Fuzzing has revealed several bugs in fmt. It is a part of the continous fuzzing at oss-fuzz.
The source code is modified to make the fuzzing possible without locking up on resource exhaustion:
#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION if(spec.precision>100000) { throw std::runtime_error("fuzz mode - avoiding large precision"); } #endif
This macro is the defacto standard for making fuzzing practically possible, see the libFuzzer documentation.
There is a helper script to build the fuzzers, which has only been tested on Debian and Ubuntu linux so far. There should be no problems fuzzing on Windows (using clang>=8) or on Mac, but the script will probably not work out of the box.
Something along
mkdir build cd build export CXX=clang++ export CXXFLAGS="-fsanitize=fuzzer-no-link -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION= -g" cmake .. -DFMT_SAFE_DURATION_CAST=On -DFMT_FUZZ=On -DFMT_FUZZ_LINKMAIN=Off -DFMT_FUZZ_LDFLAGS="-fsanitize=fuzzer" cmake --build .
should work to build the fuzzers for all platforms which clang supports.
Execute a fuzzer with for instance
cd build export UBSAN_OPTIONS=halt_on_error=1 mkdir out_chrono bin/fuzzer_chrono_duration out_chrono