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      1 //===- BitstreamReader.cpp - BitstreamReader implementation ---------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #include "llvm/Bitcode/BitstreamReader.h"
     11 
     12 using namespace llvm;
     13 
     14 //===----------------------------------------------------------------------===//
     15 //  BitstreamCursor implementation
     16 //===----------------------------------------------------------------------===//
     17 
     18 void BitstreamCursor::freeState() {
     19   // Free all the Abbrevs.
     20   CurAbbrevs.clear();
     21 
     22   // Free all the Abbrevs in the block scope.
     23   BlockScope.clear();
     24 }
     25 
     26 /// EnterSubBlock - Having read the ENTER_SUBBLOCK abbrevid, enter
     27 /// the block, and return true if the block has an error.
     28 bool BitstreamCursor::EnterSubBlock(unsigned BlockID, unsigned *NumWordsP) {
     29   // Save the current block's state on BlockScope.
     30   BlockScope.push_back(Block(CurCodeSize));
     31   BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
     32 
     33   // Add the abbrevs specific to this block to the CurAbbrevs list.
     34   if (const BitstreamReader::BlockInfo *Info =
     35       BitStream->getBlockInfo(BlockID)) {
     36     CurAbbrevs.insert(CurAbbrevs.end(), Info->Abbrevs.begin(),
     37                       Info->Abbrevs.end());
     38   }
     39 
     40   // Get the codesize of this block.
     41   CurCodeSize = ReadVBR(bitc::CodeLenWidth);
     42   // We can't read more than MaxChunkSize at a time
     43   if (CurCodeSize > MaxChunkSize)
     44     return true;
     45 
     46   SkipToFourByteBoundary();
     47   unsigned NumWords = Read(bitc::BlockSizeWidth);
     48   if (NumWordsP) *NumWordsP = NumWords;
     49 
     50   // Validate that this block is sane.
     51   return CurCodeSize == 0 || AtEndOfStream();
     52 }
     53 
     54 static uint64_t readAbbreviatedField(BitstreamCursor &Cursor,
     55                                      const BitCodeAbbrevOp &Op) {
     56   assert(!Op.isLiteral() && "Not to be used with literals!");
     57 
     58   // Decode the value as we are commanded.
     59   switch (Op.getEncoding()) {
     60   case BitCodeAbbrevOp::Array:
     61   case BitCodeAbbrevOp::Blob:
     62     llvm_unreachable("Should not reach here");
     63   case BitCodeAbbrevOp::Fixed:
     64     assert((unsigned)Op.getEncodingData() <= Cursor.MaxChunkSize);
     65     return Cursor.Read((unsigned)Op.getEncodingData());
     66   case BitCodeAbbrevOp::VBR:
     67     assert((unsigned)Op.getEncodingData() <= Cursor.MaxChunkSize);
     68     return Cursor.ReadVBR64((unsigned)Op.getEncodingData());
     69   case BitCodeAbbrevOp::Char6:
     70     return BitCodeAbbrevOp::DecodeChar6(Cursor.Read(6));
     71   }
     72   llvm_unreachable("invalid abbreviation encoding");
     73 }
     74 
     75 static void skipAbbreviatedField(BitstreamCursor &Cursor,
     76                                  const BitCodeAbbrevOp &Op) {
     77   assert(!Op.isLiteral() && "Not to be used with literals!");
     78 
     79   // Decode the value as we are commanded.
     80   switch (Op.getEncoding()) {
     81   case BitCodeAbbrevOp::Array:
     82   case BitCodeAbbrevOp::Blob:
     83     llvm_unreachable("Should not reach here");
     84   case BitCodeAbbrevOp::Fixed:
     85     assert((unsigned)Op.getEncodingData() <= Cursor.MaxChunkSize);
     86     Cursor.Read((unsigned)Op.getEncodingData());
     87     break;
     88   case BitCodeAbbrevOp::VBR:
     89     assert((unsigned)Op.getEncodingData() <= Cursor.MaxChunkSize);
     90     Cursor.ReadVBR64((unsigned)Op.getEncodingData());
     91     break;
     92   case BitCodeAbbrevOp::Char6:
     93     Cursor.Read(6);
     94     break;
     95   }
     96 }
     97 
     98 
     99 
    100 /// skipRecord - Read the current record and discard it.
    101 void BitstreamCursor::skipRecord(unsigned AbbrevID) {
    102   // Skip unabbreviated records by reading past their entries.
    103   if (AbbrevID == bitc::UNABBREV_RECORD) {
    104     unsigned Code = ReadVBR(6);
    105     (void)Code;
    106     unsigned NumElts = ReadVBR(6);
    107     for (unsigned i = 0; i != NumElts; ++i)
    108       (void)ReadVBR64(6);
    109     return;
    110   }
    111 
    112   const BitCodeAbbrev *Abbv = getAbbrev(AbbrevID);
    113 
    114   for (unsigned i = 0, e = Abbv->getNumOperandInfos(); i != e; ++i) {
    115     const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
    116     if (Op.isLiteral())
    117       continue;
    118 
    119     if (Op.getEncoding() != BitCodeAbbrevOp::Array &&
    120         Op.getEncoding() != BitCodeAbbrevOp::Blob) {
    121       skipAbbreviatedField(*this, Op);
    122       continue;
    123     }
    124 
    125     if (Op.getEncoding() == BitCodeAbbrevOp::Array) {
    126       // Array case.  Read the number of elements as a vbr6.
    127       unsigned NumElts = ReadVBR(6);
    128 
    129       // Get the element encoding.
    130       assert(i+2 == e && "array op not second to last?");
    131       const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
    132 
    133       // Read all the elements.
    134       for (; NumElts; --NumElts)
    135         skipAbbreviatedField(*this, EltEnc);
    136       continue;
    137     }
    138 
    139     assert(Op.getEncoding() == BitCodeAbbrevOp::Blob);
    140     // Blob case.  Read the number of bytes as a vbr6.
    141     unsigned NumElts = ReadVBR(6);
    142     SkipToFourByteBoundary();  // 32-bit alignment
    143 
    144     // Figure out where the end of this blob will be including tail padding.
    145     size_t NewEnd = GetCurrentBitNo()+((NumElts+3)&~3)*8;
    146 
    147     // If this would read off the end of the bitcode file, just set the
    148     // record to empty and return.
    149     if (!canSkipToPos(NewEnd/8)) {
    150       NextChar = BitStream->getBitcodeBytes().getExtent();
    151       break;
    152     }
    153 
    154     // Skip over the blob.
    155     JumpToBit(NewEnd);
    156   }
    157 }
    158 
    159 unsigned BitstreamCursor::readRecord(unsigned AbbrevID,
    160                                      SmallVectorImpl<uint64_t> &Vals,
    161                                      StringRef *Blob) {
    162   if (AbbrevID == bitc::UNABBREV_RECORD) {
    163     unsigned Code = ReadVBR(6);
    164     unsigned NumElts = ReadVBR(6);
    165     for (unsigned i = 0; i != NumElts; ++i)
    166       Vals.push_back(ReadVBR64(6));
    167     return Code;
    168   }
    169 
    170   const BitCodeAbbrev *Abbv = getAbbrev(AbbrevID);
    171 
    172   // Read the record code first.
    173   assert(Abbv->getNumOperandInfos() != 0 && "no record code in abbreviation?");
    174   const BitCodeAbbrevOp &CodeOp = Abbv->getOperandInfo(0);
    175   unsigned Code;
    176   if (CodeOp.isLiteral())
    177     Code = CodeOp.getLiteralValue();
    178   else {
    179     if (CodeOp.getEncoding() == BitCodeAbbrevOp::Array ||
    180         CodeOp.getEncoding() == BitCodeAbbrevOp::Blob)
    181       report_fatal_error("Abbreviation starts with an Array or a Blob");
    182     Code = readAbbreviatedField(*this, CodeOp);
    183   }
    184 
    185   for (unsigned i = 1, e = Abbv->getNumOperandInfos(); i != e; ++i) {
    186     const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
    187     if (Op.isLiteral()) {
    188       Vals.push_back(Op.getLiteralValue());
    189       continue;
    190     }
    191 
    192     if (Op.getEncoding() != BitCodeAbbrevOp::Array &&
    193         Op.getEncoding() != BitCodeAbbrevOp::Blob) {
    194       Vals.push_back(readAbbreviatedField(*this, Op));
    195       continue;
    196     }
    197 
    198     if (Op.getEncoding() == BitCodeAbbrevOp::Array) {
    199       // Array case.  Read the number of elements as a vbr6.
    200       unsigned NumElts = ReadVBR(6);
    201 
    202       // Get the element encoding.
    203       if (i + 2 != e)
    204         report_fatal_error("Array op not second to last");
    205       const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
    206       if (!EltEnc.isEncoding())
    207         report_fatal_error(
    208             "Array element type has to be an encoding of a type");
    209       if (EltEnc.getEncoding() == BitCodeAbbrevOp::Array ||
    210           EltEnc.getEncoding() == BitCodeAbbrevOp::Blob)
    211         report_fatal_error("Array element type can't be an Array or a Blob");
    212 
    213       // Read all the elements.
    214       for (; NumElts; --NumElts)
    215         Vals.push_back(readAbbreviatedField(*this, EltEnc));
    216       continue;
    217     }
    218 
    219     assert(Op.getEncoding() == BitCodeAbbrevOp::Blob);
    220     // Blob case.  Read the number of bytes as a vbr6.
    221     unsigned NumElts = ReadVBR(6);
    222     SkipToFourByteBoundary();  // 32-bit alignment
    223 
    224     // Figure out where the end of this blob will be including tail padding.
    225     size_t CurBitPos = GetCurrentBitNo();
    226     size_t NewEnd = CurBitPos+((NumElts+3)&~3)*8;
    227 
    228     // If this would read off the end of the bitcode file, just set the
    229     // record to empty and return.
    230     if (!canSkipToPos(NewEnd/8)) {
    231       Vals.append(NumElts, 0);
    232       NextChar = BitStream->getBitcodeBytes().getExtent();
    233       break;
    234     }
    235 
    236     // Otherwise, inform the streamer that we need these bytes in memory.
    237     const char *Ptr = (const char*)
    238       BitStream->getBitcodeBytes().getPointer(CurBitPos/8, NumElts);
    239 
    240     // If we can return a reference to the data, do so to avoid copying it.
    241     if (Blob) {
    242       *Blob = StringRef(Ptr, NumElts);
    243     } else {
    244       // Otherwise, unpack into Vals with zero extension.
    245       for (; NumElts; --NumElts)
    246         Vals.push_back((unsigned char)*Ptr++);
    247     }
    248     // Skip over tail padding.
    249     JumpToBit(NewEnd);
    250   }
    251 
    252   return Code;
    253 }
    254 
    255 
    256 void BitstreamCursor::ReadAbbrevRecord() {
    257   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
    258   unsigned NumOpInfo = ReadVBR(5);
    259   for (unsigned i = 0; i != NumOpInfo; ++i) {
    260     bool IsLiteral = Read(1);
    261     if (IsLiteral) {
    262       Abbv->Add(BitCodeAbbrevOp(ReadVBR64(8)));
    263       continue;
    264     }
    265 
    266     BitCodeAbbrevOp::Encoding E = (BitCodeAbbrevOp::Encoding)Read(3);
    267     if (BitCodeAbbrevOp::hasEncodingData(E)) {
    268       uint64_t Data = ReadVBR64(5);
    269 
    270       // As a special case, handle fixed(0) (i.e., a fixed field with zero bits)
    271       // and vbr(0) as a literal zero.  This is decoded the same way, and avoids
    272       // a slow path in Read() to have to handle reading zero bits.
    273       if ((E == BitCodeAbbrevOp::Fixed || E == BitCodeAbbrevOp::VBR) &&
    274           Data == 0) {
    275         Abbv->Add(BitCodeAbbrevOp(0));
    276         continue;
    277       }
    278 
    279       if ((E == BitCodeAbbrevOp::Fixed || E == BitCodeAbbrevOp::VBR) &&
    280           Data > MaxChunkSize)
    281         report_fatal_error(
    282             "Fixed or VBR abbrev record with size > MaxChunkData");
    283 
    284       Abbv->Add(BitCodeAbbrevOp(E, Data));
    285     } else
    286       Abbv->Add(BitCodeAbbrevOp(E));
    287   }
    288 
    289   if (Abbv->getNumOperandInfos() == 0)
    290     report_fatal_error("Abbrev record with no operands");
    291   CurAbbrevs.push_back(Abbv);
    292 }
    293 
    294 bool BitstreamCursor::ReadBlockInfoBlock() {
    295   // If this is the second stream to get to the block info block, skip it.
    296   if (BitStream->hasBlockInfoRecords())
    297     return SkipBlock();
    298 
    299   if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return true;
    300 
    301   SmallVector<uint64_t, 64> Record;
    302   BitstreamReader::BlockInfo *CurBlockInfo = nullptr;
    303 
    304   // Read all the records for this module.
    305   while (1) {
    306     BitstreamEntry Entry = advanceSkippingSubblocks(AF_DontAutoprocessAbbrevs);
    307 
    308     switch (Entry.Kind) {
    309     case llvm::BitstreamEntry::SubBlock: // Handled for us already.
    310     case llvm::BitstreamEntry::Error:
    311       return true;
    312     case llvm::BitstreamEntry::EndBlock:
    313       return false;
    314     case llvm::BitstreamEntry::Record:
    315       // The interesting case.
    316       break;
    317     }
    318 
    319     // Read abbrev records, associate them with CurBID.
    320     if (Entry.ID == bitc::DEFINE_ABBREV) {
    321       if (!CurBlockInfo) return true;
    322       ReadAbbrevRecord();
    323 
    324       // ReadAbbrevRecord installs the abbrev in CurAbbrevs.  Move it to the
    325       // appropriate BlockInfo.
    326       CurBlockInfo->Abbrevs.push_back(std::move(CurAbbrevs.back()));
    327       CurAbbrevs.pop_back();
    328       continue;
    329     }
    330 
    331     // Read a record.
    332     Record.clear();
    333     switch (readRecord(Entry.ID, Record)) {
    334       default: break;  // Default behavior, ignore unknown content.
    335       case bitc::BLOCKINFO_CODE_SETBID:
    336         if (Record.size() < 1) return true;
    337         CurBlockInfo = &BitStream->getOrCreateBlockInfo((unsigned)Record[0]);
    338         break;
    339       case bitc::BLOCKINFO_CODE_BLOCKNAME: {
    340         if (!CurBlockInfo) return true;
    341         if (BitStream->isIgnoringBlockInfoNames()) break;  // Ignore name.
    342         std::string Name;
    343         for (unsigned i = 0, e = Record.size(); i != e; ++i)
    344           Name += (char)Record[i];
    345         CurBlockInfo->Name = Name;
    346         break;
    347       }
    348       case bitc::BLOCKINFO_CODE_SETRECORDNAME: {
    349         if (!CurBlockInfo) return true;
    350         if (BitStream->isIgnoringBlockInfoNames()) break;  // Ignore name.
    351         std::string Name;
    352         for (unsigned i = 1, e = Record.size(); i != e; ++i)
    353           Name += (char)Record[i];
    354         CurBlockInfo->RecordNames.push_back(std::make_pair((unsigned)Record[0],
    355                                                            Name));
    356         break;
    357       }
    358     }
    359   }
    360 }
    361 
    362