[libfuzzer] Use UNDEFINED_WEAK_SYMBOLS_ALLOWED to support explicitly allowed weak symbols on Mac.

[Dor1s]

Summary

Discussion at llvm-dev mailing list: http://lists.llvm.org/pipermail/llvm-dev/2017-September/117185.html

[Dor1s]

[libfuzzer] Disable experimental clang coverage support by default.

It can be enabled via "-use_clang_coverage=1" flag. Reason for disabling:
libFuzzer resets Clang Counters and makes it impossible to generate coverage
report for a regular fuzz target (i.e. not standalone build).

[Dor1s]

In D37526#889855, @Dor1s wrote:

[libfuzzer] Disable experimental clang coverage support by default.

It can be enabled via "-use_clang_coverage=1" flag. Reason for disabling:
libFuzzer resets Clang Counters and makes it impossible to generate coverage
report for a regular fuzz target (i.e. not standalone build).

This is wrong. I'm abandoning this change and uploading new CL separately.

lib/fuzzer/FuzzerDriver.cpp

int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   Options.SaveArtifacts =
       !DoPlainRun || Flags.minimize_crash_internal_step;
   Options.PrintNewCovPcs = Flags.print_pcs;
   Options.PrintNewCovFuncs = Flags.print_funcs;
   Options.PrintFinalStats = Flags.print_final_stats;
   Options.PrintCorpusStats = Flags.print_corpus_stats;
   Options.PrintCoverage = Flags.print_coverage;
   Options.DumpCoverage = Flags.dump_coverage;
+  Options.UseClangCoverage = Flags.use_clang_coverage;
   if (Flags.exit_on_src_pos)
     Options.ExitOnSrcPos = Flags.exit_on_src_pos;
   if (Flags.exit_on_item)
     Options.ExitOnItem = Flags.exit_on_item;
 
   unsigned Seed = Flags.seed;
   // Initialize Seed.
   if (Seed == 0)

lib/fuzzer/FuzzerFlags.def

FUZZER_FLAG_STRING(exit_on_item, "Exit if an item with a given sha1 sum"
     "Used primarily for testing libFuzzer itself.")
 FUZZER_FLAG_INT(ignore_remaining_args, 0, "If 1, ignore all arguments passed "
                 "after this one. Useful for fuzzers that need to do their own "
                 "argument parsing.")
 
 FUZZER_FLAG_STRING(run_equivalence_server, "Experimental")
 FUZZER_FLAG_STRING(use_equivalence_server, "Experimental")
 FUZZER_FLAG_INT(analyze_dict, 0, "Experimental")
+FUZZER_FLAG_INT(use_clang_coverage, 0, "Experimental")
 
 FUZZER_DEPRECATED_FLAG(exit_on_first)
 FUZZER_DEPRECATED_FLAG(save_minimized_corpus)
 FUZZER_DEPRECATED_FLAG(sync_command)
 FUZZER_DEPRECATED_FLAG(sync_timeout)
 FUZZER_DEPRECATED_FLAG(test_single_input)
 FUZZER_DEPRECATED_FLAG(drill)
 FUZZER_DEPRECATED_FLAG(truncate_units)
 FUZZER_DEPRECATED_FLAG(output_csv)

lib/fuzzer/FuzzerLoop.cpp

Fuzzer::Fuzzer(UserCallback CB, InputCorpus &Corpus, MutationDispatcher &MD,
   assert(!F);
   F = this;
   TPC.ResetMaps();
   IsMyThread = true;
   if (Options.DetectLeaks && EF->__sanitizer_install_malloc_and_free_hooks)
     EF->__sanitizer_install_malloc_and_free_hooks(MallocHook, FreeHook);
   TPC.SetUseCounters(Options.UseCounters);
   TPC.SetUseValueProfile(Options.UseValueProfile);
+  TPC.SetUseClangCoverage(Options.UseClangCoverage);
 
   if (Options.Verbosity)
     TPC.PrintModuleInfo();
   if (!Options.OutputCorpus.empty() && Options.ReloadIntervalSec)
     EpochOfLastReadOfOutputCorpus = GetEpoch(Options.OutputCorpus);
   MaxInputLen = MaxMutationLen = Options.MaxLen;
   TmpMaxMutationLen = Max(size_t(4), Corpus.MaxInputSize());
   AllocateCurrentUnitData();

lib/fuzzer/FuzzerOptions.h

struct FuzzingOptions {
   bool SaveArtifacts = true;
   bool PrintNEW = true; // Print a status line when new units are found;
   bool PrintNewCovPcs = false;
   int PrintNewCovFuncs = 0;
   bool PrintFinalStats = false;
   bool PrintCorpusStats = false;
   bool PrintCoverage = false;
   bool DumpCoverage = false;
+  bool UseClangCoverage = false;
   bool DetectLeaks = true;
   int  TraceMalloc = 0;
   bool HandleAbrt = false;
   bool HandleBus = false;
   bool HandleFpe = false;
   bool HandleIll = false;
   bool HandleInt = false;
   bool HandleSegv = false;
   bool HandleTerm = false;
   bool HandleXfsz = false;
 };
 
 }  // namespace fuzzer
 
 #endif  // LLVM_FUZZER_OPTIONS_H

lib/fuzzer/FuzzerTracePC.h

public:
 
   void HandleInit(uint32_t *Start, uint32_t *Stop);
   void HandleInline8bitCountersInit(uint8_t *Start, uint8_t *Stop);
   void HandlePCsInit(const uintptr_t *Start, const uintptr_t *Stop);
   void HandleCallerCallee(uintptr_t Caller, uintptr_t Callee);
   template <class T> void HandleCmp(uintptr_t PC, T Arg1, T Arg2);
   size_t GetTotalPCCoverage();
   void SetUseCounters(bool UC) { UseCounters = UC; }
+  void SetUseClangCoverage(bool UCC) { UseClangCoverage = UCC; }
   void SetUseValueProfile(bool VP) { UseValueProfile = VP; }
   void SetPrintNewPCs(bool P) { DoPrintNewPCs = P; }
   void SetPrintNewFuncs(size_t P) { NumPrintNewFuncs = P; }
   void UpdateObservedPCs();
   template <class Callback> void CollectFeatures(Callback CB) const;
 
   void ResetMaps() {
     ValueProfileMap.Reset();
     if (NumModules)
       memset(Counters(), 0, GetNumPCs());
     ClearExtraCounters();
     ClearInlineCounters();
+    if (UseClangCoverage)
       ClearClangCounters();
   }
 
   void ClearInlineCounters();
 
   void UpdateFeatureSet(size_t CurrentElementIdx, size_t CurrentElementSize);
   void PrintFeatureSet();
 
   void PrintModuleInfo();
public:
   void ForEachObservedPC(CallBack CB) {
     for (auto PC : ObservedPCs)
       CB(PC);
   }
 
 private:
   bool UseCounters = false;
   bool UseValueProfile = false;
+  bool UseClangCoverage = false;
   bool DoPrintNewPCs = false;
   size_t NumPrintNewFuncs = 0;
 
   struct Module {
     uint32_t *Start, *Stop;
   };
 
   Module Modules[4096];