January 2, 2026
Trust, but Miri
Miri: Practical Undefined Behavior Detection for Rust [pdf]
Rust’s safety gets a reality check: Miri hunts hidden bugs, devs cheer and panic
TLDR: Miri is a Rust tool that catches hidden, crash-causing bugs in “unsafe” code and is now widely used, even in Rust’s own library. The community is split between grateful developers who found real issues and jokesters freaking out that “safe Rust” isn’t magic—consensus: run Miri and fix what spills out.
Rust, the “safe systems language,” just got a dramatic twist: Miri—a bug-hunting tool—claims it can catch the kind of undefined behavior that makes programs go rogue. The paper says Miri ran tests across over 100,000 Rust libraries and is now baked into the standard library’s checks. Translation: when Rust dips into “unsafe” territory, Miri is the exorcist. The community? A mix of celebration, confession, and cosmic meltdown.
Practical devs are loudest: “Run Miri on anything that uses unsafe,” urge veterans who’ve found real bugs lurking in supposedly fine code. One engineer admits Miri helped clean up “unsoundness” caused by sneaky aliasing—basically, two references stepping on each other’s toes. Another designer says they now structure projects so Miri can test more code, isolating input/output to keep things clean. But there’s no silver bullet: as one commenter notes, nothing gives 100% certainty, so people pair Miri with tools like Valgrind and LLVM sanitizers (other bug spotters).
The drama queen crown goes to the user who “experienced a Paradox Exception” after learning that “safe Rust can misbehave,” joking that celestial dev-ops are debugging their existence. Fans call Miri a hero; skeptics clutch pearls over Rust’s safety myth. The vibe? Miri is the grown-up in the room—and devs are racing to put their code on blast. Read more at miri docs.
Key Points
- •The paper introduces Miri, a tool to detect de-facto undefined behavior in deterministic Rust programs.
- •Miri’s features include pointer provenance tracking, Rust type invariant validation, data-race detection, and exploration of weak memory behaviors.
- •Miri implements enough basic OS APIs (file system, concurrency primitives) to run unmodified real-world Rust code.
- •In tests across more than 100,000 Rust libraries, Miri executed over 70% of combined test suites and found dozens of real-world bugs.
- •Miri has been integrated into the CI of the Rust standard library and many prominent Rust libraries, helping prevent new bugs.