https://github.com/Nerixyz created https://github.com/llvm/llvm-project/pull/145175
Linking executables with DWARF sections on Windows with the default link.exe will truncate the section names, as [sections in PE/COFF executable images can't be longer than 8 bytes](https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#section-table-section-headers). There's no warning about this. When trying to debug these executables in LLDB, no debug info will be loaded, because LLDB won't find the required sections and it doesn't find CodeView debug info. There's no warning here, either (this PR adds one). I ran into this myself while playing around with LLDB: - Compile some file with Clang and use DWARF: `clang-cl foo.c -gdwarf -o foo.exe` - Open in LLDB `lldb foo.exe` - Break at line 10: `b foo.c:10` ⚡ → "Unable to resolve breakpoint to any actual locations." (because no debug info is loaded) The fix would be to pass `-fuse-ld=lld-link` to Clang. --- This PR adds a warning when LLDB detects truncated DWARF sections (i.e. sections matching `^\.debug_[a-z]$`): ``` warning: (x86_64) foo.exe contains 5 truncated DWARF sections (.debug_a, .debug_i, .debug_r, .debug_s, .debug_l). Note: Executable images on Windows can't include the required names when linking with the default link.exe. A third party linker like lld-link is required (compile with -fuse-ld=lld-link on Clang). ``` I included the additional note, because to get to this point, one would have to have used Clang on windows-msvc (on MinGW, the default linker doesn't truncate the names), so they should have lld-link available as well. >From b58c2be64d0a8994c5f19b9fff073a3dcfd47b59 Mon Sep 17 00:00:00 2001 From: Nerixyz <nerix...@outlook.de> Date: Sat, 21 Jun 2025 17:36:58 +0200 Subject: [PATCH] [LLDB] Warn about truncated DWARF section names on Windows --- .../ObjectFile/PECOFF/ObjectFilePECOFF.cpp | 17 ++++++++++ .../Shell/ObjectFile/PECOFF/lit.local.cfg | 2 +- .../Shell/ObjectFile/PECOFF/truncated-dwarf.c | 7 ++++ lldb/test/Shell/helper/build.py | 33 ++++++++++++++++--- 4 files changed, 53 insertions(+), 6 deletions(-) create mode 100644 lldb/test/Shell/ObjectFile/PECOFF/truncated-dwarf.c diff --git a/lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp b/lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp index 4984445dcbab9..343d7477c66c7 100644 --- a/lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp +++ b/lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp @@ -1036,12 +1036,19 @@ void ObjectFilePECOFF::CreateSections(SectionList &unified_section_list) { m_sections_up->AddSection(header_sp); unified_section_list.AddSection(header_sp); + std::vector<llvm::StringRef> truncated_dwarf_sections; const uint32_t nsects = m_sect_headers.size(); for (uint32_t idx = 0; idx < nsects; ++idx) { llvm::StringRef sect_name = GetSectionName(m_sect_headers[idx]); ConstString const_sect_name(sect_name); SectionType section_type = GetSectionType(sect_name, m_sect_headers[idx]); + // Detect unknown sections matching ^\.debug_[a-z]$ + if (section_type == eSectionTypeOther && sect_name.size() == 8 && + sect_name.starts_with(".debug_") && llvm::isLower(sect_name.back())) { + truncated_dwarf_sections.emplace_back(sect_name); + } + SectionSP section_sp(new Section( module_sp, // Module to which this section belongs this, // Object file to which this section belongs @@ -1071,6 +1078,16 @@ void ObjectFilePECOFF::CreateSections(SectionList &unified_section_list) { m_sections_up->AddSection(section_sp); unified_section_list.AddSection(section_sp); } + + if (!truncated_dwarf_sections.empty()) { + module_sp->ReportWarning( + "contains {} truncated DWARF sections ({}).\n" + "Note: Executable images on Windows can't include the required names " + "when linking with the default link.exe. A third party linker like " + "lld-link is required (compile with -fuse-ld=lld-link on Clang).", + truncated_dwarf_sections.size(), + llvm::join(truncated_dwarf_sections, ", ")); + } } } diff --git a/lldb/test/Shell/ObjectFile/PECOFF/lit.local.cfg b/lldb/test/Shell/ObjectFile/PECOFF/lit.local.cfg index 9ef350be1dee2..1ae00d07fc3e6 100644 --- a/lldb/test/Shell/ObjectFile/PECOFF/lit.local.cfg +++ b/lldb/test/Shell/ObjectFile/PECOFF/lit.local.cfg @@ -1 +1 @@ -config.suffixes = ['.yaml', '.test'] +config.suffixes = ['.yaml', '.test', '.c'] diff --git a/lldb/test/Shell/ObjectFile/PECOFF/truncated-dwarf.c b/lldb/test/Shell/ObjectFile/PECOFF/truncated-dwarf.c new file mode 100644 index 0000000000000..92cb61050142a --- /dev/null +++ b/lldb/test/Shell/ObjectFile/PECOFF/truncated-dwarf.c @@ -0,0 +1,7 @@ +// REQUIRES: target-windows +// RUN: %build --compiler=clang-cl --force-dwarf-symbols --force-ms-link -o %t.exe -- %s +// RUN: %lldb -f %t.exe 2>&1 | FileCheck %s + +int main(void) {} + +// CHECK: warning: {{.*}} contains 4 truncated DWARF sections (.debug_{{[a-z]}}, .debug_{{[a-z]}}, .debug_{{[a-z]}}, .debug_{{[a-z]}}) diff --git a/lldb/test/Shell/helper/build.py b/lldb/test/Shell/helper/build.py index caaa14f90af1c..ecb02c1d7c87f 100755 --- a/lldb/test/Shell/helper/build.py +++ b/lldb/test/Shell/helper/build.py @@ -173,6 +173,22 @@ help="Specify the C/C++ standard.", ) +if sys.platform == "win32": + parser.add_argument( + "--force-dwarf-symbols", + dest="force_dwarf_symbols", + action="store_true", + default=False, + help="When compiling with clang-cl on Windows, use DWARF instead of CodeView", + ) + parser.add_argument( + "--force-ms-link", + dest="force_ms_link", + action="store_true", + default=False, + help="When compiling with clang-cl on Windows, always use link.exe", + ) + args = parser.parse_args(args=sys.argv[1:]) @@ -379,15 +395,20 @@ def __init__(self, toolchain_type, args): ) if self.mode == "link" or self.mode == "compile-and-link": - self.linker = ( - self._find_linker("link") - if toolchain_type == "msvc" - else self._find_linker("lld-link", args.tools_dir) - ) + if toolchain_type == "msvc" or args.force_ms_link: + search_paths = [] + if toolchain_type != "msvc": + search_paths.append( + os.path.dirname(find_executable("cl", args.tools_dir)) + ) + self.linker = self._find_linker("link", search_paths) + else: + self.linker = self._find_linker("lld-link", args.tools_dir) if not self.linker: raise ValueError("Unable to find an appropriate linker.") self.compile_env, self.link_env = self._get_visual_studio_environment() + self.force_dwarf_symbols = args.force_dwarf_symbols def _find_linker(self, name, search_paths=[]): compiler_dir = os.path.dirname(self.compiler) @@ -678,6 +699,8 @@ def _get_compilation_command(self, source, obj): args.append("/GR-") args.append("/Z7") if self.toolchain_type == "clang-cl": + if self.force_dwarf_symbols: + args.append("-gdwarf") args.append("-Xclang") args.append("-fkeep-static-consts") args.append("-fms-compatibility-version=19") _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
