llvm/lib/Target/X86/X86TargetObjectFile.cpp

//===-- X86TargetObjectFile.cpp - X86 Object Info -------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "X86TargetObjectFile.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/IR/Mangler.h"
#include "llvm/IR/Operator.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Target/TargetLowering.h"

using namespace llvm;
using namespace dwarf;

X86_64MachoTargetObjectFile::X86_64MachoTargetObjectFile()
  : TargetLoweringObjectFileMachO() {
  SupportIndirectSymViaGOTPCRel = true;
}

const MCExpr *X86_64MachoTargetObjectFile::getTTypeGlobalReference(
    const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
    const TargetMachine &TM, MachineModuleInfo *MMI,
    MCStreamer &Streamer) const {

  // On Darwin/X86-64, we can reference dwarf symbols with foo@GOTPCREL+4, which
  // is an indirect pc-relative reference.
  if ((Encoding & DW_EH_PE_indirect) && (Encoding & DW_EH_PE_pcrel)) {
    const MCSymbol *Sym = TM.getSymbol(GV, Mang);
    const MCExpr *Res =
      MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
    const MCExpr *Four = MCConstantExpr::Create(4, getContext());
    return MCBinaryExpr::CreateAdd(Res, Four, getContext());
  }

  return TargetLoweringObjectFileMachO::getTTypeGlobalReference(
      GV, Encoding, Mang, TM, MMI, Streamer);
}

MCSymbol *X86_64MachoTargetObjectFile::getCFIPersonalitySymbol(
    const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
    MachineModuleInfo *MMI) const {
  return TM.getSymbol(GV, Mang);
}

const MCExpr *X86_64MachoTargetObjectFile::getIndirectSymViaGOTPCRel(
    const MCSymbol *Sym, int64_t Offset) const {
  // On Darwin/X86-64, we need to use foo@GOTPCREL+4 to access the got entry
  // from a data section. In case there's an additional offset, then use
  // foo@GOTPCREL+4+<offset>.
  const MCExpr *Res =
    MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
  const MCExpr *Off = MCConstantExpr::Create(Offset+4, getContext());
  return MCBinaryExpr::CreateAdd(Res, Off, getContext());
}

void
X86LinuxTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM) {
  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
  InitializeELF(TM.Options.UseInitArray);
}

const MCExpr *
X86LinuxTargetObjectFile::getDebugThreadLocalSymbol(
    const MCSymbol *Sym) const {
  return MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
}

const MCExpr *X86WindowsTargetObjectFile::getExecutableRelativeSymbol(
    const ConstantExpr *CE, Mangler &Mang, const TargetMachine &TM) const {
  // We are looking for the difference of two symbols, need a subtraction
  // operation.
  const SubOperator *Sub = dyn_cast<SubOperator>(CE);
  if (!Sub)
    return nullptr;

  // Symbols must first be numbers before we can subtract them, we need to see a
  // ptrtoint on both subtraction operands.
  const PtrToIntOperator *SubLHS =
      dyn_cast<PtrToIntOperator>(Sub->getOperand(0));
  const PtrToIntOperator *SubRHS =
      dyn_cast<PtrToIntOperator>(Sub->getOperand(1));
  if (!SubLHS || !SubRHS)
    return nullptr;

  // Our symbols should exist in address space zero, cowardly no-op if
  // otherwise.
  if (SubLHS->getPointerAddressSpace() != 0 ||
      SubRHS->getPointerAddressSpace() != 0)
    return nullptr;

  // Both ptrtoint instructions must wrap global variables:
  // - Only global variables are eligible for image relative relocations.
  // - The subtrahend refers to the special symbol __ImageBase, a global.
  const GlobalVariable *GVLHS =
      dyn_cast<GlobalVariable>(SubLHS->getPointerOperand());
  const GlobalVariable *GVRHS =
      dyn_cast<GlobalVariable>(SubRHS->getPointerOperand());
  if (!GVLHS || !GVRHS)
    return nullptr;

  // We expect __ImageBase to be a global variable without a section, externally
  // defined.
  //
  // It should look something like this: @__ImageBase = external constant i8
  if (GVRHS->isThreadLocal() || GVRHS->getName() != "__ImageBase" ||
      !GVRHS->hasExternalLinkage() || GVRHS->hasInitializer() ||
      GVRHS->hasSection())
    return nullptr;

  // An image-relative, thread-local, symbol makes no sense.
  if (GVLHS->isThreadLocal())
    return nullptr;

  return MCSymbolRefExpr::Create(TM.getSymbol(GVLHS, Mang),
                                 MCSymbolRefExpr::VK_COFF_IMGREL32,
                                 getContext());
}

static std::string APIntToHexString(const APInt &AI) {
  unsigned Width = (AI.getBitWidth() / 8) * 2;
  std::string HexString = utohexstr(AI.getLimitedValue(), /*LowerCase=*/true);
  unsigned Size = HexString.size();
  assert(Width >= Size && "hex string is too large!");
  HexString.insert(HexString.begin(), Width - Size, '0');

  return HexString;
}


static std::string scalarConstantToHexString(const Constant *C) {
  Type *Ty = C->getType();
  APInt AI;
  if (isa<UndefValue>(C)) {
    AI = APInt(Ty->getPrimitiveSizeInBits(), /*val=*/0);
  } else if (Ty->isFloatTy() || Ty->isDoubleTy()) {
    const auto *CFP = cast<ConstantFP>(C);
    AI = CFP->getValueAPF().bitcastToAPInt();
  } else if (Ty->isIntegerTy()) {
    const auto *CI = cast<ConstantInt>(C);
    AI = CI->getValue();
  } else {
    llvm_unreachable("unexpected constant pool element type!");
  }
  return APIntToHexString(AI);
}

const MCSection *
X86WindowsTargetObjectFile::getSectionForConstant(SectionKind Kind,
                                                  const Constant *C) const {
  if (Kind.isReadOnly()) {
    if (C) {
      Type *Ty = C->getType();
      SmallString<32> COMDATSymName;
      if (Ty->isFloatTy() || Ty->isDoubleTy()) {
        COMDATSymName = "__real@";
        COMDATSymName += scalarConstantToHexString(C);
      } else if (const auto *VTy = dyn_cast<VectorType>(Ty)) {
        uint64_t NumBits = VTy->getBitWidth();
        if (NumBits == 128 || NumBits == 256) {
          COMDATSymName = NumBits == 128 ? "__xmm@" : "__ymm@";
          for (int I = VTy->getNumElements() - 1, E = -1; I != E; --I)
            COMDATSymName +=
                scalarConstantToHexString(C->getAggregateElement(I));
        }
      }
      if (!COMDATSymName.empty()) {
        unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                   COFF::IMAGE_SCN_MEM_READ |
                                   COFF::IMAGE_SCN_LNK_COMDAT;
        return getContext().getCOFFSection(".rdata", Characteristics, Kind,
                                           COMDATSymName,
                                           COFF::IMAGE_COMDAT_SELECT_ANY);
      }
    }
  }

  return TargetLoweringObjectFile::getSectionForConstant(Kind, C);
}