[libFuzzer] Handle unstable edges by disregarding unstable edges

Summary:
Added a new mode within flag -handle_unstable for new unstable handling algorithm that does the following:
    When an edge is shown as unstable, copy to UnstableCounters the value 0.
    During ApplyUnstableCounters we copy back the value 0 to ModuleInline8bitCounters if the edge was unstable.

This way we would be ignoring completely features that were collected through non-determinism.
Unstable hits would be counted as if it never hit.

Reviewers: metzman, Dor1s, kcc, morehouse

Reviewed By: metzman, morehouse

Subscribers: delcypher, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D49684

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@337853 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/fuzzer/FuzzerFlags.def b/lib/fuzzer/FuzzerFlags.def
index aa3a987b1..ba04bc25f 100644
--- a/lib/fuzzer/FuzzerFlags.def
+++ b/lib/fuzzer/FuzzerFlags.def
@@ -114,7 +114,9 @@ FUZZER_FLAG_INT(handle_unstable, 0, "Experimental."
                    " Executes every input 3 times in total if a unique feature"
                    " is found during the first execution."
                    " If 1, we only use the minimum hit count from the 3 runs"
-                   " to determine whether an input is interesting.")
+                   " to determine whether an input is interesting."
+                   " If 2, we disregard edges that are found unstable for"
+                   " feature collection.")
 FUZZER_FLAG_INT(print_unstable_stats, 0, "Experimental."
 				  " If 1, print unstable statistics at exit.")
 FUZZER_FLAG_INT(handle_segv, 1, "If 1, try to intercept SIGSEGV.")