xref: /frameworks/compile/mclinker/lib/Target/ARM/ARMLDBackend.cpp

//===- ARMLDBackend.cpp ---------------------------------------------------===//
//
//                     The MCLinker Project
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "ARM.h"
#include "ARMGNUInfo.h"
#include "ARMELFAttributeData.h"
#include "ARMELFDynamic.h"
#include "ARMLDBackend.h"
#include "ARMRelocator.h"
#include "ARMToARMStub.h"
#include "ARMToTHMStub.h"
#include "THMToTHMStub.h"
#include "THMToARMStub.h"

#include <mcld/IRBuilder.h>
#include <mcld/LinkerConfig.h>
#include <mcld/Fragment/FillFragment.h>
#include <mcld/Fragment/AlignFragment.h>
#include <mcld/Fragment/RegionFragment.h>
#include <mcld/Fragment/Stub.h>
#include <mcld/Fragment/NullFragment.h>
#include <mcld/Support/MemoryRegion.h>
#include <mcld/Support/MemoryArea.h>
#include <mcld/Support/MsgHandling.h>
#include <mcld/Support/TargetRegistry.h>
#include <mcld/LD/BranchIslandFactory.h>
#include <mcld/LD/StubFactory.h>
#include <mcld/LD/LDContext.h>
#include <mcld/LD/ELFFileFormat.h>
#include <mcld/LD/ELFSegmentFactory.h>
#include <mcld/LD/ELFSegment.h>
#include <mcld/Target/ELFAttribute.h>
#include <mcld/Target/GNUInfo.h>
#include <mcld/Object/ObjectBuilder.h>

#include <llvm/ADT/StringRef.h>
#include <llvm/ADT/Triple.h>
#include <llvm/ADT/Twine.h>
#include <llvm/Support/ELF.h>
#include <llvm/Support/Casting.h>

#include <cstring>

using namespace mcld;

//===----------------------------------------------------------------------===//
// ARMGNULDBackend
//===----------------------------------------------------------------------===//
ARMGNULDBackend::ARMGNULDBackend(const LinkerConfig& pConfig, GNUInfo* pInfo)
  : GNULDBackend(pConfig, pInfo),
    m_pRelocator(NULL),
    m_pGOT(NULL),
    m_pPLT(NULL),
    m_pRelDyn(NULL),
    m_pRelPLT(NULL),
    m_pAttrData(NULL),
    m_pDynamic(NULL),
    m_pGOTSymbol(NULL),
    m_pEXIDXStart(NULL),
    m_pEXIDXEnd(NULL),
    m_pEXIDX(NULL),
    m_pEXTAB(NULL),
    m_pAttributes(NULL) {
}

ARMGNULDBackend::~ARMGNULDBackend()
{
  delete m_pRelocator;
  delete m_pGOT;
  delete m_pPLT;
  delete m_pRelDyn;
  delete m_pRelPLT;
  delete m_pDynamic;
  delete m_pAttrData;
}

void ARMGNULDBackend::initTargetSections(Module& pModule, ObjectBuilder& pBuilder)
{
 // FIXME: Currently we set exidx and extab to "Exception" and directly emit
 // them from input
  m_pEXIDX        = pBuilder.CreateSection(".ARM.exidx",
                                           LDFileFormat::Target,
                                           llvm::ELF::SHT_ARM_EXIDX,
                                           llvm::ELF::SHF_ALLOC | llvm::ELF::SHF_LINK_ORDER,
                                           config().targets().bitclass() / 8);
  m_pEXTAB        = pBuilder.CreateSection(".ARM.extab",
                                           LDFileFormat::Target,
                                           llvm::ELF::SHT_PROGBITS,
                                           llvm::ELF::SHF_ALLOC,
                                           0x1);
  m_pAttributes   = pBuilder.CreateSection(".ARM.attributes",
                                           LDFileFormat::Target,
                                           llvm::ELF::SHT_ARM_ATTRIBUTES,
                                           0x0,
                                           0x1);

  // initialize "aeabi" attributes subsection
  m_pAttrData = new ARMELFAttributeData();
  attribute().registerAttributeData(*m_pAttrData);

  if (LinkerConfig::Object != config().codeGenType()) {
    ELFFileFormat* file_format = getOutputFormat();

    // initialize .got
    LDSection& got = file_format->getGOT();
    m_pGOT = new ARMGOT(got);

    // initialize .plt
    LDSection& plt = file_format->getPLT();
    m_pPLT = new ARMPLT(plt, *m_pGOT);

    // initialize .rel.plt
    LDSection& relplt = file_format->getRelPlt();
    relplt.setLink(&plt);
    // create SectionData and ARMRelDynSection
    m_pRelPLT = new OutputRelocSection(pModule, relplt);

    // initialize .rel.dyn
    LDSection& reldyn = file_format->getRelDyn();
    m_pRelDyn = new OutputRelocSection(pModule, reldyn);
  }
}

void ARMGNULDBackend::initTargetSymbols(IRBuilder& pBuilder, Module& pModule)
{
  // Define the symbol _GLOBAL_OFFSET_TABLE_ if there is a symbol with the
  // same name in input
  if (LinkerConfig::Object != config().codeGenType()) {
    m_pGOTSymbol = pBuilder.AddSymbol<IRBuilder::AsReferred, IRBuilder::Resolve>(
                                                  "_GLOBAL_OFFSET_TABLE_",
                                                  ResolveInfo::Object,
                                                  ResolveInfo::Define,
                                                  ResolveInfo::Local,
                                                  0x0,  // size
                                                  0x0,  // value
                                                  FragmentRef::Null(),
                                                  ResolveInfo::Hidden);
  }
  if (NULL != m_pEXIDX && 0x0 != m_pEXIDX->size()) {
    FragmentRef* exidx_start =
      FragmentRef::Create(m_pEXIDX->getSectionData()->front(), 0x0);
    FragmentRef* exidx_end =
      FragmentRef::Create(m_pEXIDX->getSectionData()->front(),
                          m_pEXIDX->size());
    m_pEXIDXStart =
      pBuilder.AddSymbol<IRBuilder::AsReferred, IRBuilder::Resolve>(
                                                    "__exidx_start",
                                                    ResolveInfo::Object,
                                                    ResolveInfo::Define,
                                                    ResolveInfo::Local,
                                                    0x0, // size
                                                    0x0, // value
                                                    exidx_start, // FragRef
                                                    ResolveInfo::Default);

    m_pEXIDXEnd =
      pBuilder.AddSymbol<IRBuilder::AsReferred, IRBuilder::Resolve>(
                                                    "__exidx_end",
                                                    ResolveInfo::Object,
                                                    ResolveInfo::Define,
                                                    ResolveInfo::Local,
                                                    0x0, // size
                                                    0x0, // value
                                                    exidx_end, // FragRef
                                                    ResolveInfo::Default);
    // change __exidx_start/_end to local dynamic category
    if (NULL != m_pEXIDXStart)
      pModule.getSymbolTable().changeToDynamic(*m_pEXIDXStart);
    if (NULL != m_pEXIDXEnd)
      pModule.getSymbolTable().changeToDynamic(*m_pEXIDXEnd);
  } else {
    m_pEXIDXStart =
      pBuilder.AddSymbol<IRBuilder::AsReferred, IRBuilder::Resolve>(
                                                    "__exidx_start",
                                                    ResolveInfo::NoType,
                                                    ResolveInfo::Define,
                                                    ResolveInfo::Absolute,
                                                    0x0, // size
                                                    0x0, // value
                                                    FragmentRef::Null(),
                                                    ResolveInfo::Default);

    m_pEXIDXEnd =
      pBuilder.AddSymbol<IRBuilder::AsReferred, IRBuilder::Resolve>(
                                                    "__exidx_end",
                                                    ResolveInfo::NoType,
                                                    ResolveInfo::Define,
                                                    ResolveInfo::Absolute,
                                                    0x0, // size
                                                    0x0, // value
                                                    FragmentRef::Null(),
                                                    ResolveInfo::Default);
  }
}

bool ARMGNULDBackend::initRelocator()
{
  if (NULL == m_pRelocator) {
    m_pRelocator = new ARMRelocator(*this, config());
  }
  return true;
}

const Relocator* ARMGNULDBackend::getRelocator() const
{
  assert(NULL != m_pRelocator);
  return m_pRelocator;
}

Relocator* ARMGNULDBackend::getRelocator()
{
  assert(NULL != m_pRelocator);
  return m_pRelocator;
}

void ARMGNULDBackend::doPreLayout(IRBuilder& pBuilder)
{
  // initialize .dynamic data
  if (!config().isCodeStatic() && NULL == m_pDynamic)
    m_pDynamic = new ARMELFDynamic(*this, config());

  // set attribute section size
  m_pAttributes->setSize(attribute().sizeOutput());

  // set .got size
  // when building shared object, the .got section is must
  if (LinkerConfig::Object != config().codeGenType()) {
    if (LinkerConfig::DynObj == config().codeGenType() ||
        m_pGOT->hasGOT1() ||
        NULL != m_pGOTSymbol) {
      m_pGOT->finalizeSectionSize();
      defineGOTSymbol(pBuilder);
    }

    // set .plt size
    if (m_pPLT->hasPLT1())
      m_pPLT->finalizeSectionSize();

    ELFFileFormat* file_format = getOutputFormat();
    // set .rel.dyn size
    if (!m_pRelDyn->empty()) {
      assert(!config().isCodeStatic() &&
            "static linkage should not result in a dynamic relocation section");
      file_format->getRelDyn().setSize(
                                  m_pRelDyn->numOfRelocs() * getRelEntrySize());
    }

    // set .rel.plt size
    if (!m_pRelPLT->empty()) {
      assert(!config().isCodeStatic() &&
            "static linkage should not result in a dynamic relocation section");
      file_format->getRelPlt().setSize(
                                  m_pRelPLT->numOfRelocs() * getRelEntrySize());
    }
  }
}

void ARMGNULDBackend::doPostLayout(Module& pModule, IRBuilder& pBuilder)
{
  const ELFFileFormat *file_format = getOutputFormat();

  // apply PLT
  if (file_format->hasPLT()) {
    // Since we already have the size of LDSection PLT, m_pPLT should not be
    // NULL.
    assert(NULL != m_pPLT);
    m_pPLT->applyPLT0();
    m_pPLT->applyPLT1();
  }

  // apply GOT
  if (file_format->hasGOT()) {
    // Since we already have the size of GOT, m_pGOT should not be NULL.
    assert(NULL != m_pGOT);
    if (LinkerConfig::DynObj == config().codeGenType())
      m_pGOT->applyGOT0(file_format->getDynamic().addr());
    else {
      // executable file and object file? should fill with zero.
      m_pGOT->applyGOT0(0);
    }
  }
}

/// dynamic - the dynamic section of the target machine.
/// Use co-variant return type to return its own dynamic section.
ARMELFDynamic& ARMGNULDBackend::dynamic()
{
  assert(NULL != m_pDynamic);
  return *m_pDynamic;
}

/// dynamic - the dynamic section of the target machine.
/// Use co-variant return type to return its own dynamic section.
const ARMELFDynamic& ARMGNULDBackend::dynamic() const
{
  assert(NULL != m_pDynamic);
  return *m_pDynamic;
}

void ARMGNULDBackend::defineGOTSymbol(IRBuilder& pBuilder)
{
  // define symbol _GLOBAL_OFFSET_TABLE_ when .got create
  if (m_pGOTSymbol != NULL) {
    pBuilder.AddSymbol<IRBuilder::Force, IRBuilder::Unresolve>(
                     "_GLOBAL_OFFSET_TABLE_",
                     ResolveInfo::Object,
                     ResolveInfo::Define,
                     ResolveInfo::Local,
                     0x0, // size
                     0x0, // value
                     FragmentRef::Create(*(m_pGOT->begin()), 0x0),
                     ResolveInfo::Hidden);
  }
  else {
    m_pGOTSymbol = pBuilder.AddSymbol<IRBuilder::Force, IRBuilder::Resolve>(
                     "_GLOBAL_OFFSET_TABLE_",
                     ResolveInfo::Object,
                     ResolveInfo::Define,
                     ResolveInfo::Local,
                     0x0, // size
                     0x0, // value
                     FragmentRef::Create(*(m_pGOT->begin()), 0x0),
                     ResolveInfo::Hidden);
  }

}

uint64_t ARMGNULDBackend::emitSectionData(const LDSection& pSection,
                                          MemoryRegion& pRegion) const
{
  assert(pRegion.size() && "Size of MemoryRegion is zero!");

  const ELFFileFormat* file_format = getOutputFormat();

  if (file_format->hasPLT() && (&pSection == &(file_format->getPLT()))) {
    uint64_t result = m_pPLT->emit(pRegion);
    return result;
  }

  if (file_format->hasGOT() && (&pSection == &(file_format->getGOT()))) {
    uint64_t result = m_pGOT->emit(pRegion);
    return result;
  }

  if (&pSection == m_pAttributes) {
    return attribute().emit(pRegion);
  }

  // FIXME: Currently Emitting .ARM.attributes, .ARM.exidx, and .ARM.extab
  // directly from the input file.
  const SectionData* sect_data = pSection.getSectionData();
  SectionData::const_iterator frag_iter, frag_end = sect_data->end();
  uint8_t* out_offset = pRegion.begin();
  for (frag_iter = sect_data->begin(); frag_iter != frag_end; ++frag_iter) {
    size_t size = frag_iter->size();
    switch(frag_iter->getKind()) {
      case Fragment::Fillment: {
        const FillFragment& fill_frag =
          llvm::cast<FillFragment>(*frag_iter);
        if (0 == fill_frag.getValueSize()) {
          // virtual fillment, ignore it.
          break;
        }

        memset(out_offset, fill_frag.getValue(), fill_frag.size());
        break;
      }
      case Fragment::Region: {
        const RegionFragment& region_frag =
          llvm::cast<RegionFragment>(*frag_iter);
        const char* start = region_frag.getRegion().begin();
        memcpy(out_offset, start, size);
        break;
      }
      case Fragment::Alignment: {
        const AlignFragment& align_frag = llvm::cast<AlignFragment>(*frag_iter);
        uint64_t count = size / align_frag.getValueSize();
        switch (align_frag.getValueSize()) {
          case 1u:
            std::memset(out_offset, align_frag.getValue(), count);
            break;
          default:
            llvm::report_fatal_error(
              "unsupported value size for align fragment emission yet.\n");
            break;
        } // end switch
        break;
      }
      case Fragment::Null: {
        assert(0x0 == size);
        break;
      }
      default:
        llvm::report_fatal_error("unsupported fragment type.\n");
        break;
    } // end switch
    out_offset += size;
  } // end for
  return pRegion.size();
}

/// finalizeSymbol - finalize the symbol value
bool ARMGNULDBackend::finalizeTargetSymbols()
{
  return true;
}

bool ARMGNULDBackend::mergeSection(Module& pModule,
                                   const Input& pInput,
                                   LDSection& pSection)
{
  switch (pSection.type()) {
    case llvm::ELF::SHT_ARM_ATTRIBUTES: {
      return attribute().merge(pInput, pSection);
    }
    case llvm::ELF::SHT_ARM_EXIDX: {
      assert(NULL != pSection.getLink());
      if (LDFileFormat::Ignore == pSection.getLink()->kind()) {
        // if the target section of the .ARM.exidx is Ignore, then it should be
        // ignored as well
        pSection.setKind(LDFileFormat::Ignore);
        return true;
      }
    }
    /** fall through **/
    default: {
      ObjectBuilder builder(pModule);
      builder.MergeSection(pInput, pSection);
      return true;
    }
  } // end of switch
  return true;
}

void ARMGNULDBackend::setUpReachedSectionsForGC(const Module& pModule,
            GarbageCollection::SectionReachedListMap& pSectReachedListMap) const
{
  // traverse all the input relocations to find the relocation sections applying
  // .ARM.exidx sections
  Module::const_obj_iterator input, inEnd = pModule.obj_end();
  for (input = pModule.obj_begin(); input != inEnd; ++input) {
    LDContext::const_sect_iterator rs,
                                   rsEnd = (*input)->context()->relocSectEnd();
    for (rs = (*input)->context()->relocSectBegin(); rs != rsEnd; ++rs) {
      // bypass the discarded relocation section
      // 1. its section kind is changed to Ignore. (The target section is a
      // discarded group section.)
      // 2. it has no reloc data. (All symbols in the input relocs are in the
      // discarded group sections)
      LDSection* reloc_sect = *rs;
      LDSection* apply_sect = reloc_sect->getLink();
      if ((LDFileFormat::Ignore == reloc_sect->kind()) ||
          (!reloc_sect->hasRelocData()))
        continue;

      if (llvm::ELF::SHT_ARM_EXIDX == apply_sect->type()) {
        // 1. set up the reference according to relocations
        bool add_first = false;
        GarbageCollection::SectionListTy* reached_sects = NULL;
        RelocData::iterator reloc_it, rEnd = reloc_sect->getRelocData()->end();
        for (reloc_it = reloc_sect->getRelocData()->begin(); reloc_it != rEnd;
                                                                   ++reloc_it) {
          Relocation* reloc = llvm::cast<Relocation>(reloc_it);
          ResolveInfo* sym = reloc->symInfo();
          // only the target symbols defined in the input fragments can make the
          // reference
          if (NULL == sym)
            continue;
          if (!sym->isDefine() || !sym->outSymbol()->hasFragRef())
            continue;

          // only the target symbols defined in the concerned sections can make
          // the reference
          const LDSection* target_sect =
                &sym->outSymbol()->fragRef()->frag()->getParent()->getSection();
          if (target_sect->kind() != LDFileFormat::TEXT &&
              target_sect->kind() != LDFileFormat::DATA &&
              target_sect->kind() != LDFileFormat::BSS)
            continue;

          // setup the reached list, if we first add the element to reached list
          // of this section, create an entry in ReachedSections map
          if (!add_first) {
            reached_sects = &pSectReachedListMap.getReachedList(*apply_sect);
            add_first = true;
          }
          reached_sects->insert(target_sect);
        }
        reached_sects = NULL;
        add_first = false;
        // 2. set up the reference from XXX to .ARM.exidx.XXX
        assert(apply_sect->getLink() != NULL);
        pSectReachedListMap.addReference(*apply_sect->getLink(), *apply_sect);
      }
    }
  }
}

bool ARMGNULDBackend::readSection(Input& pInput, SectionData& pSD)
{
  Fragment* frag = NULL;
  uint32_t offset = pInput.fileOffset() + pSD.getSection().offset();
  uint32_t size = pSD.getSection().size();

  llvm::StringRef region = pInput.memArea()->request(offset, size);
  if (region.size() == 0) {
    // If the input section's size is zero, we got a NULL region.
    // use a virtual fill fragment
    frag = new FillFragment(0x0, 0, 0);
  }
  else {
    frag = new RegionFragment(region);
  }

  ObjectBuilder::AppendFragment(*frag, pSD);
  return true;
}

ARMGOT& ARMGNULDBackend::getGOT()
{
  assert(NULL != m_pGOT && "GOT section not exist");
  return *m_pGOT;
}

const ARMGOT& ARMGNULDBackend::getGOT() const
{
  assert(NULL != m_pGOT && "GOT section not exist");
  return *m_pGOT;
}

ARMPLT& ARMGNULDBackend::getPLT()
{
  assert(NULL != m_pPLT && "PLT section not exist");
  return *m_pPLT;
}

const ARMPLT& ARMGNULDBackend::getPLT() const
{
  assert(NULL != m_pPLT && "PLT section not exist");
  return *m_pPLT;
}

OutputRelocSection& ARMGNULDBackend::getRelDyn()
{
  assert(NULL != m_pRelDyn && ".rel.dyn section not exist");
  return *m_pRelDyn;
}

const OutputRelocSection& ARMGNULDBackend::getRelDyn() const
{
  assert(NULL != m_pRelDyn && ".rel.dyn section not exist");
  return *m_pRelDyn;
}

OutputRelocSection& ARMGNULDBackend::getRelPLT()
{
  assert(NULL != m_pRelPLT && ".rel.plt section not exist");
  return *m_pRelPLT;
}

const OutputRelocSection& ARMGNULDBackend::getRelPLT() const
{
  assert(NULL != m_pRelPLT && ".rel.plt section not exist");
  return *m_pRelPLT;
}

ARMELFAttributeData& ARMGNULDBackend::getAttributeData()
{
  assert(NULL != m_pAttrData && ".ARM.attributes section not exist");
  return *m_pAttrData;
}

const ARMELFAttributeData& ARMGNULDBackend::getAttributeData() const
{
  assert(NULL != m_pAttrData && ".ARM.attributes section not exist");
  return *m_pAttrData;
}

unsigned int
ARMGNULDBackend::getTargetSectionOrder(const LDSection& pSectHdr) const
{
  const ELFFileFormat* file_format = getOutputFormat();

  if (file_format->hasGOT() && (&pSectHdr == &file_format->getGOT())) {
    if (config().options().hasNow())
      return SHO_RELRO_LAST;
    return SHO_DATA;
  }

  if (file_format->hasPLT() && (&pSectHdr == &file_format->getPLT()))
    return SHO_PLT;

  if (&pSectHdr == m_pEXIDX || &pSectHdr == m_pEXTAB) {
    // put ARM.exidx and ARM.extab in the same order of .eh_frame
    return SHO_EXCEPTION;
  }

  return SHO_UNDEFINED;
}

/// doRelax
bool
ARMGNULDBackend::doRelax(Module& pModule, IRBuilder& pBuilder, bool& pFinished)
{
  assert(NULL != getStubFactory() && NULL != getBRIslandFactory());

  bool isRelaxed = false;
  ELFFileFormat* file_format = getOutputFormat();
  // check branch relocs and create the related stubs if needed
  Module::obj_iterator input, inEnd = pModule.obj_end();
  for (input = pModule.obj_begin(); input != inEnd; ++input) {
    LDContext::sect_iterator rs, rsEnd = (*input)->context()->relocSectEnd();
    for (rs = (*input)->context()->relocSectBegin(); rs != rsEnd; ++rs) {
      if (LDFileFormat::Ignore == (*rs)->kind() || !(*rs)->hasRelocData())
        continue;
      RelocData::iterator reloc, rEnd = (*rs)->getRelocData()->end();
      for (reloc = (*rs)->getRelocData()->begin(); reloc != rEnd; ++reloc) {
        Relocation* relocation = llvm::cast<Relocation>(reloc);

        switch (relocation->type()) {
          case llvm::ELF::R_ARM_PC24:
          case llvm::ELF::R_ARM_CALL:
          case llvm::ELF::R_ARM_JUMP24:
          case llvm::ELF::R_ARM_PLT32:
          case llvm::ELF::R_ARM_THM_CALL:
          case llvm::ELF::R_ARM_THM_XPC22:
          case llvm::ELF::R_ARM_THM_JUMP24:
          case llvm::ELF::R_ARM_THM_JUMP19: {
            // calculate the possible symbol value
            uint64_t sym_value = 0x0;
            LDSymbol* symbol = relocation->symInfo()->outSymbol();
            if (symbol->hasFragRef()) {
              uint64_t value = symbol->fragRef()->getOutputOffset();
              uint64_t addr =
                symbol->fragRef()->frag()->getParent()->getSection().addr();
              sym_value = addr + value;
            }
            if (relocation->symInfo()->isGlobal() &&
                (relocation->symInfo()->reserved() & ARMRelocator::ReservePLT) != 0x0) {
              // FIXME: we need to find out the address of the specific plt entry
              assert(file_format->hasPLT());
              sym_value = file_format->getPLT().addr();
            }

            Stub* stub = getStubFactory()->create(*relocation, // relocation
                                                  sym_value, // symbol value
                                                  pBuilder,
                                                  *getBRIslandFactory());
            if (NULL != stub) {
              switch (config().options().getStripSymbolMode()) {
                case GeneralOptions::StripAllSymbols:
                case GeneralOptions::StripLocals:
                  break;
                default: {
                  // a stub symbol should be local
                  assert(NULL != stub->symInfo() && stub->symInfo()->isLocal());
                  LDSection& symtab = file_format->getSymTab();
                  LDSection& strtab = file_format->getStrTab();

                  // increase the size of .symtab and .strtab if needed
                  if (config().targets().is32Bits())
                    symtab.setSize(symtab.size() + sizeof(llvm::ELF::Elf32_Sym));
                  else
                    symtab.setSize(symtab.size() + sizeof(llvm::ELF::Elf64_Sym));
                  symtab.setInfo(symtab.getInfo() + 1);
                  strtab.setSize(strtab.size() + stub->symInfo()->nameSize() + 1);
                }
              } // end of switch
              isRelaxed = true;
            }
            break;
          }
          case llvm::ELF::R_ARM_V4BX:
            /* FIXME: bypass R_ARM_V4BX relocation now */
            break;
          default:
            break;
        } // end of switch

      } // for all relocations
    } // for all relocation section
  } // for all inputs

  // find the first fragment w/ invalid offset due to stub insertion
  Fragment* invalid = NULL;
  pFinished = true;
  for (BranchIslandFactory::iterator island = getBRIslandFactory()->begin(),
       island_end = getBRIslandFactory()->end(); island != island_end; ++island) {
    if ((*island).end() == file_format->getText().getSectionData()->end())
      break;

    Fragment* exit = (*island).end();
    if (((*island).offset() + (*island).size()) > exit->getOffset()) {
      invalid = exit;
      pFinished = false;
      break;
    }
  }

  // reset the offset of invalid fragments
  while (NULL != invalid) {
    invalid->setOffset(invalid->getPrevNode()->getOffset() +
                       invalid->getPrevNode()->size());
    invalid = invalid->getNextNode();
  }

  // reset the size of .text
  if (isRelaxed) {
    file_format->getText().setSize(
      file_format->getText().getSectionData()->back().getOffset() +
      file_format->getText().getSectionData()->back().size());
  }
  return isRelaxed;
}

/// initTargetStubs
bool ARMGNULDBackend::initTargetStubs()
{
  if (NULL != getStubFactory()) {
    getStubFactory()->addPrototype(new ARMToARMStub(config().isCodeIndep()));
    getStubFactory()->addPrototype(new ARMToTHMStub(config().isCodeIndep()));
    getStubFactory()->addPrototype(
        new THMToTHMStub(config().isCodeIndep(), m_pAttrData->usingThumb2()));
    getStubFactory()->addPrototype(
        new THMToARMStub(config().isCodeIndep(), m_pAttrData->usingThumb2()));
    return true;
  }
  return false;
}

/// maxFwdBranchOffset
int64_t ARMGNULDBackend::maxFwdBranchOffset()
{
  if (m_pAttrData->usingThumb2()) {
    return THM2_MAX_FWD_BRANCH_OFFSET;
  } else {
    return THM_MAX_FWD_BRANCH_OFFSET;
  }
}

/// maxBwdBranchOffset
int64_t ARMGNULDBackend::maxBwdBranchOffset()
{
  if (m_pAttrData->usingThumb2()) {
    return THM2_MAX_BWD_BRANCH_OFFSET;
  } else {
    return THM_MAX_BWD_BRANCH_OFFSET;
  }
}

/// doCreateProgramHdrs - backend can implement this function to create the
/// target-dependent segments
void ARMGNULDBackend::doCreateProgramHdrs(Module& pModule)
{
   if (NULL != m_pEXIDX && 0x0 != m_pEXIDX->size()) {
     // make PT_ARM_EXIDX
     ELFSegment* exidx_seg = elfSegmentTable().produce(llvm::ELF::PT_ARM_EXIDX,
                                                       llvm::ELF::PF_R);
     exidx_seg->append(m_pEXIDX);
   }
}

/// mayHaveUnsafeFunctionPointerAccess - check if the section may have unsafe
/// function pointer access
bool
ARMGNULDBackend::mayHaveUnsafeFunctionPointerAccess(const LDSection& pSection)
    const
{
  llvm::StringRef name(pSection.name());
  return !name.startswith(".ARM.exidx") &&
         !name.startswith(".ARM.extab") &&
         GNULDBackend::mayHaveUnsafeFunctionPointerAccess(pSection);
}


namespace mcld {

//===----------------------------------------------------------------------===//
/// createARMLDBackend - the help funtion to create corresponding ARMLDBackend
///
TargetLDBackend* createARMLDBackend(const LinkerConfig& pConfig)
{
  if (pConfig.targets().triple().isOSDarwin()) {
    assert(0 && "MachO linker is not supported yet");
    /**
    return new ARMMachOLDBackend(createARMMachOArchiveReader,
                               createARMMachOObjectReader,
                               createARMMachOObjectWriter);
    **/
  }
  if (pConfig.targets().triple().isOSWindows()) {
    assert(0 && "COFF linker is not supported yet");
    /**
    return new ARMCOFFLDBackend(createARMCOFFArchiveReader,
                               createARMCOFFObjectReader,
                               createARMCOFFObjectWriter);
    **/
  }
  return new ARMGNULDBackend(pConfig, new ARMGNUInfo(pConfig.targets().triple()));
}

} // namespace of mcld

//===----------------------------------------------------------------------===//
// Force static initialization.
//===----------------------------------------------------------------------===//
extern "C" void MCLDInitializeARMLDBackend() {
  // Register the linker backend
  mcld::TargetRegistry::RegisterTargetLDBackend(TheARMTarget, createARMLDBackend);
  mcld::TargetRegistry::RegisterTargetLDBackend(TheThumbTarget, createARMLDBackend);
}