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
24 ## Running Miri on your own project('s test suite)
26 Install Miri as a cargo subcommand:
29 cargo +nightly install --git https://github.com/solson/miri/ miri
32 If this does not work, try using the nightly version given in
33 [this file](https://raw.githubusercontent.com/solson/miri/master/rust-version). CI
34 should ensure that this nightly always works.
36 You have to use a consistent Rust version for building miri and your project, so
37 remember to either always specify the nightly version manually (like in the
38 example above), overriding it in your project directory as well, or use `rustup
39 default nightly` (or `rustup default nightly-YYYY-MM-DD`) to globally make
40 `nightly` the default toolchain.
42 Now you can run your project in Miri:
44 1. Run `cargo clean` to eliminate any cached dependencies. Miri needs your
45 dependencies to be compiled the right way, that would not happen if they have
46 previously already been compiled.
47 2. To run all tests in your project through Miri, use `cargo +nightly miri test`.
48 3. If you have a binary project, you can run it through Miri using `cargo
51 When running code via `cargo miri`, the `cargo-miri` feature is set. You can
52 use this to exclude test cases that will fail under Miri because they do things
53 Miri does not support:
56 #[cfg(not(feature = "cargo-miri"))]
58 fn does_not_work_on_miri() {
60 assert!(&x as *const _ as usize % 4 < 4);
66 When using the above instructions, you may encounter a number of confusing compiler
69 #### "found possibly newer version of crate `std` which `<dependency>` depends on"
71 Your build directory may contain artifacts from an earlier build that have/have
72 not been built for Miri. Run `cargo clean` before switching from non-Miri to
73 Miri builds and vice-versa.
75 #### "found crate `std` compiled by an incompatible version of rustc"
77 You may be running `cargo miri` with a different compiler version than the one
78 used to build the custom libstd that Miri uses, and Miri failed to detect that.
79 Try deleting `~/.cache/miri`.
81 ## Development and Debugging
83 If you want to hack on miri yourself, great! Here are some resources you might
86 ### Using a nightly rustc
88 miri heavily relies on internal rustc interfaces to execute MIR. Still, some
89 things (like adding support for a new intrinsic) can be done by working just on
92 To prepare, make sure you are using a nightly Rust compiler. You also need to
93 set up a libstd that enables execution with miri:
96 rustup override set nightly # or the nightly in `rust-version`
97 cargo run --bin cargo-miri -- miri setup
100 The last command should end in printing the directory where the libstd was
101 built. Set that as your MIRI_SYSROOT environment variable:
104 export MIRI_SYSROOT=~/.cache/miri/HOST # or whatever the previous command said
109 Now you can run Miri directly, without going through `cargo miri`:
112 cargo run tests/run-pass-fullmir/format.rs # or whatever test you like
115 You can also run the test suite with `cargo test --release`. `cargo test
116 --release FILTER` only runs those tests that contain `FILTER` in their filename
117 (including the base directory, e.g. `cargo test --release fail` will run all
118 compile-fail tests). We recommend using `--release` to make test running take
121 Now you are set up! You can write a failing test case, and tweak miri until it
124 ### Using a locally built rustc
126 Since the heart of Miri (the main interpreter engine) lives in rustc, working on
127 Miri will often require using a locally built rustc. The bug you want to fix
128 may actually be on the rustc side, or you just need to get more detailed trace
129 of the execution -- in both cases, you should develop miri against a rustc you
130 compiled yourself, with debug assertions (and hence tracing) enabled.
132 The setup for a local rustc works as follows:
134 git clone https://github.com/rust-lang/rust/ rustc
136 cp config.toml.example config.toml
137 # Now edit `config.toml` and set `debug-assertions = true` and `test-miri = true`.
138 # The latter is important to build libstd with the right flags for miri.
139 # This step can take 30 minutes and more.
140 ./x.py build src/rustc
141 # If you change something, you can get a faster rebuild by doing
142 ./x.py --keep-stage 0 build src/rustc
143 # You may have to change the architecture in the next command
144 rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
145 # Now cd to your Miri directory, then configure rustup
146 rustup override set custom
149 With this, you should now have a working development setup! See
150 ["Testing Miri"](#testing-miri) above for how to proceed.
152 Moreover, you can now run Miri with a trace of all execution steps:
154 MIRI_LOG=debug cargo run tests/run-pass/vecs.rs
157 Setting `MIRI_LOG` like this will configure logging for miri itself as well as
158 the `rustc::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
159 can also do more targeted configuration, e.g. to debug the stacked borrows
162 MIRI_LOG=rustc_mir::interpret=debug,miri::stacked_borrows cargo run tests/run-pass/vecs.rs
165 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
166 evaluation error was originally created.
168 ### Miri `-Z` flags and environment variables
170 Several `-Z` flags are relevant for Miri:
172 * `-Zmir-opt-level` controls how many MIR optimizations are performed. miri
173 overrides the default to be `0`; be advised that using any higher level can
174 make miri miss bugs in your program because they got optimized away.
175 * `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
176 functions. This is needed so that miri can execute such functions, so miri
177 sets this flag per default.
178 * `-Zmiri-disable-validation` is a custom `-Z` flag added by miri. It disables
179 enforcing the validity invariant, which is enforced by default. This is
180 mostly useful for debugging; it means miri will miss bugs in your program.
182 Moreover, Miri recognizes some environment variables:
184 * `MIRI_SYSROOT` (recognized by `miri`, `cargo miri` and the test suite)
185 indicates the sysroot to use.
186 * `MIRI_TARGET` (recognized by the test suite) indicates which target
187 architecture to test against. `miri` and `cargo miri` accept the `--target`
188 flag for the same purpose.
190 ## Contributing and getting help
192 Check out the issues on this GitHub repository for some ideas. There's lots that
193 needs to be done that I haven't documented in the issues yet, however. For more
194 ideas or help with running or hacking on Miri, you can open an issue here on
195 GitHub or contact us (`oli-obk` and `RalfJ`) on the [Rust Zulip].
197 [Rust Zulip]: https://rust-lang.zulipchat.com
201 This project began as part of an undergraduate research course in 2015 by
202 @solson at the [University of Saskatchewan][usask]. There are [slides] and a
203 [report] available from that project. In 2016, @oli-obk joined to prepare miri
204 for eventually being used as const evaluator in the Rust compiler itself
205 (basically, for `const` and `static` stuff), replacing the old evaluator that
206 worked directly on the AST. In 2017, @RalfJung did an internship with Mozilla
207 and began developing miri towards a tool for detecting undefined behavior, and
208 also using miri as a way to explore the consequences of various possible
209 definitions for undefined behavior in Rust. @oli-obk's move of the miri engine
210 into the compiler finally came to completion in early 2018. Meanwhile, later
211 that year, @RalfJung did a second internship, developing miri further with
212 support for checking basic type invariants and verifying that references are
213 used according to their aliasing restrictions.
215 [usask]: https://www.usask.ca/
216 [slides]: https://solson.me/miri-slides.pdf
217 [report]: https://solson.me/miri-report.pdf
221 Licensed under either of
222 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
223 http://www.apache.org/licenses/LICENSE-2.0)
224 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
225 http://opensource.org/licenses/MIT) at your option.
229 Unless you explicitly state otherwise, any contribution intentionally submitted
230 for inclusion in the work by you shall be dual licensed as above, without any
231 additional terms or conditions.