An experimental interpreter for [Rust][rust]'s
[mid-level intermediate representation][mir] (MIR). It can run binaries and
-test suites of cargo projects and detect certain classes of undefined behavior,
+test suites of cargo projects and detect certain classes of
+[undefined behavior](https://doc.rust-lang.org/reference/behavior-considered-undefined.html),
for example:
* Out-of-bounds memory accesses and use-after-free
* Violation of intrinsic preconditions (an [`unreachable_unchecked`] being
reached, calling [`copy_nonoverlapping`] with overlapping ranges, ...)
* Not sufficiently aligned memory accesses and references
-* Violation of basic type invariants (a `bool` that is not 0 or 1, for example,
+* Violation of *some* basic type invariants (a `bool` that is not 0 or 1, for example,
or an invalid enum discriminant)
-* WIP: Violations of the rules governing aliasing for reference types
+* **Experimental**: Violations of the [Stacked Borrows] rules governing aliasing
+ for reference types
Miri has already discovered some [real-world bugs](#bugs-found-by-miri). If you
found a bug with Miri, we'd appreciate if you tell us and we'll add it to the
list!
-Be aware that Miri will not catch all possible errors in your program, and
-cannot run all programs:
+Be aware that Miri will **not catch all cases of undefined behavior** in your
+program, and cannot run all programs:
* There are still plenty of open questions around the basic invariants for some
types and when these invariants even have to hold. Miri tries to avoid false
positives here, so if you program runs fine in Miri right now that is by no
- means a guarantee that it is UB-free when these questions get answered. In
- particular, Miri does currently not check that integers are initialized or
- that references point to valid data.
+ means a guarantee that it is UB-free when these questions get answered.
+
+ In particular, Miri does currently not check that integers/floats are
+ initialized or that references point to valid data.
* If the program relies on unspecified details of how data is laid out, it will
still run fine in Miri -- but might break (including causing UB) on different
compiler versions or different platforms.
-* Miri is fully deterministic and does not actually pick a base address in
- virtual memory for the program's allocations. If program behavior depends on
- the base address of an allocation, Miri will stop execution (with a few
- exceptions to make some common pointer comparisons work).
+* Program execution is non-deterministic when it depends, for example, on where
+ exactly in memory allocations end up. Miri tests one of many possible
+ executions of your program. If your code is sensitive to allocation base
+ addresses or other non-deterministic data, try running Miri with different
+ values for `-Zmiri-seed` to test different executions.
* Miri runs the program as a platform-independent interpreter, so the program
- has no access to any platform-specific APIs or FFI. A few APIs have been
+ has no access to most platform-specific APIs or FFI. A few APIs have been
implemented (such as printing to stdout) but most have not: for example, Miri
- currently does not support concurrency, or SIMD, or networking, or file system
- access.
+ currently does not support concurrency, or SIMD, or networking.
[rust]: https://www.rust-lang.org/
[mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
[`unreachable_unchecked`]: https://doc.rust-lang.org/stable/std/hint/fn.unreachable_unchecked.html
[`copy_nonoverlapping`]: https://doc.rust-lang.org/stable/std/ptr/fn.copy_nonoverlapping.html
+[Stacked Borrows]: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md
-## Running Miri on your own project (and its test suite)
+## Using Miri
-Install Miri via `rustup`:
+Install Miri on Rust nightly via `rustup`:
```sh
-rustup component add miri
+rustup +nightly component add miri
```
If `rustup` says the `miri` component is unavailable, that's because not all
nightly releases come with all tools. Check out
[this website](https://rust-lang.github.io/rustup-components-history) to
-determine a nightly version that comes with Miri and install that, e.g. using
-`rustup install nightly-2019-03-28`.
+determine a nightly version that comes with Miri and install that using
+`rustup toolchain install nightly-YYYY-MM-DD`.
Now you can run your project in Miri:
3. If you have a binary project, you can run it through Miri using `cargo miri run`.
The first time you run Miri, it will perform some extra setup and install some
-dependencies. It will ask you for confirmation before installing anything. If
-you run Miri on CI, run `cargo miri setup` to avoid getting interactive
-questions.
+dependencies. It will ask you for confirmation before installing anything.
+
+Miri supports cross-execution: if you want to run the program as if it was a
+Linux program, you can do `cargo miri run --target x86_64-unknown-linux-gnu`.
+This is particularly useful if you are using Windows, as the Linux target is
+much better supported than Windows targets.
You can pass arguments to Miri after the first `--`, and pass arguments to the
interpreted program or test suite after the second `--`. For example, `cargo
miri run -- -Zmiri-disable-validation` runs the program without validation of
-basic type invariants and references. `cargo miri test -- -- -Zunstable-options
---exclude-should-panic` skips `#[should_panic]` tests, which is a good idea
-because Miri does not support unwinding or catching panics.
+basic type invariants and without checking the aliasing of references.
-When running code via `cargo miri`, the `miri` config flag is set. You can
-use this to exclude test cases that will fail under Miri because they do things
+When compiling code via `cargo miri`, the `miri` config flag is set. You can
+use this to ignore test cases that will fail under Miri because they do things
Miri does not support:
```rust
-#[cfg(not(miri))]
#[test]
+#[cfg_attr(miri, ignore)]
fn does_not_work_on_miri() {
- let x = 0u8;
- assert!(&x as *const _ as usize % 4 < 4);
+ std::thread::spawn(|| println!("Hello Thread!"))
+ .join()
+ .unwrap();
}
```
```sh
MIRI_NIGHTLY=nightly-$(curl -s https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/miri)
echo "Installing latest nightly with Miri: $MIRI_NIGHTLY"
+rustup set profile minimal
rustup default "$MIRI_NIGHTLY"
rustup component add miri
cargo miri setup
-cargo miri test -- -- -Zunstable-options --exclude-should-panic
+cargo miri test
```
+We use `cargo miri setup` to avoid getting interactive questions about the extra
+setup needed for Miri.
+
### Common Problems
When using the above instructions, you may encounter a number of confusing compiler
* `-Zmiri-seed=<hex>` is a custom `-Z` flag added by Miri. It configures the
seed of the RNG that Miri uses to resolve non-determinism. This RNG is used
- to pick base addresses for allocations, and when the interpreted program
- requests system entropy. The default seed is 0.
+ to pick base addresses for allocations. When isolation is enabled (the default),
+ this is also used to emulate system entropy. The default seed is 0.
**NOTE**: This entropy is not good enough for cryptographic use! Do not
generate secret keys in Miri or perform other kinds of cryptographic
operations that rely on proper random numbers.
-* `-Zmiri-disable-validation` disables enforcing the validity invariant, which
- is enforced by default. This is mostly useful for debugging; it means Miri
- will miss bugs in your program. However, this can also help to make Miri run
+* `-Zmiri-disable-validation` disables enforcing validity invariants, which are
+ enforced by default. This is mostly useful for debugging. It means Miri will
+ miss bugs in your program. However, this can also help to make Miri run
faster.
+* `-Zmiri-disable-stacked-borrows` disables checking the experimental
+ [Stacked Borrows] aliasing rules. This can make Miri run faster, but it also
+ means no aliasing violations will be detected.
+* `-Zmiri-disable-isolation` disables host isolation. As a consequence,
+ the program has access to host resources such as environment variables, file
+ systems, and randomness.
+* `-Zmiri-ignore-leaks` disables the memory leak checker.
+* `-Zmiri-env-exclude=<var>` keeps the `var` environment variable isolated from
+ the host. Can be used multiple times to exclude several variables. The `TERM`
+ environment variable is excluded by default.
* `-Zmir-opt-level` controls how many MIR optimizations are performed. Miri
overrides the default to be `0`; be advised that using any higher level can
make Miri miss bugs in your program because they got optimized away.
sets this flag per default.
* `-Zmir-emit-retag` controls whether `Retag` statements are emitted. Miri
enables this per default because it is needed for validation.
+* `-Zmiri-track-pointer-tag=<tag>` shows a backtrace when the given pointer tag
+ is popped from a borrow stack (which is where the tag becomes invalid and any
+ future use of it will error). This helps you in finding out why UB is
+ happening and where in your code would be a good place to look for it.
+* `-Zmiri-track-alloc-id=<id>` shows a backtrace when the given allocation is
+ being allocated. This helps in debugging memory leaks.
Moreover, Miri recognizes some environment variables:
* `MIRI_TEST_TARGET` (recognized by the test suite) indicates which target
architecture to test against. `miri` and `cargo miri` accept the `--target`
flag for the same purpose.
-
-## Development and Debugging
-
-If you want to hack on miri yourself, great! Here are some resources you might
-find useful.
-
-### Using a nightly rustc
-
-Miri heavily relies on internal rustc interfaces to execute MIR. Still, some
-things (like adding support for a new intrinsic or a shim for an external
-function being called) can be done by working just on the Miri side.
-
-To prepare, make sure you are using a nightly Rust compiler. Then you should be
-able to just `cargo build` Miri.
-
-In case this fails, your nightly might be incompatible with Miri master. The
-`rust-version` file contains the commit hash of rustc that Miri is currently
-tested against; you can use that to find a nightly that works or you might have
-to wait for the next nightly to get released. You can also use
-[`rustup-toolchain-install-master`](https://github.com/kennytm/rustup-toolchain-install-master)
-to install that exact version of rustc as a toolchain:
-```
-rustup-toolchain-install-master $(cat rust-version) -c rust-src
-```
-
-Another common problem is outdated dependencies: Miri does not come with a
-lockfile (it cannot, due to how it gets embedded into the rustc build). So you
-have to run `cargo update` every now and then yourself to make sure you are
-using the latest versions of everything (which is what gets tested on CI).
-
-### Testing the Miri driver
-[testing-miri]: #testing-the-miri-driver
-
-The Miri driver in the `miri` binary is the "heart" of Miri: it is basically a
-version of `rustc` that, instead of compiling your code, runs it. It accepts
-all the same flags as `rustc` (though the ones only affecting code generation
-and linking obviously will have no effect) [and more][miri-flags].
-
-Running the Miri driver requires some fiddling with environment variables, so
-the `miri` script helps you do that. For example, you can run the driver on a
-particular file by doing
-
-```sh
-./miri run tests/run-pass/format.rs
-./miri run tests/run-pass/hello.rs --target i686-unknown-linux-gnu
-```
-
-and you can run the test suite using:
-
-```
-./miri test
-```
-
-`./miri test FILTER` only runs those tests that contain `FILTER` in their
-filename (including the base directory, e.g. `./miri test fail` will run all
-compile-fail tests).
-
-You can get a trace of which MIR statements are being executed by setting the
-`MIRI_LOG` environment variable. For example:
-
-```sh
-MIRI_LOG=info ./miri run tests/run-pass/vecs.rs
-```
-
-Setting `MIRI_LOG` like this will configure logging for Miri itself as well as
-the `rustc::mir::interpret` and `rustc_mir::interpret` modules in rustc. You
-can also do more targeted configuration, e.g. the following helps debug the
-stacked borrows implementation:
-
-```sh
-MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/run-pass/vecs.rs
-```
-
-In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
-evaluation error was originally raised.
-
-### Testing `cargo miri`
-
-Working with the driver directly gives you full control, but you also lose all
-the convenience provided by cargo. Once your test case depends on a crate, it
-is probably easier to test it with the cargo wrapper. You can install your
-development version of Miri using
-
-```
-./miri install
-```
-
-and then you can use it as if it was installed by `rustup`. Make sure you use
-the same toolchain when calling `cargo miri` that you used when installing Miri!
-
-There's a test for the cargo wrapper in the `test-cargo-miri` directory; run
-`./run-test.py` in there to execute it.
-
-### Using a locally built rustc
-
-A big part of the Miri driver lives in rustc, so working on Miri will sometimes
-require using a locally built rustc. The bug you want to fix may actually be on
-the rustc side, or you just need to get more detailed trace of the execution
-than what is possible with release builds -- in both cases, you should develop
-miri against a rustc you compiled yourself, with debug assertions (and hence
-tracing) enabled.
-
-The setup for a local rustc works as follows:
-```sh
-git clone https://github.com/rust-lang/rust/ rustc
-cd rustc
-cp config.toml.example config.toml
-# Now edit `config.toml` and set `debug-assertions = true` and `test-miri = true`.
-# The latter is important to build libstd with the right flags for miri.
-# This step can take 30 minutes and more.
-./x.py build src/rustc
-# If you change something, you can get a faster rebuild by doing
-./x.py --keep-stage 0 build src/rustc
-# You may have to change the architecture in the next command
-rustup toolchain link custom build/x86_64-unknown-linux-gnu/stage2
-# Now cd to your Miri directory, then configure rustup
-rustup override set custom
-```
-
-With this, you should now have a working development setup! See
-[above][testing-miri] for how to proceed working with the Miri driver.
+* `MIRI_TEST_FLAGS` (recognized by the test suite) defines extra flags to be
+ passed to Miri.
## Contributing and getting help
-Check out the issues on this GitHub repository for some ideas. There's lots that
-needs to be done that I haven't documented in the issues yet, however. For more
-ideas or help with running or hacking on Miri, you can open an issue here on
+If you want to contribute to Miri, great! Please check out our
+[contribution guide](CONTRIBUTING.md).
+
+For help with running Miri, you can open an issue here on
GitHub or contact us (`oli-obk` and `RalfJ`) on the [Rust Zulip].
[Rust Zulip]: https://rust-lang.zulipchat.com
* [`str` turning a shared reference into a mutable one](https://github.com/rust-lang/rust/pull/58200)
* [`rand` performing unaligned reads](https://github.com/rust-random/rand/issues/779)
* [The Unix allocator calling `posix_memalign` in an invalid way](https://github.com/rust-lang/rust/issues/62251)
+* [`getrandom` calling the `getrandom` syscall in an invalid way](https://github.com/rust-random/getrandom/pull/73)
+* [`Vec`](https://github.com/rust-lang/rust/issues/69770) and [`BTreeMap`](https://github.com/rust-lang/rust/issues/69769) leaking memory under some (panicky) conditions
+* [Memory leak in `beef`](https://github.com/maciejhirsz/beef/issues/12)
-Violations of Stacked Borrows found that are likely bugs (but Stacked Borrows is currently just an experiment):
+Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):
* [`VecDeque` creating overlapping mutable references](https://github.com/rust-lang/rust/pull/56161)
* [`BTreeMap` creating mutable references that overlap with shared references](https://github.com/rust-lang/rust/pull/58431)
* [`LinkedList` creating overlapping mutable references](https://github.com/rust-lang/rust/pull/60072)
* [`Vec::push` invalidating existing references into the vector](https://github.com/rust-lang/rust/issues/60847)
+* [`align_to_mut` violating uniqueness of mutable references](https://github.com/rust-lang/rust/issues/68549)
+* [Aliasing mutable references in `sized-chunks`](https://github.com/bodil/sized-chunks/issues/8)
## License
projects / rust.git / blobdiff