compiler-rt/lib/fuzzer/FuzzerMutate.cpp

   1 //===- FuzzerMutate.cpp - Mutate a test input -----------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 // Mutate a test input.
   9 //===----------------------------------------------------------------------===//
  10
  11 #include "FuzzerDefs.h"
  12 #include "FuzzerExtFunctions.h"
  13 #include "FuzzerIO.h"
  14 #include "FuzzerMutate.h"
  15 #include "FuzzerOptions.h"
  16 #include "FuzzerTracePC.h"
  17
  18 namespace fuzzer {
  19
  20 const size_t Dictionary::kMaxDictSize;
  21 static const size_t kMaxMutationsToPrint = 10;
  22
  23 static void PrintASCII(const Word &W, const char *PrintAfter) {
  24   PrintASCII(W.data(), W.size(), PrintAfter);
  25 }
  26
  27 MutationDispatcher::MutationDispatcher(Random &Rand,
  28                                        const FuzzingOptions &Options)
  29     : Rand(Rand), Options(Options) {
  30   DefaultMutators.insert(
  31       DefaultMutators.begin(),
  32       {
  33           {&MutationDispatcher::Mutate_EraseBytes, "EraseBytes"},
  34           {&MutationDispatcher::Mutate_InsertByte, "InsertByte"},
  35           {&MutationDispatcher::Mutate_InsertRepeatedBytes,
  36            "InsertRepeatedBytes"},
  37           {&MutationDispatcher::Mutate_ChangeByte, "ChangeByte"},
  38           {&MutationDispatcher::Mutate_ChangeBit, "ChangeBit"},
  39           {&MutationDispatcher::Mutate_ShuffleBytes, "ShuffleBytes"},
  40           {&MutationDispatcher::Mutate_ChangeASCIIInteger, "ChangeASCIIInt"},
  41           {&MutationDispatcher::Mutate_ChangeBinaryInteger, "ChangeBinInt"},
  42           {&MutationDispatcher::Mutate_CopyPart, "CopyPart"},
  43           {&MutationDispatcher::Mutate_CrossOver, "CrossOver"},
  44           {&MutationDispatcher::Mutate_AddWordFromManualDictionary,
  45            "ManualDict"},
  46           {&MutationDispatcher::Mutate_AddWordFromPersistentAutoDictionary,
  47            "PersAutoDict"},
  48       });
  49   if(Options.UseCmp)
  50     DefaultMutators.push_back(
  51         {&MutationDispatcher::Mutate_AddWordFromTORC, "CMP"});
  52
  53   if (EF->LLVMFuzzerCustomMutator)
  54     Mutators.push_back({&MutationDispatcher::Mutate_Custom, "Custom"});
  55   else
  56     Mutators = DefaultMutators;
  57
  58   if (EF->LLVMFuzzerCustomCrossOver)
  59     Mutators.push_back(
  60         {&MutationDispatcher::Mutate_CustomCrossOver, "CustomCrossOver"});
  61 }
  62
  63 static char RandCh(Random &Rand) {
  64   if (Rand.RandBool())
  65     return static_cast<char>(Rand(256));
  66   const char Special[] = "!*'();:@&=+$,/?%#[]012Az-`~.\xff\x00";
  67   return Special[Rand(sizeof(Special) - 1)];
  68 }
  69
  70 size_t MutationDispatcher::Mutate_Custom(uint8_t *Data, size_t Size,
  71                                          size_t MaxSize) {
  72   if (EF->__msan_unpoison)
  73     EF->__msan_unpoison(Data, Size);
  74   if (EF->__msan_unpoison_param)
  75     EF->__msan_unpoison_param(4);
  76   return EF->LLVMFuzzerCustomMutator(Data, Size, MaxSize,
  77                                      Rand.Rand<unsigned int>());
  78 }
  79
  80 size_t MutationDispatcher::Mutate_CustomCrossOver(uint8_t *Data, size_t Size,
  81                                                   size_t MaxSize) {
  82   if (Size == 0)
  83     return 0;
  84   if (!CrossOverWith) return 0;
  85   const Unit &Other = *CrossOverWith;
  86   if (Other.empty())
  87     return 0;
  88   CustomCrossOverInPlaceHere.resize(MaxSize);
  89   auto &U = CustomCrossOverInPlaceHere;
  90
  91   if (EF->__msan_unpoison) {
  92     EF->__msan_unpoison(Data, Size);
  93     EF->__msan_unpoison(Other.data(), Other.size());
  94     EF->__msan_unpoison(U.data(), U.size());
  95   }
  96   if (EF->__msan_unpoison_param)
  97     EF->__msan_unpoison_param(7);
  98   size_t NewSize = EF->LLVMFuzzerCustomCrossOver(
  99       Data, Size, Other.data(), Other.size(), U.data(), U.size(),
 100       Rand.Rand<unsigned int>());
 101
 102   if (!NewSize)
 103     return 0;
 104   assert(NewSize <= MaxSize && "CustomCrossOver returned overisized unit");
 105   memcpy(Data, U.data(), NewSize);
 106   return NewSize;
 107 }
 108
 109 size_t MutationDispatcher::Mutate_ShuffleBytes(uint8_t *Data, size_t Size,
 110                                                size_t MaxSize) {
 111   if (Size > MaxSize || Size == 0) return 0;
 112   size_t ShuffleAmount =
 113       Rand(std::min(Size, (size_t)8)) + 1; // [1,8] and <= Size.
 114   size_t ShuffleStart = Rand(Size - ShuffleAmount);
 115   assert(ShuffleStart + ShuffleAmount <= Size);
 116   std::shuffle(Data + ShuffleStart, Data + ShuffleStart + ShuffleAmount, Rand);
 117   return Size;
 118 }
 119
 120 size_t MutationDispatcher::Mutate_EraseBytes(uint8_t *Data, size_t Size,
 121                                              size_t MaxSize) {
 122   if (Size <= 1) return 0;
 123   size_t N = Rand(Size / 2) + 1;
 124   assert(N < Size);
 125   size_t Idx = Rand(Size - N + 1);
 126   // Erase Data[Idx:Idx+N].
 127   memmove(Data + Idx, Data + Idx + N, Size - Idx - N);
 128   // Printf("Erase: %zd %zd => %zd; Idx %zd\n", N, Size, Size - N, Idx);
 129   return Size - N;
 130 }
 131
 132 size_t MutationDispatcher::Mutate_InsertByte(uint8_t *Data, size_t Size,
 133                                              size_t MaxSize) {
 134   if (Size >= MaxSize) return 0;
 135   size_t Idx = Rand(Size + 1);
 136   // Insert new value at Data[Idx].
 137   memmove(Data + Idx + 1, Data + Idx, Size - Idx);
 138   Data[Idx] = RandCh(Rand);
 139   return Size + 1;
 140 }
 141
 142 size_t MutationDispatcher::Mutate_InsertRepeatedBytes(uint8_t *Data,
 143                                                       size_t Size,
 144                                                       size_t MaxSize) {
 145   const size_t kMinBytesToInsert = 3;
 146   if (Size + kMinBytesToInsert >= MaxSize) return 0;
 147   size_t MaxBytesToInsert = std::min(MaxSize - Size, (size_t)128);
 148   size_t N = Rand(MaxBytesToInsert - kMinBytesToInsert + 1) + kMinBytesToInsert;
 149   assert(Size + N <= MaxSize && N);
 150   size_t Idx = Rand(Size + 1);
 151   // Insert new values at Data[Idx].
 152   memmove(Data + Idx + N, Data + Idx, Size - Idx);
 153   // Give preference to 0x00 and 0xff.
 154   uint8_t Byte = static_cast<uint8_t>(
 155       Rand.RandBool() ? Rand(256) : (Rand.RandBool() ? 0 : 255));
 156   for (size_t i = 0; i < N; i++)
 157     Data[Idx + i] = Byte;
 158   return Size + N;
 159 }
 160
 161 size_t MutationDispatcher::Mutate_ChangeByte(uint8_t *Data, size_t Size,
 162                                              size_t MaxSize) {
 163   if (Size > MaxSize) return 0;
 164   size_t Idx = Rand(Size);
 165   Data[Idx] = RandCh(Rand);
 166   return Size;
 167 }
 168
 169 size_t MutationDispatcher::Mutate_ChangeBit(uint8_t *Data, size_t Size,
 170                                             size_t MaxSize) {
 171   if (Size > MaxSize) return 0;
 172   size_t Idx = Rand(Size);
 173   Data[Idx] ^= 1 << Rand(8);
 174   return Size;
 175 }
 176
 177 size_t MutationDispatcher::Mutate_AddWordFromManualDictionary(uint8_t *Data,
 178                                                               size_t Size,
 179                                                               size_t MaxSize) {
 180   return AddWordFromDictionary(ManualDictionary, Data, Size, MaxSize);
 181 }
 182
 183 size_t MutationDispatcher::ApplyDictionaryEntry(uint8_t *Data, size_t Size,
 184                                                 size_t MaxSize,
 185                                                 DictionaryEntry &DE) {
 186   const Word &W = DE.GetW();
 187   bool UsePositionHint = DE.HasPositionHint() &&
 188                          DE.GetPositionHint() + W.size() < Size &&
 189                          Rand.RandBool();
 190   if (Rand.RandBool()) {  // Insert W.
 191     if (Size + W.size() > MaxSize) return 0;
 192     size_t Idx = UsePositionHint ? DE.GetPositionHint() : Rand(Size + 1);
 193     memmove(Data + Idx + W.size(), Data + Idx, Size - Idx);
 194     memcpy(Data + Idx, W.data(), W.size());
 195     Size += W.size();
 196   } else {  // Overwrite some bytes with W.
 197     if (W.size() > Size) return 0;
 198     size_t Idx =
 199         UsePositionHint ? DE.GetPositionHint() : Rand(Size + 1 - W.size());
 200     memcpy(Data + Idx, W.data(), W.size());
 201   }
 202   return Size;
 203 }
 204
 205 // Somewhere in the past we have observed a comparison instructions
 206 // with arguments Arg1 Arg2. This function tries to guess a dictionary
 207 // entry that will satisfy that comparison.
 208 // It first tries to find one of the arguments (possibly swapped) in the
 209 // input and if it succeeds it creates a DE with a position hint.
 210 // Otherwise it creates a DE with one of the arguments w/o a position hint.
 211 DictionaryEntry MutationDispatcher::MakeDictionaryEntryFromCMP(
 212     const void *Arg1, const void *Arg2,
 213     const void *Arg1Mutation, const void *Arg2Mutation,
 214     size_t ArgSize, const uint8_t *Data,
 215     size_t Size) {
 216   bool HandleFirst = Rand.RandBool();
 217   const void *ExistingBytes, *DesiredBytes;
 218   Word W;
 219   const uint8_t *End = Data + Size;
 220   for (int Arg = 0; Arg < 2; Arg++) {
 221     ExistingBytes = HandleFirst ? Arg1 : Arg2;
 222     DesiredBytes = HandleFirst ? Arg2Mutation : Arg1Mutation;
 223     HandleFirst = !HandleFirst;
 224     W.Set(reinterpret_cast<const uint8_t*>(DesiredBytes), ArgSize);
 225     const size_t kMaxNumPositions = 8;
 226     size_t Positions[kMaxNumPositions];
 227     size_t NumPositions = 0;
 228     for (const uint8_t *Cur = Data;
 229          Cur < End && NumPositions < kMaxNumPositions; Cur++) {
 230       Cur =
 231           (const uint8_t *)SearchMemory(Cur, End - Cur, ExistingBytes, ArgSize);
 232       if (!Cur) break;
 233       Positions[NumPositions++] = Cur - Data;
 234     }
 235     if (!NumPositions) continue;
 236     return DictionaryEntry(W, Positions[Rand(NumPositions)]);
 237   }
 238   DictionaryEntry DE(W);
 239   return DE;
 240 }
 241
 242
 243 template <class T>
 244 DictionaryEntry MutationDispatcher::MakeDictionaryEntryFromCMP(
 245     T Arg1, T Arg2, const uint8_t *Data, size_t Size) {
 246   if (Rand.RandBool()) Arg1 = Bswap(Arg1);
 247   if (Rand.RandBool()) Arg2 = Bswap(Arg2);
 248   T Arg1Mutation = static_cast<T>(Arg1 + Rand(-1, 1));
 249   T Arg2Mutation = static_cast<T>(Arg2 + Rand(-1, 1));
 250   return MakeDictionaryEntryFromCMP(&Arg1, &Arg2, &Arg1Mutation, &Arg2Mutation,
 251                                     sizeof(Arg1), Data, Size);
 252 }
 253
 254 DictionaryEntry MutationDispatcher::MakeDictionaryEntryFromCMP(
 255     const Word &Arg1, const Word &Arg2, const uint8_t *Data, size_t Size) {
 256   return MakeDictionaryEntryFromCMP(Arg1.data(), Arg2.data(), Arg1.data(),
 257                                     Arg2.data(), Arg1.size(), Data, Size);
 258 }
 259
 260 size_t MutationDispatcher::Mutate_AddWordFromTORC(
 261     uint8_t *Data, size_t Size, size_t MaxSize) {
 262   Word W;
 263   DictionaryEntry DE;
 264   switch (Rand(4)) {
 265   case 0: {
 266     auto X = TPC.TORC8.Get(Rand.Rand<size_t>());
 267     DE = MakeDictionaryEntryFromCMP(X.A, X.B, Data, Size);
 268   } break;
 269   case 1: {
 270     auto X = TPC.TORC4.Get(Rand.Rand<size_t>());
 271     if ((X.A >> 16) == 0 && (X.B >> 16) == 0 && Rand.RandBool())
 272       DE = MakeDictionaryEntryFromCMP((uint16_t)X.A, (uint16_t)X.B, Data, Size);
 273     else
 274       DE = MakeDictionaryEntryFromCMP(X.A, X.B, Data, Size);
 275   } break;
 276   case 2: {
 277     auto X = TPC.TORCW.Get(Rand.Rand<size_t>());
 278     DE = MakeDictionaryEntryFromCMP(X.A, X.B, Data, Size);
 279   } break;
 280   case 3: if (Options.UseMemmem) {
 281       auto X = TPC.MMT.Get(Rand.Rand<size_t>());
 282       DE = DictionaryEntry(X);
 283   } break;
 284   default:
 285     assert(0);
 286   }
 287   if (!DE.GetW().size()) return 0;
 288   Size = ApplyDictionaryEntry(Data, Size, MaxSize, DE);
 289   if (!Size) return 0;
 290   DictionaryEntry &DERef =
 291       CmpDictionaryEntriesDeque[CmpDictionaryEntriesDequeIdx++ %
 292                                 kCmpDictionaryEntriesDequeSize];
 293   DERef = DE;
 294   CurrentDictionaryEntrySequence.push_back(&DERef);
 295   return Size;
 296 }
 297
 298 size_t MutationDispatcher::Mutate_AddWordFromPersistentAutoDictionary(
 299     uint8_t *Data, size_t Size, size_t MaxSize) {
 300   return AddWordFromDictionary(PersistentAutoDictionary, Data, Size, MaxSize);
 301 }
 302
 303 size_t MutationDispatcher::AddWordFromDictionary(Dictionary &D, uint8_t *Data,
 304                                                  size_t Size, size_t MaxSize) {
 305   if (Size > MaxSize) return 0;
 306   if (D.empty()) return 0;
 307   DictionaryEntry &DE = D[Rand(D.size())];
 308   Size = ApplyDictionaryEntry(Data, Size, MaxSize, DE);
 309   if (!Size) return 0;
 310   DE.IncUseCount();
 311   CurrentDictionaryEntrySequence.push_back(&DE);
 312   return Size;
 313 }
 314
 315 // Overwrites part of To[0,ToSize) with a part of From[0,FromSize).
 316 // Returns ToSize.
 317 size_t MutationDispatcher::CopyPartOf(const uint8_t *From, size_t FromSize,
 318                                       uint8_t *To, size_t ToSize) {
 319   // Copy From[FromBeg, FromBeg + CopySize) into To[ToBeg, ToBeg + CopySize).
 320   size_t ToBeg = Rand(ToSize);
 321   size_t CopySize = Rand(ToSize - ToBeg) + 1;
 322   assert(ToBeg + CopySize <= ToSize);
 323   CopySize = std::min(CopySize, FromSize);
 324   size_t FromBeg = Rand(FromSize - CopySize + 1);
 325   assert(FromBeg + CopySize <= FromSize);
 326   memmove(To + ToBeg, From + FromBeg, CopySize);
 327   return ToSize;
 328 }
 329
 330 // Inserts part of From[0,ToSize) into To.
 331 // Returns new size of To on success or 0 on failure.
 332 size_t MutationDispatcher::InsertPartOf(const uint8_t *From, size_t FromSize,
 333                                         uint8_t *To, size_t ToSize,
 334                                         size_t MaxToSize) {
 335   if (ToSize >= MaxToSize) return 0;
 336   size_t AvailableSpace = MaxToSize - ToSize;
 337   size_t MaxCopySize = std::min(AvailableSpace, FromSize);
 338   size_t CopySize = Rand(MaxCopySize) + 1;
 339   size_t FromBeg = Rand(FromSize - CopySize + 1);
 340   assert(FromBeg + CopySize <= FromSize);
 341   size_t ToInsertPos = Rand(ToSize + 1);
 342   assert(ToInsertPos + CopySize <= MaxToSize);
 343   size_t TailSize = ToSize - ToInsertPos;
 344   if (To == From) {
 345     MutateInPlaceHere.resize(MaxToSize);
 346     memcpy(MutateInPlaceHere.data(), From + FromBeg, CopySize);
 347     memmove(To + ToInsertPos + CopySize, To + ToInsertPos, TailSize);
 348     memmove(To + ToInsertPos, MutateInPlaceHere.data(), CopySize);
 349   } else {
 350     memmove(To + ToInsertPos + CopySize, To + ToInsertPos, TailSize);
 351     memmove(To + ToInsertPos, From + FromBeg, CopySize);
 352   }
 353   return ToSize + CopySize;
 354 }
 355
 356 size_t MutationDispatcher::Mutate_CopyPart(uint8_t *Data, size_t Size,
 357                                            size_t MaxSize) {
 358   if (Size > MaxSize || Size == 0) return 0;
 359   // If Size == MaxSize, `InsertPartOf(...)` will
 360   // fail so there's no point using it in this case.
 361   if (Size == MaxSize || Rand.RandBool())
 362     return CopyPartOf(Data, Size, Data, Size);
 363   else
 364     return InsertPartOf(Data, Size, Data, Size, MaxSize);
 365 }
 366
 367 size_t MutationDispatcher::Mutate_ChangeASCIIInteger(uint8_t *Data, size_t Size,
 368                                                      size_t MaxSize) {
 369   if (Size > MaxSize) return 0;
 370   size_t B = Rand(Size);
 371   while (B < Size && !isdigit(Data[B])) B++;
 372   if (B == Size) return 0;
 373   size_t E = B;
 374   while (E < Size && isdigit(Data[E])) E++;
 375   assert(B < E);
 376   // now we have digits in [B, E).
 377   // strtol and friends don't accept non-zero-teminated data, parse it manually.
 378   uint64_t Val = Data[B] - '0';
 379   for (size_t i = B + 1; i < E; i++)
 380     Val = Val * 10 + Data[i] - '0';
 381
 382   // Mutate the integer value.
 383   switch(Rand(5)) {
 384     case 0: Val++; break;
 385     case 1: Val--; break;
 386     case 2: Val /= 2; break;
 387     case 3: Val *= 2; break;
 388     case 4: Val = Rand(Val * Val); break;
 389     default: assert(0);
 390   }
 391   // Just replace the bytes with the new ones, don't bother moving bytes.
 392   for (size_t i = B; i < E; i++) {
 393     size_t Idx = E + B - i - 1;
 394     assert(Idx >= B && Idx < E);
 395     Data[Idx] = (Val % 10) + '0';
 396     Val /= 10;
 397   }
 398   return Size;
 399 }
 400
 401 template<class T>
 402 size_t ChangeBinaryInteger(uint8_t *Data, size_t Size, Random &Rand) {
 403   if (Size < sizeof(T)) return 0;
 404   size_t Off = Rand(Size - sizeof(T) + 1);
 405   assert(Off + sizeof(T) <= Size);
 406   T Val;
 407   if (Off < 64 && !Rand(4)) {
 408     Val = static_cast<T>(Size);
 409     if (Rand.RandBool())
 410       Val = Bswap(Val);
 411   } else {
 412     memcpy(&Val, Data + Off, sizeof(Val));
 413     T Add = static_cast<T>(Rand(21));
 414     Add -= 10;
 415     if (Rand.RandBool())
 416       Val = Bswap(T(Bswap(Val) + Add)); // Add assuming different endiannes.
 417     else
 418       Val = Val + Add;               // Add assuming current endiannes.
 419     if (Add == 0 || Rand.RandBool()) // Maybe negate.
 420       Val = -Val;
 421   }
 422   memcpy(Data + Off, &Val, sizeof(Val));
 423   return Size;
 424 }
 425
 426 size_t MutationDispatcher::Mutate_ChangeBinaryInteger(uint8_t *Data,
 427                                                       size_t Size,
 428                                                       size_t MaxSize) {
 429   if (Size > MaxSize) return 0;
 430   switch (Rand(4)) {
 431     case 3: return ChangeBinaryInteger<uint64_t>(Data, Size, Rand);
 432     case 2: return ChangeBinaryInteger<uint32_t>(Data, Size, Rand);
 433     case 1: return ChangeBinaryInteger<uint16_t>(Data, Size, Rand);
 434     case 0: return ChangeBinaryInteger<uint8_t>(Data, Size, Rand);
 435     default: assert(0);
 436   }
 437   return 0;
 438 }
 439
 440 size_t MutationDispatcher::Mutate_CrossOver(uint8_t *Data, size_t Size,
 441                                             size_t MaxSize) {
 442   if (Size > MaxSize) return 0;
 443   if (Size == 0) return 0;
 444   if (!CrossOverWith) return 0;
 445   const Unit &O = *CrossOverWith;
 446   if (O.empty()) return 0;
 447   size_t NewSize = 0;
 448   switch(Rand(3)) {
 449     case 0:
 450       MutateInPlaceHere.resize(MaxSize);
 451       NewSize = CrossOver(Data, Size, O.data(), O.size(),
 452                           MutateInPlaceHere.data(), MaxSize);
 453       memcpy(Data, MutateInPlaceHere.data(), NewSize);
 454       break;
 455     case 1:
 456       NewSize = InsertPartOf(O.data(), O.size(), Data, Size, MaxSize);
 457       if (!NewSize)
 458         NewSize = CopyPartOf(O.data(), O.size(), Data, Size);
 459       break;
 460     case 2:
 461       NewSize = CopyPartOf(O.data(), O.size(), Data, Size);
 462       break;
 463     default: assert(0);
 464   }
 465   assert(NewSize > 0 && "CrossOver returned empty unit");
 466   assert(NewSize <= MaxSize && "CrossOver returned overisized unit");
 467   return NewSize;
 468 }
 469
 470 void MutationDispatcher::StartMutationSequence() {
 471   CurrentMutatorSequence.clear();
 472   CurrentDictionaryEntrySequence.clear();
 473 }
 474
 475 // Copy successful dictionary entries to PersistentAutoDictionary.
 476 void MutationDispatcher::RecordSuccessfulMutationSequence() {
 477   for (auto DE : CurrentDictionaryEntrySequence) {
 478     // PersistentAutoDictionary.AddWithSuccessCountOne(DE);
 479     DE->IncSuccessCount();
 480     assert(DE->GetW().size());
 481     // Linear search is fine here as this happens seldom.
 482     if (!PersistentAutoDictionary.ContainsWord(DE->GetW()))
 483       PersistentAutoDictionary.push_back(*DE);
 484   }
 485 }
 486
 487 void MutationDispatcher::PrintRecommendedDictionary() {
 488   std::vector<DictionaryEntry> V;
 489   for (auto &DE : PersistentAutoDictionary)
 490     if (!ManualDictionary.ContainsWord(DE.GetW()))
 491       V.push_back(DE);
 492   if (V.empty()) return;
 493   Printf("###### Recommended dictionary. ######\n");
 494   for (auto &DE: V) {
 495     assert(DE.GetW().size());
 496     Printf("\"");
 497     PrintASCII(DE.GetW(), "\"");
 498     Printf(" # Uses: %zd\n", DE.GetUseCount());
 499   }
 500   Printf("###### End of recommended dictionary. ######\n");
 501 }
 502
 503 void MutationDispatcher::PrintMutationSequence(bool Verbose) {
 504   Printf("MS: %zd ", CurrentMutatorSequence.size());
 505   size_t EntriesToPrint =
 506       Verbose ? CurrentMutatorSequence.size()
 507               : std::min(kMaxMutationsToPrint, CurrentMutatorSequence.size());
 508   for (size_t i = 0; i < EntriesToPrint; i++)
 509     Printf("%s-", CurrentMutatorSequence[i].Name);
 510   if (!CurrentDictionaryEntrySequence.empty()) {
 511     Printf(" DE: ");
 512     EntriesToPrint = Verbose ? CurrentDictionaryEntrySequence.size()
 513                              : std::min(kMaxMutationsToPrint,
 514                                         CurrentDictionaryEntrySequence.size());
 515     for (size_t i = 0; i < EntriesToPrint; i++) {
 516       Printf("\"");
 517       PrintASCII(CurrentDictionaryEntrySequence[i]->GetW(), "\"-");
 518     }
 519   }
 520 }
 521
 522 std::string MutationDispatcher::MutationSequence() {
 523   std::string MS;
 524   for (const auto &M : CurrentMutatorSequence) {
 525     MS += M.Name;
 526     MS += "-";
 527   }
 528   return MS;
 529 }
 530
 531 size_t MutationDispatcher::Mutate(uint8_t *Data, size_t Size, size_t MaxSize) {
 532   return MutateImpl(Data, Size, MaxSize, Mutators);
 533 }
 534
 535 size_t MutationDispatcher::DefaultMutate(uint8_t *Data, size_t Size,
 536                                          size_t MaxSize) {
 537   return MutateImpl(Data, Size, MaxSize, DefaultMutators);
 538 }
 539
 540 // Mutates Data in place, returns new size.
 541 size_t MutationDispatcher::MutateImpl(uint8_t *Data, size_t Size,
 542                                       size_t MaxSize,
 543                                       std::vector<Mutator> &Mutators) {
 544   assert(MaxSize > 0);
 545   // Some mutations may fail (e.g. can't insert more bytes if Size == MaxSize),
 546   // in which case they will return 0.
 547   // Try several times before returning un-mutated data.
 548   for (int Iter = 0; Iter < 100; Iter++) {
 549     auto M = Mutators[Rand(Mutators.size())];
 550     size_t NewSize = (this->*(M.Fn))(Data, Size, MaxSize);
 551     if (NewSize && NewSize <= MaxSize) {
 552       if (Options.OnlyASCII)
 553         ToASCII(Data, NewSize);
 554       CurrentMutatorSequence.push_back(M);
 555       return NewSize;
 556     }
 557   }
 558   *Data = ' ';
 559   return 1;   // Fallback, should not happen frequently.
 560 }
 561
 562 // Mask represents the set of Data bytes that are worth mutating.
 563 size_t MutationDispatcher::MutateWithMask(uint8_t *Data, size_t Size,
 564                                           size_t MaxSize,
 565                                           const std::vector<uint8_t> &Mask) {
 566   size_t MaskedSize = std::min(Size, Mask.size());
 567   // * Copy the worthy bytes into a temporary array T
 568   // * Mutate T
 569   // * Copy T back.
 570   // This is totally unoptimized.
 571   auto &T = MutateWithMaskTemp;
 572   if (T.size() < Size)
 573     T.resize(Size);
 574   size_t OneBits = 0;
 575   for (size_t I = 0; I < MaskedSize; I++)
 576     if (Mask[I])
 577       T[OneBits++] = Data[I];
 578
 579   if (!OneBits) return 0;
 580   assert(!T.empty());
 581   size_t NewSize = Mutate(T.data(), OneBits, OneBits);
 582   assert(NewSize <= OneBits);
 583   (void)NewSize;
 584   // Even if NewSize < OneBits we still use all OneBits bytes.
 585   for (size_t I = 0, J = 0; I < MaskedSize; I++)
 586     if (Mask[I])
 587       Data[I] = T[J++];
 588   return Size;
 589 }
 590
 591 void MutationDispatcher::AddWordToManualDictionary(const Word &W) {
 592   ManualDictionary.push_back(
 593       {W, std::numeric_limits<size_t>::max()});
 594 }
 595
 596 }  // namespace fuzzer