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" 21using namespace llvm; 22 23static cl::opt<unsigned> 24SSThreshold("mips-ssection-threshold", cl::Hidden, 25 cl::desc("Small data and bss section threshold size (default=8)"), 26 cl::init(8)); 27 28static cl::opt<bool> 29LocalSData("mlocal-sdata", cl::Hidden, 30 cl::desc("MIPS: Use gp_rel for object-local data."), 31 cl::init(true)); 32 33static cl::opt<bool> 34ExternSData("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 39void 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. 54static 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. 62bool MipsTargetObjectFile:: 63IsGlobalInSmallSection(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. 75bool MipsTargetObjectFile:: 76IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM, 77 SectionKind Kind) const { 78 return (IsGlobalInSmallSectionImpl(GV, TM) && 79 (Kind.isData() || 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. 85bool MipsTargetObjectFile:: 86IsGlobalInSmallSectionImpl(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( 111 GV->getParent()->getDataLayout().getTypeAllocSize(Ty)); 112} 113 114MCSection * 115MipsTargetObjectFile::SelectSectionForGlobal(const GlobalValue *GV, 116 SectionKind Kind, Mangler &Mang, 117 const TargetMachine &TM) const { 118 // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*" 119 // sections? 120 121 // Handle Small Section classification here. 122 if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind)) 123 return SmallBSSSection; 124 if (Kind.isData() && IsGlobalInSmallSection(GV, TM, Kind)) 125 return SmallDataSection; 126 127 // Otherwise, we work the same as ELF. 128 return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM); 129} 130 131/// Return true if this constant should be placed into small data section. 132bool MipsTargetObjectFile::IsConstantInSmallSection( 133 const DataLayout &DL, const Constant *CN, const TargetMachine &TM) const { 134 return (static_cast<const MipsTargetMachine &>(TM) 135 .getSubtargetImpl() 136 ->useSmallSection() && 137 LocalSData && IsInSmallSection(DL.getTypeAllocSize(CN->getType()))); 138} 139 140/// Return true if this constant should be placed into small data section. 141MCSection *MipsTargetObjectFile::getSectionForConstant( 142 const DataLayout &DL, SectionKind Kind, const Constant *C) const { 143 if (IsConstantInSmallSection(DL, C, *TM)) 144 return SmallDataSection; 145 146 // Otherwise, we work the same as ELF. 147 return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C); 148} 149