libFuzzerIntegration.rst

libFuzzer Integration

Swift compiler comes with a built-in libFuzzer integration. In order to use it on a file myfile.swift, we define an entry point fuzzing function with a @_cdecl("LLVMFuzzerTestOneInput") annotation:

@_cdecl("LLVMFuzzerTestOneInput") public func fuzzMe(Data: UnsafePointer<CChar>, Size: CInt) -> CInt{
    // Test our code using provided Data.
  }
}

To compile it, we use -sanitize=fuzzer flag to link libFuzzer and enable coverage annotation, and -parse-as-library flag not to insert the main symbol, such that the fuzzer entry point can be used:

% swiftc -sanitize=fuzzer myfile.swift

libFuzzer can be also combined with other sanitizers:

% swiftc -sanitize=fuzzer,address myfile.swift

Finally, we launch the fuzzing process:

% ./a.out

Refer to the official libFuzzer documentation at http://llvm.org/docs/LibFuzzer.html for the description of flags the resulting binary has.