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. There's lots that
9 needs to be done that we haven't documented in the issues yet, however. For more
10 ideas or help with hacking on Miri, you can contact us (`oli-obk` and `RalfJ`)
13 [Rust Zulip]: https://rust-lang.zulipchat.com
15 ## Building Miri with a pre-built rustc
17 Miri heavily relies on internal rustc interfaces to execute MIR. Still, some
18 things (like adding support for a new intrinsic or a shim for an external
19 function being called) can be done by working just on the Miri side.
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:
29 [`rustup-toolchain-install-master`]: https://github.com/kennytm/rustup-toolchain-install-master
31 Now building Miri is just one command away:
37 Run `./miri` without arguments to see the other commands our build tool
40 ### Fixing Miri when rustc changes
42 Miri is heavily tied to rustc internals, so it is very common that rustc changes
43 break Miri. Fixing those is a good way to get starting working on Miri.
44 Usually, Miri will require changes similar to the other consumers of the changed
45 rustc API, so reading the rustc PR diff is a good way to get an idea for what is
48 To update the `rustc-version` file and install the latest rustc, you can run:
50 ./rustup-toolchain HEAD
53 Now try `./miri test`, and submit a PR once that works again.
55 ## Testing the Miri driver
56 [testing-miri]: #testing-the-miri-driver
58 The Miri driver in the `miri` binary is the "heart" of Miri: it is basically a
59 version of `rustc` that, instead of compiling your code, runs it. It accepts
60 all the same flags as `rustc` (though the ones only affecting code generation
61 and linking obviously will have no effect) [and more][miri-flags].
63 Running the Miri driver requires some fiddling with environment variables, so
64 the `miri` script helps you do that. For example, you can (cross-)run the
65 driver on a particular file by doing
68 ./miri run tests/run-pass/format.rs
69 ./miri run tests/run-pass/hello.rs --target i686-unknown-linux-gnu
72 and you can (cross-)run the test suite using:
76 MIRI_TEST_TARGET=i686-unknown-linux-gnu ./miri test
79 `./miri test FILTER` only runs those tests that contain `FILTER` in their
80 filename (including the base directory, e.g. `./miri test fail` will run all
83 You can get a trace of which MIR statements are being executed by setting the
84 `MIRI_LOG` environment variable. For example:
87 MIRI_LOG=info ./miri run tests/run-pass/vecs.rs
90 Setting `MIRI_LOG` like this will configure logging for Miri itself as well as
91 the `rustc_middle::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
92 can also do more targeted configuration, e.g. the following helps debug the
93 stacked borrows implementation:
96 MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/run-pass/vecs.rs
99 In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
100 evaluation error was originally raised.
102 ## Testing `cargo miri`
104 Working with the driver directly gives you full control, but you also lose all
105 the convenience provided by cargo. Once your test case depends on a crate, it
106 is probably easier to test it with the cargo wrapper. You can install your
107 development version of Miri using
113 and then you can use it as if it was installed by `rustup`. Make sure you use
114 the same toolchain when calling `cargo miri` that you used when installing Miri!
116 There's a test for the cargo wrapper in the `test-cargo-miri` directory; run
117 `./run-test.py` in there to execute it. Like `./miri test`, this respects the
118 `MIRI_TEST_TARGET` environment variable to execute the test for another target.
120 ## Building Miri with a locally built rustc
122 A big part of the Miri driver lives in rustc, so working on Miri will sometimes
123 require using a locally built rustc. The bug you want to fix may actually be on
124 the rustc side, or you just need to get more detailed trace of the execution
125 than what is possible with release builds -- in both cases, you should develop
126 miri against a rustc you compiled yourself, with debug assertions (and hence
129 The setup for a local rustc works as follows:
131 git clone https://github.com/rust-lang/rust/ rustc
133 cp config.toml.example config.toml
134 # Now edit `config.toml` and set `debug-assertions = true`.
135 # This step can take 30 minutes and more.
136 ./x.py build src/rustc
137 # If you change something, you can get a faster rebuild by doing
138 ./x.py --keep-stage 0 build src/rustc
139 # You may have to change the architecture in the next command
140 rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
141 # Now cd to your Miri directory, then configure rustup
142 rustup override set custom
145 With this, you should now have a working development setup! See
146 [above][testing-miri] for how to proceed working with the Miri driver.