Entropic scheduling with exec-time option can be misled, if inputs
on the right path to become crashing inputs accidentally take more
time to execute before it's added to the corpus. This patch, by letting
more of such inputs added to the corpus (four inputs of size 7 to 10,
instead of a single input of size 2), reduces possibilities of being
influenced by timing flakiness.
A longer-term fix could be to reduce timing flakiness in the fuzzer;
one way could be to execute inputs multiple times and take average of
their execution time before they are added to the corpus.
Reviewed By: morehouse
Differential Revision: https://reviews.llvm.org/D113544
This patch scales the energy computed by the Entropic schedule based on the
execution time of each input. The input execution time is compared with the
average execution time of inputs in the corpus, and, based on the amount by
which they differ, the energy is scaled from 0.1x (for inputs executing slow) to
3x (for inputs executing fast). Note that the exact scaling criteria and formula
is borrowed from AFL.
On FuzzBench, this gives a sizeable throughput increase, which in turn leads to
more coverage on several benchmarks. For details, see the following report.
https://storage.googleapis.com/fuzzer-test-suite-public/exectime-report/index.html
Differential Revision: https://reviews.llvm.org/D86092
