# Miri — Rust Undefined Behavior Detection Tool

> An interpreter for Rust's mid-level intermediate representation that detects undefined behavior, memory leaks, and data races in unsafe code.

## Install

Save in your project root:

# Miri — Rust Undefined Behavior Detection Tool

## Quick Use
```bash
# Install Miri via rustup (requires nightly)
rustup +nightly component add miri

# Run your test suite under Miri
cargo +nightly miri test

# Run a specific binary under Miri
cargo +nightly miri run
```

## Introduction
Miri is an interpreter for Rust that runs your code inside a virtual machine and checks every memory operation for correctness. It catches undefined behavior, use-after-free, out-of-bounds access, data races, and memory leaks that the compiler cannot detect statically — especially in unsafe code blocks.

## What Miri Does
- Interprets Rust MIR (Mid-level Intermediate Representation) to execute programs step by step
- Detects undefined behavior including invalid pointer arithmetic, uninitialized reads, and alignment violations
- Finds data races and deadlocks in concurrent code using a simulated thread scheduler
- Reports memory leaks at program exit
- Validates that unsafe code upholds Rust's safety invariants

## Architecture Overview
Miri hooks into the Rust compiler at the MIR stage, interpreting instructions rather than compiling them to machine code. It maintains a virtual memory model with provenance tracking for every pointer, catching aliasing violations and out-of-bounds access. Concurrency is simulated with a deterministic scheduler that explores thread interleavings to surface data races.

## Self-Hosting & Configuration
- Requires the nightly Rust toolchain; install with `rustup +nightly component add miri`
- Run via `cargo +nightly miri test` or `cargo +nightly miri run`
- Set `MIRIFLAGS` for options like `-Zmiri-disable-isolation` (allow file I/O) or `-Zmiri-seed=N` (deterministic scheduling)
- Use `-Zmiri-tag-gc=0` to disable garbage collection of stacked-borrows tags for debugging
- Add `#[cfg(miri)]` in tests to skip operations unsupported by the interpreter

## Key Features
- Stacked Borrows and Tree Borrows models for validating reference aliasing rules
- Concurrency support with data-race and deadlock detection
- Cross-platform execution — Miri simulates target platforms independent of the host
- Integration with cargo for testing entire projects without code changes
- Leak detection that reports unreleased allocations at program exit

## Comparison with Similar Tools
- **Valgrind** — C/C++ memory checker; Miri is Rust-specific and understands ownership semantics
- **AddressSanitizer (ASan)** — Runtime instrumentation; Miri catches more UB categories at the cost of speed
- **cargo-careful** — Enables extra runtime checks in std; less thorough than Miri but faster
- **ThreadSanitizer (TSan)** — Data-race detector for compiled code; Miri's scheduler is deterministic

## FAQ
**Q: Is Miri slow?**
A: Yes — Miri interprets code rather than compiling it, so execution is roughly 1000x slower. It is designed for testing, not production.

**Q: Can Miri run all Rust code?**
A: Miri supports most language features but cannot execute FFI calls to C libraries or perform real system I/O without `-Zmiri-disable-isolation`.

**Q: Does Miri find all bugs?**
A: Miri finds many classes of undefined behavior but is not a formal verifier. It checks the specific execution paths that your tests exercise.

**Q: Is Miri part of the official Rust project?**
A: Yes, Miri is maintained under the rust-lang GitHub organization and distributed via rustup.

## Sources
- https://github.com/rust-lang/miri
- https://miri.readthedocs.io/

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