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crux-mir

This is a static simulator for Rust programs. It runs a set of test cases and attempts to prove that all assertions pass on all valid inputs.

See our 2-minute demo video for an example of crux-mir's basic functionality.

Preliminaries

crux-mir uses several submodules, so make sure they're initialized:

$ git submodule update --init

Next, navigate to the crucible/dependencies/mir-json directory and install mir-json according to the instructions in the mir-json README.

Installation

Use GHC 9.2, 9.4, or 9.6. From the crux-mir directory, run:

$ cabal v2-install exe:crux-mir --overwrite-policy=always

Then translate the Rust libraries in lib/:

$ ./translate_libs.sh

If you want to cross-compile for a different target, you can optionally set the environment variable TARGET to a target triple when running ./translate_libs.sh. This is experimental and we have only tested wasm32-unknown-unknown to work; you might get build errors for other targets.

$ TARGET=wasm32-unknown-unknown ./translate_libs.sh

When upgrading from a previous version, first install the new mir-json version, then rerun the cabal v2-install and ./translate_libs.sh commands.

Usage

Writing test cases

crux-mir looks for functions with the #[crux::test] attribute and runs them as tests. You may need to add #![feature(custom_attribute)] to the crate root to use the #[crux::test] attribute. These can both be conditionally compiled by checking for the crux configuration predicate using #[cfg_attr(crux, crux::test)].

Test cases can create and manipulate symbolic values using the functions in the crucible Rust crate. See example/ffs/lib.rs or the files in test/symb_eval/ for examples of creating symbolic values and asserting properties about them.

Running on a Cargo project

Set the CRUX_RUST_LIBRARY_PATH environment variable to the path to the translated libraries:

$ export CRUX_RUST_LIBRARY_PATH=.../crux-mir/rlibs

In the directory of a Cargo project (such as the find-first-set example), run the project's symbolic tests:

$ cargo crux-test

cargo-crux-test (part of mir-json) will translate the code to MIR, then invoke crux-mir to symbolically simulate the test cases.

Running on a single file

To compile and test a single Rust program:

$ cabal v2-exec -- crux-mir test/conc_eval/prim/add1.rs

(Should print 2.)

Examples

The example/ffs/ directory in this repository contains a simple library with concrete and symbolic tests. Use cargo crux-test to run the symbolic test, which proves that an optimized find-first-set function is equivalent to a simple reference implementation.

A fork of the curve25519-dalek library with symbolic tests for the Scalar52 type is available here. This is the code that appears in the crux-mir demo video.

Test suite

To run crux-mir's test suite:

$ cabal v2-test

Expected Failures

Some tests are not yet expected to succeed, as crux-mir is still under development. These tests are marked accordingly, so that the entire test suite is still expected to pass.

Files that are not yet expected to work correctly begin with // FAIL: and a brief comment describing the reason for the expected failure.

Limitations

crux-mir does not support reasoning about certain types of unsafe code. Many functions in the standard library rely on unsafe code; we have reimplemented some of these in terms of safe code or custom crux-mir intrinsics, but many unsupported functions still remain. Test cases that call into unsupported code will produce assertion failures with messages like don't know how to call core::intrinsics::transmute.

Currently, crux-mir also has trouble supporting references and function pointers in constant expressions and static initializers.