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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185203 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 28 insertions, 3 deletions

diff --git a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 6bd4f08604..339a5d2752 100644
--- a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/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.
diff --git a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 7e7359a8fe..69d55913ca 100644
--- a/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/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
 //===----------------------------------------------------------------------===//
diff --git a/lib/Target/TargetLoweringObjectFile.cpp b/lib/Target/TargetLoweringObjectFile.cpp
index f5121e34f7..fc50aa5192 100644
--- a/lib/Target/TargetLoweringObjectFile.cpp
+++ b/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);
+}