DWP.cpp

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//===-- llvm-dwp.cpp - Split DWARF merging tool for llvm ------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// A utility for merging DWARF 5 Split DWARF .dwo files into .dwp (DWARF
// package files).
//
//===----------------------------------------------------------------------===//
#include "llvm/DWP/DWP.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/DWP/DWPError.h"
#include "llvm/DWP/ELFWriter.h"
#include "llvm/Object/Decompressor.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/EndianStream.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include <limits>
 
using namespace llvm;
using namespace llvm::object;
 
// Returns the size of debug_str_offsets section headers in bytes.
static uint64_t debugStrOffsetsHeaderSize(DataExtractor StrOffsetsData,
                                          uint16_t DwarfVersion) {
  if (DwarfVersion <= 4)
    return 0; // There is no header before dwarf 5.
  uint64_t Offset = 0;
  uint64_t Length = StrOffsetsData.getU32(&Offset);
  if (Length == llvm::dwarf::DW_LENGTH_DWARF64)
    return 16; // unit length: 12 bytes, version: 2 bytes, padding: 2 bytes.
  return 8;    // unit length: 4 bytes, version: 2 bytes, padding: 2 bytes.
}
 
static uint64_t getCUAbbrev(StringRef Abbrev, uint64_t AbbrCode) {
  uint64_t Offset = 0;
  DataExtractor AbbrevData(Abbrev, true, 0);
  while (AbbrevData.getULEB128(&Offset) != AbbrCode) {
    // Tag
    AbbrevData.getULEB128(&Offset);
    // DW_CHILDREN
    AbbrevData.getU8(&Offset);
    // Attributes
    while (AbbrevData.getULEB128(&Offset) | AbbrevData.getULEB128(&Offset))
      ;
  }
  return Offset;
}
 
static Expected<const char *>
getIndexedString(dwarf::Form Form, DataExtractor InfoData, uint64_t &InfoOffset,
                 StringRef StrOffsets, StringRef Str, uint16_t Version) {
  if (Form == dwarf::DW_FORM_string)
    return InfoData.getCStr(&InfoOffset);
  uint64_t StrIndex;
  switch (Form) {
  case dwarf::DW_FORM_strx1:
    StrIndex = InfoData.getU8(&InfoOffset);
    break;
  case dwarf::DW_FORM_strx2:
    StrIndex = InfoData.getU16(&InfoOffset);
    break;
  case dwarf::DW_FORM_strx3:
    StrIndex = InfoData.getU24(&InfoOffset);
    break;
  case dwarf::DW_FORM_strx4:
    StrIndex = InfoData.getU32(&InfoOffset);
    break;
  case dwarf::DW_FORM_strx:
  case dwarf::DW_FORM_GNU_str_index:
    StrIndex = InfoData.getULEB128(&InfoOffset);
    break;
  default:
    return make_error<DWPError>(
        "string field must be encoded with one of the following: "
        "DW_FORM_string, DW_FORM_strx, DW_FORM_strx1, DW_FORM_strx2, "
        "DW_FORM_strx3, DW_FORM_strx4, or DW_FORM_GNU_str_index.");
  }
  DataExtractor StrOffsetsData(StrOffsets, true, 0);
  uint64_t StrOffsetsOffset = 4 * StrIndex;
  StrOffsetsOffset += debugStrOffsetsHeaderSize(StrOffsetsData, Version);
 
  uint64_t StrOffset = StrOffsetsData.getU32(&StrOffsetsOffset);
  DataExtractor StrData(Str, true, 0);
  return StrData.getCStr(&StrOffset);
}
 
static Expected<CompileUnitIdentifiers>
getCUIdentifiers(InfoSectionUnitHeader &Header, StringRef Abbrev,
                 StringRef Info, StringRef StrOffsets, StringRef Str) {
  DataExtractor InfoData(Info, true, 0);
  uint64_t Offset = Header.HeaderSize;
  if (Header.Version >= 5 && Header.UnitType != dwarf::DW_UT_split_compile)
    return make_error<DWPError>(
        std::string("unit type DW_UT_split_compile type not found in "
                    "debug_info header. Unexpected unit type 0x" +
                    utostr(Header.UnitType) + " found"));
 
  CompileUnitIdentifiers ID;
 
  uint32_t AbbrCode = InfoData.getULEB128(&Offset);
  DataExtractor AbbrevData(Abbrev, true, 0);
  uint64_t AbbrevOffset = getCUAbbrev(Abbrev, AbbrCode);
  auto Tag = static_cast<dwarf::Tag>(AbbrevData.getULEB128(&AbbrevOffset));
  if (Tag != dwarf::DW_TAG_compile_unit)
    return make_error<DWPError>("top level DIE is not a compile unit");
  // DW_CHILDREN
  AbbrevData.getU8(&AbbrevOffset);
  uint32_t Name;
  dwarf::Form Form;
  while ((Name = AbbrevData.getULEB128(&AbbrevOffset)) |
             (Form = static_cast<dwarf::Form>(
                  AbbrevData.getULEB128(&AbbrevOffset))) &&
         (Name != 0 || Form != 0)) {
    switch (Name) {
    case dwarf::DW_AT_name: {
      Expected<const char *> EName = getIndexedString(
          Form, InfoData, Offset, StrOffsets, Str, Header.Version);
      if (!EName)
        return EName.takeError();
      ID.Name = *EName;
      break;
    }
    case dwarf::DW_AT_GNU_dwo_name:
    case dwarf::DW_AT_dwo_name: {
      Expected<const char *> EName = getIndexedString(
          Form, InfoData, Offset, StrOffsets, Str, Header.Version);
      if (!EName)
        return EName.takeError();
      ID.DWOName = *EName;
      break;
    }
    case dwarf::DW_AT_GNU_dwo_id:
      Header.Signature = InfoData.getU64(&Offset);
      break;
    default:
      DWARFFormValue::skipValue(
          Form, InfoData, &Offset,
          dwarf::FormParams({Header.Version, Header.AddrSize, Header.Format}));
    }
  }
  if (!Header.Signature)
    return make_error<DWPError>("compile unit missing dwo_id");
  ID.Signature = *Header.Signature;
  return ID;
}
 
static bool isSupportedSectionKind(DWARFSectionKind Kind) {
  return Kind != DW_SECT_EXT_unknown;
}
 
// Convert an internal section identifier into the index to use with
// UnitIndexEntry::Contributions.
static unsigned getContributionIndex(DWARFSectionKind Kind,
                                     uint32_t IndexVersion) {
  assert(serializeSectionKind(Kind, IndexVersion) >= DW_SECT_INFO);
  return serializeSectionKind(Kind, IndexVersion) - DW_SECT_INFO;
}
 
// Convert a UnitIndexEntry::Contributions index to the corresponding on-disk
// value of the section identifier.
static unsigned getOnDiskSectionId(unsigned Index) {
  return Index + DW_SECT_INFO;
}
 
static StringRef getSubsection(StringRef Section,
                               const DWARFUnitIndex::Entry &Entry,
                               DWARFSectionKind Kind) {
  const auto *Off = Entry.getContribution(Kind);
  if (!Off)
    return StringRef();
  return Section.substr(Off->getOffset(), Off->getLength());
}
 
static Error sectionOverflowErrorOrWarning(uint32_t PrevOffset,
                                           uint32_t OverflowedOffset,
                                           StringRef SectionName,
                                           OnCuIndexOverflow OverflowOptValue,
                                           bool &AnySectionOverflow) {
  std::string Msg =
      (SectionName +
       Twine(" Section Contribution Offset overflow 4G. Previous Offset ") +
       Twine(PrevOffset) + Twine(", After overflow offset ") +
       Twine(OverflowedOffset) + Twine("."))
          .str();
  if (OverflowOptValue == OnCuIndexOverflow::Continue) {
    WithColor::defaultWarningHandler(make_error<DWPError>(Msg));
    return Error::success();
  } else if (OverflowOptValue == OnCuIndexOverflow::SoftStop) {
    AnySectionOverflow = true;
    WithColor::defaultWarningHandler(make_error<DWPError>(Msg));
    return Error::success();
  }
  return make_error<DWPError>(Msg);
}
 
static Error addAllTypesFromDWP(
    DWPWriter &Out, MapVector<uint64_t, UnitIndexEntry> &TypeIndexEntries,
    const DWARFUnitIndex &TUIndex, DWPSectionId OutputSection, StringRef Types,
    const UnitIndexEntry &TUEntry, uint32_t &TypesOffset,
    unsigned TypesContributionIndex, OnCuIndexOverflow OverflowOptValue,
    bool &AnySectionOverflow) {
  Out.switchSection(OutputSection);
  for (const DWARFUnitIndex::Entry &E : TUIndex.getRows()) {
    auto *I = E.getContributions();
    if (!I)
      continue;
    auto P = TypeIndexEntries.insert(std::make_pair(E.getSignature(), TUEntry));
    if (!P.second)
      continue;
    auto &Entry = P.first->second;
    // Zero out the debug_info contribution
    Entry.Contributions[0] = {};
    for (auto Kind : TUIndex.getColumnKinds()) {
      if (!isSupportedSectionKind(Kind))
        continue;
      auto &C =
          Entry.Contributions[getContributionIndex(Kind, TUIndex.getVersion())];
      C.setOffset(C.getOffset() + I->getOffset());
      C.setLength(I->getLength());
      ++I;
    }
    auto &C = Entry.Contributions[TypesContributionIndex];
    Out.emitBytes(Types.substr(
        C.getOffset() -
            TUEntry.Contributions[TypesContributionIndex].getOffset(),
        C.getLength()));
    C.setOffset(TypesOffset);
    uint32_t OldOffset = TypesOffset;
    static_assert(sizeof(OldOffset) == sizeof(TypesOffset));
    TypesOffset += C.getLength();
    if (OldOffset > TypesOffset) {
      if (Error Err = sectionOverflowErrorOrWarning(OldOffset, TypesOffset,
                                                    "Types", OverflowOptValue,
                                                    AnySectionOverflow))
        return Err;
      if (AnySectionOverflow) {
        TypesOffset = OldOffset;
        return Error::success();
      }
    }
  }
  return Error::success();
}
 
static Error addAllTypesFromTypesSection(
    DWPWriter &Out, MapVector<uint64_t, UnitIndexEntry> &TypeIndexEntries,
    DWPSectionId OutputSection, const std::vector<StringRef> &TypesSections,
    const UnitIndexEntry &CUEntry, uint32_t &TypesOffset,
    OnCuIndexOverflow OverflowOptValue, bool &AnySectionOverflow) {
  for (StringRef Types : TypesSections) {
    Out.switchSection(OutputSection);
    uint64_t Offset = 0;
    DataExtractor Data(Types, true, 0);
    while (Data.isValidOffset(Offset)) {
      UnitIndexEntry Entry = CUEntry;
      // Zero out the debug_info contribution
      Entry.Contributions[0] = {};
      auto &C = Entry.Contributions[getContributionIndex(DW_SECT_EXT_TYPES, 2)];
      C.setOffset(TypesOffset);
      auto PrevOffset = Offset;
      // Length of the unit, including the 4 byte length field.
      C.setLength(Data.getU32(&Offset) + 4);
 
      Data.getU16(&Offset); // Version
      Data.getU32(&Offset); // Abbrev offset
      Data.getU8(&Offset);  // Address size
      auto Signature = Data.getU64(&Offset);
      Offset = PrevOffset + C.getLength32();
 
      auto P = TypeIndexEntries.insert(std::make_pair(Signature, Entry));
      if (!P.second)
        continue;
 
      Out.emitBytes(Types.substr(PrevOffset, C.getLength32()));
      uint32_t OldOffset = TypesOffset;
      TypesOffset += C.getLength32();
      if (OldOffset > TypesOffset) {
        if (Error Err = sectionOverflowErrorOrWarning(OldOffset, TypesOffset,
                                                      "Types", OverflowOptValue,
                                                      AnySectionOverflow))
          return Err;
        if (AnySectionOverflow) {
          TypesOffset = OldOffset;
          return Error::success();
        }
      }
    }
  }
  return Error::success();
}
 
static std::string buildDWODescription(StringRef Name, StringRef DWPName,
                                       StringRef DWOName) {
  std::string Text = "\'";
  Text += Name;
  Text += '\'';
  bool HasDWO = !DWOName.empty();
  bool HasDWP = !DWPName.empty();
  if (HasDWO || HasDWP) {
    Text += " (from ";
    if (HasDWO) {
      Text += '\'';
      Text += DWOName;
      Text += '\'';
    }
    if (HasDWO && HasDWP)
      Text += " in ";
    if (!DWPName.empty()) {
      Text += '\'';
      Text += DWPName;
      Text += '\'';
    }
    Text += ")";
  }
  return Text;
}
 
static Error createError(StringRef Name, Error E) {
  return make_error<DWPError>(
      ("failure while decompressing compressed section: '" + Name + "', " +
       llvm::toString(std::move(E)))
          .str());
}
 
static Error
handleCompressedSection(std::deque<SmallString<32>> &UncompressedSections,
                        SectionRef Sec, StringRef Name, StringRef &Contents) {
  auto *Obj = dyn_cast<ELFObjectFileBase>(Sec.getObject());
  if (!Obj ||
      !(static_cast<ELFSectionRef>(Sec).getFlags() & ELF::SHF_COMPRESSED))
    return Error::success();
  bool IsLE = isa<object::ELF32LEObjectFile>(Obj) ||
              isa<object::ELF64LEObjectFile>(Obj);
  bool Is64 = isa<object::ELF64LEObjectFile>(Obj) ||
              isa<object::ELF64BEObjectFile>(Obj);
  Expected<Decompressor> Dec = Decompressor::create(Name, Contents, IsLE, Is64);
  if (!Dec)
    return createError(Name, Dec.takeError());
 
  UncompressedSections.emplace_back();
  if (Error E = Dec->resizeAndDecompress(UncompressedSections.back()))
    return createError(Name, std::move(E));
 
  Contents = UncompressedSections.back();
  return Error::success();
}
 
static Error
buildDuplicateError(const std::pair<uint64_t, UnitIndexEntry> &PrevE,
                    const CompileUnitIdentifiers &ID, StringRef DWPName) {
  return make_error<DWPError>(
      std::string("duplicate DWO ID (") + utohexstr(PrevE.first) + ") in " +
      buildDWODescription(PrevE.second.Name, PrevE.second.DWPName,
                          PrevE.second.DWOName) +
      " and " + buildDWODescription(ID.Name, DWPName, ID.DWOName));
}
 
// Create a mask so we don't trigger a emitIntValue() assert below if the
// NewOffset is over 4GB.
static void writeNewOffsetsTo(DWPWriter &Out, DataExtractor &Data,
                              DenseMap<uint64_t, uint64_t> &OffsetRemapping,
                              uint64_t &Offset, const uint64_t Size,
                              uint32_t OldOffsetSize, uint32_t NewOffsetSize) {
  const uint64_t NewOffsetMask = NewOffsetSize == 8 ? UINT64_MAX : UINT32_MAX;
  while (Offset < Size) {
    const uint64_t OldOffset = Data.getUnsigned(&Offset, OldOffsetSize);
    const uint64_t NewOffset = OffsetRemapping[OldOffset];
    // Truncate the string offset like the old llvm-dwp would have if we aren't
    // promoting the .debug_str_offsets to DWARF64.
    Out.emitIntValue(NewOffset & NewOffsetMask, NewOffsetSize);
  }
}
 
namespace llvm {
// Parse and return the header of an info section compile/type unit.
Expected<InfoSectionUnitHeader> parseInfoSectionUnitHeader(StringRef Info) {
  InfoSectionUnitHeader Header;
  Error Err = Error::success();
  uint64_t Offset = 0;
  DWARFDataExtractor InfoData(Info, true, 0);
  std::tie(Header.Length, Header.Format) =
      InfoData.getInitialLength(&Offset, &Err);
  if (Err)
    return make_error<DWPError>("cannot parse compile unit length: " +
                                llvm::toString(std::move(Err)));
 
  if (!InfoData.isValidOffset(Offset + (Header.Length - 1))) {
    return make_error<DWPError>(
        "compile unit exceeds .debug_info section range: " +
        utostr(Offset + Header.Length) + " >= " + utostr(InfoData.size()));
  }
 
  Header.Version = InfoData.getU16(&Offset, &Err);
  if (Err)
    return make_error<DWPError>("cannot parse compile unit version: " +
                                llvm::toString(std::move(Err)));
 
  uint64_t MinHeaderLength;
  if (Header.Version >= 5) {
    // Size: Version (2), UnitType (1), AddrSize (1), DebugAbbrevOffset (4),
    // Signature (8)
    MinHeaderLength = 16;
  } else {
    // Size: Version (2), DebugAbbrevOffset (4), AddrSize (1)
    MinHeaderLength = 7;
  }
  if (Header.Length < MinHeaderLength) {
    return make_error<DWPError>("unit length is too small: expected at least " +
                                utostr(MinHeaderLength) + " got " +
                                utostr(Header.Length) + ".");
  }
  if (Header.Version >= 5) {
    Header.UnitType = InfoData.getU8(&Offset);
    Header.AddrSize = InfoData.getU8(&Offset);
    Header.DebugAbbrevOffset = InfoData.getU32(&Offset);
    Header.Signature = InfoData.getU64(&Offset);
    if (Header.UnitType == dwarf::DW_UT_split_type) {
      // Type offset.
      MinHeaderLength += 4;
      if (Header.Length < MinHeaderLength)
        return make_error<DWPError>("type unit is missing type offset");
      InfoData.getU32(&Offset);
    }
  } else {
    // Note that, address_size and debug_abbrev_offset fields have switched
    // places between dwarf version 4 and 5.
    Header.DebugAbbrevOffset = InfoData.getU32(&Offset);
    Header.AddrSize = InfoData.getU8(&Offset);
  }
 
  Header.HeaderSize = Offset;
  return Header;
}
 
static void
writeStringsAndOffsets(DWPWriter &Out, DWPStringPool &Strings,
                       StringRef CurStrSection, StringRef CurStrOffsetSection,
                       uint16_t Version, SectionLengths &SectionLength,
                       const Dwarf64StrOffsetsPromotion StrOffsetsOptValue,
                       bool SingleInput) {
  // Could possibly produce an error or warning if one of these was non-null but
  // the other was null.
  if (CurStrSection.empty() || CurStrOffsetSection.empty())
    return;
 
  // Fast path: when there is only one input, all strings are unique and offsets
  // don't need remapping. Copy both sections directly without any hashing.
  if (SingleInput && StrOffsetsOptValue != Dwarf64StrOffsetsPromotion::Always) {
    Out.switchSection(DS_Str);
    Out.emitBytes(CurStrSection);
    Out.switchSection(DS_StrOffsets);
    Out.emitBytes(CurStrOffsetSection);
    return;
  }
 
  DenseMap<uint64_t, uint64_t> OffsetRemapping;
  // Pre-reserve based on estimated string count to avoid rehashing.
  OffsetRemapping.reserve(CurStrSection.size() / 20);
 
  DataExtractor Data(CurStrSection, true, 0);
  uint64_t LocalOffset = 0;
  uint64_t PrevOffset = 0;
 
  // Keep track if any new string offsets exceed UINT32_MAX. If any do, we can
  // emit a DWARF64 .debug_str_offsets table for this compile unit. If the
  // \a StrOffsetsOptValue argument is Dwarf64StrOffsetsPromotion::Always, then
  // force the emission of DWARF64 .debug_str_offsets for testing.
  uint32_t OldOffsetSize = 4;
  uint32_t NewOffsetSize =
      StrOffsetsOptValue == Dwarf64StrOffsetsPromotion::Always ? 8 : 4;
  while (const char *S = Data.getCStr(&LocalOffset)) {
    uint64_t NewOffset = Strings.getOffset(S, LocalOffset - PrevOffset);
    OffsetRemapping[PrevOffset] = NewOffset;
    // Only promote the .debug_str_offsets to DWARF64 if our setting allows it.
    if (StrOffsetsOptValue != Dwarf64StrOffsetsPromotion::Disabled &&
        NewOffset > UINT32_MAX) {
      NewOffsetSize = 8;
    }
    PrevOffset = LocalOffset;
  }
 
  Data = DataExtractor(CurStrOffsetSection, true, 0);
 
  Out.switchSection(DS_StrOffsets);
 
  uint64_t Offset = 0;
  uint64_t Size = CurStrOffsetSection.size();
  if (Version > 4) {
    while (Offset < Size) {
      const uint64_t HeaderSize = debugStrOffsetsHeaderSize(Data, Version);
      assert(HeaderSize <= Size - Offset &&
             "StrOffsetSection size is less than its header");
 
      uint64_t ContributionEnd = 0;
      uint64_t ContributionSize = 0;
      uint64_t HeaderLengthOffset = Offset;
      if (HeaderSize == 8) {
        ContributionSize = Data.getU32(&HeaderLengthOffset);
      } else if (HeaderSize == 16) {
        OldOffsetSize = 8;
        HeaderLengthOffset += 4; // skip the dwarf64 marker
        ContributionSize = Data.getU64(&HeaderLengthOffset);
      }
      ContributionEnd = ContributionSize + HeaderLengthOffset;
 
      StringRef HeaderBytes = Data.getBytes(&Offset, HeaderSize);
      if (OldOffsetSize == 4 && NewOffsetSize == 8) {
        // We had a DWARF32 .debug_str_offsets header, but we need to emit
        // some string offsets that require 64 bit offsets on the .debug_str
        // section. Emit the .debug_str_offsets header in DWARF64 format so we
        // can emit string offsets that exceed UINT32_MAX without truncating
        // the string offset.
 
        // 2 bytes for DWARF version, 2 bytes pad.
        const uint64_t VersionPadSize = 4;
        const uint64_t NewLength =
            (ContributionSize - VersionPadSize) * 2 + VersionPadSize;
        // Emit the DWARF64 length that starts with a 4 byte DW_LENGTH_DWARF64
        // value followed by the 8 byte updated length.
        Out.emitIntValue(llvm::dwarf::DW_LENGTH_DWARF64, 4);
        Out.emitIntValue(NewLength, 8);
        // Emit DWARF version as a 2 byte integer.
        Out.emitIntValue(Version, 2);
        // Emit 2 bytes of padding.
        Out.emitIntValue(0, 2);
        // Update the .debug_str_offsets section length contribution for the
        // this .dwo file.
        for (auto &Pair : SectionLength) {
          if (Pair.first == DW_SECT_STR_OFFSETS) {
            Pair.second = NewLength + 12;
            break;
          }
        }
      } else {
        // Just emit the same .debug_str_offsets header.
        Out.emitBytes(HeaderBytes);
      }
      writeNewOffsetsTo(Out, Data, OffsetRemapping, Offset, ContributionEnd,
                        OldOffsetSize, NewOffsetSize);
    }
 
  } else {
    assert(OldOffsetSize == NewOffsetSize);
    writeNewOffsetsTo(Out, Data, OffsetRemapping, Offset, Size, OldOffsetSize,
                      NewOffsetSize);
  }
}
 
enum AccessField { Offset, Length };
 
static void
writeIndexTable(DWPWriter &Out, ArrayRef<unsigned> ContributionOffsets,
                const MapVector<uint64_t, UnitIndexEntry> &IndexEntries,
                const AccessField &Field) {
  for (const auto &E : IndexEntries)
    for (size_t I = 0; I != std::size(E.second.Contributions); ++I)
      if (ContributionOffsets[I])
        Out.emitIntValue((Field == AccessField::Offset
                              ? E.second.Contributions[I].getOffset32()
                              : E.second.Contributions[I].getLength32()),
                         4);
}
 
static void writeIndex(DWPWriter &Out, DWPSectionId Section,
                       ArrayRef<unsigned> ContributionOffsets,
                       const MapVector<uint64_t, UnitIndexEntry> &IndexEntries,
                       uint32_t IndexVersion) {
  if (IndexEntries.empty())
    return;
 
  unsigned Columns = 0;
  for (auto &C : ContributionOffsets)
    if (C)
      ++Columns;
 
  std::vector<unsigned> Buckets(NextPowerOf2(3 * IndexEntries.size() / 2));
  uint64_t Mask = Buckets.size() - 1;
  size_t I = 0;
  for (const auto &P : IndexEntries) {
    auto S = P.first;
    auto H = S & Mask;
    auto HP = ((S >> 32) & Mask) | 1;
    while (Buckets[H]) {
      assert(S != IndexEntries.begin()[Buckets[H] - 1].first &&
             "Duplicate unit");
      H = (H + HP) & Mask;
    }
    Buckets[H] = I + 1;
    ++I;
  }
 
  Out.switchSection(Section);
  Out.emitIntValue(IndexVersion, 4);        // Version
  Out.emitIntValue(Columns, 4);             // Columns
  Out.emitIntValue(IndexEntries.size(), 4); // Num Units
  Out.emitIntValue(Buckets.size(), 4);      // Num Buckets
 
  // Write the signatures.
  for (const auto &I : Buckets)
    Out.emitIntValue(I ? IndexEntries.begin()[I - 1].first : 0, 8);
 
  // Write the indexes.
  for (const auto &I : Buckets)
    Out.emitIntValue(I, 4);
 
  // Write the column headers (which sections will appear in the table)
  for (size_t I = 0; I != ContributionOffsets.size(); ++I)
    if (ContributionOffsets[I])
      Out.emitIntValue(getOnDiskSectionId(I), 4);
 
  // Write the offsets.
  writeIndexTable(Out, ContributionOffsets, IndexEntries, AccessField::Offset);
 
  // Write the lengths.
  writeIndexTable(Out, ContributionOffsets, IndexEntries, AccessField::Length);
}
 
/// Map input ELF section names to DWP section IDs and DWARF section kinds.
static const StringMap<std::pair<DWPSectionId, DWARFSectionKind>> &
getKnownSections() {
  static const StringMap<std::pair<DWPSectionId, DWARFSectionKind>> Map = {
      {"debug_info.dwo", {DS_Info, DW_SECT_INFO}},
      {"debug_types.dwo", {DS_Types, DW_SECT_EXT_TYPES}},
      {"debug_str_offsets.dwo", {DS_StrOffsets, DW_SECT_STR_OFFSETS}},
      {"debug_str.dwo", {DS_Str, static_cast<DWARFSectionKind>(0)}},
      {"debug_loc.dwo", {DS_Loc, DW_SECT_EXT_LOC}},
      {"debug_line.dwo", {DS_Line, DW_SECT_LINE}},
      {"debug_macro.dwo", {DS_Macro, DW_SECT_MACRO}},
      {"debug_abbrev.dwo", {DS_Abbrev, DW_SECT_ABBREV}},
      {"debug_loclists.dwo", {DS_Loclists, DW_SECT_LOCLISTS}},
      {"debug_rnglists.dwo", {DS_Rnglists, DW_SECT_RNGLISTS}},
      {"debug_cu_index", {DS_CUIndex, static_cast<DWARFSectionKind>(0)}},
      {"debug_tu_index", {DS_TUIndex, static_cast<DWARFSectionKind>(0)}},
  };
  return Map;
}
 
static Error handleSection(
    const StringMap<std::pair<DWPSectionId, DWARFSectionKind>> &KnownSections,
    const SectionRef &Section, DWPWriter &Out,
    std::deque<SmallString<32>> &UncompressedSections,
    uint32_t (&ContributionOffsets)[8], UnitIndexEntry &CurEntry,
    StringRef &CurStrSection, StringRef &CurStrOffsetSection,
    std::vector<StringRef> &CurTypesSection,
    std::vector<StringRef> &CurInfoSection, StringRef &AbbrevSection,
    StringRef &CurCUIndexSection, StringRef &CurTUIndexSection,
    SectionLengths &SectionLength) {
  if (Section.isBSS())
    return Error::success();
 
  if (Section.isVirtual())
    return Error::success();
 
  Expected<StringRef> NameOrErr = Section.getName();
  if (!NameOrErr)
    return NameOrErr.takeError();
  StringRef Name = *NameOrErr;
 
  Expected<StringRef> ContentsOrErr = Section.getContents();
  if (!ContentsOrErr)
    return ContentsOrErr.takeError();
  StringRef Contents = *ContentsOrErr;
 
  if (auto Err = handleCompressedSection(UncompressedSections, Section, Name,
                                         Contents))
    return Err;
 
  Name = Name.substr(Name.find_first_not_of("._"));
 
  auto SectionPair = KnownSections.find(Name);
  if (SectionPair == KnownSections.end())
    return Error::success();
 
  DWPSectionId SectionId = SectionPair->second.first;
  DWARFSectionKind Kind = SectionPair->second.second;
 
  if (Kind) {
    if (Kind != DW_SECT_EXT_TYPES && Kind != DW_SECT_INFO)
      SectionLength.push_back(std::make_pair(Kind, Contents.size()));
    if (Kind == DW_SECT_ABBREV)
      AbbrevSection = Contents;
  }
 
  switch (SectionId) {
  case DS_StrOffsets:
    CurStrOffsetSection = Contents;
    break;
  case DS_Str:
    CurStrSection = Contents;
    break;
  case DS_Types:
    CurTypesSection.push_back(Contents);
    break;
  case DS_CUIndex:
    CurCUIndexSection = Contents;
    break;
  case DS_TUIndex:
    CurTUIndexSection = Contents;
    break;
  case DS_Info:
    CurInfoSection.push_back(Contents);
    break;
  default:
    // Pass-through: emit directly to output (zero-copy).
    Out.switchSection(SectionId);
    Out.emitBytes(Contents);
    break;
  }
  return Error::success();
}
 
Error write(DWPWriter &Out, ArrayRef<std::string> Inputs,
            OnCuIndexOverflow OverflowOptValue,
            Dwarf64StrOffsetsPromotion StrOffsetsOptValue,
            raw_pwrite_stream *OutputOS) {
  const auto &KnownSections = getKnownSections();
 
  MapVector<uint64_t, UnitIndexEntry> IndexEntries;
  MapVector<uint64_t, UnitIndexEntry> TypeIndexEntries;
 
  uint32_t ContributionOffsets[8] = {};
  uint16_t Version = 0;
  uint32_t IndexVersion = 0;
  StringRef FirstInput;
  bool AnySectionOverflow = false;
 
  DWPStringPool Strings(Out.getSectionBuffer(DS_Str));
 
  SmallVector<OwningBinary<object::ObjectFile>, 128> Objects;
  Objects.reserve(Inputs.size());
 
  std::deque<SmallString<32>> UncompressedSections;
 
  bool MachineSet = false;
 
  for (const auto &Input : Inputs) {
    auto ErrOrObj = object::ObjectFile::createObjectFile(Input);
    if (!ErrOrObj) {
      return handleErrors(ErrOrObj.takeError(),
                          [&](std::unique_ptr<ECError> EC) -> Error {
                            return createFileError(Input, Error(std::move(EC)));
                          });
    }
 
    auto &Obj = *ErrOrObj->getBinary();
    Objects.push_back(std::move(*ErrOrObj));
 
    // Set output format metadata from the first input file.
    if (!MachineSet) {
      if (auto *ELFObj = dyn_cast<ELFObjectFileBase>(&Obj)) {
        Out.setMachine(ELFObj->getEMachine());
        Out.setOSABI(ELFObj->getOS());
      } else if (Obj.isWasm()) {
        Out.setIsWASM(true);
      }
      MachineSet = true;
    }
 
    UnitIndexEntry CurEntry = {};
 
    StringRef CurStrSection;
    StringRef CurStrOffsetSection;
    std::vector<StringRef> CurTypesSection;
    std::vector<StringRef> CurInfoSection;
    StringRef AbbrevSection;
    StringRef CurCUIndexSection;
    StringRef CurTUIndexSection;
 
    // This maps each section contained in this file to its length.
    // This information is later on used to calculate the contributions,
    // i.e. offset and length, of each compile/type unit to a section.
    SectionLengths SectionLength;
 
    for (const auto &Section : Obj.sections())
      if (auto Err = handleSection(
              KnownSections, Section, Out, UncompressedSections,
              ContributionOffsets, CurEntry, CurStrSection, CurStrOffsetSection,
              CurTypesSection, CurInfoSection, AbbrevSection, CurCUIndexSection,
              CurTUIndexSection, SectionLength))
        return Err;
 
    if (CurInfoSection.empty())
      continue;
 
    Expected<InfoSectionUnitHeader> HeaderOrErr =
        parseInfoSectionUnitHeader(CurInfoSection.front());
    if (!HeaderOrErr)
      return HeaderOrErr.takeError();
    InfoSectionUnitHeader &Header = *HeaderOrErr;
 
    if (Version == 0) {
      Version = Header.Version;
      IndexVersion = Version < 5 ? 2 : 5;
      FirstInput = Input;
    } else if (Version != Header.Version) {
      return make_error<DWPError>(
          "incompatible DWARF compile unit version: " + Input + " (version " +
          utostr(Header.Version) + ") and " + FirstInput.str() + " (version " +
          utostr(Version) + ")");
    }
 
    writeStringsAndOffsets(Out, Strings, CurStrSection, CurStrOffsetSection,
                           Header.Version, SectionLength, StrOffsetsOptValue,
                           Inputs.size() == 1);
 
    for (auto Pair : SectionLength) {
      auto Index = getContributionIndex(Pair.first, IndexVersion);
      CurEntry.Contributions[Index].setOffset(ContributionOffsets[Index]);
      CurEntry.Contributions[Index].setLength(Pair.second);
      uint32_t OldOffset = ContributionOffsets[Index];
      ContributionOffsets[Index] += CurEntry.Contributions[Index].getLength32();
      if (OldOffset > ContributionOffsets[Index]) {
        uint32_t SectionIndex = 0;
        for (auto &Section : Obj.sections()) {
          if (SectionIndex == Index) {
            if (Error Err = sectionOverflowErrorOrWarning(
                    OldOffset, ContributionOffsets[Index], *Section.getName(),
                    OverflowOptValue, AnySectionOverflow))
              return Err;
          }
          ++SectionIndex;
        }
        if (AnySectionOverflow)
          break;
      }
    }
 
    uint32_t &InfoSectionOffset =
        ContributionOffsets[getContributionIndex(DW_SECT_INFO, IndexVersion)];
    if (CurCUIndexSection.empty()) {
      bool FoundCUUnit = false;
      Out.switchSection(DS_Info);
      for (StringRef Info : CurInfoSection) {
        uint64_t UnitOffset = 0;
        while (Info.size() > UnitOffset) {
          Expected<InfoSectionUnitHeader> HeaderOrError =
              parseInfoSectionUnitHeader(Info.substr(UnitOffset, Info.size()));
          if (!HeaderOrError)
            return HeaderOrError.takeError();
          InfoSectionUnitHeader &Header = *HeaderOrError;
 
          UnitIndexEntry Entry = CurEntry;
          auto &C = Entry.Contributions[getContributionIndex(DW_SECT_INFO,
                                                             IndexVersion)];
          C.setOffset(InfoSectionOffset);
          C.setLength(Header.Length + 4);
 
          if (std::numeric_limits<uint32_t>::max() - InfoSectionOffset <
              C.getLength32()) {
            if (Error Err = sectionOverflowErrorOrWarning(
                    InfoSectionOffset, InfoSectionOffset + C.getLength32(),
                    "debug_info", OverflowOptValue, AnySectionOverflow))
              return Err;
            if (AnySectionOverflow) {
              FoundCUUnit = true;
              break;
            }
          }
 
          UnitOffset += C.getLength32();
          if (Header.Version < 5 ||
              Header.UnitType == dwarf::DW_UT_split_compile) {
            Expected<CompileUnitIdentifiers> EID = getCUIdentifiers(
                Header, AbbrevSection,
                Info.substr(UnitOffset - C.getLength32(), C.getLength32()),
                CurStrOffsetSection, CurStrSection);
 
            if (!EID)
              return createFileError(Input, EID.takeError());
            const auto &ID = *EID;
            auto P = IndexEntries.insert(std::make_pair(ID.Signature, Entry));
            if (!P.second)
              return buildDuplicateError(*P.first, ID, "");
            P.first->second.Name = ID.Name;
            P.first->second.DWOName = ID.DWOName;
 
            FoundCUUnit = true;
          } else if (Header.UnitType == dwarf::DW_UT_split_type) {
            auto P = TypeIndexEntries.insert(
                std::make_pair(*Header.Signature, Entry));
            if (!P.second)
              continue;
          }
          Out.emitBytes(
              Info.substr(UnitOffset - C.getLength32(), C.getLength32()));
          InfoSectionOffset += C.getLength32();
        }
        if (AnySectionOverflow)
          break;
      }
 
      if (!FoundCUUnit)
        return make_error<DWPError>("no compile unit found in file: " + Input);
 
      if (IndexVersion == 2) {
        // Add types from the .debug_types section from DWARF < 5.
        if (Error Err = addAllTypesFromTypesSection(
                Out, TypeIndexEntries, DS_Types, CurTypesSection, CurEntry,
                ContributionOffsets[getContributionIndex(DW_SECT_EXT_TYPES, 2)],
                OverflowOptValue, AnySectionOverflow))
          return Err;
      }
      if (AnySectionOverflow)
        break;
      continue;
    }
 
    if (CurInfoSection.size() != 1)
      return make_error<DWPError>("expected exactly one occurrence of a debug "
                                  "info section in a .dwp file");
    StringRef DwpSingleInfoSection = CurInfoSection.front();
 
    DWARFUnitIndex CUIndex(DW_SECT_INFO);
    DataExtractor CUIndexData(CurCUIndexSection, Obj.isLittleEndian(), 0);
    if (!CUIndex.parse(CUIndexData))
      return make_error<DWPError>("failed to parse cu_index");
    if (CUIndex.getVersion() != IndexVersion)
      return make_error<DWPError>("incompatible cu_index versions, found " +
                                  utostr(CUIndex.getVersion()) +
                                  " and expecting " + utostr(IndexVersion));
 
    Out.switchSection(DS_Info);
    for (const DWARFUnitIndex::Entry &E : CUIndex.getRows()) {
      auto *I = E.getContributions();
      if (!I)
        continue;
      auto P = IndexEntries.insert(std::make_pair(E.getSignature(), CurEntry));
      StringRef CUInfoSection =
          getSubsection(DwpSingleInfoSection, E, DW_SECT_INFO);
      Expected<InfoSectionUnitHeader> HeaderOrError =
          parseInfoSectionUnitHeader(CUInfoSection);
      if (!HeaderOrError)
        return HeaderOrError.takeError();
      InfoSectionUnitHeader &Header = *HeaderOrError;
 
      Expected<CompileUnitIdentifiers> EID = getCUIdentifiers(
          Header, getSubsection(AbbrevSection, E, DW_SECT_ABBREV),
          CUInfoSection,
          getSubsection(CurStrOffsetSection, E, DW_SECT_STR_OFFSETS),
          CurStrSection);
      if (!EID)
        return createFileError(Input, EID.takeError());
      const auto &ID = *EID;
      if (!P.second)
        return buildDuplicateError(*P.first, ID, Input);
      auto &NewEntry = P.first->second;
      NewEntry.Name = ID.Name;
      NewEntry.DWOName = ID.DWOName;
      NewEntry.DWPName = Input;
      for (auto Kind : CUIndex.getColumnKinds()) {
        if (!isSupportedSectionKind(Kind))
          continue;
        auto &C =
            NewEntry.Contributions[getContributionIndex(Kind, IndexVersion)];
        C.setOffset(C.getOffset() + I->getOffset());
        C.setLength(I->getLength());
        ++I;
      }
      unsigned Index = getContributionIndex(DW_SECT_INFO, IndexVersion);
      auto &C = NewEntry.Contributions[Index];
      Out.emitBytes(CUInfoSection);
      C.setOffset(InfoSectionOffset);
      InfoSectionOffset += C.getLength32();
    }
 
    if (!CurTUIndexSection.empty()) {
      llvm::DWARFSectionKind TUSectionKind;
      DWPSectionId OutSection;
      StringRef TypeInputSection;
      // Write type units into debug info section for DWARFv5.
      if (Version >= 5) {
        TUSectionKind = DW_SECT_INFO;
        OutSection = DS_Info;
        TypeInputSection = DwpSingleInfoSection;
      } else {
        // Write type units into debug types section for DWARF < 5.
        if (CurTypesSection.size() != 1)
          return make_error<DWPError>(
              "multiple type unit sections in .dwp file");
 
        TUSectionKind = DW_SECT_EXT_TYPES;
        OutSection = DS_Types;
        TypeInputSection = CurTypesSection.front();
      }
 
      DWARFUnitIndex TUIndex(TUSectionKind);
      DataExtractor TUIndexData(CurTUIndexSection, Obj.isLittleEndian(), 0);
      if (!TUIndex.parse(TUIndexData))
        return make_error<DWPError>("failed to parse tu_index");
      if (TUIndex.getVersion() != IndexVersion)
        return make_error<DWPError>("incompatible tu_index versions, found " +
                                    utostr(TUIndex.getVersion()) +
                                    " and expecting " + utostr(IndexVersion));
 
      unsigned TypesContributionIndex =
          getContributionIndex(TUSectionKind, IndexVersion);
      if (Error Err = addAllTypesFromDWP(
              Out, TypeIndexEntries, TUIndex, OutSection, TypeInputSection,
              CurEntry, ContributionOffsets[TypesContributionIndex],
              TypesContributionIndex, OverflowOptValue, AnySectionOverflow))
        return Err;
    }
    if (AnySectionOverflow)
      break;
  }
 
  if (Version < 5) {
    // Lie about there being no info contributions so the TU index only includes
    // the type unit contribution for DWARF < 5. In DWARFv5 the TU index has a
    // contribution to the info section, so we do not want to lie about it.
    ContributionOffsets[0] = 0;
  }
  writeIndex(Out, DS_TUIndex, ContributionOffsets, TypeIndexEntries,
             IndexVersion);
 
  if (Version < 5) {
    // Lie about the type contribution for DWARF < 5. In DWARFv5 the type
    // section does not exist, so no need to do anything about this.
    ContributionOffsets[getContributionIndex(DW_SECT_EXT_TYPES, 2)] = 0;
    // Unlie about the info contribution
    ContributionOffsets[0] = 1;
  }
 
  writeIndex(Out, DS_CUIndex, ContributionOffsets, IndexEntries, IndexVersion);
 
  // Write ELF output while input data is still alive (zero-copy chunks
  // reference mmap'd input data held by the Objects vector above).
  if (OutputOS)
    return Out.write(*OutputOS);
 
  return Error::success();
}
 
//===----------------------------------------------------------------------===//
// DWPWriter::writeELF — produce a minimal ELF64 relocatable object.
//===----------------------------------------------------------------------===//
 
Error DWPWriter::writeELF(raw_pwrite_stream &OS) {
  support::endian::Writer Wr(OS, llvm::endianness::little);
 
  // Section metadata table.
  struct SectionMeta {
    DWPSectionId Id;
    const char *Name;
    uint64_t Flags;
    uint64_t EntSize;
  };
  static constexpr SectionMeta Meta[] = {
      {DS_Loclists, ".debug_loclists.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Loc, ".debug_loc.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Abbrev, ".debug_abbrev.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Line, ".debug_line.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Rnglists, ".debug_rnglists.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Macro, ".debug_macro.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Str, ".debug_str.dwo",
       ELF::SHF_EXCLUDE | ELF::SHF_MERGE | ELF::SHF_STRINGS, 1},
      {DS_StrOffsets, ".debug_str_offsets.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Info, ".debug_info.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_Types, ".debug_types.dwo", ELF::SHF_EXCLUDE, 0},
      {DS_TUIndex, ".debug_tu_index", 0, 0},
      {DS_CUIndex, ".debug_cu_index", 0, 0},
  };
 
  // Collect non-empty sections and build the section name string table.
  struct OutputEntry {
    const SectionData *Data;
    const char *Name;
    uint64_t Flags;
    uint64_t EntSize;
    uint32_t NameOffset;
    uint64_t FileOffset; // filled in during layout
  };
  SmallVector<OutputEntry> Entries;
 
  SmallString<256> Strtab;
  Strtab.push_back('\0'); // null string at offset 0
 
  for (const auto &M : Meta) {
    if (Sections[M.Id].empty())
      continue;
    uint32_t NameOff = Strtab.size();
    Strtab.append(M.Name);
    Strtab.push_back('\0');
    Entries.push_back(
        {&Sections[M.Id], M.Name, M.Flags, M.EntSize, NameOff, 0});
  }
 
  // Add .strtab and .symtab name entries.
  uint32_t StrtabNameOff = Strtab.size();
  Strtab.append(".strtab");
  Strtab.push_back('\0');
  uint32_t SymtabNameOff = Strtab.size();
  Strtab.append(".symtab");
  Strtab.push_back('\0');
 
  // Layout:
  //   [ELF Header]              64 bytes
  //   [section data...]         variable
  //   [.strtab data]            variable
  //   [padding to 8-byte align]
  //   [.symtab data]            24 bytes (one null entry)
  //   [padding to 8-byte align]
  //   [Section Header Table]    64 * NumSections bytes
 
  constexpr uint64_t EhdrSize = sizeof(ELF::Elf64_Ehdr);
  constexpr uint64_t SymEntSize = 24;
 
  uint64_t Offset = EhdrSize;
  for (auto &E : Entries) {
    E.FileOffset = Offset;
    Offset += E.Data->totalSize();
  }
 
  uint64_t StrtabOffset = Offset;
  Offset += Strtab.size();
 
  uint64_t SymtabOffset = alignTo(Offset, 8);
  Offset = SymtabOffset + SymEntSize;
 
  uint64_t SHTOffset = alignTo(Offset, 8);
 
  // Section indices: [0]=null, [1..N]=data, [N+1]=strtab, [N+2]=symtab
  uint32_t StrtabIdx = 1 + Entries.size();
  uint32_t SymtabIdx = StrtabIdx + 1;
  uint32_t NumSections = SymtabIdx + 1;
 
  // --- Write ELF header ---
  ELF::writeHeader(Wr, /*Is64Bit=*/true, ELFOSABI, /*ABIVersion=*/0, ELFMachine,
                   /*EFlags=*/0, SHTOffset, NumSections, StrtabIdx);
 
  // --- Write section data ---
  for (const auto &E : Entries)
    E.Data->writeTo(OS);
 
  // --- Write .strtab ---
  OS.write(Strtab.data(), Strtab.size());
 
  // --- Pad + write .symtab (one null symbol entry) ---
  OS.write_zeros(SymtabOffset - (StrtabOffset + Strtab.size()));
  OS.write_zeros(SymEntSize);
 
  // --- Pad for section header table ---
  uint64_t CurPos = SymtabOffset + SymEntSize;
  OS.write_zeros(SHTOffset - CurPos);
 
  // [0] ELF::SHT_NULL
  ELF::writeSectionHeader(Wr, true, 0, ELF::SHT_NULL, 0, 0, 0, 0, 0, 0, 0, 0);
 
  // [1..N] data sections
  for (const auto &E : Entries)
    ELF::writeSectionHeader(Wr, true, E.NameOffset, ELF::SHT_PROGBITS, E.Flags,
                            0, E.FileOffset, E.Data->totalSize(), 0, 0, 1,
                            E.EntSize);
 
  // [N+1] .strtab
  ELF::writeSectionHeader(Wr, true, StrtabNameOff, ELF::SHT_STRTAB, 0, 0,
                          StrtabOffset, Strtab.size(), 0, 0, 1, 0);
 
  // [N+2] .symtab
  ELF::writeSectionHeader(Wr, true, SymtabNameOff, ELF::SHT_SYMTAB, 0, 0,
                          SymtabOffset, SymEntSize, StrtabIdx, 1, 8,
                          SymEntSize);
 
  return Error::success();
}
 
//===----------------------------------------------------------------------===//
// DWPWriter::writeWASM — produce a minimal WASM object with custom sections.
//===----------------------------------------------------------------------===//
 
Error DWPWriter::writeWASM(raw_pwrite_stream &OS) {
  // Section name table (same names as ELF but without SHF_EXCLUDE flags).
  static constexpr struct {
    DWPSectionId Id;
    const char *Name;
  } Meta[] = {
      {DS_Loclists, ".debug_loclists.dwo"},
      {DS_Loc, ".debug_loc.dwo"},
      {DS_Abbrev, ".debug_abbrev.dwo"},
      {DS_Line, ".debug_line.dwo"},
      {DS_Rnglists, ".debug_rnglists.dwo"},
      {DS_Macro, ".debug_macro.dwo"},
      {DS_Str, ".debug_str.dwo"},
      {DS_StrOffsets, ".debug_str_offsets.dwo"},
      {DS_Info, ".debug_info.dwo"},
      {DS_Types, ".debug_types.dwo"},
      {DS_TUIndex, ".debug_tu_index"},
      {DS_CUIndex, ".debug_cu_index"},
  };
 
  // WASM magic and version.
  OS.write("\0asm", 4);
  const uint8_t Version[] = {0x01, 0x00, 0x00, 0x00};
  OS.write(reinterpret_cast<const char *>(Version), 4);
 
  // Emit each non-empty section as a WASM custom section (id=0).
  for (const auto &M : Meta) {
    const SectionData &SD = Sections[M.Id];
    if (SD.empty())
      continue;
 
    size_t NameLen = strlen(M.Name);
    uint64_t PayloadSize = SD.totalSize();
 
    // Custom section payload = ULEB128(name_len) + name + data.
    uint8_t NameLenEncoded[10];
    unsigned NameLenSize = encodeULEB128(NameLen, NameLenEncoded);
    uint64_t SectionPayloadSize = NameLenSize + NameLen + PayloadSize;
 
    // Section header: id byte + ULEB128(section_payload_size).
    OS.write(0x00); // Custom section id
    uint8_t SizeEncoded[10];
    unsigned SizeLen = encodeULEB128(SectionPayloadSize, SizeEncoded);
    OS.write(reinterpret_cast<const char *>(SizeEncoded), SizeLen);
 
    // Name
    OS.write(reinterpret_cast<const char *>(NameLenEncoded), NameLenSize);
    OS.write(M.Name, NameLen);
 
    // Data
    SD.writeTo(OS);
  }
 
  return Error::success();
}
 
} // namespace llvm