path: root/lld/lib/ReaderWriter/ELF/Mips/MipsRelocationPass.cpp

//===- lib/ReaderWriter/ELF/Mips/MipsRelocationPass.cpp -------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "MipsLinkingContext.h"
#include "MipsRelocationPass.h"

#include "Atoms.h"

namespace {

using namespace lld;
using namespace lld::elf;
using namespace llvm::ELF;

// Lazy resolver
const uint8_t mipsGot0AtomContent[] = { 0x00, 0x00, 0x00, 0x00 };

// Module pointer
const uint8_t mipsGotModulePointerAtomContent[] = { 0x00, 0x00, 0x00, 0x80 };

// PLT0 entry
const uint8_t mipsPlt0AtomContent[] = {
  0x00, 0x00, 0x1c, 0x3c, // lui   $28, %hi(&GOTPLT[0])
  0x00, 0x00, 0x99, 0x8f, // lw    $25, %lo(&GOTPLT[0])($28)
  0x00, 0x00, 0x9c, 0x27, // addiu $28, $28, %lo(&GOTPLT[0])
  0x23, 0xc0, 0x1c, 0x03, // subu  $24, $24, $28
  0x21, 0x78, 0xe0, 0x03, // move  $15, $31
  0x82, 0xc0, 0x18, 0x00, // srl   $24, $24, 2
  0x09, 0xf8, 0x20, 0x03, // jalr  $25
  0xfe, 0xff, 0x18, 0x27  // subu  $24, $24, 2
};

// Regular PLT entry
const uint8_t mipsPltAAtomContent[] = {
  0x00, 0x00, 0x0f, 0x3c, // lui   $15, %hi(.got.plt entry)
  0x00, 0x00, 0xf9, 0x8d, // l[wd] $25, %lo(.got.plt entry)($15)
  0x08, 0x00, 0x20, 0x03, // jr    $25
  0x00, 0x00, 0xf8, 0x25  // addiu $24, $15, %lo(.got.plt entry)
};

/// \brief Abstract base class represent MIPS GOT entries.
class MipsGOTAtom : public GOTAtom {
public:
  MipsGOTAtom(const File &f) : GOTAtom(f, ".got") {}

  Alignment alignment() const override { return Alignment(2); }
};

/// \brief MIPS GOT entry initialized by zero.
class GOT0Atom : public MipsGOTAtom {
public:
  GOT0Atom(const File &f) : MipsGOTAtom(f) {}

  ArrayRef<uint8_t> rawContent() const override {
    return llvm::makeArrayRef(mipsGot0AtomContent);
  }
};

/// \brief MIPS GOT entry initialized by zero.
class GOTModulePointerAtom : public MipsGOTAtom {
public:
  GOTModulePointerAtom(const File &f) : MipsGOTAtom(f) {}

  ArrayRef<uint8_t> rawContent() const override {
    return llvm::makeArrayRef(mipsGotModulePointerAtomContent);
  }
};

class PLT0Atom : public PLTAtom {
public:
  PLT0Atom(const File &f) : PLTAtom(f, ".plt") {}

  ArrayRef<uint8_t> rawContent() const override {
    return llvm::makeArrayRef(mipsPlt0AtomContent);
  }
};

class PLTAAtom : public PLTAtom {
public:
  PLTAAtom(const File &f) : PLTAtom(f, ".plt") {}

  ArrayRef<uint8_t> rawContent() const override {
    return llvm::makeArrayRef(mipsPltAAtomContent);
  }
};

/// \brief MIPS GOT PLT entry
class GOTPLTAtom : public GOTAtom {
public:
  GOTPLTAtom(const File &f) : GOTAtom(f, ".got.plt") {}

  Alignment alignment() const override { return Alignment(2); }

  ArrayRef<uint8_t> rawContent() const override {
    return llvm::makeArrayRef(mipsGot0AtomContent);
  }
};

class RelocationPassFile : public SimpleFile {
public:
  RelocationPassFile(const ELFLinkingContext &ctx)
      : SimpleFile("RelocationPassFile") {
    setOrdinal(ctx.getNextOrdinalAndIncrement());
  }

  llvm::BumpPtrAllocator _alloc;
};

class RelocationPass : public Pass {
public:
  RelocationPass(MipsLinkingContext &context);

  void perform(std::unique_ptr<MutableFile> &mf) override;

private:
  /// \brief Reference to the linking context.
  const MipsLinkingContext &_context;

  /// \brief Owner of all the Atoms created by this pass.
  RelocationPassFile _file;

  /// \brief Map Atoms and addend to local GOT entries.
  typedef std::pair<const Atom *, int64_t> LocalGotMapKeyT;
  llvm::DenseMap<LocalGotMapKeyT, GOTAtom *> _gotLocalMap;

  /// \brief Map Atoms to global GOT entries.
  llvm::DenseMap<const Atom *, GOTAtom *> _gotGlobalMap;

  /// \brief the list of local GOT atoms.
  std::vector<GOTAtom *> _localGotVector;

  /// \brief the list of global GOT atoms.
  std::vector<GOTAtom *> _globalGotVector;

  /// \brief Map Atoms to their PLT entries.
  llvm::DenseMap<const Atom *, PLTAtom *> _pltMap;

  /// \brief Map Atoms to their Object entries.
  llvm::DenseMap<const Atom *, ObjectAtom *> _objectMap;

  /// \brief the list of PLT atoms.
  std::vector<PLTAtom *> _pltVector;

  /// \brief the list of GOTPLT atoms.
  std::vector<GOTAtom *> _gotpltVector;

  /// \brief the list of Object entries.
  std::vector<ObjectAtom *> _objectVector;

  /// \brief Handle a specific reference.
  void handleReference(const DefinedAtom &atom, const Reference &ref);

  /// \brief Calculate AHL addendums for the atom's references.
  void calculateAHLs(const DefinedAtom &atom);

  void handlePlain(const Reference &ref);
  void handlePLT(const Reference &ref);
  void handleGOT(const Reference &ref);

  const GOTAtom *getLocalGOTEntry(const Reference &ref);
  const GOTAtom *getGlobalGOTEntry(const Atom *a);
  const PLTAtom *getPLTEntry(const Atom *a);
  const ObjectAtom *getObjectEntry(const SharedLibraryAtom *a);

  bool isLocal(const Atom *a) const;
  bool requireLocalGOT(const Atom *a);
  void createPLTHeader();
};

RelocationPass::RelocationPass(MipsLinkingContext &context)
    : _context(context), _file(context) {
  _localGotVector.push_back(new (_file._alloc) GOT0Atom(_file));
  _localGotVector.push_back(new (_file._alloc) GOTModulePointerAtom(_file));
}

void RelocationPass::perform(std::unique_ptr<MutableFile> &mf) {
  for (const auto &atom : mf->defined())
    calculateAHLs(*atom);

  // Process all references.
  for (const auto &atom : mf->defined())
    for (const auto &ref : *atom)
      handleReference(*atom, *ref);

  uint64_t ordinal = 0;

  for (auto &got : _localGotVector) {
    DEBUG_WITH_TYPE("MipsGOT", llvm::dbgs() << "[ GOT ] Adding L "
                                            << got->name() << "\n");
    got->setOrdinal(ordinal++);
    mf->addAtom(*got);
  }

  for (auto &got : _globalGotVector) {
    DEBUG_WITH_TYPE("MipsGOT", llvm::dbgs() << "[ GOT ] Adding G "
                                            << got->name() << "\n");
    got->setOrdinal(ordinal++);
    mf->addAtom(*got);
  }

  for (auto &plt : _pltVector) {
    DEBUG_WITH_TYPE("MipsGOT", llvm::dbgs() << "[ PLT ] Adding " << plt->name()
                                            << "\n");
    plt->setOrdinal(ordinal++);
    mf->addAtom(*plt);
  }

  for (auto &gotplt : _gotpltVector) {
    DEBUG_WITH_TYPE("MipsGOT", llvm::dbgs() << "[ GOTPLT ] Adding "
                                            << gotplt->name() << "\n");
    gotplt->setOrdinal(ordinal++);
    mf->addAtom(*gotplt);
  }

  for (auto obj : _objectVector) {
    obj->setOrdinal(ordinal++);
    mf->addAtom(*obj);
  }
}

/// \brief Calculate AHL value combines addends from 'hi' and 'lo' relocations.
inline int64_t calcAHL(int64_t AHI, int64_t ALO) {
  AHI &= 0xffff;
  ALO &= 0xffff;
  return (AHI << 16) + (int16_t)ALO;
}

void RelocationPass::calculateAHLs(const DefinedAtom &atom) {
  std::vector<Reference *> references;
  for (const auto &ref : atom) {
    if (ref->kindNamespace() != lld::Reference::KindNamespace::ELF)
      continue;
    assert(ref->kindArch() == Reference::KindArch::Mips);
    switch (ref->kindValue()) {
      case R_MIPS_HI16:
        references.push_back(const_cast<Reference *>(ref));
        break;
      case R_MIPS_GOT16:
        if (isLocal(ref->target()))
          references.push_back(const_cast<Reference *>(ref));
        break;
      case R_MIPS_LO16:
        for (auto &sr : references)
          sr->setAddend(calcAHL(sr->addend(), ref->addend()));
        references.clear();
        break;
    }
  }
  if (!references.empty()) {
    for (auto &sr : references)
      sr->setAddend(0);
  }
  assert(references.empty());
}

void RelocationPass::handleReference(const DefinedAtom &atom,
                                     const Reference &ref) {
  if (ref.kindNamespace() != lld::Reference::KindNamespace::ELF)
    return;
  assert(ref.kindArch() == Reference::KindArch::Mips);
  switch (ref.kindValue()) {
  case R_MIPS_32:
  case R_MIPS_HI16:
  case R_MIPS_LO16:
    // FIXME (simon): Handle dynamic/static linking differently.
    handlePlain(ref);
    break;
  case R_MIPS_26:
    handlePLT(ref);
    break;
  case R_MIPS_GOT16:
  case R_MIPS_CALL16:
    handleGOT(ref);
    break;
  }
}

bool RelocationPass::isLocal(const Atom *a) const {
  if (auto *da = dyn_cast<DefinedAtom>(a))
    return da->scope() == Atom::scopeTranslationUnit;
  return false;
}

void RelocationPass::handlePlain(const Reference &ref) {
  if (!ref.target())
    return;
  auto sla = dyn_cast<SharedLibraryAtom>(ref.target());
  if (sla && sla->type() == SharedLibraryAtom::Type::Data)
    const_cast<Reference &>(ref).setTarget(getObjectEntry(sla));
}

void RelocationPass::handlePLT(const Reference &ref) {
  if (ref.kindValue() == R_MIPS_26 && !isLocal(ref.target()))
    const_cast<Reference &>(ref).setKindValue(LLD_R_MIPS_GLOBAL_26);

  if (isa<SharedLibraryAtom>(ref.target()))
    const_cast<Reference &>(ref).setTarget(getPLTEntry(ref.target()));
}

void RelocationPass::handleGOT(const Reference &ref) {
  if (requireLocalGOT(ref.target()))
    const_cast<Reference &>(ref).setTarget(getLocalGOTEntry(ref));
  else
    const_cast<Reference &>(ref).setTarget(getGlobalGOTEntry(ref.target()));
}

bool RelocationPass::requireLocalGOT(const Atom *a) {
  Atom::Scope scope;
  if (auto *da = dyn_cast<DefinedAtom>(a))
    scope = da->scope();
  else if (auto *aa = dyn_cast<AbsoluteAtom>(a))
    scope = aa->scope();
  else
    return false;

  // Local and hidden symbols must be local.
  if (scope == Atom::scopeTranslationUnit || scope == Atom::scopeLinkageUnit)
    return true;

  // External symbol defined in an executable file requires a local GOT entry.
  if (_context.getOutputELFType() == llvm::ELF::ET_EXEC)
    return true;

  return false;
}

const GOTAtom *RelocationPass::getLocalGOTEntry(const Reference &ref) {
  const Atom *a = ref.target();
  LocalGotMapKeyT key(a, ref.addend());

  auto got = _gotLocalMap.find(key);
  if (got != _gotLocalMap.end())
    return got->second;

  auto ga = new (_file._alloc) GOT0Atom(_file);
  _gotLocalMap[key] = ga;

  _localGotVector.push_back(ga);

  if (isLocal(a))
    ga->addReferenceELF_Mips(LLD_R_MIPS_32_HI16, 0, a, ref.addend());
  else
    ga->addReferenceELF_Mips(R_MIPS_32, 0, a, 0);

  DEBUG_WITH_TYPE("MipsGOT", {
    ga->_name = "__got_";
    ga->_name += a->name();
    llvm::dbgs() << "[ GOT ] Create L " << a->name() << "\n";
  });

  return ga;
}

const GOTAtom *RelocationPass::getGlobalGOTEntry(const Atom *a) {
  auto got = _gotGlobalMap.find(a);
  if (got != _gotGlobalMap.end())
    return got->second;

  auto ga = new (_file._alloc) GOT0Atom(_file);
  _gotGlobalMap[a] = ga;

  _globalGotVector.push_back(ga);
  ga->addReferenceELF_Mips(LLD_R_MIPS_GLOBAL_GOT, 0, a, 0);

  if (const DefinedAtom *da = dyn_cast<DefinedAtom>(a))
    ga->addReferenceELF_Mips(R_MIPS_32, 0, da, 0);

  DEBUG_WITH_TYPE("MipsGOT", {
    ga->_name = "__got_";
    ga->_name += a->name();
    llvm::dbgs() << "[ GOT ] Create G " << a->name() << "\n";
  });

  return ga;
}

void RelocationPass::createPLTHeader() {
  assert(_pltVector.empty() && _gotpltVector.empty());

  auto pa = new (_file._alloc) PLT0Atom(_file);
  _pltVector.push_back(pa);

  auto ga0 = new (_file._alloc) GOTPLTAtom(_file);
  _gotpltVector.push_back(ga0);
  auto ga1 = new (_file._alloc) GOTPLTAtom(_file);
  _gotpltVector.push_back(ga1);

  // Setup reference to fixup the PLT0 entry.
  pa->addReferenceELF_Mips(LLD_R_MIPS_HI16, 0, ga0, 0);
  pa->addReferenceELF_Mips(LLD_R_MIPS_LO16, 4, ga0, 0);
  pa->addReferenceELF_Mips(LLD_R_MIPS_LO16, 8, ga0, 0);

  DEBUG_WITH_TYPE("MipsGOT", {
    pa->_name = "__plt0";
    llvm::dbgs() << "[ PLT ] Create PLT0\n";
    ga0->_name = "__gotplt0";
    llvm::dbgs() << "[ GOTPLT ] Create GOTPLT0\n";
    ga1->_name = "__gotplt1";
    llvm::dbgs() << "[ GOTPLT ] Create GOTPLT1\n";
  });
}

const PLTAtom *RelocationPass::getPLTEntry(const Atom *a) {
  auto plt = _pltMap.find(a);
  if (plt != _pltMap.end())
    return plt->second;

  if (_pltVector.empty())
    createPLTHeader();

  auto pa = new (_file._alloc) PLTAAtom(_file);
  _pltMap[a] = pa;
  _pltVector.push_back(pa);

  auto ga = new (_file._alloc) GOTPLTAtom(_file);
  _gotpltVector.push_back(ga);

  // Setup reference to fixup the PLT entry.
  pa->addReferenceELF_Mips(LLD_R_MIPS_HI16, 0, ga, 0);
  pa->addReferenceELF_Mips(LLD_R_MIPS_LO16, 4, ga, 0);
  pa->addReferenceELF_Mips(LLD_R_MIPS_LO16, 12, ga, 0);

  // Setup reference to assign initial value to the .got.plt entry.
  ga->addReferenceELF_Mips(R_MIPS_32, 0, _pltVector.front(), 0);
  // Create dynamic relocation to adjust the .got.plt entry at runtime.
  ga->addReferenceELF_Mips(R_MIPS_JUMP_SLOT, 0, a, 0);

  DEBUG_WITH_TYPE("MipsGOT", {
    pa->_name = "__plt_";
    pa->_name += a->name();
    llvm::dbgs() << "[ PLT ] Create " << a->name() << "\n";
    ga->_name = "__got_plt_";
    ga->_name += a->name();
    llvm::dbgs() << "[ GOTPLT ] Create " << a->name() << "\n";
  });

  return pa;
}

const ObjectAtom *RelocationPass::getObjectEntry(const SharedLibraryAtom *a) {
  auto obj = _objectMap.find(a);
  if (obj != _objectMap.end())
    return obj->second;

  auto oa = new (_file._alloc) ObjectAtom(_file);
  oa->addReferenceELF_Mips(R_MIPS_COPY, 0, oa, 0);
  oa->_name = a->name();
  oa->_size = a->size();

  _objectMap[a] = oa;
  _objectVector.push_back(oa);

  return oa;
}

} // end anon namespace

std::unique_ptr<Pass>
lld::elf::createMipsRelocationPass(MipsLinkingContext &ctx) {
  switch (ctx.getOutputELFType()) {
  case llvm::ELF::ET_EXEC:
  case llvm::ELF::ET_DYN:
    return std::unique_ptr<Pass>(new RelocationPass(ctx));
  case llvm::ELF::ET_REL:
    return std::unique_ptr<Pass>();
  default:
    llvm_unreachable("Unhandled output file type");
  }
}