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[BOLT][DWARF] Slice .debug_str from the DWP for each CU #159540

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[BOLT][DWARF] Slice .debug_str from the DWP for each CU #159540

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97376e9
[Bolt] Slice debug_str from DWP
Sockke Sep 15, 2025
2c4cd38
added test for DWARF5
Sockke Sep 15, 2025
44949e5
Consider the modified str and offsets in the buffer.
Sockke Sep 24, 2025
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10 changes: 10 additions & 0 deletions bolt/include/bolt/Core/DebugData.h
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Original file line number Diff line number Diff line change
Expand Up @@ -471,6 +471,11 @@ class DebugStrOffsetsWriter {
return std::move(StrOffsetsBuffer);
}

StringRef bufferStr() {
return StringRef(reinterpret_cast<const char *>(StrOffsetsBuffer->data()),
StrOffsetsBuffer->size());
}

/// Initializes Buffer and Stream.
void initialize(DWARFUnit &Unit);

Expand Down Expand Up @@ -507,6 +512,11 @@ class DebugStrWriter {
return std::move(StrBuffer);
}

StringRef bufferStr() {
return StringRef(reinterpret_cast<const char *>(StrBuffer->data()),
StrBuffer->size());
}

/// Adds string to .debug_str.
/// On first invocation it initializes internal data structures.
uint32_t addString(StringRef Str);
Expand Down
108 changes: 107 additions & 1 deletion bolt/lib/Rewrite/DWARFRewriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1725,6 +1725,65 @@ StringRef getSectionName(const SectionRef &Section) {
return Name;
}

// Exctracts some appropriate slices of .debug_str.dwo from DWP.
// Updates the .debug_str_offets.dwo for CUs.
void UpdateStrAndStrOffsets(StringRef StrDWOContent,
StringRef StrOffsetsContent,
SmallVectorImpl<StringRef> &StrDWOOutData,
std::string &StrOffsetsOutData,
unsigned DwarfVersion, bool IsLittleEndian) {
const llvm::endianness Endian =
IsLittleEndian ? llvm::endianness::little : llvm::endianness::big;
// ignore DWARF64
const uint64_t HeaderOffset = (DwarfVersion >= 5) ? 8 : 0;
const uint64_t NumOffsets = (StrOffsetsContent.size() - HeaderOffset) / 4;

DataExtractor Extractor(StrOffsetsContent, IsLittleEndian, 0);
uint64_t ExtractionOffset = HeaderOffset;

using StringFragment = DWARFUnitIndex::Entry::SectionContribution;
auto getStringLength = [](StringRef Content, uint64_t Offset) -> uint64_t {
size_t NullPos = Content.find('\0', Offset);
return (NullPos != StringRef::npos) ? (NullPos - Offset + 1) : 0;
};
auto isContiguous = [](const StringFragment &Fragment,
uint64_t NextOffset) -> bool {
return NextOffset == Fragment.getOffset() + Fragment.getLength();
};
std::optional<StringFragment> CurrentFragment;
uint64_t AccumulatedStrLen = 0;
for (uint64_t I = 0; I < NumOffsets; ++I) {
const uint64_t StrOffset = Extractor.getU32(&ExtractionOffset);
const uint64_t StringLength = getStringLength(StrDWOContent, StrOffset);
if (!CurrentFragment) {
// first init
CurrentFragment = StringFragment(StrOffset, StringLength);
} else {
if (isContiguous(*CurrentFragment, StrOffset)) {
// expand the current fragment
CurrentFragment->setLength(CurrentFragment->getLength() + StringLength);
} else {
// save the current fragment and start a new one
StrDWOOutData.push_back(StrDWOContent.substr(
CurrentFragment->getOffset(), CurrentFragment->getLength()));
CurrentFragment = StringFragment(StrOffset, StringLength);
}
}
if (AccumulatedStrLen != StrOffset) {
// update str offsets
if (StrOffsetsOutData.empty())
StrOffsetsOutData = StrOffsetsContent.str();
llvm::support::endian::write32(&StrOffsetsOutData[HeaderOffset + I * 4],
static_cast<uint32_t>(AccumulatedStrLen),
Endian);
}
AccumulatedStrLen += StringLength;
}
if (CurrentFragment)
StrDWOOutData.push_back(StrDWOContent.substr(CurrentFragment->getOffset(),
CurrentFragment->getLength()));
}

// Exctracts an appropriate slice if input is DWP.
// Applies patches or overwrites the section.
std::optional<StringRef> updateDebugData(
Expand Down Expand Up @@ -1774,6 +1833,8 @@ std::optional<StringRef> updateDebugData(
errs() << "BOLT-WARNING: unsupported debug section: " << SectionName
<< "\n";
if (StrWriter.isInitialized()) {
if (CUDWOEntry)
return StrWriter.bufferStr();
OutputBuffer = StrWriter.releaseBuffer();
return StringRef(reinterpret_cast<const char *>(OutputBuffer->data()),
OutputBuffer->size());
Expand All @@ -1788,6 +1849,8 @@ std::optional<StringRef> updateDebugData(
}
case DWARFSectionKind::DW_SECT_STR_OFFSETS: {
if (StrOffstsWriter.isFinalized()) {
if (CUDWOEntry)
return StrOffstsWriter.bufferStr();
OutputBuffer = StrOffstsWriter.releaseBuffer();
return StringRef(reinterpret_cast<const char *>(OutputBuffer->data()),
OutputBuffer->size());
Expand Down Expand Up @@ -1890,18 +1953,61 @@ void DWARFRewriter::writeDWOFiles(
}
}

StringRef StrDWOContent;
StringRef StrOffsetsContent;
llvm::SmallVector<StringRef, 3> StrDWOOutData;
std::string StrOffsetsOutData;
for (const SectionRef &Section : File->sections()) {
std::unique_ptr<DebugBufferVector> OutputData;
StringRef SectionName = getSectionName(Section);
if (SectionName == "debug_rnglists.dwo")
continue;
Expected<StringRef> ContentsExp = Section.getContents();
assert(ContentsExp && "Invalid contents.");
if (IsDWP && SectionName == "debug_str.dwo") {
if (StrWriter.isInitialized())
StrDWOContent = StrWriter.bufferStr();
else
StrDWOContent = *ContentsExp;
continue;
}
if (std::optional<StringRef> OutData = updateDebugData(
(*DWOCU)->getContext(), SectionName, *ContentsExp, KnownSections,
*Streamer, *this, CUDWOEntry, DWOId, OutputData, RangeListssWriter,
LocWriter, StrOffstsWriter, StrWriter, OverridenSections))
LocWriter, StrOffstsWriter, StrWriter, OverridenSections)) {
if (IsDWP && SectionName == "debug_str_offsets.dwo") {
StrOffsetsContent = *OutData;
continue;
}
Streamer->emitBytes(*OutData);
}
}

if (IsDWP) {
// Handling both .debug_str.dwo and .debug_str_offsets.dwo concurrently. In
// the original DWP, .debug_str is a deduplicated global table, and the
// .debug_str.dwo slice for a single CU needs to be extracted according to
// .debug_str_offsets.dwo.
UpdateStrAndStrOffsets(StrDWOContent, StrOffsetsContent, StrDWOOutData,
StrOffsetsOutData, CU.getVersion(),
(*DWOCU)->getContext().isLittleEndian());
auto SectionIter = KnownSections.find("debug_str.dwo");
if (SectionIter != KnownSections.end()) {
Streamer->switchSection(SectionIter->second.first);
for (size_t i = 0; i < StrDWOOutData.size(); ++i) {
StringRef OutData = StrDWOOutData[i];
if (!OutData.empty())
Streamer->emitBytes(OutData);
}
}
SectionIter = KnownSections.find("debug_str_offsets.dwo");
if (SectionIter != KnownSections.end()) {
Streamer->switchSection(SectionIter->second.first);
if (!StrOffsetsOutData.empty())
Streamer->emitBytes(StrOffsetsOutData);
else
Streamer->emitBytes(StrOffsetsContent);
}
}
Streamer->finish();
TempOut->keep();
Expand Down
226 changes: 226 additions & 0 deletions bolt/test/X86/Inputs/dwarf5-debug-str-split-dwarf-helper.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,226 @@
# clang++ -g2 -gdwarf-5 -gsplit-dwarf=split -S helper.cpp
# int getReturn() {
# return 0;
# }
.file "helper.cpp"
.text
.globl _Z9getReturnv # -- Begin function _Z9getReturnv
.p2align 4
.type _Z9getReturnv,@function
_Z9getReturnv: # @_Z9getReturnv
.Lfunc_begin0:
.file 0 "." "helper.cpp" md5 0xc7d7879297b54325c71b3e0cfbb65e2d
.loc 0 1 0 # helper.cpp:1:0
.cfi_startproc
# %bb.0: # %entry
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp
.Ltmp0:
.loc 0 2 3 prologue_end # helper.cpp:2:3
xorl %eax, %eax
.loc 0 2 3 epilogue_begin is_stmt 0 # helper.cpp:2:3
popq %rbp
.cfi_def_cfa %rsp, 8
retq
.Ltmp1:
.Lfunc_end0:
.size _Z9getReturnv, .Lfunc_end0-_Z9getReturnv
.cfi_endproc
# -- End function
.section .debug_abbrev,"",@progbits
.byte 1 # Abbreviation Code
.byte 74 # DW_TAG_skeleton_unit
.byte 0 # DW_CHILDREN_no
.byte 16 # DW_AT_stmt_list
.byte 23 # DW_FORM_sec_offset
.byte 114 # DW_AT_str_offsets_base
.byte 23 # DW_FORM_sec_offset
.byte 27 # DW_AT_comp_dir
.byte 37 # DW_FORM_strx1
.ascii "\264B" # DW_AT_GNU_pubnames
.byte 25 # DW_FORM_flag_present
.byte 118 # DW_AT_dwo_name
.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 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 4 # DWARF Unit Type
.byte 8 # Address Size (in bytes)
.long .debug_abbrev # Offset Into Abbrev. Section
.quad 5976014880088676049
.byte 1 # Abbrev [1] 0x14:0x14 DW_TAG_skeleton_unit
.long .Lline_table_start0 # DW_AT_stmt_list
.long .Lstr_offsets_base0 # DW_AT_str_offsets_base
.byte 0 # DW_AT_comp_dir
# DW_AT_GNU_pubnames
.byte 1 # DW_AT_dwo_name
.byte 0 # DW_AT_low_pc
.long .Lfunc_end0-.Lfunc_begin0 # DW_AT_high_pc
.long .Laddr_table_base0 # DW_AT_addr_base
.Ldebug_info_end0:
.section .debug_str_offsets,"",@progbits
.long 12 # Length of String Offsets Set
.short 5
.short 0
.Lstr_offsets_base0:
.section .debug_str,"MS",@progbits,1
.Lskel_string0:
.asciz "." # string offset=0
.Lskel_string1:
.asciz "helper.dwo" # string offset=2
.section .debug_str_offsets,"",@progbits
.long .Lskel_string0
.long .Lskel_string1
.section .debug_str_offsets.dwo,"e",@progbits
.long 28 # Length of String Offsets Set
.short 5
.short 0
.section .debug_str.dwo,"eMS",@progbits,1
.Linfo_string0:
.asciz "_Z9getReturnv" # string offset=0
.Linfo_string1:
.asciz "getReturn" # string offset=14
.Linfo_string2:
.asciz "int" # string offset=24
.Linfo_string3:
.asciz "clang version 22.0.0" # string offset=28
.Linfo_string4:
.asciz "helper.cpp" # string offset=49
.Linfo_string5:
.asciz "helper.dwo" # string offset=60
.section .debug_str_offsets.dwo,"e",@progbits
.long 0
.long 14
.long 24
.long 28
.long 49
.long 60
.section .debug_info.dwo,"e",@progbits
.long .Ldebug_info_dwo_end0-.Ldebug_info_dwo_start0 # Length of Unit
.Ldebug_info_dwo_start0:
.short 5 # DWARF version number
.byte 5 # DWARF Unit Type
.byte 8 # Address Size (in bytes)
.long 0 # Offset Into Abbrev. Section
.quad 5976014880088676049
.byte 1 # Abbrev [1] 0x14:0x1b DW_TAG_compile_unit
.byte 3 # DW_AT_producer
.short 33 # DW_AT_language
.byte 4 # DW_AT_name
.byte 5 # DW_AT_dwo_name
.byte 2 # Abbrev [2] 0x1a:0x10 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 86
.byte 0 # DW_AT_linkage_name
.byte 1 # DW_AT_name
.byte 0 # DW_AT_decl_file
.byte 1 # DW_AT_decl_line
.long 42 # DW_AT_type
# DW_AT_external
.byte 3 # Abbrev [3] 0x2a:0x4 DW_TAG_base_type
.byte 2 # DW_AT_name
.byte 5 # DW_AT_encoding
.byte 4 # DW_AT_byte_size
.byte 0 # End Of Children Mark
.Ldebug_info_dwo_end0:
.section .debug_abbrev.dwo,"e",@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 118 # DW_AT_dwo_name
.byte 37 # DW_FORM_strx1
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 0 # DW_CHILDREN_no
.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 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 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 0 # EOM(3)
.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
.Ldebug_addr_end0:
.section .debug_gnu_pubnames,"",@progbits
.long .LpubNames_end0-.LpubNames_start0 # Length of Public Names Info
.LpubNames_start0:
.short 2 # DWARF Version
.long .Lcu_begin0 # Offset of Compilation Unit Info
.long 40 # Compilation Unit Length
.long 26 # DIE offset
.byte 48 # Attributes: FUNCTION, EXTERNAL
.asciz "getReturn" # External Name
.long 0 # End Mark
.LpubNames_end0:
.section .debug_gnu_pubtypes,"",@progbits
.long .LpubTypes_end0-.LpubTypes_start0 # Length of Public Types Info
.LpubTypes_start0:
.short 2 # DWARF Version
.long .Lcu_begin0 # Offset of Compilation Unit Info
.long 40 # Compilation Unit Length
.long 42 # DIE offset
.byte 144 # Attributes: TYPE, STATIC
.asciz "int" # External Name
.long 0 # End Mark
.LpubTypes_end0:
.ident "clang version 22.0.0"
.section ".note.GNU-stack","",@progbits
.addrsig
.section .debug_line,"",@progbits
.Lline_table_start0:
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