Add the ability to load DWARF64 .debug_str_offsets tables for DWARF32 DWARF units in .dwp files. #167986
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… DWARF units in .dwp files. This path is updating the reading capabilities of the LLVM DWARF parser for a llvm-dwp patch llvm#167457 that will emit .dwp files where the compile units are DWARF32 and the .debug_str_offsets tables will be emitted as DWARF64 to allow .debug_str sections that exceed 4GB in size.
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@llvm/pr-subscribers-debuginfo Author: Greg Clayton (clayborg) ChangesThis path is updating the reading capabilities of the LLVM DWARF parser for a llvm-dwp patch #167457 that will emit .dwp files where the compile units are DWARF32 and the .debug_str_offsets tables will be emitted as DWARF64 to allow .debug_str sections that exceed 4GB in size. Full diff: https://github.com/llvm/llvm-project/pull/167986.diff 2 Files Affected:
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp b/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
index da0bf03e1ac57..b4256ae13914c 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
@@ -1187,9 +1187,18 @@ DWARFUnit::determineStringOffsetsTableContributionDWO(DWARFDataExtractor &DA) {
if (getVersion() >= 5) {
if (DA.getData().data() == nullptr)
return std::nullopt;
- Offset += Header.getFormat() == dwarf::DwarfFormat::DWARF32 ? 8 : 16;
+ // For .dwo files, the section contribution for the .debug_str_offsets
+ // points to the string offsets table header. Decode the format from this
+ // data as llvm-dwp has been modified to be able to emit a
+ // .debug_str_offsets table as DWARF64 even if the compile unit is DWARF32.
+ // This allows .dwp files to have string tables that exceed UINT32_MAX in
+ // size.
+ uint64_t Length = 0;
+ DwarfFormat Format = dwarf::DwarfFormat::DWARF32;
+ std::tie(Length, Format) = DA.getInitialLength(&Offset);
+ Offset += 4; // Skip the DWARF version uint16_t and the uint16_t padding.
// Look for a valid contribution at the given offset.
- auto DescOrError = parseDWARFStringOffsetsTableHeader(DA, Header.getFormat(), Offset);
+ auto DescOrError = parseDWARFStringOffsetsTableHeader(DA, Format, Offset);
if (!DescOrError)
return DescOrError.takeError();
return *DescOrError;
diff --git a/llvm/test/DebugInfo/dwarfdump-dwp-str-offsets-64.yaml b/llvm/test/DebugInfo/dwarfdump-dwp-str-offsets-64.yaml
new file mode 100644
index 0000000000000..3820ca7184d62
--- /dev/null
+++ b/llvm/test/DebugInfo/dwarfdump-dwp-str-offsets-64.yaml
@@ -0,0 +1,88 @@
+# This YAML file will create a .dwp file that has a DWARF32 compile unit whose
+# .debug_str_offsets.dwo is in DWARF64 format. This test verifies that
+# llvm-dwarfdump can read the strings correctly and dump the
+# .debug_str_offsets.dwo info correctly. This paves the way for llvm-dwp to
+# promote some .debug_str_offsets tables for .dwo files to be DWARF64 and will
+# allow the .debug_str section to be larger than UINT32_MAX size in bytes
+# without losing data.
+
+# RUN: yaml2obj %s -o %t.dwp
+# RUN: llvm-dwarfdump --debug-str-offsets --debug-info %t.dwp | FileCheck %s
+
+# CHECK: 0x00000000: Compile Unit: length = 0x0000002a, format = DWARF32, version = 0x0005, unit_type = DW_UT_split_compile, abbr_offset = 0x0000, addr_size = 0x08, DWO_id = 0x1158980a3c2f811b (next unit at 0x0000002e)
+
+# CHECK: 0x00000014: DW_TAG_compile_unit
+# CHECK-NEXT: DW_AT_producer ("Apple clang version 17.0.0 (clang-1700.4.4.1)")
+# CHECK-NEXT: DW_AT_language (DW_LANG_C_plus_plus_14)
+# CHECK-NEXT: DW_AT_name ("main.minimal.cpp")
+# CHECK-NEXT: DW_AT_dwo_name ("main.minimal.dwo")
+
+# CHECK: 0x0000001a: DW_TAG_subprogram
+# CHECK-NEXT: DW_AT_low_pc (indexed (00000000) address = <unresolved>)
+# CHECK-NEXT: DW_AT_high_pc (0x0000000f)
+# CHECK-NEXT: DW_AT_frame_base (DW_OP_reg6 RBP)
+# CHECK-NEXT: DW_AT_name ("main")
+# CHECK-NEXT: DW_AT_decl_file (0x00)
+# CHECK-NEXT: DW_AT_decl_line (1)
+# CHECK-NEXT: DW_AT_type (0x00000029 "int")
+# CHECK-NEXT: DW_AT_external (true)
+
+# CHECK: 0x00000029: DW_TAG_base_type
+# CHECK-NEXT: DW_AT_name ("int")
+# CHECK-NEXT: DW_AT_encoding (DW_ATE_signed)
+# CHECK-NEXT: DW_AT_byte_size (0x04)
+
+# CHECK: 0x0000002d: NULL
+
+# CHECK: .debug_str_offsets.dwo contents:
+# CHECK-NEXT: 0x00000000: Contribution size = 44, Format = DWARF64, Version = 5
+# CHECK-NEXT: 0x00000010: 0000000000000000 "main"
+# CHECK-NEXT: 0x00000018: 0000000000000005 "int"
+# CHECK-NEXT: 0x00000020: 0000000000000009 "Apple clang version 17.0.0 (clang-1700.4.4.1)"
+# CHECK-NEXT: 0x00000028: 0000000000000037 "main.minimal.cpp"
+# CHECK-NEXT: 0x00000030: 0000000000000048 "main.minimal.dwo"
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_REL
+ Machine: EM_X86_64
+ SectionHeaderStringTable: .strtab
+Sections:
+ - Name: .debug_abbrev.dwo
+ Type: SHT_PROGBITS
+ Flags: [ SHF_EXCLUDE ]
+ AddressAlign: 0x1
+ Content: 01110125251305032576250000022E00111B1206401803253A0B3B0B49133F19000003240003253E0B0B0B000000
+ - Name: .debug_str.dwo
+ Type: SHT_PROGBITS
+ Flags: [ SHF_EXCLUDE, SHF_MERGE, SHF_STRINGS ]
+ AddressAlign: 0x1
+ EntSize: 0x1
+ Content: 6D61696E00696E74004170706C6520636C616E672076657273696F6E2031372E302E302028636C616E672D313730302E342E342E3129006D61696E2E6D696E696D616C2E637070006D61696E2E6D696E696D616C2E64776F00
+ - Name: .debug_str_offsets.dwo
+ Type: SHT_PROGBITS
+ Flags: [ SHF_EXCLUDE ]
+ AddressAlign: 0x1
+ Content: 'FFFFFFFF2C000000000000000500000000000000000000000500000000000000090000000000000037000000000000004800000000000000'
+ - Name: .debug_info.dwo
+ Type: SHT_PROGBITS
+ Flags: [ SHF_EXCLUDE ]
+ AddressAlign: 0x1
+ Content: 2A00000005000508000000001B812F3C0A98581101022100030402000F0000000156000001290000000301050400
+ - Name: .debug_cu_index
+ Type: SHT_PROGBITS
+ AddressAlign: 0x1
+ Content: 0500000003000000010000000200000000000000000000001B812F3C0A98581100000000010000000100000003000000060000000000000000000000000000002E0000002E0000001C000000
+ - Type: SectionHeaderTable
+ Sections:
+ - Name: .strtab
+ - Name: .debug_abbrev.dwo
+ - Name: .debug_str.dwo
+ - Name: .debug_str_offsets.dwo
+ - Name: .debug_info.dwo
+ - Name: .debug_cu_index
+ - Name: .symtab
+Symbols: []
+...
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dwblaikie
approved these changes
Nov 14, 2025
Comment on lines
1190
to
1195
| // For .dwo files, the section contribution for the .debug_str_offsets | ||
| // points to the string offsets table header. Decode the format from this | ||
| // data as llvm-dwp has been modified to be able to emit a | ||
| // .debug_str_offsets table as DWARF64 even if the compile unit is DWARF32. | ||
| // This allows .dwp files to have string tables that exceed UINT32_MAX in | ||
| // size. |
Collaborator
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I'd probably skip the reference to llvm-dwp - Probably mention/link to https://dwarfstd.org/issues/211101.1.html
Though it barely needs a comment - the consequence falls out pretty naturally from parsing the header.
So maybe just a small FYI:
// FYI: The .debug_str_offsets.dwo section may use DWARF64 even when the rest of the file uses DWARF32, so respect whichever encoding the header/length uses.
Collaborator
|
Hi @clayborg, the test you added in this change seems to be failing on MacOS, can you take a look? https://lab.llvm.org/buildbot/#/builders/190/builds/30982 |
Collaborator
Author
Easy fix, I will make a PR real quick. |
clayborg
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Nov 14, 2025
…ets. Fixes a buildbot issue stemming from llvm#167986
Collaborator
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Buildbot fix PR is here: #168124 |
llvm-sync bot
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…e from targets. (#168124) Fixes a buildbot issue stemming from llvm/llvm-project#167986
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This path is updating the reading capabilities of the LLVM DWARF parser for a llvm-dwp patch #167457 that will emit .dwp files where the compile units are DWARF32 and the .debug_str_offsets tables will be emitted as DWARF64 to allow .debug_str sections that exceed 4GB in size.