Implement target independent TLS compatible with glibc's emutls.c.

The 'common' section TLS is not implemented.
Current C/C++ TLS variables are not placed in common section.
DWARF debug info to get the address of TLS variables is not generated yet.

clang and driver changes in http://reviews.llvm.org/D10524

  Added -femulated-tls flag to select the emulated TLS model,
  which will be used for old targets like Android that do not
  support ELF TLS models.

Added TargetLowering::LowerToTLSEmulatedModel as a target-independent
function to convert a SDNode of TLS variable address to a function call
to __emutls_get_address.

Added into lib/Target/*/*ISelLowering.cpp to call LowerToTLSEmulatedModel
for TLSModel::Emulated. Although all targets supporting ELF TLS models are
enhanced, emulated TLS model has been tested only for Android ELF targets.
Modified AsmPrinter.cpp to print the emutls_v.* and emutls_t.* variables for
emulated TLS variables.
Modified DwarfCompileUnit.cpp to skip some DIE for emulated TLS variabls.

TODO: Add proper DIE for emulated TLS variables.
      Added new unit tests with emulated TLS.

Differential Revision: http://reviews.llvm.org/D10522

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243438 91177308-0d34-0410-b5e6-96231b3b80d8

Signed-off-by: Dmitry Moskalchuk <dm@crystax.net>

docs/LangRef.rst

@@ -494,6 +494,9 @@ model is not supported, or if a better choice of model can be made.
 A model can also be specified in a alias, but then it only governs how
 the alias is accessed. It will not have any effect in the aliasee.
 
+For platforms without linker support of ELF TLS model, the -femulated-tls
+flag can be used to generate GCC compatible emulated TLS code.
+
 .. _namedtypes:
 
 Structure Types

include/llvm/CodeGen/AsmPrinter.h

@@ -235,6 +235,11 @@ class AsmPrinter : public MachineFunctionPass {
   ///
   void EmitJumpTableInfo();
 
+  /// Emit the control variable for an emulated TLS variable.
+  virtual void EmitEmulatedTLSControlVariable(const GlobalVariable *GV,
+                                              MCSymbol *EmittedSym,
+                                              bool AllZeroInitValue);
+
   /// Emit the specified global variable to the .s file.
   virtual void EmitGlobalVariable(const GlobalVariable *GV);
 

include/llvm/CodeGen/CommandFlags.h

@@ -219,6 +219,10 @@ FunctionSections("function-sections",
                  cl::desc("Emit functions into separate sections"),
                  cl::init(false));
 
+cl::opt<bool> EmulatedTLS("emulated-tls",
+                          cl::desc("Use emulated TLS model"),
+                          cl::init(false));
+
 cl::opt<bool> UniqueSectionNames("unique-section-names",
                                  cl::desc("Give unique names to every section"),
                                  cl::init(true));
@@ -260,6 +264,7 @@ static inline TargetOptions InitTargetOptionsFromCodeGenFlags() {
   Options.DataSections = DataSections;
   Options.FunctionSections = FunctionSections;
   Options.UniqueSectionNames = UniqueSectionNames;
+  Options.EmulatedTLS = EmulatedTLS;
 
   Options.MCOptions = InitMCTargetOptionsFromFlags();
   Options.JTType = JTableType;

include/llvm/MC/MCObjectFileInfo.h

@@ -216,6 +216,7 @@ class MCObjectFileInfo {
   MCSection *getTextSection() const { return TextSection; }
   MCSection *getDataSection() const { return DataSection; }
   MCSection *getBSSSection() const { return BSSSection; }
+  MCSection *getReadOnlySection() const { return ReadOnlySection; }
   MCSection *getLSDASection() const { return LSDASection; }
   MCSection *getCompactUnwindSection() const { return CompactUnwindSection; }
   MCSection *getDwarfAbbrevSection() const { return DwarfAbbrevSection; }

include/llvm/Target/TargetLowering.h

@@ -2821,6 +2821,10 @@ class TargetLowering : public TargetLoweringBase {
   virtual bool useLoadStackGuardNode() const {
     return false;
   }
+
+  /// Lower TLS global address SDNode for target independent emulated TLS model.
+  virtual SDValue LowerToTLSEmulatedModel(const GlobalAddressSDNode *GA,
+                                          SelectionDAG &DAG) const;
 };
 
 /// Given an LLVM IR type and return type attributes, compute the return value

include/llvm/Target/TargetOptions.h

@@ -72,7 +72,7 @@ namespace llvm {
           UseInitArray(false), DisableIntegratedAS(false),
           CompressDebugSections(false), FunctionSections(false),
           DataSections(false), UniqueSectionNames(true), TrapUnreachable(false),
-          FloatABIType(FloatABI::Default),
+          EmulatedTLS(false), FloatABIType(FloatABI::Default),
           AllowFPOpFusion(FPOpFusion::Standard), Reciprocals(TargetRecip()),
           JTType(JumpTable::Single),
           ThreadModel(ThreadModel::POSIX) {}
@@ -172,6 +172,10 @@ namespace llvm {
     /// Emit target-specific trap instruction for 'unreachable' IR instructions.
     unsigned TrapUnreachable : 1;
 
+    /// EmulatedTLS - This flag enables emulated TLS model, using emutls
+    /// function in the runtime library..
+    unsigned EmulatedTLS : 1;
+
     /// FloatABIType - This setting is set by -float-abi=xxx option is specfied
     /// on the command line. This setting may either be Default, Soft, or Hard.
     /// Default selects the target's default behavior. Soft selects the ABI for
@@ -231,6 +235,7 @@ inline bool operator==(const TargetOptions &LHS,
     ARE_EQUAL(PositionIndependentExecutable) &&
     ARE_EQUAL(UseInitArray) &&
     ARE_EQUAL(TrapUnreachable) &&
+    ARE_EQUAL(EmulatedTLS) &&
     ARE_EQUAL(FloatABIType) &&
     ARE_EQUAL(AllowFPOpFusion) &&
     ARE_EQUAL(Reciprocals) &&

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -340,8 +340,58 @@ MCSymbol *AsmPrinter::getSymbol(const GlobalValue *GV) const {
   return TM.getSymbol(GV, *Mang);
 }
 
+static MCSymbol *getOrCreateEmuTLSControlSym(MCSymbol *GVSym, MCContext &C) {
+  return C.getOrCreateSymbol(Twine("__emutls_v.") + GVSym->getName());
+}
+
+static MCSymbol *getOrCreateEmuTLSInitSym(MCSymbol *GVSym, MCContext &C) {
+  return C.getOrCreateSymbol(Twine("__emutls_t.") + GVSym->getName());
+}
+
+/// EmitEmulatedTLSControlVariable - Emit the control variable for an emulated TLS variable.
+void AsmPrinter::EmitEmulatedTLSControlVariable(const GlobalVariable *GV,
+                                                MCSymbol *EmittedSym,
+                                                bool AllZeroInitValue) {
+  // If there is init value, use .data.rel.local section;
+  // otherwise use the .data section.
+  MCSection *TLSVarSection = const_cast<MCSection*>(
+      (GV->hasInitializer() && !AllZeroInitValue)
+      ? getObjFileLowering().getDataRelLocalSection()
+      : getObjFileLowering().getDataSection());
+  OutStreamer->SwitchSection(TLSVarSection);
+  MCSymbol *GVSym = getSymbol(GV);
+  EmitLinkage(GV, EmittedSym);  // same linkage as GV
+  const DataLayout &DL = GV->getParent()->getDataLayout();
+  uint64_t Size = DL.getTypeAllocSize(GV->getType()->getElementType());
+  unsigned AlignLog = getGVAlignmentLog2(GV, DL);
+  unsigned WordSize = DL.getPointerSize();
+  unsigned Alignment = DL.getPointerABIAlignment();
+  EmitAlignment(Log2_32(Alignment));
+  OutStreamer->EmitLabel(EmittedSym);
+  OutStreamer->EmitIntValue(Size, WordSize);
+  OutStreamer->EmitIntValue((1 << AlignLog), WordSize);
+  OutStreamer->EmitIntValue(0, WordSize);
+  if (GV->hasInitializer() && !AllZeroInitValue) {
+    OutStreamer->EmitSymbolValue(
+        getOrCreateEmuTLSInitSym(GVSym, OutContext), WordSize);
+  } else
+    OutStreamer->EmitIntValue(0, WordSize);
+  if (MAI->hasDotTypeDotSizeDirective())
+    OutStreamer->emitELFSize(cast<MCSymbolELF>(EmittedSym),
+                             MCConstantExpr::create(4 * WordSize, OutContext));
+  OutStreamer->AddBlankLine();  // End of the __emutls_v.* variable.
+}
+
 /// EmitGlobalVariable - Emit the specified global variable to the .s file.
 void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
+  bool IsEmuTLSVar =
+      GV->getThreadLocalMode() != llvm::GlobalVariable::NotThreadLocal &&
+      TM.Options.EmulatedTLS;
+  assert((!IsEmuTLSVar || getObjFileLowering().getDataRelLocalSection()) &&
+         "Need relocatable local section for emulated TLS variables");
+  assert(!(IsEmuTLSVar && GV->hasCommonLinkage()) &&
+         "No emulated TLS variables in the common section");
+
   if (GV->hasInitializer()) {
     // Check to see if this is a special global used by LLVM, if so, emit it.
     if (EmitSpecialLLVMGlobal(GV))
@@ -352,15 +402,22 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     if (GlobalGOTEquivs.count(getSymbol(GV)))
       return;
 
-    if (isVerbose()) {
+    if (isVerbose() && !IsEmuTLSVar) {
+      // When printing the control variable __emutls_v.*,
+      // we don't need to print the original TLS variable name.
       GV->printAsOperand(OutStreamer->GetCommentOS(),
                      /*PrintType=*/false, GV->getParent());
       OutStreamer->GetCommentOS() << '\n';
     }
   }
 
   MCSymbol *GVSym = getSymbol(GV);
-  EmitVisibility(GVSym, GV->getVisibility(), !GV->isDeclaration());
+  MCSymbol *EmittedSym = IsEmuTLSVar ?
+      getOrCreateEmuTLSControlSym(GVSym, OutContext) : GVSym;
+  // getOrCreateEmuTLSControlSym only creates the symbol with name and default attributes.
+  // GV's or GVSym's attributes will be used for the EmittedSym.
+
+  EmitVisibility(EmittedSym, GV->getVisibility(), !GV->isDeclaration());
 
   if (!GV->hasInitializer())   // External globals require no extra code.
     return;
@@ -371,7 +428,7 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
                        "' is already defined");
 
   if (MAI->hasDotTypeDotSizeDirective())
-    OutStreamer->EmitSymbolAttribute(GVSym, MCSA_ELF_TypeObject);
+    OutStreamer->EmitSymbolAttribute(EmittedSym, MCSA_ELF_TypeObject);
 
   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
 
@@ -383,13 +440,27 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
   // sections and expected to be contiguous (e.g. ObjC metadata).
   unsigned AlignLog = getGVAlignmentLog2(GV, *DL);
 
+  bool AllZeroInitValue = false;
+  const Constant *InitValue = GV->getInitializer();
+  if (isa<ConstantAggregateZero>(InitValue))
+    AllZeroInitValue = true;
+  else {
+    const ConstantInt *InitIntValue = dyn_cast<ConstantInt>(InitValue);
+    if (InitIntValue && InitIntValue->isZero())
+      AllZeroInitValue = true;
+  }
+  if (IsEmuTLSVar)
+    EmitEmulatedTLSControlVariable(GV, EmittedSym, AllZeroInitValue);
+
   for (const HandlerInfo &HI : Handlers) {
     NamedRegionTimer T(HI.TimerName, HI.TimerGroupName, TimePassesIsEnabled);
     HI.Handler->setSymbolSize(GVSym, Size);
   }
 
   // Handle common and BSS local symbols (.lcomm).
   if (GVKind.isCommon() || GVKind.isBSSLocal()) {
+    assert(!(IsEmuTLSVar && GVKind.isCommon()) &&
+           "No emulated TLS variables in the common section");
     if (Size == 0) Size = 1;   // .comm Foo, 0 is undefined, avoid it.
     unsigned Align = 1 << AlignLog;
 
@@ -434,12 +505,21 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     return;
   }
 
-  MCSection *TheSection =
+  if (IsEmuTLSVar && AllZeroInitValue)
+    return;  // No need of initialization values.
+
+  MCSymbol *EmittedInitSym = IsEmuTLSVar ?
+      getOrCreateEmuTLSInitSym(GVSym, OutContext) : GVSym;
+  // getOrCreateEmuTLSInitSym only creates the symbol with name and default attributes.
+  // GV's or GVSym's attributes will be used for the EmittedInitSym.
+
+  MCSection *TheSection = IsEmuTLSVar ?
+      getObjFileLowering().getReadOnlySection() :
       getObjFileLowering().SectionForGlobal(GV, GVKind, *Mang, TM);
 
   // Handle the zerofill directive on darwin, which is a special form of BSS
   // emission.
-  if (GVKind.isBSSExtern() && MAI->hasMachoZeroFillDirective()) {
+  if (GVKind.isBSSExtern() && MAI->hasMachoZeroFillDirective() && !IsEmuTLSVar) {
     if (Size == 0) Size = 1;  // zerofill of 0 bytes is undefined.
 
     // .globl _foo
@@ -459,7 +539,7 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
   // TLOF class.  This will also make it more obvious that stuff like
   // MCStreamer::EmitTBSSSymbol is macho specific and only called from macho
   // specific code.
-  if (GVKind.isThreadLocal() && MAI->hasMachoTBSSDirective()) {
+  if (GVKind.isThreadLocal() && MAI->hasMachoTBSSDirective() && !IsEmuTLSVar) {
     // Emit the .tbss symbol
     MCSymbol *MangSym =
       OutContext.getOrCreateSymbol(GVSym->getName() + Twine("$tlv$init"));
@@ -502,16 +582,18 @@ void AsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
 
   OutStreamer->SwitchSection(TheSection);
 
-  EmitLinkage(GV, GVSym);
+  // emutls_t.* symbols are only used in the current compilation unit.
+  if (!IsEmuTLSVar)
+    EmitLinkage(GV, EmittedInitSym);
   EmitAlignment(AlignLog, GV);
 
-  OutStreamer->EmitLabel(GVSym);
+  OutStreamer->EmitLabel(EmittedInitSym);
 
   EmitGlobalConstant(GV->getInitializer());
 
   if (MAI->hasDotTypeDotSizeDirective())
     // .size foo, 42
-    OutStreamer->emitELFSize(cast<MCSymbolELF>(GVSym),
+    OutStreamer->emitELFSize(cast<MCSymbolELF>(EmittedInitSym),
                              MCConstantExpr::create(Size, OutContext));
 
   OutStreamer->AddBlankLine();

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -151,28 +151,32 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
     DIELoc *Loc = new (DIEValueAllocator) DIELoc;
     const MCSymbol *Sym = Asm->getSymbol(Global);
     if (Global->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:
-      if (!DD->useSplitDwarf()) {
-        // 1) Start with a constNu of the appropriate pointer size
-        addUInt(*Loc, dwarf::DW_FORM_data1,
-                PointerSize == 4 ? dwarf::DW_OP_const4u : dwarf::DW_OP_const8u);
-        // 2) containing the (relocated) offset of the TLS variable
-        //    within the module's TLS block.
-        addExpr(*Loc, dwarf::DW_FORM_udata,
-                Asm->getObjFileLowering().getDebugThreadLocalSymbol(Sym));
+      if (Asm->TM.Options.EmulatedTLS) {
+        // TODO: add debug info for emulated thread local mode.
       } else {
-        addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_GNU_const_index);
-        addUInt(*Loc, dwarf::DW_FORM_udata,
-                DD->getAddressPool().getIndex(Sym, /* TLS */ true));
+        // 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:
+        if (!DD->useSplitDwarf()) {
+          // 1) Start with a constNu of the appropriate pointer size
+          addUInt(*Loc, dwarf::DW_FORM_data1,
+                  PointerSize == 4 ? dwarf::DW_OP_const4u : dwarf::DW_OP_const8u);
+          // 2) containing the (relocated) offset of the TLS variable
+          //    within the module's TLS block.
+          addExpr(*Loc, dwarf::DW_FORM_udata,
+                  Asm->getObjFileLowering().getDebugThreadLocalSymbol(Sym));
+        } else {
+          addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_GNU_const_index);
+          addUInt(*Loc, dwarf::DW_FORM_udata,
+                  DD->getAddressPool().getIndex(Sym, /* TLS */ true));
+        }
+        // 3) followed by an OP to make the debugger do a TLS lookup.
+        addUInt(*Loc, dwarf::DW_FORM_data1,
+                DD->useGNUTLSOpcode() ? dwarf::DW_OP_GNU_push_tls_address
+                                      : dwarf::DW_OP_form_tls_address);
       }
-      // 3) followed by an OP to make the debugger do a TLS lookup.
-      addUInt(*Loc, dwarf::DW_FORM_data1,
-              DD->useGNUTLSOpcode() ? dwarf::DW_OP_GNU_push_tls_address
-                                    : dwarf::DW_OP_form_tls_address);
     } else {
       DD->addArangeLabel(SymbolCU(this, Sym));
       addOpAddress(*Loc, Sym);

lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -3036,3 +3036,46 @@ bool TargetLowering::expandFP_TO_SINT(SDNode *Node, SDValue &Result,
       DAG.getConstant(0, dl, NVT), Ret, ISD::SETLT);
   return true;
 }
+
+//===----------------------------------------------------------------------===//
+// Implementation of Emulated TLS Model
+//===----------------------------------------------------------------------===//
+
+SDValue TargetLowering::LowerToTLSEmulatedModel(const GlobalAddressSDNode *GA,
+                                                SelectionDAG &DAG) const {
+  // Access to address of TLS varialbe xyz is lowered to a function call:
+  //   __emutls_get_address( address of global variable named "__emutls_v.xyz" )
+  EVT PtrVT = getPointerTy(DAG.getDataLayout());
+  PointerType *VoidPtrType = Type::getInt8PtrTy(*DAG.getContext());
+  SDLoc dl(GA);
+
+  ArgListTy Args;
+  ArgListEntry Entry;
+  std::string NameString = ("__emutls_v." + GA->getGlobal()->getName()).str();
+  Module *VariableModule = const_cast<Module*>(GA->getGlobal()->getParent());
+  StringRef EmuTlsVarName(NameString);
+  GlobalVariable *EmuTlsVar = VariableModule->getNamedGlobal(EmuTlsVarName);
+  if (!EmuTlsVar)
+    EmuTlsVar = dyn_cast_or_null<GlobalVariable>(
+        VariableModule->getOrInsertGlobal(EmuTlsVarName, VoidPtrType));
+  Entry.Node = DAG.getGlobalAddress(EmuTlsVar, dl, PtrVT);
+  Entry.Ty = VoidPtrType;
+  Args.push_back(Entry);
+
+  SDValue EmuTlsGetAddr = DAG.getExternalSymbol("__emutls_get_address", PtrVT);
+
+  TargetLowering::CallLoweringInfo CLI(DAG);
+  CLI.setDebugLoc(dl).setChain(DAG.getEntryNode());
+  CLI.setCallee(CallingConv::C, VoidPtrType, EmuTlsGetAddr, std::move(Args), 0);
+  std::pair<SDValue, SDValue> CallResult = LowerCallTo(CLI);
+
+  // TLSADDR will be codegen'ed as call. Inform MFI that function has calls.
+  // At last for X86 targets, maybe good for other targets too?
+  MachineFrameInfo *MFI = DAG.getMachineFunction().getFrameInfo();
+  MFI->setAdjustsStack(true);  // Is this only for X86 target?
+  MFI->setHasCalls(true);
+
+  assert((GA->getOffset() == 0) &&
+         "Emulated TLS must have zero offset in GlobalAddressSDNode");
+  return CallResult.first;
+}

lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -3160,6 +3160,10 @@ AArch64TargetLowering::LowerELFGlobalTLSAddress(SDValue Op,
   const GlobalAddressSDNode *GA = cast<GlobalAddressSDNode>(Op);
 
   TLSModel::Model Model = getTargetMachine().getTLSModel(GA->getGlobal());
+
+  if (DAG.getTarget().Options.EmulatedTLS)
+    return LowerToTLSEmulatedModel(GA, DAG);
+
   if (!EnableAArch64ELFLocalDynamicTLSGeneration) {
     if (Model == TLSModel::LocalDynamic)
       Model = TLSModel::GeneralDynamic;

lib/Target/ARM/ARMISelLowering.cpp

@@ -2577,6 +2577,8 @@ ARMTargetLowering::LowerGlobalTLSAddress(SDValue Op, SelectionDAG &DAG) const {
   assert(Subtarget->isTargetELF() &&
          "TLS not implemented for non-ELF targets");
   GlobalAddressSDNode *GA = cast<GlobalAddressSDNode>(Op);
+  if (DAG.getTarget().Options.EmulatedTLS)
+    return LowerToTLSEmulatedModel(GA, DAG);
 
   TLSModel::Model model = getTargetMachine().getTLSModel(GA->getGlobal());
 

lib/Target/Mips/MipsISelLowering.cpp

@@ -1719,6 +1719,9 @@ lowerGlobalTLSAddress(SDValue Op, SelectionDAG &DAG) const
   // Local Exec TLS Model.
 
   GlobalAddressSDNode *GA = cast<GlobalAddressSDNode>(Op);
+  if (DAG.getTarget().Options.EmulatedTLS)
+    return LowerToTLSEmulatedModel(GA, DAG);
+
   SDLoc DL(GA);
   const GlobalValue *GV = GA->getGlobal();
   EVT PtrVT = getPointerTy(DAG.getDataLayout());