include/llvm/Bitstream/BitstreamReader.h

   1 //===- BitstreamReader.h - Low-level bitstream reader interface -*- C++ -*-===//
   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 //
   9 // This header defines the BitstreamReader class.  This class can be used to
  10 // read an arbitrary bitstream, regardless of its contents.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_BITSTREAM_BITSTREAMREADER_H
  15 #define LLVM_BITSTREAM_BITSTREAMREADER_H
  16
  17 #include "llvm/ADT/ArrayRef.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/Bitstream/BitCodes.h"
  20 #include "llvm/Support/Endian.h"
  21 #include "llvm/Support/ErrorHandling.h"
  22 #include "llvm/Support/MathExtras.h"
  23 #include "llvm/Support/MemoryBuffer.h"
  24 #include <algorithm>
  25 #include <cassert>
  26 #include <climits>
  27 #include <cstddef>
  28 #include <cstdint>
  29 #include <memory>
  30 #include <string>
  31 #include <utility>
  32 #include <vector>
  33
  34 namespace llvm {
  35
  36 /// This class maintains the abbreviations read from a block info block.
  37 class BitstreamBlockInfo {
  38 public:
  39   /// This contains information emitted to BLOCKINFO_BLOCK blocks. These
  40   /// describe abbreviations that all blocks of the specified ID inherit.
  41   struct BlockInfo {
  42     unsigned BlockID;
  43     std::vector<std::shared_ptr<BitCodeAbbrev>> Abbrevs;
  44     std::string Name;
  45     std::vector<std::pair<unsigned, std::string>> RecordNames;
  46   };
  47
  48 private:
  49   std::vector<BlockInfo> BlockInfoRecords;
  50
  51 public:
  52   /// If there is block info for the specified ID, return it, otherwise return
  53   /// null.
  54   const BlockInfo *getBlockInfo(unsigned BlockID) const {
  55     // Common case, the most recent entry matches BlockID.
  56     if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
  57       return &BlockInfoRecords.back();
  58
  59     for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size());
  60          i != e; ++i)
  61       if (BlockInfoRecords[i].BlockID == BlockID)
  62         return &BlockInfoRecords[i];
  63     return nullptr;
  64   }
  65
  66   BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
  67     if (const BlockInfo *BI = getBlockInfo(BlockID))
  68       return *const_cast<BlockInfo*>(BI);
  69
  70     // Otherwise, add a new record.
  71     BlockInfoRecords.emplace_back();
  72     BlockInfoRecords.back().BlockID = BlockID;
  73     return BlockInfoRecords.back();
  74   }
  75 };
  76
  77 /// This represents a position within a bitstream. There may be multiple
  78 /// independent cursors reading within one bitstream, each maintaining their
  79 /// own local state.
  80 class SimpleBitstreamCursor {
  81   ArrayRef<uint8_t> BitcodeBytes;
  82   size_t NextChar = 0;
  83
  84 public:
  85   /// This is the current data we have pulled from the stream but have not
  86   /// returned to the client. This is specifically and intentionally defined to
  87   /// follow the word size of the host machine for efficiency. We use word_t in
  88   /// places that are aware of this to make it perfectly explicit what is going
  89   /// on.
  90   using word_t = size_t;
  91
  92 private:
  93   word_t CurWord = 0;
  94
  95   /// This is the number of bits in CurWord that are valid. This is always from
  96   /// [0...bits_of(size_t)-1] inclusive.
  97   unsigned BitsInCurWord = 0;
  98
  99 public:
 100   static const constexpr size_t MaxChunkSize = sizeof(word_t) * 8;
 101
 102   SimpleBitstreamCursor() = default;
 103   explicit SimpleBitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
 104       : BitcodeBytes(BitcodeBytes) {}
 105   explicit SimpleBitstreamCursor(StringRef BitcodeBytes)
 106       : BitcodeBytes(arrayRefFromStringRef(BitcodeBytes)) {}
 107   explicit SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
 108       : SimpleBitstreamCursor(BitcodeBytes.getBuffer()) {}
 109
 110   bool canSkipToPos(size_t pos) const {
 111     // pos can be skipped to if it is a valid address or one byte past the end.
 112     return pos <= BitcodeBytes.size();
 113   }
 114
 115   bool AtEndOfStream() {
 116     return BitsInCurWord == 0 && BitcodeBytes.size() <= NextChar;
 117   }
 118
 119   /// Return the bit # of the bit we are reading.
 120   uint64_t GetCurrentBitNo() const {
 121     return NextChar*CHAR_BIT - BitsInCurWord;
 122   }
 123
 124   // Return the byte # of the current bit.
 125   uint64_t getCurrentByteNo() const { return GetCurrentBitNo() / 8; }
 126
 127   ArrayRef<uint8_t> getBitcodeBytes() const { return BitcodeBytes; }
 128
 129   /// Reset the stream to the specified bit number.
 130   Error JumpToBit(uint64_t BitNo) {
 131     size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
 132     unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
 133     assert(canSkipToPos(ByteNo) && "Invalid location");
 134
 135     // Move the cursor to the right word.
 136     NextChar = ByteNo;
 137     BitsInCurWord = 0;
 138
 139     // Skip over any bits that are already consumed.
 140     if (WordBitNo) {
 141       if (Expected<word_t> Res = Read(WordBitNo))
 142         return Error::success();
 143       else
 144         return Res.takeError();
 145     }
 146
 147     return Error::success();
 148   }
 149
 150   /// Get a pointer into the bitstream at the specified byte offset.
 151   const uint8_t *getPointerToByte(uint64_t ByteNo, uint64_t NumBytes) {
 152     return BitcodeBytes.data() + ByteNo;
 153   }
 154
 155   /// Get a pointer into the bitstream at the specified bit offset.
 156   ///
 157   /// The bit offset must be on a byte boundary.
 158   const uint8_t *getPointerToBit(uint64_t BitNo, uint64_t NumBytes) {
 159     assert(!(BitNo % 8) && "Expected bit on byte boundary");
 160     return getPointerToByte(BitNo / 8, NumBytes);
 161   }
 162
 163   Error fillCurWord() {
 164     if (NextChar >= BitcodeBytes.size())
 165       return createStringError(std::errc::io_error,
 166                                "Unexpected end of file reading %u of %u bytes",
 167                                NextChar, BitcodeBytes.size());
 168
 169     // Read the next word from the stream.
 170     const uint8_t *NextCharPtr = BitcodeBytes.data() + NextChar;
 171     unsigned BytesRead;
 172     if (BitcodeBytes.size() >= NextChar + sizeof(word_t)) {
 173       BytesRead = sizeof(word_t);
 174       CurWord =
 175           support::endian::read<word_t, support::little, support::unaligned>(
 176               NextCharPtr);
 177     } else {
 178       // Short read.
 179       BytesRead = BitcodeBytes.size() - NextChar;
 180       CurWord = 0;
 181       for (unsigned B = 0; B != BytesRead; ++B)
 182         CurWord |= uint64_t(NextCharPtr[B]) << (B * 8);
 183     }
 184     NextChar += BytesRead;
 185     BitsInCurWord = BytesRead * 8;
 186     return Error::success();
 187   }
 188
 189   Expected<word_t> Read(unsigned NumBits) {
 190     static const unsigned BitsInWord = MaxChunkSize;
 191
 192     assert(NumBits && NumBits <= BitsInWord &&
 193            "Cannot return zero or more than BitsInWord bits!");
 194
 195     static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
 196
 197     // If the field is fully contained by CurWord, return it quickly.
 198     if (BitsInCurWord >= NumBits) {
 199       word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
 200
 201       // Use a mask to avoid undefined behavior.
 202       CurWord >>= (NumBits & Mask);
 203
 204       BitsInCurWord -= NumBits;
 205       return R;
 206     }
 207
 208     word_t R = BitsInCurWord ? CurWord : 0;
 209     unsigned BitsLeft = NumBits - BitsInCurWord;
 210
 211     if (Error fillResult = fillCurWord())
 212       return std::move(fillResult);
 213
 214     // If we run out of data, abort.
 215     if (BitsLeft > BitsInCurWord)
 216       return createStringError(std::errc::io_error,
 217                                "Unexpected end of file reading %u of %u bits",
 218                                BitsInCurWord, BitsLeft);
 219
 220     word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
 221
 222     // Use a mask to avoid undefined behavior.
 223     CurWord >>= (BitsLeft & Mask);
 224
 225     BitsInCurWord -= BitsLeft;
 226
 227     R |= R2 << (NumBits - BitsLeft);
 228
 229     return R;
 230   }
 231
 232   Expected<uint32_t> ReadVBR(unsigned NumBits) {
 233     Expected<unsigned> MaybeRead = Read(NumBits);
 234     if (!MaybeRead)
 235       return MaybeRead;
 236     uint32_t Piece = MaybeRead.get();
 237
 238     if ((Piece & (1U << (NumBits-1))) == 0)
 239       return Piece;
 240
 241     uint32_t Result = 0;
 242     unsigned NextBit = 0;
 243     while (true) {
 244       Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
 245
 246       if ((Piece & (1U << (NumBits-1))) == 0)
 247         return Result;
 248
 249       NextBit += NumBits-1;
 250       MaybeRead = Read(NumBits);
 251       if (!MaybeRead)
 252         return MaybeRead;
 253       Piece = MaybeRead.get();
 254     }
 255   }
 256
 257   // Read a VBR that may have a value up to 64-bits in size. The chunk size of
 258   // the VBR must still be <= 32 bits though.
 259   Expected<uint64_t> ReadVBR64(unsigned NumBits) {
 260     Expected<uint64_t> MaybeRead = Read(NumBits);
 261     if (!MaybeRead)
 262       return MaybeRead;
 263     uint32_t Piece = MaybeRead.get();
 264
 265     if ((Piece & (1U << (NumBits-1))) == 0)
 266       return uint64_t(Piece);
 267
 268     uint64_t Result = 0;
 269     unsigned NextBit = 0;
 270     while (true) {
 271       Result |= uint64_t(Piece & ((1U << (NumBits-1))-1)) << NextBit;
 272
 273       if ((Piece & (1U << (NumBits-1))) == 0)
 274         return Result;
 275
 276       NextBit += NumBits-1;
 277       MaybeRead = Read(NumBits);
 278       if (!MaybeRead)
 279         return MaybeRead;
 280       Piece = MaybeRead.get();
 281     }
 282   }
 283
 284   void SkipToFourByteBoundary() {
 285     // If word_t is 64-bits and if we've read less than 32 bits, just dump
 286     // the bits we have up to the next 32-bit boundary.
 287     if (sizeof(word_t) > 4 &&
 288         BitsInCurWord >= 32) {
 289       CurWord >>= BitsInCurWord-32;
 290       BitsInCurWord = 32;
 291       return;
 292     }
 293
 294     BitsInCurWord = 0;
 295   }
 296
 297   /// Return the size of the stream in bytes.
 298   size_t SizeInBytes() const { return BitcodeBytes.size(); }
 299
 300   /// Skip to the end of the file.
 301   void skipToEnd() { NextChar = BitcodeBytes.size(); }
 302 };
 303
 304 /// When advancing through a bitstream cursor, each advance can discover a few
 305 /// different kinds of entries:
 306 struct BitstreamEntry {
 307   enum {
 308     Error,    // Malformed bitcode was found.
 309     EndBlock, // We've reached the end of the current block, (or the end of the
 310               // file, which is treated like a series of EndBlock records.
 311     SubBlock, // This is the start of a new subblock of a specific ID.
 312     Record    // This is a record with a specific AbbrevID.
 313   } Kind;
 314
 315   unsigned ID;
 316
 317   static BitstreamEntry getError() {
 318     BitstreamEntry E; E.Kind = Error; return E;
 319   }
 320
 321   static BitstreamEntry getEndBlock() {
 322     BitstreamEntry E; E.Kind = EndBlock; return E;
 323   }
 324
 325   static BitstreamEntry getSubBlock(unsigned ID) {
 326     BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
 327   }
 328
 329   static BitstreamEntry getRecord(unsigned AbbrevID) {
 330     BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
 331   }
 332 };
 333
 334 /// This represents a position within a bitcode file, implemented on top of a
 335 /// SimpleBitstreamCursor.
 336 ///
 337 /// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
 338 /// be passed by value.
 339 class BitstreamCursor : SimpleBitstreamCursor {
 340   // This is the declared size of code values used for the current block, in
 341   // bits.
 342   unsigned CurCodeSize = 2;
 343
 344   /// Abbrevs installed at in this block.
 345   std::vector<std::shared_ptr<BitCodeAbbrev>> CurAbbrevs;
 346
 347   struct Block {
 348     unsigned PrevCodeSize;
 349     std::vector<std::shared_ptr<BitCodeAbbrev>> PrevAbbrevs;
 350
 351     explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
 352   };
 353
 354   /// This tracks the codesize of parent blocks.
 355   SmallVector<Block, 8> BlockScope;
 356
 357   BitstreamBlockInfo *BlockInfo = nullptr;
 358
 359 public:
 360   static const size_t MaxChunkSize = sizeof(word_t) * 8;
 361
 362   BitstreamCursor() = default;
 363   explicit BitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
 364       : SimpleBitstreamCursor(BitcodeBytes) {}
 365   explicit BitstreamCursor(StringRef BitcodeBytes)
 366       : SimpleBitstreamCursor(BitcodeBytes) {}
 367   explicit BitstreamCursor(MemoryBufferRef BitcodeBytes)
 368       : SimpleBitstreamCursor(BitcodeBytes) {}
 369
 370   using SimpleBitstreamCursor::AtEndOfStream;
 371   using SimpleBitstreamCursor::canSkipToPos;
 372   using SimpleBitstreamCursor::fillCurWord;
 373   using SimpleBitstreamCursor::getBitcodeBytes;
 374   using SimpleBitstreamCursor::GetCurrentBitNo;
 375   using SimpleBitstreamCursor::getCurrentByteNo;
 376   using SimpleBitstreamCursor::getPointerToByte;
 377   using SimpleBitstreamCursor::JumpToBit;
 378   using SimpleBitstreamCursor::Read;
 379   using SimpleBitstreamCursor::ReadVBR;
 380   using SimpleBitstreamCursor::ReadVBR64;
 381   using SimpleBitstreamCursor::SizeInBytes;
 382   using SimpleBitstreamCursor::skipToEnd;
 383
 384   /// Return the number of bits used to encode an abbrev #.
 385   unsigned getAbbrevIDWidth() const { return CurCodeSize; }
 386
 387   /// Flags that modify the behavior of advance().
 388   enum {
 389     /// If this flag is used, the advance() method does not automatically pop
 390     /// the block scope when the end of a block is reached.
 391     AF_DontPopBlockAtEnd = 1,
 392
 393     /// If this flag is used, abbrev entries are returned just like normal
 394     /// records.
 395     AF_DontAutoprocessAbbrevs = 2
 396   };
 397
 398   /// Advance the current bitstream, returning the next entry in the stream.
 399   Expected<BitstreamEntry> advance(unsigned Flags = 0) {
 400     while (true) {
 401       if (AtEndOfStream())
 402         return BitstreamEntry::getError();
 403
 404       Expected<unsigned> MaybeCode = ReadCode();
 405       if (!MaybeCode)
 406         return MaybeCode.takeError();
 407       unsigned Code = MaybeCode.get();
 408
 409       if (Code == bitc::END_BLOCK) {
 410         // Pop the end of the block unless Flags tells us not to.
 411         if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
 412           return BitstreamEntry::getError();
 413         return BitstreamEntry::getEndBlock();
 414       }
 415
 416       if (Code == bitc::ENTER_SUBBLOCK) {
 417         if (Expected<unsigned> MaybeSubBlock = ReadSubBlockID())
 418           return BitstreamEntry::getSubBlock(MaybeSubBlock.get());
 419         else
 420           return MaybeSubBlock.takeError();
 421       }
 422
 423       if (Code == bitc::DEFINE_ABBREV &&
 424           !(Flags & AF_DontAutoprocessAbbrevs)) {
 425         // We read and accumulate abbrev's, the client can't do anything with
 426         // them anyway.
 427         if (Error Err = ReadAbbrevRecord())
 428           return std::move(Err);
 429         continue;
 430       }
 431
 432       return BitstreamEntry::getRecord(Code);
 433     }
 434   }
 435
 436   /// This is a convenience function for clients that don't expect any
 437   /// subblocks. This just skips over them automatically.
 438   Expected<BitstreamEntry> advanceSkippingSubblocks(unsigned Flags = 0) {
 439     while (true) {
 440       // If we found a normal entry, return it.
 441       Expected<BitstreamEntry> MaybeEntry = advance(Flags);
 442       if (!MaybeEntry)
 443         return MaybeEntry;
 444       BitstreamEntry Entry = MaybeEntry.get();
 445
 446       if (Entry.Kind != BitstreamEntry::SubBlock)
 447         return Entry;
 448
 449       // If we found a sub-block, just skip over it and check the next entry.
 450       if (Error Err = SkipBlock())
 451         return std::move(Err);
 452     }
 453   }
 454
 455   Expected<unsigned> ReadCode() { return Read(CurCodeSize); }
 456
 457   // Block header:
 458   //    [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
 459
 460   /// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
 461   Expected<unsigned> ReadSubBlockID() { return ReadVBR(bitc::BlockIDWidth); }
 462
 463   /// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
 464   /// of this block.
 465   Error SkipBlock() {
 466     // Read and ignore the codelen value.
 467     if (Expected<uint32_t> Res = ReadVBR(bitc::CodeLenWidth))
 468       ; // Since we are skipping this block, we don't care what code widths are
 469         // used inside of it.
 470     else
 471       return Res.takeError();
 472
 473     SkipToFourByteBoundary();
 474     Expected<unsigned> MaybeNum = Read(bitc::BlockSizeWidth);
 475     if (!MaybeNum)
 476       return MaybeNum.takeError();
 477     size_t NumFourBytes = MaybeNum.get();
 478
 479     // Check that the block wasn't partially defined, and that the offset isn't
 480     // bogus.
 481     size_t SkipTo = GetCurrentBitNo() + NumFourBytes * 4 * 8;
 482     if (AtEndOfStream())
 483       return createStringError(std::errc::illegal_byte_sequence,
 484                                "can't skip block: already at end of stream");
 485     if (!canSkipToPos(SkipTo / 8))
 486       return createStringError(std::errc::illegal_byte_sequence,
 487                                "can't skip to bit %zu from %" PRIu64, SkipTo,
 488                                GetCurrentBitNo());
 489
 490     if (Error Res = JumpToBit(SkipTo))
 491       return Res;
 492
 493     return Error::success();
 494   }
 495
 496   /// Having read the ENTER_SUBBLOCK abbrevid, and enter the block.
 497   Error EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
 498
 499   bool ReadBlockEnd() {
 500     if (BlockScope.empty()) return true;
 501
 502     // Block tail:
 503     //    [END_BLOCK, <align4bytes>]
 504     SkipToFourByteBoundary();
 505
 506     popBlockScope();
 507     return false;
 508   }
 509
 510 private:
 511   void popBlockScope() {
 512     CurCodeSize = BlockScope.back().PrevCodeSize;
 513
 514     CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
 515     BlockScope.pop_back();
 516   }
 517
 518   //===--------------------------------------------------------------------===//
 519   // Record Processing
 520   //===--------------------------------------------------------------------===//
 521
 522 public:
 523   /// Return the abbreviation for the specified AbbrevId.
 524   const BitCodeAbbrev *getAbbrev(unsigned AbbrevID) {
 525     unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
 526     if (AbbrevNo >= CurAbbrevs.size())
 527       report_fatal_error("Invalid abbrev number");
 528     return CurAbbrevs[AbbrevNo].get();
 529   }
 530
 531   /// Read the current record and discard it, returning the code for the record.
 532   Expected<unsigned> skipRecord(unsigned AbbrevID);
 533
 534   Expected<unsigned> readRecord(unsigned AbbrevID,
 535                                 SmallVectorImpl<uint64_t> &Vals,
 536                                 StringRef *Blob = nullptr);
 537
 538   //===--------------------------------------------------------------------===//
 539   // Abbrev Processing
 540   //===--------------------------------------------------------------------===//
 541   Error ReadAbbrevRecord();
 542
 543   /// Read and return a block info block from the bitstream. If an error was
 544   /// encountered, return None.
 545   ///
 546   /// \param ReadBlockInfoNames Whether to read block/record name information in
 547   /// the BlockInfo block. Only llvm-bcanalyzer uses this.
 548   Expected<Optional<BitstreamBlockInfo>>
 549   ReadBlockInfoBlock(bool ReadBlockInfoNames = false);
 550
 551   /// Set the block info to be used by this BitstreamCursor to interpret
 552   /// abbreviated records.
 553   void setBlockInfo(BitstreamBlockInfo *BI) { BlockInfo = BI; }
 554 };
 555
 556 } // end llvm namespace
 557
 558 #endif // LLVM_BITSTREAM_BITSTREAMREADER_H