[lld] [llvm] Fix lld crash caused by dynamic bit offset patch (PR #146701)

Wed Jul 2 07:24:44 PDT 2025

llvmbot wrote:




@llvm/pr-subscribers-lld

Author: Tom Tromey (tromey)

<details>
<summary>Changes</summary>

PR #141106 changed the debuginfo metdata to allow dynamic bit offsets and sizes.  This caused a crash in lld when using LTO.

The problem is that lazyLoadOneMetadata assumes that the metadata in question can be cast to MDNode; but in the typical case where the offset is a constant, this is not true.

This patch changes this spot to allow non-MDNodes through.

The included test case comes from the report in #141106.

---
Full diff: https://github.com/llvm/llvm-project/pull/146701.diff


2 Files Affected:

- (added) lld/test/ELF/lto/lazy-debug.ll (+107) 
- (modified) llvm/lib/Bitcode/Reader/MetadataLoader.cpp (+4-2) 


``````````diff

diff --git a/lld/test/ELF/lto/lazy-debug.ll b/lld/test/ELF/lto/lazy-debug.ll
new file mode 100644
index 0000000000000..48d176f0f6bf6
--- /dev/null
+++ b/lld/test/ELF/lto/lazy-debug.ll
@@ -0,0 +1,107 @@
+; REQUIRES: aarch64
+;; Regression test for a case in lazy debuginfo loading.
+;; The bug would cause ld.lld to crash.
+
+; RUN: split-file %s %t
+; RUN: llvm-as %t/hda_codec.s -o %t/hda_codec.o
+; RUN: llvm-as %t/hda_bind.s -o %t/hda_bind.o
+; RUN: ld.lld -EL -maarch64elf -r %t/hda_bind.o %t/hda_codec.o -o %t/hda_codec
+
+;--- hda_codec.s
+; ModuleID = 'hda_codec.o'
+source_filename = "hda_codec.i"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "aarch64-unknown-linux-gnu"
+
+%struct.anon = type { i32 }
+
+ at hda_set_power_state_codec = hidden local_unnamed_addr global %struct.anon zeroinitializer, align 4, !dbg !0
+
+; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(none) uwtable
+define hidden void @snd_hda_codec_shutdown() local_unnamed_addr #0 !dbg !19 {
+entry:
+  ret void, !dbg !22
+}
+
+attributes #0 = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) uwtable "frame-pointer"="non-leaf" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+fp-armv8,+neon,+v8a,-fmv" }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!10, !11, !12, !13, !14, !15, !16, !17}
+!llvm.ident = !{!18}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "hda_set_power_state_codec", scope: !2, file: !5, line: 3, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C11, file: !3, producer: "clang version 21.0.0git (git at github.com:llvm/llvm-project.git 93849a39c432827473ca6c676f1500da69b3aaa0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "hda_codec.i", directory: "/tmp")
+!4 = !{!0}
+!5 = !DIFile(filename: "hda_codec.i", directory: "/tmp", checksumkind: CSK_MD5, checksum: "c192644b468953345ff9647026173a7b")
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, file: !5, line: 1, size: i64 32, offset: i64 0, elements: !7)
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "mfg", scope: !6, file: !5, line: 2, baseType: !9, size: i64 32, offset: i64 0)
+!9 = !DIBasicType(name: "int", size: i64 32, encoding: DW_ATE_signed)
+!10 = !{i32 7, !"Dwarf Version", i32 5}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{i32 1, !"wchar_size", i32 4}
+!13 = !{i32 8, !"PIC Level", i32 2}
+!14 = !{i32 7, !"PIE Level", i32 2}
+!15 = !{i32 7, !"uwtable", i32 2}
+!16 = !{i32 7, !"frame-pointer", i32 1}
+!17 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+!18 = !{!"clang version 21.0.0git (git at github.com:llvm/llvm-project.git 93849a39c432827473ca6c676f1500da69b3aaa0)"}
+!19 = distinct !DISubprogram(name: "snd_hda_codec_shutdown", scope: !5, file: !5, line: 4, type: !20, scopeLine: 4, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2)
+!20 = !DISubroutineType(types: !21)
+!21 = !{null}
+!22 = !DILocation(line: 4, column: 32, scope: !19)
+
+^0 = module: (path: "hda_codec.o", hash: (1120894731, 3099354915, 309166549, 2100129435, 1932081428))
+^1 = gv: (name: "snd_hda_codec_shutdown", summaries: (function: (module: ^0, flags: (linkage: external, visibility: hidden, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 1, funcFlags: (readNone: 1, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0, noInline: 0, alwaysInline: 0, noUnwind: 1, mayThrow: 0, hasUnknownCall: 0, mustBeUnreachable: 0)))) ; guid = 1539195202824839354
+^2 = gv: (name: "hda_set_power_state_codec", summaries: (variable: (module: ^0, flags: (linkage: external, visibility: hidden, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0, importType: definition), varFlags: (readonly: 1, writeonly: 1, constant: 0)))) ; guid = 10300548032946263328
+^3 = flags: 8
+^4 = blockcount: 0
+
+;--- hda_bind.s
+; ModuleID = 'hda_bind.o'
+source_filename = "hda_bind.i"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "aarch64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define hidden void @hda_codec_driver_shutdown() local_unnamed_addr #0 !dbg !11 {
+entry:
+  tail call void @snd_hda_codec_shutdown() #2, !dbg !15
+  ret void, !dbg !16
+}
+
+declare void @snd_hda_codec_shutdown(...) local_unnamed_addr #1
+
+attributes #0 = { nounwind uwtable "frame-pointer"="non-leaf" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+fp-armv8,+neon,+v8a,-fmv" }
+attributes #1 = { "frame-pointer"="non-leaf" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+fp-armv8,+neon,+v8a,-fmv" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 21.0.0git (git at github.com:llvm/llvm-project.git 93849a39c432827473ca6c676f1500da69b3aaa0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "hda_bind.i", directory: "/tmp")
+!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, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 1}
+!9 = !{i32 1, !"EnableSplitLTOUnit", i32 1}
+!10 = !{!"clang version 21.0.0git (git at github.com:llvm/llvm-project.git 93849a39c432827473ca6c676f1500da69b3aaa0)"}
+!11 = distinct !DISubprogram(name: "hda_codec_driver_shutdown", scope: !12, file: !12, line: 2, type: !13, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!12 = !DIFile(filename: "hda_bind.i", directory: "/tmp", checksumkind: CSK_MD5, checksum: "5907dd04e8964940b57448f37db201c6")
+!13 = !DISubroutineType(types: !14)
+!14 = !{null}
+!15 = !DILocation(line: 2, column: 36, scope: !11)
+!16 = !DILocation(line: 2, column: 62, scope: !11)
+
+^0 = module: (path: "hda_bind.o", hash: (1958332034, 2012675483, 855691486, 2017350850, 2779827776))
+^1 = gv: (name: "snd_hda_codec_shutdown") ; guid = 1539195202824839354
+^2 = gv: (name: "hda_codec_driver_shutdown", summaries: (function: (module: ^0, flags: (linkage: external, visibility: hidden, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 2, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 0, returnDoesNotAlias: 0, noInline: 0, alwaysInline: 0, noUnwind: 1, mayThrow: 0, hasUnknownCall: 0, mustBeUnreachable: 0), calls: ((callee: ^1, tail: 1))))) ; guid = 12817427500962331703
+^3 = flags: 8
+^4 = blockcount: 0
diff --git a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
index a9467d16c9a14..d28ab7d0bb52c 100644
--- a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
+++ b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
@@ -1156,8 +1156,10 @@ void MetadataLoader::MetadataLoaderImpl::lazyLoadOneMetadata(
   assert(ID >= MDStringRef.size() && "Unexpected lazy-loading of MDString");
   // Lookup first if the metadata hasn't already been loaded.
   if (auto *MD = MetadataList.lookup(ID)) {
-    auto *N = cast<MDNode>(MD);
-    if (!N->isTemporary())
+    auto *N = dyn_cast<MDNode>(MD);
+    // If the node is not an MDNode, or if it is not temporary, then
+    // we're done.
+    if (!N || !N->isTemporary())
       return;
   }
   SmallVector<uint64_t, 64> Record;

``````````

</details>


https://github.com/llvm/llvm-project/pull/146701
