riscairo project template

This is part of the riscairo project (https://github.com/massalabs/riscairo).

Clone this template to use the riscairo virtual machine to provably run Rust code.

General description

This repo contains a sample riscairo guest program written in Rust (guest_rs) that exposes a couple of functions:

• compute_hash computes a blake2s256 hash of the provided data using the https://crates.io/crates/blake2 crate.
• add adds the first two u8 of the argument to return the sum result u8. Panics on overflow with a message.
• prepend_hello prepends the text "hello " in ASCII to the passed bytes and returns the concatenated byte array. This uses dynamic memory allocation in Rust.

The exposed guest functions are then called from a host Starknet contract host_cairo written in Cairo, which also exports them back.

When you compile the guest_rs, make sure to use a tool like the provided convert.py to inline the ELF file into a .cairo source file within the host_cairo source.

To try it on on a contract already deployed on Sepolia, use try_me.py (don't forget to setup your API key inside of try_me.py).

Features and limitations

Embedded constraints

The rust code is meant to run on a bare metal RISC-V CPU without an operating system. This means that only no_std Rust code will compile.

Dynamic memory allocation

This template enables dynamic memory allocation through a bump allocator defined in guest_rs/src/rv.rs that never frees. This was chosen in order to minimize computing and binary size overhead, but feel free to adjust it to your needs.

Panics

The template supports panic unwinding and forwards the panic message to the riscairo VM that decodes and handles it.