llvm/lib/Fuzzer/FuzzerDriver.cpp

//===- FuzzerDriver.cpp - FuzzerDriver function and flags -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// FuzzerDriver and flag parsing.
//===----------------------------------------------------------------------===//

#include "FuzzerCorpus.h"
#include "FuzzerInterface.h"
#include "FuzzerInternal.h"
#include "FuzzerIO.h"
#include "FuzzerMutate.h"
#include "FuzzerRandom.h"
#include "FuzzerShmem.h"
#include "FuzzerTracePC.h"
#include <algorithm>
#include <atomic>
#include <chrono>
#include <cstring>
#include <mutex>
#include <string>
#include <thread>

// This function should be present in the libFuzzer so that the client
// binary can test for its existence.
extern "C" __attribute__((used)) void __libfuzzer_is_present() {}

namespace fuzzer {

// Program arguments.
struct FlagDescription {
  const char *Name;
  const char *Description;
  int   Default;
  int   *IntFlag;
  const char **StrFlag;
  unsigned int *UIntFlag;
};

struct {
#define FUZZER_DEPRECATED_FLAG(Name)
#define FUZZER_FLAG_INT(Name, Default, Description) int Name;
#define FUZZER_FLAG_UNSIGNED(Name, Default, Description) unsigned int Name;
#define FUZZER_FLAG_STRING(Name, Description) const char *Name;
#include "FuzzerFlags.def"
#undef FUZZER_DEPRECATED_FLAG
#undef FUZZER_FLAG_INT
#undef FUZZER_FLAG_UNSIGNED
#undef FUZZER_FLAG_STRING
} Flags;

static const FlagDescription FlagDescriptions [] {
#define FUZZER_DEPRECATED_FLAG(Name)                                           \
  {#Name, "Deprecated; don't use", 0, nullptr, nullptr, nullptr},
#define FUZZER_FLAG_INT(Name, Default, Description)                            \
  {#Name, Description, Default, &Flags.Name, nullptr, nullptr},
#define FUZZER_FLAG_UNSIGNED(Name, Default, Description)                       \
  {#Name,   Description, static_cast<int>(Default),                            \
   nullptr, nullptr, &Flags.Name},
#define FUZZER_FLAG_STRING(Name, Description)                                  \
  {#Name, Description, 0, nullptr, &Flags.Name, nullptr},
#include "FuzzerFlags.def"
#undef FUZZER_DEPRECATED_FLAG
#undef FUZZER_FLAG_INT
#undef FUZZER_FLAG_UNSIGNED
#undef FUZZER_FLAG_STRING
};

static const size_t kNumFlags =
    sizeof(FlagDescriptions) / sizeof(FlagDescriptions[0]);

static std::vector<std::string> *Inputs;
static std::string *ProgName;

static void PrintHelp() {
  Printf("Usage:\n");
  auto Prog = ProgName->c_str();
  Printf("\nTo run fuzzing pass 0 or more directories.\n");
  Printf("%s [-flag1=val1 [-flag2=val2 ...] ] [dir1 [dir2 ...] ]\n", Prog);

  Printf("\nTo run individual tests without fuzzing pass 1 or more files:\n");
  Printf("%s [-flag1=val1 [-flag2=val2 ...] ] file1 [file2 ...]\n", Prog);

  Printf("\nFlags: (strictly in form -flag=value)\n");
  size_t MaxFlagLen = 0;
  for (size_t F = 0; F < kNumFlags; F++)
    MaxFlagLen = std::max(strlen(FlagDescriptions[F].Name), MaxFlagLen);

  for (size_t F = 0; F < kNumFlags; F++) {
    const auto &D = FlagDescriptions[F];
    if (strstr(D.Description, "internal flag") == D.Description) continue;
    Printf(" %s", D.Name);
    for (size_t i = 0, n = MaxFlagLen - strlen(D.Name); i < n; i++)
      Printf(" ");
    Printf("\t");
    Printf("%d\t%s\n", D.Default, D.Description);
  }
  Printf("\nFlags starting with '--' will be ignored and "
            "will be passed verbatim to subprocesses.\n");
}

static const char *FlagValue(const char *Param, const char *Name) {
  size_t Len = strlen(Name);
  if (Param[0] == '-' && strstr(Param + 1, Name) == Param + 1 &&
      Param[Len + 1] == '=')
      return &Param[Len + 2];
  return nullptr;
}

// Avoid calling stol as it triggers a bug in clang/glibc build.
static long MyStol(const char *Str) {
  long Res = 0;
  long Sign = 1;
  if (*Str == '-') {
    Str++;
    Sign = -1;
  }
  for (size_t i = 0; Str[i]; i++) {
    char Ch = Str[i];
    if (Ch < '0' || Ch > '9')
      return Res;
    Res = Res * 10 + (Ch - '0');
  }
  return Res * Sign;
}

static bool ParseOneFlag(const char *Param) {
  if (Param[0] != '-') return false;
  if (Param[1] == '-') {
    static bool PrintedWarning = false;
    if (!PrintedWarning) {
      PrintedWarning = true;
      Printf("INFO: libFuzzer ignores flags that start with '--'\n");
    }
    for (size_t F = 0; F < kNumFlags; F++)
      if (FlagValue(Param + 1, FlagDescriptions[F].Name))
        Printf("WARNING: did you mean '%s' (single dash)?\n", Param + 1);
    return true;
  }
  for (size_t F = 0; F < kNumFlags; F++) {
    const char *Name = FlagDescriptions[F].Name;
    const char *Str = FlagValue(Param, Name);
    if (Str)  {
      if (FlagDescriptions[F].IntFlag) {
        int Val = MyStol(Str);
        *FlagDescriptions[F].IntFlag = Val;
        if (Flags.verbosity >= 2)
          Printf("Flag: %s %d\n", Name, Val);;
        return true;
      } else if (FlagDescriptions[F].UIntFlag) {
        unsigned int Val = std::stoul(Str);
        *FlagDescriptions[F].UIntFlag = Val;
        if (Flags.verbosity >= 2)
          Printf("Flag: %s %u\n", Name, Val);
        return true;
      } else if (FlagDescriptions[F].StrFlag) {
        *FlagDescriptions[F].StrFlag = Str;
        if (Flags.verbosity >= 2)
          Printf("Flag: %s %s\n", Name, Str);
        return true;
      } else {  // Deprecated flag.
        Printf("Flag: %s: deprecated, don't use\n", Name);
        return true;
      }
    }
  }
  Printf("\n\nWARNING: unrecognized flag '%s'; "
         "use -help=1 to list all flags\n\n", Param);
  return true;
}

// We don't use any library to minimize dependencies.
static void ParseFlags(const std::vector<std::string> &Args) {
  for (size_t F = 0; F < kNumFlags; F++) {
    if (FlagDescriptions[F].IntFlag)
      *FlagDescriptions[F].IntFlag = FlagDescriptions[F].Default;
    if (FlagDescriptions[F].UIntFlag)
      *FlagDescriptions[F].UIntFlag =
          static_cast<unsigned int>(FlagDescriptions[F].Default);
    if (FlagDescriptions[F].StrFlag)
      *FlagDescriptions[F].StrFlag = nullptr;
  }
  Inputs = new std::vector<std::string>;
  for (size_t A = 1; A < Args.size(); A++) {
    if (ParseOneFlag(Args[A].c_str())) continue;
    Inputs->push_back(Args[A]);
  }
}

static std::mutex Mu;

static void PulseThread() {
  while (true) {
    SleepSeconds(600);
    std::lock_guard<std::mutex> Lock(Mu);
    Printf("pulse...\n");
  }
}

static void WorkerThread(const std::string &Cmd, std::atomic<unsigned> *Counter,
                         unsigned NumJobs, std::atomic<bool> *HasErrors) {
  while (true) {
    unsigned C = (*Counter)++;
    if (C >= NumJobs) break;
    std::string Log = "fuzz-" + std::to_string(C) + ".log";
    std::string ToRun = Cmd + " > " + Log + " 2>&1\n";
    if (Flags.verbosity)
      Printf("%s", ToRun.c_str());
    int ExitCode = ExecuteCommand(ToRun);
    if (ExitCode != 0)
      *HasErrors = true;
    std::lock_guard<std::mutex> Lock(Mu);
    Printf("================== Job %u exited with exit code %d ============\n",
           C, ExitCode);
    fuzzer::CopyFileToErr(Log);
  }
}

std::string CloneArgsWithoutX(const std::vector<std::string> &Args,
                              const char *X1, const char *X2) {
  std::string Cmd;
  for (auto &S : Args) {
    if (FlagValue(S.c_str(), X1) || FlagValue(S.c_str(), X2))
      continue;
    Cmd += S + " ";
  }
  return Cmd;
}

static int RunInMultipleProcesses(const std::vector<std::string> &Args,
                                  unsigned NumWorkers, unsigned NumJobs) {
  std::atomic<unsigned> Counter(0);
  std::atomic<bool> HasErrors(false);
  std::string Cmd = CloneArgsWithoutX(Args, "jobs", "workers");
  std::vector<std::thread> V;
  std::thread Pulse(PulseThread);
  Pulse.detach();
  for (unsigned i = 0; i < NumWorkers; i++)
    V.push_back(std::thread(WorkerThread, Cmd, &Counter, NumJobs, &HasErrors));
  for (auto &T : V)
    T.join();
  return HasErrors ? 1 : 0;
}

static void RssThread(Fuzzer *F, size_t RssLimitMb) {
  while (true) {
    SleepSeconds(1);
    size_t Peak = GetPeakRSSMb();
    if (Peak > RssLimitMb)
      F->RssLimitCallback();
  }
}

static void StartRssThread(Fuzzer *F, size_t RssLimitMb) {
  if (!RssLimitMb) return;
  std::thread T(RssThread, F, RssLimitMb);
  T.detach();
}

int RunOneTest(Fuzzer *F, const char *InputFilePath, size_t MaxLen) {
  Unit U = FileToVector(InputFilePath);
  if (MaxLen && MaxLen < U.size())
    U.resize(MaxLen);
  F->RunOne(U.data(), U.size());
  F->TryDetectingAMemoryLeak(U.data(), U.size(), true);
  return 0;
}

static bool AllInputsAreFiles() {
  if (Inputs->empty()) return false;
  for (auto &Path : *Inputs)
    if (!IsFile(Path))
      return false;
  return true;
}

int MinimizeCrashInput(const std::vector<std::string> &Args,
                       const FuzzingOptions &Options) {
  if (Inputs->size() != 1) {
    Printf("ERROR: -minimize_crash should be given one input file\n");
    exit(1);
  }
  std::string InputFilePath = Inputs->at(0);
  std::string BaseCmd =
      CloneArgsWithoutX(Args, "minimize_crash", "exact_artifact_path");
  auto InputPos = BaseCmd.find(" " + InputFilePath + " ");
  assert(InputPos != std::string::npos);
  BaseCmd.erase(InputPos, InputFilePath.size() + 1);
  if (Flags.runs <= 0 && Flags.max_total_time == 0) {
    Printf("INFO: you need to specify -runs=N or "
           "-max_total_time=N with -minimize_crash=1\n"
           "INFO: defaulting to -max_total_time=600\n");
    BaseCmd += " -max_total_time=600";
  }
  // BaseCmd += " >  /dev/null 2>&1 ";

  std::string CurrentFilePath = InputFilePath;
  while (true) {
    Unit U = FileToVector(CurrentFilePath);
    Printf("CRASH_MIN: minimizing crash input: '%s' (%zd bytes)\n",
           CurrentFilePath.c_str(), U.size());

    auto Cmd = BaseCmd + " " + CurrentFilePath;

    Printf("CRASH_MIN: executing: %s\n", Cmd.c_str());
    int ExitCode = ExecuteCommand(Cmd);
    if (ExitCode == 0) {
      Printf("ERROR: the input %s did not crash\n", CurrentFilePath.c_str());
      exit(1);
    }
    Printf("CRASH_MIN: '%s' (%zd bytes) caused a crash. Will try to minimize "
           "it further\n",
           CurrentFilePath.c_str(), U.size());

    std::string ArtifactPath =
        Options.ArtifactPrefix + "minimized-from-" + Hash(U);
    Cmd += " -minimize_crash_internal_step=1 -exact_artifact_path=" +
        ArtifactPath;
    Printf("CRASH_MIN: executing: %s\n", Cmd.c_str());
    ExitCode = ExecuteCommand(Cmd);
    if (ExitCode == 0) {
      if (Flags.exact_artifact_path) {
        CurrentFilePath = Flags.exact_artifact_path;
        WriteToFile(U, CurrentFilePath);
      }
      Printf("CRASH_MIN: failed to minimize beyond %s (%d bytes), exiting\n",
             CurrentFilePath.c_str(), U.size());
      return 0;
    }
    CurrentFilePath = ArtifactPath;
    Printf("\n\n\n\n\n\n*********************************\n");
  }
  return 0;
}

int MinimizeCrashInputInternalStep(Fuzzer *F, InputCorpus *Corpus) {
  assert(Inputs->size() == 1);
  std::string InputFilePath = Inputs->at(0);
  Unit U = FileToVector(InputFilePath);
  Printf("INFO: Starting MinimizeCrashInputInternalStep: %zd\n", U.size());
  if (U.size() < 2) {
    Printf("INFO: The input is small enough, exiting\n");
    exit(0);
  }
  Corpus->AddToCorpus(U, 0);
  F->SetMaxInputLen(U.size());
  F->SetMaxMutationLen(U.size() - 1);
  F->MinimizeCrashLoop(U);
  Printf("INFO: Done MinimizeCrashInputInternalStep, no crashes found\n");
  exit(0);
  return 0;
}

int AnalyzeDictionary(Fuzzer *F, const std::vector<Unit>& Dict,
                      UnitVector& Corpus) {
  Printf("Started dictionary minimization (up to %d tests)\n",
         Dict.size() * Corpus.size() * 2);

  // Scores and usage count for each dictionary unit.
  std::vector<int> Scores(Dict.size());
  std::vector<int> Usages(Dict.size());

  std::vector<size_t> InitialFeatures;
  std::vector<size_t> ModifiedFeatures;
  for (auto &C : Corpus) {
    // Get coverage for the testcase without modifications.
    F->ExecuteCallback(C.data(), C.size());
    InitialFeatures.clear();
    TPC.CollectFeatures([&](size_t Feature) -> bool {
      InitialFeatures.push_back(Feature);
      return true;
    });

    for (size_t i = 0; i < Dict.size(); ++i) {
      auto Data = C;
      auto StartPos = std::search(Data.begin(), Data.end(),
                                  Dict[i].begin(), Dict[i].end());
      // Skip dictionary unit, if the testcase does not contain it.
      if (StartPos == Data.end())
        continue;

      ++Usages[i];
      while (StartPos != Data.end()) {
        // Replace all occurrences of dictionary unit in the testcase.
        auto EndPos = StartPos + Dict[i].size();
        for (auto It = StartPos; It != EndPos; ++It)
          *It ^= 0xFF;

        StartPos = std::search(EndPos, Data.end(),
                               Dict[i].begin(), Dict[i].end());
      }

      // Get coverage for testcase with masked occurrences of dictionary unit.
      F->ExecuteCallback(Data.data(), Data.size());
      ModifiedFeatures.clear();
      TPC.CollectFeatures([&](size_t Feature) -> bool {
        ModifiedFeatures.push_back(Feature);
        return true;
      });

      if (InitialFeatures == ModifiedFeatures)
        --Scores[i];
      else
        Scores[i] += 2;
    }
  }

  Printf("###### Useless dictionary elements. ######\n");
  for (size_t i = 0; i < Dict.size(); ++i) {
    // Dictionary units with positive score are treated as useful ones.
    if (Scores[i] > 0)
       continue;

    Printf("\"");
    PrintASCII(Dict[i].data(), Dict[i].size(), "\"");
    Printf(" # Score: %d, Used: %d\n", Scores[i], Usages[i]);
  }
  Printf("###### End of useless dictionary elements. ######\n");
  return 0;
}

int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
  using namespace fuzzer;
  assert(argc && argv && "Argument pointers cannot be nullptr");
  std::string Argv0((*argv)[0]);
  EF = new ExternalFunctions();
  if (EF->LLVMFuzzerInitialize)
    EF->LLVMFuzzerInitialize(argc, argv);
  const std::vector<std::string> Args(*argv, *argv + *argc);
  assert(!Args.empty());
  ProgName = new std::string(Args[0]);
  if (Argv0 != *ProgName) {
    Printf("ERROR: argv[0] has been modified in LLVMFuzzerInitialize\n");
    exit(1);
  }
  ParseFlags(Args);
  if (Flags.help) {
    PrintHelp();
    return 0;
  }

  if (Flags.close_fd_mask & 2)
    DupAndCloseStderr();
  if (Flags.close_fd_mask & 1)
    CloseStdout();

  if (Flags.jobs > 0 && Flags.workers == 0) {
    Flags.workers = std::min(NumberOfCpuCores() / 2, Flags.jobs);
    if (Flags.workers > 1)
      Printf("Running %u workers\n", Flags.workers);
  }

  if (Flags.workers > 0 && Flags.jobs > 0)
    return RunInMultipleProcesses(Args, Flags.workers, Flags.jobs);

  const size_t kMaxSaneLen = 1 << 20;
  const size_t kMinDefaultLen = 64;
  FuzzingOptions Options;
  Options.Verbosity = Flags.verbosity;
  Options.MaxLen = Flags.max_len;
  Options.ExperimentalLenControl = Flags.experimental_len_control;
  if (Flags.experimental_len_control && Flags.max_len == 64)
    Options.MaxLen = 1 << 20;
  Options.UnitTimeoutSec = Flags.timeout;
  Options.ErrorExitCode = Flags.error_exitcode;
  Options.TimeoutExitCode = Flags.timeout_exitcode;
  Options.MaxTotalTimeSec = Flags.max_total_time;
  Options.DoCrossOver = Flags.cross_over;
  Options.MutateDepth = Flags.mutate_depth;
  Options.UseCounters = Flags.use_counters;
  Options.UseIndirCalls = Flags.use_indir_calls;
  Options.UseMemmem = Flags.use_memmem;
  Options.UseCmp = Flags.use_cmp;
  Options.UseValueProfile = Flags.use_value_profile;
  Options.Shrink = Flags.shrink;
  Options.ShuffleAtStartUp = Flags.shuffle;
  Options.PreferSmall = Flags.prefer_small;
  Options.ReloadIntervalSec = Flags.reload;
  Options.OnlyASCII = Flags.only_ascii;
  Options.OutputCSV = Flags.output_csv;
  Options.DetectLeaks = Flags.detect_leaks;
  Options.TraceMalloc = Flags.trace_malloc;
  Options.RssLimitMb = Flags.rss_limit_mb;
  if (Flags.runs >= 0)
    Options.MaxNumberOfRuns = Flags.runs;
  if (!Inputs->empty() && !Flags.minimize_crash_internal_step)
    Options.OutputCorpus = (*Inputs)[0];
  Options.ReportSlowUnits = Flags.report_slow_units;
  if (Flags.artifact_prefix)
    Options.ArtifactPrefix = Flags.artifact_prefix;
  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());
  bool DoPlainRun = AllInputsAreFiles();
  Options.SaveArtifacts =
      !DoPlainRun || Flags.minimize_crash_internal_step;
  Options.PrintNewCovPcs = Flags.print_pcs;
  Options.PrintFinalStats = Flags.print_final_stats;
  Options.PrintCorpusStats = Flags.print_corpus_stats;
  Options.PrintCoverage = Flags.print_coverage;
  Options.DumpCoverage = Flags.dump_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)
    Seed =
        std::chrono::system_clock::now().time_since_epoch().count() + GetPid();
  if (Flags.verbosity)
    Printf("INFO: Seed: %u\n", Seed);

  Random Rand(Seed);
  auto *MD = new MutationDispatcher(Rand, Options);
  auto *Corpus = new InputCorpus(Options.OutputCorpus);
  auto *F = new Fuzzer(Callback, *Corpus, *MD, Options);

  for (auto &U: Dictionary)
    if (U.size() <= Word::GetMaxSize())
      MD->AddWordToManualDictionary(Word(U.data(), U.size()));

  StartRssThread(F, Flags.rss_limit_mb);

  Options.HandleAbrt = Flags.handle_abrt;
  Options.HandleBus = Flags.handle_bus;
  Options.HandleFpe = Flags.handle_fpe;
  Options.HandleIll = Flags.handle_ill;
  Options.HandleInt = Flags.handle_int;
  Options.HandleSegv = Flags.handle_segv;
  Options.HandleTerm = Flags.handle_term;
  Options.HandleXfsz = Flags.handle_xfsz;
  SetSignalHandler(Options);

  if (Flags.minimize_crash)
    return MinimizeCrashInput(Args, Options);

  if (Flags.minimize_crash_internal_step)
    return MinimizeCrashInputInternalStep(F, Corpus);

  if (auto Name = Flags.run_equivalence_server) {
    SMR.Destroy(Name);
    if (!SMR.Create(Name)) {
       Printf("ERROR: can't create shared memory region\n");
      return 1;
    }
    Printf("INFO: EQUIVALENCE SERVER UP\n");
    while (true) {
      SMR.WaitClient();
      size_t Size = SMR.ReadByteArraySize();
      SMR.WriteByteArray(nullptr, 0);
      F->RunOne(SMR.GetByteArray(), Size);
      SMR.PostServer();
    }
    return 0;
  }

  if (auto Name = Flags.use_equivalence_server) {
    if (!SMR.Open(Name)) {
      Printf("ERROR: can't open shared memory region\n");
      return 1;
    }
    Printf("INFO: EQUIVALENCE CLIENT UP\n");
  }

  if (DoPlainRun) {
    Options.SaveArtifacts = false;
    int Runs = std::max(1, Flags.runs);
    Printf("%s: Running %zd inputs %d time(s) each.\n", ProgName->c_str(),
           Inputs->size(), Runs);
    for (auto &Path : *Inputs) {
      auto StartTime = system_clock::now();
      Printf("Running: %s\n", Path.c_str());
      for (int Iter = 0; Iter < Runs; Iter++)
        RunOneTest(F, Path.c_str(), Options.MaxLen);
      auto StopTime = system_clock::now();
      auto MS = duration_cast<milliseconds>(StopTime - StartTime).count();
      Printf("Executed %s in %zd ms\n", Path.c_str(), (long)MS);
    }
    Printf("***\n"
           "*** NOTE: fuzzing was not performed, you have only\n"
           "***       executed the target code on a fixed set of inputs.\n"
           "***\n");
    F->PrintFinalStats();
    exit(0);
  }

  if (Flags.merge) {
    if (Options.MaxLen == 0)
      F->SetMaxInputLen(kMaxSaneLen);
    if (Flags.merge_control_file)
      F->CrashResistantMergeInternalStep(Flags.merge_control_file);
    else
      F->CrashResistantMerge(Args, *Inputs,
                             Flags.load_coverage_summary,
                             Flags.save_coverage_summary);
    exit(0);
  }

  size_t TemporaryMaxLen = Options.MaxLen ? Options.MaxLen : kMaxSaneLen;

  UnitVector InitialCorpus;
  for (auto &Inp : *Inputs) {
    Printf("Loading corpus dir: %s\n", Inp.c_str());
    ReadDirToVectorOfUnits(Inp.c_str(), &InitialCorpus, nullptr,
                           TemporaryMaxLen, /*ExitOnError=*/false);
  }

  if (Flags.analyze_dict) {
    if (Dictionary.empty() || Inputs->empty()) {
      Printf("ERROR: can't analyze dict without dict and corpus provided\n");
      return 1;
    }
    if (AnalyzeDictionary(F, Dictionary, InitialCorpus)) {
      Printf("Dictionary analysis failed\n");
      exit(1);
    }
    Printf("Dictionary analysis suceeded\n");
    exit(0);
  }

  if (Options.MaxLen == 0) {
    size_t MaxLen = 0;
    for (auto &U : InitialCorpus)
      MaxLen = std::max(U.size(), MaxLen);
    F->SetMaxInputLen(std::min(std::max(kMinDefaultLen, MaxLen), kMaxSaneLen));
  }

  if (InitialCorpus.empty()) {
    InitialCorpus.push_back(Unit({'\n'}));  // Valid ASCII input.
    if (Options.Verbosity)
      Printf("INFO: A corpus is not provided, starting from an empty corpus\n");
  }
  F->ShuffleAndMinimize(&InitialCorpus);
  InitialCorpus.clear();  // Don't need this memory any more.
  F->Loop();

  if (Flags.verbosity)
    Printf("Done %zd runs in %zd second(s)\n", F->getTotalNumberOfRuns(),
           F->secondsSinceProcessStartUp());
  F->PrintFinalStats();

  exit(0);  // Don't let F destroy itself.
}

// Storage for global ExternalFunctions object.
ExternalFunctions *EF = nullptr;

}  // namespace fuzzer