[BOLT]DWARF] Eagerly write out loclists

[ayermolo]

Summary

Taking advantage of us being able to re-write .debug_info to reduce memory
footprint loclists. Writing out loc-list as they are added, similar to how
we handle ranges.

Collected on clang-14
trunk
4:41.20 real, 389.50 user, 59.50 sys, 0 amem, 38412532 mmem
4:30.08 real, 376.10 user, 63.75 sys, 0 amem, 38477844 mmem
4:25.58 real, 373.76 user, 54.71 sys, 0 amem, 38439660 mmem
diff
4:34.66 real, 392.83 user, 57.73 sys, 0 amem, 38382560 mmem
4:35.96 real, 377.70 user, 58.62 sys, 0 amem, 38255840 mmem
4:27.61 real, 390.18 user, 57.02 sys, 0 amem, 38223224 mmem

[ayermolo]

rebase

[ayermolo]

clang-format

[ayermolo]

clang-format

[maksfb]

"[BOLT][DWARF] Change loclist to take not delay writing out lists." -> "[BOLT]DWARF] Eagerly write out loclists".

Could you add more background in the Summary and include memory footprint reduction data?

bolt/include/bolt/Core/DebugData.h

39

Drop const here.

527

s/relative/related/

601

Or NumEntries.

bolt/lib/Core/DebugData.cpp

76–88

No need to duplicate comments from the header.

bolt/lib/Rewrite/DWARFRewriter.cpp

178

179

[maksfb]

bolt/include/bolt/Core/DebugData.h

39

I take it back.

[ayermolo]

addressed comments

[maksfb]

LGTM

bolt/include/bolt/Core/DebugData.h

 #include <vector>
 
 #define DWARF2_FLAG_END_SEQUENCE (1 << 4)
 
 namespace llvm {
 
 namespace bolt {
 
+struct AttrInfo {
+  DWARFFormValue V;
+  const DWARFAbbreviationDeclaration *AbbrevDecl;
+  uint64_t Offset;
+  uint32_t Size; // Size of the attribute.
+};
+
+/// Finds attributes FormValue and Offset.
+///
+/// \param DIE die to look up in.
+/// \param AbbrevDecl abbrev declaration for the die.
+/// \param Index an index in Abbrev declaration entry.
+Optional<AttrInfo>
+findAttributeInfo(const DWARFDie DIE,
+                  const DWARFAbbreviationDeclaration *AbbrevDecl,
+                  uint32_t Index);
+
+/// Finds attributes FormValue and Offset.
+///
+/// \param DIE die to look up in.
+/// \param Attr the attribute to extract.
+/// \return an optional AttrInfo with DWARFFormValue and Offset.
+Optional<AttrInfo> findAttributeInfo(const DWARFDie DIE, dwarf::Attribute Attr);
+
 // DWARF5 Header in order of encoding.
 // Types represent encodnig sizes.
 using UnitLengthType = uint32_t;
 using VersionType = uint16_t;
 using AddressSizeType = uint8_t;
 using SegmentSelectorType = uint8_t;
 using OffsetEntryCountType = uint32_t;
 /// Get DWARF5 Header size.
private:
   void initialize();
   /// Creats internal data stractures.
   void create();
   std::unique_ptr<DebugStrBufferVector> StrBuffer;
   std::unique_ptr<raw_svector_ostream> StrStream;
   BinaryContext &BC;
 };
 
+class DebugInfoBinaryPatcher;
+class DebugAbbrevWriter;
 enum class LocWriterKind { DebugLocWriter, DebugLoclistWriter };
 
 /// Serializes part of a .debug_loc DWARF section with LocationLists.
 class SimpleBinaryPatcher;
 class DebugLocWriter {
+protected:
+  DebugLocWriter(uint8_t DwarfVersion, LocWriterKind Kind)
+      : DwarfVersion(DwarfVersion), Kind(Kind) {
+    init();
+  }
+
 public:
-  DebugLocWriter() = delete;
-  DebugLocWriter(BinaryContext *BC);
+  DebugLocWriter() { init(); };
   virtual ~DebugLocWriter(){};
 
   /// Writes out location lists and stores internal patches.
-  virtual void addList(uint64_t AttrOffset, uint32_t LocListIndex,
-                       DebugLocationsVector &&LocList);
+  virtual void addList(AttrInfo &AttrVal, DebugLocationsVector &LocList,
+                       DebugInfoBinaryPatcher &DebugInfoPatcher,
+                       DebugAbbrevWriter &AbbrevWriter);
 
   /// Writes out locations in to a local buffer, and adds Debug Info patches.
-  virtual void finalize(uint64_t SectionOffset,
-                        SimpleBinaryPatcher &DebugInfoPatcher);
+  virtual void finalize(DebugInfoBinaryPatcher &DebugInfoPatcher,
+                        DebugAbbrevWriter &AbbrevWriter);
 
   /// Return internal buffer.
   virtual std::unique_ptr<DebugBufferVector> getBuffer();
 
   /// Returns DWARF version.
   uint8_t getDwarfVersion() const { return DwarfVersion; }
 
   /// Offset of an empty location list.
   static constexpr uint32_t EmptyListOffset = 0;
 
   LocWriterKind getKind() const { return Kind; }
 
   static bool classof(const DebugLocWriter *Writer) {
     return Writer->getKind() == LocWriterKind::DebugLocWriter;
   }
 
 protected:
   std::unique_ptr<DebugBufferVector> LocBuffer;
   std::unique_ptr<raw_svector_ostream> LocStream;
   /// Current offset in the section (updated as new entries are written).
   /// Starts with 0 here since this only writes part of a full location lists
-  /// section. In the final section, the first 16 bytes are reserved for an
-  /// empty list.
-  uint32_t SectionOffset{0};
+  /// section. In the final section, for DWARF4, the first 16 bytes are reserved
+  /// for an empty list.
+  static uint32_t LocSectionOffset;
   uint8_t DwarfVersion{4};
   LocWriterKind Kind{LocWriterKind::DebugLocWriter};
 
 private:
+  /// Inits all the related data structures.
+  void init();
   struct LocListDebugInfoPatchType {
     uint64_t DebugInfoAttrOffset;
     uint64_t LocListOffset;
   };
   using VectorLocListDebugInfoPatchType =
       std::vector<LocListDebugInfoPatchType>;
   /// The list of debug info patches to be made once individual
   /// location list writers have been filled
   VectorLocListDebugInfoPatchType LocListDebugInfoPatches;
-
-  using VectorEmptyLocListAttributes = std::vector<uint64_t>;
-  /// Contains all the attributes pointing to empty location list.
-  VectorEmptyLocListAttributes EmptyAttrLists;
 };
 
 class DebugLoclistWriter : public DebugLocWriter {
 public:
   ~DebugLoclistWriter() {}
   DebugLoclistWriter() = delete;
-  DebugLoclistWriter(BinaryContext *BC, DWARFUnit &Unit,
-                     uint32_t LocListsBaseAttrOffset, uint8_t DV, bool SD)
-      : DebugLocWriter(BC), CU(Unit),
-        LocListsBaseAttrOffset(LocListsBaseAttrOffset), IsSplitDwarf(SD) {
-    Kind = LocWriterKind::DebugLoclistWriter;
-    DwarfVersion = DV;
+  DebugLoclistWriter(DWARFUnit &Unit, uint8_t DV, bool SD)
+      : DebugLocWriter(DV, LocWriterKind::DebugLoclistWriter), CU(Unit),
+        IsSplitDwarf(SD) {
     assert(DebugLoclistWriter::AddrWriter &&
            "Please use SetAddressWriter to initialize "
            "DebugAddrWriter before instantiation.");
+    if (DwarfVersion >= 5) {
+      LocBodyBuffer = std::make_unique<DebugBufferVector>();
+      LocBodyStream = std::make_unique<raw_svector_ostream>(*LocBodyBuffer);
+    } else {
+      // Writing out empty location list to which all references to empty
+      // location lists will point.
+      const char Zeroes[16] = {0};
+      *LocStream << StringRef(Zeroes, 16);
+    }
   }
 
   static void setAddressWriter(DebugAddrWriter *AddrW) { AddrWriter = AddrW; }
 
   /// Stores location lists internally to be written out during finalize phase.
-  virtual void addList(uint64_t AttrOffset, uint32_t LocListIndex,
-                       DebugLocationsVector &&LocList) override;
+  virtual void addList(AttrInfo &AttrVal, DebugLocationsVector &LocList,
+                       DebugInfoBinaryPatcher &DebugInfoPatcher,
+                       DebugAbbrevWriter &AbbrevWriter) override;
 
   /// Writes out locations in to a local buffer and applies debug info patches.
-  void finalize(uint64_t SectionOffset,
-                SimpleBinaryPatcher &DebugInfoPatcher) override;
+  void finalize(DebugInfoBinaryPatcher &DebugInfoPatcher,
+                DebugAbbrevWriter &AbbrevWriter) override;
 
   /// Returns CU ID.
   /// For Skelton CU it is a CU Offset.
   /// For DWO CU it is a DWO ID.
   uint64_t getCUID() const {
     return CU.isDWOUnit() ? *CU.getDWOId() : CU.getOffset();
   }
 
   LocWriterKind getKind() const { return DebugLocWriter::getKind(); }
 
   static bool classof(const DebugLocWriter *Writer) {
     return Writer->getKind() == LocWriterKind::DebugLoclistWriter;
   }
 
   bool isSplitDwarf() const { return IsSplitDwarf; }
 
   constexpr static uint32_t InvalidIndex = UINT32_MAX;
-  constexpr static uint32_t InvalidLocListsBaseAttrOffset = UINT32_MAX;
 
 private:
   /// Writes out locations in to a local buffer and applies debug info patches.
-  void finalizeDWARFLegacy(uint64_t SectionOffset,
-                           SimpleBinaryPatcher &DebugInfoPatcher);
-
-  /// Writes out locations in to a local buffer and applies debug info patches.
-  void finalizeDWARF5(uint64_t SectionOffset,
-                      SimpleBinaryPatcher &DebugInfoPatcher);
-
-  struct LocPatch {
-    uint64_t AttrOffset{0};
-    uint32_t Index;
-    DebugLocationsVector LocList;
-  };
-  using LocPatchVec = SmallVector<LocPatch, 4>;
-  LocPatchVec Patches;
+  void finalizeDWARF5(DebugInfoBinaryPatcher &DebugInfoPatcher,
+                      DebugAbbrevWriter &AbbrevWriter);
 
-  class Patch {
-  public:
-    Patch() = delete;
-    Patch(uint64_t O, uint64_t A) : Offset(O), Address(A) {}
-    uint64_t Offset{0};
-    uint64_t Address{0};
-  };
   static DebugAddrWriter *AddrWriter;
   DWARFUnit &CU;
-  uint32_t LocListsBaseAttrOffset{InvalidLocListsBaseAttrOffset};
   bool IsSplitDwarf{false};
+  // Used for DWARF5 to store location lists before being finalized.
+  std::unique_ptr<DebugBufferVector> LocBodyBuffer;
+  std::unique_ptr<raw_svector_ostream> LocBodyStream;
+  std::vector<uint32_t> RelativeLocListOffsets;
+  uint32_t NumberOfEntries{0};
+  static uint32_t LoclistBaseOffset;
 };
 
 enum class PatcherKind { SimpleBinaryPatcher, DebugInfoBinaryPatcher };
 /// Abstract interface for classes that apply modifications to a binary string.
 class BinaryPatcher {
 public:
   virtual ~BinaryPatcher() {}
   /// Applies modifications to the copy of binary string \p BinaryContents .
public:
   }
 
   /// Sets DWARF version for this line table.
   void setDwarfVersion(uint16_t V) { DwarfVersion = V; }
 
   // Returns DWARF Version for this line table.
   uint16_t getDwarfVersion() const { return DwarfVersion; }
 };
-
-struct AttrInfo {
-  DWARFFormValue V;
-  uint64_t Offset;
-  uint32_t Size; // Size of the attribute.
-};
-
-Optional<AttrInfo>
-findAttributeInfo(const DWARFDie DIE,
-                  const DWARFAbbreviationDeclaration *AbbrevDecl,
-                  uint32_t Index);
-
 } // namespace bolt
 } // namespace llvm
 
 #endif

bolt/include/bolt/Rewrite/DWARFRewriter.h

private:
   ///    attribute.
   void updateDWARFObjectAddressRanges(const DWARFDie DIE,
                                       uint64_t DebugRangesOffset,
                                       SimpleBinaryPatcher &DebugInfoPatcher,
                                       DebugAbbrevWriter &AbbrevWriter,
                                       Optional<uint64_t> RangesBase = None);
 
   std::unique_ptr<DebugBufferVector>
-  makeFinalLocListsSection(SimpleBinaryPatcher &DebugInfoPatcher,
+  makeFinalLocListsSection(DebugInfoBinaryPatcher &DebugInfoPatcher,
                            DWARFVersion Version);
 
   /// Finalize debug sections in the main binary.
   CUOffsetMap finalizeDebugSections(DebugInfoBinaryPatcher &DebugInfoPatcher);
 
   /// Patches the binary for DWARF address ranges (e.g. in functions and lexical
   /// blocks) to be updated.
   void updateDebugAddressRanges();

bolt/lib/Core/DebugData.cpp

 extern llvm::cl::opt<unsigned> Verbosity;
 } // namespace opts
 
 namespace llvm {
 class MCSymbol;
 
 namespace bolt {
 
-/// Finds attributes FormValue and Offset.
-///
-/// \param DIE die to look up in.
-/// \param Index the attribute index to extract.
-/// \return an optional AttrInfo with DWARFFormValue and Offset.
 Optional<AttrInfo>
 findAttributeInfo(const DWARFDie DIE,
                   const DWARFAbbreviationDeclaration *AbbrevDecl,
                   uint32_t Index) {
   const DWARFUnit &U = *DIE.getDwarfUnit();
   uint64_t Offset =
       AbbrevDecl->getAttributeOffsetFromIndex(Index, DIE.getOffset(), U);
   Optional<DWARFFormValue> Value =
if (ValSizeOpt) {
     uint64_t NewOffset = Offset;
     DWARFFormValue::skipValue(Value->getForm(), DebugInfoData, &NewOffset,
                               U.getFormParams());
     // This includes entire size of the entry, which might not be just the
     // encoding part. For example for DW_AT_loc it will include expression
     // location.
     ValSize = NewOffset - Offset;
   }
+  return AttrInfo{*Value, DIE.getAbbreviationDeclarationPtr(), Offset, ValSize};
+}
 
-  return AttrInfo{*Value, Offset, ValSize};
+Optional<AttrInfo> findAttributeInfo(const DWARFDie DIE,
+                                     dwarf::Attribute Attr) {
+  if (!DIE.isValid())
+    return None;
+  const DWARFAbbreviationDeclaration *AbbrevDecl =
+      DIE.getAbbreviationDeclarationPtr();
+  if (!AbbrevDecl)
+    return None;
+  Optional<uint32_t> Index = AbbrevDecl->findAttributeIndex(Attr);
+  if (!Index)
+    return None;
+  return findAttributeInfo(DIE, AbbrevDecl, *Index);
 }
 
 const DebugLineTableRowRef DebugLineTableRowRef::NULL_ROW{0, 0};
 
 namespace {
 
 LLVM_ATTRIBUTE_UNUSED
 static void printLE64(const std::string &S) {
   for (uint32_t I = 0, Size = S.size(); I < Size; ++I) {

 
 uint64_t DebugAddrWriterDwarf5::getOffset(DWARFUnit &Unit) {
   auto Iter = DWOIdToOffsetMap.find(getCUID(Unit));
   assert(Iter != DWOIdToOffsetMap.end() &&
          "Offset in to.debug_addr was not found for CU ID.");
   return Iter->second;
 }
 
-DebugLocWriter::DebugLocWriter(BinaryContext *BC) {
+void DebugLocWriter::init() {
   LocBuffer = std::make_unique<DebugBufferVector>();
   LocStream = std::make_unique<raw_svector_ostream>(*LocBuffer);
+  // Writing out empty location list to which all references to empty location
+  // lists will point.
+  if (!LocSectionOffset && DwarfVersion < 5) {
+    const char Zeroes[16] = {0};
+    *LocStream << StringRef(Zeroes, 16);
+    LocSectionOffset += 16;
+  }
 }
 
-void DebugLocWriter::addList(uint64_t AttrOffset, uint32_t LocListIndex,
-                             DebugLocationsVector &&LocList) {
+uint32_t DebugLocWriter::LocSectionOffset = 0;
+void DebugLocWriter::addList(AttrInfo &AttrVal, DebugLocationsVector &LocList,
+                             DebugInfoBinaryPatcher &DebugInfoPatcher,
+                             DebugAbbrevWriter &AbbrevWriter) {
+  const uint64_t AttrOffset = AttrVal.Offset;
   if (LocList.empty()) {
-    EmptyAttrLists.push_back(AttrOffset);
+    DebugInfoPatcher.addLE32Patch(AttrOffset, DebugLocWriter::EmptyListOffset);
     return;
   }
   // Since there is a separate DebugLocWriter for each thread,
   // we don't need a lock to read the SectionOffset and update it.
-  const uint32_t EntryOffset = SectionOffset;
+  const uint32_t EntryOffset = LocSectionOffset;
 
   for (const DebugLocationEntry &Entry : LocList) {
     support::endian::write(*LocStream, static_cast<uint64_t>(Entry.LowPC),
                            support::little);
     support::endian::write(*LocStream, static_cast<uint64_t>(Entry.HighPC),
                            support::little);
     support::endian::write(*LocStream, static_cast<uint16_t>(Entry.Expr.size()),
                            support::little);
     *LocStream << StringRef(reinterpret_cast<const char *>(Entry.Expr.data()),
                             Entry.Expr.size());
-    SectionOffset += 2 * 8 + 2 + Entry.Expr.size();
+    LocSectionOffset += 2 * 8 + 2 + Entry.Expr.size();
   }
   LocStream->write_zeros(16);
-  SectionOffset += 16;
+  LocSectionOffset += 16;
   LocListDebugInfoPatches.push_back({AttrOffset, EntryOffset});
-}
-
-void DebugLoclistWriter::addList(uint64_t AttrOffset, uint32_t LocListIndex,
-                                 DebugLocationsVector &&LocList) {
-  Patches.push_back({AttrOffset, LocListIndex, std::move(LocList)});
+  DebugInfoPatcher.addLE32Patch(AttrOffset, EntryOffset);
 }
 
 std::unique_ptr<DebugBufferVector> DebugLocWriter::getBuffer() {
   return std::move(LocBuffer);
 }
 
 // DWARF 4: 2.6.2
-void DebugLocWriter::finalize(uint64_t SectionOffset,
-                              SimpleBinaryPatcher &DebugInfoPatcher) {
-  for (const auto LocListDebugInfoPatchType : LocListDebugInfoPatches) {
-    uint64_t Offset = SectionOffset + LocListDebugInfoPatchType.LocListOffset;
-    DebugInfoPatcher.addLE32Patch(LocListDebugInfoPatchType.DebugInfoAttrOffset,
-                                  Offset);
-  }
-
-  for (uint64_t DebugInfoAttrOffset : EmptyAttrLists)
-    DebugInfoPatcher.addLE32Patch(DebugInfoAttrOffset,
-                                  DebugLocWriter::EmptyListOffset);
-}
+void DebugLocWriter::finalize(DebugInfoBinaryPatcher &DebugInfoPatcher,
+                              DebugAbbrevWriter &AbbrevWriter) {}
 
 static void writeEmptyListDwarf5(raw_svector_ostream &Stream) {
   support::endian::write(Stream, static_cast<uint32_t>(4), support::little);
   support::endian::write(Stream, static_cast<uint8_t>(dwarf::DW_LLE_start_end),
                          support::little);
 
   const char Zeroes[16] = {0};
   Stream << StringRef(Zeroes, 16);
   encodeULEB128(0, Stream);
   support::endian::write(
       Stream, static_cast<uint8_t>(dwarf::DW_LLE_end_of_list), support::little);
 }
 
-void DebugLoclistWriter::finalizeDWARF5(uint64_t SectionOffset,
-                                        SimpleBinaryPatcher &DebugInfoPatcher) {
-
-  std::unique_ptr<DebugBufferVector> LocArrayBuffer =
-      std::make_unique<DebugBufferVector>();
-  std::unique_ptr<raw_svector_ostream> LocArrayStream =
-      std::make_unique<raw_svector_ostream>(*LocArrayBuffer);
-  std::unique_ptr<DebugBufferVector> LocBodyBuffer =
-      std::make_unique<DebugBufferVector>();
-  std::unique_ptr<raw_svector_ostream> LocBodyStream =
-      std::make_unique<raw_svector_ostream>(*LocBodyBuffer);
-
-  const uint32_t SizeOfArraySection = Patches.size() * sizeof(uint32_t);
-  std::sort(Patches.begin(), Patches.end(),
-            [](const LocPatch &P1, const LocPatch &P2) -> bool {
-              return P1.Index < P2.Index;
-            });
-
-  if (LocListsBaseAttrOffset != InvalidLocListsBaseAttrOffset)
-    DebugInfoPatcher.addLE32Patch(LocListsBaseAttrOffset,
-                                  SectionOffset +
-                                      getDWARF5RngListLocListHeaderSize());
+static void writeLegacyLocList(AttrInfo &AttrVal, DebugLocationsVector &LocList,
+                               DebugInfoBinaryPatcher &DebugInfoPatcher,
+                               DebugAddrWriter &AddrWriter,
+                               DebugBufferVector &LocBuffer, DWARFUnit &CU,
+                               raw_svector_ostream &LocStream) {
+  const uint64_t AttrOffset = AttrVal.Offset;
+  if (LocList.empty()) {
+    DebugInfoPatcher.addLE32Patch(AttrOffset, DebugLocWriter::EmptyListOffset);
+    return;
+  }
 
-  uint32_t Index{0};
-  for (LocPatch &Patch : Patches) {
-    const uint32_t EntryOffset = LocBodyBuffer->size();
-    if (Patch.LocList.empty()) {
-      if (Patch.Index == DebugLoclistWriter::InvalidIndex)
-        DebugInfoPatcher.addLE32Patch(Patch.AttrOffset, EntryOffset);
+  const uint32_t EntryOffset = LocBuffer.size();
+  for (const DebugLocationEntry &Entry : LocList) {
+    support::endian::write(LocStream,
+                           static_cast<uint8_t>(dwarf::DW_LLE_startx_length),
+                           support::little);
+    const uint32_t Index = AddrWriter.getIndexFromAddress(Entry.LowPC, CU);
+    encodeULEB128(Index, LocStream);
 
-      writeEmptyListDwarf5(*LocBodyStream);
-      continue;
-    }
+    support::endian::write(LocStream,
+                           static_cast<uint32_t>(Entry.HighPC - Entry.LowPC),
+                           support::little);
+    support::endian::write(LocStream, static_cast<uint16_t>(Entry.Expr.size()),
+                           support::little);
+    LocStream << StringRef(reinterpret_cast<const char *>(Entry.Expr.data()),
+                           Entry.Expr.size());
+  }
+  support::endian::write(LocStream,
+                         static_cast<uint8_t>(dwarf::DW_LLE_end_of_list),
+                         support::little);
+  DebugInfoPatcher.addLE32Patch(AttrOffset, EntryOffset);
 
-    assert(Patch.Index == DebugLoclistWriter::InvalidIndex ||
-           Patch.Index == Index++ && "Gap in LocList Index Array.");
-    (void)Index;
+static void writeDWARF5LocList(
+    uint32_t &NumberOfEntries, AttrInfo &AttrVal, DebugLocationsVector &LocList,
+    DebugInfoBinaryPatcher &DebugInfoPatcher, DebugAbbrevWriter &AbbrevWriter,
+    DebugAddrWriter &AddrWriter, DebugBufferVector &LocBodyBuffer,
+    std::vector<uint32_t> &RelativeLocListOffsets, DWARFUnit &CU,
+    raw_svector_ostream &LocBodyStream) {
+  if (AttrVal.V.getForm() != dwarf::DW_FORM_loclistx) {
+    AbbrevWriter.addAttributePatch(CU, AttrVal.AbbrevDecl,
+                                   dwarf::DW_AT_location, dwarf::DW_AT_location,
+                                   dwarf::DW_FORM_loclistx);
+  }
+  DebugInfoPatcher.addUDataPatch(AttrVal.Offset, NumberOfEntries, AttrVal.Size);
+  RelativeLocListOffsets.push_back(LocBodyBuffer.size());
+  ++NumberOfEntries;
+  if (LocList.empty()) {
+    writeEmptyListDwarf5(LocBodyStream);
+    return;
+  }
 
-    std::vector<uint64_t> OffsetsArray;
-    for (const DebugLocationEntry &Entry : Patch.LocList) {
-      support::endian::write(*LocBodyStream,
-                             static_cast<uint8_t>(dwarf::DW_LLE_startx_length),
-                             support::little);
-      const uint32_t Index = AddrWriter->getIndexFromAddress(Entry.LowPC, CU);
-      encodeULEB128(Index, *LocBodyStream);
-      encodeULEB128(Entry.HighPC - Entry.LowPC, *LocBodyStream);
-      encodeULEB128(Entry.Expr.size(), *LocBodyStream);
-      *LocBodyStream << StringRef(
-          reinterpret_cast<const char *>(Entry.Expr.data()), Entry.Expr.size());
-    }
-    support::endian::write(*LocBodyStream,
-                           static_cast<uint8_t>(dwarf::DW_LLE_end_of_list),
-                           support::little);
+  for (const DebugLocationEntry &Entry : LocList) {
+    support::endian::write(LocBodyStream,
+    const uint32_t Index = AddrWriter.getIndexFromAddress(Entry.LowPC, CU);
+    encodeULEB128(Index, LocBodyStream);
+    encodeULEB128(Entry.HighPC - Entry.LowPC, LocBodyStream);
+    encodeULEB128(Entry.Expr.size(), LocBodyStream);
+    LocBodyStream << StringRef(
+  support::endian::write(LocBodyStream,
+}
+
+void DebugLoclistWriter::addList(AttrInfo &AttrVal,
+                                 DebugLocationsVector &LocList,
+                                 DebugInfoBinaryPatcher &DebugInfoPatcher,
+                                 DebugAbbrevWriter &AbbrevWriter) {
+  if (DwarfVersion < 5)
+    writeLegacyLocList(AttrVal, LocList, DebugInfoPatcher, *AddrWriter,
+                       *LocBuffer, CU, *LocStream);
+  else
+    writeDWARF5LocList(NumberOfEntries, AttrVal, LocList, DebugInfoPatcher,
+                       AbbrevWriter, *AddrWriter, *LocBodyBuffer,
+                       RelativeLocListOffsets, CU, *LocBodyStream);
+}
+
+uint32_t DebugLoclistWriter::LoclistBaseOffset = 0;
+void DebugLoclistWriter::finalizeDWARF5(
+    DebugInfoBinaryPatcher &DebugInfoPatcher, DebugAbbrevWriter &AbbrevWriter) {
+  if (LocBodyBuffer->empty())
+    return;
 
-    // Write out IndexArray
+  std::unique_ptr<DebugBufferVector> LocArrayBuffer =
+      std::make_unique<DebugBufferVector>();
+  std::unique_ptr<raw_svector_ostream> LocArrayStream =
+      std::make_unique<raw_svector_ostream>(*LocArrayBuffer);
+
+  const uint32_t SizeOfArraySection = NumberOfEntries * sizeof(uint32_t);
+  for (uint32_t RelativeOffset : RelativeLocListOffsets)
     support::endian::write(
         *LocArrayStream,
-        static_cast<uint32_t>(SizeOfArraySection + EntryOffset),
+        static_cast<uint32_t>(SizeOfArraySection + RelativeOffset),
         support::little);
-    // Don't need to patch Index since we are re-using them.
-    if (Patch.Index == DebugLoclistWriter::InvalidIndex)
-      DebugInfoPatcher.addLE32Patch(Patch.AttrOffset, EntryOffset);
-    clearList(Patch.LocList);
-  }
-  if (!Patches.empty()) {
-    std::unique_ptr<DebugBufferVector> Header =
-        getDWARF5Header({static_cast<uint32_t>(SizeOfArraySection +
-                                               LocBodyBuffer.get()->size()),
-                         5, 8, 0, static_cast<uint32_t>(Patches.size())});
-    *LocStream << *Header;
-    *LocStream << *LocArrayBuffer;
-    *LocStream << *LocBodyBuffer;
-  }
-  clearList(Patches);
-}
+
+  std::unique_ptr<DebugBufferVector> Header = getDWARF5Header(
+      {static_cast<uint32_t>(SizeOfArraySection + LocBodyBuffer.get()->size()),
+       5, 8, 0, NumberOfEntries});
 
-void DebugLoclistWriter::finalizeDWARFLegacy(
-    uint64_t SectionOffset, SimpleBinaryPatcher &DebugInfoPatcher) {
-  for (LocPatch &Patch : Patches) {
-    if (Patch.LocList.empty()) {
-      DebugInfoPatcher.addLE32Patch(Patch.AttrOffset,
-                                    DebugLocWriter::EmptyListOffset);
-      continue;
-    }
-    const uint32_t EntryOffset = LocBuffer->size();
-    for (const DebugLocationEntry &Entry : Patch.LocList) {
-      support::endian::write(*LocStream,
-                             static_cast<uint8_t>(dwarf::DW_LLE_startx_length),
-                             support::little);
-      const uint32_t Index = AddrWriter->getIndexFromAddress(Entry.LowPC, CU);
-      encodeULEB128(Index, *LocStream);
-
-      // TODO: Support DWARF5
-      support::endian::write(*LocStream,
-                             static_cast<uint32_t>(Entry.HighPC - Entry.LowPC),
-                             support::little);
-      support::endian::write(*LocStream,
-                             static_cast<uint16_t>(Entry.Expr.size()),
-                             support::little);
-      *LocStream << StringRef(reinterpret_cast<const char *>(Entry.Expr.data()),
-                              Entry.Expr.size());
-    }
-    support::endian::write(*LocStream,
-                           static_cast<uint8_t>(dwarf::DW_LLE_end_of_list),
-                           support::little);
-    DebugInfoPatcher.addLE32Patch(Patch.AttrOffset, EntryOffset);
-    clearList(Patch.LocList);
-  }
-  clearList(Patches);
-}
-
-void DebugLoclistWriter::finalize(uint64_t SectionOffset,
-                                  SimpleBinaryPatcher &DebugInfoPatcher) {
-  if (DwarfVersion < 5)
-    finalizeDWARFLegacy(SectionOffset, DebugInfoPatcher);
-  else
-    finalizeDWARF5(SectionOffset, DebugInfoPatcher);
+  if (!isSplitDwarf()) {
+    if (Optional<AttrInfo> AttrInfoVal =
+            findAttributeInfo(CU.getUnitDIE(), dwarf::DW_AT_loclists_base))
+      DebugInfoPatcher.addLE32Patch(AttrInfoVal->Offset,
+                                    LoclistBaseOffset +
+                                        getDWARF5RngListLocListHeaderSize());
+    else {
+      AbbrevWriter.addAttribute(
+          CU, CU.getUnitDIE().getAbbreviationDeclarationPtr(),
+          dwarf::DW_AT_loclists_base, dwarf::DW_FORM_sec_offset);
+      DebugInfoPatcher.insertNewEntry(CU.getUnitDIE(),
+                                      LoclistBaseOffset + Header->size());
+    }
+    LoclistBaseOffset += LocBuffer->size();
+  }
+  clearList(RelativeLocListOffsets);
+  clearList(*LocArrayBuffer);
+  clearList(*LocBodyBuffer);
+}
+
+void DebugLoclistWriter::finalize(DebugInfoBinaryPatcher &DebugInfoPatcher,
+                                  DebugAbbrevWriter &AbbrevWriter) {
+  if (DwarfVersion >= 5)
+    finalizeDWARF5(DebugInfoPatcher, AbbrevWriter);
 }
 
 DebugAddrWriter *DebugLoclistWriter::AddrWriter = nullptr;
 
 void DebugInfoBinaryPatcher::addUnitBaseOffsetLabel(uint64_t Offset) {
   Offset -= DWPUnitOffset;
   std::lock_guard<std::mutex> Lock(WriterMutex);
   DebugPatches.emplace_back(new DWARFUnitOffsetBaseLabel(Offset));

bolt/lib/Rewrite/DWARFRewriter.cpp

static void printDie(const DWARFDie &DIE) {
   DIE.dump(dbgs(), 0, DumpOpts);
 }
 
 namespace llvm {
 namespace bolt {
 /// Finds attributes FormValue and Offset.
 ///
 /// \param DIE die to look up in.
-/// \param Attr the attribute to extract.
-/// \return an optional AttrInfo with DWARFFormValue and Offset.
-static Optional<AttrInfo> findAttributeInfo(const DWARFDie DIE,
-                                            dwarf::Attribute Attr) {
-  if (!DIE.isValid())
-    return None;
-  const DWARFAbbreviationDeclaration *AbbrevDecl =
-      DIE.getAbbreviationDeclarationPtr();
-  if (!AbbrevDecl)
-    return None;
-  Optional<uint32_t> Index = AbbrevDecl->findAttributeIndex(Attr);
-  if (!Index)
-    return None;
-  return findAttributeInfo(DIE, AbbrevDecl, *Index);
-}
-
-/// Finds attributes FormValue and Offset.
-///
-/// \param DIE die to look up in.
 /// \param Attrs finds the first attribute that matches and extracts it.
 /// \return an optional AttrInfo with DWARFFormValue and Offset.
 Optional<AttrInfo> findAttributeInfo(const DWARFDie DIE,
                                      std::vector<dwarf::Attribute> Attrs) {
   for (dwarf::Attribute &Attr : Attrs)
     if (Optional<AttrInfo> Info = findAttributeInfo(DIE, Attr))
       return Info;
   return None;
void DWARFRewriter::updateDebugInfo() {
 
   ARangesSectionWriter = std::make_unique<DebugARangesSectionWriter>();
   StrWriter = std::make_unique<DebugStrWriter>(BC);
 
   StrOffstsWriter = std::make_unique<DebugStrOffsetsWriter>();
 
   AbbrevWriter = std::make_unique<DebugAbbrevWriter>(*BC.DwCtx);
 
-  if (BC.isDWARF5Used()) {
-    // Disabling none deterministic mode for dwarf5, to keep implementation
-    // simpler.
+  if (!opts::DeterministicDebugInfo) {
     opts::DeterministicDebugInfo = true;
+    errs() << "BOLT-WARNING: --deterministic-debuginfo is being deprecated\n";
+  }
+
+  if (BC.isDWARF5Used()) {
     AddrWriter = std::make_unique<DebugAddrWriterDwarf5>(&BC);
     RangesSectionWriter = std::make_unique<DebugRangeListsSectionWriter>();
     DebugRangeListsSectionWriter::setAddressWriter(AddrWriter.get());
   } else {
     AddrWriter = std::make_unique<DebugAddrWriter>(&BC);
     RangesSectionWriter = std::make_unique<DebugRangesSectionWriter>();
   }
 
   DebugLoclistWriter::setAddressWriter(AddrWriter.get());
 
   size_t CUIndex = 0;
   for (std::unique_ptr<DWARFUnit> &CU : BC.DwCtx->compile_units()) {
     const uint16_t DwarfVersion = CU->getVersion();
     if (DwarfVersion >= 5) {
-      uint32_t AttrInfoOffset =
-          DebugLoclistWriter::InvalidLocListsBaseAttrOffset;
-      if (Optional<AttrInfo> AttrInfoVal =
-              findAttributeInfo(CU->getUnitDIE(), dwarf::DW_AT_loclists_base)) {
-        AttrInfoOffset = AttrInfoVal->Offset;
-        LocListWritersByCU[CUIndex] = std::make_unique<DebugLoclistWriter>(
-            &BC, *CU.get(), AttrInfoOffset, DwarfVersion, false);
-      }
+      LocListWritersByCU[CUIndex] =
+          std::make_unique<DebugLoclistWriter>(*CU.get(), DwarfVersion, false);
+
       if (Optional<uint64_t> DWOId = CU->getDWOId()) {
         assert(LocListWritersByCU.count(*DWOId) == 0 &&
                "RangeLists writer for DWO unit already exists.");
         auto RangeListsSectionWriter =
             std::make_unique<DebugRangeListsSectionWriter>();
         RangeListsSectionWriter->initSection(*CU.get());
         RangeListsWritersByCU[*DWOId] = std::move(RangeListsSectionWriter);
       }
 
     } else {
-      LocListWritersByCU[CUIndex] = std::make_unique<DebugLocWriter>(&BC);
+      LocListWritersByCU[CUIndex] = std::make_unique<DebugLocWriter>();
     }
 
     if (Optional<uint64_t> DWOId = CU->getDWOId()) {
       assert(LocListWritersByCU.count(*DWOId) == 0 &&
              "LocList writer for DWO unit already exists.");
       // Work around some bug in llvm-15. If I pass in directly lld reports
       // undefined symbol.
-      auto constexpr WorkAround =
-          DebugLoclistWriter::InvalidLocListsBaseAttrOffset;
-      LocListWritersByCU[*DWOId] = std::make_unique<DebugLoclistWriter>(
-          &BC, *CU.get(), WorkAround, DwarfVersion, true);
+      LocListWritersByCU[*DWOId] =
+          std::make_unique<DebugLoclistWriter>(*CU.get(), DwarfVersion, true);
     }
     ++CUIndex;
   }
 
   // Unordered maps to handle name collision if output DWO directory is
   // specified.
   std::unordered_map<std::string, uint32_t> NameToIndexMap;
   std::unordered_map<uint64_t, std::string> DWOIdToName;
if (SplitCU) {
         DwoDebugInfoPatcher->setRangeBase(*RangesBase);
       }
 
       DwoDebugInfoPatcher->addUnitBaseOffsetLabel((*SplitCU)->getOffset());
       DebugAbbrevWriter *DWOAbbrevWriter =
           createBinaryDWOAbbrevWriter((*SplitCU)->getContext(), *DWOId);
       updateUnitDebugInfo(*(*SplitCU), *DwoDebugInfoPatcher, *DWOAbbrevWriter,
                           *DebugLocWriter, *TempRangesSectionWriter);
+      DebugLocWriter->finalize(*DwoDebugInfoPatcher, *DWOAbbrevWriter);
       DwoDebugInfoPatcher->clearDestinationLabels();
       if (!DwoDebugInfoPatcher->getWasRangBasedUsed())
         RangesBase = None;
       if (Unit->getVersion() >= 5)
         TempRangesSectionWriter->finalizeSection();
     }
 
     {
       std::lock_guard<std::mutex> Lock(AccessMutex);
       auto LocListWriterIter = LocListWritersByCU.find(CUIndex);
       if (LocListWriterIter != LocListWritersByCU.end())
         DebugLocWriter = LocListWriterIter->second.get();
     }
     if (Unit->getVersion() >= 5) {
       RangesBase = RangesSectionWriter->getSectionOffset() +
                    getDWARF5RngListLocListHeaderSize();
       RangesSectionWriter.get()->initSection(*Unit);
       StrOffstsWriter->finalizeSection();
     }
 
     DebugInfoPatcher->addUnitBaseOffsetLabel(Unit->getOffset());
     updateUnitDebugInfo(*Unit, *DebugInfoPatcher, *AbbrevWriter,
                         *DebugLocWriter, *RangesSectionWriter, RangesBase);
+    DebugLocWriter->finalize(*DebugInfoPatcher, *AbbrevWriter);
     if (Unit->getVersion() >= 5)
       RangesSectionWriter.get()->finalizeSection();
   };
 
   CUIndex = 0;
   if (opts::NoThreads || opts::DeterministicDebugInfo) {
     for (std::unique_ptr<DWARFUnit> &CU : BC.DwCtx->compile_units()) {
       processUnitDIE(CUIndex, CU.get());
default: {
           DebugLocationsVector InputLL;
 
           Optional<object::SectionedAddress> SectionAddress =
               Unit.getBaseAddress();
           uint64_t BaseAddress = 0;
           if (SectionAddress)
             BaseAddress = SectionAddress->Address;
 
-          if (Unit.getVersion() >= 5) {
+          if (Unit.getVersion() >= 5 &&
+              AttrVal->V.getForm() == dwarf::DW_FORM_loclistx) {
             Optional<uint64_t> LocOffset = Unit.getLoclistOffset(Offset);
             assert(LocOffset && "Location Offset is invalid.");
             Offset = *LocOffset;
           }
 
           Error E = Unit.getLocationTable().visitLocationList(
               &Offset, [&](const DWARFLocationEntry &Entry) {
                 switch (Entry.Kind) {
default: {
                   assert(
                       (Entry.SectionIndex == SectionedAddress::UndefSection &&
                        (!Unit.isDWOUnit() || Unit.getVersion() == 5)) &&
                       "absolute address expected");
                   InputLL.emplace_back(DebugLocationEntry{
                       BaseAddress + Entry.Value0, BaseAddress + Entry.Value1,
                       Entry.Loc});
                   break;
-                case dwarf::DW_RLE_start_length:
+                case dwarf::DW_LLE_start_length:
                   InputLL.emplace_back(DebugLocationEntry{
                       Entry.Value0, Entry.Value0 + Entry.Value1, Entry.Loc});
                   break;
                 case dwarf::DW_LLE_base_addressx: {
                   Optional<object::SectionedAddress> EntryAddress =
                       Unit.getAddrOffsetSectionItem(Entry.Value0);
                   assert(EntryAddress && "base Address not found.");
                   BaseAddress = EntryAddress->Address;
default: {
                        << Twine::utohexstr(Unit.getOffset()) << '\n';
               });
             } else {
               // It's possible for a subprogram to be removed and to have
               // address of 0. Adding this entry to output to preserve debug
               // information.
               OutputLL = InputLL;
             }
-            uint32_t LocListIndex = 0;
-            dwarf::Form Form = Value.getForm();
-            if (Form == dwarf::DW_FORM_sec_offset ||
-                Form == dwarf::DW_FORM_data4) {
-              // For DWARF5 we can access location list entry either using
-              // index, or offset. If it's offset, then it's from begnning of
-              // the file. This implementation was before we could add entries
-              // to the DIE. For DWARF4 this is no-op.
-              // TODO: For DWARF5 convert all the offset based entries to index
-              // based, and insert loclist_base if necessary.
-              LocListIndex = DebugLoclistWriter::InvalidIndex;
-            } else if (Form == dwarf::DW_FORM_loclistx) {
-              LocListIndex = Value.getRawUValue();
-            } else {
-              llvm_unreachable("Unsupported LocList access Form.");
-            }
-            DebugLocWriter.addList(AttrOffset, LocListIndex,
-                                   std::move(OutputLL));
+            DebugLocWriter.addList(*AttrVal, OutputLL, DebugInfoPatcher,
+                                   AbbrevWriter);
           }
         } else {
           assert((Value.isFormClass(DWARFFormValue::FC_Exprloc) ||
                   Value.isFormClass(DWARFFormValue::FC_Block)) &&
                  "unexpected DW_AT_location form");
           if (Unit.isDWOUnit() || Unit.getVersion() >= 5) {
             ArrayRef<uint8_t> Expr = *Value.getAsBlock();
             DataExtractor Data(
BC.registerOrUpdateNoteSection(
       llvm::isa<DebugRangeListsSectionWriter>(*RangesSectionWriter)
           ? ".debug_rnglists"
           : ".debug_ranges",
       copyByteArray(*RangesSectionContents), RangesSectionContents->size());
 
   if (BC.isDWARF5Used()) {
     std::unique_ptr<DebugBufferVector> LocationListSectionContents =
         makeFinalLocListsSection(DebugInfoPatcher, DWARFVersion::DWARF5);
-    BC.registerOrUpdateNoteSection(".debug_loclists",
-                                   copyByteArray(*LocationListSectionContents),
-                                   LocationListSectionContents->size());
+    if (!LocationListSectionContents->empty())
+      BC.registerOrUpdateNoteSection(
+          ".debug_loclists", copyByteArray(*LocationListSectionContents),
   }
 
   if (BC.isDWARFLegacyUsed()) {
     std::unique_ptr<DebugBufferVector> LocationListSectionContents =
         makeFinalLocListsSection(DebugInfoPatcher, DWARFVersion::DWARFLegacy);
-    BC.registerOrUpdateNoteSection(".debug_loc",
-                                   copyByteArray(*LocationListSectionContents),
-                                   LocationListSectionContents->size());
+    if (!LocationListSectionContents->empty())
+      BC.registerOrUpdateNoteSection(
+          ".debug_loc", copyByteArray(*LocationListSectionContents),
   }
 
   // AddrWriter should be finalized after debug_loc since more addresses can be
   // added there.
   if (AddrWriter->isInitialized()) {
     AddressSectionBuffer AddressSectionContents = AddrWriter->finalize();
     BC.registerOrUpdateNoteSection(".debug_addr",
                                    copyByteArray(AddressSectionContents),
void DWARFRewriter::updateGdbIndexSection(CUOffsetMap &CUMap) {
   // Copy over the rest of the original data.
   memcpy(Buffer, Data, TrailingSize);
 
   // Register the new section.
   BC.registerOrUpdateNoteSection(".gdb_index", NewGdbIndexContents,
                                  NewGdbIndexSize);
 }
 
-std::unique_ptr<DebugBufferVector>
-DWARFRewriter::makeFinalLocListsSection(SimpleBinaryPatcher &DebugInfoPatcher,
-                                        DWARFVersion Version) {
+std::unique_ptr<DebugBufferVector> DWARFRewriter::makeFinalLocListsSection(
+    DebugInfoBinaryPatcher &DebugInfoPatcher, DWARFVersion Version) {
   auto LocBuffer = std::make_unique<DebugBufferVector>();
   auto LocStream = std::make_unique<raw_svector_ostream>(*LocBuffer);
   auto Writer =
       std::unique_ptr<MCObjectWriter>(BC.createObjectWriter(*LocStream));
 
-  uint64_t SectionOffset = 0;
-  // Add an empty list as the first entry;
-  if (LocListWritersByCU.empty() ||
-      LocListWritersByCU.begin()->second.get()->getDwarfVersion() < 5) {
-    // Should be fine for both DWARF4 and DWARF5?
-    const char Zeroes[16] = {0};
-    *LocStream << StringRef(Zeroes, 16);
-    SectionOffset += 2 * 8;
-  }
-
   for (std::pair<const uint64_t, std::unique_ptr<DebugLocWriter>> &Loc :
        LocListWritersByCU) {
     DebugLocWriter *LocWriter = Loc.second.get();
     auto *LocListWriter = llvm::dyn_cast<DebugLoclistWriter>(LocWriter);
 
+    // Filter out DWARF4, writing out DWARF5
     if (Version == DWARFVersion::DWARF5 &&
         (!LocListWriter || LocListWriter->getDwarfVersion() <= 4))
       continue;
 
+    // Filter out DWARF5, writing out DWARF4
     if (Version == DWARFVersion::DWARFLegacy &&
         (LocListWriter && LocListWriter->getDwarfVersion() >= 5))
       continue;
+
+    // Skipping DWARF4/5 split dwarf.
     if (LocListWriter && (LocListWriter->getDwarfVersion() <= 4 ||
                           (LocListWriter->getDwarfVersion() >= 5 &&
                            LocListWriter->isSplitDwarf()))) {
-      SimpleBinaryPatcher *Patcher =
-          getBinaryDWODebugInfoPatcher(LocListWriter->getCUID());
-      LocListWriter->finalize(0, *Patcher);
       continue;
     }
-    LocWriter->finalize(SectionOffset, DebugInfoPatcher);
     std::unique_ptr<DebugBufferVector> CurrCULocationLists =
         LocWriter->getBuffer();
     *LocStream << *CurrCULocationLists;
-    SectionOffset += CurrCULocationLists->size();
   }
 
   return LocBuffer;
 }
 
 namespace {
 
 void getRangeAttrData(DWARFDie DIE, Optional<AttrInfo> &LowPCVal,

bolt/test/Inputs/dwarf5-loclist-offset-form-helper.s

+# int fooVar = 0;
+# void useFoo(int * x) {
+#   *x += 4;
+# }
+# int  foo(int argc) {
+#    int x = argc;
+#    useFoo(&x);
+#    return x;
+# }
+
+  .text
+  .file "helper.cpp"
+  .file 0 "." "helper.cpp" md5 0xf1508be63cfcbaf913e2dfef3cd5bccc
+  .globl  _Z6useFooPi                     # -- Begin function _Z6useFooPi
+  .p2align  4, 0x90
+  .type _Z6useFooPi,@function
+_Z6useFooPi:                            # @_Z6useFooPi
+.Lfunc_begin0:
+  .loc  0 2 0                           # helper.cpp:2:0
+  .cfi_startproc
+# %bb.0:                                # %entry
+  #DEBUG_VALUE: useFoo:x <- $rdi
+  .loc  0 3 5 prologue_end              # helper.cpp:3:5
+  addl  $4, (%rdi)
+  .loc  0 4 2                           # helper.cpp:4:2
+  retq
+.Ltmp0:
+.Lfunc_end0:
+  .size _Z6useFooPi, .Lfunc_end0-_Z6useFooPi
+  .cfi_endproc
+                                        # -- End function
+  .globl  _Z3fooi                         # -- Begin function _Z3fooi
+  .p2align  4, 0x90
+  .type _Z3fooi,@function
+_Z3fooi:                                # @_Z3fooi
+.Lfunc_begin1:
+  .loc  0 6 0                           # helper.cpp:6:0
+  .cfi_startproc
+# %bb.0:                                # %entry
+  #DEBUG_VALUE: foo:argc <- $edi
+  #DEBUG_VALUE: foo:x <- $edi
+                                        # kill: def $edi killed $edi def $rdi
+  #DEBUG_VALUE: useFoo:x <- undef
+  .loc  0 3 5 prologue_end              # helper.cpp:3:5
+  leal  4(%rdi), %eax
+.Ltmp1:
+  #DEBUG_VALUE: foo:x <- $eax
+  .loc  0 9 5                           # helper.cpp:9:5
+  retq
+.Ltmp2:
+.Lfunc_end1:
+  .size _Z3fooi, .Lfunc_end1-_Z3fooi
+  .cfi_endproc
+                                        # -- End function
+  .type fooVar,@object                  # @fooVar
+  .bss
+  .globl  fooVar
+  .p2align  2
+fooVar:
+  .long 0                               # 0x0
+  .size fooVar, 4
+
+  .section  .debug_loclists,"",@progbits
+  .long .Ldebug_list_header_end0-.Ldebug_list_header_start0 # Length
+.Ldebug_list_header_start0:
+  .short  5                               # Version
+  .byte 8                               # Address size
+  .byte 0                               # Segment selector size
+  .long 1                               # Offset entry count
+.Lloclists_table_base0:
+  .long .Ldebug_loc0-.Lloclists_table_base0
+.Ldebug_loc0:
+  .byte 4                               # DW_LLE_offset_pair
+  .uleb128 .Lfunc_begin1-.Lfunc_begin0    #   starting offset
+  .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
+  .byte 1                               # Loc expr size
+  .byte 85                              # super-register DW_OP_reg5
+  .byte 4                               # DW_LLE_offset_pair
+  .uleb128 .Ltmp1-.Lfunc_begin0           #   starting offset
+  .uleb128 .Lfunc_end1-.Lfunc_begin0      #   ending offset
+  .byte 1                               # Loc expr size
+  .byte 80                              # super-register DW_OP_reg0
+  .byte 0                               # DW_LLE_end_of_list
+.Ldebug_list_header_end0:
+  .section  .debug_abbrev,"",@progbits
+  .byte 1                               # Abbreviation Code
+  .byte 17                              # DW_TAG_compile_unit
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 37                              # DW_AT_producer
+  .byte 37                              # DW_FORM_strx1
+  .byte 19                              # DW_AT_language
+  .byte 5                               # DW_FORM_data2
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 114                             # DW_AT_str_offsets_base
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 16                              # DW_AT_stmt_list
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 27                              # DW_AT_comp_dir
+  .byte 37                              # DW_FORM_strx1
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 115                             # DW_AT_addr_base
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 2                               # Abbreviation Code
+  .byte 52                              # DW_TAG_variable
+  .byte 0                               # DW_CHILDREN_no
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 63                              # DW_AT_external
+  .byte 25                              # DW_FORM_flag_present
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 2                               # DW_AT_location
+  .byte 24                              # DW_FORM_exprloc
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 3                               # Abbreviation Code
+  .byte 36                              # DW_TAG_base_type
+  .byte 0                               # DW_CHILDREN_no
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 62                              # DW_AT_encoding
+  .byte 11                              # DW_FORM_data1
+  .byte 11                              # DW_AT_byte_size
+  .byte 11                              # DW_FORM_data1
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 4                               # Abbreviation Code
+  .byte 46                              # DW_TAG_subprogram
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 64                              # DW_AT_frame_base
+  .byte 24                              # DW_FORM_exprloc
+  .byte 122                             # DW_AT_call_all_calls
+  .byte 25                              # DW_FORM_flag_present
+  .byte 49                              # DW_AT_abstract_origin
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 5                               # Abbreviation Code
+  .byte 5                               # DW_TAG_formal_parameter
+  .byte 0                               # DW_CHILDREN_no
+  .byte 2                               # DW_AT_location
+  .byte 24                              # DW_FORM_exprloc
+  .byte 49                              # DW_AT_abstract_origin
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 6                               # Abbreviation Code
+  .byte 46                              # DW_TAG_subprogram
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 110                             # DW_AT_linkage_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 63                              # DW_AT_external
+  .byte 25                              # DW_FORM_flag_present
+  .byte 32                              # DW_AT_inline
+  .byte 33                              # DW_FORM_implicit_const
+  .byte 1
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 7                               # Abbreviation Code
+  .byte 5                               # DW_TAG_formal_parameter
+  .byte 0                               # DW_CHILDREN_no
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 8                               # Abbreviation Code
+  .byte 15                              # DW_TAG_pointer_type
+  .byte 0                               # DW_CHILDREN_no
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 9                               # Abbreviation Code
+  .byte 46                              # DW_TAG_subprogram
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 64                              # DW_AT_frame_base
+  .byte 24                              # DW_FORM_exprloc
+  .byte 122                             # DW_AT_call_all_calls
+  .byte 25                              # DW_FORM_flag_present
+  .byte 110                             # DW_AT_linkage_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 63                              # DW_AT_external
+  .byte 25                              # DW_FORM_flag_present
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 10                              # Abbreviation Code
+  .byte 5                               # DW_TAG_formal_parameter
+  .byte 0                               # DW_CHILDREN_no
+  .byte 2                               # DW_AT_location
+  .byte 24                              # DW_FORM_exprloc
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 11                              # Abbreviation Code
+  .byte 52                              # DW_TAG_variable
+  .byte 0                               # DW_CHILDREN_no
+  .byte 2                               # DW_AT_location
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 12                              # Abbreviation Code
+  .byte 29                              # DW_TAG_inlined_subroutine
+  .byte 0                               # DW_CHILDREN_no
+  .byte 49                              # DW_AT_abstract_origin
+  .byte 19                              # DW_FORM_ref4
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 88                              # DW_AT_call_file
+  .byte 11                              # DW_FORM_data1
+  .byte 89                              # DW_AT_call_line
+  .byte 11                              # DW_FORM_data1
+  .byte 87                              # DW_AT_call_column
+  .byte 11                              # DW_FORM_data1
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 0                               # EOM(3)
+  .section  .debug_info,"",@progbits
+.Lcu_begin0:
+  .long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
+.Ldebug_info_start0:
+  .short  5                               # DWARF version number
+  .byte 1                               # DWARF Unit Type
+  .byte 8                               # Address Size (in bytes)
+  .long .debug_abbrev                   # Offset Into Abbrev. Section
+  .byte 1                               # Abbrev [1] 0xc:0x83 DW_TAG_compile_unit
+  .byte 0                               # DW_AT_producer
+  .short  33                              # DW_AT_language
+  .byte 1                               # DW_AT_name
+  .long .Lstr_offsets_base0             # DW_AT_str_offsets_base
+  .long .Lline_table_start0             # DW_AT_stmt_list
+  .byte 2                               # DW_AT_comp_dir
+  .byte 1                               # DW_AT_low_pc
+  .long .Lfunc_end1-.Lfunc_begin0       # DW_AT_high_pc
+  .long .Laddr_table_base0              # DW_AT_addr_base
+  .byte 2                               # Abbrev [2] 0x27:0xb DW_TAG_variable
+  .byte 3                               # DW_AT_name
+  .long 50                              # DW_AT_type
+                                        # DW_AT_external
+  .byte 0                               # DW_AT_decl_file
+  .byte 1                               # DW_AT_decl_line
+  .byte 2                               # DW_AT_location
+  .byte 161
+  .byte 0
+  .byte 3                               # Abbrev [3] 0x32:0x4 DW_TAG_base_type
+  .byte 4                               # DW_AT_name
+  .byte 5                               # DW_AT_encoding
+  .byte 4                               # DW_AT_byte_size
+  .byte 4                               # Abbrev [4] 0x36:0x14 DW_TAG_subprogram
+  .byte 1                               # DW_AT_low_pc
+  .long .Lfunc_end0-.Lfunc_begin0       # DW_AT_high_pc
+  .byte 1                               # DW_AT_frame_base
+  .byte 87
+                                        # DW_AT_call_all_calls
+  .long 74                              # DW_AT_abstract_origin
+  .byte 5                               # Abbrev [5] 0x42:0x7 DW_TAG_formal_parameter
+  .byte 1                               # DW_AT_location
+  .byte 85
+  .long 79                              # DW_AT_abstract_origin
+  .byte 0                               # End Of Children Mark
+  .byte 6                               # Abbrev [6] 0x4a:0xe DW_TAG_subprogram
+  .byte 5                               # DW_AT_linkage_name
+  .byte 6                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 2                               # DW_AT_decl_line
+                                        # DW_AT_external
+                                        # DW_AT_inline
+  .byte 7                               # Abbrev [7] 0x4f:0x8 DW_TAG_formal_parameter
+  .byte 7                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 2                               # DW_AT_decl_line
+  .long 88                              # DW_AT_type
+  .byte 0                               # End Of Children Mark
+  .byte 8                               # Abbrev [8] 0x58:0x5 DW_TAG_pointer_type
+  .long 50                              # DW_AT_type
+  .byte 9                               # Abbrev [9] 0x5d:0x31 DW_TAG_subprogram
+  .byte 2                               # DW_AT_low_pc
+  .long .Lfunc_end1-.Lfunc_begin1       # DW_AT_high_pc
+  .byte 1                               # DW_AT_frame_base
+  .byte 87
+                                        # DW_AT_call_all_calls
+  .byte 8                               # DW_AT_linkage_name
+  .byte 9                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 6                               # DW_AT_decl_line
+  .long 50                              # DW_AT_type
+                                        # DW_AT_external
+  .byte 10                              # Abbrev [10] 0x6d:0xa DW_TAG_formal_parameter
+  .byte 1                               # DW_AT_location
+  .byte 85
+  .byte 10                              # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 6                               # DW_AT_decl_line
+  .long 50                              # DW_AT_type
+  .byte 11                              # Abbrev [11] 0x77:0x9 DW_TAG_variable
+  .long .Ldebug_loc0                    # DW_AT_location
+  .byte 7                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 7                               # DW_AT_decl_line
+  .long 50                              # DW_AT_type
+  .byte 12                              # Abbrev [12] 0x80:0xd DW_TAG_inlined_subroutine
+  .long 74                              # DW_AT_abstract_origin
+  .byte 2                               # DW_AT_low_pc
+  .long .Ltmp1-.Lfunc_begin1            # DW_AT_high_pc
+  .byte 0                               # DW_AT_call_file
+  .byte 8                               # DW_AT_call_line
+  .byte 5                               # DW_AT_call_column
+  .byte 0                               # End Of Children Mark
+  .byte 0                               # End Of Children Mark
+.Ldebug_info_end0:
+  .section  .debug_str_offsets,"",@progbits
+  .long 48                              # Length of String Offsets Set
+  .short  5
+  .short  0
+.Lstr_offsets_base0:
+  .section  .debug_str,"MS",@progbits,1
+.Linfo_string0:
+  .asciz  "clang version 15.0.0" # string offset=0
+.Linfo_string1:
+  .asciz  "helper.cpp"                    # string offset=134
+.Linfo_string2:
+  .asciz  "." # string offset=145
+.Linfo_string3:
+  .asciz  "fooVar"                        # string offset=183
+.Linfo_string4:
+  .asciz  "int"                           # string offset=190
+.Linfo_string5:
+  .asciz  "_Z6useFooPi"                   # string offset=194
+.Linfo_string6:
+  .asciz  "useFoo"                        # string offset=206
+.Linfo_string7:
+  .asciz  "x"                             # string offset=213
+.Linfo_string8:
+  .asciz  "_Z3fooi"                       # string offset=215
+.Linfo_string9:
+  .asciz  "foo"                           # string offset=223
+.Linfo_string10:
+  .asciz  "argc"                          # string offset=227
+  .section  .debug_str_offsets,"",@progbits
+  .long .Linfo_string0
+  .long .Linfo_string1
+  .long .Linfo_string2
+  .long .Linfo_string3
+  .long .Linfo_string4
+  .long .Linfo_string5
+  .long .Linfo_string6
+  .long .Linfo_string7
+  .long .Linfo_string8
+  .long .Linfo_string9
+  .long .Linfo_string10
+  .section  .debug_addr,"",@progbits
+  .long .Ldebug_addr_end0-.Ldebug_addr_start0 # Length of contribution
+.Ldebug_addr_start0:
+  .short  5                               # DWARF version number
+  .byte 8                               # Address size
+  .byte 0                               # Segment selector size
+.Laddr_table_base0:
+  .quad fooVar
+  .quad .Lfunc_begin0
+  .quad .Lfunc_begin1
+.Ldebug_addr_end0:
+  .ident  "clang version 15.0.0"
+  .section  ".note.GNU-stack","",@progbits
+  .addrsig
+  .section  .debug_line,"",@progbits
+.Lline_table_start0:

bolt/test/Inputs/dwarf5-loclist-offset-form-main.s

+# void use(int * x, int * y) {
+#   *x += 4;
+#   *y -= 2;
+# }
+#
+# extern int fooVar;
+# int  main(int argc, char *argv[]) {
+#    int x = argc;
+#    int y = fooVar + 3;
+#    use(&x, &y);
+#    return x + y;
+# }
+
+  .text
+  .file "main.cpp"
+  .globl  _Z3usePiS_                      # -- Begin function _Z3usePiS_
+  .p2align  4, 0x90
+  .type _Z3usePiS_,@function
+_Z3usePiS_:                             # @_Z3usePiS_
+.Lfunc_begin0:
+  .file 0 "." "main.cpp" md5 0x0df8b93231613cae17dbf82c0897c3b3
+  .loc  0 1 0                           # main.cpp:1:0
+  .cfi_startproc
+# %bb.0:                                # %entry
+  #DEBUG_VALUE: use:x <- $rdi
+  #DEBUG_VALUE: use:y <- $rsi
+  .loc  0 2 6 prologue_end              # main.cpp:2:6
+  addl  $4, (%rdi)
+  .loc  0 3 6                           # main.cpp:3:6
+  addl  $-2, (%rsi)
+  .loc  0 4 1                           # main.cpp:4:1
+  retq
+.Ltmp0:
+.Lfunc_end0:
+  .size _Z3usePiS_, .Lfunc_end0-_Z3usePiS_
+  .cfi_endproc
+                                        # -- End function
+  .globl  main                            # -- Begin function main
+  .p2align  4, 0x90
+  .type main,@function
+main:                                   # @main
+.Lfunc_begin1:
+  .loc  0 7 0                           # main.cpp:7:0
+  .cfi_startproc
+# %bb.0:                                # %entry
+  #DEBUG_VALUE: main:argc <- $edi
+  #DEBUG_VALUE: main:argv <- $rsi
+  #DEBUG_VALUE: main:x <- $edi
+                                        # kill: def $edi killed $edi def $rdi
+  .loc  0 9 13 prologue_end             # main.cpp:9:13
+  movq  fooVar@GOTPCREL(%rip), %rax
+  movl  (%rax), %eax
+.Ltmp1:
+  #DEBUG_VALUE: main:y <- [DW_OP_plus_uconst 3, DW_OP_stack_value] $eax
+  #DEBUG_VALUE: main:y <- [DW_OP_plus_uconst 1, DW_OP_stack_value] $eax
+  #DEBUG_VALUE: main:x <- [DW_OP_plus_uconst 4, DW_OP_stack_value] $edi
+  .loc  0 11 14                         # main.cpp:11:14
+  addl  %edi, %eax
+.Ltmp2:
+  addl  $5, %eax
+  .loc  0 11 5 is_stmt 0                # main.cpp:11:5
+  retq
+.Ltmp3:
+.Lfunc_end1:
+  .size main, .Lfunc_end1-main
+  .cfi_endproc
+                                        # -- End function
+  .section  .debug_loclists,"",@progbits
+  .long .Ldebug_list_header_end0-.Ldebug_list_header_start0 # Length
+.Ldebug_list_header_start0:
+  .short  5                               # Version
+  .byte 8                               # Address size
+  .byte 0                               # Segment selector size
+  .long 2                               # Offset entry count
+.Lloclists_table_base0:
+  .long .Ldebug_loc0-.Lloclists_table_base0
+  .long .Ldebug_loc1-.Lloclists_table_base0
+.Ldebug_loc0:
+  .byte 4                               # DW_LLE_offset_pair
+  .uleb128 .Lfunc_begin1-.Lfunc_begin0    #   starting offset
+  .uleb128 .Ltmp1-.Lfunc_begin0           #   ending offset
+  .byte 1                               # Loc expr size
+  .byte 85                              # super-register DW_OP_reg5
+  .byte 4                               # DW_LLE_offset_pair
+  .uleb128 .Ltmp1-.Lfunc_begin0           #   starting offset
+  .uleb128 .Lfunc_end1-.Lfunc_begin0      #   ending offset
+  .byte 10                              # Loc expr size
+  .byte 117                             # DW_OP_breg5
+  .byte 4                               # 4
+  .byte 16                              # DW_OP_constu
+  .byte 255                             # 4294967295
+  .byte 255                             #
+  .byte 255                             #
+  .byte 255                             #
+  .byte 15                              #
+  .byte 26                              # DW_OP_and
+  .byte 159                             # DW_OP_stack_value
+  .byte 0                               # DW_LLE_end_of_list
+.Ldebug_loc1:
+  .byte 4                               # DW_LLE_offset_pair
+  .uleb128 .Ltmp1-.Lfunc_begin0           #   starting offset
+  .uleb128 .Ltmp2-.Lfunc_begin0           #   ending offset
+  .byte 10                              # Loc expr size
+  .byte 112                             # DW_OP_breg0
+  .byte 1                               # 1
+  .byte 16                              # DW_OP_constu
+  .byte 255                             # 4294967295
+  .byte 255                             #
+  .byte 255                             #
+  .byte 255                             #
+  .byte 15                              #
+  .byte 26                              # DW_OP_and
+  .byte 159                             # DW_OP_stack_value
+  .byte 0                               # DW_LLE_end_of_list
+.Ldebug_list_header_end0:
+  .section  .debug_abbrev,"",@progbits
+  .byte 1                               # Abbreviation Code
+  .byte 17                              # DW_TAG_compile_unit
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 37                              # DW_AT_producer
+  .byte 37                              # DW_FORM_strx1
+  .byte 19                              # DW_AT_language
+  .byte 5                               # DW_FORM_data2
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 114                             # DW_AT_str_offsets_base
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 16                              # DW_AT_stmt_list
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 27                              # DW_AT_comp_dir
+  .byte 37                              # DW_FORM_strx1
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 115                             # DW_AT_addr_base
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 2                               # Abbreviation Code
+  .byte 46                              # DW_TAG_subprogram
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 64                              # DW_AT_frame_base
+  .byte 24                              # DW_FORM_exprloc
+  .byte 122                             # DW_AT_call_all_calls
+  .byte 25                              # DW_FORM_flag_present
+  .byte 110                             # DW_AT_linkage_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 63                              # DW_AT_external
+  .byte 25                              # DW_FORM_flag_present
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 3                               # Abbreviation Code
+  .byte 5                               # DW_TAG_formal_parameter
+  .byte 0                               # DW_CHILDREN_no
+  .byte 2                               # DW_AT_location
+  .byte 24                              # DW_FORM_exprloc
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 4                               # Abbreviation Code
+  .byte 46                              # DW_TAG_subprogram
+  .byte 1                               # DW_CHILDREN_yes
+  .byte 17                              # DW_AT_low_pc
+  .byte 27                              # DW_FORM_addrx
+  .byte 18                              # DW_AT_high_pc
+  .byte 6                               # DW_FORM_data4
+  .byte 64                              # DW_AT_frame_base
+  .byte 24                              # DW_FORM_exprloc
+  .byte 122                             # DW_AT_call_all_calls
+  .byte 25                              # DW_FORM_flag_present
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 63                              # DW_AT_external
+  .byte 25                              # DW_FORM_flag_present
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 5                               # Abbreviation Code
+  .byte 52                              # DW_TAG_variable
+  .byte 0                               # DW_CHILDREN_no
+  .byte 2                               # DW_AT_location
+  .byte 23                              # DW_FORM_sec_offset
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 58                              # DW_AT_decl_file
+  .byte 11                              # DW_FORM_data1
+  .byte 59                              # DW_AT_decl_line
+  .byte 11                              # DW_FORM_data1
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 6                               # Abbreviation Code
+  .byte 36                              # DW_TAG_base_type
+  .byte 0                               # DW_CHILDREN_no
+  .byte 3                               # DW_AT_name
+  .byte 37                              # DW_FORM_strx1
+  .byte 62                              # DW_AT_encoding
+  .byte 11                              # DW_FORM_data1
+  .byte 11                              # DW_AT_byte_size
+  .byte 11                              # DW_FORM_data1
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 7                               # Abbreviation Code
+  .byte 15                              # DW_TAG_pointer_type
+  .byte 0                               # DW_CHILDREN_no
+  .byte 73                              # DW_AT_type
+  .byte 19                              # DW_FORM_ref4
+  .byte 0                               # EOM(1)
+  .byte 0                               # EOM(2)
+  .byte 0                               # EOM(3)
+  .section  .debug_info,"",@progbits
+.Lcu_begin0:
+  .long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
+.Ldebug_info_start0:
+  .short  5                               # DWARF version number
+  .byte 1                               # DWARF Unit Type
+  .byte 8                               # Address Size (in bytes)
+  .long .debug_abbrev                   # Offset Into Abbrev. Section
+  .byte 1                               # Abbrev [1] 0xc:0x8a DW_TAG_compile_unit
+  .byte 0                               # DW_AT_producer
+  .short  33                              # DW_AT_language
+  .byte 1                               # DW_AT_name
+  .long .Lstr_offsets_base0             # DW_AT_str_offsets_base
+  .long .Lline_table_start0             # DW_AT_stmt_list
+  .byte 2                               # DW_AT_comp_dir
+  .byte 0                               # DW_AT_low_pc
+  .long .Lfunc_end1-.Lfunc_begin0       # DW_AT_high_pc
+  .long .Laddr_table_base0              # DW_AT_addr_base
+  .byte 2                               # Abbrev [2] 0x27:0x21 DW_TAG_subprogram
+  .byte 0                               # DW_AT_low_pc
+  .long .Lfunc_end0-.Lfunc_begin0       # DW_AT_high_pc
+  .byte 1                               # DW_AT_frame_base
+  .byte 87
+                                        # DW_AT_call_all_calls
+  .byte 3                               # DW_AT_linkage_name
+  .byte 4                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 1                               # DW_AT_decl_line
+                                        # DW_AT_external
+  .byte 3                               # Abbrev [3] 0x33:0xa DW_TAG_formal_parameter
+  .byte 1                               # DW_AT_location
+  .byte 85
+  .byte 7                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 1                               # DW_AT_decl_line
+  .long 130                             # DW_AT_type
+  .byte 3                               # Abbrev [3] 0x3d:0xa DW_TAG_formal_parameter
+  .byte 1                               # DW_AT_location
+  .byte 84
+  .byte 8                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 1                               # DW_AT_decl_line
+  .long 130                             # DW_AT_type
+  .byte 0                               # End Of Children Mark
+  .byte 4                               # Abbrev [4] 0x48:0x36 DW_TAG_subprogram
+  .byte 1                               # DW_AT_low_pc
+  .long .Lfunc_end1-.Lfunc_begin1       # DW_AT_high_pc
+  .byte 1                               # DW_AT_frame_base
+  .byte 87
+                                        # DW_AT_call_all_calls
+  .byte 5                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 7                               # DW_AT_decl_line
+  .long 126                             # DW_AT_type
+                                        # DW_AT_external
+  .byte 3                               # Abbrev [3] 0x57:0xa DW_TAG_formal_parameter
+  .byte 1                               # DW_AT_location
+  .byte 85
+  .byte 9                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 7                               # DW_AT_decl_line
+  .long 126                             # DW_AT_type
+  .byte 3                               # Abbrev [3] 0x61:0xa DW_TAG_formal_parameter
+  .byte 1                               # DW_AT_location
+  .byte 84
+  .byte 10                              # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 7                               # DW_AT_decl_line
+  .long 135                             # DW_AT_type
+  .byte 5                               # Abbrev [5] 0x6b:0x9 DW_TAG_variable
+  .long .Ldebug_loc0                    # DW_AT_location
+  .byte 7                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 8                               # DW_AT_decl_line
+  .long 126                             # DW_AT_type
+  .byte 5                               # Abbrev [5] 0x74:0x9 DW_TAG_variable
+  .long .Ldebug_loc1                    # DW_AT_location
+  .byte 8                               # DW_AT_name
+  .byte 0                               # DW_AT_decl_file
+  .byte 9                               # DW_AT_decl_line
+  .long 126                             # DW_AT_type
+  .byte 0                               # End Of Children Mark
+  .byte 6                               # Abbrev [6] 0x7e:0x4 DW_TAG_base_type
+  .byte 6                               # DW_AT_name
+  .byte 5                               # DW_AT_encoding
+  .byte 4                               # DW_AT_byte_size
+  .byte 7                               # Abbrev [7] 0x82:0x5 DW_TAG_pointer_type
+  .long 126                             # DW_AT_type
+  .byte 7                               # Abbrev [7] 0x87:0x5 DW_TAG_pointer_type
+  .long 140                             # DW_AT_type
+  .byte 7                               # Abbrev [7] 0x8c:0x5 DW_TAG_pointer_type
+  .long 145                             # DW_AT_type
+  .byte 6                               # Abbrev [6] 0x91:0x4 DW_TAG_base_type
+  .byte 11                              # DW_AT_name
+  .byte 6                               # DW_AT_encoding
+  .byte 1                               # DW_AT_byte_size
+  .byte 0                               # End Of Children Mark
+.Ldebug_info_end0:
+  .section  .debug_str_offsets,"",@progbits
+  .long 52                              # Length of String Offsets Set
+  .short  5
+  .short  0
+.Lstr_offsets_base0:
+  .section  .debug_str,"MS",@progbits,1
+.Linfo_string0:
+  .asciz  "clang version 15.0.0" # string offset=0
+.Linfo_string1:
+  .asciz  "main.cpp"                      # string offset=134
+.Linfo_string2:
+  .asciz  "." # string offset=143
+.Linfo_string3:
+  .asciz  "_Z3usePiS_"                    # string offset=181
+.Linfo_string4:
+  .asciz  "use"                           # string offset=192
+.Linfo_string5:
+  .asciz  "main"                          # string offset=196
+.Linfo_string6:
+  .asciz  "int"                           # string offset=201
+.Linfo_string7:
+  .asciz  "x"                             # string offset=205
+.Linfo_string8:
+  .asciz  "y"                             # string offset=207
+.Linfo_string9:
+  .asciz  "argc"                          # string offset=209
+.Linfo_string10:
+  .asciz  "argv"                          # string offset=214
+.Linfo_string11:
+  .asciz  "char"                          # string offset=219
+  .section  .debug_str_offsets,"",@progbits
+  .long .Linfo_string0
+  .long .Linfo_string1
+  .long .Linfo_string2
+  .long .Linfo_string3
+  .long .Linfo_string4
+  .long .Linfo_string5
+  .long .Linfo_string6
+  .long .Linfo_string7
+  .long .Linfo_string8
+  .long .Linfo_string9
+  .long .Linfo_string10
+  .long .Linfo_string11
+  .section  .debug_addr,"",@progbits
+  .long .Ldebug_addr_end0-.Ldebug_addr_start0 # Length of contribution
+.Ldebug_addr_start0:
+  .short  5                               # DWARF version number
+  .byte 8                               # Address size
+  .byte 0                               # Segment selector size
+.Laddr_table_base0:
+  .quad .Lfunc_begin0
+  .quad .Lfunc_begin1
+.Ldebug_addr_end0:
+  .ident  "clang version 15.0.0"
+  .section  ".note.GNU-stack","",@progbits
+  .addrsig
+  .section  .debug_line,"",@progbits
+.Lline_table_start0:

bolt/test/X86/dwarf4-df-dualcu-loclist.test

 ; PRE-BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000005, 0x0000000000000005)
 ; PRE-BOLT-DWO-MAIN: DW_TAG_formal_parameter [10]
 ; PRE-BOLT-DWO-MAIN-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000016:
 ; PRE-BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000003, 0x000000000000000c)
 ; PRE-BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000006, 0x000000000000000d)
 
 ; BOLT-DWO-MAIN: version = 0x0004
 ; BOLT-DWO-MAIN: DW_TAG_formal_parameter [10]
-; BOLT-DWO-MAIN-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000000:
+; BOLT-DWO-MAIN-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000010:
 ; BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000002, 0x0000000000000014)
 ; BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000003, 0x0000000000000005)
 ; BOLT-DWO-MAIN: DW_TAG_formal_parameter [10]
-; BOLT-DWO-MAIN-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000016:
+; BOLT-DWO-MAIN-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000026:
 ; BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000002, 0x000000000000000c)
-; BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000005, 0x000000000000000d)
+; BOLT-DWO-MAIN-NEXT: DW_LLE_startx_length   (0x0000000000000004, 0x000000000000000d)
 
 
 ; PRE-BOLT-DWO-HELPER: version = 0x0004
 ; PRE-BOLT-DWO-HELPER: DW_TAG_formal_parameter [5]
 ; PRE-BOLT-DWO-HELPER-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000000:
 ; PRE-BOLT-DWO-HELPER-NEXT: DW_LLE_startx_length   (0x0000000000000002, 0x0000000000000008)
 ; PRE-BOLT-DWO-HELPER-NEXT: DW_LLE_startx_length   (0x0000000000000003, 0x0000000000000016)
 
 ; BOLT-DWO-HELPER: version = 0x0004
 ; BOLT-DWO-HELPER: DW_TAG_formal_parameter [5]
-; BOLT-DWO-HELPER-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000000:
+; BOLT-DWO-HELPER-NEXT: DW_AT_location [DW_FORM_sec_offset] (0x00000010:
 ; BOLT-DWO-HELPER-NEXT: DW_LLE_startx_length   (0x0000000000000002, 0x0000000000000008): DW_OP_reg5 RDI
 ; BOLT-DWO-HELPER-NEXT: DW_LLE_startx_length   (0x0000000000000003, 0x0000000000000016)

bolt/test/dwarf5-loclist-offset-form.test

+# REQUIRES: system-linux
+
+# RUN: llvm-mc -dwarf-version=5 -filetype=obj -triple x86_64-unknown-linux %p/Inputs/dwarf5-loclist-offset-form-main.s -o %tmain.o
+# RUN: llvm-mc -dwarf-version=5 -filetype=obj -triple x86_64-unknown-linux %p/Inputs/dwarf5-loclist-offset-form-helper.s -o %thelper.o
+# RUN: %clang %cflags -dwarf-5 %tmain.o %thelper.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.bolt -update-debug-sections
+# RUN: llvm-dwarfdump --show-form --verbose --debug-info %t.exe | FileCheck --check-prefix=PRECHECK %s
+# RUN: llvm-dwarfdump --show-form --verbose --debug-addr %t.bolt > %t.txt
+# RUN: llvm-dwarfdump --show-form --verbose --debug-info %t.bolt >> %t.txt
+# RUN: cat %t.txt | FileCheck --check-prefix=POSTCHECK %s
+
+# Checks we can handle DWARF5 CU with DWARF4 DW_AT_location access pattern.
+
+# PRECHECK: DW_TAG_compile_unit
+# PRECHECK: DW_TAG_variable [5]
+# PRECHECK-NEXT: DW_AT_location [DW_FORM_sec_offset]
+# PRECHECK: DW_TAG_variable [5]
+# PRECHECK-NEXT: DW_AT_location [DW_FORM_sec_offset]
+# PRECHECK: DW_TAG_compile_unit
+# PRECHECK: DW_TAG_variable [11]
+# PRECHECK-NEXT: DW_AT_location [DW_FORM_sec_offset]
+
+# POSTCHECK: Addrs: [
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR1:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR2:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR3:]]
+# For second CU.
+# POSTCHECK: Addrs: [
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR4:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR5:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR6:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR7:]]
+# POSTCHECK-NEXT: 0x[[#%.16x,ADDR8:]]
+
+# POSTCHECK: DW_TAG_compile_unit
+# POSTCHECK: DW_AT_loclists_base [DW_FORM_sec_offset]  (0x0000000c)
+# POSTCHECK: DW_TAG_variable [5]
+# POSTCHECK-NEXT: DW_AT_location [DW_FORM_loclistx] (indexed (0x0)
+# POSTCHECK-NEXT: [0x[[#ADDR1]]
+# POSTCHECK-SAME: 0x[[#ADDR1 + 9]]
+# POSTCHECK-NEXT: [0x[[#ADDR3]]
+# POSTCHECK-SAME: 0x[[#ADDR3 + 6]]
+# POSTCHECK: DW_TAG_variable [5]
+# POSTCHECK-NEXT: DW_AT_location [DW_FORM_loclistx] (indexed (0x1)
+# POSTCHECK-NEXT: [0x[[#ADDR3]]
+# POSTCHECK-SAME: 0x[[#ADDR3 + 2]]
+
+# POSTCHECK: DW_TAG_compile_unit
+# POSTCHECK: DW_AT_loclists_base [DW_FORM_sec_offset]  (0x00000043)
+# POSTCHECK: DW_TAG_variable [11]
+# POSTCHECK-NEXT: DW_AT_location [DW_FORM_loclistx] (indexed (0x0)
+# POSTCHECK-NEXT: [0x[[#ADDR5]]
+# POSTCHECK-SAME: 0x[[#ADDR5 + 3]]
+# POSTCHECK-NEXT: [0x[[#ADDR8]]
+# POSTCHECK-SAME: 0x[[#ADDR8 + 1]]