llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

//===- DWARFVerifier.cpp --------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "llvm/DebugInfo/DWARF/DWARFVerifier.h"
#include "llvm/DebugInfo/DWARF/DWARFCompileUnit.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
#include "llvm/DebugInfo/DWARF/DWARFDie.h"
#include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
#include "llvm/DebugInfo/DWARF/DWARFSection.h"
#include "llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#include <set>
#include <vector>

using namespace llvm;
using namespace dwarf;
using namespace object;

DWARFVerifier::DieRangeInfo::address_range_iterator
DWARFVerifier::DieRangeInfo::insert(const DWARFAddressRange &R) {
  auto Begin = Ranges.begin();
  auto End = Ranges.end();
  auto Pos = std::lower_bound(Begin, End, R);

  if (Pos != End) {
    if (Pos->intersects(R))
      return Pos;
    if (Pos != Begin) {
      auto Iter = Pos - 1;
      if (Iter->intersects(R))
        return Iter;
    }
  }

  Ranges.insert(Pos, R);
  return Ranges.end();
}

DWARFVerifier::DieRangeInfo::die_range_info_iterator
DWARFVerifier::DieRangeInfo::insert(const DieRangeInfo &RI) {
  auto End = Children.end();
  auto Iter = Children.begin();
  while (Iter != End) {
    if (Iter->intersects(RI))
      return Iter;
    ++Iter;
  }
  Children.insert(RI);
  return Children.end();
}

bool DWARFVerifier::DieRangeInfo::contains(const DieRangeInfo &RHS) const {
  // Both list of ranges are sorted so we can make this fast.

  if (Ranges.empty() || RHS.Ranges.empty())
    return false;

  // Since the ranges are sorted we can advance where we start searching with
  // this object's ranges as we traverse RHS.Ranges.
  auto End = Ranges.end();
  auto Iter = findRange(RHS.Ranges.front());

  // Now linearly walk the ranges in this object and see if they contain each
  // ranges from RHS.Ranges.
  for (const auto &R : RHS.Ranges) {
    while (Iter != End) {
      if (Iter->contains(R))
        break;
      ++Iter;
    }
    if (Iter == End)
      return false;
  }
  return true;
}

bool DWARFVerifier::DieRangeInfo::intersects(const DieRangeInfo &RHS) const {
  if (Ranges.empty() || RHS.Ranges.empty())
    return false;

  auto End = Ranges.end();
  auto Iter = findRange(RHS.Ranges.front());
  for (const auto &R : RHS.Ranges) {
    if (R.HighPC <= Iter->LowPC)
      continue;
    while (Iter != End) {
      if (Iter->intersects(R))
        return true;
      ++Iter;
    }
  }

  return false;
}

bool DWARFVerifier::verifyUnitHeader(const DWARFDataExtractor DebugInfoData,
                                     uint32_t *Offset, unsigned UnitIndex,
                                     uint8_t &UnitType, bool &isUnitDWARF64) {
  uint32_t AbbrOffset, Length;
  uint8_t AddrSize = 0;
  uint16_t Version;
  bool Success = true;

  bool ValidLength = false;
  bool ValidVersion = false;
  bool ValidAddrSize = false;
  bool ValidType = true;
  bool ValidAbbrevOffset = true;

  uint32_t OffsetStart = *Offset;
  Length = DebugInfoData.getU32(Offset);
  if (Length == UINT32_MAX) {
    isUnitDWARF64 = true;
    OS << format(
        "Unit[%d] is in 64-bit DWARF format; cannot verify from this point.\n",
        UnitIndex);
    return false;
  }
  Version = DebugInfoData.getU16(Offset);

  if (Version >= 5) {
    UnitType = DebugInfoData.getU8(Offset);
    AddrSize = DebugInfoData.getU8(Offset);
    AbbrOffset = DebugInfoData.getU32(Offset);
    ValidType = DWARFUnit::isValidUnitType(UnitType);
  } else {
    UnitType = 0;
    AbbrOffset = DebugInfoData.getU32(Offset);
    AddrSize = DebugInfoData.getU8(Offset);
  }

  if (!DCtx.getDebugAbbrev()->getAbbreviationDeclarationSet(AbbrOffset))
    ValidAbbrevOffset = false;

  ValidLength = DebugInfoData.isValidOffset(OffsetStart + Length + 3);
  ValidVersion = DWARFContext::isSupportedVersion(Version);
  ValidAddrSize = AddrSize == 4 || AddrSize == 8;
  if (!ValidLength || !ValidVersion || !ValidAddrSize || !ValidAbbrevOffset ||
      !ValidType) {
    Success = false;
    OS << format("Units[%d] - start offset: 0x%08x \n", UnitIndex, OffsetStart);
    if (!ValidLength)
      OS << "\tError: The length for this unit is too "
            "large for the .debug_info provided.\n";
    if (!ValidVersion)
      OS << "\tError: The 16 bit unit header version is not valid.\n";
    if (!ValidType)
      OS << "\tError: The unit type encoding is not valid.\n";
    if (!ValidAbbrevOffset)
      OS << "\tError: The offset into the .debug_abbrev section is "
            "not valid.\n";
    if (!ValidAddrSize)
      OS << "\tError: The address size is unsupported.\n";
  }
  *Offset = OffsetStart + Length + 4;
  return Success;
}

bool DWARFVerifier::verifyUnitContents(DWARFUnit Unit) {
  uint32_t NumUnitErrors = 0;
  unsigned NumDies = Unit.getNumDIEs();
  for (unsigned I = 0; I < NumDies; ++I) {
    auto Die = Unit.getDIEAtIndex(I);
    if (Die.getTag() == DW_TAG_null)
      continue;
    for (auto AttrValue : Die.attributes()) {
      NumUnitErrors += verifyDebugInfoAttribute(Die, AttrValue);
      NumUnitErrors += verifyDebugInfoForm(Die, AttrValue);
    }
  }

  DieRangeInfo RI;
  DWARFDie Die = Unit.getUnitDIE(/* ExtractUnitDIEOnly = */ false);
  NumUnitErrors += verifyDieRanges(Die, RI);
  return NumUnitErrors == 0;
}

unsigned DWARFVerifier::verifyAbbrevSection(const DWARFDebugAbbrev *Abbrev) {
  unsigned NumErrors = 0;
  if (Abbrev) {
    const DWARFAbbreviationDeclarationSet *AbbrDecls =
        Abbrev->getAbbreviationDeclarationSet(0);
    for (auto AbbrDecl : *AbbrDecls) {
      SmallDenseSet<uint16_t> AttributeSet;
      for (auto Attribute : AbbrDecl.attributes()) {
        auto Result = AttributeSet.insert(Attribute.Attr);
        if (!Result.second) {
          OS << "Error: Abbreviation declaration contains multiple "
             << AttributeString(Attribute.Attr) << " attributes.\n";
          AbbrDecl.dump(OS);
          ++NumErrors;
        }
      }
    }
  }
  return NumErrors;
}

bool DWARFVerifier::handleDebugAbbrev() {
  OS << "Verifying .debug_abbrev...\n";

  const DWARFObject &DObj = DCtx.getDWARFObj();
  bool noDebugAbbrev = DObj.getAbbrevSection().empty();
  bool noDebugAbbrevDWO = DObj.getAbbrevDWOSection().empty();

  if (noDebugAbbrev && noDebugAbbrevDWO) {
    return true;
  }

  unsigned NumErrors = 0;
  if (!noDebugAbbrev)
    NumErrors += verifyAbbrevSection(DCtx.getDebugAbbrev());

  if (!noDebugAbbrevDWO)
    NumErrors += verifyAbbrevSection(DCtx.getDebugAbbrevDWO());
  return NumErrors == 0;
}

bool DWARFVerifier::handleDebugInfo() {
  OS << "Verifying .debug_info Unit Header Chain...\n";

  const DWARFObject &DObj = DCtx.getDWARFObj();
  DWARFDataExtractor DebugInfoData(DObj, DObj.getInfoSection(),
                                   DCtx.isLittleEndian(), 0);
  uint32_t NumDebugInfoErrors = 0;
  uint32_t OffsetStart = 0, Offset = 0, UnitIdx = 0;
  uint8_t UnitType = 0;
  bool isUnitDWARF64 = false;
  bool isHeaderChainValid = true;
  bool hasDIE = DebugInfoData.isValidOffset(Offset);
  while (hasDIE) {
    OffsetStart = Offset;
    if (!verifyUnitHeader(DebugInfoData, &Offset, UnitIdx, UnitType,
                          isUnitDWARF64)) {
      isHeaderChainValid = false;
      if (isUnitDWARF64)
        break;
    } else {
      std::unique_ptr<DWARFUnit> Unit;
      switch (UnitType) {
      case dwarf::DW_UT_type:
      case dwarf::DW_UT_split_type: {
        DWARFUnitSection<DWARFTypeUnit> TUSection{};
        Unit.reset(new DWARFTypeUnit(
            DCtx, DObj.getInfoSection(), DCtx.getDebugAbbrev(),
            &DObj.getRangeSection(), DObj.getStringSection(),
            DObj.getStringOffsetSection(), &DObj.getAppleObjCSection(),
            DObj.getLineSection(), DCtx.isLittleEndian(), false, TUSection,
            nullptr));
        break;
      }
      case dwarf::DW_UT_skeleton:
      case dwarf::DW_UT_split_compile:
      case dwarf::DW_UT_compile:
      case dwarf::DW_UT_partial:
      // UnitType = 0 means that we are
      // verifying a compile unit in DWARF v4.
      case 0: {
        DWARFUnitSection<DWARFCompileUnit> CUSection{};
        Unit.reset(new DWARFCompileUnit(
            DCtx, DObj.getInfoSection(), DCtx.getDebugAbbrev(),
            &DObj.getRangeSection(), DObj.getStringSection(),
            DObj.getStringOffsetSection(), &DObj.getAppleObjCSection(),
            DObj.getLineSection(), DCtx.isLittleEndian(), false, CUSection,
            nullptr));
        break;
      }
      default: { llvm_unreachable("Invalid UnitType."); }
      }
      Unit->extract(DebugInfoData, &OffsetStart);
      if (!verifyUnitContents(*Unit))
        ++NumDebugInfoErrors;
    }
    hasDIE = DebugInfoData.isValidOffset(Offset);
    ++UnitIdx;
  }
  if (UnitIdx == 0 && !hasDIE) {
    OS << "Warning: .debug_info is empty.\n";
    isHeaderChainValid = true;
  }
  NumDebugInfoErrors += verifyDebugInfoReferences();
  return (isHeaderChainValid && NumDebugInfoErrors == 0);
}

unsigned DWARFVerifier::verifyDieRanges(const DWARFDie &Die,
                                        DieRangeInfo &ParentRI) {
  unsigned NumErrors = 0;

  if (!Die.isValid())
    return NumErrors;

  DWARFAddressRangesVector Ranges = Die.getAddressRanges();

  // Build RI for this DIE and check that ranges within this DIE do not
  // overlap.
  DieRangeInfo RI(Die);
  for (auto Range : Ranges) {
    if (!Range.valid()) {
      ++NumErrors;
      OS << format("error: Invalid address range [0x%08" PRIx64
                   " - 0x%08" PRIx64 "].\n",
                   Range.LowPC, Range.HighPC);
      continue;
    }

    // Verify that ranges don't intersect.
    const auto IntersectingRange = RI.insert(Range);
    if (IntersectingRange != RI.Ranges.end()) {
      ++NumErrors;
      OS << format("error: DIE has overlapping address ranges: [0x%08" PRIx64
                   " - 0x%08" PRIx64 "] and [0x%08" PRIx64 " - 0x%08" PRIx64
                   "].\n",
                   Range.LowPC, Range.HighPC, IntersectingRange->LowPC,
                   IntersectingRange->HighPC);
      break;
    }
  }

  // Verify that children don't intersect.
  const auto IntersectingChild = ParentRI.insert(RI);
  if (IntersectingChild != ParentRI.Children.end()) {
    ++NumErrors;
    OS << "error: DIEs have overlapping address ranges:";
    Die.dump(OS, 0);
    IntersectingChild->Die.dump(OS, 0);
    OS << "\n";
  }

  // Verify that ranges are contained within their parent.
  bool ShouldBeContained = !Ranges.empty() && !ParentRI.Ranges.empty() &&
                           !(Die.getTag() == DW_TAG_subprogram &&
                             ParentRI.Die.getTag() == DW_TAG_subprogram);
  if (ShouldBeContained && !ParentRI.contains(RI)) {
    ++NumErrors;
    OS << "error: DIE address ranges are not "
          "contained in its parent's ranges:";
    Die.dump(OS, 0);
    ParentRI.Die.dump(OS, 0);
    OS << "\n";
  }

  // Recursively check children.
  for (DWARFDie Child : Die)
    NumErrors += verifyDieRanges(Child, RI);

  return NumErrors;
}

unsigned DWARFVerifier::verifyDebugInfoAttribute(const DWARFDie &Die,
                                                 DWARFAttribute &AttrValue) {
  const DWARFObject &DObj = DCtx.getDWARFObj();
  unsigned NumErrors = 0;
  const auto Attr = AttrValue.Attr;
  switch (Attr) {
  case DW_AT_ranges:
    // Make sure the offset in the DW_AT_ranges attribute is valid.
    if (auto SectionOffset = AttrValue.Value.getAsSectionOffset()) {
      if (*SectionOffset >= DObj.getRangeSection().Data.size()) {
        ++NumErrors;
        OS << "error: DW_AT_ranges offset is beyond .debug_ranges "
              "bounds:\n";
        Die.dump(OS, 0, 0, DumpOpts);
        OS << "\n";
      }
    } else {
      ++NumErrors;
      OS << "error: DIE has invalid DW_AT_ranges encoding:\n";
      Die.dump(OS, 0, 0, DumpOpts);
      OS << "\n";
    }
    break;
  case DW_AT_stmt_list:
    // Make sure the offset in the DW_AT_stmt_list attribute is valid.
    if (auto SectionOffset = AttrValue.Value.getAsSectionOffset()) {
      if (*SectionOffset >= DObj.getLineSection().Data.size()) {
        ++NumErrors;
        OS << "error: DW_AT_stmt_list offset is beyond .debug_line "
              "bounds: "
           << format("0x%08" PRIx64, *SectionOffset) << "\n";
        Die.dump(OS, 0, 0, DumpOpts);
        OS << "\n";
      }
    } else {
      ++NumErrors;
      OS << "error: DIE has invalid DW_AT_stmt_list encoding:\n";
      Die.dump(OS, 0, 0, DumpOpts);
      OS << "\n";
    }
    break;

  default:
    break;
  }
  return NumErrors;
}

unsigned DWARFVerifier::verifyDebugInfoForm(const DWARFDie &Die,
                                            DWARFAttribute &AttrValue) {
  const DWARFObject &DObj = DCtx.getDWARFObj();
  unsigned NumErrors = 0;
  const auto Form = AttrValue.Value.getForm();
  switch (Form) {
  case DW_FORM_ref1:
  case DW_FORM_ref2:
  case DW_FORM_ref4:
  case DW_FORM_ref8:
  case DW_FORM_ref_udata: {
    // Verify all CU relative references are valid CU offsets.
    Optional<uint64_t> RefVal = AttrValue.Value.getAsReference();
    assert(RefVal);
    if (RefVal) {
      auto DieCU = Die.getDwarfUnit();
      auto CUSize = DieCU->getNextUnitOffset() - DieCU->getOffset();
      auto CUOffset = AttrValue.Value.getRawUValue();
      if (CUOffset >= CUSize) {
        ++NumErrors;
        OS << "error: " << FormEncodingString(Form) << " CU offset "
           << format("0x%08" PRIx64, CUOffset)
           << " is invalid (must be less than CU size of "
           << format("0x%08" PRIx32, CUSize) << "):\n";
        Die.dump(OS, 0, 0, DumpOpts);
        OS << "\n";
      } else {
        // Valid reference, but we will verify it points to an actual
        // DIE later.
        ReferenceToDIEOffsets[*RefVal].insert(Die.getOffset());
      }
    }
    break;
  }
  case DW_FORM_ref_addr: {
    // Verify all absolute DIE references have valid offsets in the
    // .debug_info section.
    Optional<uint64_t> RefVal = AttrValue.Value.getAsReference();
    assert(RefVal);
    if (RefVal) {
      if (*RefVal >= DObj.getInfoSection().Data.size()) {
        ++NumErrors;
        OS << "error: DW_FORM_ref_addr offset beyond .debug_info "
              "bounds:\n";
        Die.dump(OS, 0, 0, DumpOpts);
        OS << "\n";
      } else {
        // Valid reference, but we will verify it points to an actual
        // DIE later.
        ReferenceToDIEOffsets[*RefVal].insert(Die.getOffset());
      }
    }
    break;
  }
  case DW_FORM_strp: {
    auto SecOffset = AttrValue.Value.getAsSectionOffset();
    assert(SecOffset); // DW_FORM_strp is a section offset.
    if (SecOffset && *SecOffset >= DObj.getStringSection().size()) {
      ++NumErrors;
      OS << "error: DW_FORM_strp offset beyond .debug_str bounds:\n";
      Die.dump(OS, 0, 0, DumpOpts);
      OS << "\n";
    }
    break;
  }
  default:
    break;
  }
  return NumErrors;
}

unsigned DWARFVerifier::verifyDebugInfoReferences() {
  // Take all references and make sure they point to an actual DIE by
  // getting the DIE by offset and emitting an error
  OS << "Verifying .debug_info references...\n";
  unsigned NumErrors = 0;
  for (auto Pair : ReferenceToDIEOffsets) {
    auto Die = DCtx.getDIEForOffset(Pair.first);
    if (Die)
      continue;
    ++NumErrors;
    OS << "error: invalid DIE reference " << format("0x%08" PRIx64, Pair.first)
       << ". Offset is in between DIEs:\n";
    for (auto Offset : Pair.second) {
      auto ReferencingDie = DCtx.getDIEForOffset(Offset);
      ReferencingDie.dump(OS, 0, 0, DumpOpts);
      OS << "\n";
    }
    OS << "\n";
  }
  return NumErrors;
}

void DWARFVerifier::verifyDebugLineStmtOffsets() {
  std::map<uint64_t, DWARFDie> StmtListToDie;
  for (const auto &CU : DCtx.compile_units()) {
    auto Die = CU->getUnitDIE();
    // Get the attribute value as a section offset. No need to produce an
    // error here if the encoding isn't correct because we validate this in
    // the .debug_info verifier.
    auto StmtSectionOffset = toSectionOffset(Die.find(DW_AT_stmt_list));
    if (!StmtSectionOffset)
      continue;
    const uint32_t LineTableOffset = *StmtSectionOffset;
    auto LineTable = DCtx.getLineTableForUnit(CU.get());
    if (LineTableOffset < DCtx.getDWARFObj().getLineSection().Data.size()) {
      if (!LineTable) {
        ++NumDebugLineErrors;
        OS << "error: .debug_line[" << format("0x%08" PRIx32, LineTableOffset)
           << "] was not able to be parsed for CU:\n";
        Die.dump(OS, 0, 0, DumpOpts);
        OS << '\n';
        continue;
      }
    } else {
      // Make sure we don't get a valid line table back if the offset is wrong.
      assert(LineTable == nullptr);
      // Skip this line table as it isn't valid. No need to create an error
      // here because we validate this in the .debug_info verifier.
      continue;
    }
    auto Iter = StmtListToDie.find(LineTableOffset);
    if (Iter != StmtListToDie.end()) {
      ++NumDebugLineErrors;
      OS << "error: two compile unit DIEs, "
         << format("0x%08" PRIx32, Iter->second.getOffset()) << " and "
         << format("0x%08" PRIx32, Die.getOffset())
         << ", have the same DW_AT_stmt_list section offset:\n";
      Iter->second.dump(OS, 0, 0, DumpOpts);
      Die.dump(OS, 0, 0, DumpOpts);
      OS << '\n';
      // Already verified this line table before, no need to do it again.
      continue;
    }
    StmtListToDie[LineTableOffset] = Die;
  }
}

void DWARFVerifier::verifyDebugLineRows() {
  for (const auto &CU : DCtx.compile_units()) {
    auto Die = CU->getUnitDIE();
    auto LineTable = DCtx.getLineTableForUnit(CU.get());
    // If there is no line table we will have created an error in the
    // .debug_info verifier or in verifyDebugLineStmtOffsets().
    if (!LineTable)
      continue;

    // Verify prologue.
    uint32_t MaxFileIndex = LineTable->Prologue.FileNames.size();
    uint32_t MaxDirIndex = LineTable->Prologue.IncludeDirectories.size();
    uint32_t FileIndex = 1;
    StringMap<uint16_t> FullPathMap;
    for (const auto &FileName : LineTable->Prologue.FileNames) {
      // Verify directory index.
      if (FileName.DirIdx > MaxDirIndex) {
        ++NumDebugLineErrors;
        OS << "error: .debug_line["
           << format("0x%08" PRIx64,
                     *toSectionOffset(Die.find(DW_AT_stmt_list)))
           << "].prologue.file_names[" << FileIndex
           << "].dir_idx contains an invalid index: " << FileName.DirIdx
           << "\n";
      }

      // Check file paths for duplicates.
      std::string FullPath;
      const bool HasFullPath = LineTable->getFileNameByIndex(
          FileIndex, CU->getCompilationDir(),
          DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, FullPath);
      assert(HasFullPath && "Invalid index?");
      (void)HasFullPath;
      auto It = FullPathMap.find(FullPath);
      if (It == FullPathMap.end())
        FullPathMap[FullPath] = FileIndex;
      else if (It->second != FileIndex) {
        OS << "warning: .debug_line["
           << format("0x%08" PRIx64,
                     *toSectionOffset(Die.find(DW_AT_stmt_list)))
           << "].prologue.file_names[" << FileIndex
           << "] is a duplicate of file_names[" << It->second << "]\n";
      }

      FileIndex++;
    }

    // Verify rows.
    uint64_t PrevAddress = 0;
    uint32_t RowIndex = 0;
    for (const auto &Row : LineTable->Rows) {
      // Verify row address.
      if (Row.Address < PrevAddress) {
        ++NumDebugLineErrors;
        OS << "error: .debug_line["
           << format("0x%08" PRIx64,
                     *toSectionOffset(Die.find(DW_AT_stmt_list)))
           << "] row[" << RowIndex
           << "] decreases in address from previous row:\n";

        DWARFDebugLine::Row::dumpTableHeader(OS);
        if (RowIndex > 0)
          LineTable->Rows[RowIndex - 1].dump(OS);
        Row.dump(OS);
        OS << '\n';
      }

      // Verify file index.
      if (Row.File > MaxFileIndex) {
        ++NumDebugLineErrors;
        OS << "error: .debug_line["
           << format("0x%08" PRIx64,
                     *toSectionOffset(Die.find(DW_AT_stmt_list)))
           << "][" << RowIndex << "] has invalid file index " << Row.File
           << " (valid values are [1," << MaxFileIndex << "]):\n";
        DWARFDebugLine::Row::dumpTableHeader(OS);
        Row.dump(OS);
        OS << '\n';
      }
      if (Row.EndSequence)
        PrevAddress = 0;
      else
        PrevAddress = Row.Address;
      ++RowIndex;
    }
  }
}

bool DWARFVerifier::handleDebugLine() {
  NumDebugLineErrors = 0;
  OS << "Verifying .debug_line...\n";
  verifyDebugLineStmtOffsets();
  verifyDebugLineRows();
  return NumDebugLineErrors == 0;
}

unsigned DWARFVerifier::verifyAccelTable(const DWARFSection *AccelSection,
                                         DataExtractor *StrData,
                                         const char *SectionName) {
  unsigned NumErrors = 0;
  DWARFDataExtractor AccelSectionData(DCtx.getDWARFObj(), *AccelSection,
                                      DCtx.isLittleEndian(), 0);
  DWARFAcceleratorTable AccelTable(AccelSectionData, *StrData);

  OS << "Verifying " << SectionName << "...\n";
  // Verify that the fixed part of the header is not too short.

  if (!AccelSectionData.isValidOffset(AccelTable.getSizeHdr())) {
    OS << "\terror: Section is too small to fit a section header.\n";
    return 1;
  }
  // Verify that the section is not too short.
  if (!AccelTable.extract()) {
    OS << "\terror: Section is smaller than size described in section header.\n";
    return 1;
  }
  // Verify that all buckets have a valid hash index or are empty.
  uint32_t NumBuckets = AccelTable.getNumBuckets();
  uint32_t NumHashes = AccelTable.getNumHashes();

  uint32_t BucketsOffset =
      AccelTable.getSizeHdr() + AccelTable.getHeaderDataLength();
  uint32_t HashesBase = BucketsOffset + NumBuckets * 4;
  uint32_t OffsetsBase = HashesBase + NumHashes * 4;
  for (uint32_t BucketIdx = 0; BucketIdx < NumBuckets; ++BucketIdx) {
    uint32_t HashIdx = AccelSectionData.getU32(&BucketsOffset);
    if (HashIdx >= NumHashes && HashIdx != UINT32_MAX) {
      OS << format("\terror: Bucket[%d] has invalid hash index: %u.\n", BucketIdx,
                   HashIdx);
      ++NumErrors;
    }
  }
  uint32_t NumAtoms = AccelTable.getAtomsDesc().size();
  if (NumAtoms == 0) {
    OS << "\terror: no atoms; failed to read HashData.\n";
    return 1;
  }
  if (!AccelTable.validateForms()) {
    OS << "\terror: unsupported form; failed to read HashData.\n";
    return 1;
  }

  for (uint32_t HashIdx = 0; HashIdx < NumHashes; ++HashIdx) {
    uint32_t HashOffset = HashesBase + 4 * HashIdx;
    uint32_t DataOffset = OffsetsBase + 4 * HashIdx;
    uint32_t Hash = AccelSectionData.getU32(&HashOffset);
    uint32_t HashDataOffset = AccelSectionData.getU32(&DataOffset);
    if (!AccelSectionData.isValidOffsetForDataOfSize(HashDataOffset,
                                                     sizeof(uint64_t))) {
      OS << format("\terror: Hash[%d] has invalid HashData offset: 0x%08x.\n",
                   HashIdx, HashDataOffset);
      ++NumErrors;
    }

    uint32_t StrpOffset;
    uint32_t StringOffset;
    uint32_t StringCount = 0;
    unsigned Offset;
    unsigned Tag;
    while ((StrpOffset = AccelSectionData.getU32(&HashDataOffset)) != 0) {
      const uint32_t NumHashDataObjects =
          AccelSectionData.getU32(&HashDataOffset);
      for (uint32_t HashDataIdx = 0; HashDataIdx < NumHashDataObjects;
           ++HashDataIdx) {
        std::tie(Offset, Tag) = AccelTable.readAtoms(HashDataOffset);
        auto Die = DCtx.getDIEForOffset(Offset);
        if (!Die) {
          const uint32_t BucketIdx =
              NumBuckets ? (Hash % NumBuckets) : UINT32_MAX;
          StringOffset = StrpOffset;
          const char *Name = StrData->getCStr(&StringOffset);
          if (!Name)
            Name = "<NULL>";

          OS << format(
              "\terror: %s Bucket[%d] Hash[%d] = 0x%08x "
              "Str[%u] = 0x%08x "
              "DIE[%d] = 0x%08x is not a valid DIE offset for \"%s\".\n",
              SectionName, BucketIdx, HashIdx, Hash, StringCount, StrpOffset,
              HashDataIdx, Offset, Name);

          ++NumErrors;
          continue;
        }
        if ((Tag != dwarf::DW_TAG_null) && (Die.getTag() != Tag)) {
          OS << "\terror: Tag " << dwarf::TagString(Tag)
             << " in accelerator table does not match Tag "
             << dwarf::TagString(Die.getTag()) << " of DIE[" << HashDataIdx
             << "].\n";
          ++NumErrors;
        }
      }
      ++StringCount;
    }
  }
  return NumErrors;
}

bool DWARFVerifier::handleAccelTables() {
  const DWARFObject &D = DCtx.getDWARFObj();
  DataExtractor StrData(D.getStringSection(), DCtx.isLittleEndian(), 0);
  unsigned NumErrors = 0;
  if (!D.getAppleNamesSection().Data.empty())
    NumErrors +=
        verifyAccelTable(&D.getAppleNamesSection(), &StrData, ".apple_names");
  if (!D.getAppleTypesSection().Data.empty())
    NumErrors +=
        verifyAccelTable(&D.getAppleTypesSection(), &StrData, ".apple_types");
  if (!D.getAppleNamespacesSection().Data.empty())
    NumErrors += verifyAccelTable(&D.getAppleNamespacesSection(), &StrData,
                                  ".apple_namespaces");
  if (!D.getAppleObjCSection().Data.empty())
    NumErrors +=
        verifyAccelTable(&D.getAppleObjCSection(), &StrData, ".apple_objc");
  return NumErrors == 0;
}