The libfuzzer-sys Crate

Barebones wrapper around LLVM's libFuzzer runtime library.

The CPP parts are extracted from compiler-rt git repository with git filter-branch.

libFuzzer relies on LLVM sanitizer support. The Rust compiler has built-in support for LLVM sanitizer support, for now, it's limited to Linux. As a result, libfuzzer-sys only works on Linux.


Use cargo fuzz!

The recommended way to use this crate with cargo fuzz!.

Manual Usage

This crate can also be used manually as following:

First create a new cargo project:

$ cargo new --bin fuzzed
$ cd fuzzed

Then add a dependency on the fuzzer-sys crate and your own crate:

libfuzzer-sys = "0.4.0"
your_crate = { path = "../path/to/your/crate" }

Change the fuzzed/src/ to fuzz your code:


use libfuzzer_sys::fuzz_target;

fuzz_target!(|data: &[u8]| {
    // code to fuzz goes here

Build by running the following command:

$ cargo rustc -- \
    -C passes='sancov' \
    -C llvm-args='-sanitizer-coverage-level=3' \
    -C llvm-args='-sanitizer-coverage-inline-8bit-counters' \
    -Z sanitizer=address

And finally, run the fuzzer:

$ ./target/debug/fuzzed

Updating libfuzzer from upstream

./ < SHA1>


All files in libfuzzer directory are licensed NCSA.

Everything else is dual-licensed Apache 2.0 and MIT.