183 lines
7.2 KiB
Markdown
183 lines
7.2 KiB
Markdown
# Miri [[slides](https://solson.me/miri-slides.pdf)] [[report](https://solson.me/miri-report.pdf)] [](https://travis-ci.org/solson/miri) [](https://ci.appveyor.com/project/solson63299/miri)
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An experimental interpreter for [Rust][rust]'s [mid-level intermediate
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representation][mir] (MIR). This project began as part of my work for the
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undergraduate research course at the [University of Saskatchewan][usask].
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## Building Miri
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I recommend that you install [rustup][rustup] to obtain Rust. Then all you have
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to do is:
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```sh
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cargo +nightly build
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```
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This uses the very latest Rust version. If you experience any problem, refer to
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the `rust-version` file which contains a particular Rust nightly version that
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has been tested against the version of miri you are using. Make sure to use
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that particular `nightly-YYYY-MM-DD` whenever the instructions just say
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`nightly`.
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To avoid repeating the nightly version all the time, you can use
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`rustup override set nightly` (or `rustup override set nightly-YYYY-MM-DD`),
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which means `nightly` Rust will automatically be used whenever you are working
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in this directory.
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## Running Miri
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```sh
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cargo +nightly run tests/run-pass/vecs.rs # Or whatever test you like.
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```
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## Running Miri with full libstd
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Per default libstd does not contain the MIR of non-polymorphic functions. When
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Miri hits a call to such a function, execution terminates. To fix this, it is
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possible to compile libstd with full MIR:
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```sh
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rustup component add --toolchain nightly rust-src
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cargo +nightly install xargo
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rustup run nightly xargo/build.sh
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```
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Now you can run Miri against the libstd compiled by xargo:
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```sh
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MIRI_SYSROOT=~/.xargo/HOST cargo +nightly run tests/run-pass-fullmir/hashmap.rs
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```
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Notice that you will have to re-run the last step of the preparations above
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(`xargo/build.sh`) when your toolchain changes (e.g., when you update the
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nightly).
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## Running Miri on your own project('s test suite)
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Install Miri as a cargo subcommand with `cargo install +nightly --all-features
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--path .`. Be aware that if you used `rustup override set` to fix a particular
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Rust version for the miri directory, that will *not* apply to your own project
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directory! You have to use a consistent Rust version for building miri and your
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project for this to work, so remember to either always specify the nightly
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version manually, overriding it in your project directory as well, or use
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`rustup default nightly` (or `rustup default nightly-YYYY-MM-DD`) to globally
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make `nightly` the default toolchain.
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We assume that you have prepared a MIR-enabled libstd as described above. Now
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compile your project and its dependencies against that libstd:
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1. Run `cargo clean` to eliminate any cached dependencies that were built against
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the non-MIR `libstd`.
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2. To run all tests in your project through, Miri, use
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`MIRI_SYSROOT=~/.xargo/HOST cargo +nightly miri test`.
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3. If you have a binary project, you can run it through Miri using
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`MIRI_SYSROOT=~/.xargo/HOST cargo +nightly miri`.
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### Common Problems
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When using the above instructions, you may encounter a number of confusing compiler
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errors.
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#### "constant evaluation error: no mir for `<function>`"
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You may have forgotten to set `MIRI_SYSROOT` when calling `cargo miri`, and
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your program called into `std` or `core`. Be sure to set `MIRI_SYSROOT=~/.xargo/HOST`.
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#### "found possibly newer version of crate `std` which `<dependency>` depends on"
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Your build directory may contain artifacts from an earlier build that did/did not
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have `MIRI_SYSROOT` set. Run `cargo clean` before switching from non-Miri to Miri
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builds and vice-versa.
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#### "found crate `std` compiled by an incompatible version of rustc"
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You may be running `cargo miri` with a different compiler version than the one
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used to build the MIR-enabled `std`. Be sure to consistently use the same toolchain,
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which should be the toolchain specified in the `rust-version` file.
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## Miri `-Z` flags
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Several `-Z` flags are relevant for miri:
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* `-Zmir-opt-level` controls how many MIR optimizations are performed. miri
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overrides the default to be `0`; be advised that using any higher level can
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make miri miss bugs in your program because they got optimized away.
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* `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
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functions. This is needed so that miri can execute such functions, so miri
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sets this flag per default.
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* `-Zmiri-disable-validation` is a custom `-Z` flag added by miri. It disables
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enforcing the validity invariant, which is enforced by default. This is
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mostly useful for debugging; it means miri will miss bugs in your program.
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## Development and Debugging
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Since the heart of Miri (the main interpreter engine) lives in rustc, working on
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Miri will often require using a locally built rustc. This includes getting a
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trace of the execution, as distributed rustc has `debug!` and `trace!` disabled.
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The first-time setup for a local rustc looks as follows:
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```
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git clone https://github.com/rust-lang/rust/ rustc
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cd rustc
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cp config.toml.example config.toml
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# Now edit `config.toml` and set `debug-assertions = true`
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./x.py build src/rustc
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# You may have to change the architecture in the next command
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rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
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# Now cd to your Miri directory
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rustup override set custom
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```
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The `build` step can take 30 minutes and more.
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Now you can `cargo build` Miri, and you can `cargo test` it. But the key point
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is, you can now run Miri with a trace of all execution steps:
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```sh
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MIRI_LOG=debug cargo run tests/run-pass/vecs.rs
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```
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Setting `MIRI_LOG` like this will configure logging for miri itself as well as
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the `rustc::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
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can also do more targeted configuration, e.g. to debug the stacked borrows
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implementation:
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```sh
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MIRI_LOG=miri::stacked_borrows=trace,rustc_mir::interpret=debug cargo run tests/run-pass/vecs.rs
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```
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In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
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evaluation error was originally created.
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If you changed something in rustc and want to re-build, run
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```
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./x.py --keep-stage 0 build src/rustc
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```
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This avoids rebuilding the entire stage 0, which can save a lot of time.
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## Contributing and getting help
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Check out the issues on this GitHub repository for some ideas. There's lots that
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needs to be done that I haven't documented in the issues yet, however. For more
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ideas or help with running or hacking on Miri, you can contact me (`scott`) on
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Mozilla IRC in any of the Rust IRC channels (`#rust`, `#rust-offtopic`, etc).
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## License
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Licensed under either of
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* Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
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http://www.apache.org/licenses/LICENSE-2.0)
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* MIT license ([LICENSE-MIT](LICENSE-MIT) or
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http://opensource.org/licenses/MIT) at your option.
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### Contribution
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in the work by you shall be dual licensed as above, without any
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additional terms or conditions.
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[rust]: https://www.rust-lang.org/
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[mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
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[usask]: https://www.usask.ca/
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[rustup]: https://www.rustup.rs
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