[llvm][DebugInfo] Drop \01 mangling prefix when inserting linkage name into accelerator table

[Michael137]

On some platforms (particularly macOS), a \01 prefix gets added to the name in an asm label. This gets stripped when we emit the DW_AT_linkage_name. But we weren't stripping this prefix when inserting the linkage name into accelerator tables.

This manifested in an issue where LLDB tried to look up a name in the index by linkage name, but wasn't able to find it because we indexed it with the \01 unstripped.

This patch strips the prefix before indexing.

[llvmbot]

@llvm/pr-subscribers-debuginfo

Author: Michael Buch (Michael137)

Changes

On some platforms (particularly macOS), a \01 prefix gets added to the name in an asm label. This gets stripped when we emit the DW_AT_linkage_name. But we weren't stripping this prefix when inserting the linkage name into accelerator tables.

This manifested in an issue where LLDB tried to look up a name in the index by linkage name, but wasn't able to find it because we indexed it with the \01 unstripped.

This patch strips the prefix before indexing.

---

Full diff: https://github.com/llvm/llvm-project/pull/138852.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (+7-2)
• (added) llvm/test/DebugInfo/Generic/debug-names-asm-label.ll (+55)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index b331854d1ee8f..010c3d6562cc1 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -489,12 +489,17 @@ void DwarfDebug::addSubprogramNames(
   if (SP->getName() != "")
     addAccelName(Unit, NameTableKind, SP->getName(), Die);
 
+  // We drop the mangling escape prefix when emitting the DW_AT_linkage_name. So
+  // ensure we don't include it when inserting into the accelerator tables.
+  llvm::StringRef LinkageName =
+      GlobalValue::dropLLVMManglingEscape(SP->getLinkageName());
+
   // If the linkage name is different than the name, go ahead and output that as
   // well into the name table. Only do that if we are going to actually emit
   // that name.
-  if (SP->getLinkageName() != "" && SP->getName() != SP->getLinkageName() &&
+  if (LinkageName != "" && SP->getName() != LinkageName &&
       (useAllLinkageNames() || InfoHolder.getAbstractScopeDIEs().lookup(SP)))
-    addAccelName(Unit, NameTableKind, SP->getLinkageName(), Die);
+    addAccelName(Unit, NameTableKind, LinkageName, Die);
 
   // If this is an Objective-C selector name add it to the ObjC accelerator
   // too.
diff --git a/llvm/test/DebugInfo/Generic/debug-names-asm-label.ll b/llvm/test/DebugInfo/Generic/debug-names-asm-label.ll
new file mode 100644
index 0000000000000..23c03c5c02371
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/debug-names-asm-label.ll
@@ -0,0 +1,55 @@
+; Tests the mangling escape prefix gets stripped from the linkage name.
+;
+; RUN: %llc_dwarf -accel-tables=Dwarf -dwarf-linkage-names=All -filetype=obj -o %t < %s
+;
+; RUN: llvm-dwarfdump -debug-info -debug-names %t | FileCheck %s
+; RUN: llvm-dwarfdump -debug-names -verify %t | FileCheck --check-prefix=VERIFY %s
+
+; CHECK: .debug_info contents:
+; CHECK: DW_AT_linkage_name	("bar")
+; CHECK: .debug_names contents:
+; CHECK: String: {{.*}} "bar"
+
+; There should be no verification errors for both files.
+; VERIFY: No errors.
+
+; Input generated from the following C++ code using
+; clang -g -S -emit-llvm -target aarch64-apple-macos
+
+; void foo() asm("bar");
+; void foo() {}
+; 
+; void g() { foo(); }
+
+define void @"\01bar"() !dbg !9 {
+entry:
+  ret void, !dbg !13
+}
+
+define void @_Z1gv() !dbg !14 {
+entry:
+  call void @"\01bar"(), !dbg !15
+  ret void, !dbg !16
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 21.0.0git", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: Apple, sysroot: "/")
+!1 = !DIFile(filename: "asm.cpp", directory: "/tmp", checksumkind: CSK_MD5, checksum: "d053f9249cc5548d446ceb58411ad625")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"uwtable", i32 1}
+!7 = !{i32 7, !"frame-pointer", i32 1}
+!8 = !{!"clang version 21.0.0git"}
+!9 = distinct !DISubprogram(name: "foo", linkageName: "\01bar", scope: !10, file: !10, line: 2, type: !11, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!10 = !DIFile(filename: "asm.cpp", directory: "/tmp", checksumkind: CSK_MD5, checksum: "d053f9249cc5548d446ceb58411ad625")
+!11 = !DISubroutineType(types: !12)
+!12 = !{null}
+!13 = !DILocation(line: 2, column: 13, scope: !9)
+!14 = distinct !DISubprogram(name: "g", linkageName: "_Z1gv", scope: !10, file: !10, line: 4, type: !11, scopeLine: 4, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!15 = !DILocation(line: 4, column: 12, scope: !14)
+!16 = !DILocation(line: 4, column: 19, scope: !14)

[Jlalond]

@Michael137 mostly asking for myself, but is there a reason we check for "" instead of empty?

[Michael137]

Nope no reason in particular. This is the way the code was prior to my changes, so wanted to keep the diff as small as possible

[Michael137]

CI error is unrelated. Seems like a flang build failure:

fatal error: file '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-g6cdk-1/llvm-project/github-pull-requests/llvm/include/llvm/ADT/bit.h' has been modified since the precompiled header '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-g6cdk-1/llvm-project/github-pull-requests/build/tools/flang/lib/Evaluate/CMakeFiles/FortranEvaluate.dir/cmake_pch.hxx.pch' was built: size changed (was 12409, now 12384)
note: please rebuild precompiled header '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-g6cdk-1/llvm-project/github-pull-requests/build/tools/flang/lib/Evaluate/CMakeFiles/FortranEvaluate.dir/cmake_pch.hxx.pch'
1 error generated.