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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/DerivedTypes.h"
     13 #include "llvm/GlobalVariable.h"
     14 #include "llvm/MC/MCContext.h"
     15 #include "llvm/MC/MCSectionELF.h"
     16 #include "llvm/Target/TargetData.h"
     17 #include "llvm/Target/TargetMachine.h"
     18 #include "llvm/Support/CommandLine.h"
     19 #include "llvm/Support/ELF.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 
     30   SmallDataSection =
     31     getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
     32                                ELF::SHF_WRITE |ELF::SHF_ALLOC,
     33                                SectionKind::getDataRel());
     34 
     35   SmallBSSSection =
     36     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
     37                                ELF::SHF_WRITE |ELF::SHF_ALLOC,
     38                                SectionKind::getBSS());
     39 
     40 }
     41 
     42 // A address must be loaded from a small section if its size is less than the
     43 // small section size threshold. Data in this section must be addressed using
     44 // gp_rel operator.
     45 static bool IsInSmallSection(uint64_t Size) {
     46   return Size > 0 && Size <= SSThreshold;
     47 }
     48 
     49 bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
     50                                                 const TargetMachine &TM) const {
     51   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
     52     return false;
     53 
     54   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
     55 }
     56 
     57 /// IsGlobalInSmallSection - Return true if this global address should be
     58 /// placed into small data/bss section.
     59 bool MipsTargetObjectFile::
     60 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
     61                        SectionKind Kind) const {
     62 
     63   // Only use small section for non linux targets.
     64   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
     65   if (Subtarget.isLinux())
     66     return false;
     67 
     68   // Only global variables, not functions.
     69   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
     70   if (!GVA)
     71     return false;
     72 
     73   // We can only do this for datarel or BSS objects for now.
     74   if (!Kind.isBSS() && !Kind.isDataRel())
     75     return false;
     76 
     77   // If this is a internal constant string, there is a special
     78   // section for it, but not in small data/bss.
     79   if (Kind.isMergeable1ByteCString())
     80     return false;
     81 
     82   Type *Ty = GV->getType()->getElementType();
     83   return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
     84 }
     85 
     86 
     87 
     88 const MCSection *MipsTargetObjectFile::
     89 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
     90                        Mangler *Mang, const TargetMachine &TM) const {
     91   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
     92   // sections?
     93 
     94   // Handle Small Section classification here.
     95   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
     96     return SmallBSSSection;
     97   if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
     98     return SmallDataSection;
     99 
    100   // Otherwise, we work the same as ELF.
    101   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
    102 }
    103