[libFuzzer] Update InputInfo.TimeOfUnit when replacing it in the corpus.

[pzread]

Summary

Previously, when the fuzzing loop replaced an input in the corpus, it didn't update the execution time of the input. Therefore, some schedulers (e.g. Entropic) would adjust weights based on the incorrect execution time.

This patch updates the execution time of the input when replacing it.

[pzread]

Fix format.

[morehouse]

Thanks for the fix!

compiler-rt/lib/fuzzer/FuzzerCorpus.h

for (auto II : Inputs) {
         Printf(" ");
         PrintFeatureSet(II->UniqFeatureSet);
         Printf("\n");
       }
       i++;
     }
   }
 
-  void Replace(InputInfo *II, const Unit &U) {
+  void Replace(InputInfo *II, const Unit &U,
+               std::chrono::microseconds TimeOfUnit) {
     assert(II->U.size() > U.size());
     Hashes.erase(Sha1ToString(II->Sha1));
     DeleteFile(*II);
     ComputeSHA1(U.data(), U.size(), II->Sha1);
     Hashes.insert(Sha1ToString(II->Sha1));
     II->U = U;
     II->Reduced = true;
+    II->TimeOfUnit = TimeOfUnit;
     DistributionNeedsUpdate = true;
   }
 
   bool HasUnit(const Unit &U) { return Hashes.count(Hash(U)); }
   bool HasUnit(const std::string &H) { return Hashes.count(H); }
   InputInfo &ChooseUnitToMutate(Random &Rand) {
     InputInfo &II = *Inputs[ChooseUnitIdxToMutate(Rand)];
     assert(!II.U.empty());

compiler-rt/lib/fuzzer/FuzzerLoop.cpp

WriteEdgeToMutationGraphFile(Options.MutationGraphFile, NewII, II,
                                  MD.MutationSequence());
     return true;
   }
   if (II && FoundUniqFeaturesOfII &&
       II->DataFlowTraceForFocusFunction.empty() &&
       FoundUniqFeaturesOfII == II->UniqFeatureSet.size() &&
       II->U.size() > Size) {
     auto OldFeaturesFile = Sha1ToString(II->Sha1);
-    Corpus.Replace(II, {Data, Data + Size});
+    Corpus.Replace(II, {Data, Data + Size}, TimeOfUnit);
     RenameFeatureSetFile(Options.FeaturesDir, OldFeaturesFile,
                          Sha1ToString(II->Sha1));
     return true;
   }
   return false;
 }
 
 void Fuzzer::TPCUpdateObservedPCs() { TPC.UpdateObservedPCs(); }

compiler-rt/lib/fuzzer/tests/FuzzerUnittest.cpp

for (size_t i = 0; i < N * TriesPerUnit; i++) {
     Hist[C->ChooseUnitIdxToMutate(Rand)]++;
   }
   for (size_t i = 0; i < N; i++) {
     // A weak sanity check that every unit gets invoked.
     EXPECT_GT(Hist[i], TriesPerUnit / N / 3);
   }
 }
 
+TEST(Corpus, Replace) {
+  DataFlowTrace DFT;
+  struct EntropicOptions Entropic = {false, 0xFF, 100, false};
+  std::unique_ptr<InputCorpus> C(new InputCorpus(/*OutputCorpus*/ "", Entropic));
+  InputInfo *FirstII =
+      C->AddToCorpus(Unit{0x01, 0x00}, /*NumFeatures*/ 1,
+                     /*MayDeleteFile*/ false, /*HasFocusFunction*/ false,
+                     /*ForceAddToCorpus*/ false,
+                     /*TimeOfUnit*/ std::chrono::microseconds(1234),
+                     /*FeatureSet*/ {}, DFT,
+                     /*BaseII*/ nullptr);
+  InputInfo *SecondII =
+      C->AddToCorpus(Unit{0x02}, /*NumFeatures*/ 1,
+                     /*MayDeleteFile*/ false, /*HasFocusFunction*/ false,
+                     /*ForceAddToCorpus*/ false,
+                     /*TimeOfUnit*/ std::chrono::microseconds(5678),
+                     /*FeatureSet*/ {}, DFT,
+                     /*BaseII*/ nullptr);
+  Unit ReplacedU = Unit{0x03};
+
+  C->Replace(FirstII, ReplacedU,
+             /*TimeOfUnit*/ std::chrono::microseconds(321));
+
+  EXPECT_EQ(FirstII->U, Unit{0x03});
+  EXPECT_EQ(FirstII->Reduced, true);
+  EXPECT_EQ(FirstII->TimeOfUnit, std::chrono::microseconds(321));
+  std::vector<uint8_t> ExpectedSha1(kSHA1NumBytes);
+  ComputeSHA1(ReplacedU.data(), ReplacedU.size(), ExpectedSha1.data());
+  std::vector<uint8_t> IISha1(FirstII->Sha1, FirstII->Sha1 + kSHA1NumBytes);
+  EXPECT_EQ(IISha1, ExpectedSha1);
+}
+
 template <typename T>
 void EQ(const std::vector<T> &A, const std::vector<T> &B) {
   EXPECT_EQ(A, B);
 }
 
 template <typename T> void EQ(const std::set<T> &A, const std::vector<T> &B) {
   EXPECT_EQ(A, std::set<T>(B.begin(), B.end()));
 }