3 An experimental interpreter for [Rust][rust]'s
4 [mid-level intermediate representation][mir] (MIR). It can run binaries and
5 test suites of cargo projects and detect certain classes of
6 [undefined behavior](https://doc.rust-lang.org/reference/behavior-considered-undefined.html),
9 * Out-of-bounds memory accesses and use-after-free
10 * Invalid use of uninitialized data
11 * Violation of intrinsic preconditions (an [`unreachable_unchecked`] being
12 reached, calling [`copy_nonoverlapping`] with overlapping ranges, ...)
13 * Not sufficiently aligned memory accesses and references
14 * Violation of *some* basic type invariants (a `bool` that is not 0 or 1, for example,
15 or an invalid enum discriminant)
16 * **Experimental**: Violations of the [Stacked Borrows] rules governing aliasing
18 * **Experimental**: Data races
20 On top of that, Miri will also tell you about memory leaks: when there is memory
21 still allocated at the end of the execution, and that memory is not reachable
22 from a global `static`, Miri will raise an error.
24 Miri supports almost all Rust language features; in particular, unwinding and
25 concurrency are properly supported (including some experimental emulation of
26 weak memory effects, i.e., reads can return outdated values).
28 You can use Miri to emulate programs on other targets, e.g. to ensure that
29 byte-level data manipulation works correctly both on little-endian and
30 big-endian systems. See
31 [cross-interpretation](#cross-interpretation-running-for-different-targets)
34 Miri has already discovered some [real-world bugs](#bugs-found-by-miri). If you
35 found a bug with Miri, we'd appreciate if you tell us and we'll add it to the
38 By default, Miri ensures a fully deterministic execution and isolates the
39 program from the host system. Some APIs that would usually access the host, such
40 as gathering entropy for random number generators, environment variables, and
41 clocks, are replaced by deterministic "fake" implementations. Set
42 `MIRIFLAGS="-Zmiri-disable-isolation"` to access the real system APIs instead.
43 (In particular, the "fake" system RNG APIs make Miri **not suited for
44 cryptographic use**! Do not generate keys using Miri.)
46 All that said, be aware that Miri will **not catch all cases of undefined
47 behavior** in your program, and cannot run all programs:
49 * There are still plenty of open questions around the basic invariants for some
50 types and when these invariants even have to hold. Miri tries to avoid false
51 positives here, so if your program runs fine in Miri right now that is by no
52 means a guarantee that it is UB-free when these questions get answered.
54 In particular, Miri does currently not check that references point to valid data.
55 * If the program relies on unspecified details of how data is laid out, it will
56 still run fine in Miri -- but might break (including causing UB) on different
57 compiler versions or different platforms.
58 * Program execution is non-deterministic when it depends, for example, on where
59 exactly in memory allocations end up, or on the exact interleaving of
60 concurrent threads. Miri tests one of many possible executions of your
61 program. You can alleviate this to some extent by running Miri with different
62 values for `-Zmiri-seed`, but that will still by far not explore all possible
64 * Miri runs the program as a platform-independent interpreter, so the program
65 has no access to most platform-specific APIs or FFI. A few APIs have been
66 implemented (such as printing to stdout, accessing environment variables, and
67 basic file system access) but most have not: for example, Miri currently does
68 not support networking. System API support varies between targets; if you run
69 on Windows it is a good idea to use `--target x86_64-unknown-linux-gnu` to get
71 * Weak memory emulation may [produce weak behaviours](https://github.com/rust-lang/miri/issues/2301)
72 unobservable by compiled programs running on real hardware when `SeqCst` fences are used, and it
73 cannot produce all behaviors possibly observable on real hardware.
75 [rust]: https://www.rust-lang.org/
76 [mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
77 [`unreachable_unchecked`]: https://doc.rust-lang.org/stable/std/hint/fn.unreachable_unchecked.html
78 [`copy_nonoverlapping`]: https://doc.rust-lang.org/stable/std/ptr/fn.copy_nonoverlapping.html
79 [Stacked Borrows]: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md
84 Install Miri on Rust nightly via `rustup`:
87 rustup +nightly component add miri
90 If `rustup` says the `miri` component is unavailable, that's because not all
91 nightly releases come with all tools. Check out
92 [this website](https://rust-lang.github.io/rustup-components-history) to
93 determine a nightly version that comes with Miri and install that using `rustup
94 toolchain install nightly-YYYY-MM-DD`. Either way, all of the following commands
95 assume the right toolchain is pinned via `rustup override set nightly` or
96 `rustup override set nightly-YYYY-MM-DD`. (Alternatively, use `cargo
97 +nightly`/`cargo +nightly-YYYY-MM-DD` for each of the following commands.)
99 Now you can run your project in Miri:
101 1. Run `cargo clean` to eliminate any cached dependencies. Miri needs your
102 dependencies to be compiled the right way, that would not happen if they have
103 previously already been compiled.
104 2. To run all tests in your project through Miri, use `cargo miri test`.
105 3. If you have a binary project, you can run it through Miri using `cargo miri run`.
107 The first time you run Miri, it will perform some extra setup and install some
108 dependencies. It will ask you for confirmation before installing anything.
110 `cargo miri run/test` supports the exact same flags as `cargo run/test`. For
111 example, `cargo miri test filter` only runs the tests containing `filter` in
114 You can pass arguments to Miri via `MIRIFLAGS`. For example,
115 `MIRIFLAGS="-Zmiri-disable-stacked-borrows" cargo miri run` runs the program
116 without checking the aliasing of references.
118 When compiling code via `cargo miri`, the `cfg(miri)` config flag is set for code
119 that will be interpret under Miri. You can use this to ignore test cases that fail
120 under Miri because they do things Miri does not support:
124 #[cfg_attr(miri, ignore)]
125 fn does_not_work_on_miri() {
126 tokio::run(futures::future::ok::<_, ()>(()));
130 There is no way to list all the infinite things Miri cannot do, but the
131 interpreter will explicitly tell you when it finds something unsupported:
134 error: unsupported operation: can't call foreign function: bind
136 = help: this is likely not a bug in the program; it indicates that the program \
137 performed an operation that the interpreter does not support
140 ### Cross-interpretation: running for different targets
142 Miri can not only run a binary or test suite for your host target, it can also
143 perform cross-interpretation for arbitrary foreign targets: `cargo miri run
144 --target x86_64-unknown-linux-gnu` will run your program as if it was a Linux
145 program, no matter your host OS. This is particularly useful if you are using
146 Windows, as the Linux target is much better supported than Windows targets.
148 You can also use this to test platforms with different properties than your host
149 platform. For example `cargo miri test --target mips64-unknown-linux-gnuabi64`
150 will run your test suite on a big-endian target, which is useful for testing
151 endian-sensitive code.
153 ### Running Miri on CI
155 To run Miri on CI, make sure that you handle the case where the latest nightly
156 does not ship the Miri component because it currently does not build. `rustup
157 toolchain install --component` knows how to handle this situation, so the
158 following snippet should always work:
161 rustup toolchain install nightly --component miri
162 rustup override set nightly
167 Here is an example job for GitHub Actions:
172 runs-on: ubuntu-latest
174 - uses: actions/checkout@v3
177 rustup toolchain install nightly --component miri
178 rustup override set nightly
180 - name: Test with Miri
184 The explicit `cargo miri setup` helps to keep the output of the actual test step
187 ### Testing for alignment issues
189 Miri can sometimes miss misaligned accesses since allocations can "happen to be"
190 aligned just right. You can use `-Zmiri-symbolic-alignment-check` to definitely
191 catch all such issues, but that flag will also cause false positives when code
192 does manual pointer arithmetic to account for alignment. Another alternative is
193 to call Miri with various values for `-Zmiri-seed`; that will alter the
194 randomness that is used to determine allocation base addresses. The following
195 snippet calls Miri in a loop with different values for the seed:
198 for SEED in $(seq 0 255); do
199 echo "Trying seed: $SEED"
200 MIRIFLAGS=-Zmiri-seed=$SEED cargo miri test || { echo "Failing seed: $SEED"; break; };
204 ### Supported targets
206 Miri does not support all targets supported by Rust. The good news, however, is
207 that no matter your host OS/platform, it is easy to run code for *any* target
210 The following targets are tested on CI and thus should always work (to the
211 degree documented below):
213 - The best-supported target is `x86_64-unknown-linux-gnu`. Miri releases are
214 blocked on things working with this target. Most other Linux targets should
215 also work well; we do run the test suite on `i686-unknown-linux-gnu` as a
216 32bit target and `mips64-unknown-linux-gnuabi64` as a big-endian target.
217 - `x86_64-apple-darwin` should work basically as well as Linux. We also test
218 `aarch64-apple-darwin`. However, we might ship Miri with a nightly even when
219 some features on these targets regress.
220 - `x86_64-pc-windows-msvc` works, but supports fewer features than the Linux and
221 Apple targets. For example, file system access and concurrency are not
222 supported on Windows. We also test `i686-pc-windows-msvc`, with the same
223 reduced feature set. We might ship Miri with a nightly even when some features
224 on these targets regress.
228 When using the above instructions, you may encounter a number of confusing compiler
231 #### "note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace"
233 You may see this when trying to get Miri to display a backtrace. By default, Miri
234 doesn't expose any environment to the program, so running
235 `RUST_BACKTRACE=1 cargo miri test` will not do what you expect.
237 To get a backtrace, you need to disable isolation
238 [using `-Zmiri-disable-isolation`][miri-flags]:
241 RUST_BACKTRACE=1 MIRIFLAGS="-Zmiri-disable-isolation" cargo miri test
244 #### "found possibly newer version of crate `std` which `<dependency>` depends on"
246 Your build directory may contain artifacts from an earlier build that have/have
247 not been built for Miri. Run `cargo clean` before switching from non-Miri to
248 Miri builds and vice-versa.
250 #### "found crate `std` compiled by an incompatible version of rustc"
252 You may be running `cargo miri` with a different compiler version than the one
253 used to build the custom libstd that Miri uses, and Miri failed to detect that.
254 Try deleting `~/.cache/miri`.
256 #### "no mir for `std::rt::lang_start_internal`"
258 This means the sysroot you are using was not compiled with Miri in mind. This
259 should never happen when you use `cargo miri` because that takes care of setting
260 up the sysroot. If you are using `miri` (the Miri driver) directly, see the
261 [contributors' guide](CONTRIBUTING.md) for how to use `./miri` to best do that.
264 ## Miri `-Z` flags and environment variables
265 [miri-flags]: #miri--z-flags-and-environment-variables
267 Miri adds its own set of `-Z` flags, which are usually set via the `MIRIFLAGS`
268 environment variable. We first document the most relevant and most commonly used flags:
270 * `-Zmiri-compare-exchange-weak-failure-rate=<rate>` changes the failure rate of
271 `compare_exchange_weak` operations. The default is `0.8` (so 4 out of 5 weak ops will fail).
272 You can change it to any value between `0.0` and `1.0`, where `1.0` means it
273 will always fail and `0.0` means it will never fail. Note than setting it to
274 `1.0` will likely cause hangs, since it means programs using
275 `compare_exchange_weak` cannot make progress.
276 * `-Zmiri-disable-isolation` disables host isolation. As a consequence,
277 the program has access to host resources such as environment variables, file
278 systems, and randomness.
279 * `-Zmiri-isolation-error=<action>` configures Miri's response to operations
280 requiring host access while isolation is enabled. `abort`, `hide`, `warn`,
281 and `warn-nobacktrace` are the supported actions. The default is to `abort`,
282 which halts the machine. Some (but not all) operations also support continuing
283 execution with a "permission denied" error being returned to the program.
284 `warn` prints a full backtrace when that happens; `warn-nobacktrace` is less
285 verbose. `hide` hides the warning entirely.
286 * `-Zmiri-env-forward=<var>` forwards the `var` environment variable to the interpreted program. Can
287 be used multiple times to forward several variables. Execution will still be deterministic if the
288 value of forwarded variables stays the same. Has no effect if `-Zmiri-disable-isolation` is set.
289 * `-Zmiri-ignore-leaks` disables the memory leak checker, and also allows some
290 remaining threads to exist when the main thread exits.
291 * `-Zmiri-num-cpus` states the number of available CPUs to be reported by miri. By default, the
292 number of available CPUs is `1`. Note that this flag does not affect how miri handles threads in
294 * `-Zmiri-permissive-provenance` disables the warning for integer-to-pointer casts and
295 [`ptr::from_exposed_addr`](https://doc.rust-lang.org/nightly/std/ptr/fn.from_exposed_addr.html).
296 This will necessarily miss some bugs as those operations are not efficiently and accurately
297 implementable in a sanitizer, but it will only miss bugs that concern memory/pointers which is
298 subject to these operations.
299 * `-Zmiri-preemption-rate` configures the probability that at the end of a basic block, the active
300 thread will be preempted. The default is `0.01` (i.e., 1%). Setting this to `0` disables
302 * `-Zmiri-report-progress` makes Miri print the current stacktrace every now and then, so you can
303 tell what it is doing when a program just keeps running. You can customize how frequently the
304 report is printed via `-Zmiri-report-progress=<blocks>`, which prints the report every N basic
306 * `-Zmiri-seed=<num>` configures the seed of the RNG that Miri uses to resolve non-determinism. This
307 RNG is used to pick base addresses for allocations, to determine preemption and failure of
308 `compare_exchange_weak`, and to control store buffering for weak memory emulation. When isolation
309 is enabled (the default), this is also used to emulate system entropy. The default seed is 0. You
310 can increase test coverage by running Miri multiple times with different seeds.
311 * `-Zmiri-strict-provenance` enables [strict
312 provenance](https://github.com/rust-lang/rust/issues/95228) checking in Miri. This means that
313 casting an integer to a pointer yields a result with 'invalid' provenance, i.e., with provenance
314 that cannot be used for any memory access.
315 * `-Zmiri-symbolic-alignment-check` makes the alignment check more strict. By default, alignment is
316 checked by casting the pointer to an integer, and making sure that is a multiple of the alignment.
317 This can lead to cases where a program passes the alignment check by pure chance, because things
318 "happened to be" sufficiently aligned -- there is no UB in this execution but there would be UB in
319 others. To avoid such cases, the symbolic alignment check only takes into account the requested
320 alignment of the relevant allocation, and the offset into that allocation. This avoids missing
321 such bugs, but it also incurs some false positives when the code does manual integer arithmetic to
322 ensure alignment. (The standard library `align_to` method works fine in both modes; under
323 symbolic alignment it only fills the middle slice when the allocation guarantees sufficient
326 The remaining flags are for advanced use only, and more likely to change or be removed.
327 Some of these are **unsound**, which means they can lead
328 to Miri failing to detect cases of undefined behavior in a program.
330 * `-Zmiri-disable-abi-check` disables checking [function ABI]. Using this flag
332 * `-Zmiri-disable-alignment-check` disables checking pointer alignment, so you
333 can focus on other failures, but it means Miri can miss bugs in your program.
334 Using this flag is **unsound**.
335 * `-Zmiri-disable-data-race-detector` disables checking for data races. Using
336 this flag is **unsound**. This implies `-Zmiri-disable-weak-memory-emulation`.
337 * `-Zmiri-disable-stacked-borrows` disables checking the experimental
338 [Stacked Borrows] aliasing rules. This can make Miri run faster, but it also
339 means no aliasing violations will be detected. Using this flag is **unsound**
340 (but the affected soundness rules are experimental).
341 * `-Zmiri-disable-validation` disables enforcing validity invariants, which are
342 enforced by default. This is mostly useful to focus on other failures (such
343 as out-of-bounds accesses) first. Setting this flag means Miri can miss bugs
344 in your program. However, this can also help to make Miri run faster. Using
345 this flag is **unsound**.
346 * `-Zmiri-disable-weak-memory-emulation` disables the emulation of some C++11 weak
348 * `-Zmiri-extern-so-file=<path to a shared object file>` is an experimental flag for providing support
349 for FFI calls. Functions not provided by that file are still executed via the usual Miri shims.
350 **WARNING**: If an invalid/incorrect `.so` file is specified, this can cause undefined behaviour in Miri itself!
351 And of course, Miri cannot do any checks on the actions taken by the external code.
352 Note that Miri has its own handling of file descriptors, so if you want to replace *some* functions
353 working on file descriptors, you will have to replace *all* of them, or the two kinds of
354 file descriptors will be mixed up.
355 This is **work in progress**; currently, only integer arguments and return values are
356 supported (and no, pointer/integer casts to work around this limitation will not work;
357 they will fail horribly). It also only works on unix hosts for now.
358 Follow [the discussion on supporting other types](https://github.com/rust-lang/miri/issues/2365).
359 * `-Zmiri-measureme=<name>` enables `measureme` profiling for the interpreted program.
360 This can be used to find which parts of your program are executing slowly under Miri.
361 The profile is written out to a file with the prefix `<name>`, and can be processed
362 using the tools in the repository https://github.com/rust-lang/measureme.
363 * `-Zmiri-mute-stdout-stderr` silently ignores all writes to stdout and stderr,
364 but reports to the program that it did actually write. This is useful when you
365 are not interested in the actual program's output, but only want to see Miri's
367 * `-Zmiri-panic-on-unsupported` will makes some forms of unsupported functionality,
368 such as FFI and unsupported syscalls, panic within the context of the emulated
369 application instead of raising an error within the context of Miri (and halting
370 execution). Note that code might not expect these operations to ever panic, so
371 this flag can lead to strange (mis)behavior.
372 * `-Zmiri-retag-fields` changes Stacked Borrows retagging to recurse into *all* fields.
373 This means that references in fields of structs/enums/tuples/arrays/... are retagged,
374 and in particular, they are protected when passed as function arguments.
375 (The default is to recurse only in cases where rustc would actually emit a `noalias` attribute.)
376 * `-Zmiri-retag-fields=<all|none|scalar>` controls when Stacked Borrows retagging recurses into
377 fields. `all` means it always recurses (like `-Zmiri-retag-fields`), `none` means it never
378 recurses, `scalar` (the default) means it only recurses for types where we would also emit
379 `noalias` annotations in the generated LLVM IR (types passed as indivudal scalars or pairs of
380 scalars). Setting this to `none` is **unsound**.
381 * `-Zmiri-tag-gc=<blocks>` configures how often the pointer tag garbage collector runs. The default
382 is to search for and remove unreachable tags once every `10000` basic blocks. Setting this to
383 `0` disables the garbage collector, which causes some programs to have explosive memory usage
384 and/or super-linear runtime.
385 * `-Zmiri-track-alloc-id=<id1>,<id2>,...` shows a backtrace when the given allocations are
386 being allocated or freed. This helps in debugging memory leaks and
387 use after free bugs. Specifying this argument multiple times does not overwrite the previous
388 values, instead it appends its values to the list. Listing an id multiple times has no effect.
389 * `-Zmiri-track-call-id=<id1>,<id2>,...` shows a backtrace when the given call ids are
390 assigned to a stack frame. This helps in debugging UB related to Stacked
391 Borrows "protectors". Specifying this argument multiple times does not overwrite the previous
392 values, instead it appends its values to the list. Listing an id multiple times has no effect.
393 * `-Zmiri-track-pointer-tag=<tag1>,<tag2>,...` shows a backtrace when a given pointer tag
394 is created and when (if ever) it is popped from a borrow stack (which is where the tag becomes invalid
395 and any future use of it will error). This helps you in finding out why UB is
396 happening and where in your code would be a good place to look for it.
397 Specifying this argument multiple times does not overwrite the previous
398 values, instead it appends its values to the list. Listing a tag multiple times has no effect.
399 * `-Zmiri-track-weak-memory-loads` shows a backtrace when weak memory emulation returns an outdated
400 value from a load. This can help diagnose problems that disappear under
401 `-Zmiri-disable-weak-memory-emulation`.
402 * `-Zmiri-force-page-size=<num>` overrides the default page size for an architecture, in multiples of 1k.
403 `4` is default for most targets. This value should always be a power of 2 and nonzero.
405 [function ABI]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
407 Some native rustc `-Z` flags are also very relevant for Miri:
409 * `-Zmir-opt-level` controls how many MIR optimizations are performed. Miri
410 overrides the default to be `0`; be advised that using any higher level can
411 make Miri miss bugs in your program because they got optimized away.
412 * `-Zalways-encode-mir` makes rustc dump MIR even for completely monomorphic
413 functions. This is needed so that Miri can execute such functions, so Miri
414 sets this flag per default.
415 * `-Zmir-emit-retag` controls whether `Retag` statements are emitted. Miri
416 enables this per default because it is needed for [Stacked Borrows].
418 Moreover, Miri recognizes some environment variables:
420 * `MIRI_AUTO_OPS` indicates whether the automatic execution of rustfmt, clippy and toolchain setup
421 should be skipped. If it is set to any value, they are skipped. This is used for avoiding infinite
422 recursion in `./miri` and to allow automated IDE actions to avoid the auto ops.
423 * `MIRI_LOG`, `MIRI_BACKTRACE` control logging and backtrace printing during
424 Miri executions, also [see "Testing the Miri driver" in `CONTRIBUTING.md`][testing-miri].
425 * `MIRIFLAGS` (recognized by `cargo miri` and the test suite) defines extra
426 flags to be passed to Miri.
427 * `MIRI_LIB_SRC` defines the directory where Miri expects the sources of the
428 standard library that it will build and use for interpretation. This directory
429 must point to the `library` subdirectory of a `rust-lang/rust` repository
430 checkout. Note that changing files in that directory does not automatically
431 trigger a re-build of the standard library; you have to clear the Miri build
432 cache manually (on Linux, `rm -rf ~/.cache/miri`;
433 on Windows, `rmdir /S "%LOCALAPPDATA%\rust-lang\miri\cache"`;
434 and on macOS, `rm -rf ~/Library/Caches/org.rust-lang.miri`).
435 * `MIRI_SYSROOT` (recognized by `cargo miri` and the Miri driver) indicates the sysroot to use. When
436 using `cargo miri`, this skips the automatic setup -- only set this if you do not want to use the
437 automatically created sysroot. For directly invoking the Miri driver, this variable (or a
438 `--sysroot` flag) is mandatory. When invoking `cargo miri setup`, this indicates where the sysroot
440 * `MIRI_TEST_TARGET` (recognized by the test suite and the `./miri` script) indicates which target
441 architecture to test against. `miri` and `cargo miri` accept the `--target` flag for the same
443 * `MIRI_NO_STD` (recognized by `cargo miri` and the test suite) makes sure that the target's
444 sysroot is built without libstd. This allows testing and running no_std programs.
445 * `MIRI_BLESS` (recognized by the test suite and `cargo-miri-test/run-test.py`): overwrite all
446 `stderr` and `stdout` files instead of checking whether the output matches.
447 * `MIRI_SKIP_UI_CHECKS` (recognized by the test suite): don't check whether the
448 `stderr` or `stdout` files match the actual output.
450 The following environment variables are *internal* and must not be used by
451 anyone but Miri itself. They are used to communicate between different Miri
452 binaries, and as such worth documenting:
454 * `MIRI_BE_RUSTC` can be set to `host` or `target`. It tells the Miri driver to
455 actually not interpret the code but compile it like rustc would. With `target`, Miri sets
456 some compiler flags to prepare the code for interpretation; with `host`, this is not done.
457 This environment variable is useful to be sure that the compiled `rlib`s are compatible
459 * `MIRI_CALLED_FROM_SETUP` is set during the Miri sysroot build,
460 which will re-invoke `cargo-miri` as the `rustc` to use for this build.
461 * `MIRI_CALLED_FROM_RUSTDOC` when set to any value tells `cargo-miri` that it is
462 running as a child process of `rustdoc`, which invokes it twice for each doc-test
463 and requires special treatment, most notably a check-only build before interpretation.
464 This is set by `cargo-miri` itself when running as a `rustdoc`-wrapper.
465 * `MIRI_CWD` when set to any value tells the Miri driver to change to the given
466 directory after loading all the source files, but before commencing
467 interpretation. This is useful if the interpreted program wants a different
468 working directory at run-time than at build-time.
469 * `MIRI_LOCAL_CRATES` is set by `cargo-miri` to tell the Miri driver which
470 crates should be given special treatment in diagnostics, in addition to the
471 crate currently being compiled.
472 * `MIRI_VERBOSE` when set to any value tells the various `cargo-miri` phases to
473 perform verbose logging.
474 * `MIRI_HOST_SYSROOT` is set by bootstrap to tell `cargo-miri` which sysroot to use for *host*
477 [testing-miri]: CONTRIBUTING.md#testing-the-miri-driver
479 ## Miri `extern` functions
481 Miri provides some `extern` functions that programs can import to access
482 Miri-specific functionality:
487 /// Miri-provided extern function to mark the block `ptr` points to as a "root"
488 /// for some static memory. This memory and everything reachable by it is not
489 /// considered leaking even if it still exists when the program terminates.
491 /// `ptr` has to point to the beginning of an allocated block.
492 fn miri_static_root(ptr: *const u8);
494 // Miri-provided extern function to get the amount of frames in the current backtrace.
495 // The `flags` argument must be `0`.
496 fn miri_backtrace_size(flags: u64) -> usize;
498 /// Miri-provided extern function to obtain a backtrace of the current call stack.
499 /// This writes a slice of pointers into `buf` - each pointer is an opaque value
500 /// that is only useful when passed to `miri_resolve_frame`.
501 /// `buf` must have `miri_backtrace_size(0) * pointer_size` bytes of space.
502 /// The `flags` argument must be `1`.
503 fn miri_get_backtrace(flags: u64, buf: *mut *mut ());
505 /// Miri-provided extern function to resolve a frame pointer obtained
506 /// from `miri_get_backtrace`. The `flags` argument must be `1`,
507 /// and `MiriFrame` should be declared as follows:
511 /// struct MiriFrame {
512 /// // The size of the name of the function being executed, encoded in UTF-8
514 /// // The size of filename of the function being executed, encoded in UTF-8
515 /// filename_len: usize,
516 /// // The line number currently being executed in `filename`, starting from '1'.
518 /// // The column number currently being executed in `filename`, starting from '1'.
520 /// // The function pointer to the function currently being executed.
521 /// // This can be compared against function pointers obtained by
522 /// // casting a function (e.g. `my_fn as *mut ()`)
527 /// The fields must be declared in exactly the same order as they appear in `MiriFrame` above.
528 /// This function can be called on any thread (not just the one which obtained `frame`).
529 fn miri_resolve_frame(frame: *mut (), flags: u64) -> MiriFrame;
531 /// Miri-provided extern function to get the name and filename of the frame provided by `miri_resolve_frame`.
532 /// `name_buf` and `filename_buf` should be allocated with the `name_len` and `filename_len` fields of `MiriFrame`.
533 /// The flags argument must be `0`.
534 fn miri_resolve_frame_names(ptr: *mut (), flags: u64, name_buf: *mut u8, filename_buf: *mut u8);
536 /// Miri-provided extern function to begin unwinding with the given payload.
538 /// This is internal and unstable and should not be used; we give it here
539 /// just to be complete.
540 fn miri_start_panic(payload: *mut u8) -> !;
542 /// Miri-provided extern function to get the internal unique identifier for the allocation that a pointer
543 /// points to. If this pointer is invalid (not pointing to an allocation), interpretation will abort.
545 /// This is only useful as an input to `miri_print_borrow_stacks`, and it is a separate call because
546 /// getting a pointer to an allocation at runtime can change the borrow stacks in the allocation.
547 /// This function should be considered unstable. It exists only to support `miri_print_borrow_stacks` and so
548 /// inherits all of its instability.
549 fn miri_get_alloc_id(ptr: *const ()) -> u64;
551 /// Miri-provided extern function to print (from the interpreter, not the program) the contents of all
552 /// borrow stacks in an allocation. The leftmost tag is the bottom of the stack.
553 /// The format of what this emits is unstable and may change at any time. In particular, users should be
554 /// aware that Miri will periodically attempt to garbage collect the contents of all stacks. Callers of
555 /// this function may wish to pass `-Zmiri-tag-gc=0` to disable the GC.
557 /// This function is extremely unstable. At any time the format of its output may change, its signature may
558 /// change, or it may be removed entirely.
559 fn miri_print_borrow_stacks(alloc_id: u64);
561 /// Miri-provided extern function to print (from the interpreter, not the
562 /// program) the contents of a section of program memory, as bytes. Bytes
563 /// written using this function will emerge from the interpreter's stdout.
564 fn miri_write_to_stdout(bytes: &[u8]);
566 /// Miri-provided extern function to print (from the interpreter, not the
567 /// program) the contents of a section of program memory, as bytes. Bytes
568 /// written using this function will emerge from the interpreter's stderr.
569 fn miri_write_to_stderr(bytes: &[u8]);
571 /// Miri-provided extern function to allocate memory from the interpreter.
573 /// This is useful when no fundamental way of allocating memory is
574 /// available, e.g. when using `no_std` + `alloc`.
575 fn miri_alloc(size: usize, align: usize) -> *mut u8;
577 /// Miri-provided extern function to deallocate memory.
578 fn miri_dealloc(ptr: *mut u8, size: usize, align: usize);
580 /// Convert a path from the host Miri runs on to the target Miri interprets.
581 /// Performs conversion of path separators as needed.
583 /// Usually Miri performs this kind of conversion automatically. However, manual conversion
584 /// might be necessary when reading an environment variable that was set on the host
585 /// (such as TMPDIR) and using it as a target path.
587 /// Only works with isolation disabled.
589 /// `in` must point to a null-terminated string, and will be read as the input host path.
590 /// `out` must point to at least `out_size` many bytes, and the result will be stored there
591 /// with a null terminator.
592 /// Returns 0 if the `out` buffer was large enough, and the required size otherwise.
593 fn miri_host_to_target_path(path: *const i8, out: *mut i8, out_size: usize) -> usize;
597 ## Contributing and getting help
599 If you want to contribute to Miri, great! Please check out our
600 [contribution guide](CONTRIBUTING.md).
602 For help with running Miri, you can open an issue here on
603 GitHub or use the [Miri stream on the Rust Zulip][zulip].
605 [zulip]: https://rust-lang.zulipchat.com/#narrow/stream/269128-miri
609 This project began as part of an undergraduate research course in 2015 by
610 @solson at the [University of Saskatchewan][usask]. There are [slides] and a
611 [report] available from that project. In 2016, @oli-obk joined to prepare Miri
612 for eventually being used as const evaluator in the Rust compiler itself
613 (basically, for `const` and `static` stuff), replacing the old evaluator that
614 worked directly on the AST. In 2017, @RalfJung did an internship with Mozilla
615 and began developing Miri towards a tool for detecting undefined behavior, and
616 also using Miri as a way to explore the consequences of various possible
617 definitions for undefined behavior in Rust. @oli-obk's move of the Miri engine
618 into the compiler finally came to completion in early 2018. Meanwhile, later
619 that year, @RalfJung did a second internship, developing Miri further with
620 support for checking basic type invariants and verifying that references are
621 used according to their aliasing restrictions.
623 [usask]: https://www.usask.ca/
624 [slides]: https://solson.me/miri-slides.pdf
625 [report]: https://solson.me/miri-report.pdf
627 ## Bugs found by Miri
629 Miri has already found a number of bugs in the Rust standard library and beyond, which we collect here.
633 * [`Debug for vec_deque::Iter` accessing uninitialized memory](https://github.com/rust-lang/rust/issues/53566)
634 * [`Vec::into_iter` doing an unaligned ZST read](https://github.com/rust-lang/rust/pull/53804)
635 * [`From<&[T]> for Rc` creating a not sufficiently aligned reference](https://github.com/rust-lang/rust/issues/54908)
636 * [`BTreeMap` creating a shared reference pointing to a too small allocation](https://github.com/rust-lang/rust/issues/54957)
637 * [`Vec::append` creating a dangling reference](https://github.com/rust-lang/rust/pull/61082)
638 * [Futures turning a shared reference into a mutable one](https://github.com/rust-lang/rust/pull/56319)
639 * [`str` turning a shared reference into a mutable one](https://github.com/rust-lang/rust/pull/58200)
640 * [`rand` performing unaligned reads](https://github.com/rust-random/rand/issues/779)
641 * [The Unix allocator calling `posix_memalign` in an invalid way](https://github.com/rust-lang/rust/issues/62251)
642 * [`getrandom` calling the `getrandom` syscall in an invalid way](https://github.com/rust-random/getrandom/pull/73)
643 * [`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
644 * [`beef` leaking memory](https://github.com/maciejhirsz/beef/issues/12)
645 * [`EbrCell` using uninitialized memory incorrectly](https://github.com/Firstyear/concread/commit/b15be53b6ec076acb295a5c0483cdb4bf9be838f#diff-6282b2fc8e98bd089a1f0c86f648157cR229)
646 * [TiKV performing an unaligned pointer access](https://github.com/tikv/tikv/issues/7613)
647 * [`servo_arc` creating a dangling shared reference](https://github.com/servo/servo/issues/26357)
648 * [TiKV constructing out-of-bounds pointers (and overlapping mutable references)](https://github.com/tikv/tikv/pull/7751)
649 * [`encoding_rs` doing out-of-bounds pointer arithmetic](https://github.com/hsivonen/encoding_rs/pull/53)
650 * [TiKV using `Vec::from_raw_parts` incorrectly](https://github.com/tikv/agatedb/pull/24)
651 * 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)
652 * [Insufficient alignment in `ThinVec`](https://github.com/Gankra/thin-vec/pull/27)
653 * [`crossbeam-epoch` calling `assume_init` on a partly-initialized `MaybeUninit`](https://github.com/crossbeam-rs/crossbeam/pull/779)
654 * [`integer-encoding` dereferencing a misaligned pointer](https://github.com/dermesser/integer-encoding-rs/pull/23)
655 * [`rkyv` constructing a `Box<[u8]>` from an overaligned allocation](https://github.com/rkyv/rkyv/commit/a9417193a34757e12e24263178be8b2eebb72456)
656 * [Data race in `thread::scope`](https://github.com/rust-lang/rust/issues/98498)
657 * [`regex` incorrectly handling unaligned `Vec<u8>` buffers](https://www.reddit.com/r/rust/comments/vq3mmu/comment/ienc7t0?context=3)
658 * [Incorrect use of `compare_exchange_weak` in `once_cell`](https://github.com/matklad/once_cell/issues/186)
659 * [Dropping with unaligned pointers in `vec::IntoIter`](https://github.com/rust-lang/rust/pull/106084)
661 Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):
663 * [`VecDeque::drain` creating overlapping mutable references](https://github.com/rust-lang/rust/pull/56161)
664 * Various `BTreeMap` problems
665 * [`BTreeMap` iterators creating mutable references that overlap with shared references](https://github.com/rust-lang/rust/pull/58431)
666 * [`BTreeMap::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/73915)
667 * [`BTreeMap` node insertion using raw pointers outside their valid memory area](https://github.com/rust-lang/rust/issues/78477)
668 * [`LinkedList` cursor insertion creating overlapping mutable references](https://github.com/rust-lang/rust/pull/60072)
669 * [`Vec::push` invalidating existing references into the vector](https://github.com/rust-lang/rust/issues/60847)
670 * [`align_to_mut` violating uniqueness of mutable references](https://github.com/rust-lang/rust/issues/68549)
671 * [`sized-chunks` creating aliasing mutable references](https://github.com/bodil/sized-chunks/issues/8)
672 * [`String::push_str` invalidating existing references into the string](https://github.com/rust-lang/rust/issues/70301)
673 * [`ryu` using raw pointers outside their valid memory area](https://github.com/dtolnay/ryu/issues/24)
674 * [ink! creating overlapping mutable references](https://github.com/rust-lang/miri/issues/1364)
675 * [TiKV creating overlapping mutable reference and raw pointer](https://github.com/tikv/tikv/pull/7709)
676 * [Windows `Env` iterator using a raw pointer outside its valid memory area](https://github.com/rust-lang/rust/pull/70479)
677 * [`VecDeque::iter_mut` creating overlapping mutable references](https://github.com/rust-lang/rust/issues/74029)
678 * [Various standard library aliasing issues involving raw pointers](https://github.com/rust-lang/rust/pull/78602)
679 * [`<[T]>::copy_within` using a loan after invalidating it](https://github.com/rust-lang/rust/pull/85610)
681 ## Scientific papers employing Miri
683 * [Stacked Borrows: An Aliasing Model for Rust](https://plv.mpi-sws.org/rustbelt/stacked-borrows/)
684 * [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)
685 * [SyRust: Automatic Testing of Rust Libraries with Semantic-Aware Program Synthesis](https://dl.acm.org/doi/10.1145/3453483.3454084)
689 Licensed under either of
691 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
692 http://www.apache.org/licenses/LICENSE-2.0)
693 * MIT license ([LICENSE-MIT](LICENSE-MIT) or
694 http://opensource.org/licenses/MIT)
700 Unless you explicitly state otherwise, any contribution intentionally submitted
701 for inclusion in the work by you shall be dual licensed as above, without any
702 additional terms or conditions.