pk19604014
0b4e9b5ecb
This is a workaround for #1208, allowing to remove manual tag to allow building and testing fuzzer code during precommits and in bazel test ... Tested: bazel test -k ... bazel build -c opt executable_semantics/fuzzing:executable_semantics_fuzzer bazel-bin/executable_semantics/fuzzing/executable_semantics_fuzzer
Executable semantics structured fuzzer
Overview
Fuzz testing is based on generating a large amount of random inputs for a software component in order to trigger bugs and unexpected behavior. Basic fuzzing uses randomly generated arrays of bytes as inputs, which works great for some applications but is problematic for testing the logic that operates on highly structured data, as most random inputs are immediately rejected as invalid before any interesting parts of the code get a chance to run.
Structured fuzzing addresses this issue by ensuring the randomly generated data is itself structured, and as such has a high chance of presenting a valid input.
executable_semantics_fuzzer is a structured fuzzer based on
libprotobuf-mutator, which is a
library to randomly mutate
protobuffers.
The input to the fuzzer is an instance of Carbon::Fuzzing::Carbon proto
randomly generated by the libprotobuf-mutator framework.
executable_semantics_fuzzer converts the proto to a Carbon source code string,
and tries to parse and execute the code using executable_semantics
implementation.
Fuzzer data format
libprotobuf-mutator supports fuzzer inputs in either text or binary protocol
buffer format. executable_semantics_fuzzer uses text proto format with
Carbon proto message definition in common/fuzzing/carbon.proto.
Running the fuzzer
The fuzzer can be run in 'unit test' mode, where the fuzzer executes on each
input file from the fuzzer_corpus/ folder, or in 'fuzzing' mode, where the
fuzzer will keep generating random inputs and executing the logic on them until
a crash is triggered, or forever in a bug-free program ;).
To run in 'unit test' mode:
bazel test --config=proto-fuzzer --test_output=all //executable_semantics/fuzzing:executable_semantics_fuzzer
To run in 'fuzzing' mode:
bazel build --config=proto-fuzzer //executable_semantics/fuzzing:executable_semantics_fuzzer
bazel-bin/executable_semantics/fuzzing/executable_semantics_fuzzer
It's also possible to run the fuzzer on a single input:
bazel-bin/executable_semantics/fuzzing/executable_semantics_fuzzer /tmp/crash.textproto
Investigating a crash
To reproduce a crash, run the fuzzer on the crashing input as described above.
A separate tool called fuzzverter can be used for things like converting a
crashing input to Carbon source code for running executable_semantics on the
code directly.
To convert a Fuzzing::Carbon text proto to Carbon source:
bazel-bin/executable_semantics/fuzzing/fuzzverter --mode proto_to_carbon --input /tmp/crash.textproto
Generating new fuzzer corpus entries
The ability of the fuzzing framework to generate 'interesting' inputs can be
improved by providing 'seed' inputs known as the fuzzer corpus. The inputs need
to be a Fuzzing::Carbon text proto.
To generate a text proto from Carbon source:
bazel-bin/executable_semantics/fuzzing/fuzzverter --mode carbon_to_proto --input /tmp/crash.carbon --output /tmp/crash.textproto