Custom mutator for libFuzzer mode

[turbolent]

I've read about custom mutators in LLVM's libFuzzer. Would it be possible to add support for it to go-fuzz's libFuzzer mode?

Would that basically involve adding a LLVMFuzzerCustomMutator function just like LLVMFuzzerTestOneInput is implemented, here:

go-fuzz/go-fuzz-build/main.go

Line 868 in 2fedac3

func LLVMFuzzerTestOneInput(data uintptr, size uint64) int {

?

[dvyukov]

Hi @turbolent,

Would it be possible to add support for it to go-fuzz's libFuzzer mode?

Adding new significant features to go-fuzz today makes little sense in the light of the fuzzing support in the standard library (you can find proposal and tracking issue in the Go issue tracker).

But if you want to do it locally, it should be possible.

Would that basically involve adding a LLVMFuzzerCustomMutator function just like LLVMFuzzerTestOneInput is implemented,

I guess so. Have you tried? Does it work?