[libfuzzer] print_new_cov_pcs experimental option.

[kcc]

LGTM with a nit

lib/Fuzzer/test/fuzzer.test

35

maybe something like this?
PCS:{{^0x[A-F0-9]+}}

[aizatsky]

nit

lib/Fuzzer/FuzzerDriver.cpp

if (Flags.exact_artifact_path)
     Options.ExactArtifactPath = Flags.exact_artifact_path;
   std::vector<Unit> Dictionary;
   if (Flags.dict)
     if (!ParseDictionaryFile(FileToString(Flags.dict), &Dictionary))
       return 1;
   if (Flags.verbosity > 0 && !Dictionary.empty())
     Printf("Dictionary: %zd entries\n", Dictionary.size());
   Options.SaveArtifacts = !Flags.test_single_input;
+  Options.PrintNewCovPcs = Flags.print_new_cov_pcs;
 
   Fuzzer F(USF, Options);
 
   for (auto &U: Dictionary)
     USF.GetMD().AddWordToDictionary(U.data(), U.size());
 
   // Timer
   if (Flags.timeout > 0)

lib/Fuzzer/FuzzerFlags.def

 FUZZER_FLAG_STRING(exact_artifact_path,
                    "Write the single artifact on failure (crash, timeout) "
                    "as $(exact_artifact_path). This overrides -artifact_prefix "
                    "and will not use checksum in the file name. Do not "
                    "use the same path for several parallel processes.")
 FUZZER_FLAG_INT(drill, 0, "Experimental: fuzz using a single unit as the seed "
                           "corpus, then merge with the initial corpus")
 FUZZER_FLAG_INT(output_csv, 0, "Enable pulse output in CSV format.")
+FUZZER_FLAG_INT(print_new_cov_pcs, 0, "If 1, print out new covered pcs.")
+

lib/Fuzzer/FuzzerInternal.h

struct FuzzingOptions {
     int TBMWidth = 10;
     std::string OutputCorpus;
     std::string SyncCommand;
     std::string ArtifactPrefix = "./";
     std::string ExactArtifactPath;
     bool SaveArtifacts = true;
     bool PrintNEW = true;  // Print a status line when new units are found;
     bool OutputCSV = false;
+    bool PrintNewCovPcs = false;
   };
   Fuzzer(UserSuppliedFuzzer &USF, FuzzingOptions Options);
   void AddToCorpus(const Unit &U) { Corpus.push_back(U); }
   size_t ChooseUnitIdxToMutate();
   const Unit &ChooseUnitToMutate() { return Corpus[ChooseUnitIdxToMutate()]; };
   void Loop();
   void Drill();
   void ShuffleAndMinimize();
private:
   FuzzingOptions Options;
   system_clock::time_point ProcessStartTime = system_clock::now();
   system_clock::time_point LastExternalSync = system_clock::now();
   system_clock::time_point UnitStartTime;
   long TimeOfLongestUnitInSeconds = 0;
   long EpochOfLastReadOfOutputCorpus = 0;
   size_t LastRecordedBlockCoverage = 0;
   size_t LastRecordedCallerCalleeCoverage = 0;
+  size_t LastCoveragePcBufferLen = 0;
 };
 
 class SimpleUserSuppliedFuzzer: public UserSuppliedFuzzer {
  public:
   SimpleUserSuppliedFuzzer(FuzzerRandomBase *Rand, UserCallback Callback)
       : UserSuppliedFuzzer(Rand), Callback(Callback) {}
 
   virtual int TargetFunction(const uint8_t *Data, size_t Size) override {

lib/Fuzzer/FuzzerLoop.cpp

 __attribute__((weak)) void __sanitizer_reset_coverage();
 __attribute__((weak)) size_t __sanitizer_get_total_unique_caller_callee_pairs();
 __attribute__((weak)) size_t __sanitizer_get_total_unique_coverage();
 __attribute__((weak))
 void __sanitizer_set_death_callback(void (*callback)(void));
 __attribute__((weak)) size_t __sanitizer_get_number_of_counters();
 __attribute__((weak))
 uintptr_t __sanitizer_update_counter_bitset_and_clear_counters(uint8_t *bitset);
+__attribute__((weak)) uintptr_t
+__sanitizer_get_coverage_pc_buffer(uintptr_t **data);
 }
 
 namespace fuzzer {
 static const size_t kMaxUnitSizeToPrint = 256;
 
 static void MissingWeakApiFunction(const char *FnName) {
   Printf("ERROR: %s is not defined. Exiting.\n"
          "Did you use -fsanitize-coverage=... to build your code?\n", FnName);
if (!Data)
     Data = &EmptyData;
   int Res = USF.TargetFunction(Data, U.size());
   (void)Res;
   assert(Res == 0);
 }
 
 size_t Fuzzer::RecordBlockCoverage() {
   CHECK_WEAK_API_FUNCTION(__sanitizer_get_total_unique_coverage);
-  return LastRecordedBlockCoverage = __sanitizer_get_total_unique_coverage();
+  uintptr_t PrevCoverage = LastRecordedBlockCoverage;
+  LastRecordedBlockCoverage = __sanitizer_get_total_unique_coverage();
+
+  if (PrevCoverage == LastRecordedBlockCoverage || !Options.PrintNewCovPcs)
+    return LastRecordedBlockCoverage;
+
+  uintptr_t PrevBufferLen = LastCoveragePcBufferLen;
+  uintptr_t *CoverageBuf;
+  LastCoveragePcBufferLen = __sanitizer_get_coverage_pc_buffer(&CoverageBuf);
+  assert(CoverageBuf);
+  for (size_t i = PrevBufferLen; i < LastCoveragePcBufferLen; ++i) {
+    Printf("0x%x\n", CoverageBuf[i]);
+  }
+
+  return LastRecordedBlockCoverage;
 }
 
 size_t Fuzzer::RecordCallerCalleeCoverage() {
   if (!Options.UseIndirCalls)
     return 0;
   if (!__sanitizer_get_total_unique_caller_callee_pairs)
     return 0;
   return LastRecordedCallerCalleeCoverage =

lib/Fuzzer/test/fuzzer.test

 
 RUN: not LLVMFuzzer-UserSuppliedFuzzerTest -seed=1 -timeout=15 2>&1 | FileCheck %s
 
 RUN: not LLVMFuzzer-SimpleDictionaryTest -dict=%S/dict1.txt -seed=1 -runs=1000003  2>&1 | FileCheck %s
 RUN:     LLVMFuzzer-SimpleDictionaryTest                    -seed=1 -runs=1000000  2>&1 | FileCheck %s --check-prefix=Done1000000
 
 RUN: not LLVMFuzzer-UninstrumentedTest-Uninstrumented 2>&1 | FileCheck %s --check-prefix=UNINSTRUMENTED
 UNINSTRUMENTED: ERROR: __sanitizer_set_death_callback is not defined. Exiting.
+
+RUN: LLVMFuzzer-SimpleTest -print_new_cov_pcs=1 2>&1 | FileCheck %s --check-prefix=PCS
+PCS:0x
+PCS:NEW
+PCS:BINGO
+