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