or an invalid enum discriminant)
* **Experimental**: Violations of the [Stacked Borrows] rules governing aliasing
for reference types
+* **Experimental**: Data races (but no weak memory effects)
On top of that, Miri will also tell you about memory leaks: when there is memory
still allocated at the end of the execution, and that memory is not reachable
from a global `static`, Miri will raise an error.
+You can use Miri to emulate programs on other targets, e.g. to ensure that
+byte-level data manipulation works correctly both on little-endian and
+big-endian systems. See
+[cross-interpretation](#cross-interpretation-running-for-different-targets)
+below.
+
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!
still run fine in Miri -- but might break (including causing UB) on different
compiler versions or different platforms.
* 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.
+ exactly in memory allocations end up, or on the exact interleaving of
+ concurrent threads. Miri tests one of many possible executions of your
+ program. You can alleviate this to some extent by running Miri with different
+ values for `-Zmiri-seed`, but that will still by far not explore all possible
+ executions.
* Miri runs the program as a platform-independent interpreter, so the program
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 SIMD or networking.
-* Miri currently does not check for data-races and most other concurrency-related
- issues.
[rust]: https://www.rust-lang.org/
[mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
Miri adds its own set of `-Z` flags, which are usually set via the `MIRIFLAGS`
environment variable:
+* `-Zmiri-compare-exchange-weak-failure-rate=<rate>` changes the failure rate of
+ `compare_exchange_weak` operations. The default is `0.8` (so 4 out of 5 weak ops will fail).
+ You can change it to any value between `0.0` and `1.0`, where `1.0` means it
+ will always fail and `0.0` means it will never fail.
* `-Zmiri-disable-alignment-check` disables checking pointer alignment, so you
can focus on other failures, but it means Miri can miss bugs in your program.
Using this flag is **unsound**.
+* `-Zmiri-disable-data-race-detector` disables checking for data races. Using
+ this flag is **unsound**.
* `-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. Using this flag is **unsound**
* `-Zmiri-track-alloc-id=<id>` shows a backtrace when the given allocation is
being allocated or freed. This helps in debugging memory leaks and
use after free bugs.
+* `-Zmiri-track-call-id=<id>` shows a backtrace when the given call id is
+ assigned to a stack frame. This helps in debugging UB related to Stacked
+ Borrows "protectors".
* `-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-call-id=<id>` shows a backtrace when the given call id is
- assigned to a stack frame. This helps in debugging UB related to Stacked
- Borrows "protectors".
+* `-Zmiri-track-raw-pointers` makes Stacked Borrows track a pointer tag even for
+ raw pointers. This can make valid code fail to pass the checks, but also can
+ help identify latent aliasing issues in code that Miri accepts by default. You
+ can recognize false positives by "<untagged>" occurring in the message -- this
+ indicates a pointer that was cast from an integer, so Miri was unable to track
+ this pointer.
Some native rustc `-Z` flags are also very relevant for Miri:
Moreover, Miri recognizes some environment variables:
* `MIRI_LOG`, `MIRI_BACKTRACE` control logging and backtrace printing during
- Miri executions, also [see above][testing-miri].
+ Miri executions, also [see "Testing the Miri driver" in `CONTRIBUTING.md`][testing-miri].
* `MIRIFLAGS` (recognized by `cargo miri` and the test suite) defines extra
flags to be passed to Miri.
* `MIRI_SYSROOT` (recognized by `cargo miri` and the test suite)
directory after loading all the source files, but before commencing
interpretation. This is useful if the interpreted program wants a different
working directory at run-time than at build-time.
+* `MIRI_VERBOSE` when set to any value tells the various `cargo-miri` phases to
+ perform verbose logging.
+
+[testing-miri]: CONTRIBUTING.md#testing-the-miri-driver
## Miri `extern` functions
[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].
+GitHub or use the [Miri stream on the Rust Zulip][zulip].
-[Rust Zulip]: https://rust-lang.zulipchat.com
+[zulip]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri
## History
Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):
* [`VecDeque::drain` creating overlapping mutable references](https://github.com/rust-lang/rust/pull/56161)
-* [`BTreeMap` iterators creating mutable references that overlap with shared references](https://github.com/rust-lang/rust/pull/58431)
+* Various `BTreeMap` problems
+ * [`BTreeMap` iterators creating mutable references that overlap with shared references](https://github.com/rust-lang/rust/pull/58431)
+ * [`BTreeMap::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/73915)
+ * [`BTreeMap` node insertion using raw pointers outside their valid memory area](https://github.com/rust-lang/rust/issues/78477)
* [`LinkedList` cursor insertion 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)
* [`ryu` using raw pointers outside their valid memory area](https://github.com/dtolnay/ryu/issues/24)
* [ink! creating overlapping mutable references](https://github.com/rust-lang/miri/issues/1364)
* [TiKV creating overlapping mutable reference and raw pointer](https://github.com/tikv/tikv/pull/7709)
-* [Windows `Env` iterator creating `*const T` from `&T` to read memory outside of `T`](https://github.com/rust-lang/rust/pull/70479)
-* [`BTreeMap::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/73915)
+* [Windows `Env` iterator using a raw pointer outside its valid memory area](https://github.com/rust-lang/rust/pull/70479)
* [`VecDeque::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/74029)
+* [Various standard library aliasing issues involving raw pointers](https://github.com/rust-lang/rust/pull/78602)
## License
projects / rust.git / blobdiff