DebugInfo: PR14728: TLS support

Based on GCC's output for TLS variables (OP_constNu, x@dtpoff,
OP_lo_user), this implements debug info support for TLS in ELF. Verified
that this output is correct/sufficient on Linux (using gold - if you're
using binutils-ld, you'll need something with the fix for
http://sourceware.org/bugzilla/show_bug.cgi?id=15685 in it).

Support on non-ELF is sort of "arbitrary" at the moment - if Apple folks
want to discuss (or just go ahead & implement) how this should work in
MachO, etc, I'm open.

llvm-svn: 185203

llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

@@ -72,6 +72,9 @@ public:
   getStaticCtorSection(unsigned Priority = 65535) const;
   virtual const MCSection *
   getStaticDtorSection(unsigned Priority = 65535) const;
+
+  /// \brief Describe a TLS variable address within debug info.
+  virtual const MCSymbolRefExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const;
 };
 
 

llvm/include/llvm/Target/TargetLoweringObjectFile.h

@@ -138,6 +138,10 @@ public:
     return StaticDtorSection;
   }
 
+  /// \brief Create a symbol reference to describe the given TLS variable when
+  /// emitting the address in debug info.
+  virtual const MCSymbolRefExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const;
+
 protected:
   virtual const MCSection *
   SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -27,6 +27,7 @@
 #include "llvm/Target/Mangler.h"
 #include "llvm/Target/TargetFrameLowering.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 
 using namespace llvm;
@@ -1351,7 +1352,23 @@ void CompileUnit::createGlobalVariableDIE(const MDNode *N) {
   if (isGlobalVariable) {
     addToAccelTable = true;
     DIEBlock *Block = new (DIEValueAllocator) DIEBlock();
-    addOpAddress(Block, Asm->Mang->getSymbol(GV.getGlobal()));
+    const MCSymbol *Sym = Asm->Mang->getSymbol(GV.getGlobal());
+    if (GV.getGlobal()->isThreadLocal()) {
+      // FIXME: Make this work with -gsplit-dwarf.
+      unsigned PointerSize = Asm->getDataLayout().getPointerSize();
+      assert((PointerSize == 4 || PointerSize == 8) &&
+             "Add support for other sizes if necessary");
+      // Based on GCC's support for TLS:
+      // 1) Start with a constNu of the appropriate pointer size
+      addUInt(Block, 0, dwarf::DW_FORM_data1,
+              PointerSize == 4 ? dwarf::DW_OP_const4u : dwarf::DW_OP_const8u);
+      // 2) containing the (relocated) address of the TLS variable
+      addLabel(Block, 0, dwarf::DW_FORM_udata,
+               Asm->getObjFileLowering().getDebugThreadLocalSymbol(Sym));
+      // 3) followed by a custom OP to tell the debugger about TLS (presumably)
+      addUInt(Block, 0, dwarf::DW_FORM_data1, dwarf::DW_OP_lo_user);
+    } else
+      addOpAddress(Block, Sym);
     // Do not create specification DIE if context is either compile unit
     // or a subprogram.
     if (GVContext && GV.isDefinition() && !GVContext.isCompileUnit() &&
@@ -1413,8 +1430,6 @@ void CompileUnit::createGlobalVariableDIE(const MDNode *N) {
     if (GV.getLinkageName() != "" && GV.getName() != GV.getLinkageName())
       addAccelName(GV.getLinkageName(), AddrDIE);
   }
-
-  return;
 }
 
 /// constructSubrangeDIE - Construct subrange DIE from DISubrange.

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -401,6 +401,10 @@ TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
                                SectionKind::getDataRel());
 }
 
+const MCSymbolRefExpr *TargetLoweringObjectFileELF::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
+  return MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
+}
+
 //===----------------------------------------------------------------------===//
 //                                 MachO
 //===----------------------------------------------------------------------===//

llvm/lib/Target/TargetLoweringObjectFile.cpp

@@ -317,3 +317,9 @@ getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
   }
   }
 }
+
+const MCSymbolRefExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
+  // FIXME: It's not clear what, if any, default this should have - perhaps a
+  // null return could mean 'no location' & we should just do that here.
+  return MCSymbolRefExpr::Create(Sym, *Ctx);
+}

llvm/test/DebugInfo/X86/tls.ll

@@ -0,0 +1,34 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown -O0 -filetype=asm < %s | FileCheck %s
+; RUN: llc -mtriple=i386-unknown-unknown -O0 -filetype=asm < %s | FileCheck --check-prefix=CHECK-32 %s
+
+; FIXME: add relocation and DWARF expression support to llvm-dwarfdump & use
+; that here instead of raw assembly printing
+
+; 10 bytes of data in this DW_FORM_block1 representation of the location of 'tls'
+; CHECK: .byte	10{{ *}}# DW_AT_location
+; DW_OP_const8u (0x0e == 14) of adress
+; CHECK: .byte	14
+; The debug relocation of the address of the tls variable
+; CHECK: .quad	tls@DTPOFF
+; DW_OP_lo_user based on GCC/GDB extension presumably (by experiment) to support TLS
+; CHECK: .byte	224
+
+; same again, except with a 32 bit address
+; CHECK-32: .byte	6{{ *}}# DW_AT_location
+; CHECK-32: .byte	12
+; CHECK-32: .long	tls@DTPOFF
+; CHECK-32: .byte	224
+
+@tls = thread_local global i32 7, align 4
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!7}
+
+!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.4 ", i1 false, metadata !"", i32 0, metadata !2, metadata !2, metadata !2, metadata !3, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [/tmp/tls.cpp] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !"tls.cpp", metadata !"/tmp"}
+!2 = metadata !{i32 0}
+!3 = metadata !{metadata !4}
+!4 = metadata !{i32 786484, i32 0, null, metadata !"tls", metadata !"tls", metadata !"", metadata !5, i32 1, metadata !6, i32 0, i32 1, i32* @tls, null} ; [ DW_TAG_variable ] [tls] [line 1] [def]
+!5 = metadata !{i32 786473, metadata !1}          ; [ DW_TAG_file_type ] [/tmp/tls.cpp]
+!6 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!7 = metadata !{i32 2, metadata !"Dwarf Version", i32 3}