[CodeView] Avoid NULL deref of Scope

[glandium]

Summary

Regression from D131400: cross-language LTO causes a crash in the
compiler on the NULL deref of Scope in isa call when Rust IR is
involved. Presumably, this might affect other languages too, and
even Rust itself without cross-language LTO when the Rust compiler
switched to LLVM 16.

[glandium]

@rnk ping

[rnk]

Code looks good, but can you add a globals-rust.ll file next to llvm/test/DebugInfo/COFF/global_visibility.ll with some representative debug info? Or limit it to globals-noscope.ll or something like that to hit this codepath.

[glandium]

Adding a testcase that crashes without the patch and passes with the patch.

[rnk]

lgtm

[glandium]

Thank you. Could you publish this for me (I don't have commit access)?

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

void CodeViewDebug::emitDebugInfoForGlobal(const CVGlobalVariable &CVGV) {
   // For static data members, get the scope from the declaration.
   if (const auto *MemberDecl = dyn_cast_or_null<DIDerivedType>(
           DIGV->getRawStaticDataMemberDeclaration()))
     Scope = MemberDecl->getScope();
   // For static local variables and Fortran, the scoping portion is elided
   // in its name so that we can reference the variable in the command line
   // of the VS debugger.
   std::string QualifiedName =
-      (moduleIsInFortran() || isa<DILocalScope>(Scope))
+      (moduleIsInFortran() || (Scope && isa<DILocalScope>(Scope)))
           ? std::string(DIGV->getName())
           : getFullyQualifiedName(Scope, DIGV->getName());
 
   if (const GlobalVariable *GV =
           CVGV.GVInfo.dyn_cast<const GlobalVariable *>()) {
     // DataSym record, see SymbolRecord.h for more info. Thread local data
     // happens to have the same format as global data.
     MCSymbol *GVSym = Asm->getSymbol(GV);

llvm/test/DebugInfo/COFF/global_rust.ll

+; RUN: llc < %s -filetype=obj | llvm-readobj - --codeview | FileCheck %s
+;
+; This test verifies global variables with no scope, as rust generates them for vtables, are handled correctly.
+;
+; -- global_rust.rs ----------------------------------------------------
+; #![crate_type = "lib"]
+; pub trait Foo {
+;     fn foo(&self) {}
+; }
+;
+; impl Foo for u32 {}
+;
+; pub fn foo(_: &dyn Foo) {}
+;
+; pub fn bar() {
+;     foo(&42);
+; }
+; -----------------------------------------------------------------------------
+;
+; $ rustc -emit=llvm-ir --target=x86_64-pc-windows-msvc -C debuginfo=2 global_rust.rs
+;
+
+; CHECK: CodeViewDebugInfo [
+; CHECK:   Section: .debug$S (6)
+
+; CHECK:   Subsection [
+; CHECK:     SubSectionType: Symbols (0xF1)
+; CHECK:     SubSectionSize: 0x34
+; CHECK:     DataSym {
+; CHECK:       Kind: S_LDATA32 (0x110C)
+; CHECK:       DataOffset: .rdata+0x8
+; CHECK:       Type: impl$<u32, global_rust::Foo>::vtable_type$ (0x101D)
+; CHECK:       DisplayName: impl$<u32, global_rust::Foo>::vtable$
+; CHECK:       LinkageName: .rdata
+; CHECK:     }
+; CHECK:   ]
+
+; ModuleID = 'global_rust.5984dd87-cgu.0'
+source_filename = "global_rust.5984dd87-cgu.0"
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+@alloc7 = private unnamed_addr constant <{ [4 x i8] }> <{ [4 x i8] c"*\00\00\00" }>, align 4
+@vtable.0 = private unnamed_addr constant <{ i8*, [16 x i8], i8* }> <{ i8* bitcast (void (i32*)* @"_ZN4core3ptr24drop_in_place$LT$u32$GT$17h5aa897c8344c34eaE" to i8*), [16 x i8] c"\04\00\00\00\00\00\00\00\04\00\00\00\00\00\00\00", i8* bitcast (void (i32*)* @_ZN11global_rust3Foo3foo17h17696ada84e467feE to i8*) }>, align 8, !dbg !0
+
+; core::ptr::drop_in_place<u32>
+; Function Attrs: inlinehint uwtable
+define internal void @"_ZN4core3ptr24drop_in_place$LT$u32$GT$17h5aa897c8344c34eaE"(i32* %_1) unnamed_addr #0 !dbg !22 {
+start:
+  %_1.dbg.spill = alloca i32*, align 8
+  store i32* %_1, i32** %_1.dbg.spill, align 8
+  call void @llvm.dbg.declare(metadata i32** %_1.dbg.spill, metadata !30, metadata !DIExpression()), !dbg !33
+  ret void, !dbg !33
+}
+
+; global_rust::Foo::foo
+; Function Attrs: uwtable
+define void @_ZN11global_rust3Foo3foo17h17696ada84e467feE(i32* align 4 %self) unnamed_addr #1 !dbg !34 {
+start:
+  %self.dbg.spill = alloca i32*, align 8
+  store i32* %self, i32** %self.dbg.spill, align 8
+  call void @llvm.dbg.declare(metadata i32** %self.dbg.spill, metadata !42, metadata !DIExpression()), !dbg !45
+  ret void, !dbg !45
+}
+
+; global_rust::foo
+; Function Attrs: uwtable
+define void @_ZN11global_rust3foo17hbb4da99a7bb855e3E({}* align 1 %_1.0, [3 x i64]* align 8 %_1.1) unnamed_addr #1 !dbg !46 {
+start:
+  %_1.dbg.spill = alloca { {}*, [3 x i64]* }, align 8
+  %0 = getelementptr inbounds { {}*, [3 x i64]* }, { {}*, [3 x i64]* }* %_1.dbg.spill, i32 0, i32 0
+  store {}* %_1.0, {}** %0, align 8
+  %1 = getelementptr inbounds { {}*, [3 x i64]* }, { {}*, [3 x i64]* }* %_1.dbg.spill, i32 0, i32 1
+  store [3 x i64]* %_1.1, [3 x i64]** %1, align 8
+  call void @llvm.dbg.declare(metadata { {}*, [3 x i64]* }* %_1.dbg.spill, metadata !60, metadata !DIExpression()), !dbg !61
+  ret void, !dbg !61
+}
+
+; global_rust::bar
+; Function Attrs: uwtable
+define void @_ZN11global_rust3bar17h9ea8de32fc3f1360E() unnamed_addr #1 !dbg !62 {
+start:
+; call global_rust::foo
+  call void @_ZN11global_rust3foo17hbb4da99a7bb855e3E({}* align 1 bitcast (<{ [4 x i8] }>* @alloc7 to {}*), [3 x i64]* align 8 bitcast (<{ i8*, [16 x i8], i8* }>* @vtable.0 to [3 x i64]*)), !dbg !65
+  br label %bb1, !dbg !65
+
+bb1:                                              ; preds = %start
+  ret void, !dbg !66
+}
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #2
+
+attributes #0 = { inlinehint uwtable "target-cpu"="x86-64" }
+attributes #1 = { uwtable "target-cpu"="x86-64" }
+attributes #2 = { nofree nosync nounwind readnone speculatable willreturn }
+
+!llvm.module.flags = !{!16, !17, !18}
+!llvm.dbg.cu = !{!19}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "impl$<u32, global_rust::Foo>::vtable$", scope: null, file: !2, type: !3, isLocal: true, isDefinition: true)
+!2 = !DIFile(filename: "<unknown>", directory: "")
+!3 = !DICompositeType(tag: DW_TAG_structure_type, name: "impl$<u32, global_rust::Foo>::vtable_type$", file: !2, size: 256, align: 64, flags: DIFlagArtificial, elements: !4, vtableHolder: !14, templateParams: !8, identifier: "4a384a40e448d9d82ef8cb395527d231")
+!4 = !{!5, !9, !12, !13}
+!5 = !DIDerivedType(tag: DW_TAG_member, name: "drop_in_place", scope: !3, file: !2, baseType: !6, size: 64, align: 64)
+!6 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "ptr_const$<tuple$<> >", baseType: !7, size: 64, align: 64, dwarfAddressSpace: 0)
+!7 = !DICompositeType(tag: DW_TAG_structure_type, name: "tuple$<>", file: !2, align: 8, elements: !8, identifier: "65e33f3994015bcf158992dbe0323c0")
+!8 = !{}
+!9 = !DIDerivedType(tag: DW_TAG_member, name: "size", scope: !3, file: !2, baseType: !10, size: 64, align: 64, offset: 64)
+!10 = !DIDerivedType(tag: DW_TAG_typedef, name: "usize", file: !2, baseType: !11)
+!11 = !DIBasicType(name: "size_t", size: 64, encoding: DW_ATE_unsigned)
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "align", scope: !3, file: !2, baseType: !10, size: 64, align: 64, offset: 128)
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "__method3", scope: !3, file: !2, baseType: !6, size: 64, align: 64, offset: 192)
+!14 = !DIDerivedType(tag: DW_TAG_typedef, name: "u32", file: !2, baseType: !15)
+!15 = !DIBasicType(name: "unsigned __int32", size: 32, encoding: DW_ATE_unsigned)
+!16 = !{i32 7, !"PIC Level", i32 2}
+!17 = !{i32 2, !"CodeView", i32 1}
+!18 = !{i32 2, !"Debug Info Version", i32 3}
+!19 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !20, producer: "clang LLVM (rustc version 1.64.0 (a55dd71d5 2022-09-19))", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !21)
+!20 = !DIFile(filename: "global_rust.rs/@/global_rust.5984dd87-cgu.0", directory: "/tmp/llvm2")
+!21 = !{!0}
+!22 = distinct !DISubprogram(name: "drop_in_place<u32>", linkageName: "_ZN4core3ptr24drop_in_place$LT$u32$GT$17h5aa897c8344c34eaE", scope: !24, file: !23, line: 487, type: !26, scopeLine: 487, flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition, unit: !19, templateParams: !31, retainedNodes: !29)
+!23 = !DIFile(filename: "/rustc/a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52\\library\\core\\src\\ptr\\mod.rs", directory: "", checksumkind: CSK_SHA1, checksum: "09826e1d72e15b98151545882632f685c97dc29f")
+!24 = !DINamespace(name: "ptr", scope: !25)
+!25 = !DINamespace(name: "core", scope: null)
+!26 = !DISubroutineType(types: !27)
+!27 = !{null, !28}
+!28 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "ptr_mut$<u32>", baseType: !14, size: 64, align: 64, dwarfAddressSpace: 0)
+!29 = !{!30}
+!30 = !DILocalVariable(arg: 1, scope: !22, file: !23, line: 487, type: !28)
+!31 = !{!32}
+!32 = !DITemplateTypeParameter(name: "T", type: !14)
+!33 = !DILocation(line: 487, scope: !22)
+!34 = distinct !DISubprogram(name: "foo<u32>", linkageName: "_ZN11global_rust3Foo3foo17h17696ada84e467feE", scope: !36, file: !35, line: 3, type: !38, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition, unit: !19, templateParams: !43, retainedNodes: !41)
+!35 = !DIFile(filename: "global_rust.rs", directory: "/tmp/llvm2", checksumkind: CSK_SHA1, checksum: "d28353083c5fcd457fffa5827b0372c4a843c302")
+!36 = !DINamespace(name: "Foo", scope: !37)
+!37 = !DINamespace(name: "global_rust", scope: null)
+!38 = !DISubroutineType(types: !39)
+!39 = !{null, !40}
+!40 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "ref$<u32>", baseType: !14, size: 64, align: 64, dwarfAddressSpace: 0)
+!41 = !{!42}
+!42 = !DILocalVariable(name: "self", arg: 1, scope: !34, file: !35, line: 3, type: !40)
+!43 = !{!44}
+!44 = !DITemplateTypeParameter(name: "Self", type: !14)
+!45 = !DILocation(line: 3, scope: !34)
+!46 = distinct !DISubprogram(name: "foo", linkageName: "_ZN11global_rust3foo17hbb4da99a7bb855e3E", scope: !37, file: !35, line: 8, type: !47, scopeLine: 8, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !19, templateParams: !8, retainedNodes: !59)
+!47 = !DISubroutineType(types: !48)
+!48 = !{null, !49}
+!49 = !DICompositeType(tag: DW_TAG_structure_type, name: "ref$<dyn$<global_rust::Foo> >", file: !2, size: 128, align: 64, elements: !50, templateParams: !8, identifier: "2c39c7f196ba93e4e4fbfefe6e460dfb")
+!50 = !{!51, !54}
+!51 = !DIDerivedType(tag: DW_TAG_member, name: "pointer", scope: !49, file: !2, baseType: !52, size: 64, align: 64)
+!52 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !53, size: 64, align: 64, dwarfAddressSpace: 0)
+!53 = !DICompositeType(tag: DW_TAG_structure_type, name: "dyn$<global_rust::Foo>", file: !2, align: 8, elements: !8, identifier: "dc5af67081d01f4b3cf3420f9b3ec7fa")
+!54 = !DIDerivedType(tag: DW_TAG_member, name: "vtable", scope: !49, file: !2, baseType: !55, size: 64, align: 64, offset: 64)
+!55 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "ref$<array$<usize,3> >", baseType: !56, size: 64, align: 64, dwarfAddressSpace: 0)
+!56 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, size: 192, align: 64, elements: !57)
+!57 = !{!58}
+!58 = !DISubrange(count: 3, lowerBound: 0)
+!59 = !{!60}
+!60 = !DILocalVariable(arg: 1, scope: !46, file: !35, line: 8, type: !49)
+!61 = !DILocation(line: 8, scope: !46)
+!62 = distinct !DISubprogram(name: "bar", linkageName: "_ZN11global_rust3bar17h9ea8de32fc3f1360E", scope: !37, file: !35, line: 10, type: !63, scopeLine: 10, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !19, templateParams: !8, retainedNodes: !8)
+!63 = !DISubroutineType(types: !64)
+!64 = !{null}
+!65 = !DILocation(line: 11, scope: !62)
+!66 = !DILocation(line: 12, scope: !62)