[PATCH] D48054: [libFuzzer] Mutation tracking and logging implemented

[Kuba (Brecka) Mracek via Phabricator via llvm-commits]

kubamracek added a comment.

I have seen the same failure when the commit was landed and I debugged it a little bit. The problem was that CustomMutatorTest.cpp's LLVMFuzzerCustomMutator implementation calls LLVMFuzzerMutate, which uses the default set of mutators. This causes a discrepancy: MutateImpl will log into CurrentMutatorIdxSequence that a mutator with an index between 0..12 (from the default set) was used, but when printing the sequence (in PrintMutationSequence), we only expect to find indexes from MutationDispatcher::Mutators. When using a custom mutator (like in this test), MutationDispatcher::Mutators only has one element. So PrintMutationSequence overflows the vector when it tries to use an index from 0..12. Add a `if (M >= Mutators.size()) abort();` line into PrintMutationSequence and run the test to reproduce this.


Repository:
  rCRT Compiler Runtime

https://reviews.llvm.org/D48054