Home | History | Annotate | Download | only in Mips 
      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,
     45       ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_MIPS_GPREL);
     46 
     47   SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
     48                                                ELF::SHF_WRITE | ELF::SHF_ALLOC |
     49                                                    ELF::SHF_MIPS_GPREL);
     50   this->TM = &static_cast<const MipsTargetMachine &>(TM);
     51 }
     52 
     53 // A address must be loaded from a small section if its size is less than the
     54 // small section size threshold. Data in this section must be addressed using
     55 // gp_rel operator.
     56 static bool IsInSmallSection(uint64_t Size) {
     57   // gcc has traditionally not treated zero-sized objects as small data, so this
     58   // is effectively part of the ABI.
     59   return Size > 0 && Size <= SSThreshold;
     60 }
     61 
     62 /// Return true if this global address should be placed into small data/bss
     63 /// section.
     64 bool MipsTargetObjectFile::
     65 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM) const {
     66   // We first check the case where global is a declaration, because finding
     67   // section kind using getKindForGlobal() is only allowed for global
     68   // definitions.
     69   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
     70     return IsGlobalInSmallSectionImpl(GV, TM);
     71 
     72   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
     73 }
     74 
     75 /// Return true if this global address should be placed into small data/bss
     76 /// section.
     77 bool MipsTargetObjectFile::
     78 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
     79                        SectionKind Kind) const {
     80   return (IsGlobalInSmallSectionImpl(GV, TM) &&
     81           (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
     82 }
     83 
     84 /// Return true if this global address should be placed into small data/bss
     85 /// section. This method does all the work, except for checking the section
     86 /// kind.
     87 bool MipsTargetObjectFile::
     88 IsGlobalInSmallSectionImpl(const GlobalValue *GV,
     89                            const TargetMachine &TM) const {
     90   const MipsSubtarget &Subtarget =
     91       *static_cast<const MipsTargetMachine &>(TM).getSubtargetImpl();
     92 
     93   // Return if small section is not available.
     94   if (!Subtarget.useSmallSection())
     95     return false;
     96 
     97   // Only global variables, not functions.
     98   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
     99   if (!GVA)
    100     return false;
    101 
    102   // Enforce -mlocal-sdata.
    103   if (!LocalSData && GV->hasLocalLinkage())
    104     return false;
    105 
    106   // Enforce -mextern-sdata.
    107   if (!ExternSData && ((GV->hasExternalLinkage() && GV->isDeclaration()) ||
    108                        GV->hasCommonLinkage()))
    109     return false;
    110 
    111   Type *Ty = GV->getValueType();
    112   return IsInSmallSection(
    113       GV->getParent()->getDataLayout().getTypeAllocSize(Ty));
    114 }
    115 
    116 MCSection *
    117 MipsTargetObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
    118                                              SectionKind Kind, Mangler &Mang,
    119                                              const TargetMachine &TM) const {
    120   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
    121   // sections?
    122 
    123   // Handle Small Section classification here.
    124   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
    125     return SmallBSSSection;
    126   if (Kind.isData() && IsGlobalInSmallSection(GV, TM, Kind))
    127     return SmallDataSection;
    128 
    129   // Otherwise, we work the same as ELF.
    130   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
    131 }
    132 
    133 /// Return true if this constant should be placed into small data section.
    134 bool MipsTargetObjectFile::IsConstantInSmallSection(
    135     const DataLayout &DL, const Constant *CN, const TargetMachine &TM) const {
    136   return (static_cast<const MipsTargetMachine &>(TM)
    137               .getSubtargetImpl()
    138               ->useSmallSection() &&
    139           LocalSData && IsInSmallSection(DL.getTypeAllocSize(CN->getType())));
    140 }
    141 
    142 /// Return true if this constant should be placed into small data section.
    143 MCSection *MipsTargetObjectFile::getSectionForConstant(const DataLayout &DL,
    144                                                        SectionKind Kind,
    145                                                        const Constant *C,
    146                                                        unsigned &Align) const {
    147   if (IsConstantInSmallSection(DL, C, *TM))
    148     return SmallDataSection;
    149 
    150   // Otherwise, we work the same as ELF.
    151   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
    152 }
    153