---
title: Fuzz testing with libFuzzer
---

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# Fuzz Testing with libFuzzer

The utilities library contains fuzz targets that can be built with
[LLVM libFuzzer](https://llvm.org/docs/LibFuzzer.html).  Fuzzing is
enabled when using the Clang compiler and the `UTILS_LIBFUZZER` CMake
option.

## Building

Configure CMake with Clang and enable the libFuzzer option:

```bash
cmake \
  -G Ninja \
  -S . -B build \
  -DCMAKE_C_COMPILER=clang \
  -DCMAKE_CXX_COMPILER=clang++ \
  -DENABLE_FUZZING=ON
```

Build the fuzzer executables:

```bash
cmake --build build --parallel --target celix_properties_fuzzer celix_version_fuzzer celix_filter_fuzzer
```

## Corpus

The `corpus` directories for the fuzzers contain a few seed inputs, which help guide the initial fuzzing process. 
More files can be added to these directories to improve coverage. The fuzzer will automatically use all files in the 
specified corpus directory as starting points for mutation and exploration.

## Running
The resulting fuzzers accept standard libFuzzer command line options. For example, to run each fuzzer for 30 seconds 
using the provided seed corpus and print coverage information:

```bash
./build/libs/utils/celix_filter_fuzzer -max_total_time=30 -print_coverage=1 ./build/libs/utils/filter_corpus
```

Replace `celix_filter_fuzzer` and `filter_corpus` with the appropriate fuzzer executable and corpus directory as needed.
To see a list of supported command-line flags, run the fuzzer executable with the `-help=1` option. For example:

```bash
./build/libs/utils/celix_filter_fuzzer -help=1
```

This will display all available LibFuzzer options.

## Continuous Fuzzing

A GitHub Actions workflow runs the fuzzer periodically. The workflow
configuration can be found at `.github/workflows/fuzzing.yml`.