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diff --git a/src/zstd/tests/fuzz/README.md b/src/zstd/tests/fuzz/README.md new file mode 100644 index 000000000..71afa4063 --- /dev/null +++ b/src/zstd/tests/fuzz/README.md @@ -0,0 +1,101 @@ +# Fuzzing + +Each fuzzing target can be built with multiple engines. +Zstd provides a fuzz corpus for each target that can be downloaded with +the command: + +``` +make corpora +``` + +It will download each corpus into `./corpora/TARGET`. + +## fuzz.py + +`fuzz.py` is a helper script for building and running fuzzers. +Run `./fuzz.py -h` for the commands and run `./fuzz.py COMMAND -h` for +command specific help. + +### Generating Data + +`fuzz.py` provides a utility to generate seed data for each fuzzer. + +``` +make -C ../tests decodecorpus +./fuzz.py gen TARGET +``` + +By default it outputs 100 samples, each at most 8KB into `corpora/TARGET-seed`, +but that can be configured with the `--number`, `--max-size-log` and `--seed` +flags. + +### Build +It respects the usual build environment variables `CC`, `CFLAGS`, etc. +The environment variables can be overridden with the corresponding flags +`--cc`, `--cflags`, etc. +The specific fuzzing engine is selected with `LIB_FUZZING_ENGINE` or +`--lib-fuzzing-engine`, the default is `libregression.a`. +Alternatively, you can use Clang's built in fuzzing engine with +`--enable-fuzzer`. +It has flags that can easily set up sanitizers `--enable-{a,ub,m}san`, and +coverage instrumentation `--enable-coverage`. +It sets sane defaults which can be overridden with flags `--debug`, +`--enable-ubsan-pointer-overflow`, etc. +Run `./fuzz.py build -h` for help. + +### Running Fuzzers + +`./fuzz.py` can run `libfuzzer`, `afl`, and `regression` tests. +See the help of the relevant command for options. +Flags not parsed by `fuzz.py` are passed to the fuzzing engine. +The command used to run the fuzzer is printed for debugging. + +## LibFuzzer + +``` +# Build the fuzz targets +./fuzz.py build all --enable-fuzzer --enable-asan --enable-ubsan --cc clang --cxx clang++ +# OR equivalently +CC=clang CXX=clang++ ./fuzz.py build all --enable-fuzzer --enable-asan --enable-ubsan +# Run the fuzzer +./fuzz.py libfuzzer TARGET <libfuzzer args like -jobs=4> +``` + +where `TARGET` could be `simple_decompress`, `stream_round_trip`, etc. + +### MSAN + +Fuzzing with `libFuzzer` and `MSAN` is as easy as: + +``` +CC=clang CXX=clang++ ./fuzz.py build all --enable-fuzzer --enable-msan +./fuzz.py libfuzzer TARGET <libfuzzer args> +``` + +`fuzz.py` respects the environment variables / flags `MSAN_EXTRA_CPPFLAGS`, +`MSAN_EXTRA_CFLAGS`, `MSAN_EXTRA_CXXFLAGS`, `MSAN_EXTRA_LDFLAGS` to easily pass +the extra parameters only for MSAN. + +## AFL + +The default `LIB_FUZZING_ENGINE` is `libregression.a`, which produces a binary +that AFL can use. + +``` +# Build the fuzz targets +CC=afl-clang CXX=afl-clang++ ./fuzz.py build all --enable-asan --enable-ubsan +# Run the fuzzer without a memory limit because of ASAN +./fuzz.py afl TARGET -m none +``` + +## Regression Testing + +The regression test supports the `all` target to run all the fuzzers in one +command. + +``` +CC=clang CXX=clang++ ./fuzz.py build all --enable-asan --enable-ubsan +./fuzz.py regression all +CC=clang CXX=clang++ ./fuzz.py build all --enable-msan +./fuzz.py regression all +``` |