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/MC/MCValue.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Target/TargetLowering.h"

using namespace llvm;
using namespace dwarf;

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, const MCValue &MV, int64_t Offset,
    MachineModuleInfo *MMI, MCStreamer &Streamer) 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>.
  unsigned FinalOff = Offset+MV.getConstant()+4;
  const MCExpr *Res =
    MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
  const MCExpr *Off = MCConstantExpr::create(FinalOff, getContext());
  return MCBinaryExpr::createAdd(Res, Off, getContext());
}

const MCExpr *X86ELFTargetObjectFile::getDebugThreadLocalSymbol(
    const MCSymbol *Sym) const {
  return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
}

void
X86LinuxNaClTargetObjectFile::Initialize(MCContext &Ctx,
                                         const TargetMachine &TM) {
  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
  InitializeELF(TM.Options.UseInitArray);
}

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 objects:
  // - Only global variables are eligible for image relative relocations.
  // - The subtrahend refers to the special symbol __ImageBase, a GlobalVariable.
  const auto *GOLHS = dyn_cast<GlobalObject>(SubLHS->getPointerOperand());
  const auto *GVRHS = dyn_cast<GlobalVariable>(SubRHS->getPointerOperand());
  if (!GOLHS || !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 (GOLHS->isThreadLocal())
    return nullptr;

  return MCSymbolRefExpr::create(TM.getSymbol(GOLHS, 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();
  if (isa<UndefValue>(C)) {
    return APIntToHexString(APInt::getNullValue(Ty->getPrimitiveSizeInBits()));
  } else if (const auto *CFP = dyn_cast<ConstantFP>(C)) {
    return APIntToHexString(CFP->getValueAPF().bitcastToAPInt());
  } else if (const auto *CI = dyn_cast<ConstantInt>(C)) {
    return APIntToHexString(CI->getValue());
  } else {
    unsigned NumElements;
    if (isa<VectorType>(Ty))
      NumElements = Ty->getVectorNumElements();
    else
      NumElements = Ty->getArrayNumElements();
    std::string HexString;
    for (int I = NumElements - 1, E = -1; I != E; --I)
      HexString += scalarConstantToHexString(C->getAggregateElement(I));
    return HexString;
  }
}

MCSection *
X86WindowsTargetObjectFile::getSectionForConstant(SectionKind Kind,
                                                  const Constant *C) const {
  if (Kind.isMergeableConst() && C) {
    const unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                     COFF::IMAGE_SCN_MEM_READ |
                                     COFF::IMAGE_SCN_LNK_COMDAT;
    std::string COMDATSymName;
    if (Kind.isMergeableConst4() || Kind.isMergeableConst8())
      COMDATSymName = "__real@" + scalarConstantToHexString(C);
    else if (Kind.isMergeableConst16())
      COMDATSymName = "__xmm@" + scalarConstantToHexString(C);

    if (!COMDATSymName.empty())
      return getContext().getCOFFSection(".rdata", Characteristics, Kind,
                                         COMDATSymName,
                                         COFF::IMAGE_COMDAT_SELECT_ANY);
  }

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