1 # Miri [[slides](https://solson.me/miri-slides.pdf)] [[report](https://solson.me/miri-report.pdf)] [![Build Status](https://travis-ci.org/solson/miri.svg?branch=master)](https://travis-ci.org/solson/miri) [![Windows build status](https://ci.appveyor.com/api/projects/status/github/solson/miri?svg=true)](https://ci.appveyor.com/project/solson63299/miri)
4 An experimental interpreter for [Rust][rust]'s
5 [mid-level intermediate representation][mir] (MIR). It can run binaries and
6 test suites of cargo projects and detect certain classes of undefined behavior,
9 * Out-of-bounds memory accesses and use-after-free
10 * Invalid use of uninitialized data
11 * Violation of intrinsic preconditions (an [`unreachable_unchecked`] being
12 reached, calling [`copy_nonoverlapping`] with overlapping ranges, ...)
13 * Not sufficiently aligned memory accesses and references
14 * Violation of basic type invariants (a `bool` that is not 0 or 1, for example,
15 or an invalid enum discriminant)
16 * WIP: Violations of the rules governing aliasing for reference types
18 [rust]: https://www.rust-lang.org/
19 [mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
20 [`unreachable_unchecked`]: https://doc.rust-lang.org/stable/std/hint/fn.unreachable_unchecked.html
21 [`copy_nonoverlapping`]: https://doc.rust-lang.org/stable/std/ptr/fn.copy_nonoverlapping.html
25 We recommend that you install [rustup] to obtain Rust. Then all you have
32 This uses the very latest Rust version. If you experience any problem, refer to
33 the `rust-version` file which contains a particular Rust nightly version that
34 has been tested against the version of miri you are using. Make sure to use
35 that particular `nightly-YYYY-MM-DD` whenever the instructions just say
38 To avoid repeating the nightly version all the time, you can use
39 `rustup override set nightly` (or `rustup override set nightly-YYYY-MM-DD`),
40 which means `nightly` Rust will automatically be used whenever you are working
43 [rustup]: https://www.rustup.rs
48 cargo +nightly run tests/run-pass/vecs.rs # Or whatever test you like.
51 ## Running Miri with full libstd
53 Per default libstd does not contain the MIR of non-polymorphic functions. When
54 Miri hits a call to such a function, execution terminates. To fix this, it is
55 possible to compile libstd with full MIR:
58 rustup component add --toolchain nightly rust-src
59 cargo +nightly install xargo
60 rustup run nightly xargo/build.sh
63 Now you can run Miri against the libstd compiled by xargo:
66 MIRI_SYSROOT=~/.xargo/HOST cargo +nightly run tests/run-pass-fullmir/hashmap.rs
69 Notice that you will have to re-run the last step of the preparations above
70 (`xargo/build.sh`) when your toolchain changes (e.g., when you update the
73 ## Running Miri on your own project('s test suite)
75 Install Miri as a cargo subcommand with `cargo install +nightly --all-features
76 --path .`. Be aware that if you used `rustup override set` to fix a particular
77 Rust version for the miri directory, that will *not* apply to your own project
78 directory! You have to use a consistent Rust version for building miri and your
79 project for this to work, so remember to either always specify the nightly
80 version manually, overriding it in your project directory as well, or use
81 `rustup default nightly` (or `rustup default nightly-YYYY-MM-DD`) to globally
82 make `nightly` the default toolchain.
84 We assume that you have prepared a MIR-enabled libstd as described above. Now
85 compile your project and its dependencies against that libstd:
87 1. Run `cargo clean` to eliminate any cached dependencies that were built against
89 2. To run all tests in your project through, Miri, use
90 `MIRI_SYSROOT=~/.xargo/HOST cargo +nightly miri test`. **NOTE**: This is
91 currently broken, see the discussion in
92 [#479](https://github.com/solson/miri/issues/479).
93 3. If you have a binary project, you can run it through Miri using
94 `MIRI_SYSROOT=~/.xargo/HOST cargo +nightly miri`.
98 When using the above instructions, you may encounter a number of confusing compiler
101 #### "constant evaluation error: no mir for `<function>`"
103 You may have forgotten to set `MIRI_SYSROOT` when calling `cargo miri`, and
104 your program called into `std` or `core`. Be sure to set `MIRI_SYSROOT=~/.xargo/HOST`.
106 #### "found possibly newer version of crate `std` which `<dependency>` depends on"
108 Your build directory may contain artifacts from an earlier build that did/did not
109 have `MIRI_SYSROOT` set. Run `cargo clean` before switching from non-Miri to Miri
110 builds and vice-versa.
112 #### "found crate `std` compiled by an incompatible version of rustc"
114 You may be running `cargo miri` with a different compiler version than the one
115 used to build the MIR-enabled `std`. Be sure to consistently use the same toolchain,
116 which should be the toolchain specified in the `rust-version` file.
120 Several `-Z` flags are relevant for miri:
122 * `-Zmir-opt-level` controls how many MIR optimizations are performed. miri
123 overrides the default to be `0`; be advised that using any higher level can
124 make miri miss bugs in your program because they got optimized away.
125 * `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
126 functions. This is needed so that miri can execute such functions, so miri
127 sets this flag per default.
128 * `-Zmiri-disable-validation` is a custom `-Z` flag added by miri. It disables
129 enforcing the validity invariant, which is enforced by default. This is
130 mostly useful for debugging; it means miri will miss bugs in your program.
132 ## Development and Debugging
134 Since the heart of Miri (the main interpreter engine) lives in rustc, working on
135 Miri will often require using a locally built rustc. This includes getting a
136 trace of the execution, as distributed rustc has `debug!` and `trace!` disabled.
138 The first-time setup for a local rustc looks as follows:
140 git clone https://github.com/rust-lang/rust/ rustc
142 cp config.toml.example config.toml
143 # Now edit `config.toml` and set `debug-assertions = true` and `test-miri = true`.
144 # The latter is important to build libstd with the right flags for miri.
145 ./x.py build src/rustc
146 # You may have to change the architecture in the next command
147 rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
148 # Now cd to your Miri directory
149 rustup override set custom
151 The `build` step can take 30 minutes and more.
153 Now you can `cargo build` Miri, and you can `cargo test --release` it. `cargo
154 test --release FILTER` only runs those tests that contain `FILTER` in their
155 filename (including the base directory, e.g. `cargo test --release fail` will
156 run all compile-fail tests). We recommend using `--release` to make test
157 running take less time.
159 Notice that the "fullmir" tests only run if you have `MIRI_SYSROOT` set, the
160 test runner does not realized that your libstd comes with full MIR. The
161 following will set it correctly:
163 MIRI_SYSROOT=$(rustc --print sysroot) cargo test --release
166 Moreover, you can now run Miri with a trace of all execution steps:
168 MIRI_LOG=debug cargo run tests/run-pass/vecs.rs
171 Setting `MIRI_LOG` like this will configure logging for miri itself as well as
172 the `rustc::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
173 can also do more targeted configuration, e.g. to debug the stacked borrows
176 MIRI_LOG=rustc_mir::interpret=debug,miri::stacked_borrows cargo run tests/run-pass/vecs.rs
179 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
180 evaluation error was originally created.
182 If you changed something in rustc and want to re-build, run
184 ./x.py --keep-stage 0 build src/rustc
186 This avoids rebuilding the entire stage 0, which can save a lot of time.
188 ## Contributing and getting help
190 Check out the issues on this GitHub repository for some ideas. There's lots that
191 needs to be done that I haven't documented in the issues yet, however. For more
192 ideas or help with running or hacking on Miri, you can contact me (`scott`) on
193 Mozilla IRC in any of the Rust IRC channels (`#rust`, `#rust-offtopic`, etc).
197 This project began as part of an undergraduate research course in 2015 by
198 @solson at the [University of Saskatchewan][usask]. In 2016, @oli-obk joined to
199 prepare miri for eventually being used as const evaluator in the Rust compiler
200 itself (basically, for `const` and `static` stuff), replacing the old evaluator
201 that worked directly on the AST. In 2017, @RalfJung did an internship with
202 Mozilla and began developing miri towards a tool for detecting undefined
203 behavior, and also using miri as a way to explore the consequences of various
204 possible definitions for undefined behavior in Rust. @oli-obk's move of the
205 miri engine into the compiler finally came to completion in early 2018.
206 Meanwhile, later that year, @RalfJung did a second internship, developing miri
207 further with support for checking basic type invariants and verifying that
208 references are used according to their aliasing restrictions.
210 [usask]: https://www.usask.ca/
214 Licensed under either of
215 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
216 http://www.apache.org/licenses/LICENSE-2.0)
217 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
218 http://opensource.org/licenses/MIT) at your option.
222 Unless you explicitly state otherwise, any contribution intentionally submitted
223 for inclusion in the work by you shall be dual licensed as above, without any
224 additional terms or conditions.