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diff --git a/docs/contributing.rst b/docs/contributing.rst index 7c199d53..6717a8b9 100644 --- a/docs/contributing.rst +++ b/docs/contributing.rst @@ -170,6 +170,57 @@ and re-run the test. It will now pass again: Please choose a name for the contract file, that is self-explainatory in the sense of what is been tested, e.g. ``double_variable_declaration.sol``. Do not put more than one contract into a single file. ``isoltest`` is currently not able to recognize them individually. + +Running the Fuzzer via AFL +========================== + +Fuzzing is a technique that runs programs on more or less random inputs to find exceptional execution +states (segmentation faults, exceptions, etc). Modern fuzzers are clever and do a directed search +inside the input. We have a specialized binary called ``solfuzzer`` which takes source code as input +and fails whenever it encounters an internal compiler error, segmentation fault or similar, but +does not fail if e.g. the code contains an error. This way, internal problems in the compiler +can be found by fuzzing tools. + +We mainly use `AFL <http://lcamtuf.coredump.cx/afl/>`_ for fuzzing. You need to download and +build AFL manually. Next, build Solidity (or just the ``solfuzzer`` binary) with AFL as your compiler: + +:: + + cd build + # if needed + make clean + cmake .. -DCMAKE_C_COMPILER=path/to/afl-gcc -DCMAKE_CXX_COMPILER=path/to/afl-g++ + make solfuzzer + +Next, you need some example source files. This will make it much easer for the fuzzer +to find errors. You can either copy some files from the syntax tests or extract test files +from the documentation or the other tests: + +:: + + mkdir /tmp/test_cases + cd /tmp/test_cases + # extract from tests: + path/to/solidity/scripts/isolate_tests.py path/to/solidity/test/libsolidity/SolidityEndToEndTest.cpp + # extract from documentation: + path/to/solidity/scripts/isolate_tests.py path/to/solidity/docs docs + +The AFL documentation states that the corpus (the initial input files) should not be +too large. The files themselves should not be larger than 1 kB and there should be +at most one input file per functionality, so better start with a small number of +input files. There is also a tool called ``afl-cmin`` that can trim input files +that result in similar behaviour of the binary. + +Now run the fuzzer (the ``-m`` extends the size of memory to 60 MB): + +:: + + afl-fuzz -m 60 -i /tmp/test_cases -o /tmp/fuzzer_reports -- /path/to/solfuzzer + +The fuzzer will create source files that lead to failures in ``/tmp/fuzzer_reports``. +Often it finds many similar source files that produce the same error. You can +use the tool ``scripts/uniqueErrors.sh`` to filter out the unique errors. + Whiskers ======== |