FuzzerTracePC.cpp

//===- FuzzerTracePC.cpp - PC tracing--------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// Trace PCs.
// This module implements __sanitizer_cov_trace_pc_guard[_init],
// the callback required for -fsanitize-coverage=trace-pc-guard instrumentation.
//
//===----------------------------------------------------------------------===//

#include "FuzzerTracePC.h"
#include "FuzzerCorpus.h"
#include "FuzzerDefs.h"
#include "FuzzerDictionary.h"
#include "FuzzerExtFunctions.h"
#include "FuzzerIO.h"
#include "FuzzerUtil.h"
#include "FuzzerValueBitMap.h"
#include <set>

// The coverage counters and PCs.
// These are declared as global variables named "__sancov_*" to simplify
// experiments with inlined instrumentation.
alignas(64) ATTRIBUTE_INTERFACE
uint8_t __sancov_trace_pc_guard_8bit_counters[fuzzer::TracePC::kNumPCs];

ATTRIBUTE_INTERFACE
uintptr_t __sancov_trace_pc_pcs[fuzzer::TracePC::kNumPCs];

// Used by -fsanitize-coverage=stack-depth to track stack depth
ATTRIBUTE_INTERFACE __attribute__((tls_model("initial-exec")))
thread_local uintptr_t __sancov_lowest_stack;

namespace fuzzer {

TracePC TPC;

uint8_t *TracePC::Counters() const {
  return __sancov_trace_pc_guard_8bit_counters;
}

uintptr_t *TracePC::PCs() const {
  return __sancov_trace_pc_pcs;
}

size_t TracePC::GetTotalPCCoverage() {
  if (ObservedPCs.size())
    return ObservedPCs.size();
  size_t Res = 0;
  for (size_t i = 1, N = GetNumPCs(); i < N; i++)
    if (PCs()[i])
      Res++;
  return Res;
}

template<class CallBack>
void TracePC::IterateInline8bitCounters(CallBack CB) const {
  if (NumInline8bitCounters && NumInline8bitCounters == NumPCsInPCTables) {
    size_t CounterIdx = 0;
    for (size_t i = 0; i < NumModulesWithInline8bitCounters; i++) {
      uint8_t *Beg = ModuleCounters[i].Start;
      size_t Size = ModuleCounters[i].Stop - Beg;
      assert(Size == (size_t)(ModulePCTable[i].Stop - ModulePCTable[i].Start));
      for (size_t j = 0; j < Size; j++, CounterIdx++)
        CB(i, j, CounterIdx);
    }
  }
}

// Initializes unstable counters by copying Inline8bitCounters to unstable
// counters.
void TracePC::InitializeUnstableCounters() {
  IterateInline8bitCounters([&](int i, int j, int UnstableIdx) {
    if (UnstableCounters[UnstableIdx] != kUnstableCounter)
      UnstableCounters[UnstableIdx] = ModuleCounters[i].Start[j];
  });
}

// Compares the current counters with counters from previous runs
// and records differences as unstable edges.
void TracePC::UpdateUnstableCounters() {
  IterateInline8bitCounters([&](int i, int j, int UnstableIdx) {
    if (ModuleCounters[i].Start[j] != UnstableCounters[UnstableIdx])
      UnstableCounters[UnstableIdx] = kUnstableCounter;
  });
}

void TracePC::HandleInline8bitCountersInit(uint8_t *Start, uint8_t *Stop) {
  if (Start == Stop) return;
  if (NumModulesWithInline8bitCounters &&
      ModuleCounters[NumModulesWithInline8bitCounters-1].Start == Start) return;
  assert(NumModulesWithInline8bitCounters <
         sizeof(ModuleCounters) / sizeof(ModuleCounters[0]));
  ModuleCounters[NumModulesWithInline8bitCounters++] = {Start, Stop};
  NumInline8bitCounters += Stop - Start;
}

void TracePC::HandlePCsInit(const uintptr_t *Start, const uintptr_t *Stop) {
  const PCTableEntry *B = reinterpret_cast<const PCTableEntry *>(Start);
  const PCTableEntry *E = reinterpret_cast<const PCTableEntry *>(Stop);
  if (NumPCTables && ModulePCTable[NumPCTables - 1].Start == B) return;
  assert(NumPCTables < sizeof(ModulePCTable) / sizeof(ModulePCTable[0]));
  ModulePCTable[NumPCTables++] = {B, E};
  NumPCsInPCTables += E - B;
}

void TracePC::HandleInit(uint32_t *Start, uint32_t *Stop) {
  if (Start == Stop || *Start) return;
  assert(NumModules < sizeof(Modules) / sizeof(Modules[0]));
  for (uint32_t *P = Start; P < Stop; P++) {
    NumGuards++;
    if (NumGuards == kNumPCs) {
      RawPrint(
          "WARNING: The binary has too many instrumented PCs.\n"
          "         You may want to reduce the size of the binary\n"
          "         for more efficient fuzzing and precise coverage data\n");
    }
    *P = NumGuards % kNumPCs;
  }
  Modules[NumModules].Start = Start;
  Modules[NumModules].Stop = Stop;
  NumModules++;
}

void TracePC::PrintModuleInfo() {
  if (NumGuards) {
    Printf("INFO: Loaded %zd modules   (%zd guards): ", NumModules, NumGuards);
    for (size_t i = 0; i < NumModules; i++)
      Printf("%zd [%p, %p), ", Modules[i].Stop - Modules[i].Start,
             Modules[i].Start, Modules[i].Stop);
    Printf("\n");
  }
  if (NumModulesWithInline8bitCounters) {
    Printf("INFO: Loaded %zd modules   (%zd inline 8-bit counters): ",
           NumModulesWithInline8bitCounters, NumInline8bitCounters);
    for (size_t i = 0; i < NumModulesWithInline8bitCounters; i++)
      Printf("%zd [%p, %p), ", ModuleCounters[i].Stop - ModuleCounters[i].Start,
             ModuleCounters[i].Start, ModuleCounters[i].Stop);
    Printf("\n");
  }
  if (NumPCTables) {
    Printf("INFO: Loaded %zd PC tables (%zd PCs): ", NumPCTables,
           NumPCsInPCTables);
    for (size_t i = 0; i < NumPCTables; i++) {
      Printf("%zd [%p,%p), ", ModulePCTable[i].Stop - ModulePCTable[i].Start,
             ModulePCTable[i].Start, ModulePCTable[i].Stop);
    }
    Printf("\n");

    if ((NumGuards && NumGuards != NumPCsInPCTables) ||
        (NumInline8bitCounters && NumInline8bitCounters != NumPCsInPCTables)) {
      Printf("ERROR: The size of coverage PC tables does not match the\n"
             "number of instrumented PCs. This might be a compiler bug,\n"
             "please contact the libFuzzer developers.\n"
             "Also check https://bugs.llvm.org/show_bug.cgi?id=34636\n"
             "for possible workarounds (tl;dr: don't use the old GNU ld)\n");
      _Exit(1);
    }
  }
  if (size_t NumExtraCounters = ExtraCountersEnd() - ExtraCountersBegin())
    Printf("INFO: %zd Extra Counters\n", NumExtraCounters);
}

ATTRIBUTE_NO_SANITIZE_ALL
void TracePC::HandleCallerCallee(uintptr_t Caller, uintptr_t Callee) {
  const uintptr_t kBits = 12;
  const uintptr_t kMask = (1 << kBits) - 1;
  uintptr_t Idx = (Caller & kMask) | ((Callee & kMask) << kBits);
  ValueProfileMap.AddValueModPrime(Idx);
}

void TracePC::UpdateObservedPCs() {
  Vector<uintptr_t> CoveredFuncs;
  auto ObservePC = [&](uintptr_t PC) {
    if (ObservedPCs.insert(PC).second && DoPrintNewPCs) {
      PrintPC("\tNEW_PC: %p %F %L", "\tNEW_PC: %p", PC + 1);
      Printf("\n");
    }
  };

  auto Observe = [&](const PCTableEntry &TE) {
    if (TE.PCFlags & 1)
      if (ObservedFuncs.insert(TE.PC).second && NumPrintNewFuncs)
        CoveredFuncs.push_back(TE.PC);
    ObservePC(TE.PC);
  };

  if (NumPCsInPCTables) {
    if (NumInline8bitCounters == NumPCsInPCTables) {
      IterateInline8bitCounters([&](int i, int j, int CounterIdx) {
        if (ModuleCounters[i].Start[j])
          Observe(ModulePCTable[i].Start[j]);
      });
    } else if (NumGuards == NumPCsInPCTables) {
      size_t GuardIdx = 1;
      for (size_t i = 0; i < NumModules; i++) {
        uint32_t *Beg = Modules[i].Start;
        size_t Size = Modules[i].Stop - Beg;
        assert(Size ==
               (size_t)(ModulePCTable[i].Stop - ModulePCTable[i].Start));
        for (size_t j = 0; j < Size; j++, GuardIdx++)
          if (Counters()[GuardIdx])
            Observe(ModulePCTable[i].Start[j]);
      }
    }
  }

  for (size_t i = 0, N = Min(CoveredFuncs.size(), NumPrintNewFuncs); i < N; i++) {
    Printf("\tNEW_FUNC[%zd/%zd]: ", i + 1, CoveredFuncs.size());
    PrintPC("%p %F %L", "%p", CoveredFuncs[i] + 1);
    Printf("\n");
  }
}

inline ALWAYS_INLINE uintptr_t GetPreviousInstructionPc(uintptr_t PC) {
  // TODO: this implementation is x86 only.
  // see sanitizer_common GetPreviousInstructionPc for full implementation.
  return PC - 1;
}

inline ALWAYS_INLINE uintptr_t GetNextInstructionPc(uintptr_t PC) {
  // TODO: this implementation is x86 only.
  // see sanitizer_common GetPreviousInstructionPc for full implementation.
  return PC + 1;
}

static std::string GetModuleName(uintptr_t PC) {
  char ModulePathRaw[4096] = "";  // What's PATH_MAX in portable C++?
  void *OffsetRaw = nullptr;
  if (!EF->__sanitizer_get_module_and_offset_for_pc(
      reinterpret_cast<void *>(PC), ModulePathRaw,
      sizeof(ModulePathRaw), &OffsetRaw))
    return "";
  return ModulePathRaw;
}

template<class CallBack>
void TracePC::IterateCoveredFunctions(CallBack CB) {
  for (size_t i = 0; i < NumPCTables; i++) {
    auto &M = ModulePCTable[i];
    assert(M.Start < M.Stop);
    auto ModuleName = GetModuleName(M.Start->PC);
    for (auto NextFE = M.Start; NextFE < M.Stop; ) {
      auto FE = NextFE;
      assert((FE->PCFlags & 1) && "Not a function entry point");
      do {
        NextFE++;
      } while (NextFE < M.Stop && !(NextFE->PCFlags & 1));
      if (ObservedFuncs.count(FE->PC))
        CB(FE, NextFE);
    }
  }
}

void TracePC::SetFocusFunction(const std::string &FuncName) {
  // This function should be called once.
  assert(FocusFunction.first > NumModulesWithInline8bitCounters);
  if (FuncName.empty())
    return;
  for (size_t M = 0; M < NumModulesWithInline8bitCounters; M++) {
    auto &PCTE = ModulePCTable[M];
    size_t N = PCTE.Stop - PCTE.Start;
    for (size_t I = 0; I < N; I++) {
      if (!(PCTE.Start[I].PCFlags & 1)) continue;  // not a function entry.
      auto Name = DescribePC("%F", GetNextInstructionPc(PCTE.Start[I].PC));
      if (Name[0] == 'i' && Name[1] == 'n' && Name[2] == ' ')
        Name = Name.substr(3, std::string::npos);
      if (FuncName != Name) continue;
      Printf("INFO: Focus function is set to '%s'\n", Name.c_str());
      FocusFunction = {M, I};
      return;
    }
  }
}

bool TracePC::ObservedFocusFunction() {
  size_t I = FocusFunction.first;
  size_t J = FocusFunction.second;
  if (I >= NumModulesWithInline8bitCounters)
    return false;
  auto &MC = ModuleCounters[I];
  size_t Size = MC.Stop - MC.Start;
  if (J >= Size)
    return false;
  return MC.Start[J] != 0;
}

void TracePC::PrintCoverage() {
  if (!EF->__sanitizer_symbolize_pc ||
      !EF->__sanitizer_get_module_and_offset_for_pc) {
    Printf("INFO: __sanitizer_symbolize_pc or "
           "__sanitizer_get_module_and_offset_for_pc is not available,"
           " not printing coverage\n");
    return;
  }
  Printf("COVERAGE:\n");
  auto CoveredFunctionCallback = [&](const PCTableEntry *First, const PCTableEntry *Last) {
    assert(First < Last);
    auto VisualizePC = GetNextInstructionPc(First->PC);
    std::string FileStr = DescribePC("%s", VisualizePC);
    if (!IsInterestingCoverageFile(FileStr)) return;
    std::string FunctionStr = DescribePC("%F", VisualizePC);
    std::string LineStr = DescribePC("%l", VisualizePC);
    size_t Line = std::stoul(LineStr);
    Vector<uintptr_t> UncoveredPCs;
    for (auto TE = First; TE < Last; TE++)
      if (!ObservedPCs.count(TE->PC))
        UncoveredPCs.push_back(TE->PC);
    Printf("COVERED_FUNC: ");
    UncoveredPCs.empty()
        ? Printf("all")
        : Printf("%zd/%zd", (Last - First) - UncoveredPCs.size(), Last - First);
    Printf(" PCs covered %s %s:%zd\n", FunctionStr.c_str(), FileStr.c_str(),
           Line);
    for (auto PC: UncoveredPCs) {
      Printf("  UNCOVERED_PC: %s\n",
             DescribePC("%s:%l", GetNextInstructionPc(PC)).c_str());
    }
  };

  IterateCoveredFunctions(CoveredFunctionCallback);
}

void TracePC::DumpCoverage() {
  if (EF->__sanitizer_dump_coverage) {
    Vector<uintptr_t> PCsCopy(GetNumPCs());
    for (size_t i = 0; i < GetNumPCs(); i++)
      PCsCopy[i] = PCs()[i] ? GetPreviousInstructionPc(PCs()[i]) : 0;
    EF->__sanitizer_dump_coverage(PCsCopy.data(), PCsCopy.size());
  }
}

void TracePC::PrintUnstableStats() {
  size_t count = 0;
  for (size_t i = 0; i < NumInline8bitCounters; i++)
    if (UnstableCounters[i] == kUnstableCounter)
      count++;
  Printf("stat::stability_rate: %.2f\n",
         100 - static_cast<float>(count * 100) / NumInline8bitCounters);
}

// Value profile.
// We keep track of various values that affect control flow.
// These values are inserted into a bit-set-based hash map.
// Every new bit in the map is treated as a new coverage.
//
// For memcmp/strcmp/etc the interesting value is the length of the common
// prefix of the parameters.
// For cmp instructions the interesting value is a XOR of the parameters.
// The interesting value is mixed up with the PC and is then added to the map.

ATTRIBUTE_NO_SANITIZE_ALL
void TracePC::AddValueForMemcmp(void *caller_pc, const void *s1, const void *s2,
                                size_t n, bool StopAtZero) {
  if (!n) return;
  size_t Len = std::min(n, Word::GetMaxSize());
  const uint8_t *A1 = reinterpret_cast<const uint8_t *>(s1);
  const uint8_t *A2 = reinterpret_cast<const uint8_t *>(s2);
  uint8_t B1[Word::kMaxSize];
  uint8_t B2[Word::kMaxSize];
  // Copy the data into locals in this non-msan-instrumented function
  // to avoid msan complaining further.
  size_t Hash = 0;  // Compute some simple hash of both strings.
  for (size_t i = 0; i < Len; i++) {
    B1[i] = A1[i];
    B2[i] = A2[i];
    size_t T = B1[i];
    Hash ^= (T << 8) | B2[i];
  }
  size_t I = 0;
  for (; I < Len; I++)
    if (B1[I] != B2[I] || (StopAtZero && B1[I] == 0))
      break;
  size_t PC = reinterpret_cast<size_t>(caller_pc);
  size_t Idx = (PC & 4095) | (I << 12);
  ValueProfileMap.AddValue(Idx);
  TORCW.Insert(Idx ^ Hash, Word(B1, Len), Word(B2, Len));
}

template <class T>
ATTRIBUTE_TARGET_POPCNT ALWAYS_INLINE
ATTRIBUTE_NO_SANITIZE_ALL
void TracePC::HandleCmp(uintptr_t PC, T Arg1, T Arg2) {
  uint64_t ArgXor = Arg1 ^ Arg2;
  uint64_t ArgDistance = __builtin_popcountll(ArgXor) + 1; // [1,65]
  uintptr_t Idx = ((PC & 4095) + 1) * ArgDistance;
  if (sizeof(T) == 4)
      TORC4.Insert(ArgXor, Arg1, Arg2);
  else if (sizeof(T) == 8)
      TORC8.Insert(ArgXor, Arg1, Arg2);
  // TODO: remove these flags and instead use all metrics at once.
  if (UseValueProfileMask & 1)
    ValueProfileMap.AddValue(Idx);
  if (UseValueProfileMask & 2)
    ValueProfileMap.AddValue(
        PC * 64 + (Arg1 == Arg2 ? 0 : __builtin_clzll(Arg1 - Arg2) + 1));
  if (UseValueProfileMask & 4)  // alternative way to use the hamming distance
    ValueProfileMap.AddValue(PC * 64 + ArgDistance);
}

static size_t InternalStrnlen(const char *S, size_t MaxLen) {
  size_t Len = 0;
  for (; Len < MaxLen && S[Len]; Len++) {}
  return Len;
}

// Finds min of (strlen(S1), strlen(S2)).
// Needed bacause one of these strings may actually be non-zero terminated.
static size_t InternalStrnlen2(const char *S1, const char *S2) {
  size_t Len = 0;
  for (; S1[Len] && S2[Len]; Len++)  {}
  return Len;
}

void TracePC::ClearInlineCounters() {
  for (size_t i = 0; i < NumModulesWithInline8bitCounters; i++) {
    uint8_t *Beg = ModuleCounters[i].Start;
    size_t Size = ModuleCounters[i].Stop - Beg;
    memset(Beg, 0, Size);
  }
}

ATTRIBUTE_NO_SANITIZE_ALL
void TracePC::RecordInitialStack() {
  int stack;
  __sancov_lowest_stack = InitialStack = reinterpret_cast<uintptr_t>(&stack);
}

uintptr_t TracePC::GetMaxStackOffset() const {
  return InitialStack - __sancov_lowest_stack;  // Stack grows down
}

} // namespace fuzzer

extern "C" {
ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
void __sanitizer_cov_trace_pc_guard(uint32_t *Guard) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  uint32_t Idx = *Guard;
  __sancov_trace_pc_pcs[Idx] = PC;
  __sancov_trace_pc_guard_8bit_counters[Idx]++;
}

// Best-effort support for -fsanitize-coverage=trace-pc, which is available
// in both Clang and GCC.
ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
void __sanitizer_cov_trace_pc() {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  uintptr_t Idx = PC & (((uintptr_t)1 << fuzzer::TracePC::kTracePcBits) - 1);
  __sancov_trace_pc_pcs[Idx] = PC;
  __sancov_trace_pc_guard_8bit_counters[Idx]++;
}

ATTRIBUTE_INTERFACE
void __sanitizer_cov_trace_pc_guard_init(uint32_t *Start, uint32_t *Stop) {
  fuzzer::TPC.HandleInit(Start, Stop);
}

ATTRIBUTE_INTERFACE
void __sanitizer_cov_8bit_counters_init(uint8_t *Start, uint8_t *Stop) {
  fuzzer::TPC.HandleInline8bitCountersInit(Start, Stop);
}

ATTRIBUTE_INTERFACE
void __sanitizer_cov_pcs_init(const uintptr_t *pcs_beg,
                              const uintptr_t *pcs_end) {
  fuzzer::TPC.HandlePCsInit(pcs_beg, pcs_end);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
void __sanitizer_cov_trace_pc_indir(uintptr_t Callee) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCallerCallee(PC, Callee);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_cmp8(uint64_t Arg1, uint64_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
// Now the __sanitizer_cov_trace_const_cmp[1248] callbacks just mimic
// the behaviour of __sanitizer_cov_trace_cmp[1248] ones. This, however,
// should be changed later to make full use of instrumentation.
void __sanitizer_cov_trace_const_cmp8(uint64_t Arg1, uint64_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_cmp4(uint32_t Arg1, uint32_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_const_cmp4(uint32_t Arg1, uint32_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_cmp2(uint16_t Arg1, uint16_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_const_cmp2(uint16_t Arg1, uint16_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_cmp1(uint8_t Arg1, uint8_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_const_cmp1(uint8_t Arg1, uint8_t Arg2) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Arg1, Arg2);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_switch(uint64_t Val, uint64_t *Cases) {
  uint64_t N = Cases[0];
  uint64_t ValSizeInBits = Cases[1];
  uint64_t *Vals = Cases + 2;
  // Skip the most common and the most boring case.
  if (Vals[N - 1]  < 256 && Val < 256)
    return;
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  size_t i;
  uint64_t Token = 0;
  for (i = 0; i < N; i++) {
    Token = Val ^ Vals[i];
    if (Val < Vals[i])
      break;
  }

  if (ValSizeInBits == 16)
    fuzzer::TPC.HandleCmp(PC + i, static_cast<uint16_t>(Token), (uint16_t)(0));
  else if (ValSizeInBits == 32)
    fuzzer::TPC.HandleCmp(PC + i, static_cast<uint32_t>(Token), (uint32_t)(0));
  else
    fuzzer::TPC.HandleCmp(PC + i, Token, (uint64_t)(0));
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_div4(uint32_t Val) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Val, (uint32_t)0);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_div8(uint64_t Val) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Val, (uint64_t)0);
}

ATTRIBUTE_INTERFACE
ATTRIBUTE_NO_SANITIZE_ALL
ATTRIBUTE_TARGET_POPCNT
void __sanitizer_cov_trace_gep(uintptr_t Idx) {
  uintptr_t PC = reinterpret_cast<uintptr_t>(__builtin_return_address(0));
  fuzzer::TPC.HandleCmp(PC, Idx, (uintptr_t)0);
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_memcmp(void *caller_pc, const void *s1,
                                  const void *s2, size_t n, int result) {
  if (!fuzzer::RunningUserCallback) return;
  if (result == 0) return;  // No reason to mutate.
  if (n <= 1) return;  // Not interesting.
  fuzzer::TPC.AddValueForMemcmp(caller_pc, s1, s2, n, /*StopAtZero*/false);
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_strncmp(void *caller_pc, const char *s1,
                                   const char *s2, size_t n, int result) {
  if (!fuzzer::RunningUserCallback) return;
  if (result == 0) return;  // No reason to mutate.
  size_t Len1 = fuzzer::InternalStrnlen(s1, n);
  size_t Len2 = fuzzer::InternalStrnlen(s2, n);
  n = std::min(n, Len1);
  n = std::min(n, Len2);
  if (n <= 1) return;  // Not interesting.
  fuzzer::TPC.AddValueForMemcmp(caller_pc, s1, s2, n, /*StopAtZero*/true);
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_strcmp(void *caller_pc, const char *s1,
                                   const char *s2, int result) {
  if (!fuzzer::RunningUserCallback) return;
  if (result == 0) return;  // No reason to mutate.
  size_t N = fuzzer::InternalStrnlen2(s1, s2);
  if (N <= 1) return;  // Not interesting.
  fuzzer::TPC.AddValueForMemcmp(caller_pc, s1, s2, N, /*StopAtZero*/true);
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_strncasecmp(void *called_pc, const char *s1,
                                       const char *s2, size_t n, int result) {
  if (!fuzzer::RunningUserCallback) return;
  return __sanitizer_weak_hook_strncmp(called_pc, s1, s2, n, result);
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_strcasecmp(void *called_pc, const char *s1,
                                      const char *s2, int result) {
  if (!fuzzer::RunningUserCallback) return;
  return __sanitizer_weak_hook_strcmp(called_pc, s1, s2, result);
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_strstr(void *called_pc, const char *s1,
                                  const char *s2, char *result) {
  if (!fuzzer::RunningUserCallback) return;
  fuzzer::TPC.MMT.Add(reinterpret_cast<const uint8_t *>(s2), strlen(s2));
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_strcasestr(void *called_pc, const char *s1,
                                      const char *s2, char *result) {
  if (!fuzzer::RunningUserCallback) return;
  fuzzer::TPC.MMT.Add(reinterpret_cast<const uint8_t *>(s2), strlen(s2));
}

ATTRIBUTE_INTERFACE ATTRIBUTE_NO_SANITIZE_MEMORY
void __sanitizer_weak_hook_memmem(void *called_pc, const void *s1, size_t len1,
                                  const void *s2, size_t len2, void *result) {
  if (!fuzzer::RunningUserCallback) return;
  fuzzer::TPC.MMT.Add(reinterpret_cast<const uint8_t *>(s2), len2);
}
}  // extern "C"