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      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 "llvm/IR/DataLayout.h"
     13 #include "llvm/IR/DerivedTypes.h"
     14 #include "llvm/IR/GlobalVariable.h"
     15 #include "llvm/MC/MCContext.h"
     16 #include "llvm/MC/MCSectionELF.h"
     17 #include "llvm/Support/CommandLine.h"
     18 #include "llvm/Support/ELF.h"
     19 #include "llvm/Target/TargetMachine.h"
     20 using namespace llvm;
     21 
     22 static cl::opt<unsigned>
     23 SSThreshold("mips-ssection-threshold", cl::Hidden,
     24             cl::desc("Small data and bss section threshold size (default=8)"),
     25             cl::init(8));
     26 
     27 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
     28   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
     29   InitializeELF(TM.Options.UseInitArray);
     30 
     31   SmallDataSection =
     32     getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
     33                                ELF::SHF_WRITE |ELF::SHF_ALLOC,
     34                                SectionKind::getDataRel());
     35 
     36   SmallBSSSection =
     37     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
     38                                ELF::SHF_WRITE |ELF::SHF_ALLOC,
     39                                SectionKind::getBSS());
     40 
     41   // Register info information
     42   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
     43   if (Subtarget.isABI_N64() || Subtarget.isABI_N32())
     44     ReginfoSection =
     45       getContext().getELFSection(".MIPS.options",
     46                                  ELF::SHT_MIPS_OPTIONS,
     47                                  ELF::SHF_ALLOC |ELF::SHF_MIPS_NOSTRIP,
     48                                  SectionKind::getMetadata());
     49   else
     50     ReginfoSection =
     51       getContext().getELFSection(".reginfo",
     52                                  ELF::SHT_MIPS_REGINFO,
     53                                  ELF::SHF_ALLOC,
     54                                  SectionKind::getMetadata());
     55 }
     56 
     57 // A address must be loaded from a small section if its size is less than the
     58 // small section size threshold. Data in this section must be addressed using
     59 // gp_rel operator.
     60 static bool IsInSmallSection(uint64_t Size) {
     61   return Size > 0 && Size <= SSThreshold;
     62 }
     63 
     64 bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
     65                                                 const TargetMachine &TM) const {
     66   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
     67     return false;
     68 
     69   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
     70 }
     71 
     72 /// IsGlobalInSmallSection - Return true if this global address should be
     73 /// placed into small data/bss section.
     74 bool MipsTargetObjectFile::
     75 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
     76                        SectionKind Kind) const {
     77 
     78   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
     79 
     80   // Return if small section is not available.
     81   if (!Subtarget.useSmallSection())
     82     return false;
     83 
     84   // Only global variables, not functions.
     85   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
     86   if (!GVA)
     87     return false;
     88 
     89   // We can only do this for datarel or BSS objects for now.
     90   if (!Kind.isBSS() && !Kind.isDataRel())
     91     return false;
     92 
     93   // If this is a internal constant string, there is a special
     94   // section for it, but not in small data/bss.
     95   if (Kind.isMergeable1ByteCString())
     96     return false;
     97 
     98   Type *Ty = GV->getType()->getElementType();
     99   return IsInSmallSection(TM.getDataLayout()->getTypeAllocSize(Ty));
    100 }
    101 
    102 
    103 
    104 const MCSection *MipsTargetObjectFile::
    105 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
    106                        Mangler *Mang, const TargetMachine &TM) const {
    107   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
    108   // sections?
    109 
    110   // Handle Small Section classification here.
    111   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
    112     return SmallBSSSection;
    113   if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
    114     return SmallDataSection;
    115 
    116   // Otherwise, we work the same as ELF.
    117   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
    118 }
    119