[WIP] Randomize fuzzing params with prob

[jiradeto]

This PR randomly adjusts AFL's fuzzing parameters which typically are constants. Basically at the beginning of the fuzzing cycle, we repeatedly randomize parameter's value with some probabilities that can be set with env variable AFL_RP_PROB.

[wuestholz]

@jiradeto Thanks! Somehow I must have missed this PR... It looks like it's going in the right direction. Have you already tested this a bit? If so, you can probably start extending it to cover more parameters.

[jiradeto]

@wuestholz, I have started the initial experiment with just a single parameter tweak HAVOC_STACK_POW2. The results are available for bloaty_sqlite and libjpeg_libxml.

And yeah, if this PR looks good I will add more fuzzing parameters and start experimenting shortly.

[wuestholz]

@jiradeto Oh, wow! The differences are quite big and it looks like in some benchmarks the randomization helps.

What value did you use for AFL_RP_PROB?

[jiradeto]

@wuestholz, sorry I gave you the wrong experiment. The one I shown you is the initial experiment with AFL_RP_PROB = 0 just to confirm that there is no issue with this PR. The differences shown is solely because of the changes from #6 in which this PR is based.

I just pushed the latest changes which adds more parameters with a set of random values from our discussion.

[wuestholz]

@jiradeto Oh, I see. :) No problem! Yeah, let's see what the effect is once we enable this. I might start with AFL_RP_PROB=20.