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 "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 
     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   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
     64 
     65   // Return if small section is not available.
     66   if (!Subtarget.useSmallSection())
     67     return false;
     68 
     69   // Only global variables, not functions.
     70   const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
     71   if (!GVA)
     72     return false;
     73 
     74   // We can only do this for datarel or BSS objects for now.
     75   if (!Kind.isBSS() && !Kind.isDataRel())
     76     return false;
     77 
     78   // If this is a internal constant string, there is a special
     79   // section for it, but not in small data/bss.
     80   if (Kind.isMergeable1ByteCString())
     81     return false;
     82 
     83   Type *Ty = GV->getType()->getElementType();
     84   return IsInSmallSection(TM.getDataLayout()->getTypeAllocSize(Ty));
     85 }
     86 
     87 
     88 
     89 const MCSection *MipsTargetObjectFile::
     90 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
     91                        Mangler &Mang, const TargetMachine &TM) const {
     92   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
     93   // sections?
     94 
     95   // Handle Small Section classification here.
     96   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
     97     return SmallBSSSection;
     98   if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
     99     return SmallDataSection;
    100 
    101   // Otherwise, we work the same as ELF.
    102   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
    103 }
    104