R55

R55 is an experimental Ethereum Execution Environment that seamlessly integrates RISCV smart contracts alongside traditional EVM smart contracts. This dual support operates over the same Ethereum state, and communication happens via ABI-encoded calls.

On the high level, R55 enables the use of pure Rust smart contracts, opening the door for a vast Rust developer community to engage in Ethereum development with minimal barriers to entry, and increasing language and compiler diversity.

On the low level, RISCV code allows for optimization opportunities distinct from the EVM, including the use of off-the-shelf ASICs. This potential for performance gains can be particularly advantageous in specialized domains.

Off-the-shelf tooling

R55 relies on standard tooling that programmers are used to, such as Rust, Cargo and LLVM. This directly enables tooling such as linters, static analyzers, testing, fuzzing, and formal verification tools to be applied to these smart contracts without extra development and research.

Pure & Clean Rust Smart Contracts

Differently from other platforms that offer Rust smart contracts, R55 lets the user code in [no_std] Rust without weird edges. The code below implements a basic ERC20 token with infinite minting for testing. Because the struct and impl are just Rust code, the user can write normal tests and run them natively (as long as they don't need Ethereum host functions). Note that alloy-rs types work out-of-the-box.

#![no_std]
#![no_main]

use core::default::Default;

use contract_derive::contract;
use eth_riscv_runtime::types::Mapping;

use alloy_core::primitives::Address;

#[derive(Default)]
pub struct ERC20 {
    balance: Mapping<Address, u64>,
}

#[contract]
impl ERC20 {
    pub fn balance_of(&self, owner: Address) -> u64 {
        self.balance.read(owner)
    }

    pub fn transfer(&self, from: Address, to: Address, value: u64) {
        let from_balance = self.balance.read(from);
        let to_balance = self.balance.read(to);

        if from == to || from_balance < value {
            revert();
        }

        self.balance.write(from, from_balance - value);
        self.balance.write(to, to_balance + value);
    }

    pub fn mint(&self, to: Address, value: u64) {
        let to_balance = self.balance.read(to);
        self.balance.write(to, to_balance + value);
    }
}

The macro #[contract] above is the only special treatment the user needs to apply to their code. Specifically, it is responsible for the init code (deployer), and for creating the function dispatcher based on the given methods. Note that Rust pub methods are exposed as public functions in the deployed contract, similarly to Solidity's public functions.

Client Integration

R55 is a fork of revm without any API changes. Therefore it can be used seamlessly in Anvil/Reth to deploy a testnet/network with support to RISCV smart contracts. Nothing has to be changed in how transactions are handled or created.

Relevant Links

Test

The R55 crate has a binary that puts everything together in an end-to-end PoC, compiling the erc20 contract, deploying it to an internal instance of revm-r55, and running two transactions on it, first a mint then a balance_of check.

You'll need to install Rust's RISCV toolchain:

$ rustup install nightly-2024-02-01-x86_64-unknown-linux-gnu

Now run:

$ cargo run
...
Compiling deploy: erc20
Cargo command completed successfully
Deployed at addr: 0x522b3294e6d06aa25ad0f1b8891242e335d3b459
Tx result: 0x
Tx result: 0x000000000000000000000000000000000000000000000000000000000000002a

First R55 compiles the runtime RISCV-ELF binary that will be deployed. This is needed to also compile the initcode RISCV-ELF binary that runs the constructor and creates the contract. The mint function has no return values, seen in Tx result: 0x. We minted 42 tokens to our test account in the first transaction, and we can see in the second transaction that indeed the balance is 42 (0x2a).

Architecture

The compiler uses rustc, llvm, eth-riscv-syscalls, eth-riscv-runtime and riscv-rt to compile and link ELF binaries with low-level syscalls to be executed by rvemu-r55:

graph TD;
    RustContract[Rust contract] --> CompiledContract[compiled contract]
    rustc --> CompiledContract
    llvm --> CompiledContract
    EthRiscVSyscalls[eth-riscv-syscalls] --> CompiledContract
    EthRiscVRuntime1[eth-riscv-runtime] --> CompiledContract
    CompiledContract --> LinkedRuntimeBytecode[linked runtime bytecode]
    EthRiscVRuntime2[eth-riscv-runtime] --> LinkedRuntimeBytecode
    riscv_rt[riscv-rt] --> LinkedRuntimeBytecode
    LinkedRuntimeBytecode --> LinkedInitBytecode[linked init bytecode]
    EthRiscVRuntime3[eth-riscv-runtime] --> LinkedInitBytecode

The execution environment depends on revm, and relies on the rvemu-r55 RISCV interpreter and eth-riscv-runtime.

graph TD;
    revm --> revm-r55
    rvemu-r55 --> revm-r55
    eth-riscv-runtime --> revm-r55