riscairo

RISC-V ELF interpreter in cairo.

Intro

This cairo library implements an ELF file parser and a RISC-V virtual machine. The machine implements the RV32i instruction set, without extensions.

For usage information, please check https://github.com/massalabs/riscairo_template .

Tests and benchmarks

To run all tests and benchmarks, use ./run_tests.sh.

Compliance tests

The VM is tested for compliance under the rv32ui-p-* test suite from https://github.com/riscv-software-src/riscv-tests . Those are self-test ELF files in the folder risc_compliance_checks.

Those tests check the register and memory behavior of every instruction in the target set, as well as combinations of multiple instructions.

Benchmarks

Below are benchmark results on three reference tasks:

• array_reverse: return a new array containing the elements of a provided random u8 array in reverse order. Input complexity is the number of elements in the array. This is a memory read-write heavy task.
• fibonacci: compute the fibonacci sequence element as u32 at index Input complexity. This is an iterative arithmetics-heavy task.
• find_max: return the maximum value in a provided array of random u8. Input complexity is the number of elements in the array. This is a branch-heavy task.

For each benchmark, there are two variants:

• One in which the algorithm is written in Rust and the pre-compiled ELF file. The benchmark accounts for loading the ELF file into the riscairo VM and running it from Cairo code.
• Another variant where the algorithm is written natively in Cairo and does not involve the riscairo VM.

Linear fits on the benchmark results:

In Rust guest within the Riscairo VM for array_reverse:
  Intercept (gas used at zero input complexity): 3429.72
  Slope (gas per unit of input complexity): 22.51
In native Cairo for array_reverse:
  Intercept (gas used at zero input complexity): 1.18
  Slope (gas per unit of input complexity): 0.28

In Rust guest within the Riscairo VM for fibonacci:
  Intercept (gas used at zero input complexity): 3520.50
  Slope (gas per unit of input complexity): 9.87
In native Cairo for fibonacci:
  Intercept (gas used at zero input complexity): 0.50
  Slope (gas per unit of input complexity): 0.16

In Rust guest within the Riscairo VM for find_max:
  Intercept (gas used at zero input complexity): 3449.98
  Slope (gas per unit of input complexity): 15.96
In native Cairo for find_max:
  Intercept (gas used at zero input complexity): 1.00
  Slope (gas per unit of input complexity): 0.20

Here is a hot spot analysis for the find_max task with input complexity 100: