206 lines
8.6 KiB
Markdown
206 lines
8.6 KiB
Markdown
# Miri [](https://travis-ci.org/solson/miri) [](https://ci.appveyor.com/project/solson63299/miri)
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An experimental interpreter for [Rust][rust]'s
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[mid-level intermediate representation][mir] (MIR). It can run binaries and
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test suites of cargo projects and detect certain classes of undefined behavior,
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for example:
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* Out-of-bounds memory accesses and use-after-free
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* Invalid use of uninitialized data
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* Violation of intrinsic preconditions (an [`unreachable_unchecked`] being
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reached, calling [`copy_nonoverlapping`] with overlapping ranges, ...)
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* Not sufficiently aligned memory accesses and references
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* Violation of basic type invariants (a `bool` that is not 0 or 1, for example,
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or an invalid enum discriminant)
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* WIP: Violations of the rules governing aliasing for reference types
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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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[`unreachable_unchecked`]: https://doc.rust-lang.org/stable/std/hint/fn.unreachable_unchecked.html
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[`copy_nonoverlapping`]: https://doc.rust-lang.org/stable/std/ptr/fn.copy_nonoverlapping.html
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## Building Miri
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We recommend that you install [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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[rustup]: https://www.rustup.rs
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## Running Miri on tiny examples
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```sh
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cargo +nightly run -- -Zmiri-disable-validation tests/run-pass/vecs.rs # Or whatever test you like.
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```
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We have to disable validation because that can lead to errors when libstd is not
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compiled the right way.
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## Running Miri on your own project('s test suite)
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Install Miri as a cargo subcommand:
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```sh
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cargo +nightly install --git https://github.com/solson/miri/
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```
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Be aware that if you used `rustup override set` to fix a particular Rust version
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for the miri directory, that will *not* apply to your own project directory!
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You have to use a consistent Rust version for building miri and your project for
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this to work, so remember to either always specify the nightly version manually,
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overriding it in your project directory as well, or use `rustup default nightly`
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(or `rustup default nightly-YYYY-MM-DD`) to globally make `nightly` the default
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toolchain.
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1. Run `cargo clean` to eliminate any cached dependencies. Miri needs your
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dependencies to be compiled the right way, that would not happen if they have
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previously already been compiled.
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2. To run all tests in your project through Miri, use `cargo +nightly miri test`.
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**NOTE**: This is currently broken, see the discussion in
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[#479](https://github.com/solson/miri/issues/479).
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3. If you have a binary project, you can run it through Miri using `cargo
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+nightly miri run`.
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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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#### "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 have/have
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not been built for Miri. Run `cargo clean` before switching from non-Miri to
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Miri 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 custom libstd that Miri uses, and Miri failed to detect that.
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Try deleting `~/.miri`.
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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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```sh
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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` and `test-miri = true`.
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# The latter is important to build libstd with the right flags for miri.
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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 --release` it. `cargo
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test --release FILTER` only runs those tests that contain `FILTER` in their
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filename (including the base directory, e.g. `cargo test --release fail` will
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run all compile-fail tests). We recommend using `--release` to make test
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running take less time.
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Notice that the "fullmir" tests only run if you have `MIRI_SYSROOT` set, the
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test runner does not realized that your libstd comes with full MIR. The
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following will set it correctly:
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```sh
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MIRI_SYSROOT=$(rustc --print sysroot) cargo test --release
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```
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Moreover, 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=rustc_mir::interpret=debug,miri::stacked_borrows 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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## History
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This project began as part of an undergraduate research course in 2015 by
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@solson at the [University of Saskatchewan][usask]. There are [slides] and a
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[report] available from that project. In 2016, @oli-obk joined to prepare miri
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for eventually being used as const evaluator in the Rust compiler itself
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(basically, for `const` and `static` stuff), replacing the old evaluator that
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worked directly on the AST. In 2017, @RalfJung did an internship with Mozilla
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and began developing miri towards a tool for detecting undefined behavior, and
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also using miri as a way to explore the consequences of various possible
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definitions for undefined behavior in Rust. @oli-obk's move of the miri engine
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into the compiler finally came to completion in early 2018. Meanwhile, later
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that year, @RalfJung did a second internship, developing miri further with
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support for checking basic type invariants and verifying that references are
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used according to their aliasing restrictions.
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[usask]: https://www.usask.ca/
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[slides]: https://solson.me/miri-slides.pdf
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[report]: https://solson.me/miri-report.pdf
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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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