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      1 // Copyright 2016 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "src/eh-frame.h"
      6 
      7 #include <iomanip>
      8 #include <ostream>
      9 
     10 #if !defined(V8_TARGET_ARCH_X64) && !defined(V8_TARGET_ARCH_ARM) && \
     11     !defined(V8_TARGET_ARCH_ARM64)
     12 
     13 // Placeholders for unsupported architectures.
     14 
     15 namespace v8 {
     16 namespace internal {
     17 
     18 const int EhFrameConstants::kCodeAlignmentFactor = 1;
     19 const int EhFrameConstants::kDataAlignmentFactor = 1;
     20 
     21 void EhFrameWriter::WriteReturnAddressRegisterCode() { UNIMPLEMENTED(); }
     22 
     23 void EhFrameWriter::WriteInitialStateInCie() { UNIMPLEMENTED(); }
     24 
     25 int EhFrameWriter::RegisterToDwarfCode(Register) {
     26   UNIMPLEMENTED();
     27   return -1;
     28 }
     29 
     30 #ifdef ENABLE_DISASSEMBLER
     31 
     32 const char* EhFrameDisassembler::DwarfRegisterCodeToString(int) {
     33   UNIMPLEMENTED();
     34   return nullptr;
     35 }
     36 
     37 #endif
     38 
     39 }  // namespace internal
     40 }  // namespace v8
     41 
     42 #endif
     43 
     44 namespace v8 {
     45 namespace internal {
     46 
     47 STATIC_CONST_MEMBER_DEFINITION const int
     48     EhFrameConstants::kEhFrameTerminatorSize;
     49 STATIC_CONST_MEMBER_DEFINITION const int EhFrameConstants::kEhFrameHdrVersion;
     50 STATIC_CONST_MEMBER_DEFINITION const int EhFrameConstants::kEhFrameHdrSize;
     51 
     52 STATIC_CONST_MEMBER_DEFINITION const uint32_t EhFrameWriter::kInt32Placeholder;
     53 
     54 // static
     55 void EhFrameWriter::WriteEmptyEhFrame(std::ostream& stream) {  // NOLINT
     56   stream.put(EhFrameConstants::kEhFrameHdrVersion);
     57 
     58   // .eh_frame pointer encoding specifier.
     59   stream.put(EhFrameConstants::kSData4 | EhFrameConstants::kPcRel);
     60 
     61   // Lookup table size encoding.
     62   stream.put(EhFrameConstants::kUData4);
     63 
     64   // Lookup table entries encoding.
     65   stream.put(EhFrameConstants::kSData4 | EhFrameConstants::kDataRel);
     66 
     67   // Dummy pointers and 0 entries in the lookup table.
     68   char dummy_data[EhFrameConstants::kEhFrameHdrSize - 4] = {0};
     69   stream.write(&dummy_data[0], sizeof(dummy_data));
     70 }
     71 
     72 EhFrameWriter::EhFrameWriter(Zone* zone)
     73     : cie_size_(0),
     74       last_pc_offset_(0),
     75       writer_state_(InternalState::kUndefined),
     76       base_register_(no_reg),
     77       base_offset_(0),
     78       eh_frame_buffer_(zone) {}
     79 
     80 void EhFrameWriter::Initialize() {
     81   DCHECK(writer_state_ == InternalState::kUndefined);
     82   eh_frame_buffer_.reserve(128);
     83   writer_state_ = InternalState::kInitialized;
     84   WriteCie();
     85   WriteFdeHeader();
     86 }
     87 
     88 void EhFrameWriter::WriteCie() {
     89   static const int kCIEIdentifier = 0;
     90   static const int kCIEVersion = 3;
     91   static const int kAugmentationDataSize = 2;
     92   static const byte kAugmentationString[] = {'z', 'L', 'R', 0};
     93 
     94   // Placeholder for the size of the CIE.
     95   int size_offset = eh_frame_offset();
     96   WriteInt32(kInt32Placeholder);
     97 
     98   // CIE identifier and version.
     99   int record_start_offset = eh_frame_offset();
    100   WriteInt32(kCIEIdentifier);
    101   WriteByte(kCIEVersion);
    102 
    103   // Augmentation data contents descriptor: LSDA and FDE encoding.
    104   WriteBytes(&kAugmentationString[0], sizeof(kAugmentationString));
    105 
    106   // Alignment factors.
    107   WriteSLeb128(EhFrameConstants::kCodeAlignmentFactor);
    108   WriteSLeb128(EhFrameConstants::kDataAlignmentFactor);
    109 
    110   WriteReturnAddressRegisterCode();
    111 
    112   // Augmentation data.
    113   WriteULeb128(kAugmentationDataSize);
    114   // No language-specific data area (LSDA).
    115   WriteByte(EhFrameConstants::kOmit);
    116   // FDE pointers encoding.
    117   WriteByte(EhFrameConstants::kSData4 | EhFrameConstants::kPcRel);
    118 
    119   // Write directives to build the initial state of the unwinding table.
    120   DCHECK_EQ(eh_frame_offset() - size_offset,
    121             EhFrameConstants::kInitialStateOffsetInCie);
    122   WriteInitialStateInCie();
    123 
    124   WritePaddingToAlignedSize(eh_frame_offset() - record_start_offset);
    125 
    126   int record_end_offset = eh_frame_offset();
    127   int encoded_cie_size = record_end_offset - record_start_offset;
    128   cie_size_ = record_end_offset - size_offset;
    129 
    130   // Patch the size of the CIE now that we know it.
    131   PatchInt32(size_offset, encoded_cie_size);
    132 }
    133 
    134 void EhFrameWriter::WriteFdeHeader() {
    135   DCHECK_NE(cie_size_, 0);
    136 
    137   // Placeholder for size of the FDE. Will be filled in Finish().
    138   DCHECK_EQ(eh_frame_offset(), fde_offset());
    139   WriteInt32(kInt32Placeholder);
    140 
    141   // Backwards offset to the CIE.
    142   WriteInt32(cie_size_ + kInt32Size);
    143 
    144   // Placeholder for pointer to procedure. Will be filled in Finish().
    145   DCHECK_EQ(eh_frame_offset(), GetProcedureAddressOffset());
    146   WriteInt32(kInt32Placeholder);
    147 
    148   // Placeholder for size of the procedure. Will be filled in Finish().
    149   DCHECK_EQ(eh_frame_offset(), GetProcedureSizeOffset());
    150   WriteInt32(kInt32Placeholder);
    151 
    152   // No augmentation data.
    153   WriteByte(0);
    154 }
    155 
    156 void EhFrameWriter::WriteEhFrameHdr(int code_size) {
    157   DCHECK(writer_state_ == InternalState::kInitialized);
    158 
    159   //
    160   // In order to calculate offsets in the .eh_frame_hdr, we must know the layout
    161   // of the DSO generated by perf inject, which is assumed to be the following:
    162   //
    163   //  |      ...      |                        |
    164   //  +---------------+ <-- (F) ---            |  Larger offsets in file
    165   //  |               |           ^            |
    166   //  |  Instructions |           | .text      v
    167   //  |               |           v
    168   //  +---------------+ <-- (E) ---
    169   //  |///////////////|
    170   //  |////Padding////|
    171   //  |///////////////|
    172   //  +---------------+ <-- (D) ---
    173   //  |               |           ^
    174   //  |      CIE      |           |
    175   //  |               |           |
    176   //  +---------------+ <-- (C)   |
    177   //  |               |           | .eh_frame
    178   //  |      FDE      |           |
    179   //  |               |           |
    180   //  +---------------+           |
    181   //  |   terminator  |           v
    182   //  +---------------+ <-- (B) ---
    183   //  |    version    |           ^
    184   //  +---------------+           |
    185   //  |   encoding    |           |
    186   //  |  specifiers   |           |
    187   //  +---------------+ <---(A)   | .eh_frame_hdr
    188   //  |   offset to   |           |
    189   //  |   .eh_frame   |           |
    190   //  +---------------+           |
    191   //  |      ...      |          ...
    192   //
    193   // (F) is aligned to a 16-byte boundary.
    194   // (D) is aligned to a  8-byte boundary.
    195   // (B) is aligned to a  4-byte boundary.
    196   // (C), (E) and (A) have no alignment requirements.
    197   //
    198   // The distance between (A) and (B) is 4 bytes.
    199   //
    200   // The size of the FDE is required to be a multiple of the pointer size, which
    201   // means that (B) will be naturally aligned to a 4-byte boundary on all the
    202   // architectures we support.
    203   //
    204   // Because (E) has no alignment requirements, there is padding between (E) and
    205   // (D). (F) is aligned at a 16-byte boundary, thus to a 8-byte one as well.
    206   //
    207 
    208   int eh_frame_size = eh_frame_offset();
    209 
    210   WriteByte(EhFrameConstants::kEhFrameHdrVersion);
    211 
    212   // .eh_frame pointer encoding specifier.
    213   WriteByte(EhFrameConstants::kSData4 | EhFrameConstants::kPcRel);
    214   // Lookup table size encoding specifier.
    215   WriteByte(EhFrameConstants::kUData4);
    216   // Lookup table entries encoding specifier.
    217   WriteByte(EhFrameConstants::kSData4 | EhFrameConstants::kDataRel);
    218 
    219   // Pointer to .eh_frame, relative to this offset (A -> D in the diagram).
    220   WriteInt32(-(eh_frame_size + EhFrameConstants::kFdeVersionSize +
    221                EhFrameConstants::kFdeEncodingSpecifiersSize));
    222 
    223   // Number of entries in the LUT, one for the only routine.
    224   WriteInt32(1);
    225 
    226   // Pointer to the start of the routine, relative to the beginning of the
    227   // .eh_frame_hdr (B -> F in the diagram).
    228   WriteInt32(-(RoundUp(code_size, 8) + eh_frame_size));
    229 
    230   // Pointer to the start of the associated FDE, relative to the start of the
    231   // .eh_frame_hdr (B -> C  in the diagram).
    232   WriteInt32(-(eh_frame_size - cie_size_));
    233 
    234   DCHECK_EQ(eh_frame_offset() - eh_frame_size,
    235             EhFrameConstants::kEhFrameHdrSize);
    236 }
    237 
    238 void EhFrameWriter::WritePaddingToAlignedSize(int unpadded_size) {
    239   DCHECK(writer_state_ == InternalState::kInitialized);
    240   DCHECK_GE(unpadded_size, 0);
    241 
    242   int padding_size = RoundUp(unpadded_size, kPointerSize) - unpadded_size;
    243 
    244   byte nop = static_cast<byte>(EhFrameConstants::DwarfOpcodes::kNop);
    245   static const byte kPadding[] = {nop, nop, nop, nop, nop, nop, nop, nop};
    246   DCHECK_LE(padding_size, static_cast<int>(sizeof(kPadding)));
    247   WriteBytes(&kPadding[0], padding_size);
    248 }
    249 
    250 void EhFrameWriter::AdvanceLocation(int pc_offset) {
    251   DCHECK(writer_state_ == InternalState::kInitialized);
    252   DCHECK_GE(pc_offset, last_pc_offset_);
    253   uint32_t delta = pc_offset - last_pc_offset_;
    254 
    255   DCHECK_EQ(delta % EhFrameConstants::kCodeAlignmentFactor, 0u);
    256   uint32_t factored_delta = delta / EhFrameConstants::kCodeAlignmentFactor;
    257 
    258   if (factored_delta <= EhFrameConstants::kLocationMask) {
    259     WriteByte((EhFrameConstants::kLocationTag
    260                << EhFrameConstants::kLocationMaskSize) |
    261               (factored_delta & EhFrameConstants::kLocationMask));
    262   } else if (factored_delta <= kMaxUInt8) {
    263     WriteOpcode(EhFrameConstants::DwarfOpcodes::kAdvanceLoc1);
    264     WriteByte(factored_delta);
    265   } else if (factored_delta <= kMaxUInt16) {
    266     WriteOpcode(EhFrameConstants::DwarfOpcodes::kAdvanceLoc2);
    267     WriteInt16(factored_delta);
    268   } else {
    269     WriteOpcode(EhFrameConstants::DwarfOpcodes::kAdvanceLoc4);
    270     WriteInt32(factored_delta);
    271   }
    272 
    273   last_pc_offset_ = pc_offset;
    274 }
    275 
    276 void EhFrameWriter::SetBaseAddressOffset(int base_offset) {
    277   DCHECK(writer_state_ == InternalState::kInitialized);
    278   DCHECK_GE(base_offset, 0);
    279   WriteOpcode(EhFrameConstants::DwarfOpcodes::kDefCfaOffset);
    280   WriteULeb128(base_offset);
    281   base_offset_ = base_offset;
    282 }
    283 
    284 void EhFrameWriter::SetBaseAddressRegister(Register base_register) {
    285   DCHECK(writer_state_ == InternalState::kInitialized);
    286   int code = RegisterToDwarfCode(base_register);
    287   WriteOpcode(EhFrameConstants::DwarfOpcodes::kDefCfaRegister);
    288   WriteULeb128(code);
    289   base_register_ = base_register;
    290 }
    291 
    292 void EhFrameWriter::SetBaseAddressRegisterAndOffset(Register base_register,
    293                                                     int base_offset) {
    294   DCHECK(writer_state_ == InternalState::kInitialized);
    295   DCHECK_GE(base_offset, 0);
    296   int code = RegisterToDwarfCode(base_register);
    297   WriteOpcode(EhFrameConstants::DwarfOpcodes::kDefCfa);
    298   WriteULeb128(code);
    299   WriteULeb128(base_offset);
    300   base_offset_ = base_offset;
    301   base_register_ = base_register;
    302 }
    303 
    304 void EhFrameWriter::RecordRegisterSavedToStack(int register_code, int offset) {
    305   DCHECK(writer_state_ == InternalState::kInitialized);
    306   DCHECK_EQ(offset % EhFrameConstants::kDataAlignmentFactor, 0);
    307   int factored_offset = offset / EhFrameConstants::kDataAlignmentFactor;
    308   if (factored_offset >= 0) {
    309     DCHECK_LE(register_code, EhFrameConstants::kSavedRegisterMask);
    310     WriteByte((EhFrameConstants::kSavedRegisterTag
    311                << EhFrameConstants::kSavedRegisterMaskSize) |
    312               (register_code & EhFrameConstants::kSavedRegisterMask));
    313     WriteULeb128(factored_offset);
    314   } else {
    315     WriteOpcode(EhFrameConstants::DwarfOpcodes::kOffsetExtendedSf);
    316     WriteULeb128(register_code);
    317     WriteSLeb128(factored_offset);
    318   }
    319 }
    320 
    321 void EhFrameWriter::RecordRegisterNotModified(Register name) {
    322   DCHECK(writer_state_ == InternalState::kInitialized);
    323   WriteOpcode(EhFrameConstants::DwarfOpcodes::kSameValue);
    324   WriteULeb128(RegisterToDwarfCode(name));
    325 }
    326 
    327 void EhFrameWriter::RecordRegisterFollowsInitialRule(Register name) {
    328   DCHECK(writer_state_ == InternalState::kInitialized);
    329   int code = RegisterToDwarfCode(name);
    330   DCHECK_LE(code, EhFrameConstants::kFollowInitialRuleMask);
    331   WriteByte((EhFrameConstants::kFollowInitialRuleTag
    332              << EhFrameConstants::kFollowInitialRuleMaskSize) |
    333             (code & EhFrameConstants::kFollowInitialRuleMask));
    334 }
    335 
    336 void EhFrameWriter::Finish(int code_size) {
    337   DCHECK(writer_state_ == InternalState::kInitialized);
    338   DCHECK_GE(eh_frame_offset(), cie_size_);
    339 
    340   DCHECK_GE(eh_frame_offset(), fde_offset() + kInt32Size);
    341   WritePaddingToAlignedSize(eh_frame_offset() - fde_offset() - kInt32Size);
    342 
    343   // Write the size of the FDE now that we know it.
    344   // The encoded size does not include the size field itself.
    345   int encoded_fde_size = eh_frame_offset() - fde_offset() - kInt32Size;
    346   PatchInt32(fde_offset(), encoded_fde_size);
    347 
    348   // Write size and offset to procedure.
    349   PatchInt32(GetProcedureAddressOffset(),
    350              -(RoundUp(code_size, 8) + GetProcedureAddressOffset()));
    351   PatchInt32(GetProcedureSizeOffset(), code_size);
    352 
    353   // Terminate the .eh_frame.
    354   static const byte kTerminator[EhFrameConstants::kEhFrameTerminatorSize] = {0};
    355   WriteBytes(&kTerminator[0], EhFrameConstants::kEhFrameTerminatorSize);
    356 
    357   WriteEhFrameHdr(code_size);
    358 
    359   writer_state_ = InternalState::kFinalized;
    360 }
    361 
    362 void EhFrameWriter::GetEhFrame(CodeDesc* desc) {
    363   DCHECK(writer_state_ == InternalState::kFinalized);
    364   desc->unwinding_info_size = static_cast<int>(eh_frame_buffer_.size());
    365   desc->unwinding_info = eh_frame_buffer_.data();
    366 }
    367 
    368 void EhFrameWriter::WriteULeb128(uint32_t value) {
    369   do {
    370     byte chunk = value & 0x7f;
    371     value >>= 7;
    372     if (value != 0) chunk |= 0x80;
    373     WriteByte(chunk);
    374   } while (value != 0);
    375 }
    376 
    377 void EhFrameWriter::WriteSLeb128(int32_t value) {
    378   static const int kSignBitMask = 0x40;
    379   bool done;
    380   do {
    381     byte chunk = value & 0x7f;
    382     value >>= 7;
    383     done = ((value == 0) && ((chunk & kSignBitMask) == 0)) ||
    384            ((value == -1) && ((chunk & kSignBitMask) != 0));
    385     if (!done) chunk |= 0x80;
    386     WriteByte(chunk);
    387   } while (!done);
    388 }
    389 
    390 uint32_t EhFrameIterator::GetNextULeb128() {
    391   int size = 0;
    392   uint32_t result = DecodeULeb128(next_, &size);
    393   DCHECK_LE(next_ + size, end_);
    394   next_ += size;
    395   return result;
    396 }
    397 
    398 int32_t EhFrameIterator::GetNextSLeb128() {
    399   int size = 0;
    400   int32_t result = DecodeSLeb128(next_, &size);
    401   DCHECK_LE(next_ + size, end_);
    402   next_ += size;
    403   return result;
    404 }
    405 
    406 // static
    407 uint32_t EhFrameIterator::DecodeULeb128(const byte* encoded,
    408                                         int* encoded_size) {
    409   const byte* current = encoded;
    410   uint32_t result = 0;
    411   int shift = 0;
    412 
    413   do {
    414     DCHECK_LT(shift, 8 * static_cast<int>(sizeof(result)));
    415     result |= (*current & 0x7f) << shift;
    416     shift += 7;
    417   } while (*current++ >= 128);
    418 
    419   DCHECK_NOT_NULL(encoded_size);
    420   *encoded_size = static_cast<int>(current - encoded);
    421 
    422   return result;
    423 }
    424 
    425 // static
    426 int32_t EhFrameIterator::DecodeSLeb128(const byte* encoded, int* encoded_size) {
    427   static const byte kSignBitMask = 0x40;
    428 
    429   const byte* current = encoded;
    430   int32_t result = 0;
    431   int shift = 0;
    432   byte chunk;
    433 
    434   do {
    435     chunk = *current++;
    436     DCHECK_LT(shift, 8 * static_cast<int>(sizeof(result)));
    437     result |= (chunk & 0x7f) << shift;
    438     shift += 7;
    439   } while (chunk >= 128);
    440 
    441   // Sign extend the result if the last chunk has the sign bit set.
    442   if (chunk & kSignBitMask) result |= (~0ull) << shift;
    443 
    444   DCHECK_NOT_NULL(encoded_size);
    445   *encoded_size = static_cast<int>(current - encoded);
    446 
    447   return result;
    448 }
    449 
    450 #ifdef ENABLE_DISASSEMBLER
    451 
    452 namespace {
    453 
    454 class StreamModifiersScope final {
    455  public:
    456   explicit StreamModifiersScope(std::ostream* stream)
    457       : stream_(stream), flags_(stream->flags()) {}
    458   ~StreamModifiersScope() { stream_->flags(flags_); }
    459 
    460  private:
    461   std::ostream* stream_;
    462   std::ios::fmtflags flags_;
    463 };
    464 
    465 }  // namespace
    466 
    467 // static
    468 void EhFrameDisassembler::DumpDwarfDirectives(std::ostream& stream,  // NOLINT
    469                                               const byte* start,
    470                                               const byte* end) {
    471   StreamModifiersScope modifiers_scope(&stream);
    472 
    473   EhFrameIterator eh_frame_iterator(start, end);
    474   uint32_t offset_in_procedure = 0;
    475 
    476   while (!eh_frame_iterator.Done()) {
    477     stream << eh_frame_iterator.current_address() << "  ";
    478 
    479     byte bytecode = eh_frame_iterator.GetNextByte();
    480 
    481     if (((bytecode >> EhFrameConstants::kLocationMaskSize) & 0xff) ==
    482         EhFrameConstants::kLocationTag) {
    483       int value = (bytecode & EhFrameConstants::kLocationMask) *
    484                   EhFrameConstants::kCodeAlignmentFactor;
    485       offset_in_procedure += value;
    486       stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
    487              << ")\n";
    488       continue;
    489     }
    490 
    491     if (((bytecode >> EhFrameConstants::kSavedRegisterMaskSize) & 0xff) ==
    492         EhFrameConstants::kSavedRegisterTag) {
    493       int32_t decoded_offset = eh_frame_iterator.GetNextULeb128();
    494       stream << "| " << DwarfRegisterCodeToString(
    495                             bytecode & EhFrameConstants::kLocationMask)
    496              << " saved at base" << std::showpos
    497              << decoded_offset * EhFrameConstants::kDataAlignmentFactor
    498              << std::noshowpos << '\n';
    499       continue;
    500     }
    501 
    502     if (((bytecode >> EhFrameConstants::kFollowInitialRuleMaskSize) & 0xff) ==
    503         EhFrameConstants::kFollowInitialRuleTag) {
    504       stream << "| " << DwarfRegisterCodeToString(
    505                             bytecode & EhFrameConstants::kLocationMask)
    506              << " follows rule in CIE\n";
    507       continue;
    508     }
    509 
    510     switch (static_cast<EhFrameConstants::DwarfOpcodes>(bytecode)) {
    511       case EhFrameConstants::DwarfOpcodes::kOffsetExtendedSf: {
    512         stream << "| "
    513                << DwarfRegisterCodeToString(eh_frame_iterator.GetNextULeb128());
    514         int32_t decoded_offset = eh_frame_iterator.GetNextSLeb128();
    515         stream << " saved at base" << std::showpos
    516                << decoded_offset * EhFrameConstants::kDataAlignmentFactor
    517                << std::noshowpos << '\n';
    518         break;
    519       }
    520       case EhFrameConstants::DwarfOpcodes::kAdvanceLoc1: {
    521         int value = eh_frame_iterator.GetNextByte() *
    522                     EhFrameConstants::kCodeAlignmentFactor;
    523         offset_in_procedure += value;
    524         stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
    525                << ")\n";
    526         break;
    527       }
    528       case EhFrameConstants::DwarfOpcodes::kAdvanceLoc2: {
    529         int value = eh_frame_iterator.GetNextUInt16() *
    530                     EhFrameConstants::kCodeAlignmentFactor;
    531         offset_in_procedure += value;
    532         stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
    533                << ")\n";
    534         break;
    535       }
    536       case EhFrameConstants::DwarfOpcodes::kAdvanceLoc4: {
    537         int value = eh_frame_iterator.GetNextUInt32() *
    538                     EhFrameConstants::kCodeAlignmentFactor;
    539         offset_in_procedure += value;
    540         stream << "| pc_offset=" << offset_in_procedure << " (delta=" << value
    541                << ")\n";
    542         break;
    543       }
    544       case EhFrameConstants::DwarfOpcodes::kDefCfa: {
    545         uint32_t base_register = eh_frame_iterator.GetNextULeb128();
    546         uint32_t base_offset = eh_frame_iterator.GetNextULeb128();
    547         stream << "| base_register=" << DwarfRegisterCodeToString(base_register)
    548                << ", base_offset=" << base_offset << '\n';
    549         break;
    550       }
    551       case EhFrameConstants::DwarfOpcodes::kDefCfaOffset: {
    552         stream << "| base_offset=" << eh_frame_iterator.GetNextULeb128()
    553                << '\n';
    554         break;
    555       }
    556       case EhFrameConstants::DwarfOpcodes::kDefCfaRegister: {
    557         stream << "| base_register="
    558                << DwarfRegisterCodeToString(eh_frame_iterator.GetNextULeb128())
    559                << '\n';
    560         break;
    561       }
    562       case EhFrameConstants::DwarfOpcodes::kSameValue: {
    563         stream << "| "
    564                << DwarfRegisterCodeToString(eh_frame_iterator.GetNextULeb128())
    565                << " not modified from previous frame\n";
    566         break;
    567       }
    568       case EhFrameConstants::DwarfOpcodes::kNop:
    569         stream << "| nop\n";
    570         break;
    571       default:
    572         UNREACHABLE();
    573         return;
    574     }
    575   }
    576 }
    577 
    578 void EhFrameDisassembler::DisassembleToStream(std::ostream& stream) {  // NOLINT
    579   // The encoded CIE size does not include the size field itself.
    580   const int cie_size = ReadUnalignedUInt32(start_) + kInt32Size;
    581   const int fde_offset = cie_size;
    582 
    583   const byte* cie_directives_start =
    584       start_ + EhFrameConstants::kInitialStateOffsetInCie;
    585   const byte* cie_directives_end = start_ + cie_size;
    586   DCHECK_LE(cie_directives_start, cie_directives_end);
    587 
    588   stream << reinterpret_cast<const void*>(start_) << "  .eh_frame: CIE\n";
    589   DumpDwarfDirectives(stream, cie_directives_start, cie_directives_end);
    590 
    591   const byte* procedure_offset_address =
    592       start_ + fde_offset + EhFrameConstants::kProcedureAddressOffsetInFde;
    593   int32_t procedure_offset =
    594       ReadUnalignedValue<int32_t>(procedure_offset_address);
    595 
    596   const byte* procedure_size_address =
    597       start_ + fde_offset + EhFrameConstants::kProcedureSizeOffsetInFde;
    598   uint32_t procedure_size = ReadUnalignedUInt32(procedure_size_address);
    599 
    600   const byte* fde_start = start_ + fde_offset;
    601   stream << reinterpret_cast<const void*>(fde_start) << "  .eh_frame: FDE\n"
    602          << reinterpret_cast<const void*>(procedure_offset_address)
    603          << "  | procedure_offset=" << procedure_offset << '\n'
    604          << reinterpret_cast<const void*>(procedure_size_address)
    605          << "  | procedure_size=" << procedure_size << '\n';
    606 
    607   const int fde_directives_offset = fde_offset + 4 * kInt32Size + 1;
    608 
    609   const byte* fde_directives_start = start_ + fde_directives_offset;
    610   const byte* fde_directives_end = end_ - EhFrameConstants::kEhFrameHdrSize -
    611                                    EhFrameConstants::kEhFrameTerminatorSize;
    612   DCHECK_LE(fde_directives_start, fde_directives_end);
    613 
    614   DumpDwarfDirectives(stream, fde_directives_start, fde_directives_end);
    615 
    616   const byte* fde_terminator_start = fde_directives_end;
    617   stream << reinterpret_cast<const void*>(fde_terminator_start)
    618          << "  .eh_frame: terminator\n";
    619 
    620   const byte* eh_frame_hdr_start =
    621       fde_terminator_start + EhFrameConstants::kEhFrameTerminatorSize;
    622   stream << reinterpret_cast<const void*>(eh_frame_hdr_start)
    623          << "  .eh_frame_hdr\n";
    624 }
    625 
    626 #endif
    627 
    628 }  // namespace internal
    629 }  // namespace v8
    630