3 [![Actions build status][actions-badge]][actions-url]
5 [actions-badge]: https://github.com/rust-lang/miri/workflows/CI/badge.svg?branch=master
6 [actions-url]: https://github.com/rust-lang/miri/actions
8 An experimental interpreter for [Rust][rust]'s
9 [mid-level intermediate representation][mir] (MIR). It can run binaries and
10 test suites of cargo projects and detect certain classes of
11 [undefined behavior](https://doc.rust-lang.org/reference/behavior-considered-undefined.html),
14 * Out-of-bounds memory accesses and use-after-free
15 * Invalid use of uninitialized data
16 * Violation of intrinsic preconditions (an [`unreachable_unchecked`] being
17 reached, calling [`copy_nonoverlapping`] with overlapping ranges, ...)
18 * Not sufficiently aligned memory accesses and references
19 * Violation of *some* basic type invariants (a `bool` that is not 0 or 1, for example,
20 or an invalid enum discriminant)
21 * **Experimental**: Violations of the [Stacked Borrows] rules governing aliasing
23 * **Experimental**: Data races
25 On top of that, Miri will also tell you about memory leaks: when there is memory
26 still allocated at the end of the execution, and that memory is not reachable
27 from a global `static`, Miri will raise an error.
29 Miri supports almost all Rust language features; in particular, unwinding and
30 concurrency are properly supported (including some experimental emulation of
31 weak memory effects, i.e., reads can return outdated values).
33 You can use Miri to emulate programs on other targets, e.g. to ensure that
34 byte-level data manipulation works correctly both on little-endian and
35 big-endian systems. See
36 [cross-interpretation](#cross-interpretation-running-for-different-targets)
39 Miri has already discovered some [real-world bugs](#bugs-found-by-miri). If you
40 found a bug with Miri, we'd appreciate if you tell us and we'll add it to the
43 By default, Miri ensures a fully deterministic execution and isolates the
44 program from the host system. Some APIs that would usually access the host, such
45 as gathering entropy for random number generators, environment variables, and
46 clocks, are replaced by deterministic "fake" implementations. Set
47 `MIRIFLAGS="-Zmiri-disable-isolation"` to access the real system APIs instead.
48 (In particular, the "fake" system RNG APIs make Miri **not suited for
49 cryptographic use**! Do not generate keys using Miri.)
51 All that said, be aware that Miri will **not catch all cases of undefined
52 behavior** in your program, and cannot run all programs:
54 * There are still plenty of open questions around the basic invariants for some
55 types and when these invariants even have to hold. Miri tries to avoid false
56 positives here, so if your program runs fine in Miri right now that is by no
57 means a guarantee that it is UB-free when these questions get answered.
59 In particular, Miri does currently not check that references point to valid data.
60 * If the program relies on unspecified details of how data is laid out, it will
61 still run fine in Miri -- but might break (including causing UB) on different
62 compiler versions or different platforms.
63 * Program execution is non-deterministic when it depends, for example, on where
64 exactly in memory allocations end up, or on the exact interleaving of
65 concurrent threads. Miri tests one of many possible executions of your
66 program. You can alleviate this to some extent by running Miri with different
67 values for `-Zmiri-seed`, but that will still by far not explore all possible
69 * Miri runs the program as a platform-independent interpreter, so the program
70 has no access to most platform-specific APIs or FFI. A few APIs have been
71 implemented (such as printing to stdout, accessing environment variables, and
72 basic file system access) but most have not: for example, Miri currently does
73 not support networking. System API support varies between targets; if you run
74 on Windows it is a good idea to use `--target x86_64-unknown-linux-gnu` to get
76 * Weak memory emulation may [produce weak behaviours](https://github.com/rust-lang/miri/issues/2301)
77 unobservable by compiled programs running on real hardware when `SeqCst` fences are used, and it
78 cannot produce all behaviors possibly observable on real hardware.
80 [rust]: https://www.rust-lang.org/
81 [mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
82 [`unreachable_unchecked`]: https://doc.rust-lang.org/stable/std/hint/fn.unreachable_unchecked.html
83 [`copy_nonoverlapping`]: https://doc.rust-lang.org/stable/std/ptr/fn.copy_nonoverlapping.html
84 [Stacked Borrows]: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md
89 Install Miri on Rust nightly via `rustup`:
92 rustup +nightly component add miri
95 If `rustup` says the `miri` component is unavailable, that's because not all
96 nightly releases come with all tools. Check out
97 [this website](https://rust-lang.github.io/rustup-components-history) to
98 determine a nightly version that comes with Miri and install that using `rustup
99 toolchain install nightly-YYYY-MM-DD`. Either way, all of the following commands
100 assume the right toolchain is pinned via `rustup override set nightly` or
101 `rustup override set nightly-YYYY-MM-DD`. (Alternatively, use `cargo
102 +nightly`/`cargo +nightly-YYYY-MM-DD` for each of the following commands.)
104 Now you can run your project in Miri:
106 1. Run `cargo clean` to eliminate any cached dependencies. Miri needs your
107 dependencies to be compiled the right way, that would not happen if they have
108 previously already been compiled.
109 2. To run all tests in your project through Miri, use `cargo miri test`.
110 3. If you have a binary project, you can run it through Miri using `cargo miri run`.
112 The first time you run Miri, it will perform some extra setup and install some
113 dependencies. It will ask you for confirmation before installing anything.
115 `cargo miri run/test` supports the exact same flags as `cargo run/test`. For
116 example, `cargo miri test filter` only runs the tests containing `filter` in
119 You can pass arguments to Miri via `MIRIFLAGS`. For example,
120 `MIRIFLAGS="-Zmiri-disable-stacked-borrows" cargo miri run` runs the program
121 without checking the aliasing of references.
123 When compiling code via `cargo miri`, the `cfg(miri)` config flag is set for code
124 that will be interpret under Miri. You can use this to ignore test cases that fail
125 under Miri because they do things Miri does not support:
129 #[cfg_attr(miri, ignore)]
130 fn does_not_work_on_miri() {
131 tokio::run(futures::future::ok::<_, ()>(()));
135 There is no way to list all the infinite things Miri cannot do, but the
136 interpreter will explicitly tell you when it finds something unsupported:
139 error: unsupported operation: can't call foreign function: bind
141 = help: this is likely not a bug in the program; it indicates that the program \
142 performed an operation that the interpreter does not support
145 ### Cross-interpretation: running for different targets
147 Miri can not only run a binary or test suite for your host target, it can also
148 perform cross-interpretation for arbitrary foreign targets: `cargo miri run
149 --target x86_64-unknown-linux-gnu` will run your program as if it was a Linux
150 program, no matter your host OS. This is particularly useful if you are using
151 Windows, as the Linux target is much better supported than Windows targets.
153 You can also use this to test platforms with different properties than your host
154 platform. For example `cargo miri test --target mips64-unknown-linux-gnuabi64`
155 will run your test suite on a big-endian target, which is useful for testing
156 endian-sensitive code.
158 ### Running Miri on CI
160 To run Miri on CI, make sure that you handle the case where the latest nightly
161 does not ship the Miri component because it currently does not build. `rustup
162 toolchain install --component` knows how to handle this situation, so the
163 following snippet should always work:
166 rustup toolchain install nightly --component miri
167 rustup override set nightly
172 Here is an example job for GitHub Actions:
177 runs-on: ubuntu-latest
179 - uses: actions/checkout@v3
182 rustup toolchain install nightly --component miri
183 rustup override set nightly
185 - name: Test with Miri
189 The explicit `cargo miri setup` helps to keep the output of the actual test step
192 ### Testing for alignment issues
194 Miri can sometimes miss misaligned accesses since allocations can "happen to be"
195 aligned just right. You can use `-Zmiri-symbolic-alignment-check` to definitely
196 catch all such issues, but that flag will also cause false positives when code
197 does manual pointer arithmetic to account for alignment. Another alternative is
198 to call Miri with various values for `-Zmiri-seed`; that will alter the
199 randomness that is used to determine allocation base addresses. The following
200 snippet calls Miri in a loop with different values for the seed:
203 for SEED in $({ echo obase=16; seq 0 255; } | bc); do
204 echo "Trying seed: $SEED"
205 MIRIFLAGS=-Zmiri-seed=$SEED cargo miri test || { echo "Failing seed: $SEED"; break; };
209 ### Supported targets
211 Miri does not support all targets supported by Rust. The good news, however, is
212 that no matter your host OS/platform, it is easy to run code for *any* target
215 The following targets are tested on CI and thus should always work (to the
216 degree documented below):
218 - The best-supported target is `x86_64-unknown-linux-gnu`. Miri releases are
219 blocked on things working with this target. Most other Linux targets should
220 also work well; we do run the test suite on `i686-unknown-linux-gnu` as a
221 32bit target and `mips64-unknown-linux-gnuabi64` as a big-endian target.
222 - `x86_64-apple-darwin` should work basically as well as Linux. We also test
223 `aarch64-apple-darwin`. However, we might ship Miri with a nightly even when
224 some features on these targets regress.
225 - `x86_64-pc-windows-msvc` works, but supports fewer features than the Linux and
226 Apple targets. For example, file system access and concurrency are not
227 supported on Windows. We also test `i686-pc-windows-msvc`, with the same
228 reduced feature set. We might ship Miri with a nightly even when some features
229 on these targets regress.
233 When using the above instructions, you may encounter a number of confusing compiler
236 #### "note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace"
238 You may see this when trying to get Miri to display a backtrace. By default, Miri
239 doesn't expose any environment to the program, so running
240 `RUST_BACKTRACE=1 cargo miri test` will not do what you expect.
242 To get a backtrace, you need to disable isolation
243 [using `-Zmiri-disable-isolation`][miri-flags]:
246 RUST_BACKTRACE=1 MIRIFLAGS="-Zmiri-disable-isolation" cargo miri test
249 #### "found possibly newer version of crate `std` which `<dependency>` depends on"
251 Your build directory may contain artifacts from an earlier build that have/have
252 not been built for Miri. Run `cargo clean` before switching from non-Miri to
253 Miri builds and vice-versa.
255 #### "found crate `std` compiled by an incompatible version of rustc"
257 You may be running `cargo miri` with a different compiler version than the one
258 used to build the custom libstd that Miri uses, and Miri failed to detect that.
259 Try deleting `~/.cache/miri`.
261 #### "no mir for `std::rt::lang_start_internal`"
263 This means the sysroot you are using was not compiled with Miri in mind. This
264 should never happen when you use `cargo miri` because that takes care of setting
265 up the sysroot. If you are using `miri` (the Miri driver) directly, see the
266 [contributors' guide](CONTRIBUTING.md) for how to use `./miri` to best do that.
269 ## Miri `-Z` flags and environment variables
270 [miri-flags]: #miri--z-flags-and-environment-variables
272 Miri adds its own set of `-Z` flags, which are usually set via the `MIRIFLAGS`
273 environment variable. We first document the most relevant and most commonly used flags:
275 * `-Zmiri-compare-exchange-weak-failure-rate=<rate>` changes the failure rate of
276 `compare_exchange_weak` operations. The default is `0.8` (so 4 out of 5 weak ops will fail).
277 You can change it to any value between `0.0` and `1.0`, where `1.0` means it
278 will always fail and `0.0` means it will never fail. Note than setting it to
279 `1.0` will likely cause hangs, since it means programs using
280 `compare_exchange_weak` cannot make progress.
281 * `-Zmiri-disable-isolation` disables host isolation. As a consequence,
282 the program has access to host resources such as environment variables, file
283 systems, and randomness.
284 * `-Zmiri-isolation-error=<action>` configures Miri's response to operations
285 requiring host access while isolation is enabled. `abort`, `hide`, `warn`,
286 and `warn-nobacktrace` are the supported actions. The default is to `abort`,
287 which halts the machine. Some (but not all) operations also support continuing
288 execution with a "permission denied" error being returned to the program.
289 `warn` prints a full backtrace when that happens; `warn-nobacktrace` is less
290 verbose. `hide` hides the warning entirely.
291 * `-Zmiri-env-forward=<var>` forwards the `var` environment variable to the interpreted program. Can
292 be used multiple times to forward several variables. Execution will still be deterministic if the
293 value of forwarded variables stays the same. Has no effect if `-Zmiri-disable-isolation` is set.
294 * `-Zmiri-ignore-leaks` disables the memory leak checker, and also allows some
295 remaining threads to exist when the main thread exits.
296 * `-Zmiri-num-cpus` states the number of available CPUs to be reported by miri. By default, the
297 number of available CPUs is `1`. Note that this flag does not affect how miri handles threads in
299 * `-Zmiri-permissive-provenance` disables the warning for integer-to-pointer casts and
300 [`ptr::from_exposed_addr`](https://doc.rust-lang.org/nightly/std/ptr/fn.from_exposed_addr.html).
301 This will necessarily miss some bugs as those operations are not efficiently and accurately
302 implementable in a sanitizer, but it will only miss bugs that concern memory/pointers which is
303 subject to these operations.
304 * `-Zmiri-preemption-rate` configures the probability that at the end of a basic block, the active
305 thread will be preempted. The default is `0.01` (i.e., 1%). Setting this to `0` disables
307 * `-Zmiri-report-progress` makes Miri print the current stacktrace every now and then, so you can
308 tell what it is doing when a program just keeps running. You can customize how frequently the
309 report is printed via `-Zmiri-report-progress=<blocks>`, which prints the report every N basic
311 * `-Zmiri-seed=<hex>` configures the seed of the RNG that Miri uses to resolve non-determinism. This
312 RNG is used to pick base addresses for allocations, to determine preemption and failure of
313 `compare_exchange_weak`, and to control store buffering for weak memory emulation. When isolation
314 is enabled (the default), this is also used to emulate system entropy. The default seed is 0. You
315 can increase test coverage by running Miri multiple times with different seeds.
316 * `-Zmiri-strict-provenance` enables [strict
317 provenance](https://github.com/rust-lang/rust/issues/95228) checking in Miri. This means that
318 casting an integer to a pointer yields a result with 'invalid' provenance, i.e., with provenance
319 that cannot be used for any memory access.
320 * `-Zmiri-symbolic-alignment-check` makes the alignment check more strict. By default, alignment is
321 checked by casting the pointer to an integer, and making sure that is a multiple of the alignment.
322 This can lead to cases where a program passes the alignment check by pure chance, because things
323 "happened to be" sufficiently aligned -- there is no UB in this execution but there would be UB in
324 others. To avoid such cases, the symbolic alignment check only takes into account the requested
325 alignment of the relevant allocation, and the offset into that allocation. This avoids missing
326 such bugs, but it also incurs some false positives when the code does manual integer arithmetic to
327 ensure alignment. (The standard library `align_to` method works fine in both modes; under
328 symbolic alignment it only fills the middle slice when the allocation guarantees sufficient
331 The remaining flags are for advanced use only, and more likely to change or be removed.
332 Some of these are **unsound**, which means they can lead
333 to Miri failing to detect cases of undefined behavior in a program.
335 * `-Zmiri-disable-abi-check` disables checking [function ABI]. Using this flag
337 * `-Zmiri-disable-alignment-check` disables checking pointer alignment, so you
338 can focus on other failures, but it means Miri can miss bugs in your program.
339 Using this flag is **unsound**.
340 * `-Zmiri-disable-data-race-detector` disables checking for data races. Using
341 this flag is **unsound**. This implies `-Zmiri-disable-weak-memory-emulation`.
342 * `-Zmiri-disable-stacked-borrows` disables checking the experimental
343 [Stacked Borrows] aliasing rules. This can make Miri run faster, but it also
344 means no aliasing violations will be detected. Using this flag is **unsound**
345 (but the affected soundness rules are experimental).
346 * `-Zmiri-disable-validation` disables enforcing validity invariants, which are
347 enforced by default. This is mostly useful to focus on other failures (such
348 as out-of-bounds accesses) first. Setting this flag means Miri can miss bugs
349 in your program. However, this can also help to make Miri run faster. Using
350 this flag is **unsound**.
351 * `-Zmiri-disable-weak-memory-emulation` disables the emulation of some C++11 weak
353 * `-Zmiri-extern-so-file=<path to a shared object file>` is an experimental flag for providing support
354 for FFI calls. Functions not provided by that file are still executed via the usual Miri shims.
355 **WARNING**: If an invalid/incorrect `.so` file is specified, this can cause undefined behaviour in Miri itself!
356 And of course, Miri cannot do any checks on the actions taken by the external code.
357 Note that Miri has its own handling of file descriptors, so if you want to replace *some* functions
358 working on file descriptors, you will have to replace *all* of them, or the two kinds of
359 file descriptors will be mixed up.
360 This is **work in progress**; currently, only integer arguments and return values are
361 supported (and no, pointer/integer casts to work around this limitation will not work;
362 they will fail horribly). It also only works on unix hosts for now.
363 Follow [the discussion on supporting other types](https://github.com/rust-lang/miri/issues/2365).
364 * `-Zmiri-measureme=<name>` enables `measureme` profiling for the interpreted program.
365 This can be used to find which parts of your program are executing slowly under Miri.
366 The profile is written out to a file with the prefix `<name>`, and can be processed
367 using the tools in the repository https://github.com/rust-lang/measureme.
368 * `-Zmiri-mute-stdout-stderr` silently ignores all writes to stdout and stderr,
369 but reports to the program that it did actually write. This is useful when you
370 are not interested in the actual program's output, but only want to see Miri's
372 * `-Zmiri-panic-on-unsupported` will makes some forms of unsupported functionality,
373 such as FFI and unsupported syscalls, panic within the context of the emulated
374 application instead of raising an error within the context of Miri (and halting
375 execution). Note that code might not expect these operations to ever panic, so
376 this flag can lead to strange (mis)behavior.
377 * `-Zmiri-retag-fields` changes Stacked Borrows retagging to recurse into fields.
378 This means that references in fields of structs/enums/tuples/arrays/... are retagged,
379 and in particular, they are protected when passed as function arguments.
380 * `-Zmiri-tag-gc=<blocks>` configures how often the pointer tag garbage collector runs. The default
381 is to search for and remove unreachable tags once every `10000` basic blocks. Setting this to
382 `0` disables the garbage collector, which causes some programs to have explosive memory usage
383 and/or super-linear runtime.
384 * `-Zmiri-track-alloc-id=<id1>,<id2>,...` shows a backtrace when the given allocations are
385 being allocated or freed. This helps in debugging memory leaks and
386 use after free bugs. Specifying this argument multiple times does not overwrite the previous
387 values, instead it appends its values to the list. Listing an id multiple times has no effect.
388 * `-Zmiri-track-call-id=<id1>,<id2>,...` shows a backtrace when the given call ids are
389 assigned to a stack frame. This helps in debugging UB related to Stacked
390 Borrows "protectors". Specifying this argument multiple times does not overwrite the previous
391 values, instead it appends its values to the list. Listing an id multiple times has no effect.
392 * `-Zmiri-track-pointer-tag=<tag1>,<tag2>,...` shows a backtrace when a given pointer tag
393 is created and when (if ever) it is popped from a borrow stack (which is where the tag becomes invalid
394 and any future use of it will error). This helps you in finding out why UB is
395 happening and where in your code would be a good place to look for it.
396 Specifying this argument multiple times does not overwrite the previous
397 values, instead it appends its values to the list. Listing a tag multiple times has no effect.
398 * `-Zmiri-track-weak-memory-loads` shows a backtrace when weak memory emulation returns an outdated
399 value from a load. This can help diagnose problems that disappear under
400 `-Zmiri-disable-weak-memory-emulation`.
402 [function ABI]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
404 Some native rustc `-Z` flags are also very relevant for Miri:
406 * `-Zmir-opt-level` controls how many MIR optimizations are performed. Miri
407 overrides the default to be `0`; be advised that using any higher level can
408 make Miri miss bugs in your program because they got optimized away.
409 * `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
410 functions. This is needed so that Miri can execute such functions, so Miri
411 sets this flag per default.
412 * `-Zmir-emit-retag` controls whether `Retag` statements are emitted. Miri
413 enables this per default because it is needed for [Stacked Borrows].
415 Moreover, Miri recognizes some environment variables:
417 * `MIRI_AUTO_OPS` indicates whether the automatic execution of rustfmt, clippy and rustup-toolchain
418 should be skipped. If it is set to any value, they are skipped. This is used for avoiding
419 infinite recursion in `./miri` and to allow automated IDE actions to avoid the auto ops.
420 * `MIRI_LOG`, `MIRI_BACKTRACE` control logging and backtrace printing during
421 Miri executions, also [see "Testing the Miri driver" in `CONTRIBUTING.md`][testing-miri].
422 * `MIRIFLAGS` (recognized by `cargo miri` and the test suite) defines extra
423 flags to be passed to Miri.
424 * `MIRI_LIB_SRC` defines the directory where Miri expects the sources of the
425 standard library that it will build and use for interpretation. This directory
426 must point to the `library` subdirectory of a `rust-lang/rust` repository
427 checkout. Note that changing files in that directory does not automatically
428 trigger a re-build of the standard library; you have to clear the Miri build
429 cache manually (on Linux, `rm -rf ~/.cache/miri`).
430 * `MIRI_SYSROOT` (recognized by `cargo miri` and the Miri driver) indicates the sysroot to use. When
431 using `cargo miri`, only set this if you do not want to use the automatically created sysroot. For
432 directly invoking the Miri driver, this variable (or a `--sysroot` flag) is mandatory.
433 * `MIRI_TEST_TARGET` (recognized by the test suite and the `./miri` script) indicates which target
434 architecture to test against. `miri` and `cargo miri` accept the `--target` flag for the same
436 * `MIRI_NO_STD` (recognized by `cargo miri` and the test suite) makes sure that the target's
437 sysroot is built without libstd. This allows testing and running no_std programs.
438 * `MIRI_BLESS` (recognized by the test suite and `cargo-miri-test/run-test.py`): overwrite all
439 `stderr` and `stdout` files instead of checking whether the output matches.
440 * `MIRI_SKIP_UI_CHECKS` (recognized by the test suite): don't check whether the
441 `stderr` or `stdout` files match the actual output.
443 The following environment variables are *internal* and must not be used by
444 anyone but Miri itself. They are used to communicate between different Miri
445 binaries, and as such worth documenting:
447 * `MIRI_BE_RUSTC` can be set to `host` or `target`. It tells the Miri driver to
448 actually not interpret the code but compile it like rustc would. With `target`, Miri sets
449 some compiler flags to prepare the code for interpretation; with `host`, this is not done.
450 This environment variable is useful to be sure that the compiled `rlib`s are compatible
452 * `MIRI_CALLED_FROM_SETUP` is set during the Miri sysroot build,
453 which will re-invoke `cargo-miri` as the `rustc` to use for this build.
454 * `MIRI_CALLED_FROM_RUSTDOC` when set to any value tells `cargo-miri` that it is
455 running as a child process of `rustdoc`, which invokes it twice for each doc-test
456 and requires special treatment, most notably a check-only build before interpretation.
457 This is set by `cargo-miri` itself when running as a `rustdoc`-wrapper.
458 * `MIRI_CWD` when set to any value tells the Miri driver to change to the given
459 directory after loading all the source files, but before commencing
460 interpretation. This is useful if the interpreted program wants a different
461 working directory at run-time than at build-time.
462 * `MIRI_LOCAL_CRATES` is set by `cargo-miri` to tell the Miri driver which
463 crates should be given special treatment in diagnostics, in addition to the
464 crate currently being compiled.
465 * `MIRI_VERBOSE` when set to any value tells the various `cargo-miri` phases to
466 perform verbose logging.
467 * `MIRI_HOST_SYSROOT` is set by bootstrap to tell `cargo-miri` which sysroot to use for *host*
470 [testing-miri]: CONTRIBUTING.md#testing-the-miri-driver
472 ## Miri `extern` functions
474 Miri provides some `extern` functions that programs can import to access
475 Miri-specific functionality:
480 /// Miri-provided extern function to mark the block `ptr` points to as a "root"
481 /// for some static memory. This memory and everything reachable by it is not
482 /// considered leaking even if it still exists when the program terminates.
484 /// `ptr` has to point to the beginning of an allocated block.
485 fn miri_static_root(ptr: *const u8);
487 // Miri-provided extern function to get the amount of frames in the current backtrace.
488 // The `flags` argument must be `0`.
489 fn miri_backtrace_size(flags: u64) -> usize;
491 /// Miri-provided extern function to obtain a backtrace of the current call stack.
492 /// This writes a slice of pointers into `buf` - each pointer is an opaque value
493 /// that is only useful when passed to `miri_resolve_frame`.
494 /// `buf` must have `miri_backtrace_size(0) * pointer_size` bytes of space.
495 /// The `flags` argument must be `1`.
496 fn miri_get_backtrace(flags: u64, buf: *mut *mut ());
498 /// Miri-provided extern function to resolve a frame pointer obtained
499 /// from `miri_get_backtrace`. The `flags` argument must be `1`,
500 /// and `MiriFrame` should be declared as follows:
504 /// struct MiriFrame {
505 /// // The size of the name of the function being executed, encoded in UTF-8
507 /// // The size of filename of the function being executed, encoded in UTF-8
508 /// filename_len: usize,
509 /// // The line number currently being executed in `filename`, starting from '1'.
511 /// // The column number currently being executed in `filename`, starting from '1'.
513 /// // The function pointer to the function currently being executed.
514 /// // This can be compared against function pointers obtained by
515 /// // casting a function (e.g. `my_fn as *mut ()`)
520 /// The fields must be declared in exactly the same order as they appear in `MiriFrame` above.
521 /// This function can be called on any thread (not just the one which obtained `frame`).
522 fn miri_resolve_frame(frame: *mut (), flags: u64) -> MiriFrame;
524 /// Miri-provided extern function to get the name and filename of the frame provided by `miri_resolve_frame`.
525 /// `name_buf` and `filename_buf` should be allocated with the `name_len` and `filename_len` fields of `MiriFrame`.
526 /// The flags argument must be `0`.
527 fn miri_resolve_frame_names(ptr: *mut (), flags: u64, name_buf: *mut u8, filename_buf: *mut u8);
529 /// Miri-provided extern function to begin unwinding with the given payload.
531 /// This is internal and unstable and should not be used; we give it here
532 /// just to be complete.
533 fn miri_start_panic(payload: *mut u8) -> !;
535 /// Miri-provided extern function to get the internal unique identifier for the allocation that a pointer
536 /// points to. This is only useful as an input to `miri_print_stacks`, and it is a separate call because
537 /// getting a pointer to an allocation at runtime can change the borrow stacks in the allocation.
538 fn miri_get_alloc_id(ptr: *const ()) -> u64;
540 /// Miri-provided extern function to print (from the interpreter, not the program) the contents of all
541 /// borrow stacks in an allocation. The format of what this emits is unstable and may change at any time.
542 /// In particular, users should be aware that Miri will periodically attempt to garbage collect the
543 /// contents of all stacks. Callers of this function may wish to pass `-Zmiri-tag-gc=0` to disable the GC.
544 fn miri_print_stacks(alloc_id: u64);
548 ## Contributing and getting help
550 If you want to contribute to Miri, great! Please check out our
551 [contribution guide](CONTRIBUTING.md).
553 For help with running Miri, you can open an issue here on
554 GitHub or use the [Miri stream on the Rust Zulip][zulip].
556 [zulip]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri
560 This project began as part of an undergraduate research course in 2015 by
561 @solson at the [University of Saskatchewan][usask]. There are [slides] and a
562 [report] available from that project. In 2016, @oli-obk joined to prepare Miri
563 for eventually being used as const evaluator in the Rust compiler itself
564 (basically, for `const` and `static` stuff), replacing the old evaluator that
565 worked directly on the AST. In 2017, @RalfJung did an internship with Mozilla
566 and began developing Miri towards a tool for detecting undefined behavior, and
567 also using Miri as a way to explore the consequences of various possible
568 definitions for undefined behavior in Rust. @oli-obk's move of the Miri engine
569 into the compiler finally came to completion in early 2018. Meanwhile, later
570 that year, @RalfJung did a second internship, developing Miri further with
571 support for checking basic type invariants and verifying that references are
572 used according to their aliasing restrictions.
574 [usask]: https://www.usask.ca/
575 [slides]: https://solson.me/miri-slides.pdf
576 [report]: https://solson.me/miri-report.pdf
578 ## Bugs found by Miri
580 Miri has already found a number of bugs in the Rust standard library and beyond, which we collect here.
584 * [`Debug for vec_deque::Iter` accessing uninitialized memory](https://github.com/rust-lang/rust/issues/53566)
585 * [`Vec::into_iter` doing an unaligned ZST read](https://github.com/rust-lang/rust/pull/53804)
586 * [`From<&[T]> for Rc` creating a not sufficiently aligned reference](https://github.com/rust-lang/rust/issues/54908)
587 * [`BTreeMap` creating a shared reference pointing to a too small allocation](https://github.com/rust-lang/rust/issues/54957)
588 * [`Vec::append` creating a dangling reference](https://github.com/rust-lang/rust/pull/61082)
589 * [Futures turning a shared reference into a mutable one](https://github.com/rust-lang/rust/pull/56319)
590 * [`str` turning a shared reference into a mutable one](https://github.com/rust-lang/rust/pull/58200)
591 * [`rand` performing unaligned reads](https://github.com/rust-random/rand/issues/779)
592 * [The Unix allocator calling `posix_memalign` in an invalid way](https://github.com/rust-lang/rust/issues/62251)
593 * [`getrandom` calling the `getrandom` syscall in an invalid way](https://github.com/rust-random/getrandom/pull/73)
594 * [`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
595 * [`beef` leaking memory](https://github.com/maciejhirsz/beef/issues/12)
596 * [`EbrCell` using uninitialized memory incorrectly](https://github.com/Firstyear/concread/commit/b15be53b6ec076acb295a5c0483cdb4bf9be838f#diff-6282b2fc8e98bd089a1f0c86f648157cR229)
597 * [TiKV performing an unaligned pointer access](https://github.com/tikv/tikv/issues/7613)
598 * [`servo_arc` creating a dangling shared reference](https://github.com/servo/servo/issues/26357)
599 * [TiKV constructing out-of-bounds pointers (and overlapping mutable references)](https://github.com/tikv/tikv/pull/7751)
600 * [`encoding_rs` doing out-of-bounds pointer arithmetic](https://github.com/hsivonen/encoding_rs/pull/53)
601 * [TiKV using `Vec::from_raw_parts` incorrectly](https://github.com/tikv/agatedb/pull/24)
602 * Incorrect doctests for [`AtomicPtr`](https://github.com/rust-lang/rust/pull/84052) and [`Box::from_raw_in`](https://github.com/rust-lang/rust/pull/84053)
603 * [Insufficient alignment in `ThinVec`](https://github.com/Gankra/thin-vec/pull/27)
604 * [`crossbeam-epoch` calling `assume_init` on a partly-initialized `MaybeUninit`](https://github.com/crossbeam-rs/crossbeam/pull/779)
605 * [`integer-encoding` dereferencing a misaligned pointer](https://github.com/dermesser/integer-encoding-rs/pull/23)
606 * [`rkyv` constructing a `Box<[u8]>` from an overaligned allocation](https://github.com/rkyv/rkyv/commit/a9417193a34757e12e24263178be8b2eebb72456)
607 * [Data race in `thread::scope`](https://github.com/rust-lang/rust/issues/98498)
608 * [`regex` incorrectly handling unaligned `Vec<u8>` buffers](https://www.reddit.com/r/rust/comments/vq3mmu/comment/ienc7t0?context=3)
609 * [Incorrect use of `compare_exchange_weak` in `once_cell`](https://github.com/matklad/once_cell/issues/186)
611 Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):
613 * [`VecDeque::drain` creating overlapping mutable references](https://github.com/rust-lang/rust/pull/56161)
614 * Various `BTreeMap` problems
615 * [`BTreeMap` iterators creating mutable references that overlap with shared references](https://github.com/rust-lang/rust/pull/58431)
616 * [`BTreeMap::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/73915)
617 * [`BTreeMap` node insertion using raw pointers outside their valid memory area](https://github.com/rust-lang/rust/issues/78477)
618 * [`LinkedList` cursor insertion creating overlapping mutable references](https://github.com/rust-lang/rust/pull/60072)
619 * [`Vec::push` invalidating existing references into the vector](https://github.com/rust-lang/rust/issues/60847)
620 * [`align_to_mut` violating uniqueness of mutable references](https://github.com/rust-lang/rust/issues/68549)
621 * [`sized-chunks` creating aliasing mutable references](https://github.com/bodil/sized-chunks/issues/8)
622 * [`String::push_str` invalidating existing references into the string](https://github.com/rust-lang/rust/issues/70301)
623 * [`ryu` using raw pointers outside their valid memory area](https://github.com/dtolnay/ryu/issues/24)
624 * [ink! creating overlapping mutable references](https://github.com/rust-lang/miri/issues/1364)
625 * [TiKV creating overlapping mutable reference and raw pointer](https://github.com/tikv/tikv/pull/7709)
626 * [Windows `Env` iterator using a raw pointer outside its valid memory area](https://github.com/rust-lang/rust/pull/70479)
627 * [`VecDeque::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/74029)
628 * [Various standard library aliasing issues involving raw pointers](https://github.com/rust-lang/rust/pull/78602)
629 * [`<[T]>::copy_within` using a loan after invalidating it](https://github.com/rust-lang/rust/pull/85610)
631 ## Scientific papers employing Miri
633 * [Stacked Borrows: An Aliasing Model for Rust](https://plv.mpi-sws.org/rustbelt/stacked-borrows/)
634 * [Using Lightweight Formal Methods to Validate a Key-Value Storage Node in Amazon S3](https://www.amazon.science/publications/using-lightweight-formal-methods-to-validate-a-key-value-storage-node-in-amazon-s3)
635 * [SyRust: Automatic Testing of Rust Libraries with Semantic-Aware Program Synthesis](https://dl.acm.org/doi/10.1145/3453483.3454084)
639 Licensed under either of
641 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
642 http://www.apache.org/licenses/LICENSE-2.0)
643 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
644 http://opensource.org/licenses/MIT)
650 Unless you explicitly state otherwise, any contribution intentionally submitted
651 for inclusion in the work by you shall be dual licensed as above, without any
652 additional terms or conditions.