1 //===-- MipsTargetObjectFile.cpp - Mips Object Files ----------------------===// 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 "MipsTargetObjectFile.h" 11 #include "MipsSubtarget.h" 12 #include "MipsTargetMachine.h" 13 #include "llvm/BinaryFormat/ELF.h" 14 #include "llvm/IR/DataLayout.h" 15 #include "llvm/IR/DerivedTypes.h" 16 #include "llvm/IR/GlobalVariable.h" 17 #include "llvm/MC/MCContext.h" 18 #include "llvm/MC/MCSectionELF.h" 19 #include "llvm/Support/CommandLine.h" 20 #include "llvm/Target/TargetMachine.h" 21 using namespace llvm; 22 23 static cl::opt<unsigned> 24 SSThreshold("mips-ssection-threshold", cl::Hidden, 25 cl::desc("Small data and bss section threshold size (default=8)"), 26 cl::init(8)); 27 28 static cl::opt<bool> 29 LocalSData("mlocal-sdata", cl::Hidden, 30 cl::desc("MIPS: Use gp_rel for object-local data."), 31 cl::init(true)); 32 33 static cl::opt<bool> 34 ExternSData("mextern-sdata", cl::Hidden, 35 cl::desc("MIPS: Use gp_rel for data that is not defined by the " 36 "current object."), 37 cl::init(true)); 38 39 static cl::opt<bool> 40 EmbeddedData("membedded-data", cl::Hidden, 41 cl::desc("MIPS: Try to allocate variables in the following" 42 " sections if possible: .rodata, .sdata, .data ."), 43 cl::init(false)); 44 45 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){ 46 TargetLoweringObjectFileELF::Initialize(Ctx, TM); 47 InitializeELF(TM.Options.UseInitArray); 48 49 SmallDataSection = getContext().getELFSection( 50 ".sdata", ELF::SHT_PROGBITS, 51 ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_MIPS_GPREL); 52 53 SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS, 54 ELF::SHF_WRITE | ELF::SHF_ALLOC | 55 ELF::SHF_MIPS_GPREL); 56 this->TM = &static_cast<const MipsTargetMachine &>(TM); 57 } 58 59 // A address must be loaded from a small section if its size is less than the 60 // small section size threshold. Data in this section must be addressed using 61 // gp_rel operator. 62 static bool IsInSmallSection(uint64_t Size) { 63 // gcc has traditionally not treated zero-sized objects as small data, so this 64 // is effectively part of the ABI. 65 return Size > 0 && Size <= SSThreshold; 66 } 67 68 /// Return true if this global address should be placed into small data/bss 69 /// section. 70 bool MipsTargetObjectFile::IsGlobalInSmallSection( 71 const GlobalObject *GO, const TargetMachine &TM) const { 72 // We first check the case where global is a declaration, because finding 73 // section kind using getKindForGlobal() is only allowed for global 74 // definitions. 75 if (GO->isDeclaration() || GO->hasAvailableExternallyLinkage()) 76 return IsGlobalInSmallSectionImpl(GO, TM); 77 78 return IsGlobalInSmallSection(GO, TM, getKindForGlobal(GO, TM)); 79 } 80 81 /// Return true if this global address should be placed into small data/bss 82 /// section. 83 bool MipsTargetObjectFile:: 84 IsGlobalInSmallSection(const GlobalObject *GO, const TargetMachine &TM, 85 SectionKind Kind) const { 86 return IsGlobalInSmallSectionImpl(GO, TM) && 87 (Kind.isData() || Kind.isBSS() || Kind.isCommon() || 88 Kind.isReadOnly()); 89 } 90 91 /// Return true if this global address should be placed into small data/bss 92 /// section. This method does all the work, except for checking the section 93 /// kind. 94 bool MipsTargetObjectFile:: 95 IsGlobalInSmallSectionImpl(const GlobalObject *GO, 96 const TargetMachine &TM) const { 97 const MipsSubtarget &Subtarget = 98 *static_cast<const MipsTargetMachine &>(TM).getSubtargetImpl(); 99 100 // Return if small section is not available. 101 if (!Subtarget.useSmallSection()) 102 return false; 103 104 // Only global variables, not functions. 105 const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GO); 106 if (!GVA) 107 return false; 108 109 // Enforce -mlocal-sdata. 110 if (!LocalSData && GVA->hasLocalLinkage()) 111 return false; 112 113 // Enforce -mextern-sdata. 114 if (!ExternSData && ((GVA->hasExternalLinkage() && GVA->isDeclaration()) || 115 GVA->hasCommonLinkage())) 116 return false; 117 118 // Enforce -membedded-data. 119 if (EmbeddedData && GVA->isConstant()) 120 return false; 121 122 Type *Ty = GVA->getValueType(); 123 return IsInSmallSection( 124 GVA->getParent()->getDataLayout().getTypeAllocSize(Ty)); 125 } 126 127 MCSection *MipsTargetObjectFile::SelectSectionForGlobal( 128 const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { 129 // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*" 130 // sections? 131 132 // Handle Small Section classification here. 133 if (Kind.isBSS() && IsGlobalInSmallSection(GO, TM, Kind)) 134 return SmallBSSSection; 135 if (Kind.isData() && IsGlobalInSmallSection(GO, TM, Kind)) 136 return SmallDataSection; 137 if (Kind.isReadOnly() && IsGlobalInSmallSection(GO, TM, Kind)) 138 return SmallDataSection; 139 140 // Otherwise, we work the same as ELF. 141 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM); 142 } 143 144 /// Return true if this constant should be placed into small data section. 145 bool MipsTargetObjectFile::IsConstantInSmallSection( 146 const DataLayout &DL, const Constant *CN, const TargetMachine &TM) const { 147 return (static_cast<const MipsTargetMachine &>(TM) 148 .getSubtargetImpl() 149 ->useSmallSection() && 150 LocalSData && IsInSmallSection(DL.getTypeAllocSize(CN->getType()))); 151 } 152 153 /// Return true if this constant should be placed into small data section. 154 MCSection *MipsTargetObjectFile::getSectionForConstant(const DataLayout &DL, 155 SectionKind Kind, 156 const Constant *C, 157 unsigned &Align) const { 158 if (IsConstantInSmallSection(DL, C, *TM)) 159 return SmallDataSection; 160 161 // Otherwise, we work the same as ELF. 162 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align); 163 } 164 165 const MCExpr * 166 MipsTargetObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const { 167 const MCExpr *Expr = 168 MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_None, getContext()); 169 return MCBinaryExpr::createAdd( 170 Expr, MCConstantExpr::create(0x8000, getContext()), getContext()); 171 } 172