[llvm] r329392 - DWARFVerifier: validate information in name index entries
Jonas Devlieghere via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 6 06:45:56 PDT 2018
Did you forget to add the same warning in DWARFVerifier::verifyNameIndexEntries or was that on purpose?
> On Apr 6, 2018, at 2:34 PM, Pavel Labath via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>
> Author: labath
> Date: Fri Apr 6 06:34:12 2018
> New Revision: 329392
>
> URL: http://llvm.org/viewvc/llvm-project?rev=329392&view=rev
> Log:
> DWARFVerifier: validate information in name index entries
>
> 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.
>
> Reviewers: JDevlieghere, aprantl, dblaikie
>
> Subscribers: llvm-commits
>
> Differential Revision: https://reviews.llvm.org/D45323
>
> Added:
> llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-entries.s
> Modified:
> llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h
> llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFVerifier.h
> llvm/trunk/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
> llvm/trunk/lib/DebugInfo/DWARF/DWARFVerifier.cpp
> llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-abbrev-forms.s
>
> Modified: llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h?rev=329392&r1=329391&r2=329392&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h (original)
> +++ llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h Fri Apr 6 06:34:12 2018
> @@ -283,6 +283,11 @@ public:
>
> 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
> @@ -293,11 +298,6 @@ public:
> /// 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; }
> @@ -319,7 +319,6 @@ public:
> 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> {
> @@ -330,6 +329,7 @@ private:
> std::error_code convertToErrorCode() const override;
> };
>
> +private:
> /// DenseMapInfo for struct Abbrev.
> struct AbbrevMapInfo {
> static Abbrev getEmptyKey();
> @@ -373,8 +373,6 @@ public:
> 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;
> @@ -429,6 +427,8 @@ public:
> 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; }
>
> Modified: llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFVerifier.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFVerifier.h?rev=329392&r1=329391&r2=329392&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFVerifier.h (original)
> +++ llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFVerifier.h Fri Apr 6 06:34:12 2018
> @@ -240,6 +240,8 @@ private:
> 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.
> ///
> @@ -251,6 +253,8 @@ private:
> /// - 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
>
> Modified: llvm/trunk/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp?rev=329392&r1=329391&r2=329392&view=diff
> ==============================================================================
> --- llvm/trunk/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp (original)
> +++ llvm/trunk/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp Fri Apr 6 06:34:12 2018
> @@ -601,7 +601,7 @@ 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);
> @@ -610,7 +610,7 @@ DWARFDebugNames::NameIndex::getEntry(uin
>
> 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);
> @@ -618,7 +618,7 @@ DWARFDebugNames::NameIndex::getEntry(uin
> 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);
>
> Modified: llvm/trunk/lib/DebugInfo/DWARF/DWARFVerifier.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/DebugInfo/DWARF/DWARFVerifier.cpp?rev=329392&r1=329391&r2=329392&view=diff
> ==============================================================================
> --- llvm/trunk/lib/DebugInfo/DWARF/DWARFVerifier.cpp (original)
> +++ llvm/trunk/lib/DebugInfo/DWARF/DWARFVerifier.cpp Fri Apr 6 06:34:12 2018
> @@ -1000,6 +1000,13 @@ unsigned DWARFVerifier::verifyNameIndexA
>
> unsigned
> DWARFVerifier::verifyNameIndexAbbrevs(const DWARFDebugNames::NameIndex &NI) {
> + if (NI.getLocalTUCount() + NI.getForeignTUCount() > 0) {
> + warn() << formatv("Name Index @ {0:x}: Verifying indexes of type units is "
> + "not currently supported.\n",
> + NI.getUnitOffset());
> + return 0;
> + }
> +
> unsigned NumErrors = 0;
> for (const auto &Abbrev : NI.getAbbrevs()) {
> StringRef TagName = dwarf::TagString(Abbrev.Tag);
> @@ -1019,7 +1026,119 @@ DWARFVerifier::verifyNameIndexAbbrevs(co
> }
> 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;
> }
>
> @@ -1045,6 +1164,13 @@ unsigned DWARFVerifier::verifyDebugNames
> 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;
> }
>
>
> Modified: llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-abbrev-forms.s
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-abbrev-forms.s?rev=329392&r1=329391&r2=329392&view=diff
> ==============================================================================
> --- llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-abbrev-forms.s (original)
> +++ llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-abbrev-forms.s Fri Apr 6 06:34:12 2018
> @@ -8,6 +8,8 @@
> # 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", at progbits,1
> .Lstring_producer:
> @@ -39,6 +41,30 @@
> .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,"", at progbits
> .long .Lnames_end0-.Lnames_start0 # Header: contribution length
> .Lnames_start0:
> @@ -87,6 +113,36 @@
> .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:
>
> Added: llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-entries.s
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-entries.s?rev=329392&view=auto
> ==============================================================================
> --- llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-entries.s (added)
> +++ llvm/trunk/test/tools/llvm-dwarfdump/X86/debug-names-verify-entries.s Fri Apr 6 06:34:12 2018
> @@ -0,0 +1,188 @@
> +# 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", at 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,"", at 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,"", at 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,"", at 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:
>
>
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