# HG changeset patch
# User Christian Holler <choller@mozilla.com>
# Date 1586345312 -7200
#      Wed Apr 08 13:28:32 2020 +0200
# Node ID 169280b21031865a2fb217af759ad3124dd87ae2
# Parent  8244be44ec9b52eb81b56e39d04c97a1e4eb13ab
[libFuzzer] Allow custom mutators to fail

diff --git a/tools/fuzzing/libfuzzer/FuzzerLoop.cpp b/tools/fuzzing/libfuzzer/FuzzerLoop.cpp
--- a/tools/fuzzing/libfuzzer/FuzzerLoop.cpp
+++ b/tools/fuzzing/libfuzzer/FuzzerLoop.cpp
@@ -659,16 +659,20 @@ void Fuzzer::MutateAndTestOne() {
     MaybeExitGracefully();
     size_t NewSize = 0;
     if (II.HasFocusFunction && !II.DataFlowTraceForFocusFunction.empty() &&
         Size <= CurrentMaxMutationLen)
       NewSize = MD.MutateWithMask(CurrentUnitData, Size, Size,
                                   II.DataFlowTraceForFocusFunction);
     else
       NewSize = MD.Mutate(CurrentUnitData, Size, CurrentMaxMutationLen);
+
+    if (!NewSize)
+      continue;
+
     assert(NewSize > 0 && "Mutator returned empty unit");
     assert(NewSize <= CurrentMaxMutationLen && "Mutator return oversized unit");
     Size = NewSize;
     II.NumExecutedMutations++;
 
     bool FoundUniqFeatures = false;
     bool NewCov = RunOne(CurrentUnitData, Size, /*MayDeleteFile=*/true, &II,
                          &FoundUniqFeatures);
@@ -827,17 +831,19 @@ void Fuzzer::Loop(const Vector<std::stri
 void Fuzzer::MinimizeCrashLoop(const Unit &U) {
   if (U.size() <= 1)
     return;
   while (!TimedOut() && TotalNumberOfRuns < Options.MaxNumberOfRuns) {
     MD.StartMutationSequence();
     memcpy(CurrentUnitData, U.data(), U.size());
     for (int i = 0; i < Options.MutateDepth; i++) {
       size_t NewSize = MD.Mutate(CurrentUnitData, U.size(), MaxMutationLen);
-      assert(NewSize > 0 && NewSize <= MaxMutationLen);
+      assert(NewSize <= MaxMutationLen);
+      if (!NewSize)
+        continue;
       ExecuteCallback(CurrentUnitData, NewSize);
       PrintPulseAndReportSlowInput(CurrentUnitData, NewSize);
       TryDetectingAMemoryLeak(CurrentUnitData, NewSize,
                               /*DuringInitialCorpusExecution*/ false);
     }
   }
 }