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 [`rustup-toolchain-install-master`]: https://github.com/kennytm/rustup-toolchain-install-master
33 ## Building and testing Miri
35 Invoking Miri requires getting a bunch of flags right and setting up a custom
36 sysroot with xargo. The `miri` script takes care of that for you. With the
37 build environment prepared, compiling Miri is just one command away:
43 Run `./miri` without arguments to see the other commands our build tool
46 ### Testing the Miri driver
48 The Miri driver compiled from `src/bin/miri.rs` is the "heart" of Miri: it is
49 basically a version of `rustc` that, instead of compiling your code, runs it.
50 It accepts all the same flags as `rustc` (though the ones only affecting code
51 generation and linking obviously will have no effect) [and more][miri-flags].
53 [miri-flags]: README.md#miri--z-flags-and-environment-variables
55 For example, you can (cross-)run the driver on a particular file by doing
58 ./miri run tests/run-pass/format.rs
59 ./miri run tests/run-pass/hello.rs --target i686-unknown-linux-gnu
62 and you can (cross-)run the entire test suite using:
66 MIRI_TEST_TARGET=i686-unknown-linux-gnu ./miri test
69 `./miri test FILTER` only runs those tests that contain `FILTER` in their
70 filename (including the base directory, e.g. `./miri test fail` will run all
73 You can get a trace of which MIR statements are being executed by setting the
74 `MIRI_LOG` environment variable. For example:
77 MIRI_LOG=info ./miri run tests/run-pass/vec.rs
80 Setting `MIRI_LOG` like this will configure logging for Miri itself as well as
81 the `rustc_middle::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
82 can also do more targeted configuration, e.g. the following helps debug the
83 stacked borrows implementation:
86 MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/run-pass/vec.rs
89 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
90 evaluation error was originally raised.
92 ### Testing `cargo miri`
94 Working with the driver directly gives you full control, but you also lose all
95 the convenience provided by cargo. Once your test case depends on a crate, it
96 is probably easier to test it with the cargo wrapper. You can install your
97 development version of Miri using
103 and then you can use it as if it was installed by `rustup`. Make sure you use
104 the same toolchain when calling `cargo miri` that you used when installing Miri!
106 There's a test for the cargo wrapper in the `test-cargo-miri` directory; run
107 `./run-test.py` in there to execute it. Like `./miri test`, this respects the
108 `MIRI_TEST_TARGET` environment variable to execute the test for another target.
110 ## Configuring `rust-analyzer`
112 To configure `rust-analyzer` and VS Code for working on Miri, save the following
113 to `.vscode/settings.json` in your local Miri clone:
117 "rust-analyzer.checkOnSave.overrideCommand": [
120 "--message-format=json"
122 "rust-analyzer.rustfmt.extraArgs": [
125 "rust-analyzer.rustcSource": "discover",
126 "rust-analyzer.linkedProjects": [
128 "./cargo-miri/Cargo.toml"
135 > If you are [building Miri with a locally built rustc][], set
136 > `rust-analyzer.rustcSource` to the relative path from your Miri clone to the
137 > root `Cargo.toml` of the locally built rustc. For example, the path might look
138 > like `../rust/Cargo.toml`.
140 See the rustc-dev-guide's docs on ["Configuring `rust-analyzer` for `rustc`"][rdg-r-a]
141 for more information about configuring VS Code and `rust-analyzer`.
143 [rdg-r-a]: https://rustc-dev-guide.rust-lang.org/building/suggested.html#configuring-rust-analyzer-for-rustc
145 ## Advanced topic: other build environments
147 We described above the simplest way to get a working build environment for Miri,
148 which is to use the version of rustc indicated by `rustc-version`. But
149 sometimes, that is not enough.
151 ### Updating `rustc-version`
153 The `rustc-version` file is regularly updated to keep Miri close to the latest
154 version of rustc. Usually, new contributors do not have to worry about this. But
155 sometimes a newer rustc is needed for a patch, and sometimes Miri needs fixing
156 for changes in rustc. In both cases, `rustc-version` needs updating.
158 To update the `rustc-version` file and install the latest rustc, you can run:
160 ./rustup-toolchain HEAD
163 Now edit Miri until `./miri test` passes, and submit a PR. Generally, it is
164 preferred to separate updating `rustc-version` and doing what it takes to get
165 Miri working again, from implementing new features that rely on the updated
166 rustc. This avoids blocking all Miri development on landing a big PR.
168 ### Building Miri with a locally built rustc
170 [building Miri with a locally built rustc]: #building-miri-with-a-locally-built-rustc
172 A big part of the Miri driver lives in rustc, so working on Miri will sometimes
173 require using a locally built rustc. The bug you want to fix may actually be on
174 the rustc side, or you just need to get more detailed trace of the execution
175 than what is possible with release builds -- in both cases, you should develop
176 miri against a rustc you compiled yourself, with debug assertions (and hence
179 The setup for a local rustc works as follows:
181 # Clone the rust-lang/rust repo.
182 git clone https://github.com/rust-lang/rust rustc
184 # Create a config.toml with defaults for working on miri.
185 ./x.py setup compiler
186 # Now edit `config.toml` and under `[rust]` set `debug-assertions = true`.
188 # Build a stage 2 rustc, and build the rustc libraries with that rustc.
189 # This step can take 30 minutes or more.
190 ./x.py build --stage 2 compiler/rustc
191 # If you change something, you can get a faster rebuild by doing
192 ./x.py build --keep-stage 0 --stage 2 compiler/rustc
193 # You may have to change the architecture in the next command
194 rustup toolchain link stage2 build/x86_64-unknown-linux-gnu/stage2
195 # Now cd to your Miri directory, then configure rustup
196 rustup override set stage2
199 For more information about building and configuring a local compiler,
200 see <https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html>.
202 With this, you should now have a working development setup! See
203 [above](#building-and-testing-miri) for how to proceed working on Miri.