powdrVM template

This template is a basic structure for a powdrVM host/guest project.

Dependencies

• Rust/cargo

Usage

This will run the host and generate ZK proofs.

cargo run -r

AVX / Neon

You can enable AVX or Neon support by using the simd feature and running the host with extra flags:

RUSTFLAGS='-C target-cpu=native' cargo run --features simd -r

Structure

• src/main.rs: the host code. This is where you create a powdr Session, prepare data to be shared with the guest, and run the prover.
• guest: this is the guest crate. It contains the code that will be run inside the powdrVM.
• powdr-target: this is where all generated artifacts reside. This includes the compiled guest code to powdr-asm, the compiled PIL constraints, setup artifacts such as proving and verifying keys, and the final ZK proofs.

Troubleshooting

powdrVM uses a default chunk size of 2^20 cycles for production cases. In some machines, key generation can run out-of-memory. To solve this, use

export MAX_DEGREE_LOG=20

and use a chunk size of 2^18 in the host, as explained in the section below. This is being improved at the moment.

Workflow

Let's look at src/main.rs line by line:

Here we create some data we want to share with the guest:

let some_data = vec![1, 2, 3, 4, 5];

Create a new powdr session where we'll be running crate guest in powdrVM and all artifacts will be stored in powdr-target:

let mut session = Session::new("./guest", "powdr-target")

Write some_data to channel 1 and the sum of some_data to channel 2. The guest will read this data from the channels:

.write(1, &some_data).write(2, &some_data.iter().sum::<u32>());

The line below also creates a powdr Session, but tells powdrVM to use 2^18 rows per chunk, if needed. In that case, make sure to also use export MAX_DEGREE_LOG=20. This tells the powdr compiler to generate smaller circuits than the default production size of 2^22. This is being improved at the moment.

let mut session = Session::new_with_chunk_size("./guest", "powdr-target", 18)

Run the session without generating a proof. Useful for testing the guest code:

session.run();

Generate the ZK proof:

session.prove();

Before generating a proof, powdrVM has to create the proving and verifying keys (setup) for the given guest program. When run for the first time, this can take a while. Subsequent runs will be faster as the setup only changes if the guest changes.

You can also run the host with INFO logs to have a deeper look at what's happening:

RUST_LOG=info cargo run -r