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DartLibFuzzer is a fuzzing tool built with LibFuzzer, which is an in-process, coverage-guided, evolutionary fuzzing engine. The DartLibFuzzer tool consists of a collection of “target functions”, each of which stresses a particular part of the Dart runtime and compiler.

How to build and run DartLibFuzzer

Build the dart_libfuzzer binary as follows (first either export DART_USE_ASAN=1 or run ./tools/ --mode=debug --asan):

./tools/ \
  -m [all|debug|release|product] \
  -a [x64|arm64|simarm64] \

Then, to start a blank fuzzing session on a particular target function (as defined in, run:

dart_libfuzzer [--t=<target-function>]

To start a fuzzing session with an initial corpus inside the directory CORPUS, run:

dart_libfuzzer CORPUS


Although test suites are extremely useful to validate the correctness of a system and to ensure that no regressions occur, any test suite is necessarily finite in size and scope. Tests typically focus on validating particular features by means of code sequences most programmers would expect. Regression tests often use slightly less idiomatic code sequences, since they reflect problems that were not anticipated originally, but occurred “in the field”. Still, any test suite leaves the developer wondering whether undetected bugs and flaws still linger in the system.

Over the years, fuzz testing has gained popularity as a testing technique for discovering such lingering bugs, including bugs that can bring down a system in an unexpected way. Fuzzing refers to feeding a large amount of random data as input to a system in an attempt to find bugs or make it crash. Generation-based fuzz testing constructs random, but properly formatted input data. Mutation-based fuzz testing applies small random changes to existing inputs in order to detect shortcomings in a system. Profile-guided or coverage-guided fuzz testing adds a direction to the way these random changes are applied. Multi-layered approaches generate random inputs that are subsequently mutated at various stages of execution.

The randomness of fuzz testing implies that the size and scope of testing is no longer bounded. Every new run can potentially discover bugs and crashes that were hereto undetected.