Miri [slides] [report]

An experimental interpreter for Rust's mid-level intermediate representation (MIR). This project began as part of my work for the undergraduate research course at the University of Saskatchewan.

Installing Rust

I recommend that you install rustup and then use it to install the current Rust nightly version:

rustup update nightly

You should also make nightly the default version for your Miri directory by running the following command while you're in it. If you don't do this, you can run the later cargo commands by using cargo +nightly instead.

rustup override add nightly

Building Miri

cargo build

If Miri fails to build, it's likely because a change in the latest nightly compiler broke it. You could try an older nightly with rustup update nightly-<date> where <date> is a few days or weeks ago, e.g. 2016-05-20 for May 20th. Otherwise, you could notify me in an issue or on IRC. Or, if you know how to fix it, you could send a PR. 😄

Running tests

cargo run tests/run-pass/vecs.rs # Or whatever test you like.

Running miri on your own project('s test suite)

Install miri as a cargo subcommand with cargo install --debug. Then, inside your own project, use cargo +nightly miri to run your project, if it is a bin project, or run cargo +nightly miri test to run all tests in your project through miri.

Running miri with full libstd

Per default libstd does not contain the MIR of non-polymorphic functions. When miri hits a call to such a function, execution terminates. To fix this, it is possible to compile libstd with full MIR:

rustup component add rust-src
cargo install xargo
cd xargo/
RUSTFLAGS='-Zalways-encode-mir' xargo build

Now you can run miri against the libstd compiled by xargo:

MIRI_SYSROOT=~/.xargo/HOST cargo run tests/run-pass-fullmir/hashmap.rs

Notice that you will have to re-run the last step of the preparations above when your toolchain changes (e.g., when you update the nightly).

You can also set -Zmiri-start-fn to make miri start evaluation with the start_fn lang item, instead of starting at the main function.

Development and Debugging

Since the heart of miri (the main interpreter engine) lives in rustc, working on miri will often require using a locally built rustc. This includes getting a trace of the execution, as distributed rustc has trace! disabled.

The first-time setup for a local rustc looks as follows:

git clone https://github.com/rust-lang/rust/ rustc
cd rustc
cp config.toml.example config.toml
# Now edit `config.toml` and set `debug-assertions = true`
./x.py build src/rustc
# You may have to change the architecture in the next command
rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
# Now cd to your miri directory
rustup override set custom

The build step can take 30 minutes and more.

Now you can cargo build miri, and you can cargo test --tests. (--tests is needed to skip doctests because we have not built rustdoc for your custom toolchain.) You can also set RUST_LOG=rustc_mir::interpret=trace as environment variable to get a step-by-step trace.

If you changed something in rustc and want to re-build, run

./x.py build src/rustc --keep-stage 0

This avoids rebuilding the entire stage 0, which can save a lot of time.

Contributing and getting help

Check out the issues on this GitHub repository for some ideas. There's lots that needs to be done that I haven't documented in the issues yet, however. For more ideas or help with running or hacking on Miri, you can contact me (scott) on Mozilla IRC in any of the Rust IRC channels (#rust, #rust-offtopic, etc).

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be dual licensed as above, without any additional terms or conditions.