InsTrim: Lightweight Instrumentation for Coverage-guided Fuzzing
InsTrim uses CFG and markers to instrument just what is necessary in the binary in llvm_mode. It is about 10-15% faster without disadvantages. It requires at least llvm version 3.8.0.
Set the environment variable AFL_LLVM_INSTRUMENT=CFG or AFL_LLVM_INSTRIM=1 during compilation of the target.
There is also an advanced mode which instruments loops in a way so that afl-fuzz can see which loop path has been selected but not being able to see how often the loop has been rerun. This again is a tradeoff for speed for less path information. To enable this mode set AFL_LLVM_INSTRIM_LOOPHEAD=1.
The paper: [InsTrim: Lightweight Instrumentation for Coverage-guided Fuzzing] (https://www.ndss-symposium.org/wp-content/uploads/2018/07/bar2018_14_Hsu_paper.pdf)