tree-sitter/test/fuzz

Fuzzing tree-sitter

The tree-sitter fuzzing support requires 1) the libFuzzer runtime library and 2) a recent version of clang

libFuzzer

The main fuzzing logic is implemented by libFuzzer which is part of the compiler-rt project but is not shipped by distros. libFuzzer will need to be built from source, e.g.:

cd ~/src
git clone https://github.com/llvm-mirror/compiler-rt
cd compiler-rt/lib/fuzzer
./build.sh

clang

Using libFuzzer requires at least version 7 of clang and may not work with your system-installed version. If your system-installed version is too old, the easiest way to get started is to use the version provided by the Chromium team. Instructions are available at libFuzzer.info.

The fuzzers can then be built with:

export CLANG_DIR=$HOME/src/third_party/llvm-build/Release+Asserts/bin
CC="$CLANG_DIR/clang" CXX="$CLANG_DIR/clang++" LINK="$CLANG_DIR/clang++" \
  LIB_FUZZER_PATH=$HOME/src/compiler-rt/lib/fuzzer/libFuzzer.a \
  ./script/build_fuzzers

This will generate a separate fuzzer for each grammar defined in test/fixtures/grammars and will be instrumented with AddressSanitizer and UndefinedBehaviorSanitizer. Individual fuzzers can be built with, for example, ./script/build_fuzzers python ruby.

The run-fuzzer script handles running an individual fuzzer with a sensible default set of arguments:

./script/run-fuzzer <grammar-name> (halt|recover) <extra libFuzzer arguments...>

which will log information to stdout. Failing testcases and a fuzz corpus will be saved to fuzz-results/<grammar-name>. The most important extra libFuzzer options are -jobs and -workers which allow parallel fuzzing. This is can done with, e.g.:

./script/run-fuzzer <grammer-name> halt -jobs=32 -workers=32

The testcase can be used to reproduce the crash by running:

./script/reproduce <grammar-name> (halt|recover) <path-to-testcase>