Finding bugs with libFuzzer

To test your application, you’ll need to write unit tests. This is a great way to make sure your software behaves correctly and as you might expect. However, because of the exponential number of possible inputs, you’ll probably miss certain weird inputs, and a few bugs as well.

Fuzz testing can help here. The idea is to present your application with randomly generated data, or data based on valid input but with random changes. This is done repeatedly, so your application is tested with a large number of inputs, which is why fuzz testing can be a powerful testing approach. It has been noted that fuzz testing has assisted in finding hundreds of bugs within web browsers and other software.

Interestingly, LLVM comes with its own fuzz testing library. Originally part of the LLVM core libraries, the libFuzzer implementation was finally moved to compiler-rt. The library is designed to test small and fast functions.

Let’s run a small...