[AArch64] DWARF: do not generate AT_location for thread local

Lei Liu · Lei Liu · commit 8e422b8403eb · 2018-08-01T23:46:49.000Z
AArch64 ELF ABI does not define a static relocation type for TLS offset within a module, which makes it impossible for compiler to generate a valid DW_AT_location content for thread local variables. Currently LLVM generates an invalid R_AARCH64_ABS64 relocation at the DW_AT_location field for a TLS variable. That causes trouble for linker because thread local variable does not have an absolute address at link time. AArch64 GCC solves the problem by not generating DW_AT_location for thread local variables. We should do the same in LLVM. Differential Revision: https://reviews.llvm.org/D43860 llvm-svn: 338655
diff --git a/llvm/include/llvm/Target/TargetLoweringObjectFile.h b/llvm/include/llvm/Target/TargetLoweringObjectFile.h
@@ -45,6 +45,7 @@ class TargetLoweringObjectFile : public MCObjectFileInfo {
 protected:
   bool SupportIndirectSymViaGOTPCRel = false;
   bool SupportGOTPCRelWithOffset = true;
+  bool SupportDebugThreadLocalLocation = true;
 
   /// This section contains the static constructor pointer list.
   MCSection *StaticCtorSection = nullptr;
@@ -170,6 +171,11 @@ class TargetLoweringObjectFile : public MCObjectFileInfo {
     return SupportGOTPCRelWithOffset;
   }
 
+  /// Target supports TLS offset relocation in debug section?
+  bool supportDebugThreadLocalLocation() const {
+    return SupportDebugThreadLocalLocation;
+  }
+
   /// Get the target specific PC relative GOT entry relocation
   virtual const MCExpr *getIndirectSymViaGOTPCRel(const MCSymbol *Sym,
                                                   const MCValue &MV,
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -186,6 +186,10 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
     if (!Global && (!Expr || !Expr->isConstant()))
       continue;
 
+    if (Global && Global->isThreadLocal() &&
+        !Asm->getObjFileLowering().supportDebugThreadLocalLocation())
+      continue;
+
     if (!Loc) {
       addToAccelTable = true;
       Loc = new (DIEValueAllocator) DIELoc;
diff --git a/llvm/lib/Target/AArch64/AArch64TargetObjectFile.cpp b/llvm/lib/Target/AArch64/AArch64TargetObjectFile.cpp
@@ -22,6 +22,9 @@ void AArch64_ELFTargetObjectFile::Initialize(MCContext &Ctx,
                                              const TargetMachine &TM) {
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
   InitializeELF(TM.Options.UseInitArray);
+  // AARCH64 ELF ABI does not define static relocation type for TLS offset
+  // within a module.  Do not generate AT_location for TLS variables.
+  SupportDebugThreadLocalLocation = false;
 }
 
 AArch64_MachoTargetObjectFile::AArch64_MachoTargetObjectFile()
diff --git a/llvm/test/DebugInfo/AArch64/tls-at-location.ll b/llvm/test/DebugInfo/AArch64/tls-at-location.ll
@@ -0,0 +1,37 @@
+; RUN: llc -filetype=obj -mtriple=aarch64--linux-gnu -o - %s | llvm-dwarfdump -v - | FileCheck %s
+;
+; CHECK: .debug_info contents:
+; CHECK: DW_TAG_variable
+; CHECK-NOT: DW_AT_location
+
+@var = thread_local global i32 0, align 4, !dbg !0
+
+; Function Attrs: noinline nounwind optnone
+define i32 @foo() #0 !dbg !11 {
+entry:
+  %0 = load i32, i32* @var, align 4, !dbg !14
+  ret i32 %0, !dbg !15
+}
+
+attributes #0 = { noinline nounwind optnone }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "var", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 7.0.0 (https://github.com/llvm-mirror/clang.git 43eac1f9d7d2c985831b485d9ccc807416d1cf29) (https://github.com/llvm-mirror/llvm.git d53cdbf4cc5414ea540174a036202c555ce8fc4b)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "tls-at-location.c", directory: "/home/lliu0/llvm/tls-at-location/DebugInfo/AArch64")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{!"clang version 7.0.0 (https://github.com/llvm-mirror/clang.git 43eac1f9d7d2c985831b485d9ccc807416d1cf29) (https://github.com/llvm-mirror/llvm.git d53cdbf4cc5414ea540174a036202c555ce8fc4b)"}
+!11 = distinct !DISubprogram(name: "foo", scope: !3, file: !3, line: 3, type: !12, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: false, unit: !2)
+!12 = !DISubroutineType(types: !13)
+!13 = !{!6}
+!14 = !DILocation(line: 4, column: 10, scope: !11)
+!15 = !DILocation(line: 4, column: 3, scope: !11)

Original file line number	Diff line number	Diff line change
`@@ -22,6 +22,9 @@ void AArch64_ELFTargetObjectFile::Initialize(MCContext &Ctx,`
`22`	`22`	`const TargetMachine &TM) {`
`23`	`23`	`TargetLoweringObjectFileELF::Initialize(Ctx, TM);`
`24`	`24`	`InitializeELF(TM.Options.UseInitArray);`
	`25`	`+ // AARCH64 ELF ABI does not define static relocation type for TLS offset`
	`26`	`+ // within a module. Do not generate AT_location for TLS variables.`
	`27`	`+ SupportDebugThreadLocalLocation = false;`
`25`	`28`	`}`
`26`	`29`
`27`	`30`	`AArch64_MachoTargetObjectFile::AArch64_MachoTargetObjectFile()`