libgit2 is currently using libFuzzer to perform automated fuzz testing. libFuzzer only works with clang.
- All the prerequisites for building libgit2.
- A recent version of clang. 6.0 is preferred. pre-build Debian/Ubuntu packages
- Create a build directory beneath the libgit2 source directory, and change
into it:
mkdir build && cd build - Choose one sanitizers to add. The currently supported sanitizers are
address,undefined, andleak/address,leak. - Create the cmake build environment and configure the build with the
sanitizer chosen:
CC=/usr/bin/clang-6.0 CFLAGS="-fsanitize=address" cmake -DBUILD_TESTS=OFF -DBUILD_FUZZERS=ON -DCMAKE_BUILD_TYPE=RelWithDebInfo ... Note that building the fuzzer targets is incompatible with the tests and examples. - Build libgit2:
cmake --build . - Exit the cmake build environment:
cd ..
ASAN_SYMBOLIZER_PATH=/usr/bin/llvm-symbolize LSAN_OPTIONS=allocator_may_return_null=1 ASAN_OPTIONS=allocator_may_return_null=1 ./build/fuzzers/packfile_fuzzer fuzzers/corpora/packfile/
The LSAN_OPTIONS and ASAN_OPTIONS are there to allow malloc(3) to return
NULL, which is expected if a huge chunk of memory is allocated. The
LLVM_PROFILE_FILE environment string can also be added to override the path
where libFuzzer will write the coverage report.
In order to get coverage information, you need to add the "-fcoverage-mapping"
and "-fprofile-instr-generate CFLAGS, and then run the fuzz target with
-runs=0. That will produce a file called default.profraw (this behavior can
be overridden by setting the LLVM_PROFILE_FILE="yourfile.profraw" environment
variable).
llvm-profdata-6.0 merge -sparse default.profraw -o fuzz_packfile_raw.profdatatransforms the data from a sparse representation into a format that can be used by the other tools.llvm-cov-6.0 report ./build/fuzz/fuzz_packfile_raw -instr-profile=fuzz_packfile_raw.profdatashows a high-level per-file coverage report.llvm-cov-6.0 show ./build/fuzz/fuzz_packfile_raw -instr-profile=fuzz_packfile_raw.profdata [source file]shows a line-by-line coverage analysis of all the codebase (or a single source file).
In order to ensure that there are no regresions, each fuzzer target can be run
in a standalone mode. This can be done by passing -DUSE_STANDALONE_FUZZERS=ON.
This makes it compatible with gcc. This does not use the fuzzing engine, but
just invokes every file in the chosen corpus.
In order to get full coverage, though, you might want to also enable one of the sanitizers. You might need a recent version of clang to get full support.
- libFuzzer documentation.
- Source-based Code Coverage.