lib/Target/Mips/MipsTargetObjectFile.cpp

   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   const 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 }