3 files changed, 13 insertions, 4 deletions
diff --git a/llvm/lib/Fuzzer/FuzzerInternal.h b/llvm/lib/Fuzzer/FuzzerInternal.h
index 6ffaaf29236..861be803349 100644
--- a/llvm/lib/Fuzzer/FuzzerInternal.h
+++ b/llvm/lib/Fuzzer/FuzzerInternal.h
@@ -120,6 +120,7 @@ size_t GetPeakRSSMb();
 static const int kSHA1NumBytes = 20;
 // Computes SHA1 hash of 'Len' bytes in 'Data', writes kSHA1NumBytes to 'Out'.
 void ComputeSHA1(const uint8_t *Data, size_t Len, uint8_t *Out);
+std::string Sha1ToString(uint8_t Sha1[kSHA1NumBytes]);
 
 // Changes U to contain only ASCII (isprint+isspace) characters.
 // Returns true iff U has been changed.
@@ -482,6 +483,7 @@ private:
   void LazyAllocateCurrentUnitData();
   uint8_t *CurrentUnitData = nullptr;
   std::atomic<size_t> CurrentUnitSize;
+  uint8_t BaseSha1[kSHA1NumBytes];  // Checksum of the base unit.
 
   size_t TotalNumberOfRuns = 0;
   size_t NumberOfNewUnitsAdded = 0;
diff --git a/llvm/lib/Fuzzer/FuzzerLoop.cpp b/llvm/lib/Fuzzer/FuzzerLoop.cpp
index 07de3c7c8b9..5d94483b8f9 100644
--- a/llvm/lib/Fuzzer/FuzzerLoop.cpp
+++ b/llvm/lib/Fuzzer/FuzzerLoop.cpp
@@ -204,6 +204,8 @@ void Fuzzer::StaticDeathCallback() {
 
 void Fuzzer::DumpCurrentUnit(const char *Prefix) {
   if (!CurrentUnitData) return;  // Happens when running individual inputs.
+  MD.PrintMutationSequence();
+  Printf("; base unit: %s\n", Sha1ToString(BaseSha1).c_str());
   size_t UnitSize = CurrentUnitSize;
   if (UnitSize <= kMaxUnitSizeToPrint) {
     PrintHexArray(CurrentUnitData, UnitSize, "\n");
@@ -693,6 +695,7 @@ void Fuzzer::MutateAndTestOne() {
   MD.StartMutationSequence();
 
   auto &U = ChooseUnitToMutate();
+  ComputeSHA1(U.data(), U.size(), BaseSha1);  // Remember where we started.
   assert(CurrentUnitData);
   size_t Size = U.size();
   assert(Size <= Options.MaxLen && "Oversized Unit");
diff --git a/llvm/lib/Fuzzer/FuzzerUtil.cpp b/llvm/lib/Fuzzer/FuzzerUtil.cpp
index a5218d422da..6764a46e7d6 100644
--- a/llvm/lib/Fuzzer/FuzzerUtil.cpp
+++ b/llvm/lib/Fuzzer/FuzzerUtil.cpp
@@ -63,15 +63,19 @@ void PrintASCII(const Unit &U, const char *PrintAfter) {
   PrintASCII(U.data(), U.size(), PrintAfter);
 }
 
-std::string Hash(const Unit &U) {
-  uint8_t Hash[kSHA1NumBytes];
-  ComputeSHA1(U.data(), U.size(), Hash);
+std::string Sha1ToString(uint8_t Sha1[kSHA1NumBytes]) {
   std::stringstream SS;
   for (int i = 0; i < kSHA1NumBytes; i++)
-    SS << std::hex << std::setfill('0') << std::setw(2) << (unsigned)Hash[i];
+    SS << std::hex << std::setfill('0') << std::setw(2) << (unsigned)Sha1[i];
   return SS.str();
 }
 
+std::string Hash(const Unit &U) {
+  uint8_t Hash[kSHA1NumBytes];
+  ComputeSHA1(U.data(), U.size(), Hash);
+  return Sha1ToString(Hash);
+}
+
 static void AlarmHandler(int, siginfo_t *, void *) {
   Fuzzer::StaticAlarmCallback();
 }