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)
+* **Experimental**: Data races
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.
+Miri supports almost all Rust language features; in particular, unwinding and
+concurrency are properly supported (including some experimental emulation of
+weak memory effects, i.e., reads can return outdated values).
+
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
not support networking. System API support varies between targets; if you run
on Windows it is a good idea to use `--target x86_64-unknown-linux-gnu` to get
better support.
-* Threading support is not finished yet. E.g., weak memory effects are not
- emulated and spin loops (without syscalls) just loop forever. There is no
- threading support on Windows.
+* Weak memory emulation may produce weak behaivours unobservable by compiled
+ programs running on real hardware when `SeqCst` fences are used, and it cannot
+ produce all behaviors possibly observable on real hardware.
[rust]: https://www.rust-lang.org/
[mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md
snippet calls Miri in a loop with different values for the seed:
```
-for seed in $({ echo obase=16; seq 255; } | bc); do
+for seed in $({ echo obase=16; seq 0 255; } | bc); do
MIRIFLAGS=-Zmiri-seed=$seed cargo miri test || { echo "Last seed: $seed"; break; };
done
```
* `-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.
+ will always fail and `0.0` means it will never fail. Note than setting it to
+ `1.0` will likely cause hangs, since it means programs using
+ `compare_exchange_weak` cannot make progress.
* `-Zmiri-disable-isolation` disables host isolation. As a consequence,
the program has access to host resources such as environment variables, file
systems, and randomness.
and `warn-nobacktrace` are the supported actions. The default is to `abort`,
which halts the machine. Some (but not all) operations also support continuing
execution with a "permission denied" error being returned to the program.
- `warn` prints a full backtrace when that happen; `warn-nobacktrace` is less
+ `warn` prints a full backtrace when that happens; `warn-nobacktrace` is less
verbose. `hide` hides the warning entirely.
* `-Zmiri-env-exclude=<var>` keeps the `var` environment variable isolated from the host so that it
cannot be accessed by the program. Can be used multiple times to exclude several variables. The
`-Zmiri-disable-isolation` is set.
* `-Zmiri-ignore-leaks` disables the memory leak checker, and also allows some
remaining threads to exist when the main thread exits.
-* `-Zmiri-seed=<hex>` configures the seed of the RNG that Miri uses to resolve
- non-determinism. This RNG is used 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. You can increase test coverage by running Miri
- multiple times with different seeds.
- **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-permissive-provenance` disables the warning for integer-to-pointer casts and
+ [`ptr::from_exposed_addr`](https://doc.rust-lang.org/nightly/std/ptr/fn.from_exposed_addr.html).
+ This will necessarily miss some bugs as those operations are not efficiently and accurately
+ implementable in a sanitizer, but it will only miss bugs that concern memory/pointers which is
+ subject to these operations.
+* `-Zmiri-preemption-rate` configures the probability that at the end of a basic block, the active
+ thread will be preempted. The default is `0.01` (i.e., 1%). Setting this to `0` disables
+ preemption.
+* `-Zmiri-report-progress` makes Miri print the current stacktrace every now and then, so you can
+ tell what it is doing when a program just keeps running. You can customize how frequently the
+ report is printed via `-Zmiri-report-progress=<blocks>`, which prints the report every N basic
+ blocks.
+* `-Zmiri-seed=<hex>` configures the seed of the RNG that Miri uses to resolve non-determinism. This
+ RNG is used to pick base addresses for allocations, to determine preemption and failure of
+ `compare_exchange_weak`, and to control store buffering for weak memory emulation. When isolation
+ is enabled (the default), this is also used to emulate system entropy. The default seed is 0. You
+ can increase test coverage by running Miri multiple times with different seeds. **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-strict-provenance` enables [strict
provenance](https://github.com/rust-lang/rust/issues/95228) checking in Miri. This means that
casting an integer to a pointer yields a result with 'invalid' provenance, i.e., with provenance
- that cannot be used for any memory access. Also implies `-Zmiri-tag-raw-pointers` and
- `-Zmiri-check-number-validity`.
+ that cannot be used for any memory access.
+* `-Zmiri-symbolic-alignment-check` makes the alignment check more strict. By default, alignment is
+ checked by casting the pointer to an integer, and making sure that is a multiple of the alignment.
+ This can lead to cases where a program passes the alignment check by pure chance, because things
+ "happened to be" sufficiently aligned -- there is no UB in this execution but there would be UB in
+ others. To avoid such cases, the symbolic alignment check only takes into account the requested
+ alignment of the relevant allocation, and the offset into that allocation. This avoids missing
+ such bugs, but it also incurs some false positives when the code does manual integer arithmetic to
+ ensure alignment. (The standard library `align_to` method works fine in both modes; under
+ symbolic alignment it only fills the middle slice when the allocation guarantees sufficient
+ alignment.)
The remaining flags are for advanced use only, and more likely to change or be removed.
Some of these are **unsound**, which means they can lead
* `-Zmiri-allow-uninit-numbers` disables the check to ensure that number types (integer and float
types) always hold initialized data. (They must still be initialized when any actual operation,
- such as arithmetic, is performed.) Using this flag is **unsound**. This has no effect when
+ such as arithmetic, is performed.) Using this flag is **unsound** and
+ [deprecated](https://github.com/rust-lang/miri/issues/2187). This has no effect when
`-Zmiri-disable-validation` is present.
* `-Zmiri-allow-ptr-int-transmute` makes Miri more accepting of transmutation between pointers and
integers via `mem::transmute` or union/pointer type punning. This has two effects: it disables the
check against integers storing a pointer (i.e., data with provenance), thus allowing
pointer-to-integer transmutation, and it treats integer-to-pointer transmutation as equivalent to
- a cast. Using this flag is **unsound**.
+ a cast. Implies `-Zmiri-permissive-provenance`. Using this flag is **unsound** and
+ [deprecated](https://github.com/rust-lang/miri/issues/2188).
* `-Zmiri-disable-abi-check` disables checking [function ABI]. Using this flag
is **unsound**.
* `-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**.
+ this flag is **unsound**. This implies `-Zmiri-disable-weak-memory-emulation`.
* `-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**
as out-of-bounds accesses) first. Setting this flag means Miri can miss bugs
in your program. However, this can also help to make Miri run faster. Using
this flag is **unsound**.
+* `-Zmiri-disable-weak-memory-emulation` disables the emulation of some C++11 weak
+ memory effects.
* `-Zmiri-measureme=<name>` enables `measureme` profiling for the interpreted program.
This can be used to find which parts of your program are executing slowly under Miri.
The profile is written out to a file with the prefix `<name>`, and can be processed
application instead of raising an error within the context of Miri (and halting
execution). Note that code might not expect these operations to ever panic, so
this flag can lead to strange (mis)behavior.
-* `-Zmiri-permissive-provenance` is **experimental**. This will make Miri do a
- best-effort attempt to implement the semantics of
- [`expose_addr`](https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.expose_addr)
- and
- [`ptr::from_exposed_addr`](https://doc.rust-lang.org/nightly/std/ptr/fn.from_exposed_addr.html)
- for pointer-to-int and int-to-pointer casts, respectively. This will
- necessarily miss some bugs as those semantics are not efficiently
- implementable in a sanitizer, but it will only miss bugs that concerns
- memory/pointers which is subject to these operations. Also note that this flag
- is currently incompatible with Stacked Borrows, so you will have to also pass
- `-Zmiri-disable-stacked-borrows` to use this.
-* `-Zmiri-symbolic-alignment-check` makes the alignment check more strict. By
- default, alignment is checked by casting the pointer to an integer, and making
- sure that is a multiple of the alignment. This can lead to cases where a
- program passes the alignment check by pure chance, because things "happened to
- be" sufficiently aligned -- there is no UB in this execution but there would
- be UB in others. To avoid such cases, the symbolic alignment check only takes
- into account the requested alignment of the relevant allocation, and the
- offset into that allocation. This avoids missing such bugs, but it also
- incurs some false positives when the code does manual integer arithmetic to
- ensure alignment. (The standard library `align_to` method works fine in both
- modes; under symbolic alignment it only fills the middle slice when the
- allocation guarantees sufficient alignment.)
+* `-Zmiri-retag-fields` changes Stacked Borrows retagging to recurse into fields.
+ This means that references in fields of structs/enums/tuples/arrays/... are retagged,
+ and in particular, they are protected when passed as function arguments.
* `-Zmiri-track-alloc-id=<id1>,<id2>,...` shows a backtrace when the given allocations are
being allocated or freed. This helps in debugging memory leaks and
use after free bugs. Specifying this argument multiple times does not overwrite the previous
happening and where in your code would be a good place to look for it.
Specifying this argument multiple times does not overwrite the previous
values, instead it appends its values to the list. Listing a tag multiple times has no effect.
-* `-Zmiri-tag-raw-pointers` makes Stacked Borrows assign proper tags even for raw pointers. This can
- make valid code using int-to-ptr casts 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. Note that it is not currently guaranteed that code that
- works with `-Zmiri-tag-raw-pointers` also works without `-Zmiri-tag-raw-pointers`, but for the
- vast majority of code, this will be the case.
[function ABI]: https://doc.rust-lang.org/reference/items/functions.html#extern-function-qualifier
* `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.
+* `MIRI_NO_STD` (recognized by `cargo miri` and the test suite) makes sure that the target's
+ sysroot is built without libstd. This allows testing and running no_std programs.
* `MIRI_BLESS` (recognized by the test suite) overwrite all `stderr` and `stdout` files
instead of checking whether the output matches.
* `MIRI_SKIP_UI_CHECKS` (recognized by the test suite) don't check whether the
* [`crossbeam-epoch` calling `assume_init` on a partly-initialized `MaybeUninit`](https://github.com/crossbeam-rs/crossbeam/pull/779)
* [`integer-encoding` dereferencing a misaligned pointer](https://github.com/dermesser/integer-encoding-rs/pull/23)
* [`rkyv` constructing a `Box<[u8]>` from an overaligned allocation](https://github.com/rkyv/rkyv/commit/a9417193a34757e12e24263178be8b2eebb72456)
+* [Data race in `thread::scope`](https://github.com/rust-lang/rust/issues/98498)
Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):
projects / rust.git / blobdiff