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/IR/DataLayout.h" 14 #include "llvm/IR/DerivedTypes.h" 15 #include "llvm/IR/GlobalVariable.h" 16 #include "llvm/MC/MCContext.h" 17 #include "llvm/MC/MCSectionELF.h" 18 #include "llvm/Support/CommandLine.h" 19 #include "llvm/Support/ELF.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 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){ 40 TargetLoweringObjectFileELF::Initialize(Ctx, TM); 41 InitializeELF(TM.Options.UseInitArray); 42 43 SmallDataSection = getContext().getELFSection( 44 ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC); 45 46 SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS, 47 ELF::SHF_WRITE | ELF::SHF_ALLOC); 48 this->TM = &static_cast<const MipsTargetMachine &>(TM); 49 } 50 51 // A address must be loaded from a small section if its size is less than the 52 // small section size threshold. Data in this section must be addressed using 53 // gp_rel operator. 54 static bool IsInSmallSection(uint64_t Size) { 55 // gcc has traditionally not treated zero-sized objects as small data, so this 56 // is effectively part of the ABI. 57 return Size > 0 && Size <= SSThreshold; 58 } 59 60 /// Return true if this global address should be placed into small data/bss 61 /// section. 62 bool MipsTargetObjectFile:: 63 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM) const { 64 // We first check the case where global is a declaration, because finding 65 // section kind using getKindForGlobal() is only allowed for global 66 // definitions. 67 if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage()) 68 return IsGlobalInSmallSectionImpl(GV, TM); 69 70 return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM)); 71 } 72 73 /// Return true if this global address should be placed into small data/bss 74 /// section. 75 bool MipsTargetObjectFile:: 76 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM, 77 SectionKind Kind) const { 78 return (IsGlobalInSmallSectionImpl(GV, TM) && 79 (Kind.isDataRel() || Kind.isBSS() || Kind.isCommon())); 80 } 81 82 /// Return true if this global address should be placed into small data/bss 83 /// section. This method does all the work, except for checking the section 84 /// kind. 85 bool MipsTargetObjectFile:: 86 IsGlobalInSmallSectionImpl(const GlobalValue *GV, 87 const TargetMachine &TM) const { 88 const MipsSubtarget &Subtarget = 89 *static_cast<const MipsTargetMachine &>(TM).getSubtargetImpl(); 90 91 // Return if small section is not available. 92 if (!Subtarget.useSmallSection()) 93 return false; 94 95 // Only global variables, not functions. 96 const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV); 97 if (!GVA) 98 return false; 99 100 // Enforce -mlocal-sdata. 101 if (!LocalSData && GV->hasLocalLinkage()) 102 return false; 103 104 // Enforce -mextern-sdata. 105 if (!ExternSData && ((GV->hasExternalLinkage() && GV->isDeclaration()) || 106 GV->hasCommonLinkage())) 107 return false; 108 109 Type *Ty = GV->getType()->getElementType(); 110 return IsInSmallSection(TM.getDataLayout()->getTypeAllocSize(Ty)); 111 } 112 113 const MCSection *MipsTargetObjectFile:: 114 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind, 115 Mangler &Mang, const TargetMachine &TM) const { 116 // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*" 117 // sections? 118 119 // Handle Small Section classification here. 120 if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind)) 121 return SmallBSSSection; 122 if (Kind.isDataRel() && IsGlobalInSmallSection(GV, TM, Kind)) 123 return SmallDataSection; 124 125 // Otherwise, we work the same as ELF. 126 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM); 127 } 128 129 /// Return true if this constant should be placed into small data section. 130 bool MipsTargetObjectFile:: 131 IsConstantInSmallSection(const Constant *CN, const TargetMachine &TM) const { 132 return (static_cast<const MipsTargetMachine &>(TM) 133 .getSubtargetImpl() 134 ->useSmallSection() && 135 LocalSData && IsInSmallSection(TM.getDataLayout()->getTypeAllocSize( 136 CN->getType()))); 137 } 138 139 const MCSection *MipsTargetObjectFile:: 140 getSectionForConstant(SectionKind Kind, const Constant *C) const { 141 if (IsConstantInSmallSection(C, *TM)) 142 return SmallDataSection; 143 144 // Otherwise, we work the same as ELF. 145 return TargetLoweringObjectFileELF::getSectionForConstant(Kind, C); 146 } 147