lld/ELF/OutputSections.cpp

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

#include "OutputSections.h"
#include "Config.h"
#include "SymbolTable.h"
#include "Target.h"

using namespace llvm;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace llvm::ELF;

using namespace lld;
using namespace lld::elf2;

template <class ELFT>
OutputSectionBase<ELFT>::OutputSectionBase(StringRef Name, uint32_t sh_type,
                                           uintX_t sh_flags)
    : Name(Name) {
  memset(&Header, 0, sizeof(Elf_Shdr));
  Header.sh_type = sh_type;
  Header.sh_flags = sh_flags;
}

template <class ELFT>
GotSection<ELFT>::GotSection()
    : OutputSectionBase<ELFT>(".got", llvm::ELF::SHT_PROGBITS,
                              llvm::ELF::SHF_ALLOC | llvm::ELF::SHF_WRITE) {
  this->Header.sh_addralign = sizeof(uintX_t);
}

template <class ELFT> void GotSection<ELFT>::addEntry(SymbolBody *Sym) {
  Sym->GotIndex = Entries.size();
  Entries.push_back(Sym);
}

template <class ELFT>
typename GotSection<ELFT>::uintX_t
GotSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
  return this->getVA() + B.GotIndex * sizeof(uintX_t);
}

template <class ELFT> void GotSection<ELFT>::writeTo(uint8_t *Buf) {
  for (const SymbolBody *B : Entries) {
    uint8_t *Entry = Buf;
    Buf += sizeof(uintX_t);
    if (canBePreempted(B, false))
      continue; // The dynamic linker will take care of it.
    uintX_t VA = getSymVA<ELFT>(*B);
    write<uintX_t, ELFT::TargetEndianness, sizeof(uintX_t)>(Entry, VA);
  }
}

template <class ELFT>
PltSection<ELFT>::PltSection()
    : OutputSectionBase<ELFT>(".plt", llvm::ELF::SHT_PROGBITS,
                              llvm::ELF::SHF_ALLOC | llvm::ELF::SHF_EXECINSTR) {
  this->Header.sh_addralign = 16;
}

template <class ELFT> void PltSection<ELFT>::writeTo(uint8_t *Buf) {
  size_t Off = 0;
  for (const SymbolBody *E : Entries) {
    uint64_t Got = Out<ELFT>::Got->getEntryAddr(*E);
    uint64_t Plt = this->getVA() + Off;
    Target->writePltEntry(Buf + Off, Got, Plt);
    Off += Target->getPltEntrySize();
  }
}

template <class ELFT> void PltSection<ELFT>::addEntry(SymbolBody *Sym) {
  Sym->PltIndex = Entries.size();
  Entries.push_back(Sym);
}

template <class ELFT>
typename PltSection<ELFT>::uintX_t
PltSection<ELFT>::getEntryAddr(const SymbolBody &B) const {
  return this->getVA() + B.PltIndex * Target->getPltEntrySize();
}

template <class ELFT>
void PltSection<ELFT>::finalize() {
  this->Header.sh_size = Entries.size() * Target->getPltEntrySize();
}

template <class ELFT>
RelocationSection<ELFT>::RelocationSection(bool IsRela)
    : OutputSectionBase<ELFT>(IsRela ? ".rela.dyn" : ".rel.dyn",
                              IsRela ? llvm::ELF::SHT_RELA : llvm::ELF::SHT_REL,
                              llvm::ELF::SHF_ALLOC),
      IsRela(IsRela) {
  this->Header.sh_entsize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
  this->Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}

template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
  const unsigned EntrySize = IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
  for (const DynamicReloc<ELFT> &Rel : Relocs) {
    auto *P = reinterpret_cast<Elf_Rel *>(Buf);
    Buf += EntrySize;

    const InputSection<ELFT> &C = Rel.C;
    const Elf_Rel &RI = Rel.RI;
    uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
    const ObjectFile<ELFT> &File = *C.getFile();
    SymbolBody *Body = File.getSymbolBody(SymIndex);
    if (Body)
      Body = Body->repl();

    uint32_t Type = RI.getType(Config->Mips64EL);
    bool NeedsGot = Body && Target->relocNeedsGot(Type, *Body);
    bool CanBePreempted = canBePreempted(Body, NeedsGot);

    if (CanBePreempted) {
      if (NeedsGot)
        P->setSymbolAndType(Body->getDynamicSymbolTableIndex(),
                            Target->getGotReloc(), Config->Mips64EL);
      else
        P->setSymbolAndType(Body->getDynamicSymbolTableIndex(), Type,
                            Config->Mips64EL);
    } else {
      P->setSymbolAndType(0, Target->getRelativeReloc(), Config->Mips64EL);
    }

    if (NeedsGot)
      P->r_offset = Out<ELFT>::Got->getEntryAddr(*Body);
    else
      P->r_offset = RI.r_offset + C.OutSec->getVA() + C.OutSecOff;

    uintX_t OrigAddend = 0;
    if (IsRela && !NeedsGot)
      OrigAddend = static_cast<const Elf_Rela &>(RI).r_addend;

    uintX_t Addend;
    if (CanBePreempted)
      Addend = OrigAddend;
    else if (Body)
      Addend = getSymVA<ELFT>(cast<ELFSymbolBody<ELFT>>(*Body)) + OrigAddend;
    else if (IsRela)
      Addend = getLocalRelTarget(File, static_cast<const Elf_Rela &>(RI));
    else
      Addend = getLocalRelTarget(File, RI);

    if (IsRela)
      static_cast<Elf_Rela *>(P)->r_addend = Addend;
  }
}

template <class ELFT> void RelocationSection<ELFT>::finalize() {
  this->Header.sh_link = Out<ELFT>::DynSymTab->SectionIndex;
  this->Header.sh_size = Relocs.size() * this->Header.sh_entsize;
}

template <class ELFT>
InterpSection<ELFT>::InterpSection()
    : OutputSectionBase<ELFT>(".interp", llvm::ELF::SHT_PROGBITS,
                              llvm::ELF::SHF_ALLOC) {
  this->Header.sh_size = Config->DynamicLinker.size() + 1;
  this->Header.sh_addralign = 1;
}

template <class ELFT>
void OutputSectionBase<ELFT>::writeHeaderTo(Elf_Shdr *SHdr) {
  *SHdr = Header;
}

template <class ELFT> void InterpSection<ELFT>::writeTo(uint8_t *Buf) {
  memcpy(Buf, Config->DynamicLinker.data(), Config->DynamicLinker.size());
}

template <class ELFT>
HashTableSection<ELFT>::HashTableSection()
    : OutputSectionBase<ELFT>(".hash", llvm::ELF::SHT_HASH,
                              llvm::ELF::SHF_ALLOC) {
  this->Header.sh_entsize = sizeof(Elf_Word);
  this->Header.sh_addralign = sizeof(Elf_Word);
}

static uint32_t hash(StringRef Name) {
  uint32_t H = 0;
  for (char C : Name) {
    H = (H << 4) + C;
    uint32_t G = H & 0xf0000000;
    if (G)
      H ^= G >> 24;
    H &= ~G;
  }
  return H;
}

template <class ELFT> void HashTableSection<ELFT>::addSymbol(SymbolBody *S) {
  StringRef Name = S->getName();
  Out<ELFT>::DynSymTab->addSymbol(Name);
  Hashes.push_back(hash(Name));
  S->setDynamicSymbolTableIndex(Hashes.size());
}

template <class ELFT> void HashTableSection<ELFT>::finalize() {
  this->Header.sh_link = Out<ELFT>::DynSymTab->SectionIndex;

  assert(Out<ELFT>::DynSymTab->getNumSymbols() == Hashes.size() + 1);
  unsigned NumEntries = 2;                 // nbucket and nchain.
  NumEntries += Out<ELFT>::DynSymTab->getNumSymbols(); // The chain entries.

  // Create as many buckets as there are symbols.
  // FIXME: This is simplistic. We can try to optimize it, but implementing
  // support for SHT_GNU_HASH is probably even more profitable.
  NumEntries += Out<ELFT>::DynSymTab->getNumSymbols();
  this->Header.sh_size = NumEntries * sizeof(Elf_Word);
}

template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
  unsigned NumSymbols = Out<ELFT>::DynSymTab->getNumSymbols();
  auto *P = reinterpret_cast<Elf_Word *>(Buf);
  *P++ = NumSymbols; // nbucket
  *P++ = NumSymbols; // nchain

  Elf_Word *Buckets = P;
  Elf_Word *Chains = P + NumSymbols;

  for (unsigned I = 1; I < NumSymbols; ++I) {
    uint32_t Hash = Hashes[I - 1] % NumSymbols;
    Chains[I] = Buckets[Hash];
    Buckets[Hash] = I;
  }
}

template <class ELFT>
DynamicSection<ELFT>::DynamicSection(SymbolTable<ELFT> &SymTab)
    : OutputSectionBase<ELFT>(".dynamic", llvm::ELF::SHT_DYNAMIC,
                              llvm::ELF::SHF_ALLOC | llvm::ELF::SHF_WRITE),
      SymTab(SymTab) {
  Elf_Shdr &Header = this->Header;
  Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
  Header.sh_entsize = ELFT::Is64Bits ? 16 : 8;
}

template <class ELFT> void DynamicSection<ELFT>::finalize() {
  if (this->Header.sh_size)
    return; // Already finalized.

  Elf_Shdr &Header = this->Header;
  Header.sh_link = Out<ELFT>::DynStrTab->SectionIndex;

  unsigned NumEntries = 0;
  if (Out<ELFT>::RelaDyn->hasRelocs()) {
    ++NumEntries; // DT_RELA / DT_REL
    ++NumEntries; // DT_RELASZ / DT_RELSZ
    ++NumEntries; // DT_RELAENT / DT_RELENT
  }
  ++NumEntries; // DT_SYMTAB
  ++NumEntries; // DT_SYMENT
  ++NumEntries; // DT_STRTAB
  ++NumEntries; // DT_STRSZ
  ++NumEntries; // DT_HASH

  if (!Config->RPath.empty()) {
    ++NumEntries; // DT_RUNPATH / DT_RPATH
    Out<ELFT>::DynStrTab->add(Config->RPath);
  }

  if (!Config->SoName.empty()) {
    ++NumEntries; // DT_SONAME
    Out<ELFT>::DynStrTab->add(Config->SoName);
  }

  if (PreInitArraySec)
    NumEntries += 2;
  if (InitArraySec)
    NumEntries += 2;
  if (FiniArraySec)
    NumEntries += 2;

  for (const std::unique_ptr<SharedFile<ELFT>> &F : SymTab.getSharedFiles()) {
    if (!F->isNeeded())
      continue;
    Out<ELFT>::DynStrTab->add(F->getSoName());
    ++NumEntries;
  }

  if (Symbol *S = SymTab.getSymbols().lookup(Config->Init))
    InitSym = dyn_cast<ELFSymbolBody<ELFT>>(S->Body);
  if (Symbol *S = SymTab.getSymbols().lookup(Config->Fini))
    FiniSym = dyn_cast<ELFSymbolBody<ELFT>>(S->Body);
  if (InitSym)
    ++NumEntries; // DT_INIT
  if (FiniSym)
    ++NumEntries; // DT_FINI
  if (Config->ZNow || Config->Bsymbolic)
    ++NumEntries; // DT_FLAGS_1
  ++NumEntries; // DT_NULL

  Header.sh_size = NumEntries * Header.sh_entsize;
}

template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
  auto *P = reinterpret_cast<Elf_Dyn *>(Buf);

  auto WritePtr = [&](int32_t Tag, uint64_t Val) {
    P->d_tag = Tag;
    P->d_un.d_ptr = Val;
    ++P;
  };

  auto WriteVal = [&](int32_t Tag, uint32_t Val) {
    P->d_tag = Tag;
    P->d_un.d_val = Val;
    ++P;
  };

  if (Out<ELFT>::RelaDyn->hasRelocs()) {
    bool IsRela = Out<ELFT>::RelaDyn->isRela();
    WritePtr(IsRela ? DT_RELA : DT_REL, Out<ELFT>::RelaDyn->getVA());
    WriteVal(IsRela ? DT_RELASZ : DT_RELSZ, Out<ELFT>::RelaDyn->getSize());
    WriteVal(IsRela ? DT_RELAENT : DT_RELENT,
             IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel));
  }

  WritePtr(DT_SYMTAB, Out<ELFT>::DynSymTab->getVA());
  WritePtr(DT_SYMENT, sizeof(Elf_Sym));
  WritePtr(DT_STRTAB, Out<ELFT>::DynStrTab->getVA());
  WriteVal(DT_STRSZ, Out<ELFT>::DynStrTab->data().size());
  WritePtr(DT_HASH, Out<ELFT>::HashTab->getVA());

  if (!Config->RPath.empty())

    // If --enable-new-dtags is set lld emits DT_RUNPATH
    // instead of DT_RPATH. The two tags are functionally
    // equivalent except for the following:
    // - DT_RUNPATH is searched after LD_LIBRARY_PATH, while
    // DT_RPATH is searched before.
    // - DT_RUNPATH is used only to search for direct
    // dependencies of the object it's contained in, while
    // DT_RPATH is used for indirect dependencies as well.
    WriteVal(Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
             Out<ELFT>::DynStrTab->getFileOff(Config->RPath));

  if (!Config->SoName.empty())
    WriteVal(DT_SONAME, Out<ELFT>::DynStrTab->getFileOff(Config->SoName));

  auto WriteArray = [&](int32_t T1, int32_t T2,
                        const OutputSectionBase<ELFT> *Sec) {
    if (!Sec)
      return;
    WritePtr(T1, Sec->getVA());
    WriteVal(T2, Sec->getSize());
  };
  WriteArray(DT_PREINIT_ARRAY, DT_PREINIT_ARRAYSZ, PreInitArraySec);
  WriteArray(DT_INIT_ARRAY, DT_INIT_ARRAYSZ, InitArraySec);
  WriteArray(DT_FINI_ARRAY, DT_FINI_ARRAYSZ, FiniArraySec);

  for (const std::unique_ptr<SharedFile<ELFT>> &F : SymTab.getSharedFiles())
    if (F->isNeeded())
      WriteVal(DT_NEEDED, Out<ELFT>::DynStrTab->getFileOff(F->getSoName()));

  if (InitSym)
    WritePtr(DT_INIT, getSymVA<ELFT>(*InitSym));
  if (FiniSym)
    WritePtr(DT_FINI, getSymVA<ELFT>(*FiniSym));

  uint32_t Flags = 0;
  if (Config->Bsymbolic)
    Flags |= DF_SYMBOLIC;
  if (Flags)
    WriteVal(DT_FLAGS, Flags);
  Flags = 0;
  if (Config->ZNow)
    Flags |= DF_1_NOW;
  if (Flags)
    WriteVal(DT_FLAGS_1, Flags);

  WriteVal(DT_NULL, 0);
}

template <class ELFT>
OutputSection<ELFT>::OutputSection(StringRef Name, uint32_t sh_type,
                                   uintX_t sh_flags)
    : OutputSectionBase<ELFT>(Name, sh_type, sh_flags) {}

template <class ELFT>
void OutputSection<ELFT>::addSection(InputSection<ELFT> *C) {
  Sections.push_back(C);
  C->OutSec = this;
  uint32_t Align = C->getAlign();
  if (Align > this->Header.sh_addralign)
    this->Header.sh_addralign = Align;

  uintX_t Off = this->Header.sh_size;
  Off = RoundUpToAlignment(Off, Align);
  C->OutSecOff = Off;
  Off += C->getSize();
  this->Header.sh_size = Off;
}

template <class ELFT>
typename ELFFile<ELFT>::uintX_t lld::elf2::getSymVA(const SymbolBody &S) {
  switch (S.kind()) {
  case SymbolBody::DefinedSyntheticKind: {
    auto &D = cast<DefinedSynthetic<ELFT>>(S);
    return D.Section.getVA() + D.Sym.st_value;
  }
  case SymbolBody::DefinedAbsoluteKind:
    return cast<DefinedAbsolute<ELFT>>(S).Sym.st_value;
  case SymbolBody::DefinedRegularKind: {
    const auto &DR = cast<DefinedRegular<ELFT>>(S);
    const InputSectionBase<ELFT> &SC = DR.Section;
    return SC.OutSec->getVA() + SC.getOffset(DR.Sym);
  }
  case SymbolBody::DefinedCommonKind:
    return Out<ELFT>::Bss->getVA() + cast<DefinedCommon<ELFT>>(S).OffsetInBSS;
  case SymbolBody::SharedKind:
  case SymbolBody::UndefinedKind:
    return 0;
  case SymbolBody::LazyKind:
    assert(S.isUsedInRegularObj() && "Lazy symbol reached writer");
    return 0;
  }
  llvm_unreachable("Invalid symbol kind");
}

// Returns a VA which a relocatin RI refers to. Used only for local symbols.
// For non-local symbols, use getSymVA instead.
template <class ELFT, bool IsRela>
typename ELFFile<ELFT>::uintX_t
lld::elf2::getLocalRelTarget(const ObjectFile<ELFT> &File,
                             const Elf_Rel_Impl<ELFT, IsRela> &RI) {
  typedef typename ELFFile<ELFT>::Elf_Sym Elf_Sym;
  typedef typename ELFFile<ELFT>::uintX_t uintX_t;

  uintX_t Addend = getAddend<ELFT>(RI);

  // PPC64 has a special relocation representing the TOC base pointer
  // that does not have a corresponding symbol.
  if (Config->EMachine == EM_PPC64 && RI.getType(false) == R_PPC64_TOC)
    return getPPC64TocBase() + Addend;

  const Elf_Sym *Sym =
      File.getObj().getRelocationSymbol(&RI, File.getSymbolTable());

  if (!Sym)
    error("Unsupported relocation without symbol");

  // According to the ELF spec reference to a local symbol from outside
  // the group are not allowed. Unfortunately .eh_frame breaks that rule
  // and must be treated specially. For now we just replace the symbol with
  // 0.
  InputSectionBase<ELFT> *Section = File.getSection(*Sym);
  if (Section == &InputSection<ELFT>::Discarded)
    return Addend;

  uintX_t VA = Section->OutSec->getVA();
  if (isa<InputSection<ELFT>>(Section))
    return VA + Section->getOffset(*Sym) + Addend;

  uintX_t Offset = Sym->st_value;
  if (Sym->getType() == STT_SECTION) {
    Offset += Addend;
    Addend = Offset % Section->getSectionHdr()->sh_entsize;
    Offset -= Addend;
  }
  return VA + cast<MergeInputSection<ELFT>>(Section)->getOffset(Offset) +
         Addend;
}

// Returns true if a symbol can be replaced at load-time by a symbol
// with the same name defined in other ELF executable or DSO.
bool lld::elf2::canBePreempted(const SymbolBody *Body, bool NeedsGot) {
  if (!Body)
    return false;  // Body is a local symbol.
  if (Body->isShared())
    return true;

  if (Body->isUndefined()) {
    if (!Body->isWeak())
      return true;

    // This is an horrible corner case. Ideally we would like to say that any
    // undefined symbol can be preempted so that the dynamic linker has a
    // chance of finding it at runtime.
    //
    // The problem is that the code sequence used to test for weak undef
    // functions looks like
    // if (func) func()
    // If the code is -fPIC the first reference is a load from the got and
    // everything works.
    // If the code is not -fPIC there is no reasonable way to solve it:
    // * A relocation writing to the text segment will fail (it is ro).
    // * A copy relocation doesn't work for functions.
    // * The trick of using a plt entry as the address would fail here since
    //   the plt entry would have a non zero address.
    // Since we cannot do anything better, we just resolve the symbol to 0 and
    // don't produce a dynamic relocation.
    //
    // As an extra hack, assume that if we are producing a shared library the
    // user knows what he or she is doing and can handle a dynamic relocation.
    return Config->Shared || NeedsGot;
  }
  if (!Config->Shared)
    return false;
  return Body->getMostConstrainingVisibility() == STV_DEFAULT;
}

template <class ELFT> void OutputSection<ELFT>::writeTo(uint8_t *Buf) {
  for (InputSection<ELFT> *C : Sections)
    C->writeTo(Buf);
}

template <class ELFT>
MergeOutputSection<ELFT>::MergeOutputSection(StringRef Name, uint32_t sh_type,
                                             uintX_t sh_flags)
    : OutputSectionBase<ELFT>(Name, sh_type, sh_flags) {}

template <class ELFT> void MergeOutputSection<ELFT>::writeTo(uint8_t *Buf) {
  for (const std::pair<ArrayRef<uint8_t>, uintX_t> &P : Offsets) {
    ArrayRef<uint8_t> Data = P.first;
    memcpy(Buf, Data.data(), Data.size());
    Buf += Data.size();
  }
}

template <class ELFT>
void MergeOutputSection<ELFT>::addSection(MergeInputSection<ELFT> *S) {
  S->OutSec = this;
  uint32_t Align = S->getAlign();
  if (Align > this->Header.sh_addralign)
    this->Header.sh_addralign = Align;

  uintX_t Off = this->Header.sh_size;
  ArrayRef<uint8_t> Data = S->getSectionData();
  uintX_t EntSize = S->getSectionHdr()->sh_entsize;
  if (Data.size() % EntSize)
    error("SHF_MERGE section size must be a multiple of sh_entsize");
  for (unsigned I = 0, N = Data.size(); I != N; I += EntSize) {
    auto P = Offsets.insert(std::make_pair(Data.slice(I, EntSize), Off));
    if (P.second)
      Off += EntSize;
  }
  this->Header.sh_size = Off;
}

template <class ELFT>
unsigned MergeOutputSection<ELFT>::getOffset(ArrayRef<uint8_t> Val) {
  return Offsets.find(Val)->second;
}

template <class ELFT>
StringTableSection<ELFT>::StringTableSection(bool Dynamic)
    : OutputSectionBase<ELFT>(Dynamic ? ".dynstr" : ".strtab",
                              llvm::ELF::SHT_STRTAB,
                              Dynamic ? (uintX_t)llvm::ELF::SHF_ALLOC : 0),
      Dynamic(Dynamic) {
  this->Header.sh_addralign = 1;
}

template <class ELFT> void StringTableSection<ELFT>::writeTo(uint8_t *Buf) {
  StringRef Data = StrTabBuilder.data();
  memcpy(Buf, Data.data(), Data.size());
}

template <class ELFT> bool lld::elf2::includeInSymtab(const SymbolBody &B) {
  if (!B.isUsedInRegularObj())
    return false;

  // Don't include synthetic symbols like __init_array_start in every output.
  if (auto *U = dyn_cast<DefinedAbsolute<ELFT>>(&B))
    if (&U->Sym == &DefinedAbsolute<ELFT>::IgnoreUndef)
      return false;

  return true;
}

bool lld::elf2::includeInDynamicSymtab(const SymbolBody &B) {
  uint8_t V = B.getMostConstrainingVisibility();
  if (V != STV_DEFAULT && V != STV_PROTECTED)
    return false;

  if (Config->ExportDynamic || Config->Shared)
    return true;
  return B.isUsedInDynamicReloc();
}

template <class ELFT>
bool lld::elf2::shouldKeepInSymtab(const ObjectFile<ELFT> &File,
                                   StringRef SymName,
                                   const typename ELFFile<ELFT>::Elf_Sym &Sym) {
  if (Sym.getType() == STT_SECTION)
    return false;

  // If sym references a section in a discarded group, don't keep it.
  if (File.getSection(Sym) == &InputSection<ELFT>::Discarded)
    return false;

  if (Config->DiscardNone)
    return true;

  // ELF defines dynamic locals as symbols which name starts with ".L".
  return !(Config->DiscardLocals && SymName.startswith(".L"));
}

template <class ELFT>
SymbolTableSection<ELFT>::SymbolTableSection(
    SymbolTable<ELFT> &Table, StringTableSection<ELFT> &StrTabSec)
    : OutputSectionBase<ELFT>(
          StrTabSec.isDynamic() ? ".dynsym" : ".symtab",
          StrTabSec.isDynamic() ? llvm::ELF::SHT_DYNSYM : llvm::ELF::SHT_SYMTAB,
          StrTabSec.isDynamic() ? (uintX_t)llvm::ELF::SHF_ALLOC : 0),
      Table(Table), StrTabSec(StrTabSec) {
  typedef OutputSectionBase<ELFT> Base;
  typename Base::Elf_Shdr &Header = this->Header;

  Header.sh_entsize = sizeof(Elf_Sym);
  Header.sh_addralign = ELFT::Is64Bits ? 8 : 4;
}

template <class ELFT> void SymbolTableSection<ELFT>::finalize() {
  this->Header.sh_size = getNumSymbols() * sizeof(Elf_Sym);
  this->Header.sh_link = StrTabSec.SectionIndex;
  this->Header.sh_info = NumLocals + 1;
}

template <class ELFT>
void SymbolTableSection<ELFT>::addSymbol(StringRef Name, bool isLocal) {
  StrTabSec.add(Name);
  ++NumVisible;
  if (isLocal)
    ++NumLocals;
}

template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
  Buf += sizeof(Elf_Sym);

  // All symbols with STB_LOCAL binding precede the weak and global symbols.
  // .dynsym only contains global symbols.
  if (!Config->DiscardAll && !StrTabSec.isDynamic())
    writeLocalSymbols(Buf);

  writeGlobalSymbols(Buf);
}

template <class ELFT>
void SymbolTableSection<ELFT>::writeLocalSymbols(uint8_t *&Buf) {
  // Iterate over all input object files to copy their local symbols
  // to the output symbol table pointed by Buf.
  for (const std::unique_ptr<ObjectFile<ELFT>> &File : Table.getObjectFiles()) {
    Elf_Sym_Range Syms = File->getLocalSymbols();
    for (const Elf_Sym &Sym : Syms) {
      ErrorOr<StringRef> SymNameOrErr = Sym.getName(File->getStringTable());
      error(SymNameOrErr);
      StringRef SymName = *SymNameOrErr;
      if (!shouldKeepInSymtab<ELFT>(*File, SymName, Sym))
        continue;

      auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
      Buf += sizeof(*ESym);
      ESym->st_name = StrTabSec.getFileOff(SymName);
      ESym->st_size = Sym.st_size;
      ESym->setBindingAndType(Sym.getBinding(), Sym.getType());
      uintX_t VA = 0;
      if (Sym.st_shndx == SHN_ABS) {
        ESym->st_shndx = SHN_ABS;
        VA = Sym.st_value;
      } else {
        const InputSectionBase<ELFT> *Section = File->getSection(Sym);
        const OutputSectionBase<ELFT> *OutSec = Section->OutSec;
        ESym->st_shndx = OutSec->SectionIndex;
        VA += OutSec->getVA() + Section->getOffset(Sym);
      }
      ESym->st_value = VA;
    }
  }
}

template <class ELFT>
void SymbolTableSection<ELFT>::writeGlobalSymbols(uint8_t *Buf) {
  // Write the internal symbol table contents to the output symbol table
  // pointed by Buf.
  uint8_t *Start = Buf;
  for (const std::pair<StringRef, Symbol *> &P : Table.getSymbols()) {
    StringRef Name = P.first;
    Symbol *Sym = P.second;
    SymbolBody *Body = Sym->Body;
    if (!includeInSymtab<ELFT>(*Body))
      continue;
    if (StrTabSec.isDynamic() && !includeInDynamicSymtab(*Body))
      continue;

    auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
    Buf += sizeof(*ESym);

    ESym->st_name = StrTabSec.getFileOff(Name);

    const OutputSectionBase<ELFT> *OutSec = nullptr;
    const InputSectionBase<ELFT> *Section = nullptr;

    switch (Body->kind()) {
    case SymbolBody::DefinedSyntheticKind:
      OutSec = &cast<DefinedSynthetic<ELFT>>(Body)->Section;
      break;
    case SymbolBody::DefinedRegularKind:
      Section = &cast<DefinedRegular<ELFT>>(Body)->Section;
      break;
    case SymbolBody::DefinedCommonKind:
      OutSec = Out<ELFT>::Bss;
      break;
    case SymbolBody::UndefinedKind:
    case SymbolBody::DefinedAbsoluteKind:
    case SymbolBody::SharedKind:
    case SymbolBody::LazyKind:
      break;
    }

    unsigned char Binding = Body->isWeak() ? STB_WEAK : STB_GLOBAL;
    unsigned char Type = STT_NOTYPE;
    uintX_t Size = 0;
    if (const auto *EBody = dyn_cast<ELFSymbolBody<ELFT>>(Body)) {
      const Elf_Sym &InputSym = EBody->Sym;
      Binding = InputSym.getBinding();
      Type = InputSym.getType();
      Size = InputSym.st_size;
    }

    unsigned char Visibility = Body->getMostConstrainingVisibility();
    if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
      Binding = STB_LOCAL;

    ESym->setBindingAndType(Binding, Type);
    ESym->st_size = Size;
    ESym->setVisibility(Visibility);
    ESym->st_value = getSymVA<ELFT>(*Body);

    if (Section)
      OutSec = Section->OutSec;

    if (isa<DefinedAbsolute<ELFT>>(Body))
      ESym->st_shndx = SHN_ABS;
    else if (OutSec)
      ESym->st_shndx = OutSec->SectionIndex;
  }
  if (!StrTabSec.isDynamic())
    std::stable_sort(
        reinterpret_cast<Elf_Sym *>(Start), reinterpret_cast<Elf_Sym *>(Buf),
        [](const Elf_Sym &A, const Elf_Sym &B) -> bool {
          return A.getBinding() == STB_LOCAL && B.getBinding() != STB_LOCAL;
        });
}

namespace lld {
namespace elf2 {
template class OutputSectionBase<ELF32LE>;
template class OutputSectionBase<ELF32BE>;
template class OutputSectionBase<ELF64LE>;
template class OutputSectionBase<ELF64BE>;

template class GotSection<ELF32LE>;
template class GotSection<ELF32BE>;
template class GotSection<ELF64LE>;
template class GotSection<ELF64BE>;

template class PltSection<ELF32LE>;
template class PltSection<ELF32BE>;
template class PltSection<ELF64LE>;
template class PltSection<ELF64BE>;

template class RelocationSection<ELF32LE>;
template class RelocationSection<ELF32BE>;
template class RelocationSection<ELF64LE>;
template class RelocationSection<ELF64BE>;

template class InterpSection<ELF32LE>;
template class InterpSection<ELF32BE>;
template class InterpSection<ELF64LE>;
template class InterpSection<ELF64BE>;

template class HashTableSection<ELF32LE>;
template class HashTableSection<ELF32BE>;
template class HashTableSection<ELF64LE>;
template class HashTableSection<ELF64BE>;

template class DynamicSection<ELF32LE>;
template class DynamicSection<ELF32BE>;
template class DynamicSection<ELF64LE>;
template class DynamicSection<ELF64BE>;

template class OutputSection<ELF32LE>;
template class OutputSection<ELF32BE>;
template class OutputSection<ELF64LE>;
template class OutputSection<ELF64BE>;

template class MergeOutputSection<ELF32LE>;
template class MergeOutputSection<ELF32BE>;
template class MergeOutputSection<ELF64LE>;
template class MergeOutputSection<ELF64BE>;

template class StringTableSection<ELF32LE>;
template class StringTableSection<ELF32BE>;
template class StringTableSection<ELF64LE>;
template class StringTableSection<ELF64BE>;

template class SymbolTableSection<ELF32LE>;
template class SymbolTableSection<ELF32BE>;
template class SymbolTableSection<ELF64LE>;
template class SymbolTableSection<ELF64BE>;

template ELFFile<ELF32LE>::uintX_t getSymVA<ELF32LE>(const SymbolBody &);
template ELFFile<ELF32BE>::uintX_t getSymVA<ELF32BE>(const SymbolBody &);
template ELFFile<ELF64LE>::uintX_t getSymVA<ELF64LE>(const SymbolBody &);
template ELFFile<ELF64BE>::uintX_t getSymVA<ELF64BE>(const SymbolBody &);

template ELFFile<ELF32LE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF32LE> &,
                  const ELFFile<ELF32LE>::Elf_Rel &);
template ELFFile<ELF32BE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF32BE> &,
                  const ELFFile<ELF32BE>::Elf_Rel &);
template ELFFile<ELF64LE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF64LE> &,
                  const ELFFile<ELF64LE>::Elf_Rel &);
template ELFFile<ELF64BE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF64BE> &,
                  const ELFFile<ELF64BE>::Elf_Rel &);

template ELFFile<ELF32LE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF32LE> &,
                  const ELFFile<ELF32LE>::Elf_Rela &);
template ELFFile<ELF32BE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF32BE> &,
                  const ELFFile<ELF32BE>::Elf_Rela &);
template ELFFile<ELF64LE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF64LE> &,
                  const ELFFile<ELF64LE>::Elf_Rela &);
template ELFFile<ELF64BE>::uintX_t
getLocalRelTarget(const ObjectFile<ELF64BE> &,
                  const ELFFile<ELF64BE>::Elf_Rela &);

template bool includeInSymtab<ELF32LE>(const SymbolBody &);
template bool includeInSymtab<ELF32BE>(const SymbolBody &);
template bool includeInSymtab<ELF64LE>(const SymbolBody &);
template bool includeInSymtab<ELF64BE>(const SymbolBody &);

template bool shouldKeepInSymtab<ELF32LE>(const ObjectFile<ELF32LE> &,
                                          StringRef,
                                          const ELFFile<ELF32LE>::Elf_Sym &);
template bool shouldKeepInSymtab<ELF32BE>(const ObjectFile<ELF32BE> &,
                                          StringRef,
                                          const ELFFile<ELF32BE>::Elf_Sym &);
template bool shouldKeepInSymtab<ELF64LE>(const ObjectFile<ELF64LE> &,
                                          StringRef,
                                          const ELFFile<ELF64LE>::Elf_Sym &);
template bool shouldKeepInSymtab<ELF64BE>(const ObjectFile<ELF64BE> &,
                                          StringRef,
                                          const ELFFile<ELF64BE>::Elf_Sym &);
}
}