3 If you want to hack on Miri yourself, great! Here are some resources you might
8 Check out the issues on this GitHub repository for some ideas. In particular,
9 look for the green `E-*` labels which mark issues that should be rather
10 well-suited for onboarding. For more ideas or help with hacking on Miri, you can
11 contact us (`oli-obk` and `RalfJ`) on the [Rust Zulip].
13 [Rust Zulip]: https://rust-lang.zulipchat.com
15 ## Preparing the build environment
17 Miri heavily relies on internal and unstable rustc interfaces to execute MIR,
18 which means it is important that you install a version of rustc that Miri
21 The `rust-version` file contains the commit hash of rustc that Miri is currently
22 tested against. Other versions will likely not work. After installing
23 [`rustup-toolchain-install-master`], you can run the following command to
24 install that exact version of rustc as a toolchain:
28 This will set up a rustup toolchain called `miri` and set it as an override for
29 the current directory.
31 You can also create a `.auto-everything` file (contents don't matter, can be empty), which
32 will cause any `./miri` command to automatically call `./miri toolchain`, `clippy` and `rustfmt`
33 for you. If you don't want all of these to happen, you can add individual `.auto-toolchain`,
34 `.auto-clippy` and `.auto-fmt` files respectively.
36 [`rustup-toolchain-install-master`]: https://github.com/kennytm/rustup-toolchain-install-master
38 ## Building and testing Miri
40 Invoking Miri requires getting a bunch of flags right and setting up a custom
41 sysroot. The `miri` script takes care of that for you. With the
42 build environment prepared, compiling Miri is just one command away:
48 Run `./miri` without arguments to see the other commands our build tool
51 ### Testing the Miri driver
53 The Miri driver compiled from `src/bin/miri.rs` is the "heart" of Miri: it is
54 basically a version of `rustc` that, instead of compiling your code, runs it.
55 It accepts all the same flags as `rustc` (though the ones only affecting code
56 generation and linking obviously will have no effect) [and more][miri-flags].
58 [miri-flags]: README.md#miri--z-flags-and-environment-variables
60 For example, you can (cross-)run the driver on a particular file by doing
63 ./miri run tests/pass/format.rs
64 ./miri run tests/pass/hello.rs --target i686-unknown-linux-gnu
67 and you can (cross-)run the entire test suite using:
71 MIRI_TEST_TARGET=i686-unknown-linux-gnu ./miri test
74 If your target doesn't support libstd, you can run miri with
77 MIRI_NO_STD=1 MIRI_TEST_TARGET=thumbv7em-none-eabihf ./miri test tests/fail/alloc/no_global_allocator.rs
78 MIRI_NO_STD=1 ./miri run tests/pass/no_std.rs --target thumbv7em-none-eabihf
81 to avoid attempting (and failing) to build libstd. Note that almost no tests will pass
82 this way, but you can run individual tests.
84 `./miri test FILTER` only runs those tests that contain `FILTER` in their
85 filename (including the base directory, e.g. `./miri test fail` will run all
88 You can get a trace of which MIR statements are being executed by setting the
89 `MIRI_LOG` environment variable. For example:
92 MIRI_LOG=info ./miri run tests/pass/vec.rs
95 Setting `MIRI_LOG` like this will configure logging for Miri itself as well as
96 the `rustc_middle::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
97 can also do more targeted configuration, e.g. the following helps debug the
98 stacked borrows implementation:
101 MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/pass/vec.rs
104 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
105 evaluation error was originally raised.
109 We use ui-testing in Miri, meaning we generate `.stderr` and `.stdout` files for the output
110 produced by Miri. You can use `./miri bless` to automatically (re)generate these files when
111 you add new tests or change how Miri presents certain output.
113 Note that when you also use `MIRIFLAGS` to change optimizations and similar, the ui output
114 will change in unexpected ways. In order to still be able
115 to run the other checks while ignoring the ui output, use `MIRI_SKIP_UI_CHECKS=1 ./miri test`.
117 For more info on how to configure ui tests see [the documentation on the ui test crate][ui_test]
119 [ui_test]: ui_test/README.md
121 ### Testing `cargo miri`
123 Working with the driver directly gives you full control, but you also lose all
124 the convenience provided by cargo. Once your test case depends on a crate, it
125 is probably easier to test it with the cargo wrapper. You can install your
126 development version of Miri using
132 and then you can use it as if it was installed by `rustup`. Make sure you use
133 the same toolchain when calling `cargo miri` that you used when installing Miri!
134 Usually this means you have to write `cargo +miri miri ...` to select the `miri`
135 toolchain that was installed by `./miri toolchain`.
137 There's a test for the cargo wrapper in the `test-cargo-miri` directory; run
138 `./run-test.py` in there to execute it. Like `./miri test`, this respects the
139 `MIRI_TEST_TARGET` environment variable to execute the test for another target.
141 Note that installing Miri like this will "take away" Miri management from `rustup`.
142 If you want to later go back to a rustup-installed Miri, run `rustup update`.
144 ### Using a modified standard library
146 Miri re-builds the standard library into a custom sysroot, so it is fairly easy
147 to test Miri against a modified standard library -- you do not even have to
148 build Miri yourself, the Miri shipped by `rustup` will work. All you have to do
149 is set the `MIRI_LIB_SRC` environment variable to the `library` folder of a
150 `rust-lang/rust` repository checkout. Note that changing files in that directory
151 does not automatically trigger a re-build of the standard library; you have to
152 clear the Miri build cache manually (on Linux, `rm -rf ~/.cache/miri`;
153 on Windows, `rmdir /S "%LOCALAPPDATA%\rust-lang\miri\cache"`;
154 and on macOS, `rm -rf ~/Library/Caches/org.rust-lang.miri`).
158 Miri comes with a few benchmarks; you can run `./miri bench` to run them with the locally built
159 Miri. Note: this will run `./miri install` as a side-effect. Also requires `hyperfine` to be
160 installed (`cargo install hyperfine`).
162 ## Configuring `rust-analyzer`
164 To configure `rust-analyzer` and VS Code for working on Miri, save the following
165 to `.vscode/settings.json` in your local Miri clone:
169 "rust-analyzer.rustc.source": "discover",
170 "rust-analyzer.linkedProjects": [
172 "./cargo-miri/Cargo.toml"
174 "rust-analyzer.checkOnSave.overrideCommand": [
179 "clippy", // make this `check` when working with a locally built rustc
180 "--message-format=json"
182 // Contrary to what the name suggests, this also affects proc macros.
183 "rust-analyzer.cargo.buildScripts.overrideCommand": [
189 "--message-format=json",
196 > If you are [building Miri with a locally built rustc][], set
197 > `rust-analyzer.rustcSource` to the relative path from your Miri clone to the
198 > root `Cargo.toml` of the locally built rustc. For example, the path might look
199 > like `../rust/Cargo.toml`.
201 See the rustc-dev-guide's docs on ["Configuring `rust-analyzer` for `rustc`"][rdg-r-a]
202 for more information about configuring VS Code and `rust-analyzer`.
204 [rdg-r-a]: https://rustc-dev-guide.rust-lang.org/building/suggested.html#configuring-rust-analyzer-for-rustc
206 ## Advanced topic: Working on Miri in the rustc tree
208 We described above the simplest way to get a working build environment for Miri,
209 which is to use the version of rustc indicated by `rustc-version`. But
210 sometimes, that is not enough.
212 A big part of the Miri driver is shared with rustc, so working on Miri will
213 sometimes require also working on rustc itself. In this case, you should *not*
214 work in a clone of the Miri repository, but in a clone of the
215 [main Rust repository](https://github.com/rust-lang/rust/). There is a copy of
216 Miri located at `src/tools/miri` that you can work on directly. A maintainer
217 will eventually sync those changes back into this repository.
219 When working on Miri in the rustc tree, here's how you can run tests:
222 ./x.py test miri --stage 0
225 `--bless` will work, too.
227 You can also directly run Miri on a Rust source file:
230 ./x.py run miri --stage 0 --args src/tools/miri/tests/pass/hello.rs
233 ## Advanced topic: Syncing with the rustc repo
235 We use the [`josh` proxy](https://github.com/josh-project/josh) to transmit changes between the
236 rustc and Miri repositories.
239 cargo +stable install josh-proxy --git https://github.com/josh-project/josh --tag r22.12.06
240 josh-proxy --local=$HOME/.cache/josh --remote=https://github.com --no-background
243 This uses a directory `$HOME/.cache/josh` as a cache, to speed up repeated pulling/pushing.
245 ### Importing changes from the rustc repo
247 Josh needs to be running, as described above.
248 We assume we start on an up-to-date master branch in the Miri repo.
251 # Fetch and merge rustc side of the history. Takes ca 5 min the first time.
252 # This will also update the 'rustc-version' file.
254 # Update local toolchain and apply formatting.
255 ./miri toolchain && ./miri fmt
256 git commit -am "rustup"
259 Now push this to a new branch in your Miri fork, and create a PR. It is worth
260 running `./miri test` locally in parallel, since the test suite in the Miri repo
261 is stricter than the one on the rustc side, so some small tweaks might be
264 ### Exporting changes to the rustc repo
266 Keep in mind that pushing is the most complicated job that josh has to do --
267 pulling just filters the rustc history, but pushing needs to construct a new
268 rustc history that would filter to the given Miri history! To avoid problems, it
269 is a good idea to always pull immediately before you push. In particular, you
270 should never do two josh pushes without an intermediate pull; that can lead to
273 Josh needs to be running, as described above. We will use the josh proxy to push
274 to your fork of rustc. Run the following in the Miri repo, assuming we are on an
275 up-to-date master branch:
278 # Push the Miri changes to your rustc fork (substitute your github handle for YOUR_NAME).
279 ./miri rustc-push YOUR_NAME miri
282 This will create a new branch called 'miri' in your fork, and the output should
283 include a link to create a rustc PR that will integrate those changes into the