[PATCH] D43860: [AArch64] DWARF: do not generate AT_location for thread local
Liu, Lei via llvm-commits
llvm-commits at lists.llvm.org
Mon Mar 5 18:51:29 PST 2018
The problem is really a limitation of AArch64 ELF ABI. I don't think
frontend should change its behavior based on such low level target information.
Thanks,
Lei
On 2018年03月06日 02:43, David Blaikie wrote:
> Could the frontend just generate a description of the variable witohut a location instead?
>
> On Tue, Feb 27, 2018 at 11:14 PM Lei Liu via Phabricator via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
>
> lliu0 created this revision.
> Herald added subscribers: llvm-commits, JDevlieghere, kristof.beyls, javed.absar, rengolin.
>
> 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.
>
>
> Repository:
> rL LLVM
>
> https://reviews.llvm.org/D43860
>
> Files:
> include/llvm/CodeGen/TargetLoweringObjectFile.h
> lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> lib/Target/AArch64/AArch64TargetObjectFile.cpp
> test/DebugInfo/AArch64/tls-at-location.ll
>
>
> Index: test/DebugInfo/AArch64/tls-at-location.ll
> ===================================================================
> --- /dev/null
> +++ test/DebugInfo/AArch64/tls-at-location.ll
> @@ -0,0 +1,42 @@
> +; RUN: llc -filetype=obj -o - %s | llvm-dwarfdump -v - | FileCheck %s
> +;
> +; CHECK: .debug_info contents:
> +; CHECK: DW_TAG_variable
> +; CHECK-NOT: DW_AT_location
> +
> +; ModuleID = 'tls-at-location.c'
> +source_filename = "tls-at-location.c"
> +target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
> +target triple = "arm64"
> +
> + at 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 "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+neon" "unsafe-fp-math"="false" "use-soft-float"="false" }
> +
> +!llvm.dbg.cu <http://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, variables: !4)
> +!12 = !DISubroutineType(types: !13)
> +!13 = !{!6}
> +!14 = !DILocation(line: 4, column: 10, scope: !11)
> +!15 = !DILocation(line: 4, column: 3, scope: !11)
> Index: lib/Target/AArch64/AArch64TargetObjectFile.cpp
> ===================================================================
> --- lib/Target/AArch64/AArch64TargetObjectFile.cpp
> +++ lib/Target/AArch64/AArch64TargetObjectFile.cpp
> @@ -22,6 +22,9 @@
> 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()
> Index: lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> ===================================================================
> --- lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> +++ lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
> @@ -186,6 +186,10 @@
> if (!Global && (!Expr || !Expr->isConstant()))
> continue;
>
> + if (Global && Global->isThreadLocal() &&
> + !Asm->getObjFileLowering().supportDebugThreadLocalLocation())
> + continue;
> +
> if (!Loc) {
> addToAccelTable = true;
> Loc = new (DIEValueAllocator) DIELoc;
> Index: include/llvm/CodeGen/TargetLoweringObjectFile.h
> ===================================================================
> --- include/llvm/CodeGen/TargetLoweringObjectFile.h
> +++ include/llvm/CodeGen/TargetLoweringObjectFile.h
> @@ -45,6 +45,7 @@
> protected:
> bool SupportIndirectSymViaGOTPCRel = false;
> bool SupportGOTPCRelWithOffset = true;
> + bool SupportDebugThreadLocalLocation = true;
>
> /// This section contains the static constructor pointer list.
> MCSection *StaticCtorSection = nullptr;
> @@ -171,6 +172,11 @@
> return SupportGOTPCRelWithOffset;
> }
>
> + /// \brief Target supports TLS offset relocation in debug section?
> + bool supportDebugThreadLocalLocation() const {
> + return SupportDebugThreadLocalLocation;
> + }
> +
> /// \brief Get the target specific PC relative GOT entry relocation
> virtual const MCExpr *getIndirectSymViaGOTPCRel(const MCSymbol *Sym,
> const MCValue &MV,
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
More information about the llvm-commits
mailing list