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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           getBitStreamReader()->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       // Decode the value as we are commanded.
    135       switch (EltEnc.getEncoding()) {
    136       default:
    137         report_fatal_error("Array element type can't be an Array or a Blob");
    138       case BitCodeAbbrevOp::Fixed:
    139         assert((unsigned)Op.getEncodingData() <= MaxChunkSize);
    140         for (; NumElts; --NumElts)
    141           Read((unsigned)EltEnc.getEncodingData());
    142         break;
    143       case BitCodeAbbrevOp::VBR:
    144         assert((unsigned)Op.getEncodingData() <= MaxChunkSize);
    145         for (; NumElts; --NumElts)
    146           ReadVBR64((unsigned)EltEnc.getEncodingData());
    147         break;
    148       case BitCodeAbbrevOp::Char6:
    149         for (; NumElts; --NumElts)
    150           Read(6);
    151         break;
    152       }
    153       continue;
    154     }
    155 
    156     assert(Op.getEncoding() == BitCodeAbbrevOp::Blob);
    157     // Blob case.  Read the number of bytes as a vbr6.
    158     unsigned NumElts = ReadVBR(6);
    159     SkipToFourByteBoundary();  // 32-bit alignment
    160 
    161     // Figure out where the end of this blob will be including tail padding.
    162     size_t NewEnd = GetCurrentBitNo()+((NumElts+3)&~3)*8;
    163 
    164     // If this would read off the end of the bitcode file, just set the
    165     // record to empty and return.
    166     if (!canSkipToPos(NewEnd/8)) {
    167       skipToEnd();
    168       break;
    169     }
    170 
    171     // Skip over the blob.
    172     JumpToBit(NewEnd);
    173   }
    174 }
    175 
    176 unsigned BitstreamCursor::readRecord(unsigned AbbrevID,
    177                                      SmallVectorImpl<uint64_t> &Vals,
    178                                      StringRef *Blob) {
    179   if (AbbrevID == bitc::UNABBREV_RECORD) {
    180     unsigned Code = ReadVBR(6);
    181     unsigned NumElts = ReadVBR(6);
    182     for (unsigned i = 0; i != NumElts; ++i)
    183       Vals.push_back(ReadVBR64(6));
    184     return Code;
    185   }
    186 
    187   const BitCodeAbbrev *Abbv = getAbbrev(AbbrevID);
    188 
    189   // Read the record code first.
    190   assert(Abbv->getNumOperandInfos() != 0 && "no record code in abbreviation?");
    191   const BitCodeAbbrevOp &CodeOp = Abbv->getOperandInfo(0);
    192   unsigned Code;
    193   if (CodeOp.isLiteral())
    194     Code = CodeOp.getLiteralValue();
    195   else {
    196     if (CodeOp.getEncoding() == BitCodeAbbrevOp::Array ||
    197         CodeOp.getEncoding() == BitCodeAbbrevOp::Blob)
    198       report_fatal_error("Abbreviation starts with an Array or a Blob");
    199     Code = readAbbreviatedField(*this, CodeOp);
    200   }
    201 
    202   for (unsigned i = 1, e = Abbv->getNumOperandInfos(); i != e; ++i) {
    203     const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
    204     if (Op.isLiteral()) {
    205       Vals.push_back(Op.getLiteralValue());
    206       continue;
    207     }
    208 
    209     if (Op.getEncoding() != BitCodeAbbrevOp::Array &&
    210         Op.getEncoding() != BitCodeAbbrevOp::Blob) {
    211       Vals.push_back(readAbbreviatedField(*this, Op));
    212       continue;
    213     }
    214 
    215     if (Op.getEncoding() == BitCodeAbbrevOp::Array) {
    216       // Array case.  Read the number of elements as a vbr6.
    217       unsigned NumElts = ReadVBR(6);
    218 
    219       // Get the element encoding.
    220       if (i + 2 != e)
    221         report_fatal_error("Array op not second to last");
    222       const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
    223       if (!EltEnc.isEncoding())
    224         report_fatal_error(
    225             "Array element type has to be an encoding of a type");
    226 
    227       // Read all the elements.
    228       switch (EltEnc.getEncoding()) {
    229       default:
    230         report_fatal_error("Array element type can't be an Array or a Blob");
    231       case BitCodeAbbrevOp::Fixed:
    232         for (; NumElts; --NumElts)
    233           Vals.push_back(Read((unsigned)EltEnc.getEncodingData()));
    234         break;
    235       case BitCodeAbbrevOp::VBR:
    236         for (; NumElts; --NumElts)
    237           Vals.push_back(ReadVBR64((unsigned)EltEnc.getEncodingData()));
    238         break;
    239       case BitCodeAbbrevOp::Char6:
    240         for (; NumElts; --NumElts)
    241           Vals.push_back(BitCodeAbbrevOp::DecodeChar6(Read(6)));
    242       }
    243       continue;
    244     }
    245 
    246     assert(Op.getEncoding() == BitCodeAbbrevOp::Blob);
    247     // Blob case.  Read the number of bytes as a vbr6.
    248     unsigned NumElts = ReadVBR(6);
    249     SkipToFourByteBoundary();  // 32-bit alignment
    250 
    251     // Figure out where the end of this blob will be including tail padding.
    252     size_t CurBitPos = GetCurrentBitNo();
    253     size_t NewEnd = CurBitPos+((NumElts+3)&~3)*8;
    254 
    255     // If this would read off the end of the bitcode file, just set the
    256     // record to empty and return.
    257     if (!canSkipToPos(NewEnd/8)) {
    258       Vals.append(NumElts, 0);
    259       skipToEnd();
    260       break;
    261     }
    262 
    263     // Otherwise, inform the streamer that we need these bytes in memory.  Skip
    264     // over tail padding first, in case jumping to NewEnd invalidates the Blob
    265     // pointer.
    266     JumpToBit(NewEnd);
    267     const char *Ptr = (const char *)getPointerToBit(CurBitPos, NumElts);
    268 
    269     // If we can return a reference to the data, do so to avoid copying it.
    270     if (Blob) {
    271       *Blob = StringRef(Ptr, NumElts);
    272     } else {
    273       // Otherwise, unpack into Vals with zero extension.
    274       for (; NumElts; --NumElts)
    275         Vals.push_back((unsigned char)*Ptr++);
    276     }
    277   }
    278 
    279   return Code;
    280 }
    281 
    282 
    283 void BitstreamCursor::ReadAbbrevRecord() {
    284   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
    285   unsigned NumOpInfo = ReadVBR(5);
    286   for (unsigned i = 0; i != NumOpInfo; ++i) {
    287     bool IsLiteral = Read(1);
    288     if (IsLiteral) {
    289       Abbv->Add(BitCodeAbbrevOp(ReadVBR64(8)));
    290       continue;
    291     }
    292 
    293     BitCodeAbbrevOp::Encoding E = (BitCodeAbbrevOp::Encoding)Read(3);
    294     if (BitCodeAbbrevOp::hasEncodingData(E)) {
    295       uint64_t Data = ReadVBR64(5);
    296 
    297       // As a special case, handle fixed(0) (i.e., a fixed field with zero bits)
    298       // and vbr(0) as a literal zero.  This is decoded the same way, and avoids
    299       // a slow path in Read() to have to handle reading zero bits.
    300       if ((E == BitCodeAbbrevOp::Fixed || E == BitCodeAbbrevOp::VBR) &&
    301           Data == 0) {
    302         Abbv->Add(BitCodeAbbrevOp(0));
    303         continue;
    304       }
    305 
    306       if ((E == BitCodeAbbrevOp::Fixed || E == BitCodeAbbrevOp::VBR) &&
    307           Data > MaxChunkSize)
    308         report_fatal_error(
    309             "Fixed or VBR abbrev record with size > MaxChunkData");
    310 
    311       Abbv->Add(BitCodeAbbrevOp(E, Data));
    312     } else
    313       Abbv->Add(BitCodeAbbrevOp(E));
    314   }
    315 
    316   if (Abbv->getNumOperandInfos() == 0)
    317     report_fatal_error("Abbrev record with no operands");
    318   CurAbbrevs.push_back(Abbv);
    319 }
    320 
    321 bool BitstreamCursor::ReadBlockInfoBlock() {
    322   // If this is the second stream to get to the block info block, skip it.
    323   if (getBitStreamReader()->hasBlockInfoRecords())
    324     return SkipBlock();
    325 
    326   if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return true;
    327 
    328   SmallVector<uint64_t, 64> Record;
    329   BitstreamReader::BlockInfo *CurBlockInfo = nullptr;
    330 
    331   // Read all the records for this module.
    332   while (1) {
    333     BitstreamEntry Entry = advanceSkippingSubblocks(AF_DontAutoprocessAbbrevs);
    334 
    335     switch (Entry.Kind) {
    336     case llvm::BitstreamEntry::SubBlock: // Handled for us already.
    337     case llvm::BitstreamEntry::Error:
    338       return true;
    339     case llvm::BitstreamEntry::EndBlock:
    340       return false;
    341     case llvm::BitstreamEntry::Record:
    342       // The interesting case.
    343       break;
    344     }
    345 
    346     // Read abbrev records, associate them with CurBID.
    347     if (Entry.ID == bitc::DEFINE_ABBREV) {
    348       if (!CurBlockInfo) return true;
    349       ReadAbbrevRecord();
    350 
    351       // ReadAbbrevRecord installs the abbrev in CurAbbrevs.  Move it to the
    352       // appropriate BlockInfo.
    353       CurBlockInfo->Abbrevs.push_back(std::move(CurAbbrevs.back()));
    354       CurAbbrevs.pop_back();
    355       continue;
    356     }
    357 
    358     // Read a record.
    359     Record.clear();
    360     switch (readRecord(Entry.ID, Record)) {
    361       default: break;  // Default behavior, ignore unknown content.
    362       case bitc::BLOCKINFO_CODE_SETBID:
    363         if (Record.size() < 1) return true;
    364         CurBlockInfo =
    365             &getBitStreamReader()->getOrCreateBlockInfo((unsigned)Record[0]);
    366         break;
    367       case bitc::BLOCKINFO_CODE_BLOCKNAME: {
    368         if (!CurBlockInfo) return true;
    369         if (getBitStreamReader()->isIgnoringBlockInfoNames())
    370           break; // Ignore name.
    371         std::string Name;
    372         for (unsigned i = 0, e = Record.size(); i != e; ++i)
    373           Name += (char)Record[i];
    374         CurBlockInfo->Name = Name;
    375         break;
    376       }
    377       case bitc::BLOCKINFO_CODE_SETRECORDNAME: {
    378         if (!CurBlockInfo) return true;
    379         if (getBitStreamReader()->isIgnoringBlockInfoNames())
    380           break; // Ignore name.
    381         std::string Name;
    382         for (unsigned i = 1, e = Record.size(); i != e; ++i)
    383           Name += (char)Record[i];
    384         CurBlockInfo->RecordNames.push_back(std::make_pair((unsigned)Record[0],
    385                                                            Name));
    386         break;
    387       }
    388     }
    389   }
    390 }
    391 
    392