[ELF] Simpler scheme for handling common symbols

Convert all common symbols to regular symbols after scan.
This means that the downstream code does not to handle common symbols as a special case.

Differential Revision: https://reviews.llvm.org/D38137

llvm-svn: 314495

8 files changed, 2486 insertions, 45 deletions

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 9aab6fd3d3a..e272f00fd80 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -1086,6 +1086,14 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   if (!Config->Relocatable)
     InputSections.push_back(createCommentSection<ELFT>());
 
+  // Create a .bss section for each common symbol and then replace the common
+  // symbol with a DefinedRegular symbol. As a result, all common symbols are
+  // "instantiated" as regular defined symbols, so that we don't need to care
+  // about common symbols beyond this point. Note that if -r is given, we just
+  // need to pass through common symbols as-is.
+  if (Config->DefineCommon)
+    createCommonSections<ELFT>();
+
   // Do size optimizations: garbage collection, merging of SHF_MERGE sections
   // and identical code folding.
   if (Config->GcSections)
diff --git a/lld/ELF/MarkLive.cpp b/lld/ELF/MarkLive.cpp
index f3438c86821..8579b148a1b 100644
--- a/lld/ELF/MarkLive.cpp
+++ b/lld/ELF/MarkLive.cpp
@@ -64,11 +64,6 @@ static void resolveReloc(InputSectionBase &Sec, RelT &Rel,
                          std::function<void(InputSectionBase *, uint64_t)> Fn) {
   SymbolBody &B = Sec.getFile<ELFT>()->getRelocTargetSym(Rel);
 
-  if (auto *Sym = dyn_cast<DefinedCommon>(&B)) {
-    Sym->Live = true;
-    return;
-  }
-
   if (auto *D = dyn_cast<DefinedRegular>(&B)) {
     if (!D->Section)
       return;
@@ -223,13 +218,9 @@ template <class ELFT> void elf::markLive() {
   };
 
   auto MarkSymbol = [&](SymbolBody *Sym) {
-    if (auto *D = dyn_cast_or_null<DefinedRegular>(Sym)) {
+    if (auto *D = dyn_cast_or_null<DefinedRegular>(Sym))
       if (auto *IS = cast_or_null<InputSectionBase>(D->Section))
         Enqueue(IS, D->Value);
-      return;
-    }
-    if (auto *S = dyn_cast_or_null<DefinedCommon>(Sym))
-      S->Live = true;
   };
 
   // Add GC root symbols.
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 9cfe6f4701e..934358f6da4 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -99,14 +99,8 @@ static uint64_t getSymVA(const SymbolBody &Body, int64_t &Addend) {
     }
     return VA;
   }
-  case SymbolBody::DefinedCommonKind: {
-    if (!Config->DefineCommon)
-      return 0;
-    auto DC = cast<DefinedCommon>(Body);
-    if (!DC.Live)
-      return 0;
-    return DC.Section->getParent()->Addr + DC.Section->OutSecOff;
-  }
+  case SymbolBody::DefinedCommonKind:
+    llvm_unreachable("common are converted to bss");
   case SymbolBody::SharedKind: {
     auto &SS = cast<SharedSymbol>(Body);
     if (SS.CopyRelSec)
@@ -286,7 +280,7 @@ DefinedCommon::DefinedCommon(StringRef Name, uint64_t Size, uint32_t Alignment,
                              uint8_t StOther, uint8_t Type)
     : Defined(SymbolBody::DefinedCommonKind, Name, /*IsLocal=*/false, StOther,
               Type),
-      Live(!Config->GcSections), Alignment(Alignment), Size(Size) {}
+      Alignment(Alignment), Size(Size) {}
 
 // If a shared symbol is referred via a copy relocation, its alignment
 // becomes part of the ABI. This function returns a symbol alignment.
diff --git a/lld/ELF/Symbols.h b/lld/ELF/Symbols.h
index 798325e377e..6c95968c8ca 100644
--- a/lld/ELF/Symbols.h
+++ b/lld/ELF/Symbols.h
@@ -167,11 +167,6 @@ public:
     return S->kind() == SymbolBody::DefinedCommonKind;
   }
 
-  // True if this symbol is not GC'ed. Liveness is usually a notion of
-  // input sections and not of symbols, but since common symbols don't
-  // belong to any input section, their liveness is managed by this bit.
-  bool Live;
-
   // The maximum alignment we have seen for this symbol.
   uint32_t Alignment;
 
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index ec3b9b7a404..4f94755b027 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -54,24 +54,28 @@ uint64_t SyntheticSection::getVA() const {
   return 0;
 }
 
-std::vector<InputSection *> elf::createCommonSections() {
-  if (!Config->DefineCommon)
-    return {};
-
-  std::vector<InputSection *> Ret;
+// Create a .bss section for each common section and replace the common symbol
+// with a DefinedRegular symbol.
+template <class ELFT> void elf::createCommonSections() {
   for (Symbol *S : Symtab->getSymbols()) {
     auto *Sym = dyn_cast<DefinedCommon>(S->body());
-    if (!Sym || !Sym->Live)
+
+    if (!Sym)
       continue;
 
-    Sym->Section = make<BssSection>("COMMON");
-    size_t Pos = Sym->Section->reserveSpace(Sym->Size, Sym->Alignment);
-    assert(Pos == 0);
-    (void)Pos;
-    Sym->Section->File = Sym->getFile();
-    Ret.push_back(Sym->Section);
+    // Create a synthetic section for the common data.
+    auto *Section = make<BssSection>("COMMON");
+    Section->File = Sym->getFile();
+    Section->Live = !Config->GcSections;
+    Section->reserveSpace(Sym->Size, Sym->Alignment);
+    InputSections.push_back(Section);
+
+    // Replace all DefinedCommon symbols with DefinedRegular symbols so that we
+    // don't have to care about DefinedCommon symbols beyond this point.
+    replaceBody<DefinedRegular>(S, Sym->getFile(), Sym->getName(),
+                                static_cast<bool>(Sym->IsLocal), Sym->StOther,
+                                Sym->Type, 0, Sym->getSize<ELFT>(), Section);
   }
-  return Ret;
 }
 
 // Returns an LLD version string.
@@ -2378,6 +2382,11 @@ template void PltSection::addEntry<ELF32BE>(SymbolBody &Sym);
 template void PltSection::addEntry<ELF64LE>(SymbolBody &Sym);
 template void PltSection::addEntry<ELF64BE>(SymbolBody &Sym);
 
+template void elf::createCommonSections<ELF32LE>();
+template void elf::createCommonSections<ELF32BE>();
+template void elf::createCommonSections<ELF64LE>();
+template void elf::createCommonSections<ELF64BE>();
+
 template MergeInputSection *elf::createCommentSection<ELF32LE>();
 template MergeInputSection *elf::createCommentSection<ELF32BE>();
 template MergeInputSection *elf::createCommentSection<ELF64LE>();
diff --git a/lld/ELF/SyntheticSections.cpp~RF2791d30b.TMP b/lld/ELF/SyntheticSections.cpp~RF2791d30b.TMP
new file mode 100644
index 00000000000..1790134f8fd
--- /dev/null
+++ b/lld/ELF/SyntheticSections.cpp~RF2791d30b.TMP
@@ -0,0 +1,2451 @@
+//===- SyntheticSections.cpp ----------------------------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains linker-synthesized sections. Currently,
+// synthetic sections are created either output sections or input sections,
+// but we are rewriting code so that all synthetic sections are created as
+// input sections.
+//
+//===----------------------------------------------------------------------===//
+
+#include "SyntheticSections.h"
+#include "Config.h"
+#include "Error.h"
+#include "InputFiles.h"
+#include "LinkerScript.h"
+#include "Memory.h"
+#include "OutputSections.h"
+#include "Strings.h"
+#include "SymbolTable.h"
+#include "Target.h"
+#include "Threads.h"
+#include "Writer.h"
+#include "lld/Config/Version.h"
+#include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
+#include "llvm/Object/Decompressor.h"
+#include "llvm/Object/ELFObjectFile.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/MD5.h"
+#include "llvm/Support/RandomNumberGenerator.h"
+#include "llvm/Support/SHA1.h"
+#include "llvm/Support/xxhash.h"
+#include <cstdlib>
+
+using namespace llvm;
+using namespace llvm::dwarf;
+using namespace llvm::ELF;
+using namespace llvm::object;
+using namespace llvm::support;
+using namespace llvm::support::endian;
+
+using namespace lld;
+using namespace lld::elf;
+
+uint64_t SyntheticSection::getVA() const {
+  if (OutputSection *Sec = getParent())
+    return Sec->Addr + OutSecOff;
+  return 0;
+}
+
+// Create a .bss section for each common section and replace the common symbol
+// with a DefinedRegular symbol.
+template <class ELFT> void elf::createCommonSections() {
+  for (Symbol *S : Symtab->getSymbols()) {
+    auto *Sym = dyn_cast<DefinedCommon>(S->body());
+
+    if (!Sym)
+      continue;
+
+    // Create a synthetic section for the common data.
+    auto *Section = make<BssSection>("COMMON");
+    Section->File = Sym->getFile();
+    Section->Live = !Config->GcSections;
+    Section->reserveSpace(Sym->Size, Sym->Alignment);
+    InputSections.push_back(Section);
+
+    // Replace all DefinedCommon symbols with DefinedRegular symbols so that we
+    // don't have to care about DefinedCommon symbols beyond this point.
+    replaceBody<DefinedRegular>(S, Sym->getFile(), Sym->getName(), Sym->IsLocal,
+                                Sym->StOther, Sym->Type, 0,
+                                Sym->getSize<ELFT>(), Section);
+  }
+}
+
+// Returns an LLD version string.
+static ArrayRef<uint8_t> getVersion() {
+  // Check LLD_VERSION first for ease of testing.
+  // You can get consitent output by using the environment variable.
+  // This is only for testing.
+  StringRef S = getenv("LLD_VERSION");
+  if (S.empty())
+    S = Saver.save(Twine("Linker: ") + getLLDVersion());
+
+  // +1 to include the terminating '\0'.
+  return {(const uint8_t *)S.data(), S.size() + 1};
+}
+
+// Creates a .comment section containing LLD version info.
+// With this feature, you can identify LLD-generated binaries easily
+// by "readelf --string-dump .comment <file>".
+// The returned object is a mergeable string section.
+template <class ELFT> MergeInputSection *elf::createCommentSection() {
+  typename ELFT::Shdr Hdr = {};
+  Hdr.sh_flags = SHF_MERGE | SHF_STRINGS;
+  Hdr.sh_type = SHT_PROGBITS;
+  Hdr.sh_entsize = 1;
+  Hdr.sh_addralign = 1;
+
+  auto *Ret =
+      make<MergeInputSection>((ObjFile<ELFT> *)nullptr, &Hdr, ".comment");
+  Ret->Data = getVersion();
+  return Ret;
+}
+
+// .MIPS.abiflags section.
+template <class ELFT>
+MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags Flags)
+    : SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"),
+      Flags(Flags) {
+  this->Entsize = sizeof(Elf_Mips_ABIFlags);
+}
+
+template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *Buf) {
+  memcpy(Buf, &Flags, sizeof(Flags));
+}
+
+template <class ELFT>
+MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() {
+  Elf_Mips_ABIFlags Flags = {};
+  bool Create = false;
+
+  for (InputSectionBase *Sec : InputSections) {
+    if (Sec->Type != SHT_MIPS_ABIFLAGS)
+      continue;
+    Sec->Live = false;
+    Create = true;
+
+    std::string Filename = toString(Sec->getFile<ELFT>());
+    const size_t Size = Sec->Data.size();
+    // Older version of BFD (such as the default FreeBSD linker) concatenate
+    // .MIPS.abiflags instead of merging. To allow for this case (or potential
+    // zero padding) we ignore everything after the first Elf_Mips_ABIFlags
+    if (Size < sizeof(Elf_Mips_ABIFlags)) {
+      error(Filename + ": invalid size of .MIPS.abiflags section: got " +
+            Twine(Size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags)));
+      return nullptr;
+    }
+    auto *S = reinterpret_cast<const Elf_Mips_ABIFlags *>(Sec->Data.data());
+    if (S->version != 0) {
+      error(Filename + ": unexpected .MIPS.abiflags version " +
+            Twine(S->version));
+      return nullptr;
+    }
+
+    // LLD checks ISA compatibility in getMipsEFlags(). Here we just
+    // select the highest number of ISA/Rev/Ext.
+    Flags.isa_level = std::max(Flags.isa_level, S->isa_level);
+    Flags.isa_rev = std::max(Flags.isa_rev, S->isa_rev);
+    Flags.isa_ext = std::max(Flags.isa_ext, S->isa_ext);
+    Flags.gpr_size = std::max(Flags.gpr_size, S->gpr_size);
+    Flags.cpr1_size = std::max(Flags.cpr1_size, S->cpr1_size);
+    Flags.cpr2_size = std::max(Flags.cpr2_size, S->cpr2_size);
+    Flags.ases |= S->ases;
+    Flags.flags1 |= S->flags1;
+    Flags.flags2 |= S->flags2;
+    Flags.fp_abi = elf::getMipsFpAbiFlag(Flags.fp_abi, S->fp_abi, Filename);
+  };
+
+  if (Create)
+    return make<MipsAbiFlagsSection<ELFT>>(Flags);
+  return nullptr;
+}
+
+// .MIPS.options section.
+template <class ELFT>
+MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo Reginfo)
+    : SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"),
+      Reginfo(Reginfo) {
+  this->Entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
+}
+
+template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *Buf) {
+  auto *Options = reinterpret_cast<Elf_Mips_Options *>(Buf);
+  Options->kind = ODK_REGINFO;
+  Options->size = getSize();
+
+  if (!Config->Relocatable)
+    Reginfo.ri_gp_value = InX::MipsGot->getGp();
+  memcpy(Buf + sizeof(Elf_Mips_Options), &Reginfo, sizeof(Reginfo));
+}
+
+template <class ELFT>
+MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() {
+  // N64 ABI only.
+  if (!ELFT::Is64Bits)
+    return nullptr;
+
+  Elf_Mips_RegInfo Reginfo = {};
+  bool Create = false;
+
+  for (InputSectionBase *Sec : InputSections) {
+    if (Sec->Type != SHT_MIPS_OPTIONS)
+      continue;
+    Sec->Live = false;
+    Create = true;
+
+    std::string Filename = toString(Sec->getFile<ELFT>());
+    ArrayRef<uint8_t> D = Sec->Data;
+
+    while (!D.empty()) {
+      if (D.size() < sizeof(Elf_Mips_Options)) {
+        error(Filename + ": invalid size of .MIPS.options section");
+        break;
+      }
+
+      auto *Opt = reinterpret_cast<const Elf_Mips_Options *>(D.data());
+      if (Opt->kind == ODK_REGINFO) {
+        if (Config->Relocatable && Opt->getRegInfo().ri_gp_value)
+          error(Filename + ": unsupported non-zero ri_gp_value");
+        Reginfo.ri_gprmask |= Opt->getRegInfo().ri_gprmask;
+        Sec->getFile<ELFT>()->MipsGp0 = Opt->getRegInfo().ri_gp_value;
+        break;
+      }
+
+      if (!Opt->size)
+        fatal(Filename + ": zero option descriptor size");
+      D = D.slice(Opt->size);
+    }
+  };
+
+  if (Create)
+    return make<MipsOptionsSection<ELFT>>(Reginfo);
+  return nullptr;
+}
+
+// MIPS .reginfo section.
+template <class ELFT>
+MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo Reginfo)
+    : SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"),
+      Reginfo(Reginfo) {
+  this->Entsize = sizeof(Elf_Mips_RegInfo);
+}
+
+template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *Buf) {
+  if (!Config->Relocatable)
+    Reginfo.ri_gp_value = InX::MipsGot->getGp();
+  memcpy(Buf, &Reginfo, sizeof(Reginfo));
+}
+
+template <class ELFT>
+MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() {
+  // Section should be alive for O32 and N32 ABIs only.
+  if (ELFT::Is64Bits)
+    return nullptr;
+
+  Elf_Mips_RegInfo Reginfo = {};
+  bool Create = false;
+
+  for (InputSectionBase *Sec : InputSections) {
+    if (Sec->Type != SHT_MIPS_REGINFO)
+      continue;
+    Sec->Live = false;
+    Create = true;
+
+    if (Sec->Data.size() != sizeof(Elf_Mips_RegInfo)) {
+      error(toString(Sec->getFile<ELFT>()) +
+            ": invalid size of .reginfo section");
+      return nullptr;
+    }
+    auto *R = reinterpret_cast<const Elf_Mips_RegInfo *>(Sec->Data.data());
+    if (Config->Relocatable && R->ri_gp_value)
+      error(toString(Sec->getFile<ELFT>()) +
+            ": unsupported non-zero ri_gp_value");
+
+    Reginfo.ri_gprmask |= R->ri_gprmask;
+    Sec->getFile<ELFT>()->MipsGp0 = R->ri_gp_value;
+  };
+
+  if (Create)
+    return make<MipsReginfoSection<ELFT>>(Reginfo);
+  return nullptr;
+}
+
+InputSection *elf::createInterpSection() {
+  // StringSaver guarantees that the returned string ends with '\0'.
+  StringRef S = Saver.save(Config->DynamicLinker);
+  ArrayRef<uint8_t> Contents = {(const uint8_t *)S.data(), S.size() + 1};
+
+  auto *Sec =
+      make<InputSection>(SHF_ALLOC, SHT_PROGBITS, 1, Contents, ".interp");
+  Sec->Live = true;
+  return Sec;
+}
+
+SymbolBody *elf::addSyntheticLocal(StringRef Name, uint8_t Type, uint64_t Value,
+                                   uint64_t Size, InputSectionBase *Section) {
+  auto *S = make<DefinedRegular>(Name, /*IsLocal*/ true, STV_DEFAULT, Type,
+                                 Value, Size, Section);
+  if (InX::SymTab)
+    InX::SymTab->addSymbol(S);
+  return S;
+}
+
+static size_t getHashSize() {
+  switch (Config->BuildId) {
+  case BuildIdKind::Fast:
+    return 8;
+  case BuildIdKind::Md5:
+  case BuildIdKind::Uuid:
+    return 16;
+  case BuildIdKind::Sha1:
+    return 20;
+  case BuildIdKind::Hexstring:
+    return Config->BuildIdVector.size();
+  default:
+    llvm_unreachable("unknown BuildIdKind");
+  }
+}
+
+BuildIdSection::BuildIdSection()
+    : SyntheticSection(SHF_ALLOC, SHT_NOTE, 1, ".note.gnu.build-id"),
+      HashSize(getHashSize()) {}
+
+void BuildIdSection::writeTo(uint8_t *Buf) {
+  endianness E = Config->Endianness;
+  write32(Buf, 4, E);                   // Name size
+  write32(Buf + 4, HashSize, E);        // Content size
+  write32(Buf + 8, NT_GNU_BUILD_ID, E); // Type
+  memcpy(Buf + 12, "GNU", 4);           // Name string
+  HashBuf = Buf + 16;
+}
+
+// Split one uint8 array into small pieces of uint8 arrays.
+static std::vector<ArrayRef<uint8_t>> split(ArrayRef<uint8_t> Arr,
+                                            size_t ChunkSize) {
+  std::vector<ArrayRef<uint8_t>> Ret;
+  while (Arr.size() > ChunkSize) {
+    Ret.push_back(Arr.take_front(ChunkSize));
+    Arr = Arr.drop_front(ChunkSize);
+  }
+  if (!Arr.empty())
+    Ret.push_back(Arr);
+  return Ret;
+}
+
+// Computes a hash value of Data using a given hash function.
+// In order to utilize multiple cores, we first split data into 1MB
+// chunks, compute a hash for each chunk, and then compute a hash value
+// of the hash values.
+void BuildIdSection::computeHash(
+    llvm::ArrayRef<uint8_t> Data,
+    std::function<void(uint8_t *Dest, ArrayRef<uint8_t> Arr)> HashFn) {
+  std::vector<ArrayRef<uint8_t>> Chunks = split(Data, 1024 * 1024);
+  std::vector<uint8_t> Hashes(Chunks.size() * HashSize);
+
+  // Compute hash values.
+  parallelForEachN(0, Chunks.size(), [&](size_t I) {
+    HashFn(Hashes.data() + I * HashSize, Chunks[I]);
+  });
+
+  // Write to the final output buffer.
+  HashFn(HashBuf, Hashes);
+}
+
+BssSection::BssSection(StringRef Name)
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 0, Name) {}
+
+size_t BssSection::reserveSpace(uint64_t Size, uint32_t Alignment) {
+  if (OutputSection *Sec = getParent())
+    Sec->updateAlignment(Alignment);
+  this->Size = alignTo(this->Size, Alignment) + Size;
+  this->Alignment = std::max(this->Alignment, Alignment);
+  return this->Size - Size;
+}
+
+void BuildIdSection::writeBuildId(ArrayRef<uint8_t> Buf) {
+  switch (Config->BuildId) {
+  case BuildIdKind::Fast:
+    computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
+      write64le(Dest, xxHash64(toStringRef(Arr)));
+    });
+    break;
+  case BuildIdKind::Md5:
+    computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
+      memcpy(Dest, MD5::hash(Arr).data(), 16);
+    });
+    break;
+  case BuildIdKind::Sha1:
+    computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
+      memcpy(Dest, SHA1::hash(Arr).data(), 20);
+    });
+    break;
+  case BuildIdKind::Uuid:
+    if (getRandomBytes(HashBuf, HashSize))
+      error("entropy source failure");
+    break;
+  case BuildIdKind::Hexstring:
+    memcpy(HashBuf, Config->BuildIdVector.data(), Config->BuildIdVector.size());
+    break;
+  default:
+    llvm_unreachable("unknown BuildIdKind");
+  }
+}
+
+template <class ELFT>
+EhFrameSection<ELFT>::EhFrameSection()
+    : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame") {}
+
+// Search for an existing CIE record or create a new one.
+// CIE records from input object files are uniquified by their contents
+// and where their relocations point to.
+template <class ELFT>
+template <class RelTy>
+CieRecord *EhFrameSection<ELFT>::addCie(EhSectionPiece &Cie,
+                                        ArrayRef<RelTy> Rels) {
+  auto *Sec = cast<EhInputSection>(Cie.Sec);
+  const endianness E = ELFT::TargetEndianness;
+  if (read32<E>(Cie.data().data() + 4) != 0)
+    fatal(toString(Sec) + ": CIE expected at beginning of .eh_frame");
+
+  SymbolBody *Personality = nullptr;
+  unsigned FirstRelI = Cie.FirstRelocation;
+  if (FirstRelI != (unsigned)-1)
+    Personality =
+        &Sec->template getFile<ELFT>()->getRelocTargetSym(Rels[FirstRelI]);
+
+  // Search for an existing CIE by CIE contents/relocation target pair.
+  CieRecord *&Rec = CieMap[{Cie.data(), Personality}];
+
+  // If not found, create a new one.
+  if (!Rec) {
+    Rec = make<CieRecord>();
+    Rec->Cie = &Cie;
+    CieRecords.push_back(Rec);
+  }
+  return Rec;
+}
+
+// There is one FDE per function. Returns true if a given FDE
+// points to a live function.
+template <class ELFT>
+template <class RelTy>
+bool EhFrameSection<ELFT>::isFdeLive(EhSectionPiece &Fde,
+                                     ArrayRef<RelTy> Rels) {
+  auto *Sec = cast<EhInputSection>(Fde.Sec);
+  unsigned FirstRelI = Fde.FirstRelocation;
+
+  // An FDE should point to some function because FDEs are to describe
+  // functions. That's however not always the case due to an issue of
+  // ld.gold with -r. ld.gold may discard only functions and leave their
+  // corresponding FDEs, which results in creating bad .eh_frame sections.
+  // To deal with that, we ignore such FDEs.
+  if (FirstRelI == (unsigned)-1)
+    return false;
+
+  const RelTy &Rel = Rels[FirstRelI];
+  SymbolBody &B = Sec->template getFile<ELFT>()->getRelocTargetSym(Rel);
+  if (auto *D = dyn_cast<DefinedRegular>(&B))
+    if (D->Section)
+      return cast<InputSectionBase>(D->Section)->Repl->Live;
+  return false;
+}
+
+// .eh_frame is a sequence of CIE or FDE records. In general, there
+// is one CIE record per input object file which is followed by
+// a list of FDEs. This function searches an existing CIE or create a new
+// one and associates FDEs to the CIE.
+template <class ELFT>
+template <class RelTy>
+void EhFrameSection<ELFT>::addSectionAux(EhInputSection *Sec,
+                                         ArrayRef<RelTy> Rels) {
+  const endianness E = ELFT::TargetEndianness;
+
+  DenseMap<size_t, CieRecord *> OffsetToCie;
+  for (EhSectionPiece &Piece : Sec->Pieces) {
+    // The empty record is the end marker.
+    if (Piece.Size == 4)
+      return;
+
+    size_t Offset = Piece.InputOff;
+    uint32_t ID = read32<E>(Piece.data().data() + 4);
+    if (ID == 0) {
+      OffsetToCie[Offset] = addCie(Piece, Rels);
+      continue;
+    }
+
+    uint32_t CieOffset = Offset + 4 - ID;
+    CieRecord *Rec = OffsetToCie[CieOffset];
+    if (!Rec)
+      fatal(toString(Sec) + ": invalid CIE reference");
+
+    if (!isFdeLive(Piece, Rels))
+      continue;
+    Rec->Fdes.push_back(&Piece);
+    NumFdes++;
+  }
+}
+
+template <class ELFT>
+void EhFrameSection<ELFT>::addSection(InputSectionBase *C) {
+  auto *Sec = cast<EhInputSection>(C);
+  Sec->Parent = this;
+  updateAlignment(Sec->Alignment);
+  Sections.push_back(Sec);
+  for (auto *DS : Sec->DependentSections)
+    DependentSections.push_back(DS);
+
+  // .eh_frame is a sequence of CIE or FDE records. This function
+  // splits it into pieces so that we can call
+  // SplitInputSection::getSectionPiece on the section.
+  Sec->split<ELFT>();
+  if (Sec->Pieces.empty())
+    return;
+
+  if (Sec->NumRelocations == 0)
+    addSectionAux(Sec, makeArrayRef<Elf_Rela>(nullptr, nullptr));
+  else if (Sec->AreRelocsRela)
+    addSectionAux(Sec, Sec->template relas<ELFT>());
+  else
+    addSectionAux(Sec, Sec->template rels<ELFT>());
+}
+
+template <class ELFT>
+static void writeCieFde(uint8_t *Buf, ArrayRef<uint8_t> D) {
+  memcpy(Buf, D.data(), D.size());
+
+  size_t Aligned = alignTo(D.size(), sizeof(typename ELFT::uint));
+
+  // Zero-clear trailing padding if it exists.
+  memset(Buf + D.size(), 0, Aligned - D.size());
+
+  // Fix the size field. -4 since size does not include the size field itself.
+  const endianness E = ELFT::TargetEndianness;
+  write32<E>(Buf, Aligned - 4);
+}
+
+template <class ELFT> void EhFrameSection<ELFT>::finalizeContents() {
+  if (this->Size)
+    return; // Already finalized.
+
+  size_t Off = 0;
+  for (CieRecord *Rec : CieRecords) {
+    Rec->Cie->OutputOff = Off;
+    Off += alignTo(Rec->Cie->Size, Config->Wordsize);
+
+    for (EhSectionPiece *Fde : Rec->Fdes) {
+      Fde->OutputOff = Off;
+      Off += alignTo(Fde->Size, Config->Wordsize);
+    }
+  }
+
+  // The LSB standard does not allow a .eh_frame section with zero
+  // Call Frame Information records. Therefore add a CIE record length
+  // 0 as a terminator if this .eh_frame section is empty.
+  if (Off == 0)
+    Off = 4;
+
+  this->Size = Off;
+}
+
+template <class ELFT> static uint64_t readFdeAddr(uint8_t *Buf, int Size) {
+  const endianness E = ELFT::TargetEndianness;
+  switch (Size) {
+  case DW_EH_PE_udata2:
+    return read16<E>(Buf);
+  case DW_EH_PE_udata4:
+    return read32<E>(Buf);
+  case DW_EH_PE_udata8:
+    return read64<E>(Buf);
+  case DW_EH_PE_absptr:
+    if (ELFT::Is64Bits)
+      return read64<E>(Buf);
+    return read32<E>(Buf);
+  }
+  fatal("unknown FDE size encoding");
+}
+
+// Returns the VA to which a given FDE (on a mmap'ed buffer) is applied to.
+// We need it to create .eh_frame_hdr section.
+template <class ELFT>
+uint64_t EhFrameSection<ELFT>::getFdePc(uint8_t *Buf, size_t FdeOff,
+                                        uint8_t Enc) {
+  // The starting address to which this FDE applies is
+  // stored at FDE + 8 byte.
+  size_t Off = FdeOff + 8;
+  uint64_t Addr = readFdeAddr<ELFT>(Buf + Off, Enc & 0x7);
+  if ((Enc & 0x70) == DW_EH_PE_absptr)
+    return Addr;
+  if ((Enc & 0x70) == DW_EH_PE_pcrel)
+    return Addr + getParent()->Addr + Off;
+  fatal("unknown FDE size relative encoding");
+}
+
+template <class ELFT> void EhFrameSection<ELFT>::writeTo(uint8_t *Buf) {
+  const endianness E = ELFT::TargetEndianness;
+  for (CieRecord *Rec : CieRecords) {
+    size_t CieOffset = Rec->Cie->OutputOff;
+    writeCieFde<ELFT>(Buf + CieOffset, Rec->Cie->data());
+
+    for (EhSectionPiece *Fde : Rec->Fdes) {
+      size_t Off = Fde->OutputOff;
+      writeCieFde<ELFT>(Buf + Off, Fde->data());
+
+      // FDE's second word should have the offset to an associated CIE.
+      // Write it.
+      write32<E>(Buf + Off + 4, Off + 4 - CieOffset);
+    }
+  }
+
+  for (EhInputSection *S : Sections)
+    S->relocateAlloc(Buf, nullptr);
+
+  // Construct .eh_frame_hdr. .eh_frame_hdr is a binary search table
+  // to get a FDE from an address to which FDE is applied. So here
+  // we obtain two addresses and pass them to EhFrameHdr object.
+  if (In<ELFT>::EhFrameHdr) {
+    for (CieRecord *Rec : CieRecords) {
+      uint8_t Enc = getFdeEncoding<ELFT>(Rec->Cie);
+      for (EhSectionPiece *Fde : Rec->Fdes) {
+        uint64_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
+        uint64_t FdeVA = getParent()->Addr + Fde->OutputOff;
+        In<ELFT>::EhFrameHdr->addFde(Pc, FdeVA);
+      }
+    }
+  }
+}
+
+GotSection::GotSection()
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
+                       Target->GotEntrySize, ".got") {}
+
+void GotSection::addEntry(SymbolBody &Sym) {
+  Sym.GotIndex = NumEntries;
+  ++NumEntries;
+}
+
+bool GotSection::addDynTlsEntry(SymbolBody &Sym) {
+  if (Sym.GlobalDynIndex != -1U)
+    return false;
+  Sym.GlobalDynIndex = NumEntries;
+  // Global Dynamic TLS entries take two GOT slots.
+  NumEntries += 2;
+  return true;
+}
+
+// Reserves TLS entries for a TLS module ID and a TLS block offset.
+// In total it takes two GOT slots.
+bool GotSection::addTlsIndex() {
+  if (TlsIndexOff != uint32_t(-1))
+    return false;
+  TlsIndexOff = NumEntries * Config->Wordsize;
+  NumEntries += 2;
+  return true;
+}
+
+uint64_t GotSection::getGlobalDynAddr(const SymbolBody &B) const {
+  return this->getVA() + B.GlobalDynIndex * Config->Wordsize;
+}
+
+uint64_t GotSection::getGlobalDynOffset(const SymbolBody &B) const {
+  return B.GlobalDynIndex * Config->Wordsize;
+}
+
+void GotSection::finalizeContents() { Size = NumEntries * Config->Wordsize; }
+
+bool GotSection::empty() const {
+  // We need to emit a GOT even if it's empty if there's a relocation that is
+  // relative to GOT(such as GOTOFFREL) or there's a symbol that points to a GOT
+  // (i.e. _GLOBAL_OFFSET_TABLE_).
+  return NumEntries == 0 && !HasGotOffRel && !ElfSym::GlobalOffsetTable;
+}
+
+void GotSection::writeTo(uint8_t *Buf) {
+  // Buf points to the start of this section's buffer,
+  // whereas InputSectionBase::relocateAlloc() expects its argument
+  // to point to the start of the output section.
+  relocateAlloc(Buf - OutSecOff, Buf - OutSecOff + Size);
+}
+
+MipsGotSection::MipsGotSection()
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
+                       ".got") {}
+
+void MipsGotSection::addEntry(SymbolBody &Sym, int64_t Addend, RelExpr Expr) {
+  // For "true" local symbols which can be referenced from the same module
+  // only compiler creates two instructions for address loading:
+  //
+  // lw   $8, 0($gp) # R_MIPS_GOT16
+  // addi $8, $8, 0  # R_MIPS_LO16
+  //
+  // The first instruction loads high 16 bits of the symbol address while
+  // the second adds an offset. That allows to reduce number of required
+  // GOT entries because only one global offset table entry is necessary
+  // for every 64 KBytes of local data. So for local symbols we need to
+  // allocate number of GOT entries to hold all required "page" addresses.
+  //
+  // All global symbols (hidden and regular) considered by compiler uniformly.
+  // It always generates a single `lw` instruction and R_MIPS_GOT16 relocation
+  // to load address of the symbol. So for each such symbol we need to
+  // allocate dedicated GOT entry to store its address.
+  //
+  // If a symbol is preemptible we need help of dynamic linker to get its
+  // final address. The corresponding GOT entries are allocated in the
+  // "global" part of GOT. Entries for non preemptible global symbol allocated
+  // in the "local" part of GOT.
+  //
+  // See "Global Offset Table" in Chapter 5:
+  // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+  if (Expr == R_MIPS_GOT_LOCAL_PAGE) {
+    // At this point we do not know final symbol value so to reduce number
+    // of allocated GOT entries do the following trick. Save all output
+    // sections referenced by GOT relocations. Then later in the `finalize`
+    // method calculate number of "pages" required to cover all saved output
+    // section and allocate appropriate number of GOT entries.
+    PageIndexMap.insert({Sym.getOutputSection(), 0});
+    return;
+  }
+  if (Sym.isTls()) {
+    // GOT entries created for MIPS TLS relocations behave like
+    // almost GOT entries from other ABIs. They go to the end
+    // of the global offset table.
+    Sym.GotIndex = TlsEntries.size();
+    TlsEntries.push_back(&Sym);
+    return;
+  }
+  auto AddEntry = [&](SymbolBody &S, uint64_t A, GotEntries &Items) {
+    if (S.isInGot() && !A)
+      return;
+    size_t NewIndex = Items.size();
+    if (!EntryIndexMap.insert({{&S, A}, NewIndex}).second)
+      return;
+    Items.emplace_back(&S, A);
+    if (!A)
+      S.GotIndex = NewIndex;
+  };
+  if (Sym.isPreemptible()) {
+    // Ignore addends for preemptible symbols. They got single GOT entry anyway.
+    AddEntry(Sym, 0, GlobalEntries);
+    Sym.IsInGlobalMipsGot = true;
+  } else if (Expr == R_MIPS_GOT_OFF32) {
+    AddEntry(Sym, Addend, LocalEntries32);
+    Sym.Is32BitMipsGot = true;
+  } else {
+    // Hold local GOT entries accessed via a 16-bit index separately.
+    // That allows to write them in the beginning of the GOT and keep
+    // their indexes as less as possible to escape relocation's overflow.
+    AddEntry(Sym, Addend, LocalEntries);
+  }
+}
+
+bool MipsGotSection::addDynTlsEntry(SymbolBody &Sym) {
+  if (Sym.GlobalDynIndex != -1U)
+    return false;
+  Sym.GlobalDynIndex = TlsEntries.size();
+  // Global Dynamic TLS entries take two GOT slots.
+  TlsEntries.push_back(nullptr);
+  TlsEntries.push_back(&Sym);
+  return true;
+}
+
+// Reserves TLS entries for a TLS module ID and a TLS block offset.
+// In total it takes two GOT slots.
+bool MipsGotSection::addTlsIndex() {
+  if (TlsIndexOff != uint32_t(-1))
+    return false;
+  TlsIndexOff = TlsEntries.size() * Config->Wordsize;
+  TlsEntries.push_back(nullptr);
+  TlsEntries.push_back(nullptr);
+  return true;
+}
+
+static uint64_t getMipsPageAddr(uint64_t Addr) {
+  return (Addr + 0x8000) & ~0xffff;
+}
+
+static uint64_t getMipsPageCount(uint64_t Size) {
+  return (Size + 0xfffe) / 0xffff + 1;
+}
+
+uint64_t MipsGotSection::getPageEntryOffset(const SymbolBody &B,
+                                            int64_t Addend) const {
+  const OutputSection *OutSec = B.getOutputSection();
+  uint64_t SecAddr = getMipsPageAddr(OutSec->Addr);
+  uint64_t SymAddr = getMipsPageAddr(B.getVA(Addend));
+  uint64_t Index = PageIndexMap.lookup(OutSec) + (SymAddr - SecAddr) / 0xffff;
+  assert(Index < PageEntriesNum);
+  return (HeaderEntriesNum + Index) * Config->Wordsize;
+}
+
+uint64_t MipsGotSection::getBodyEntryOffset(const SymbolBody &B,
+                                            int64_t Addend) const {
+  // Calculate offset of the GOT entries block: TLS, global, local.
+  uint64_t Index = HeaderEntriesNum + PageEntriesNum;
+  if (B.isTls())
+    Index += LocalEntries.size() + LocalEntries32.size() + GlobalEntries.size();
+  else if (B.IsInGlobalMipsGot)
+    Index += LocalEntries.size() + LocalEntries32.size();
+  else if (B.Is32BitMipsGot)
+    Index += LocalEntries.size();
+  // Calculate offset of the GOT entry in the block.
+  if (B.isInGot())
+    Index += B.GotIndex;
+  else {
+    auto It = EntryIndexMap.find({&B, Addend});
+    assert(It != EntryIndexMap.end());
+    Index += It->second;
+  }
+  return Index * Config->Wordsize;
+}
+
+uint64_t MipsGotSection::getTlsOffset() const {
+  return (getLocalEntriesNum() + GlobalEntries.size()) * Config->Wordsize;
+}
+
+uint64_t MipsGotSection::getGlobalDynOffset(const SymbolBody &B) const {
+  return B.GlobalDynIndex * Config->Wordsize;
+}
+
+const SymbolBody *MipsGotSection::getFirstGlobalEntry() const {
+  return GlobalEntries.empty() ? nullptr : GlobalEntries.front().first;
+}
+
+unsigned MipsGotSection::getLocalEntriesNum() const {
+  return HeaderEntriesNum + PageEntriesNum + LocalEntries.size() +
+         LocalEntries32.size();
+}
+
+void MipsGotSection::finalizeContents() { updateAllocSize(); }
+
+void MipsGotSection::updateAllocSize() {
+  PageEntriesNum = 0;
+  for (std::pair<const OutputSection *, size_t> &P : PageIndexMap) {
+    // For each output section referenced by GOT page relocations calculate
+    // and save into PageIndexMap an upper bound of MIPS GOT entries required
+    // to store page addresses of local symbols. We assume the worst case -
+    // each 64kb page of the output section has at least one GOT relocation
+    // against it. And take in account the case when the section intersects
+    // page boundaries.
+    P.second = PageEntriesNum;
+    PageEntriesNum += getMipsPageCount(P.first->Size);
+  }
+  Size = (getLocalEntriesNum() + GlobalEntries.size() + TlsEntries.size()) *
+         Config->Wordsize;
+}
+
+bool MipsGotSection::empty() const {
+  // We add the .got section to the result for dynamic MIPS target because
+  // its address and properties are mentioned in the .dynamic section.
+  return Config->Relocatable;
+}
+
+uint64_t MipsGotSection::getGp() const { return ElfSym::MipsGp->getVA(0); }
+
+static uint64_t readUint(uint8_t *Buf) {
+  if (Config->Is64)
+    return read64(Buf, Config->Endianness);
+  return read32(Buf, Config->Endianness);
+}
+
+static void writeUint(uint8_t *Buf, uint64_t Val) {
+  if (Config->Is64)
+    write64(Buf, Val, Config->Endianness);
+  else
+    write32(Buf, Val, Config->Endianness);
+}
+
+void MipsGotSection::writeTo(uint8_t *Buf) {
+  // Set the MSB of the second GOT slot. This is not required by any
+  // MIPS ABI documentation, though.
+  //
+  // There is a comment in glibc saying that "The MSB of got[1] of a
+  // gnu object is set to identify gnu objects," and in GNU gold it
+  // says "the second entry will be used by some runtime loaders".
+  // But how this field is being used is unclear.
+  //
+  // We are not really willing to mimic other linkers behaviors
+  // without understanding why they do that, but because all files
+  // generated by GNU tools have this special GOT value, and because
+  // we've been doing this for years, it is probably a safe bet to
+  // keep doing this for now. We really need to revisit this to see
+  // if we had to do this.
+  writeUint(Buf + Config->Wordsize, (uint64_t)1 << (Config->Wordsize * 8 - 1));
+  Buf += HeaderEntriesNum * Config->Wordsize;
+  // Write 'page address' entries to the local part of the GOT.
+  for (std::pair<const OutputSection *, size_t> &L : PageIndexMap) {
+    size_t PageCount = getMipsPageCount(L.first->Size);
+    uint64_t FirstPageAddr = getMipsPageAddr(L.first->Addr);
+    for (size_t PI = 0; PI < PageCount; ++PI) {
+      uint8_t *Entry = Buf + (L.second + PI) * Config->Wordsize;
+      writeUint(Entry, FirstPageAddr + PI * 0x10000);
+    }
+  }
+  Buf += PageEntriesNum * Config->Wordsize;
+  auto AddEntry = [&](const GotEntry &SA) {
+    uint8_t *Entry = Buf;
+    Buf += Config->Wordsize;
+    const SymbolBody *Body = SA.first;
+    uint64_t VA = Body->getVA(SA.second);
+    writeUint(Entry, VA);
+  };
+  std::for_each(std::begin(LocalEntries), std::end(LocalEntries), AddEntry);
+  std::for_each(std::begin(LocalEntries32), std::end(LocalEntries32), AddEntry);
+  std::for_each(std::begin(GlobalEntries), std::end(GlobalEntries), AddEntry);
+  // Initialize TLS-related GOT entries. If the entry has a corresponding
+  // dynamic relocations, leave it initialized by zero. Write down adjusted
+  // TLS symbol's values otherwise. To calculate the adjustments use offsets
+  // for thread-local storage.
+  // https://www.linux-mips.org/wiki/NPTL
+  if (TlsIndexOff != -1U && !Config->Pic)
+    writeUint(Buf + TlsIndexOff, 1);
+  for (const SymbolBody *B : TlsEntries) {
+    if (!B || B->isPreemptible())
+      continue;
+    uint64_t VA = B->getVA();
+    if (B->GotIndex != -1U) {
+      uint8_t *Entry = Buf + B->GotIndex * Config->Wordsize;
+      writeUint(Entry, VA - 0x7000);
+    }
+    if (B->GlobalDynIndex != -1U) {
+      uint8_t *Entry = Buf + B->GlobalDynIndex * Config->Wordsize;
+      writeUint(Entry, 1);
+      Entry += Config->Wordsize;
+      writeUint(Entry, VA - 0x8000);
+    }
+  }
+}
+
+GotPltSection::GotPltSection()
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
+                       Target->GotPltEntrySize, ".got.plt") {}
+
+void GotPltSection::addEntry(SymbolBody &Sym) {
+  Sym.GotPltIndex = Target->GotPltHeaderEntriesNum + Entries.size();
+  Entries.push_back(&Sym);
+}
+
+size_t GotPltSection::getSize() const {
+  return (Target->GotPltHeaderEntriesNum + Entries.size()) *
+         Target->GotPltEntrySize;
+}
+
+void GotPltSection::writeTo(uint8_t *Buf) {
+  Target->writeGotPltHeader(Buf);
+  Buf += Target->GotPltHeaderEntriesNum * Target->GotPltEntrySize;
+  for (const SymbolBody *B : Entries) {
+    Target->writeGotPlt(Buf, *B);
+    Buf += Config->Wordsize;
+  }
+}
+
+// On ARM the IgotPltSection is part of the GotSection, on other Targets it is
+// part of the .got.plt
+IgotPltSection::IgotPltSection()
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
+                       Target->GotPltEntrySize,
+                       Config->EMachine == EM_ARM ? ".got" : ".got.plt") {}
+
+void IgotPltSection::addEntry(SymbolBody &Sym) {
+  Sym.IsInIgot = true;
+  Sym.GotPltIndex = Entries.size();
+  Entries.push_back(&Sym);
+}
+
+size_t IgotPltSection::getSize() const {
+  return Entries.size() * Target->GotPltEntrySize;
+}
+
+void IgotPltSection::writeTo(uint8_t *Buf) {
+  for (const SymbolBody *B : Entries) {
+    Target->writeIgotPlt(Buf, *B);
+    Buf += Config->Wordsize;
+  }
+}
+
+StringTableSection::StringTableSection(StringRef Name, bool Dynamic)
+    : SyntheticSection(Dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, Name),
+      Dynamic(Dynamic) {
+  // ELF string tables start with a NUL byte.
+  addString("");
+}
+
+// Adds a string to the string table. If HashIt is true we hash and check for
+// duplicates. It is optional because the name of global symbols are already
+// uniqued and hashing them again has a big cost for a small value: uniquing
+// them with some other string that happens to be the same.
+unsigned StringTableSection::addString(StringRef S, bool HashIt) {
+  if (HashIt) {
+    auto R = StringMap.insert(std::make_pair(S, this->Size));
+    if (!R.second)
+      return R.first->second;
+  }
+  unsigned Ret = this->Size;
+  this->Size = this->Size + S.size() + 1;
+  Strings.push_back(S);
+  return Ret;
+}
+
+void StringTableSection::writeTo(uint8_t *Buf) {
+  for (StringRef S : Strings) {
+    memcpy(Buf, S.data(), S.size());
+    Buf[S.size()] = '\0';
+    Buf += S.size() + 1;
+  }
+}
+
+// Returns the number of version definition entries. Because the first entry
+// is for the version definition itself, it is the number of versioned symbols
+// plus one. Note that we don't support multiple versions yet.
+static unsigned getVerDefNum() { return Config->VersionDefinitions.size() + 1; }
+
+template <class ELFT>
+DynamicSection<ELFT>::DynamicSection()
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, Config->Wordsize,
+                       ".dynamic") {
+  this->Entsize = ELFT::Is64Bits ? 16 : 8;
+
+  // .dynamic section is not writable on MIPS and on Fuchsia OS
+  // which passes -z rodynamic.
+  // See "Special Section" in Chapter 4 in the following document:
+  // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+  if (Config->EMachine == EM_MIPS || Config->ZRodynamic)
+    this->Flags = SHF_ALLOC;
+
+  addEntries();
+}
+
+// There are some dynamic entries that don't depend on other sections.
+// Such entries can be set early.
+template <class ELFT> void DynamicSection<ELFT>::addEntries() {
+  // Add strings to .dynstr early so that .dynstr's size will be
+  // fixed early.
+  for (StringRef S : Config->FilterList)
+    add({DT_FILTER, InX::DynStrTab->addString(S)});
+  for (StringRef S : Config->AuxiliaryList)
+    add({DT_AUXILIARY, InX::DynStrTab->addString(S)});
+  if (!Config->Rpath.empty())
+    add({Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
+         InX::DynStrTab->addString(Config->Rpath)});
+  for (InputFile *File : SharedFiles) {
+    SharedFile<ELFT> *F = cast<SharedFile<ELFT>>(File);
+    if (F->isNeeded())
+      add({DT_NEEDED, InX::DynStrTab->addString(F->SoName)});
+  }
+  if (!Config->SoName.empty())
+    add({DT_SONAME, InX::DynStrTab->addString(Config->SoName)});
+
+  // Set DT_FLAGS and DT_FLAGS_1.
+  uint32_t DtFlags = 0;
+  uint32_t DtFlags1 = 0;
+  if (Config->Bsymbolic)
+    DtFlags |= DF_SYMBOLIC;
+  if (Config->ZNodelete)
+    DtFlags1 |= DF_1_NODELETE;
+  if (Config->ZNodlopen)
+    DtFlags1 |= DF_1_NOOPEN;
+  if (Config->ZNow) {
+    DtFlags |= DF_BIND_NOW;
+    DtFlags1 |= DF_1_NOW;
+  }
+  if (Config->ZOrigin) {
+    DtFlags |= DF_ORIGIN;
+    DtFlags1 |= DF_1_ORIGIN;
+  }
+
+  if (DtFlags)
+    add({DT_FLAGS, DtFlags});
+  if (DtFlags1)
+    add({DT_FLAGS_1, DtFlags1});
+
+  // DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
+  // need it for each process, so we don't write it for DSOs. The loader writes
+  // the pointer into this entry.
+  //
+  // DT_DEBUG is the only .dynamic entry that needs to be written to. Some
+  // systems (currently only Fuchsia OS) provide other means to give the
+  // debugger this information. Such systems may choose make .dynamic read-only.
+  // If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
+  if (!Config->Shared && !Config->Relocatable && !Config->ZRodynamic)
+    add({DT_DEBUG, (uint64_t)0});
+}
+
+// Add remaining entries to complete .dynamic contents.
+template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
+  if (this->Size)
+    return; // Already finalized.
+
+  this->Link = InX::DynStrTab->getParent()->SectionIndex;
+  if (In<ELFT>::RelaDyn->getParent() && !In<ELFT>::RelaDyn->empty()) {
+    bool IsRela = Config->IsRela;
+    add({IsRela ? DT_RELA : DT_REL, In<ELFT>::RelaDyn});
+    add({IsRela ? DT_RELASZ : DT_RELSZ, In<ELFT>::RelaDyn->getParent(),
+         Entry::SecSize});
+    add({IsRela ? DT_RELAENT : DT_RELENT,
+         uint64_t(IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel))});
+
+    // MIPS dynamic loader does not support RELCOUNT tag.
+    // The problem is in the tight relation between dynamic
+    // relocations and GOT. So do not emit this tag on MIPS.
+    if (Config->EMachine != EM_MIPS) {
+      size_t NumRelativeRels = In<ELFT>::RelaDyn->getRelativeRelocCount();
+      if (Config->ZCombreloc && NumRelativeRels)
+        add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
+    }
+  }
+  if (In<ELFT>::RelaPlt->getParent() && !In<ELFT>::RelaPlt->empty()) {
+    add({DT_JMPREL, In<ELFT>::RelaPlt});
+    add({DT_PLTRELSZ, In<ELFT>::RelaPlt->getParent(), Entry::SecSize});
+    switch (Config->EMachine) {
+    case EM_MIPS:
+      add({DT_MIPS_PLTGOT, In<ELFT>::GotPlt});
+      break;
+    case EM_SPARCV9:
+      add({DT_PLTGOT, In<ELFT>::Plt});
+      break;
+    default:
+      add({DT_PLTGOT, In<ELFT>::GotPlt});
+      break;
+    }
+    add({DT_PLTREL, uint64_t(Config->IsRela ? DT_RELA : DT_REL)});
+  }
+
+  add({DT_SYMTAB, InX::DynSymTab});
+  add({DT_SYMENT, sizeof(Elf_Sym)});
+  add({DT_STRTAB, InX::DynStrTab});
+  add({DT_STRSZ, InX::DynStrTab->getSize()});
+  if (!Config->ZText)
+    add({DT_TEXTREL, (uint64_t)0});
+  if (InX::GnuHashTab)
+    add({DT_GNU_HASH, InX::GnuHashTab});
+  if (In<ELFT>::HashTab)
+    add({DT_HASH, In<ELFT>::HashTab});
+
+  if (Out::PreinitArray) {
+    add({DT_PREINIT_ARRAY, Out::PreinitArray});
+    add({DT_PREINIT_ARRAYSZ, Out::PreinitArray, Entry::SecSize});
+  }
+  if (Out::InitArray) {
+    add({DT_INIT_ARRAY, Out::InitArray});
+    add({DT_INIT_ARRAYSZ, Out::InitArray, Entry::SecSize});
+  }
+  if (Out::FiniArray) {
+    add({DT_FINI_ARRAY, Out::FiniArray});
+    add({DT_FINI_ARRAYSZ, Out::FiniArray, Entry::SecSize});
+  }
+
+  if (SymbolBody *B = Symtab->find(Config->Init))
+    if (B->isInCurrentDSO())
+      add({DT_INIT, B});
+  if (SymbolBody *B = Symtab->find(Config->Fini))
+    if (B->isInCurrentDSO())
+      add({DT_FINI, B});
+
+  bool HasVerNeed = In<ELFT>::VerNeed->getNeedNum() != 0;
+  if (HasVerNeed || In<ELFT>::VerDef)
+    add({DT_VERSYM, In<ELFT>::VerSym});
+  if (In<ELFT>::VerDef) {
+    add({DT_VERDEF, In<ELFT>::VerDef});
+    add({DT_VERDEFNUM, getVerDefNum()});
+  }
+  if (HasVerNeed) {
+    add({DT_VERNEED, In<ELFT>::VerNeed});
+    add({DT_VERNEEDNUM, In<ELFT>::VerNeed->getNeedNum()});
+  }
+
+  if (Config->EMachine == EM_MIPS) {
+    add({DT_MIPS_RLD_VERSION, 1});
+    add({DT_MIPS_FLAGS, RHF_NOTPOT});
+    add({DT_MIPS_BASE_ADDRESS, Config->ImageBase});
+    add({DT_MIPS_SYMTABNO, InX::DynSymTab->getNumSymbols()});
+    add({DT_MIPS_LOCAL_GOTNO, InX::MipsGot->getLocalEntriesNum()});
+    if (const SymbolBody *B = InX::MipsGot->getFirstGlobalEntry())
+      add({DT_MIPS_GOTSYM, B->DynsymIndex});
+    else
+      add({DT_MIPS_GOTSYM, InX::DynSymTab->getNumSymbols()});
+    add({DT_PLTGOT, InX::MipsGot});
+    if (InX::MipsRldMap)
+      add({DT_MIPS_RLD_MAP, InX::MipsRldMap});
+  }
+
+  getParent()->Link = this->Link;
+
+  // +1 for DT_NULL
+  this->Size = (Entries.size() + 1) * this->Entsize;
+}
+
+template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
+  auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
+
+  for (const Entry &E : Entries) {
+    P->d_tag = E.Tag;
+    switch (E.Kind) {
+    case Entry::SecAddr:
+      P->d_un.d_ptr = E.OutSec->Addr;
+      break;
+    case Entry::InSecAddr:
+      P->d_un.d_ptr = E.InSec->getParent()->Addr + E.InSec->OutSecOff;
+      break;
+    case Entry::SecSize:
+      P->d_un.d_val = E.OutSec->Size;
+      break;
+    case Entry::SymAddr:
+      P->d_un.d_ptr = E.Sym->getVA();
+      break;
+    case Entry::PlainInt:
+      P->d_un.d_val = E.Val;
+      break;
+    }
+    ++P;
+  }
+}
+
+uint64_t DynamicReloc::getOffset() const {
+  return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
+}
+
+int64_t DynamicReloc::getAddend() const {
+  if (UseSymVA)
+    return Sym->getVA(Addend);
+  return Addend;
+}
+
+uint32_t DynamicReloc::getSymIndex() const {
+  if (Sym && !UseSymVA)
+    return Sym->DynsymIndex;
+  return 0;
+}
+
+template <class ELFT>
+RelocationSection<ELFT>::RelocationSection(StringRef Name, bool Sort)
+    : SyntheticSection(SHF_ALLOC, Config->IsRela ? SHT_RELA : SHT_REL,
+                       Config->Wordsize, Name),
+      Sort(Sort) {
+  this->Entsize = Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
+}
+
+template <class ELFT>
+void RelocationSection<ELFT>::addReloc(const DynamicReloc &Reloc) {
+  if (Reloc.Type == Target->RelativeRel)
+    ++NumRelativeRelocs;
+  Relocs.push_back(Reloc);
+}
+
+template <class ELFT, class RelTy>
+static bool compRelocations(const RelTy &A, const RelTy &B) {
+  bool AIsRel = A.getType(Config->IsMips64EL) == Target->RelativeRel;
+  bool BIsRel = B.getType(Config->IsMips64EL) == Target->RelativeRel;
+  if (AIsRel != BIsRel)
+    return AIsRel;
+
+  return A.getSymbol(Config->IsMips64EL) < B.getSymbol(Config->IsMips64EL);
+}
+
+template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
+  uint8_t *BufBegin = Buf;
+  for (const DynamicReloc &Rel : Relocs) {
+    auto *P = reinterpret_cast<Elf_Rela *>(Buf);
+    Buf += Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
+
+    if (Config->IsRela)
+      P->r_addend = Rel.getAddend();
+    P->r_offset = Rel.getOffset();
+    if (Config->EMachine == EM_MIPS && Rel.getInputSec() == InX::MipsGot)
+      // Dynamic relocation against MIPS GOT section make deal TLS entries
+      // allocated in the end of the GOT. We need to adjust the offset to take
+      // in account 'local' and 'global' GOT entries.
+      P->r_offset += InX::MipsGot->getTlsOffset();
+    P->setSymbolAndType(Rel.getSymIndex(), Rel.Type, Config->IsMips64EL);
+  }
+
+  if (Sort) {
+    if (Config->IsRela)
+      std::stable_sort((Elf_Rela *)BufBegin,
+                       (Elf_Rela *)BufBegin + Relocs.size(),
+                       compRelocations<ELFT, Elf_Rela>);
+    else
+      std::stable_sort((Elf_Rel *)BufBegin, (Elf_Rel *)BufBegin + Relocs.size(),
+                       compRelocations<ELFT, Elf_Rel>);
+  }
+}
+
+template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
+  return this->Entsize * Relocs.size();
+}
+
+template <class ELFT> void RelocationSection<ELFT>::finalizeContents() {
+  this->Link = InX::DynSymTab ? InX::DynSymTab->getParent()->SectionIndex
+                              : InX::SymTab->getParent()->SectionIndex;
+
+  // Set required output section properties.
+  getParent()->Link = this->Link;
+}
+
+SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &StrTabSec)
+    : SyntheticSection(StrTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
+                       StrTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
+                       Config->Wordsize,
+                       StrTabSec.isDynamic() ? ".dynsym" : ".symtab"),
+      StrTabSec(StrTabSec) {}
+
+// Orders symbols according to their positions in the GOT,
+// in compliance with MIPS ABI rules.
+// See "Global Offset Table" in Chapter 5 in the following document
+// for detailed description:
+// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+static bool sortMipsSymbols(const SymbolTableEntry &L,
+                            const SymbolTableEntry &R) {
+  // Sort entries related to non-local preemptible symbols by GOT indexes.
+  // All other entries go to the first part of GOT in arbitrary order.
+  bool LIsInLocalGot = !L.Symbol->IsInGlobalMipsGot;
+  bool RIsInLocalGot = !R.Symbol->IsInGlobalMipsGot;
+  if (LIsInLocalGot || RIsInLocalGot)
+    return !RIsInLocalGot;
+  return L.Symbol->GotIndex < R.Symbol->GotIndex;
+}
+
+// Finalize a symbol table. The ELF spec requires that all local
+// symbols precede global symbols, so we sort symbol entries in this
+// function. (For .dynsym, we don't do that because symbols for
+// dynamic linking are inherently all globals.)
+void SymbolTableBaseSection::finalizeContents() {
+  getParent()->Link = StrTabSec.getParent()->SectionIndex;
+
+  // If it is a .dynsym, there should be no local symbols, but we need
+  // to do a few things for the dynamic linker.
+  if (this->Type == SHT_DYNSYM) {
+    // Section's Info field has the index of the first non-local symbol.
+    // Because the first symbol entry is a null entry, 1 is the first.
+    getParent()->Info = 1;
+
+    if (InX::GnuHashTab) {
+      // NB: It also sorts Symbols to meet the GNU hash table requirements.
+      InX::GnuHashTab->addSymbols(Symbols);
+    } else if (Config->EMachine == EM_MIPS) {
+      std::stable_sort(Symbols.begin(), Symbols.end(), sortMipsSymbols);
+    }
+
+    size_t I = 0;
+    for (const SymbolTableEntry &S : Symbols)
+      S.Symbol->DynsymIndex = ++I;
+    return;
+  }
+}
+
+void SymbolTableBaseSection::postThunkContents() {
+  if (this->Type == SHT_DYNSYM)
+    return;
+  // move all local symbols before global symbols.
+  auto It = std::stable_partition(
+      Symbols.begin(), Symbols.end(), [](const SymbolTableEntry &S) {
+        return S.Symbol->isLocal() ||
+               S.Symbol->symbol()->computeBinding() == STB_LOCAL;
+      });
+  size_t NumLocals = It - Symbols.begin();
+  getParent()->Info = NumLocals + 1;
+}
+
+void SymbolTableBaseSection::addSymbol(SymbolBody *B) {
+  // Adding a local symbol to a .dynsym is a bug.
+  assert(this->Type != SHT_DYNSYM || !B->isLocal());
+
+  bool HashIt = B->isLocal();
+  Symbols.push_back({B, StrTabSec.addString(B->getName(), HashIt)});
+}
+
+size_t SymbolTableBaseSection::getSymbolIndex(SymbolBody *Body) {
+  auto I = llvm::find_if(Symbols, [&](const SymbolTableEntry &E) {
+    if (E.Symbol == Body)
+      return true;
+    // This is used for -r, so we have to handle multiple section
+    // symbols being combined.
+    if (Body->Type == STT_SECTION && E.Symbol->Type == STT_SECTION)
+      return Body->getOutputSection() == E.Symbol->getOutputSection();
+    return false;
+  });
+  if (I == Symbols.end())
+    return 0;
+  return I - Symbols.begin() + 1;
+}
+
+template <class ELFT>
+SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &StrTabSec)
+    : SymbolTableBaseSection(StrTabSec) {
+  this->Entsize = sizeof(Elf_Sym);
+}
+
+// Write the internal symbol table contents to the output symbol table.
+template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
+  // The first entry is a null entry as per the ELF spec.
+  Buf += sizeof(Elf_Sym);
+
+  auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
+
+  for (SymbolTableEntry &Ent : Symbols) {
+    SymbolBody *Body = Ent.Symbol;
+
+    // Set st_info and st_other.
+    if (Body->isLocal()) {
+      ESym->setBindingAndType(STB_LOCAL, Body->Type);
+    } else {
+      ESym->setBindingAndType(Body->symbol()->computeBinding(), Body->Type);
+      ESym->setVisibility(Body->symbol()->Visibility);
+    }
+
+    ESym->st_name = Ent.StrTabOffset;
+
+    // Set a section index.
+    if (const OutputSection *OutSec = Body->getOutputSection())
+      ESym->st_shndx = OutSec->SectionIndex;
+    else if (isa<DefinedRegular>(Body))
+      ESym->st_shndx = SHN_ABS;
+    else if (isa<DefinedCommon>(Body))
+      ESym->st_shndx = SHN_COMMON;
+
+    // Copy symbol size if it is a defined symbol. st_size is not significant
+    // for undefined symbols, so whether copying it or not is up to us if that's
+    // the case. We'll leave it as zero because by not setting a value, we can
+    // get the exact same outputs for two sets of input files that differ only
+    // in undefined symbol size in DSOs.
+    if (ESym->st_shndx != SHN_UNDEF)
+      ESym->st_size = Body->getSize<ELFT>();
+
+    // st_value is usually an address of a symbol, but that has a
+    // special meaining for uninstantiated common symbols (this can
+    // occur if -r is given).
+    if (!Config->DefineCommon && isa<DefinedCommon>(Body))
+      ESym->st_value = cast<DefinedCommon>(Body)->Alignment;
+    else
+      ESym->st_value = Body->getVA();
+
+    ++ESym;
+  }
+
+  // On MIPS we need to mark symbol which has a PLT entry and requires
+  // pointer equality by STO_MIPS_PLT flag. That is necessary to help
+  // dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
+  // https://sourceware.org/ml/binutils/2008-07/txt00000.txt
+  if (Config->EMachine == EM_MIPS) {
+    auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
+
+    for (SymbolTableEntry &Ent : Symbols) {
+      SymbolBody *Body = Ent.Symbol;
+      if (Body->isInPlt() && Body->NeedsPltAddr)
+        ESym->st_other |= STO_MIPS_PLT;
+
+      if (Config->Relocatable)
+        if (auto *D = dyn_cast<DefinedRegular>(Body))
+          if (D->isMipsPIC<ELFT>())
+            ESym->st_other |= STO_MIPS_PIC;
+      ++ESym;
+    }
+  }
+}
+
+// .hash and .gnu.hash sections contain on-disk hash tables that map
+// symbol names to their dynamic symbol table indices. Their purpose
+// is to help the dynamic linker resolve symbols quickly. If ELF files
+// don't have them, the dynamic linker has to do linear search on all
+// dynamic symbols, which makes programs slower. Therefore, a .hash
+// section is added to a DSO by default. A .gnu.hash is added if you
+// give the -hash-style=gnu or -hash-style=both option.
+//
+// The Unix semantics of resolving dynamic symbols is somewhat expensive.
+// Each ELF file has a list of DSOs that the ELF file depends on and a
+// list of dynamic symbols that need to be resolved from any of the
+// DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
+// where m is the number of DSOs and n is the number of dynamic
+// symbols. For modern large programs, both m and n are large.  So
+// making each step faster by using hash tables substiantially
+// improves time to load programs.
+//
+// (Note that this is not the only way to design the shared library.
+// For instance, the Windows DLL takes a different approach. On
+// Windows, each dynamic symbol has a name of DLL from which the symbol
+// has to be resolved. That makes the cost of symbol resolution O(n).
+// This disables some hacky techniques you can use on Unix such as
+// LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
+//
+// Due to historical reasons, we have two different hash tables, .hash
+// and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
+// and better version of .hash. .hash is just an on-disk hash table, but
+// .gnu.hash has a bloom filter in addition to a hash table to skip
+// DSOs very quickly. If you are sure that your dynamic linker knows
+// about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
+// safe bet is to specify -hash-style=both for backward compatibilty.
+GnuHashTableSection::GnuHashTableSection()
+    : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, Config->Wordsize, ".gnu.hash") {
+}
+
+void GnuHashTableSection::finalizeContents() {
+  getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
+
+  // Computes bloom filter size in word size. We want to allocate 8
+  // bits for each symbol. It must be a power of two.
+  if (Symbols.empty())
+    MaskWords = 1;
+  else
+    MaskWords = NextPowerOf2((Symbols.size() - 1) / Config->Wordsize);
+
+  Size = 16;                            // Header
+  Size += Config->Wordsize * MaskWords; // Bloom filter
+  Size += NBuckets * 4;                 // Hash buckets
+  Size += Symbols.size() * 4;           // Hash values
+}
+
+void GnuHashTableSection::writeTo(uint8_t *Buf) {
+  // Write a header.
+  write32(Buf, NBuckets, Config->Endianness);
+  write32(Buf + 4, InX::DynSymTab->getNumSymbols() - Symbols.size(),
+          Config->Endianness);
+  write32(Buf + 8, MaskWords, Config->Endianness);
+  write32(Buf + 12, getShift2(), Config->Endianness);
+  Buf += 16;
+
+  // Write a bloom filter and a hash table.
+  writeBloomFilter(Buf);
+  Buf += Config->Wordsize * MaskWords;
+  writeHashTable(Buf);
+}
+
+// This function writes a 2-bit bloom filter. This bloom filter alone
+// usually filters out 80% or more of all symbol lookups [1].
+// The dynamic linker uses the hash table only when a symbol is not
+// filtered out by a bloom filter.
+//
+// [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
+//     p.9, https://www.akkadia.org/drepper/dsohowto.pdf
+void GnuHashTableSection::writeBloomFilter(uint8_t *Buf) {
+  const unsigned C = Config->Wordsize * 8;
+  for (const Entry &Sym : Symbols) {
+    size_t I = (Sym.Hash / C) & (MaskWords - 1);
+    uint64_t Val = readUint(Buf + I * Config->Wordsize);
+    Val |= uint64_t(1) << (Sym.Hash % C);
+    Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
+    writeUint(Buf + I * Config->Wordsize, Val);
+  }
+}
+
+void GnuHashTableSection::writeHashTable(uint8_t *Buf) {
+  // Group symbols by hash value.
+  std::vector<std::vector<Entry>> Syms(NBuckets);
+  for (const Entry &Ent : Symbols)
+    Syms[Ent.Hash % NBuckets].push_back(Ent);
+
+  // Write hash buckets. Hash buckets contain indices in the following
+  // hash value table.
+  uint32_t *Buckets = reinterpret_cast<uint32_t *>(Buf);
+  for (size_t I = 0; I < NBuckets; ++I)
+    if (!Syms[I].empty())
+      write32(Buckets + I, Syms[I][0].Body->DynsymIndex, Config->Endianness);
+
+  // Write a hash value table. It represents a sequence of chains that
+  // share the same hash modulo value. The last element of each chain
+  // is terminated by LSB 1.
+  uint32_t *Values = Buckets + NBuckets;
+  size_t I = 0;
+  for (std::vector<Entry> &Vec : Syms) {
+    if (Vec.empty())
+      continue;
+    for (const Entry &Ent : makeArrayRef(Vec).drop_back())
+      write32(Values + I++, Ent.Hash & ~1, Config->Endianness);
+    write32(Values + I++, Vec.back().Hash | 1, Config->Endianness);
+  }
+}
+
+static uint32_t hashGnu(StringRef Name) {
+  uint32_t H = 5381;
+  for (uint8_t C : Name)
+    H = (H << 5) + H + C;
+  return H;
+}
+
+// Returns a number of hash buckets to accomodate given number of elements.
+// We want to choose a moderate number that is not too small (which
+// causes too many hash collisions) and not too large (which wastes
+// disk space.)
+//
+// We return a prime number because it (is believed to) achieve good
+// hash distribution.
+static size_t getBucketSize(size_t NumSymbols) {
+  // List of largest prime numbers that are not greater than 2^n + 1.
+  for (size_t N : {131071, 65521, 32749, 16381, 8191, 4093, 2039, 1021, 509,
+                   251, 127, 61, 31, 13, 7, 3, 1})
+    if (N <= NumSymbols)
+      return N;
+  return 0;
+}
+
+// Add symbols to this symbol hash table. Note that this function
+// destructively sort a given vector -- which is needed because
+// GNU-style hash table places some sorting requirements.
+void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
+  // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
+  // its type correctly.
+  std::vector<SymbolTableEntry>::iterator Mid =
+      std::stable_partition(V.begin(), V.end(), [](const SymbolTableEntry &S) {
+        return S.Symbol->isUndefined();
+      });
+  if (Mid == V.end())
+    return;
+
+  for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
+    SymbolBody *B = Ent.Symbol;
+    Symbols.push_back({B, Ent.StrTabOffset, hashGnu(B->getName())});
+  }
+
+  NBuckets = getBucketSize(Symbols.size());
+  std::stable_sort(Symbols.begin(), Symbols.end(),
+                   [&](const Entry &L, const Entry &R) {
+                     return L.Hash % NBuckets < R.Hash % NBuckets;
+                   });
+
+  V.erase(Mid, V.end());
+  for (const Entry &Ent : Symbols)
+    V.push_back({Ent.Body, Ent.StrTabOffset});
+}
+
+template <class ELFT>
+HashTableSection<ELFT>::HashTableSection()
+    : SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
+  this->Entsize = 4;
+}
+
+template <class ELFT> void HashTableSection<ELFT>::finalizeContents() {
+  getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
+
+  unsigned NumEntries = 2;                       // nbucket and nchain.
+  NumEntries += InX::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 += InX::DynSymTab->getNumSymbols();
+  this->Size = NumEntries * 4;
+}
+
+template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
+  // A 32-bit integer type in the target endianness.
+  typedef typename ELFT::Word Elf_Word;
+
+  unsigned NumSymbols = InX::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 (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
+    SymbolBody *Body = S.Symbol;
+    StringRef Name = Body->getName();
+    unsigned I = Body->DynsymIndex;
+    uint32_t Hash = hashSysV(Name) % NumSymbols;
+    Chains[I] = Buckets[Hash];
+    Buckets[Hash] = I;
+  }
+}
+
+PltSection::PltSection(size_t S)
+    : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
+      HeaderSize(S) {
+  // The PLT needs to be writable on SPARC as the dynamic linker will
+  // modify the instructions in the PLT entries.
+  if (Config->EMachine == EM_SPARCV9)
+    this->Flags |= SHF_WRITE;
+}
+
+void PltSection::writeTo(uint8_t *Buf) {
+  // At beginning of PLT but not the IPLT, we have code to call the dynamic
+  // linker to resolve dynsyms at runtime. Write such code.
+  if (HeaderSize != 0)
+    Target->writePltHeader(Buf);
+  size_t Off = HeaderSize;
+  // The IPlt is immediately after the Plt, account for this in RelOff
+  unsigned PltOff = getPltRelocOff();
+
+  for (auto &I : Entries) {
+    const SymbolBody *B = I.first;
+    unsigned RelOff = I.second + PltOff;
+    uint64_t Got = B->getGotPltVA();
+    uint64_t Plt = this->getVA() + Off;
+    Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
+    Off += Target->PltEntrySize;
+  }
+}
+
+template <class ELFT> void PltSection::addEntry(SymbolBody &Sym) {
+  Sym.PltIndex = Entries.size();
+  RelocationSection<ELFT> *PltRelocSection = In<ELFT>::RelaPlt;
+  if (HeaderSize == 0) {
+    PltRelocSection = In<ELFT>::RelaIplt;
+    Sym.IsInIplt = true;
+  }
+  unsigned RelOff = PltRelocSection->getRelocOffset();
+  Entries.push_back(std::make_pair(&Sym, RelOff));
+}
+
+size_t PltSection::getSize() const {
+  return HeaderSize + Entries.size() * Target->PltEntrySize;
+}
+
+// Some architectures such as additional symbols in the PLT section. For
+// example ARM uses mapping symbols to aid disassembly
+void PltSection::addSymbols() {
+  // The PLT may have symbols defined for the Header, the IPLT has no header
+  if (HeaderSize != 0)
+    Target->addPltHeaderSymbols(this);
+  size_t Off = HeaderSize;
+  for (size_t I = 0; I < Entries.size(); ++I) {
+    Target->addPltSymbols(this, Off);
+    Off += Target->PltEntrySize;
+  }
+}
+
+unsigned PltSection::getPltRelocOff() const {
+  return (HeaderSize == 0) ? InX::Plt->getSize() : 0;
+}
+
+// The string hash function for .gdb_index.
+static uint32_t computeGdbHash(StringRef S) {
+  uint32_t H = 0;
+  for (uint8_t C : S)
+    H = H * 67 + tolower(C) - 113;
+  return H;
+}
+
+static std::vector<GdbIndexChunk::CuEntry> readCuList(DWARFContext &Dwarf) {
+  std::vector<GdbIndexChunk::CuEntry> Ret;
+  for (std::unique_ptr<DWARFCompileUnit> &Cu : Dwarf.compile_units())
+    Ret.push_back({Cu->getOffset(), Cu->getLength() + 4});
+  return Ret;
+}
+
+static std::vector<GdbIndexChunk::AddressEntry>
+readAddressAreas(DWARFContext &Dwarf, InputSection *Sec) {
+  std::vector<GdbIndexChunk::AddressEntry> Ret;
+
+  uint32_t CuIdx = 0;
+  for (std::unique_ptr<DWARFCompileUnit> &Cu : Dwarf.compile_units()) {
+    DWARFAddressRangesVector Ranges;
+    Cu->collectAddressRanges(Ranges);
+
+    ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
+    for (DWARFAddressRange &R : Ranges) {
+      InputSectionBase *S = Sections[R.SectionIndex];
+      if (!S || S == &InputSection::Discarded || !S->Live)
+        continue;
+      // Range list with zero size has no effect.
+      if (R.LowPC == R.HighPC)
+        continue;
+      auto *IS = cast<InputSection>(S);
+      uint64_t Offset = IS->getOffsetInFile();
+      Ret.push_back({IS, R.LowPC - Offset, R.HighPC - Offset, CuIdx});
+    }
+    ++CuIdx;
+  }
+  return Ret;
+}
+
+static std::vector<GdbIndexChunk::NameTypeEntry>
+readPubNamesAndTypes(DWARFContext &Dwarf) {
+  StringRef Sec1 = Dwarf.getDWARFObj().getGnuPubNamesSection();
+  StringRef Sec2 = Dwarf.getDWARFObj().getGnuPubTypesSection();
+
+  std::vector<GdbIndexChunk::NameTypeEntry> Ret;
+  for (StringRef Sec : {Sec1, Sec2}) {
+    DWARFDebugPubTable Table(Sec, Config->IsLE, true);
+    for (const DWARFDebugPubTable::Set &Set : Table.getData()) {
+      for (const DWARFDebugPubTable::Entry &Ent : Set.Entries) {
+        CachedHashStringRef S(Ent.Name, computeGdbHash(Ent.Name));
+        Ret.push_back({S, Ent.Descriptor.toBits()});
+      }
+    }
+  }
+  return Ret;
+}
+
+static std::vector<InputSection *> getDebugInfoSections() {
+  std::vector<InputSection *> Ret;
+  for (InputSectionBase *S : InputSections)
+    if (InputSection *IS = dyn_cast<InputSection>(S))
+      if (IS->Name == ".debug_info")
+        Ret.push_back(IS);
+  return Ret;
+}
+
+void GdbIndexSection::fixCuIndex() {
+  uint32_t Idx = 0;
+  for (GdbIndexChunk &Chunk : Chunks) {
+    for (GdbIndexChunk::AddressEntry &Ent : Chunk.AddressAreas)
+      Ent.CuIndex += Idx;
+    Idx += Chunk.CompilationUnits.size();
+  }
+}
+
+std::vector<std::vector<uint32_t>> GdbIndexSection::createCuVectors() {
+  std::vector<std::vector<uint32_t>> Ret;
+  uint32_t Idx = 0;
+  uint32_t Off = 0;
+
+  for (GdbIndexChunk &Chunk : Chunks) {
+    for (GdbIndexChunk::NameTypeEntry &Ent : Chunk.NamesAndTypes) {
+      GdbSymbol *&Sym = Symbols[Ent.Name];
+      if (!Sym) {
+        Sym = make<GdbSymbol>(GdbSymbol{Ent.Name.hash(), Off, Ret.size()});
+        Off += Ent.Name.size() + 1;
+        Ret.push_back({});
+      }
+
+      // gcc 5.4.1 produces a buggy .debug_gnu_pubnames that contains
+      // duplicate entries, so we want to dedup them.
+      std::vector<uint32_t> &Vec = Ret[Sym->CuVectorIndex];
+      uint32_t Val = (Ent.Type << 24) | Idx;
+      if (Vec.empty() || Vec.back() != Val)
+        Vec.push_back(Val);
+    }
+    Idx += Chunk.CompilationUnits.size();
+  }
+
+  StringPoolSize = Off;
+  return Ret;
+}
+
+template <class ELFT> GdbIndexSection *elf::createGdbIndex() {
+  std::vector<InputSection *> Sections = getDebugInfoSections();
+  std::vector<GdbIndexChunk> Chunks(Sections.size());
+
+  parallelForEachN(0, Chunks.size(), [&](size_t I) {
+    ObjFile<ELFT> *File = Sections[I]->getFile<ELFT>();
+    DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(File));
+
+    Chunks[I].DebugInfoSec = Sections[I];
+    Chunks[I].CompilationUnits = readCuList(Dwarf);
+    Chunks[I].AddressAreas = readAddressAreas(Dwarf, Sections[I]);
+    Chunks[I].NamesAndTypes = readPubNamesAndTypes(Dwarf);
+  });
+
+  return make<GdbIndexSection>(std::move(Chunks));
+}
+
+static size_t getCuSize(ArrayRef<GdbIndexChunk> Arr) {
+  size_t Ret = 0;
+  for (const GdbIndexChunk &D : Arr)
+    Ret += D.CompilationUnits.size();
+  return Ret;
+}
+
+static size_t getAddressAreaSize(ArrayRef<GdbIndexChunk> Arr) {
+  size_t Ret = 0;
+  for (const GdbIndexChunk &D : Arr)
+    Ret += D.AddressAreas.size();
+  return Ret;
+}
+
+std::vector<GdbSymbol *> GdbIndexSection::createGdbSymtab() {
+  uint32_t Size = NextPowerOf2(Symbols.size() * 4 / 3);
+  if (Size < 1024)
+    Size = 1024;
+
+  uint32_t Mask = Size - 1;
+  std::vector<GdbSymbol *> Ret(Size);
+
+  for (auto &KV : Symbols) {
+    GdbSymbol *Sym = KV.second;
+    uint32_t I = Sym->NameHash & Mask;
+    uint32_t Step = ((Sym->NameHash * 17) & Mask) | 1;
+
+    while (Ret[I])
+      I = (I + Step) & Mask;
+    Ret[I] = Sym;
+  }
+  return Ret;
+}
+
+GdbIndexSection::GdbIndexSection(std::vector<GdbIndexChunk> &&C)
+    : SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index"), Chunks(std::move(C)) {
+  fixCuIndex();
+  CuVectors = createCuVectors();
+  GdbSymtab = createGdbSymtab();
+
+  // Compute offsets early to know the section size.
+  // Each chunk size needs to be in sync with what we write in writeTo.
+  CuTypesOffset = CuListOffset + getCuSize(Chunks) * 16;
+  SymtabOffset = CuTypesOffset + getAddressAreaSize(Chunks) * 20;
+  ConstantPoolOffset = SymtabOffset + GdbSymtab.size() * 8;
+
+  size_t Off = 0;
+  for (ArrayRef<uint32_t> Vec : CuVectors) {
+    CuVectorOffsets.push_back(Off);
+    Off += (Vec.size() + 1) * 4;
+  }
+  StringPoolOffset = ConstantPoolOffset + Off;
+}
+
+size_t GdbIndexSection::getSize() const {
+  return StringPoolOffset + StringPoolSize;
+}
+
+void GdbIndexSection::writeTo(uint8_t *Buf) {
+  // Write the section header.
+  write32le(Buf, 7);
+  write32le(Buf + 4, CuListOffset);
+  write32le(Buf + 8, CuTypesOffset);
+  write32le(Buf + 12, CuTypesOffset);
+  write32le(Buf + 16, SymtabOffset);
+  write32le(Buf + 20, ConstantPoolOffset);
+  Buf += 24;
+
+  // Write the CU list.
+  for (GdbIndexChunk &D : Chunks) {
+    for (GdbIndexChunk::CuEntry &Cu : D.CompilationUnits) {
+      write64le(Buf, D.DebugInfoSec->OutSecOff + Cu.CuOffset);
+      write64le(Buf + 8, Cu.CuLength);
+      Buf += 16;
+    }
+  }
+
+  // Write the address area.
+  for (GdbIndexChunk &D : Chunks) {
+    for (GdbIndexChunk::AddressEntry &E : D.AddressAreas) {
+      uint64_t BaseAddr =
+          E.Section->getParent()->Addr + E.Section->getOffset(0);
+      write64le(Buf, BaseAddr + E.LowAddress);
+      write64le(Buf + 8, BaseAddr + E.HighAddress);
+      write32le(Buf + 16, E.CuIndex);
+      Buf += 20;
+    }
+  }
+
+  // Write the symbol table.
+  for (GdbSymbol *Sym : GdbSymtab) {
+    if (Sym) {
+      write32le(Buf, Sym->NameOffset + StringPoolOffset - ConstantPoolOffset);
+      write32le(Buf + 4, CuVectorOffsets[Sym->CuVectorIndex]);
+    }
+    Buf += 8;
+  }
+
+  // Write the CU vectors.
+  for (ArrayRef<uint32_t> Vec : CuVectors) {
+    write32le(Buf, Vec.size());
+    Buf += 4;
+    for (uint32_t Val : Vec) {
+      write32le(Buf, Val);
+      Buf += 4;
+    }
+  }
+
+  // Write the string pool.
+  for (auto &KV : Symbols) {
+    CachedHashStringRef S = KV.first;
+    GdbSymbol *Sym = KV.second;
+    size_t Off = Sym->NameOffset;
+    memcpy(Buf + Off, S.val().data(), S.size());
+    Buf[Off + S.size()] = '\0';
+  }
+}
+
+bool GdbIndexSection::empty() const { return !Out::DebugInfo; }
+
+template <class ELFT>
+EhFrameHeader<ELFT>::EhFrameHeader()
+    : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame_hdr") {}
+
+// .eh_frame_hdr contains a binary search table of pointers to FDEs.
+// Each entry of the search table consists of two values,
+// the starting PC from where FDEs covers, and the FDE's address.
+// It is sorted by PC.
+template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
+  const endianness E = ELFT::TargetEndianness;
+
+  // Sort the FDE list by their PC and uniqueify. Usually there is only
+  // one FDE for a PC (i.e. function), but if ICF merges two functions
+  // into one, there can be more than one FDEs pointing to the address.
+  auto Less = [](const FdeData &A, const FdeData &B) { return A.Pc < B.Pc; };
+  std::stable_sort(Fdes.begin(), Fdes.end(), Less);
+  auto Eq = [](const FdeData &A, const FdeData &B) { return A.Pc == B.Pc; };
+  Fdes.erase(std::unique(Fdes.begin(), Fdes.end(), Eq), Fdes.end());
+
+  Buf[0] = 1;
+  Buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
+  Buf[2] = DW_EH_PE_udata4;
+  Buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
+  write32<E>(Buf + 4, In<ELFT>::EhFrame->getParent()->Addr - this->getVA() - 4);
+  write32<E>(Buf + 8, Fdes.size());
+  Buf += 12;
+
+  uint64_t VA = this->getVA();
+  for (FdeData &Fde : Fdes) {
+    write32<E>(Buf, Fde.Pc - VA);
+    write32<E>(Buf + 4, Fde.FdeVA - VA);
+    Buf += 8;
+  }
+}
+
+template <class ELFT> size_t EhFrameHeader<ELFT>::getSize() const {
+  // .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
+  return 12 + In<ELFT>::EhFrame->NumFdes * 8;
+}
+
+template <class ELFT>
+void EhFrameHeader<ELFT>::addFde(uint32_t Pc, uint32_t FdeVA) {
+  Fdes.push_back({Pc, FdeVA});
+}
+
+template <class ELFT> bool EhFrameHeader<ELFT>::empty() const {
+  return In<ELFT>::EhFrame->empty();
+}
+
+template <class ELFT>
+VersionDefinitionSection<ELFT>::VersionDefinitionSection()
+    : SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
+                       ".gnu.version_d") {}
+
+static StringRef getFileDefName() {
+  if (!Config->SoName.empty())
+    return Config->SoName;
+  return Config->OutputFile;
+}
+
+template <class ELFT> void VersionDefinitionSection<ELFT>::finalizeContents() {
+  FileDefNameOff = InX::DynStrTab->addString(getFileDefName());
+  for (VersionDefinition &V : Config->VersionDefinitions)
+    V.NameOff = InX::DynStrTab->addString(V.Name);
+
+  getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
+
+  // sh_info should be set to the number of definitions. This fact is missed in
+  // documentation, but confirmed by binutils community:
+  // https://sourceware.org/ml/binutils/2014-11/msg00355.html
+  getParent()->Info = getVerDefNum();
+}
+
+template <class ELFT>
+void VersionDefinitionSection<ELFT>::writeOne(uint8_t *Buf, uint32_t Index,
+                                              StringRef Name, size_t NameOff) {
+  auto *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
+  Verdef->vd_version = 1;
+  Verdef->vd_cnt = 1;
+  Verdef->vd_aux = sizeof(Elf_Verdef);
+  Verdef->vd_next = sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
+  Verdef->vd_flags = (Index == 1 ? VER_FLG_BASE : 0);
+  Verdef->vd_ndx = Index;
+  Verdef->vd_hash = hashSysV(Name);
+
+  auto *Verdaux = reinterpret_cast<Elf_Verdaux *>(Buf + sizeof(Elf_Verdef));
+  Verdaux->vda_name = NameOff;
+  Verdaux->vda_next = 0;
+}
+
+template <class ELFT>
+void VersionDefinitionSection<ELFT>::writeTo(uint8_t *Buf) {
+  writeOne(Buf, 1, getFileDefName(), FileDefNameOff);
+
+  for (VersionDefinition &V : Config->VersionDefinitions) {
+    Buf += sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
+    writeOne(Buf, V.Id, V.Name, V.NameOff);
+  }
+
+  // Need to terminate the last version definition.
+  Elf_Verdef *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
+  Verdef->vd_next = 0;
+}
+
+template <class ELFT> size_t VersionDefinitionSection<ELFT>::getSize() const {
+  return (sizeof(Elf_Verdef) + sizeof(Elf_Verdaux)) * getVerDefNum();
+}
+
+template <class ELFT>
+VersionTableSection<ELFT>::VersionTableSection()
+    : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
+                       ".gnu.version") {
+  this->Entsize = sizeof(Elf_Versym);
+}
+
+template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
+  // At the moment of june 2016 GNU docs does not mention that sh_link field
+  // should be set, but Sun docs do. Also readelf relies on this field.
+  getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
+}
+
+template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
+  return sizeof(Elf_Versym) * (InX::DynSymTab->getSymbols().size() + 1);
+}
+
+template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
+  auto *OutVersym = reinterpret_cast<Elf_Versym *>(Buf) + 1;
+  for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
+    OutVersym->vs_index = S.Symbol->symbol()->VersionId;
+    ++OutVersym;
+  }
+}
+
+template <class ELFT> bool VersionTableSection<ELFT>::empty() const {
+  return !In<ELFT>::VerDef && In<ELFT>::VerNeed->empty();
+}
+
+template <class ELFT>
+VersionNeedSection<ELFT>::VersionNeedSection()
+    : SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
+                       ".gnu.version_r") {
+  // Identifiers in verneed section start at 2 because 0 and 1 are reserved
+  // for VER_NDX_LOCAL and VER_NDX_GLOBAL.
+  // First identifiers are reserved by verdef section if it exist.
+  NextIndex = getVerDefNum() + 1;
+}
+
+template <class ELFT>
+void VersionNeedSection<ELFT>::addSymbol(SharedSymbol *SS) {
+  auto *Ver = reinterpret_cast<const typename ELFT::Verdef *>(SS->Verdef);
+  if (!Ver) {
+    SS->symbol()->VersionId = VER_NDX_GLOBAL;
+    return;
+  }
+
+  SharedFile<ELFT> *File = SS->getFile<ELFT>();
+
+  // If we don't already know that we need an Elf_Verneed for this DSO, prepare
+  // to create one by adding it to our needed list and creating a dynstr entry
+  // for the soname.
+  if (File->VerdefMap.empty())
+    Needed.push_back({File, InX::DynStrTab->addString(File->SoName)});
+  typename SharedFile<ELFT>::NeededVer &NV = File->VerdefMap[Ver];
+  // If we don't already know that we need an Elf_Vernaux for this Elf_Verdef,
+  // prepare to create one by allocating a version identifier and creating a
+  // dynstr entry for the version name.
+  if (NV.Index == 0) {
+    NV.StrTab = InX::DynStrTab->addString(File->getStringTable().data() +
+                                          Ver->getAux()->vda_name);
+    NV.Index = NextIndex++;
+  }
+  SS->symbol()->VersionId = NV.Index;
+}
+
+template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *Buf) {
+  // The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
+  auto *Verneed = reinterpret_cast<Elf_Verneed *>(Buf);
+  auto *Vernaux = reinterpret_cast<Elf_Vernaux *>(Verneed + Needed.size());
+
+  for (std::pair<SharedFile<ELFT> *, size_t> &P : Needed) {
+    // Create an Elf_Verneed for this DSO.
+    Verneed->vn_version = 1;
+    Verneed->vn_cnt = P.first->VerdefMap.size();
+    Verneed->vn_file = P.second;
+    Verneed->vn_aux =
+        reinterpret_cast<char *>(Vernaux) - reinterpret_cast<char *>(Verneed);
+    Verneed->vn_next = sizeof(Elf_Verneed);
+    ++Verneed;
+
+    // Create the Elf_Vernauxs for this Elf_Verneed. The loop iterates over
+    // VerdefMap, which will only contain references to needed version
+    // definitions. Each Elf_Vernaux is based on the information contained in
+    // the Elf_Verdef in the source DSO. This loop iterates over a std::map of
+    // pointers, but is deterministic because the pointers refer to Elf_Verdef
+    // data structures within a single input file.
+    for (auto &NV : P.first->VerdefMap) {
+      Vernaux->vna_hash = NV.first->vd_hash;
+      Vernaux->vna_flags = 0;
+      Vernaux->vna_other = NV.second.Index;
+      Vernaux->vna_name = NV.second.StrTab;
+      Vernaux->vna_next = sizeof(Elf_Vernaux);
+      ++Vernaux;
+    }
+
+    Vernaux[-1].vna_next = 0;
+  }
+  Verneed[-1].vn_next = 0;
+}
+
+template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
+  getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
+  getParent()->Info = Needed.size();
+}
+
+template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
+  unsigned Size = Needed.size() * sizeof(Elf_Verneed);
+  for (const std::pair<SharedFile<ELFT> *, size_t> &P : Needed)
+    Size += P.first->VerdefMap.size() * sizeof(Elf_Vernaux);
+  return Size;
+}
+
+template <class ELFT> bool VersionNeedSection<ELFT>::empty() const {
+  return getNeedNum() == 0;
+}
+
+MergeSyntheticSection::MergeSyntheticSection(StringRef Name, uint32_t Type,
+                                             uint64_t Flags, uint32_t Alignment)
+    : SyntheticSection(Flags, Type, Alignment, Name),
+      Builder(StringTableBuilder::RAW, Alignment) {}
+
+void MergeSyntheticSection::addSection(MergeInputSection *MS) {
+  MS->Parent = this;
+  Sections.push_back(MS);
+}
+
+void MergeSyntheticSection::writeTo(uint8_t *Buf) { Builder.write(Buf); }
+
+bool MergeSyntheticSection::shouldTailMerge() const {
+  return (this->Flags & SHF_STRINGS) && Config->Optimize >= 2;
+}
+
+void MergeSyntheticSection::finalizeTailMerge() {
+  // Add all string pieces to the string table builder to create section
+  // contents.
+  for (MergeInputSection *Sec : Sections)
+    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
+      if (Sec->Pieces[I].Live)
+        Builder.add(Sec->getData(I));
+
+  // Fix the string table content. After this, the contents will never change.
+  Builder.finalize();
+
+  // finalize() fixed tail-optimized strings, so we can now get
+  // offsets of strings. Get an offset for each string and save it
+  // to a corresponding StringPiece for easy access.
+  for (MergeInputSection *Sec : Sections)
+    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
+      if (Sec->Pieces[I].Live)
+        Sec->Pieces[I].OutputOff = Builder.getOffset(Sec->getData(I));
+}
+
+void MergeSyntheticSection::finalizeNoTailMerge() {
+  // Add all string pieces to the string table builder to create section
+  // contents. Because we are not tail-optimizing, offsets of strings are
+  // fixed when they are added to the builder (string table builder contains
+  // a hash table from strings to offsets).
+  for (MergeInputSection *Sec : Sections)
+    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
+      if (Sec->Pieces[I].Live)
+        Sec->Pieces[I].OutputOff = Builder.add(Sec->getData(I));
+
+  Builder.finalizeInOrder();
+}
+
+void MergeSyntheticSection::finalizeContents() {
+  if (shouldTailMerge())
+    finalizeTailMerge();
+  else
+    finalizeNoTailMerge();
+}
+
+size_t MergeSyntheticSection::getSize() const { return Builder.getSize(); }
+
+// This function decompresses compressed sections and scans over the input
+// sections to create mergeable synthetic sections. It removes
+// MergeInputSections from the input section array and adds new synthetic
+// sections at the location of the first input section that it replaces. It then
+// finalizes each synthetic section in order to compute an output offset for
+// each piece of each input section.
+void elf::decompressAndMergeSections() {
+  // splitIntoPieces needs to be called on each MergeInputSection before calling
+  // finalizeContents(). Do that first.
+  parallelForEach(InputSections, [](InputSectionBase *S) {
+    if (!S->Live)
+      return;
+    if (Decompressor::isCompressedELFSection(S->Flags, S->Name))
+      S->uncompress();
+    if (auto *MS = dyn_cast<MergeInputSection>(S))
+      MS->splitIntoPieces();
+  });
+
+  std::vector<MergeSyntheticSection *> MergeSections;
+  for (InputSectionBase *&S : InputSections) {
+    MergeInputSection *MS = dyn_cast<MergeInputSection>(S);
+    if (!MS)
+      continue;
+
+    // We do not want to handle sections that are not alive, so just remove
+    // them instead of trying to merge.
+    if (!MS->Live)
+      continue;
+
+    StringRef OutsecName = getOutputSectionName(MS->Name);
+    uint32_t Alignment = std::max<uint32_t>(MS->Alignment, MS->Entsize);
+
+    auto I = llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
+      return Sec->Name == OutsecName && Sec->Flags == MS->Flags &&
+             Sec->Alignment == Alignment;
+    });
+    if (I == MergeSections.end()) {
+      MergeSyntheticSection *Syn = make<MergeSyntheticSection>(
+          OutsecName, MS->Type, MS->Flags, Alignment);
+      MergeSections.push_back(Syn);
+      I = std::prev(MergeSections.end());
+      S = Syn;
+    } else {
+      S = nullptr;
+    }
+    (*I)->addSection(MS);
+  }
+  for (auto *MS : MergeSections)
+    MS->finalizeContents();
+
+  std::vector<InputSectionBase *> &V = InputSections;
+  V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
+}
+
+MipsRldMapSection::MipsRldMapSection()
+    : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, Config->Wordsize,
+                       ".rld_map") {}
+
+ARMExidxSentinelSection::ARMExidxSentinelSection()
+    : SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
+                       Config->Wordsize, ".ARM.exidx") {}
+
+// Write a terminating sentinel entry to the end of the .ARM.exidx table.
+// This section will have been sorted last in the .ARM.exidx table.
+// This table entry will have the form:
+// | PREL31 upper bound of code that has exception tables | EXIDX_CANTUNWIND |
+// The sentinel must have the PREL31 value of an address higher than any
+// address described by any other table entry.
+void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
+  // The Sections are sorted in order of ascending PREL31 address with the
+  // sentinel last. We need to find the InputSection that precedes the
+  // sentinel. By construction the Sentinel is in the last
+  // InputSectionDescription as the InputSection that precedes it.
+  OutputSection *C = getParent();
+  auto ISD = std::find_if(C->Commands.rbegin(), C->Commands.rend(),
+                          [](const BaseCommand *Base) {
+                            return isa<InputSectionDescription>(Base);
+                          });
+  auto L = cast<InputSectionDescription>(*ISD);
+  InputSection *Highest = L->Sections[L->Sections.size() - 2];
+  InputSection *LS = Highest->getLinkOrderDep();
+  uint64_t S = LS->getParent()->Addr + LS->getOffset(LS->getSize());
+  uint64_t P = getVA();
+  Target->relocateOne(Buf, R_ARM_PREL31, S - P);
+  write32le(Buf + 4, 0x1);
+}
+
+ThunkSection::ThunkSection(OutputSection *OS, uint64_t Off)
+    : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
+                       Config->Wordsize, ".text.thunk") {
+  this->Parent = OS;
+  this->OutSecOff = Off;
+}
+
+void ThunkSection::addThunk(Thunk *T) {
+  uint64_t Off = alignTo(Size, T->Alignment);
+  T->Offset = Off;
+  Thunks.push_back(T);
+  T->addSymbols(*this);
+  Size = Off + T->size();
+}
+
+void ThunkSection::writeTo(uint8_t *Buf) {
+  for (const Thunk *T : Thunks)
+    T->writeTo(Buf + T->Offset, *this);
+}
+
+InputSection *ThunkSection::getTargetInputSection() const {
+  const Thunk *T = Thunks.front();
+  return T->getTargetInputSection();
+}
+
+InputSection *InX::ARMAttributes;
+BssSection *InX::Bss;
+BssSection *InX::BssRelRo;
+BuildIdSection *InX::BuildId;
+SyntheticSection *InX::Dynamic;
+StringTableSection *InX::DynStrTab;
+SymbolTableBaseSection *InX::DynSymTab;
+InputSection *InX::Interp;
+GdbIndexSection *InX::GdbIndex;
+GotSection *InX::Got;
+GotPltSection *InX::GotPlt;
+GnuHashTableSection *InX::GnuHashTab;
+IgotPltSection *InX::IgotPlt;
+MipsGotSection *InX::MipsGot;
+MipsRldMapSection *InX::MipsRldMap;
+PltSection *InX::Plt;
+PltSection *InX::Iplt;
+StringTableSection *InX::ShStrTab;
+StringTableSection *InX::StrTab;
+SymbolTableBaseSection *InX::SymTab;
+
+template GdbIndexSection *elf::createGdbIndex<ELF32LE>();
+template GdbIndexSection *elf::createGdbIndex<ELF32BE>();
+template GdbIndexSection *elf::createGdbIndex<ELF64LE>();
+template GdbIndexSection *elf::createGdbIndex<ELF64BE>();
+
+template void PltSection::addEntry<ELF32LE>(SymbolBody &Sym);
+template void PltSection::addEntry<ELF32BE>(SymbolBody &Sym);
+template void PltSection::addEntry<ELF64LE>(SymbolBody &Sym);
+template void PltSection::addEntry<ELF64BE>(SymbolBody &Sym);
+
+template void elf::createCommonSections<ELF32LE>();
+template void elf::createCommonSections<ELF32BE>();
+template void elf::createCommonSections<ELF64LE>();
+template void elf::createCommonSections<ELF64BE>();
+
+template MergeInputSection *elf::createCommentSection<ELF32LE>();
+template MergeInputSection *elf::createCommentSection<ELF32BE>();
+template MergeInputSection *elf::createCommentSection<ELF64LE>();
+template MergeInputSection *elf::createCommentSection<ELF64BE>();
+
+template class elf::MipsAbiFlagsSection<ELF32LE>;
+template class elf::MipsAbiFlagsSection<ELF32BE>;
+template class elf::MipsAbiFlagsSection<ELF64LE>;
+template class elf::MipsAbiFlagsSection<ELF64BE>;
+
+template class elf::MipsOptionsSection<ELF32LE>;
+template class elf::MipsOptionsSection<ELF32BE>;
+template class elf::MipsOptionsSection<ELF64LE>;
+template class elf::MipsOptionsSection<ELF64BE>;
+
+template class elf::MipsReginfoSection<ELF32LE>;
+template class elf::MipsReginfoSection<ELF32BE>;
+template class elf::MipsReginfoSection<ELF64LE>;
+template class elf::MipsReginfoSection<ELF64BE>;
+
+template class elf::DynamicSection<ELF32LE>;
+template class elf::DynamicSection<ELF32BE>;
+template class elf::DynamicSection<ELF64LE>;
+template class elf::DynamicSection<ELF64BE>;
+
+template class elf::RelocationSection<ELF32LE>;
+template class elf::RelocationSection<ELF32BE>;
+template class elf::RelocationSection<ELF64LE>;
+template class elf::RelocationSection<ELF64BE>;
+
+template class elf::SymbolTableSection<ELF32LE>;
+template class elf::SymbolTableSection<ELF32BE>;
+template class elf::SymbolTableSection<ELF64LE>;
+template class elf::SymbolTableSection<ELF64BE>;
+
+template class elf::HashTableSection<ELF32LE>;
+template class elf::HashTableSection<ELF32BE>;
+template class elf::HashTableSection<ELF64LE>;
+template class elf::HashTableSection<ELF64BE>;
+
+template class elf::EhFrameHeader<ELF32LE>;
+template class elf::EhFrameHeader<ELF32BE>;
+template class elf::EhFrameHeader<ELF64LE>;
+template class elf::EhFrameHeader<ELF64BE>;
+
+template class elf::VersionTableSection<ELF32LE>;
+template class elf::VersionTableSection<ELF32BE>;
+template class elf::VersionTableSection<ELF64LE>;
+template class elf::VersionTableSection<ELF64BE>;
+
+template class elf::VersionNeedSection<ELF32LE>;
+template class elf::VersionNeedSection<ELF32BE>;
+template class elf::VersionNeedSection<ELF64LE>;
+template class elf::VersionNeedSection<ELF64BE>;
+
+template class elf::VersionDefinitionSection<ELF32LE>;
+template class elf::VersionDefinitionSection<ELF32BE>;
+template class elf::VersionDefinitionSection<ELF64LE>;
+template class elf::VersionDefinitionSection<ELF64BE>;
+
+template class elf::EhFrameSection<ELF32LE>;
+template class elf::EhFrameSection<ELF32BE>;
+template class elf::EhFrameSection<ELF64LE>;
+template class elf::EhFrameSection<ELF64BE>;
diff --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h
index b807408e5c7..0b5b84e0b76 100644
--- a/lld/ELF/SyntheticSections.h
+++ b/lld/ELF/SyntheticSections.h
@@ -786,7 +786,7 @@ private:
   size_t Size = 0;
 };
 
-std::vector<InputSection *> createCommonSections();
+template <class ELFT> void createCommonSections();
 InputSection *createInterpSection();
 template <class ELFT> MergeInputSection *createCommentSection();
 void decompressAndMergeSections();
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 4442f44b0e2..1926f1bd7b0 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -290,9 +290,6 @@ template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
     Add(InX::BuildId);
   }
 
-  for (InputSection *S : createCommonSections())
-    Add(S);
-
   InX::Bss = make<BssSection>(".bss");
   Add(InX::Bss);
   InX::BssRelRo = make<BssSection>(".bss.rel.ro");
@@ -441,11 +438,7 @@ static bool includeInSymtab(const SymbolBody &B) {
     if (auto *S = dyn_cast<MergeInputSection>(Sec))
       if (!S->getSectionPiece(D->Value)->Live)
         return false;
-    return true;
   }
-
-  if (auto *Sym = dyn_cast<DefinedCommon>(&B))
-    return Sym->Live;
   return true;
 }