1 # Miri [![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 -- -Zmiri-disable-validation tests/run-pass/vecs.rs # Or whatever test you like.
51 We have to disable validation because that can lead to errors when libstd is not
52 compiled the right way.
54 ## Running Miri with full libstd
56 Per default libstd does not contain the MIR of non-polymorphic functions, and
57 also does not contain some extra MIR statements that miri needs for validation.
58 When Miri hits a call to such a function, execution terminates, and even when
59 the MIR is present, validation can fail. To fix this, it is possible to compile
63 rustup component add --toolchain nightly rust-src
64 cargo +nightly install xargo
65 rustup run nightly xargo/build.sh
68 Now you can run Miri against the libstd compiled by xargo:
71 MIRI_SYSROOT=~/.xargo/HOST cargo +nightly run tests/run-pass-fullmir/hashmap.rs
74 Notice that you will have to re-run the last step of the preparations above
75 (`xargo/build.sh`) when your toolchain changes (e.g., when you update the
78 ## Running Miri on your own project('s test suite)
80 Install Miri as a cargo subcommand with `cargo +nightly install --all-features
81 --path .`. Be aware that if you used `rustup override set` to fix a particular
82 Rust version for the miri directory, that will *not* apply to your own project
83 directory! You have to use a consistent Rust version for building miri and your
84 project for this to work, so remember to either always specify the nightly
85 version manually, overriding it in your project directory as well, or use
86 `rustup default nightly` (or `rustup default nightly-YYYY-MM-DD`) to globally
87 make `nightly` the default toolchain.
89 We assume that you have prepared a MIR-enabled libstd as described above. Now
90 compile your project and its dependencies against that libstd:
92 1. Run `cargo clean` to eliminate any cached dependencies that were built against
94 2. To run all tests in your project through, Miri, use
95 `MIRI_SYSROOT=~/.xargo/HOST cargo +nightly miri test`. **NOTE**: This is
96 currently broken, see the discussion in
97 [#479](https://github.com/solson/miri/issues/479).
98 3. If you have a binary project, you can run it through Miri using
99 `MIRI_SYSROOT=~/.xargo/HOST cargo +nightly miri`.
103 When using the above instructions, you may encounter a number of confusing compiler
106 #### "constant evaluation error: no mir for `<function>`"
108 You may have forgotten to set `MIRI_SYSROOT` when calling `cargo miri`, and
109 your program called into `std` or `core`. Be sure to set `MIRI_SYSROOT=~/.xargo/HOST`.
111 #### "found possibly newer version of crate `std` which `<dependency>` depends on"
113 Your build directory may contain artifacts from an earlier build that did/did not
114 have `MIRI_SYSROOT` set. Run `cargo clean` before switching from non-Miri to Miri
115 builds and vice-versa.
117 #### "found crate `std` compiled by an incompatible version of rustc"
119 You may be running `cargo miri` with a different compiler version than the one
120 used to build the MIR-enabled `std`. Be sure to consistently use the same toolchain,
121 which should be the toolchain specified in the `rust-version` file.
125 Several `-Z` flags are relevant for miri:
127 * `-Zmir-opt-level` controls how many MIR optimizations are performed. miri
128 overrides the default to be `0`; be advised that using any higher level can
129 make miri miss bugs in your program because they got optimized away.
130 * `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
131 functions. This is needed so that miri can execute such functions, so miri
132 sets this flag per default.
133 * `-Zmiri-disable-validation` is a custom `-Z` flag added by miri. It disables
134 enforcing the validity invariant, which is enforced by default. This is
135 mostly useful for debugging; it means miri will miss bugs in your program.
137 ## Development and Debugging
139 Since the heart of Miri (the main interpreter engine) lives in rustc, working on
140 Miri will often require using a locally built rustc. This includes getting a
141 trace of the execution, as distributed rustc has `debug!` and `trace!` disabled.
143 The first-time setup for a local rustc looks as follows:
145 git clone https://github.com/rust-lang/rust/ rustc
147 cp config.toml.example config.toml
148 # Now edit `config.toml` and set `debug-assertions = true` and `test-miri = true`.
149 # The latter is important to build libstd with the right flags for miri.
150 ./x.py build src/rustc
151 # You may have to change the architecture in the next command
152 rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
153 # Now cd to your Miri directory
154 rustup override set custom
156 The `build` step can take 30 minutes and more.
158 Now you can `cargo build` Miri, and you can `cargo test --release` it. `cargo
159 test --release FILTER` only runs those tests that contain `FILTER` in their
160 filename (including the base directory, e.g. `cargo test --release fail` will
161 run all compile-fail tests). We recommend using `--release` to make test
162 running take less time.
164 Notice that the "fullmir" tests only run if you have `MIRI_SYSROOT` set, the
165 test runner does not realized that your libstd comes with full MIR. The
166 following will set it correctly:
168 MIRI_SYSROOT=$(rustc --print sysroot) cargo test --release
171 Moreover, you can now run Miri with a trace of all execution steps:
173 MIRI_LOG=debug cargo run tests/run-pass/vecs.rs
176 Setting `MIRI_LOG` like this will configure logging for miri itself as well as
177 the `rustc::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
178 can also do more targeted configuration, e.g. to debug the stacked borrows
181 MIRI_LOG=rustc_mir::interpret=debug,miri::stacked_borrows cargo run tests/run-pass/vecs.rs
184 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
185 evaluation error was originally created.
187 If you changed something in rustc and want to re-build, run
189 ./x.py --keep-stage 0 build src/rustc
191 This avoids rebuilding the entire stage 0, which can save a lot of time.
193 ## Contributing and getting help
195 Check out the issues on this GitHub repository for some ideas. There's lots that
196 needs to be done that I haven't documented in the issues yet, however. For more
197 ideas or help with running or hacking on Miri, you can contact me (`scott`) on
198 Mozilla IRC in any of the Rust IRC channels (`#rust`, `#rust-offtopic`, etc).
202 This project began as part of an undergraduate research course in 2015 by
203 @solson at the [University of Saskatchewan][usask]. There are [slides] and a
204 [report] available from that project. In 2016, @oli-obk joined to prepare miri
205 for eventually being used as const evaluator in the Rust compiler itself
206 (basically, for `const` and `static` stuff), replacing the old evaluator that
207 worked directly on the AST. In 2017, @RalfJung did an internship with Mozilla
208 and began developing miri towards a tool for detecting undefined behavior, and
209 also using miri as a way to explore the consequences of various possible
210 definitions for undefined behavior in Rust. @oli-obk's move of the miri engine
211 into the compiler finally came to completion in early 2018. Meanwhile, later
212 that year, @RalfJung did a second internship, developing miri further with
213 support for checking basic type invariants and verifying that references are
214 used according to their aliasing restrictions.
216 [usask]: https://www.usask.ca/
217 [slides]: https://solson.me/miri-slides.pdf
218 [report]: https://solson.me/miri-report.pdf
222 Licensed under either of
223 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
224 http://www.apache.org/licenses/LICENSE-2.0)
225 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
226 http://opensource.org/licenses/MIT) at your option.
230 Unless you explicitly state otherwise, any contribution intentionally submitted
231 for inclusion in the work by you shall be dual licensed as above, without any
232 additional terms or conditions.