Using EVM Smart Contracts on Linera

Thanks to the experimental integration of Revm in Linera, it is now possible to run smart contracts compiled for the Ethereum Virtual Machine (EVM) within Linera microchains.

The main purpose of this integration is to allow opensource smart contracts originally written for Ethereum to be more easily migrated to the Linera protocol and composed with existing Linera applications.

Overview and code examples

We generally assume that EVM smart contracts are written in Solidity and compiled to EVM bytecode using the Solidity compiler.

Transactions running on the EVM are still following the programming model of the Linera protocol, notably they can only access the local state of the microchain that executes them. Inside a microchain, contracts may call each other as usual, possibly across virtual machines.

The main features of Linera, such as cross-chain messaging, are also supported in the EVM. These functionalities are exposed through a Solidity library Linera.sol.

Frontends may interact with EVM contracts using custom EVM-like RPCs or using a Rust/Wasm application as a proxy.

Code examples for the features described below can be found under the directory linera-service/tests/fixtures.

Publishing EVM smart contracts

The process for publishing EVM smart contracts is similar to that for Wasm smart contracts, with the key difference being the need to specify the virtual machine used (the default is Wasm).

For EVM contracts, there is only one bytecode file (unlike Wasm, which requires separate contract and service binaries). Therefore, the same file must be passed twice:

bash

linera publish-and-create \
  counter.bytecode counter.bytecode \
  --vm-runtime evm \
  --json-parameters "42"

Here, counter.bytecode contains the compiled contract, and "42" is passed as a constructor argument via the --json-parameters flag.

Constructor arguments for the EVM contract are passed through application parameters. Instantiation-specific arguments are provided separately.

Calling other smart contracts.

EVM smart contracts on Linera can invoke other EVM contracts using standard Solidity syntax.

EVM Contracts calling Wasm smart contracts.

To call a Wasm smart contract from an EVM contract, use the following Solidity command:

solidity

	bytes memory return_value = Linera.try_call_application(address, input);

address: the address of the Wasm smart contract, as a bytes32.
input: the bytes representing the BCS-serialized ContractAbi::Operation input.

The serialization code can be generated using the serde-reflection crate.

Wasm smart contracts calling EVM Contracts.

Wasm smart contracts can call EVM contracts using the alloy-sol-types crate. This crate enables construction of Solidity-compatible types and supports RLP serialization/deserialization.

The Wasm contract call-evm-counter demonstrates this functionality.

For operations, the input type is Vec<u8>.
For service calls, the input type is EvmQuery.

Note: Linera distinguishes between contract and service code execution contexts.

Multichain EVM applications.

To operate across multiple chains, an EVM application must implement the following functions:

solidity

    function instantiate(bytes memory input) external
    function execute_message(bytes memory input) external

instantiate is called on the creator chain.
execute_message handles incoming cross-chain messages.

Additional SDK functions available include:

solidity

    Linera.chain_ownership()
    Linera.read_data_blob()
    Linera.assert_data_blob_exists()
    Linera.validation_round()
    Linera.message_id()
    Linera.message_is_bouncing()

Difference between EVM applications in Ethereum and Linera.

Reentrancy: Reentrancy is currently not supported on Linera. Contracts relying on it will fail with a clean error. In the future, reentrancy may be allowed as an option.
Address Computation: Contract addresses are computed differently from Ethereum.
Gas Limits: Following Infura's practice, Linera imposes a gas limit of 20,000,000 for service calls in EVM contracts. Contract execution is similarly constrained.