thodg/libgit2/fuzzers/README.md

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• Hash : 59328ed8
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  Date : 2018-07-19T13:29:46
  

  fuzzers: rename "fuzz" directory to match our style Our layout uses names like "examples" or "tests" which is why the "fuzz" directory doesn't really fit in here. Rename the directory to be called "fuzzers" instead. Furthermore, we rename the fuzzer "fuzz_packfile_raw" to "packfile_raw_fuzzer", which is also in line with the already existing fuzzer at google/oss-fuzz. While at it, rename the "packfile_raw" fuzzer to instead just be called "packfile" fuzzer.

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• fuzzers/README.md

• # Fuzzing
  
  libgit2 is currently using [libFuzzer](https://libfuzzer.info) to perform
  automated fuzz testing. libFuzzer only works with clang.
  
  ## Prerequisites** for building fuzz targets:
  
  1. All the prerequisites for [building libgit2](https://github.com/libgit2/libgit2).
  2. A recent version of clang. 6.0 is preferred. [pre-build Debian/Ubuntu
     packages](https://github.com/libgit2/libgit2)
  
  ## Build
  
  1. Create a build directory beneath the libgit2 source directory, and change
     into it: `mkdir build && cd build`
  2. Choose one sanitizers to add. The currently supported sanitizers are
     [`address`](https://clang.llvm.org/docs/AddressSanitizer.html),
     [`undefined`](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html),
     and [`leak`/`address,leak`](https://clang.llvm.org/docs/LeakSanitizer.html).
  3. Create the cmake build environment and configure the build with the
     sanitizer chosen: `CC=/usr/bin/clang-6.0 cmake
     -DBUILD_CLAR=OFF -DBUILD_FUZZERS=ON -DUSE_SANIZER=address
     -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=fuzzer"
     -DCMAKE_BUILD_TYPE=RelWithDebInfo ..`. Note that building the fuzzer targets
     is incompatible with the tests and examples.
  4. Build libgit2: `cmake --build .`
  5. Exit the cmake build environment: `cd ..`
  
  ## Run the fuzz targets
  
  1. `ASAN_SYMBOLIZER_PATH=/usr/bin/llvm-symbolize-6.0
     LSAN_OPTIONS=allocator_may_return_null=1
     ASAN_OPTIONS=allocator_may_return_null=1 ./build/fuzz/fuzz_packfile_raw
     fuzz/corpora/fuzz_packfile_raw/`
  
  The `LSAN_OPTIONS` and `ASAN_OPTIONS` are there to allow `malloc(3)` to return
  `NULL`. The `LLVM_PROFILE_FILE` is there to override the path where libFuzzer
  will write the coverage report.
  
  ## Get coverage
  
  In order to get coverage information, you also need to add the
  `-DUSE_COVERAGE=ON` flag to `cmake`, 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).
  
  1. `llvm-profdata-6.0 merge -sparse default.profraw -o
     fuzz_packfile_raw.profdata` transforms the data from a sparse representation
     into a format that can be used by the other tools.
  2. `llvm-cov-6.0 report ./build/fuzz/fuzz_packfile_raw
     -instr-profile=fuzz_packfile_raw.profdata` shows a high-level per-file
     coverage report.
  3. `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).
  
  ## Standalone mode
  
  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`
  to `cmake` without setting `-DCMAKE_EXE_LINKER_FLAGS`. 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.
  
  ## References
  
  * [libFuzzer](https://llvm.org/docs/LibFuzzer.html) documentation.
  * [Source-based Code
    Coverage](https://clang.llvm.org/docs/SourceBasedCodeCoverage.html).
  

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