//===- BitstreamReader.h - Low-level bitstream reader interface -*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This header defines the BitstreamReader class. This class can be used to
// read an arbitrary bitstream, regardless of its contents.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_BITSTREAM_BITSTREAMREADER_H
#define LLVM_BITSTREAM_BITSTREAMREADER_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Bitstream/BitCodes.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/MemoryBufferRef.h"
#include <algorithm>
#include <cassert>
#include <climits>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <optional>
#include <string>
#include <utility>
#include <vector>
namespace llvm {
/// This class maintains the abbreviations read from a block info block.
class BitstreamBlockInfo {
public:
/// This contains information emitted to BLOCKINFO_BLOCK blocks. These
/// describe abbreviations that all blocks of the specified ID inherit.
struct BlockInfo {
unsigned BlockID = 0;
std::vector<std::shared_ptr<BitCodeAbbrev>> Abbrevs;
std::string Name;
std::vector<std::pair<unsigned, std::string>> RecordNames;
};
private:
std::vector<BlockInfo> BlockInfoRecords;
public:
/// If there is block info for the specified ID, return it, otherwise return
/// null.
const BlockInfo *getBlockInfo(unsigned BlockID) const {
// Common case, the most recent entry matches BlockID.
if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID)
return &BlockInfoRecords.back();
for (const BlockInfo &BI : BlockInfoRecords)
if (BI.BlockID == BlockID)
return &BI;
return nullptr;
}
BlockInfo &getOrCreateBlockInfo(unsigned BlockID) {
if (const BlockInfo *BI = getBlockInfo(BlockID))
return *const_cast<BlockInfo*>(BI);
// Otherwise, add a new record.
BlockInfoRecords.emplace_back();
BlockInfoRecords.back().BlockID = BlockID;
return BlockInfoRecords.back();
}
};
/// This represents a position within a bitstream. There may be multiple
/// independent cursors reading within one bitstream, each maintaining their
/// own local state.
class SimpleBitstreamCursor {
ArrayRef<uint8_t> BitcodeBytes;
size_t NextChar = 0;
public:
/// This is the current data we have pulled from the stream but have not
/// returned to the client. This is specifically and intentionally defined to
/// follow the word size of the host machine for efficiency. We use word_t in
/// places that are aware of this to make it perfectly explicit what is going
/// on.
using word_t = size_t;
private:
word_t CurWord = 0;
/// This is the number of bits in CurWord that are valid. This is always from
/// [0...bits_of(size_t)-1] inclusive.
unsigned BitsInCurWord = 0;
public:
SimpleBitstreamCursor() = default;
explicit SimpleBitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
: BitcodeBytes(BitcodeBytes) {}
explicit SimpleBitstreamCursor(StringRef BitcodeBytes)
: BitcodeBytes(arrayRefFromStringRef(BitcodeBytes)) {}
explicit SimpleBitstreamCursor(MemoryBufferRef BitcodeBytes)
: SimpleBitstreamCursor(BitcodeBytes.getBuffer()) {}
bool canSkipToPos(size_t pos) const {
// pos can be skipped to if it is a valid address or one byte past the end.
return pos <= BitcodeBytes.size();
}
bool AtEndOfStream() {
return BitsInCurWord == 0 && BitcodeBytes.size() <= NextChar;
}
/// Return the bit # of the bit we are reading.
uint64_t GetCurrentBitNo() const {
return NextChar*CHAR_BIT - BitsInCurWord;
}
// Return the byte # of the current bit.
uint64_t getCurrentByteNo() const { return GetCurrentBitNo() / 8; }
ArrayRef<uint8_t> getBitcodeBytes() const { return BitcodeBytes; }
/// Reset the stream to the specified bit number.
Error JumpToBit(uint64_t BitNo) {
size_t ByteNo = size_t(BitNo/8) & ~(sizeof(word_t)-1);
unsigned WordBitNo = unsigned(BitNo & (sizeof(word_t)*8-1));
assert(canSkipToPos(ByteNo) && "Invalid location");
// Move the cursor to the right word.
NextChar = ByteNo;
BitsInCurWord = 0;
// Skip over any bits that are already consumed.
if (WordBitNo) {
if (Expected<word_t> Res = Read(WordBitNo))
return Error::success();
else
return Res.takeError();
}
return Error::success();
}
/// Get a pointer into the bitstream at the specified byte offset.
const uint8_t *getPointerToByte(uint64_t ByteNo, uint64_t NumBytes) {
return BitcodeBytes.data() + ByteNo;
}
/// Get a pointer into the bitstream at the specified bit offset.
///
/// The bit offset must be on a byte boundary.
const uint8_t *getPointerToBit(uint64_t BitNo, uint64_t NumBytes) {
assert(!(BitNo % 8) && "Expected bit on byte boundary");
return getPointerToByte(BitNo / 8, NumBytes);
}
Error fillCurWord() {
if (NextChar >= BitcodeBytes.size())
return createStringError(std::errc::io_error,
"Unexpected end of file reading %u of %u bytes",
NextChar, BitcodeBytes.size());
// Read the next word from the stream.
const uint8_t *NextCharPtr = BitcodeBytes.data() + NextChar;
unsigned BytesRead;
if (BitcodeBytes.size() >= NextChar + sizeof(word_t)) {
BytesRead = sizeof(word_t);
CurWord =
support::endian::read<word_t, support::little, support::unaligned>(
NextCharPtr);
} else {
// Short read.
BytesRead = BitcodeBytes.size() - NextChar;
CurWord = 0;
for (unsigned B = 0; B != BytesRead; ++B)
CurWord |= uint64_t(NextCharPtr[B]) << (B * 8);
}
NextChar += BytesRead;
BitsInCurWord = BytesRead * 8;
return Error::success();
}
Expected<word_t> Read(unsigned NumBits) {
static const unsigned BitsInWord = sizeof(word_t) * 8;
assert(NumBits && NumBits <= BitsInWord &&
"Cannot return zero or more than BitsInWord bits!");
static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
// If the field is fully contained by CurWord, return it quickly.
if (BitsInCurWord >= NumBits) {
word_t R = CurWord & (~word_t(0) >> (BitsInWord - NumBits));
// Use a mask to avoid undefined behavior.
CurWord >>= (NumBits & Mask);
BitsInCurWord -= NumBits;
return R;
}
word_t R = BitsInCurWord ? CurWord : 0;
unsigned BitsLeft = NumBits - BitsInCurWord;
if (Error fillResult = fillCurWord())
return std::move(fillResult);
// If we run out of data, abort.
if (BitsLeft > BitsInCurWord)
return createStringError(std::errc::io_error,
"Unexpected end of file reading %u of %u bits",
BitsInCurWord, BitsLeft);
word_t R2 = CurWord & (~word_t(0) >> (BitsInWord - BitsLeft));
// Use a mask to avoid undefined behavior.
CurWord >>= (BitsLeft & Mask);
BitsInCurWord -= BitsLeft;
R |= R2 << (NumBits - BitsLeft);
return R;
}
Expected<uint32_t> ReadVBR(const unsigned NumBits) {
Expected<unsigned> MaybeRead = Read(NumBits);
if (!MaybeRead)
return MaybeRead;
uint32_t Piece = MaybeRead.get();
assert(NumBits <= 32 && NumBits >= 1 && "Invalid NumBits value");
const uint32_t MaskBitOrder = (NumBits - 1);
const uint32_t Mask = 1UL << MaskBitOrder;
if ((Piece & Mask) == 0)
return Piece;
uint32_t Result = 0;
unsigned NextBit = 0;
while (true) {
Result |= (Piece & (Mask - 1)) << NextBit;
if ((Piece & Mask) == 0)
return Result;
NextBit += NumBits-1;
if (NextBit >= 32)
return createStringError(std::errc::illegal_byte_sequence,
"Unterminated VBR");
MaybeRead = Read(NumBits);
if (!MaybeRead)
return MaybeRead;
Piece = MaybeRead.get();
}
}
// Read a VBR that may have a value up to 64-bits in size. The chunk size of
// the VBR must still be <= 32 bits though.
Expected<uint64_t> ReadVBR64(const unsigned NumBits) {
Expected<uint64_t> MaybeRead = Read(NumBits);
if (!MaybeRead)
return MaybeRead;
uint32_t Piece = MaybeRead.get();
assert(NumBits <= 32 && NumBits >= 1 && "Invalid NumBits value");
const uint32_t MaskBitOrder = (NumBits - 1);
const uint32_t Mask = 1UL << MaskBitOrder;
if ((Piece & Mask) == 0)
return uint64_t(Piece);
uint64_t Result = 0;
unsigned NextBit = 0;
while (true) {
Result |= uint64_t(Piece & (Mask - 1)) << NextBit;
if ((Piece & Mask) == 0)
return Result;
NextBit += NumBits-1;
if (NextBit >= 64)
return createStringError(std::errc::illegal_byte_sequence,
"Unterminated VBR");
MaybeRead = Read(NumBits);
if (!MaybeRead)
return MaybeRead;
Piece = MaybeRead.get();
}
}
void SkipToFourByteBoundary() {
// If word_t is 64-bits and if we've read less than 32 bits, just dump
// the bits we have up to the next 32-bit boundary.
if (sizeof(word_t) > 4 &&
BitsInCurWord >= 32) {
CurWord >>= BitsInCurWord-32;
BitsInCurWord = 32;
return;
}
BitsInCurWord = 0;
}
/// Return the size of the stream in bytes.
size_t SizeInBytes() const { return BitcodeBytes.size(); }
/// Skip to the end of the file.
void skipToEnd() { NextChar = BitcodeBytes.size(); }
/// Check whether a reservation of Size elements is plausible.
bool isSizePlausible(size_t Size) const {
// Don't allow reserving more elements than the number of bits, assuming
// at least one bit is needed to encode an element.
return Size < BitcodeBytes.size() * 8;
}
};
/// When advancing through a bitstream cursor, each advance can discover a few
/// different kinds of entries:
struct BitstreamEntry {
enum {
Error, // Malformed bitcode was found.
EndBlock, // We've reached the end of the current block, (or the end of the
// file, which is treated like a series of EndBlock records.
SubBlock, // This is the start of a new subblock of a specific ID.
Record // This is a record with a specific AbbrevID.
} Kind;
unsigned ID;
static BitstreamEntry getError() {
BitstreamEntry E; E.Kind = Error; return E;
}
static BitstreamEntry getEndBlock() {
BitstreamEntry E; E.Kind = EndBlock; return E;
}
static BitstreamEntry getSubBlock(unsigned ID) {
BitstreamEntry E; E.Kind = SubBlock; E.ID = ID; return E;
}
static BitstreamEntry getRecord(unsigned AbbrevID) {
BitstreamEntry E; E.Kind = Record; E.ID = AbbrevID; return E;
}
};
/// This represents a position within a bitcode file, implemented on top of a
/// SimpleBitstreamCursor.
///
/// Unlike iterators, BitstreamCursors are heavy-weight objects that should not
/// be passed by value.
class BitstreamCursor : SimpleBitstreamCursor {
// This is the declared size of code values used for the current block, in
// bits.
unsigned CurCodeSize = 2;
/// Abbrevs installed at in this block.
std::vector<std::shared_ptr<BitCodeAbbrev>> CurAbbrevs;
struct Block {
unsigned PrevCodeSize;
std::vector<std::shared_ptr<BitCodeAbbrev>> PrevAbbrevs;
explicit Block(unsigned PCS) : PrevCodeSize(PCS) {}
};
/// This tracks the codesize of parent blocks.
SmallVector<Block, 8> BlockScope;
BitstreamBlockInfo *BlockInfo = nullptr;
public:
static const size_t MaxChunkSize = 32;
BitstreamCursor() = default;
explicit BitstreamCursor(ArrayRef<uint8_t> BitcodeBytes)
: SimpleBitstreamCursor(BitcodeBytes) {}
explicit BitstreamCursor(StringRef BitcodeBytes)
: SimpleBitstreamCursor(BitcodeBytes) {}
explicit BitstreamCursor(MemoryBufferRef BitcodeBytes)
: SimpleBitstreamCursor(BitcodeBytes) {}
using SimpleBitstreamCursor::AtEndOfStream;
using SimpleBitstreamCursor::canSkipToPos;
using SimpleBitstreamCursor::fillCurWord;
using SimpleBitstreamCursor::getBitcodeBytes;
using SimpleBitstreamCursor::GetCurrentBitNo;
using SimpleBitstreamCursor::getCurrentByteNo;
using SimpleBitstreamCursor::getPointerToByte;
using SimpleBitstreamCursor::JumpToBit;
using SimpleBitstreamCursor::Read;
using SimpleBitstreamCursor::ReadVBR;
using SimpleBitstreamCursor::ReadVBR64;
using SimpleBitstreamCursor::SizeInBytes;
using SimpleBitstreamCursor::skipToEnd;
/// Return the number of bits used to encode an abbrev #.
unsigned getAbbrevIDWidth() const { return CurCodeSize; }
/// Flags that modify the behavior of advance().
enum {
/// If this flag is used, the advance() method does not automatically pop
/// the block scope when the end of a block is reached.
AF_DontPopBlockAtEnd = 1,
/// If this flag is used, abbrev entries are returned just like normal
/// records.
AF_DontAutoprocessAbbrevs = 2
};
/// Advance the current bitstream, returning the next entry in the stream.
Expected<BitstreamEntry> advance(unsigned Flags = 0) {
while (true) {
if (AtEndOfStream())
return BitstreamEntry::getError();
Expected<unsigned> MaybeCode = ReadCode();
if (!MaybeCode)
return MaybeCode.takeError();
unsigned Code = MaybeCode.get();
if (Code == bitc::END_BLOCK) {
// Pop the end of the block unless Flags tells us not to.
if (!(Flags & AF_DontPopBlockAtEnd) && ReadBlockEnd())
return BitstreamEntry::getError();
return BitstreamEntry::getEndBlock();
}
if (Code == bitc::ENTER_SUBBLOCK) {
if (Expected<unsigned> MaybeSubBlock = ReadSubBlockID())
return BitstreamEntry::getSubBlock(MaybeSubBlock.get());
else
return MaybeSubBlock.takeError();
}
if (Code == bitc::DEFINE_ABBREV &&
!(Flags & AF_DontAutoprocessAbbrevs)) {
// We read and accumulate abbrev's, the client can't do anything with
// them anyway.
if (Error Err = ReadAbbrevRecord())
return std::move(Err);
continue;
}
return BitstreamEntry::getRecord(Code);
}
}
/// This is a convenience function for clients that don't expect any
/// subblocks. This just skips over them automatically.
Expected<BitstreamEntry> advanceSkippingSubblocks(unsigned Flags = 0) {
while (true) {
// If we found a normal entry, return it.
Expected<BitstreamEntry> MaybeEntry = advance(Flags);
if (!MaybeEntry)
return MaybeEntry;
BitstreamEntry Entry = MaybeEntry.get();
if (Entry.Kind != BitstreamEntry::SubBlock)
return Entry;
// If we found a sub-block, just skip over it and check the next entry.
if (Error Err = SkipBlock())
return std::move(Err);
}
}
Expected<unsigned> ReadCode() { return Read(CurCodeSize); }
// Block header:
// [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
/// Having read the ENTER_SUBBLOCK code, read the BlockID for the block.
Expected<unsigned> ReadSubBlockID() { return ReadVBR(bitc::BlockIDWidth); }
/// Having read the ENTER_SUBBLOCK abbrevid and a BlockID, skip over the body
/// of this block.
Error SkipBlock() {
// Read and ignore the codelen value.
if (Expected<uint32_t> Res = ReadVBR(bitc::CodeLenWidth))
; // Since we are skipping this block, we don't care what code widths are
// used inside of it.
else
return Res.takeError();
SkipToFourByteBoundary();
Expected<unsigned> MaybeNum = Read(bitc::BlockSizeWidth);
if (!MaybeNum)
return MaybeNum.takeError();
size_t NumFourBytes = MaybeNum.get();
// Check that the block wasn't partially defined, and that the offset isn't
// bogus.
size_t SkipTo = GetCurrentBitNo() + NumFourBytes * 4 * 8;
if (AtEndOfStream())
return createStringError(std::errc::illegal_byte_sequence,
"can't skip block: already at end of stream");
if (!canSkipToPos(SkipTo / 8))
return createStringError(std::errc::illegal_byte_sequence,
"can't skip to bit %zu from %" PRIu64, SkipTo,
GetCurrentBitNo());
if (Error Res = JumpToBit(SkipTo))
return Res;
return Error::success();
}
/// Having read the ENTER_SUBBLOCK abbrevid, and enter the block.
Error EnterSubBlock(unsigned BlockID, unsigned *NumWordsP = nullptr);
bool ReadBlockEnd() {
if (BlockScope.empty()) return true;
// Block tail:
// [END_BLOCK, <align4bytes>]
SkipToFourByteBoundary();
popBlockScope();
return false;
}
private:
void popBlockScope() {
CurCodeSize = BlockScope.back().PrevCodeSize;
CurAbbrevs = std::move(BlockScope.back().PrevAbbrevs);
BlockScope.pop_back();
}
//===--------------------------------------------------------------------===//
// Record Processing
//===--------------------------------------------------------------------===//
public:
/// Return the abbreviation for the specified AbbrevId.
Expected<const BitCodeAbbrev *> getAbbrev(unsigned AbbrevID) {
unsigned AbbrevNo = AbbrevID - bitc::FIRST_APPLICATION_ABBREV;
if (AbbrevNo >= CurAbbrevs.size())
return createStringError(
std::errc::illegal_byte_sequence, "Invalid abbrev number");
return CurAbbrevs[AbbrevNo].get();
}
/// Read the current record and discard it, returning the code for the record.
Expected<unsigned> skipRecord(unsigned AbbrevID);
Expected<unsigned> readRecord(unsigned AbbrevID,
SmallVectorImpl<uint64_t> &Vals,
StringRef *Blob = nullptr);
//===--------------------------------------------------------------------===//
// Abbrev Processing
//===--------------------------------------------------------------------===//
Error ReadAbbrevRecord();
/// Read and return a block info block from the bitstream. If an error was
/// encountered, return std::nullopt.
///
/// \param ReadBlockInfoNames Whether to read block/record name information in
/// the BlockInfo block. Only llvm-bcanalyzer uses this.
Expected<std::optional<BitstreamBlockInfo>>
ReadBlockInfoBlock(bool ReadBlockInfoNames = false);
/// Set the block info to be used by this BitstreamCursor to interpret
/// abbreviated records.
void setBlockInfo(BitstreamBlockInfo *BI) { BlockInfo = BI; }
};
} // end llvm namespace
#endif // LLVM_BITSTREAM_BITSTREAMREADER_H