1 //===-- X86TargetObjectFile.cpp - X86 Object Info -------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "X86TargetObjectFile.h" 11 #include "llvm/ADT/StringExtras.h" 12 #include "llvm/IR/Mangler.h" 13 #include "llvm/IR/Operator.h" 14 #include "llvm/MC/MCContext.h" 15 #include "llvm/MC/MCExpr.h" 16 #include "llvm/MC/MCSectionCOFF.h" 17 #include "llvm/MC/MCSectionELF.h" 18 #include "llvm/MC/MCValue.h" 19 #include "llvm/Support/Dwarf.h" 20 #include "llvm/Target/TargetLowering.h" 21 22 using namespace llvm; 23 using namespace dwarf; 24 25 const MCExpr *X86_64MachoTargetObjectFile::getTTypeGlobalReference( 26 const GlobalValue *GV, unsigned Encoding, Mangler &Mang, 27 const TargetMachine &TM, MachineModuleInfo *MMI, 28 MCStreamer &Streamer) const { 29 30 // On Darwin/X86-64, we can reference dwarf symbols with foo@GOTPCREL+4, which 31 // is an indirect pc-relative reference. 32 if ((Encoding & DW_EH_PE_indirect) && (Encoding & DW_EH_PE_pcrel)) { 33 const MCSymbol *Sym = TM.getSymbol(GV, Mang); 34 const MCExpr *Res = 35 MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext()); 36 const MCExpr *Four = MCConstantExpr::Create(4, getContext()); 37 return MCBinaryExpr::CreateAdd(Res, Four, getContext()); 38 } 39 40 return TargetLoweringObjectFileMachO::getTTypeGlobalReference( 41 GV, Encoding, Mang, TM, MMI, Streamer); 42 } 43 44 MCSymbol *X86_64MachoTargetObjectFile::getCFIPersonalitySymbol( 45 const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM, 46 MachineModuleInfo *MMI) const { 47 return TM.getSymbol(GV, Mang); 48 } 49 50 const MCExpr *X86_64MachoTargetObjectFile::getIndirectSymViaGOTPCRel( 51 const MCSymbol *Sym, const MCValue &MV, int64_t Offset, 52 MachineModuleInfo *MMI, MCStreamer &Streamer) const { 53 // On Darwin/X86-64, we need to use foo@GOTPCREL+4 to access the got entry 54 // from a data section. In case there's an additional offset, then use 55 // foo@GOTPCREL+4+<offset>. 56 unsigned FinalOff = Offset+MV.getConstant()+4; 57 const MCExpr *Res = 58 MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext()); 59 const MCExpr *Off = MCConstantExpr::Create(FinalOff, getContext()); 60 return MCBinaryExpr::CreateAdd(Res, Off, getContext()); 61 } 62 63 const MCExpr *X86ELFTargetObjectFile::getDebugThreadLocalSymbol( 64 const MCSymbol *Sym) const { 65 return MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext()); 66 } 67 68 void 69 X86LinuxTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM) { 70 TargetLoweringObjectFileELF::Initialize(Ctx, TM); 71 InitializeELF(TM.Options.UseInitArray); 72 } 73 74 const MCExpr *X86WindowsTargetObjectFile::getExecutableRelativeSymbol( 75 const ConstantExpr *CE, Mangler &Mang, const TargetMachine &TM) const { 76 // We are looking for the difference of two symbols, need a subtraction 77 // operation. 78 const SubOperator *Sub = dyn_cast<SubOperator>(CE); 79 if (!Sub) 80 return nullptr; 81 82 // Symbols must first be numbers before we can subtract them, we need to see a 83 // ptrtoint on both subtraction operands. 84 const PtrToIntOperator *SubLHS = 85 dyn_cast<PtrToIntOperator>(Sub->getOperand(0)); 86 const PtrToIntOperator *SubRHS = 87 dyn_cast<PtrToIntOperator>(Sub->getOperand(1)); 88 if (!SubLHS || !SubRHS) 89 return nullptr; 90 91 // Our symbols should exist in address space zero, cowardly no-op if 92 // otherwise. 93 if (SubLHS->getPointerAddressSpace() != 0 || 94 SubRHS->getPointerAddressSpace() != 0) 95 return nullptr; 96 97 // Both ptrtoint instructions must wrap global objects: 98 // - Only global variables are eligible for image relative relocations. 99 // - The subtrahend refers to the special symbol __ImageBase, a GlobalVariable. 100 const auto *GOLHS = dyn_cast<GlobalObject>(SubLHS->getPointerOperand()); 101 const auto *GVRHS = dyn_cast<GlobalVariable>(SubRHS->getPointerOperand()); 102 if (!GOLHS || !GVRHS) 103 return nullptr; 104 105 // We expect __ImageBase to be a global variable without a section, externally 106 // defined. 107 // 108 // It should look something like this: @__ImageBase = external constant i8 109 if (GVRHS->isThreadLocal() || GVRHS->getName() != "__ImageBase" || 110 !GVRHS->hasExternalLinkage() || GVRHS->hasInitializer() || 111 GVRHS->hasSection()) 112 return nullptr; 113 114 // An image-relative, thread-local, symbol makes no sense. 115 if (GOLHS->isThreadLocal()) 116 return nullptr; 117 118 return MCSymbolRefExpr::Create(TM.getSymbol(GOLHS, Mang), 119 MCSymbolRefExpr::VK_COFF_IMGREL32, 120 getContext()); 121 } 122 123 static std::string APIntToHexString(const APInt &AI) { 124 unsigned Width = (AI.getBitWidth() / 8) * 2; 125 std::string HexString = utohexstr(AI.getLimitedValue(), /*LowerCase=*/true); 126 unsigned Size = HexString.size(); 127 assert(Width >= Size && "hex string is too large!"); 128 HexString.insert(HexString.begin(), Width - Size, '0'); 129 130 return HexString; 131 } 132 133 134 static std::string scalarConstantToHexString(const Constant *C) { 135 Type *Ty = C->getType(); 136 APInt AI; 137 if (isa<UndefValue>(C)) { 138 AI = APInt(Ty->getPrimitiveSizeInBits(), /*val=*/0); 139 } else if (Ty->isFloatTy() || Ty->isDoubleTy()) { 140 const auto *CFP = cast<ConstantFP>(C); 141 AI = CFP->getValueAPF().bitcastToAPInt(); 142 } else if (Ty->isIntegerTy()) { 143 const auto *CI = cast<ConstantInt>(C); 144 AI = CI->getValue(); 145 } else { 146 llvm_unreachable("unexpected constant pool element type!"); 147 } 148 return APIntToHexString(AI); 149 } 150 151 const MCSection * 152 X86WindowsTargetObjectFile::getSectionForConstant(SectionKind Kind, 153 const Constant *C) const { 154 if (Kind.isReadOnly()) { 155 if (C) { 156 Type *Ty = C->getType(); 157 SmallString<32> COMDATSymName; 158 if (Ty->isFloatTy() || Ty->isDoubleTy()) { 159 COMDATSymName = "__real@"; 160 COMDATSymName += scalarConstantToHexString(C); 161 } else if (const auto *VTy = dyn_cast<VectorType>(Ty)) { 162 uint64_t NumBits = VTy->getBitWidth(); 163 if (NumBits == 128 || NumBits == 256) { 164 COMDATSymName = NumBits == 128 ? "__xmm@" : "__ymm@"; 165 for (int I = VTy->getNumElements() - 1, E = -1; I != E; --I) 166 COMDATSymName += 167 scalarConstantToHexString(C->getAggregateElement(I)); 168 } 169 } 170 if (!COMDATSymName.empty()) { 171 unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | 172 COFF::IMAGE_SCN_MEM_READ | 173 COFF::IMAGE_SCN_LNK_COMDAT; 174 return getContext().getCOFFSection(".rdata", Characteristics, Kind, 175 COMDATSymName, 176 COFF::IMAGE_COMDAT_SELECT_ANY); 177 } 178 } 179 } 180 181 return TargetLoweringObjectFile::getSectionForConstant(Kind, C); 182 } 183