of spec)
  • find L1SLOAD usage here

L1blocks contract

We created a new system contract to Scroll called L1Blocks . The contract is used to hold the data from L1 block headers.

The L1Blocks contract currently stores eight fields from the L1 block headers for the most recent BLOCK_BUFFER_SIZE blocks. The protocol and contract guarantees the continuity of the imported L1 blocks. The header fields that are stored in the contract are:

• block number