DWARFVerifier: validate information in name index entries

[labath]

Summary

This patch add checks to verify that the information in the name index
entries is consistent with the debug_info section. Specifically, we
check that entries point to valid DIEs, and their names, tags, and
compile units match the information in the debug_info sections.

These checks are only run if the previous checks did not find any errors
in the name index headers. Attempting to proceed with the checks anyway
would likely produce a lot of spurious errors and the verification code
would need to be very careful to avoid crashing.

I also add a couple of more checks to the abbreviation-validation code
to verify that some attributes are always present (an index without a
DW_IDX_die_offset attribute is fairly useless).

The entry verification works only on indexes without any type units - I
haven't attempted to extend it to type units, as we don't even have a
DWARF v5-compatible type unit generator at the moment.

[JDevlieghere]

LGTM

lib/DebugInfo/DWARF/DWARFVerifier.cpp

1004

Should we somehow inform the users of this? Either with a note or even a warning?

[labath]

lib/DebugInfo/DWARF/DWARFVerifier.cpp

1004

Good point. I'll add a warning.

include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h

public:
 
   /// DWARF v5-specific implementation of an Accelerator Entry.
   class Entry final : public DWARFAcceleratorTable::Entry {
     const NameIndex *NameIdx;
     const Abbrev *Abbr;
 
     Entry(const NameIndex &NameIdx, const Abbrev &Abbr);
 
+  public:
+    Optional<uint64_t> getCUOffset() const override;
+    Optional<uint64_t> getDIESectionOffset() const override;
+    Optional<dwarf::Tag> getTag() const override { return tag(); }
+
     /// Returns the Index into the Compilation Unit list of the owning Name
     /// Index or None if this Accelerator Entry does not have an associated
     /// Compilation Unit. It is up to the user to verify that the returned Index
     /// is valid in the owning NameIndex (or use getCUOffset(), which will
     /// handle that check itself). Note that entries in NameIndexes which index
     /// just a single Compilation Unit are implicitly associated with that unit,
     /// so this function will return 0 even without an explicit
     /// DW_IDX_compile_unit attribute.
     Optional<uint64_t> getCUIndex() const;
 
-  public:
-    Optional<uint64_t> getCUOffset() const override;
-    Optional<uint64_t> getDIESectionOffset() const override;
-    Optional<dwarf::Tag> getTag() const override { return tag(); }
-
     /// .debug_names-specific getter, which always succeeds (DWARF v5 index
     /// entries always have a tag).
     dwarf::Tag tag() const { return Abbr->Tag; }
 
     /// Returns the Offset of the DIE within the containing CU or TU.
     Optional<uint64_t> getDIEUnitOffset() const;
 
     /// Return the Abbreviation that can be used to interpret the raw values of
     /// this Accelerator Entry.
     const Abbrev &getAbbrev() const { return *Abbr; }
 
     /// Returns the value of the Index Attribute in this Accelerator Entry, if
     /// the Entry contains such Attribute.
     Optional<DWARFFormValue> lookup(dwarf::Index Index) const;
 
     void dump(ScopedPrinter &W) const;
 
     friend class NameIndex;
     friend class ValueIterator;
   };
 
-private:
   /// Error returned by NameIndex::getEntry to report it has reached the end of
   /// the entry list.
   class SentinelError : public ErrorInfo<SentinelError> {
   public:
     static char ID;
 
     void log(raw_ostream &OS) const override { OS << "Sentinel"; }
     std::error_code convertToErrorCode() const override;
   };
 
+private:
   /// DenseMapInfo for struct Abbrev.
   struct AbbrevMapInfo {
     static Abbrev getEmptyKey();
     static Abbrev getTombstoneKey();
     static unsigned getHashValue(uint32_t Code) {
       return DenseMapInfo<uint32_t>::getHashValue(Code);
     }
     static unsigned getHashValue(const Abbrev &Abbr) {
class NameIndex {
     uint32_t Base;
     uint32_t CUsBase;
     uint32_t BucketsBase;
     uint32_t HashesBase;
     uint32_t StringOffsetsBase;
     uint32_t EntryOffsetsBase;
     uint32_t EntriesBase;
 
-    Expected<Entry> getEntry(uint32_t *Offset) const;
-
     void dumpCUs(ScopedPrinter &W) const;
     void dumpLocalTUs(ScopedPrinter &W) const;
     void dumpForeignTUs(ScopedPrinter &W) const;
     void dumpAbbreviations(ScopedPrinter &W) const;
     bool dumpEntry(ScopedPrinter &W, uint32_t *Offset) const;
     void dumpName(ScopedPrinter &W, uint32_t Index,
                   Optional<uint32_t> Hash) const;
     void dumpBucket(ScopedPrinter &W, uint32_t Bucket) const;
public:
     NameTableEntry getNameTableEntry(uint32_t Index) const;
 
     uint32_t getNameCount() const { return Hdr.NameCount; }
 
     const DenseSet<Abbrev, AbbrevMapInfo> &getAbbrevs() const {
       return Abbrevs;
     }
 
+    Expected<Entry> getEntry(uint32_t *Offset) const;
+
     llvm::Error extract();
     uint32_t getUnitOffset() const { return Base; }
     uint32_t getNextUnitOffset() const { return Base + 4 + Hdr.UnitLength; }
     void dump(ScopedPrinter &W) const;
 
     friend class DWARFDebugNames;
   };
 

include/llvm/DebugInfo/DWARF/DWARFVerifier.h

private:
 
   unsigned verifyDebugNamesCULists(const DWARFDebugNames &AccelTable);
   unsigned verifyNameIndexBuckets(const DWARFDebugNames::NameIndex &NI,
                                   const DataExtractor &StrData);
   unsigned verifyNameIndexAbbrevs(const DWARFDebugNames::NameIndex &NI);
   unsigned verifyNameIndexAttribute(const DWARFDebugNames::NameIndex &NI,
                                     const DWARFDebugNames::Abbrev &Abbr,
                                     DWARFDebugNames::AttributeEncoding AttrEnc);
+  unsigned verifyNameIndexEntries(const DWARFDebugNames::NameIndex &NI,
+                                  uint32_t Name, const DataExtractor &StrData);
 
   /// Verify that the DWARF v5 accelerator table is valid.
   ///
   /// This function currently checks that:
   /// - Headers individual Name Indices fit into the section and can be parsed.
   /// - Abbreviation tables can be parsed and contain valid index attributes
   ///   with correct form encodings.
   /// - The CU lists reference existing compile units.
   /// - The buckets have a valid index, or they are empty.
   /// - All names are reachable via the hash table (they have the correct hash,
   ///   and the hash is in the correct bucket).
+  /// - Information in the index entries is consistent with the debug_info
+  ///   section DIEs.
   ///
   /// \param AccelSection section containing the acceleration table
   /// \param StrData string section
   ///
   /// \returns The number of errors occurred during verification
   unsigned verifyDebugNames(const DWARFSection &AccelSection,
                             const DataExtractor &StrData);
 

lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp

uint64_t DWARFDebugNames::NameIndex::getForeignTUSignature(uint32_t TU) const {
   uint32_t Offset = CUsBase + (Hdr.CompUnitCount + Hdr.LocalTypeUnitCount) * 4;
   return Section.AccelSection.getU64(&Offset);
 }
 
 Expected<DWARFDebugNames::Entry>
 DWARFDebugNames::NameIndex::getEntry(uint32_t *Offset) const {
   const DWARFDataExtractor &AS = Section.AccelSection;
   if (!AS.isValidOffset(*Offset))
-    return make_error<StringError>("Incorrectly terminated entry list",
+    return make_error<StringError>("Incorrectly terminated entry list.",
                                    inconvertibleErrorCode());
 
   uint32_t AbbrevCode = AS.getULEB128(Offset);
   if (AbbrevCode == 0)
     return make_error<SentinelError>();
 
   const auto AbbrevIt = Abbrevs.find_as(AbbrevCode);
   if (AbbrevIt == Abbrevs.end())
-    return make_error<StringError>("Invalid abbreviation",
+    return make_error<StringError>("Invalid abbreviation.",
                                    inconvertibleErrorCode());
 
   Entry E(*this, *AbbrevIt);
 
   dwarf::FormParams FormParams = {Hdr.Version, 0, dwarf::DwarfFormat::DWARF32};
   for (auto &Value : E.Values) {
     if (!Value.extractValue(AS, Offset, FormParams))
-      return make_error<StringError>("Error extracting index attribute values",
+      return make_error<StringError>("Error extracting index attribute values.",
                                      inconvertibleErrorCode());
   }
   return std::move(E);
 }
 
 DWARFDebugNames::NameTableEntry
 DWARFDebugNames::NameIndex::getNameTableEntry(uint32_t Index) const {
   assert(0 < Index && Index <= Hdr.NameCount);

lib/DebugInfo/DWARF/DWARFVerifier.cpp

error() << formatv("NameIndex @ {0:x}: Abbreviation {1:x}: {2} uses an "
                        AttrEnc.Form, Iter->ClassName);
     return 1;
   }
   return 0;
 }
 
 unsigned
 DWARFVerifier::verifyNameIndexAbbrevs(const DWARFDebugNames::NameIndex &NI) {
+  // Verifying type unit indexes not supported.
+  if (NI.getLocalTUCount() + NI.getForeignTUCount() > 0)
+    return 0;
+
   unsigned NumErrors = 0;
   for (const auto &Abbrev : NI.getAbbrevs()) {
     StringRef TagName = dwarf::TagString(Abbrev.Tag);
     if (TagName.empty()) {
       warn() << formatv("NameIndex @ {0:x}: Abbreviation {1:x} references an "
                         "unknown tag: {2}.\n",
                         NI.getUnitOffset(), Abbrev.Code, Abbrev.Tag);
     }
     SmallSet<unsigned, 5> Attributes;
     for (const auto &AttrEnc : Abbrev.Attributes) {
       if (!Attributes.insert(AttrEnc.Index).second) {
         error() << formatv("NameIndex @ {0:x}: Abbreviation {1:x} contains "
                            "multiple {2} attributes.\n",
                            NI.getUnitOffset(), Abbrev.Code, AttrEnc.Index);
         ++NumErrors;
         continue;
       }
       NumErrors += verifyNameIndexAttribute(NI, Abbrev, AttrEnc);
     }
+
+    if (NI.getCUCount() > 1 && !Attributes.count(dwarf::DW_IDX_compile_unit)) {
+      error() << formatv("NameIndex @ {0:x}: Indexing multiple compile units "
+                         "and abbreviation {1:x} has no {2} attribute.\n",
+                         NI.getUnitOffset(), Abbrev.Code,
+                         dwarf::DW_IDX_compile_unit);
+      ++NumErrors;
+    }
+    if (!Attributes.count(dwarf::DW_IDX_die_offset)) {
+      error() << formatv(
+          "NameIndex @ {0:x}: Abbreviation {1:x} has no {2} attribute.\n",
+          NI.getUnitOffset(), Abbrev.Code, dwarf::DW_IDX_die_offset);
+      ++NumErrors;
+    }
   }
   return NumErrors;
 }
 
+static SmallVector<StringRef, 2> getNames(const DWARFDie &DIE) {
+  SmallVector<StringRef, 2> Result;
+  if (const char *Str = DIE.getName(DINameKind::ShortName))
+    Result.emplace_back(Str);
+  else if (DIE.getTag() == dwarf::DW_TAG_namespace)
+    Result.emplace_back("(anonymous namespace)");
+
+  if (const char *Str = DIE.getName(DINameKind::LinkageName)) {
+    if (Result.empty() || Result[0] != Str)
+      Result.emplace_back(Str);
+  }
+
+  return Result;
+}
+
+unsigned
+DWARFVerifier::verifyNameIndexEntries(const DWARFDebugNames::NameIndex &NI,
+                                      uint32_t Name,
+                                      const DataExtractor &StrData) {
+  // Verifying type unit indexes not supported.
+  if (NI.getLocalTUCount() + NI.getForeignTUCount() > 0)
+    return 0;
+
+  DWARFDebugNames::NameTableEntry NTE = NI.getNameTableEntry(Name);
+  const char *CStr = StrData.getCStr(&NTE.StringOffset);
+  if (!CStr) {
+    error() << formatv(
+        "Name Index @ {0:x}: Unable to get string associated with name {1}.\n",
+        NI.getUnitOffset(), Name);
+    return 1;
+  }
+  StringRef Str(CStr);
+
+  unsigned NumErrors = 0;
+  unsigned NumEntries = 0;
+  uint32_t EntryID = NTE.EntryOffset;
+  Expected<DWARFDebugNames::Entry> EntryOr = NI.getEntry(&NTE.EntryOffset);
+  for (; EntryOr; ++NumEntries, EntryID = NTE.EntryOffset,
+                                EntryOr = NI.getEntry(&NTE.EntryOffset)) {
+    uint32_t CUIndex = *EntryOr->getCUIndex();
+    if (CUIndex > NI.getCUCount()) {
+      error() << formatv("Name Index @ {0:x}: Entry @ {1:x} contains an "
+                         "invalid CU index ({2}).\n",
+                         NI.getUnitOffset(), EntryID, CUIndex);
+      ++NumErrors;
+      continue;
+    }
+    uint32_t CUOffset = NI.getCUOffset(CUIndex);
+    uint64_t DIEOffset = *EntryOr->getDIESectionOffset();
+    DWARFDie DIE = DCtx.getDIEForOffset(DIEOffset);
+    if (!DIE) {
+      error() << formatv("Name Index @ {0:x}: Entry @ {1:x} references a "
+                         "non-existing DIE @ {2:x}.\n",
+                         NI.getUnitOffset(), EntryID, DIEOffset);
+      ++NumErrors;
+      continue;
+    }
+    if (DIE.getDwarfUnit()->getOffset() != CUOffset) {
+      error() << formatv("Name Index @ {0:x}: Entry @ {1:x}: mismatched CU of "
+                         "DIE @ {2:x}: index - {3:x}; debug_info - {4:x}.\n",
+                         NI.getUnitOffset(), EntryID, DIEOffset, CUOffset,
+                         DIE.getDwarfUnit()->getOffset());
+      ++NumErrors;
+    }
+    if (DIE.getTag() != EntryOr->tag()) {
+      error() << formatv("Name Index @ {0:x}: Entry @ {1:x}: mismatched Tag of "
+                         "DIE @ {2:x}: index - {3}; debug_info - {4}.\n",
+                         NI.getUnitOffset(), EntryID, DIEOffset, EntryOr->tag(),
+                         DIE.getTag());
+      ++NumErrors;
+    }
+
+    auto EntryNames = getNames(DIE);
+    if (!is_contained(EntryNames, Str)) {
+      error() << formatv("Name Index @ {0:x}: Entry @ {1:x}: mismatched Name "
+                         "of DIE @ {2:x}: index - {3}; debug_info - {4}.\n",
+                         NI.getUnitOffset(), EntryID, DIEOffset, Str,
+                         make_range(EntryNames.begin(), EntryNames.end()));
+    }
+  }
+  handleAllErrors(EntryOr.takeError(),
+                  [&](const DWARFDebugNames::SentinelError &) {
+                    if (NumEntries > 0)
+                      return;
+                    error() << formatv("Name Index @ {0:x}: Name {1} ({2}) is "
+                                       "not associated with any entries.\n",
+                                       NI.getUnitOffset(), Name, Str);
+                    ++NumErrors;
+                  },
+                  [&](const ErrorInfoBase &Info) {
+                    error() << formatv(
+                        "Name Index @ {0:x}: Name {1} ({2}): {3}\n",
+                        NI.getUnitOffset(), Name, Str, Info.message());
+                    ++NumErrors;
+                  });
+  return NumErrors;
+}
+
 unsigned DWARFVerifier::verifyDebugNames(const DWARFSection &AccelSection,
                                          const DataExtractor &StrData) {
   unsigned NumErrors = 0;
   DWARFDataExtractor AccelSectionData(DCtx.getDWARFObj(), AccelSection,
                                       DCtx.isLittleEndian(), 0);
   DWARFDebugNames AccelTable(AccelSectionData, StrData);
 
   OS << "Verifying .debug_names...\n";
 
   // This verifies that we can read individual name indices and their
   // abbreviation tables.
   if (Error E = AccelTable.extract()) {
     error() << toString(std::move(E)) << '\n';
     return 1;
   }
 
   NumErrors += verifyDebugNamesCULists(AccelTable);
   for (const auto &NI : AccelTable)
     NumErrors += verifyNameIndexBuckets(NI, StrData);
   for (const auto &NI : AccelTable)
     NumErrors += verifyNameIndexAbbrevs(NI);
 
+  // Don't attempt Entry validation if any of the previous checks found errors
+  if (NumErrors > 0)
+    return NumErrors;
+  for (const auto &NI : AccelTable)
+    for (uint64_t Name = 1; Name <= NI.getNameCount(); ++Name)
+      NumErrors += verifyNameIndexEntries(NI, Name, StrData);
+
   return NumErrors;
 }
 
 bool DWARFVerifier::handleAccelTables() {
   const DWARFObject &D = DCtx.getDWARFObj();
   DataExtractor StrData(D.getStringSection(), DCtx.isLittleEndian(), 0);
   unsigned NumErrors = 0;
   if (!D.getAppleNamesSection().Data.empty())

test/tools/llvm-dwarfdump/X86/debug-names-verify-abbrev-forms.s

 # RUN: llvm-mc -triple x86_64-pc-linux %s -filetype=obj | \
 # RUN:   not llvm-dwarfdump -verify - | FileCheck %s
 
 # CHECK: error: NameIndex @ 0x0: Abbreviation 0x2: DW_IDX_compile_unit uses an unexpected form DW_FORM_ref1 (expected form class constant).
 # CHECK: error: NameIndex @ 0x0: Abbreviation 0x2: DW_IDX_type_unit uses an unexpected form DW_FORM_ref1 (expected form class constant).
 # CHECK: error: NameIndex @ 0x0: Abbreviation 0x2: DW_IDX_type_hash uses an unexpected form DW_FORM_data4 (should be DW_FORM_data8).
 # CHECK: warning: NameIndex @ 0x0: Abbreviation 0x2 contains an unknown index attribute: DW_IDX_unknown_2020.
 # CHECK: error: NameIndex @ 0x0: Abbreviation 0x4 contains multiple DW_IDX_die_offset attributes.
 # CHECK: NameIndex @ 0x0: Abbreviation 0x1: DW_IDX_die_offset uses an unknown form: DW_FORM_unknown_1fff.
 # CHECK: warning: NameIndex @ 0x0: Abbreviation 0x3 references an unknown tag: DW_TAG_unknown_8080.
+# CHECK: error: NameIndex @ 0x0: Abbreviation 0x5 has no DW_IDX_die_offset attribute.
+# CHECK: error: NameIndex @ 0x55: Indexing multiple compile units and abbreviation 0x1 has no DW_IDX_compile_unit attribute.
 
   .section  .debug_str,"MS",@progbits,1
 .Lstring_producer:
   .asciz  "Hand-written dwarf"
 
   .section  .debug_abbrev,"",@progbits
 .Lsection_abbrev:
   .byte 1                       # Abbreviation Code
.Lcu_start0:
   .long .Lsection_abbrev        # Offset Into Abbrev. Section
   .byte 8                       # Address Size (in bytes)
   .byte 1                       # Abbrev [1] DW_TAG_compile_unit
   .long .Lstring_producer       # DW_AT_producer
   .short  12                      # DW_AT_language
   .byte 0                       # End Of Children Mark
 .Lcu_end0:
 
+.Lcu_begin1:
+  .long .Lcu_end1-.Lcu_start1   # Length of Unit
+.Lcu_start1:
+  .short  4                       # DWARF version number
+  .long .Lsection_abbrev        # Offset Into Abbrev. Section
+  .byte 8                       # Address Size (in bytes)
+  .byte 1                       # Abbrev [1] DW_TAG_compile_unit
+  .long .Lstring_producer       # DW_AT_producer
+  .short  12                      # DW_AT_language
+  .byte 0                       # End Of Children Mark
+.Lcu_end1:
+
+.Lcu_begin2:
+  .long .Lcu_end2-.Lcu_start2   # Length of Unit
+.Lcu_start2:
+  .short  4                       # DWARF version number
+  .long .Lsection_abbrev        # Offset Into Abbrev. Section
+  .byte 8                       # Address Size (in bytes)
+  .byte 1                       # Abbrev [1] DW_TAG_compile_unit
+  .long .Lstring_producer       # DW_AT_producer
+  .short  12                      # DW_AT_language
+  .byte 0                       # End Of Children Mark
+.Lcu_end2:
+
   .section  .debug_names,"",@progbits
   .long .Lnames_end0-.Lnames_start0 # Header: contribution length
 .Lnames_start0:
   .short  5                       # Header: version
   .short  0                       # Header: padding
   .long 1                       # Header: compilation unit count
   .long 0                       # Header: local type unit count
   .long 0                       # Header: foreign type unit count
.Lnames_abbrev_start0:
   .byte 4                       # Abbrev code
   .byte 46                      # DW_TAG_subprogram
   .byte 3                       # DW_IDX_die_offset
   .byte   17                      # DW_FORM_ref1
   .byte 3                       # DW_IDX_die_offset
   .byte   17                      # DW_FORM_ref1
   .byte 0                       # End of abbrev
   .byte 0                       # End of abbrev
+  .byte 5                       # Abbrev code
+  .byte 46                      # DW_TAG_subprogram
+  .byte 4                       # DW_IDX_parent
+  .byte   5                       # DW_FORM_data2
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev
   .byte 0                       # End of abbrev list
 .Lnames_abbrev_end0:
 .Lnames_end0:
+
+  .long .Lnames_end1-.Lnames_start1 # Header: contribution length
+.Lnames_start1:
+  .short  5                       # Header: version
+  .short  0                       # Header: padding
+  .long 2                       # Header: compilation unit count
+  .long 0                       # Header: local type unit count
+  .long 0                       # Header: foreign type unit count
+  .long 0                       # Header: bucket count
+  .long 0                       # Header: name count
+  .long .Lnames_abbrev_end1-.Lnames_abbrev_start1 # Header: abbreviation table size
+  .long 0                       # Header: augmentation length
+  .long .Lcu_begin1             # Compilation unit 0
+  .long .Lcu_begin2             # Compilation unit 1
+.Lnames_abbrev_start1:
+  .byte 1                       # Abbrev code
+  .byte 46                      # DW_TAG_subprogram
+  .byte 3                       # DW_IDX_die_offset
+  .byte   17                      # DW_FORM_ref1
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev list
+.Lnames_abbrev_end1:
+.Lnames_end1:

test/tools/llvm-dwarfdump/X86/debug-names-verify-entries.s

+# RUN: llvm-mc -triple x86_64-pc-linux %s -filetype=obj -o - | not llvm-dwarfdump -verify - | FileCheck %s
+
+# CHECK: error: Name Index @ 0x0: Unable to get string associated with name 1.
+# CHECK: error: Name Index @ 0x0: Entry @ 0x73 contains an invalid CU index (47).
+# CHECK: error: Name Index @ 0x0: Entry @ 0x79 references a non-existing DIE @ 0x3fa.
+# CHECK: error: Name Index @ 0x0: Entry @ 0x85: mismatched CU of DIE @ 0x30: index - 0x0; debug_info - 0x1e.
+# CHECK: error: Name Index @ 0x0: Entry @ 0x8b: mismatched Tag of DIE @ 0x17: index - DW_TAG_subprogram; debug_info - DW_TAG_variable.
+# CHECK: error: Name Index @ 0x0: Entry @ 0x91: mismatched Name of DIE @ 0x35: index - foo; debug_info - bar, _Z3bar.
+# CHECK: error: Name Index @ 0x0: Name 2 (foo): Incorrectly terminated entry list.
+# CHECK: error: Name Index @ 0x0: Name 3 (bar) is not associated with any entries.
+# CHECK: error: Name Index @ 0x0: Entry @ 0x69: mismatched Name of DIE @ 0x1c: index - (pseudonymous namespace); debug_info - (anonymous namespace).
+
+  .section  .debug_str,"MS",@progbits,1
+.Lstring_foo:
+  .asciz  "foo"
+.Lstring_bar:
+  .asciz  "bar"
+.Lstring_bar_mangled:
+  .asciz  "_Z3bar"
+.Lstring_pseudo_namespace:
+  .asciz  "(pseudonymous namespace)"
+.Lstring_producer:
+  .asciz  "Hand-written dwarf"
+
+  .section  .debug_abbrev,"",@progbits
+.Lsection_abbrev:
+  .byte 1                       # Abbreviation Code
+  .byte 17                      # DW_TAG_compile_unit
+  .byte 1                       # DW_CHILDREN_yes
+  .byte 37                      # DW_AT_producer
+  .byte 14                      # DW_FORM_strp
+  .byte 19                      # DW_AT_language
+  .byte 5                       # DW_FORM_data2
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 2                       # Abbreviation Code
+  .byte 46                      # DW_TAG_subprogram
+  .byte 0                       # DW_CHILDREN_no
+  .byte 3                       # DW_AT_name
+  .byte 14                      # DW_FORM_strp
+  .byte 63                      # DW_AT_external
+  .byte 25                      # DW_FORM_flag_present
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 3                       # Abbreviation Code
+  .byte 52                      # DW_TAG_variable
+  .byte 0                       # DW_CHILDREN_no
+  .byte 3                       # DW_AT_name
+  .byte 14                      # DW_FORM_strp
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 4                       # Abbreviation Code
+  .byte 57                      # DW_TAG_namespace
+  .byte 0                       # DW_CHILDREN_no
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 5                       # Abbreviation Code
+  .byte 52                      # DW_TAG_variable
+  .byte 0                       # DW_CHILDREN_no
+  .byte 3                       # DW_AT_name
+  .byte 14                      # DW_FORM_strp
+  .byte 110                     # DW_AT_linkage_name
+  .byte 14                      # DW_FORM_strp
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 0                       # EOM(3)
+
+  .section  .debug_info,"",@progbits
+.Lcu_begin0:
+  .long .Lcu_end0-.Lcu_start0   # Length of Unit
+.Lcu_start0:
+  .short  4                       # DWARF version number
+  .long .Lsection_abbrev        # Offset Into Abbrev. Section
+  .byte 8                       # Address Size (in bytes)
+  .byte 1                       # Abbrev [1] DW_TAG_compile_unit
+  .long .Lstring_producer       # DW_AT_producer
+  .short  12                      # DW_AT_language
+.Ldie_foo:
+  .byte 2                       # Abbrev [2] DW_TAG_subprogram
+  .long .Lstring_foo            # DW_AT_name
+                                        # DW_AT_external
+.Ldie_foo_var:
+  .byte 3                       # Abbrev [3] DW_TAG_variable
+  .long .Lstring_foo            # DW_AT_name
+.Ldie_namespace:
+  .byte 4                       # Abbrev [3] DW_TAG_namespace
+  .byte 0                       # End Of Children Mark
+.Lcu_end0:
+
+.Lcu_begin1:
+  .long .Lcu_end1-.Lcu_start1   # Length of Unit
+.Lcu_start1:
+  .short  4                       # DWARF version number
+  .long .Lsection_abbrev        # Offset Into Abbrev. Section
+  .byte 8                       # Address Size (in bytes)
+  .byte 1                       # Abbrev [1] DW_TAG_compile_unit
+  .long .Lstring_producer       # DW_AT_producer
+  .short  12                      # DW_AT_language
+.Ldie_foo2:
+  .byte 2                       # Abbrev [2] DW_TAG_subprogram
+  .long .Lstring_foo            # DW_AT_name
+                                        # DW_AT_external
+.Ldie_bar_linkage:
+  .byte 5                       # Abbrev [2] DW_TAG_variable
+  .long .Lstring_bar            # DW_AT_name
+  .long .Lstring_bar_mangled    # DW_AT_linkage_name
+  .byte 0                       # End Of Children Mark
+.Lcu_end1:
+
+
+  .section  .debug_names,"",@progbits
+  .long .Lnames_end0-.Lnames_start0 # Header: contribution length
+.Lnames_start0:
+  .short  5                       # Header: version
+  .short  0                       # Header: padding
+  .long 2                       # Header: compilation unit count
+  .long 0                       # Header: local type unit count
+  .long 0                       # Header: foreign type unit count
+  .long 0                       # Header: bucket count
+  .long 4                       # Header: name count
+  .long .Lnames_abbrev_end0-.Lnames_abbrev_start0 # Header: abbreviation table size
+  .long 0                       # Header: augmentation length
+  .long .Lcu_begin0             # Compilation unit 0
+  .long .Lcu_begin1             # Compilation unit 1
+  .long .Lstring_foo+1000       # String 1: <broken>
+  .long .Lstring_foo            # String 2: foo
+  .long .Lstring_bar            # String 3: bar
+  .long .Lstring_pseudo_namespace # String 4: (pseudonymous namespace)
+  .long .Lnames0-.Lnames_entries0 # Offset 1
+  .long .Lnames0-.Lnames_entries0 # Offset 2
+  .long .Lnames1-.Lnames_entries0 # Offset 3
+  .long .Lnames2-.Lnames_entries0 # Offset 4
+.Lnames_abbrev_start0:
+  .byte 46                      # Abbrev code
+  .byte 46                      # DW_TAG_subprogram
+  .byte 1                       # DW_IDX_compile_unit
+  .byte 11                      # DW_FORM_data1
+  .byte 3                       # DW_IDX_die_offset
+  .byte 19                      # DW_FORM_ref4
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev
+  .byte 57                      # Abbrev code
+  .byte 57                      # DW_TAG_namespace
+  .byte 1                       # DW_IDX_compile_unit
+  .byte 11                      # DW_FORM_data1
+  .byte 3                       # DW_IDX_die_offset
+  .byte 19                      # DW_FORM_ref4
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev
+  .byte 52                      # Abbrev code
+  .byte 52                      # DW_TAG_variable
+  .byte 1                       # DW_IDX_compile_unit
+  .byte 11                      # DW_FORM_data1
+  .byte 3                       # DW_IDX_die_offset
+  .byte 19                      # DW_FORM_ref4
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev
+  .byte 0                       # End of abbrev list
+.Lnames_abbrev_end0:
+.Lnames_entries0:
+.Lnames1:
+  .long 0                       # End of list: bar
+.Lnames2:
+  .byte 57                      # Abbrev code
+  .byte 0                       # DW_IDX_compile_unit
+  .long .Ldie_namespace-.Lcu_begin0 # DW_IDX_die_offset
+  .long 0                       # End of list: (pseudonymous namespace)
+.Lnames0:
+  .byte 46                      # Abbrev code
+  .byte 47                      # DW_IDX_compile_unit
+  .long .Ldie_foo-.Lcu_begin0   # DW_IDX_die_offset
+  .byte 46                      # Abbrev code
+  .byte 0                       # DW_IDX_compile_unit
+  .long .Ldie_foo-.Lcu_begin0+1000 # DW_IDX_die_offset
+  .byte 46                      # Abbrev code
+  .byte 0                       # DW_IDX_compile_unit
+  .long .Ldie_foo-.Lcu_begin0   # DW_IDX_die_offset
+  .byte 46                      # Abbrev code
+  .byte 0                       # DW_IDX_compile_unit
+  .long .Ldie_foo2-.Lcu_begin0  # DW_IDX_die_offset
+  .byte 46                      # Abbrev code
+  .byte 0                       # DW_IDX_compile_unit
+  .long .Ldie_foo_var-.Lcu_begin0 # DW_IDX_die_offset
+  .byte 52                      # Abbrev code
+  .byte 1                       # DW_IDX_compile_unit
+  .long .Ldie_bar_linkage-.Lcu_begin1 # DW_IDX_die_offset
+  #.long  0                       # End of list deliberately missing
+.Lnames_end0: