[ELF] Convert VersionDefinitionSection, VersionTableSection and VersionNeedSection to input sections

[evgeny777]

Summary

Those sections are small and closely related, so I decided to convert them altogether.

[ruiu]

LGTM

ELF/OutputSections.h

 // non-overlapping file offsets and VAs.
 class OutputSectionBase {
 public:
   enum Kind {
     Base,
     EHFrame,
     Merge,
     Regular,
-    VersDef,
-    VersNeed,
-    VersTable
   };
 
   OutputSectionBase(StringRef Name, uint32_t Type, uint64_t Flags);
   void setLMAOffset(uint64_t LMAOff) { LMAOffset = LMAOff; }
   uint64_t getLMA() const { return Addr + LMAOffset; }
   template <typename ELFT> void writeHeaderTo(typename ELFT::Shdr *SHdr);
   StringRef getName() const { return Name; }
 
public:
   uint64_t LMAOffset = 0;
   uint64_t Addr = 0;
   uint32_t ShName = 0;
   uint32_t Type = 0;
   uint32_t Info = 0;
   uint32_t Link = 0;
 };
 
-// For more information about .gnu.version and .gnu.version_r see:
-// https://www.akkadia.org/drepper/symbol-versioning
-
-// The .gnu.version_d section which has a section type of SHT_GNU_verdef shall
-// contain symbol version definitions. The number of entries in this section
-// shall be contained in the DT_VERDEFNUM entry of the .dynamic section.
-// The section shall contain an array of Elf_Verdef structures, optionally
-// followed by an array of Elf_Verdaux structures.
-template <class ELFT>
-class VersionDefinitionSection final : public OutputSectionBase {
-  typedef typename ELFT::Verdef Elf_Verdef;
-  typedef typename ELFT::Verdaux Elf_Verdaux;
-
-public:
-  VersionDefinitionSection();
-  void finalize() override;
-  void writeTo(uint8_t *Buf) override;
-  Kind getKind() const override { return VersDef; }
-  static bool classof(const OutputSectionBase *B) {
-    return B->getKind() == VersDef;
-  }
-
-private:
-  void writeOne(uint8_t *Buf, uint32_t Index, StringRef Name, size_t NameOff);
-
-  unsigned FileDefNameOff;
-};
-
-// The .gnu.version section specifies the required version of each symbol in the
-// dynamic symbol table. It contains one Elf_Versym for each dynamic symbol
-// table entry. An Elf_Versym is just a 16-bit integer that refers to a version
-// identifier defined in the either .gnu.version_r or .gnu.version_d section.
-// The values 0 and 1 are reserved. All other values are used for versions in
-// the own object or in any of the dependencies.
-template <class ELFT>
-class VersionTableSection final : public OutputSectionBase {
-  typedef typename ELFT::Versym Elf_Versym;
-
-public:
-  VersionTableSection();
-  void finalize() override;
-  void writeTo(uint8_t *Buf) override;
-  Kind getKind() const override { return VersTable; }
-  static bool classof(const OutputSectionBase *B) {
-    return B->getKind() == VersTable;
-  }
-};
-
-// The .gnu.version_r section defines the version identifiers used by
-// .gnu.version. It contains a linked list of Elf_Verneed data structures. Each
-// Elf_Verneed specifies the version requirements for a single DSO, and contains
-// a reference to a linked list of Elf_Vernaux data structures which define the
-// mapping from version identifiers to version names.
-template <class ELFT>
-class VersionNeedSection final : public OutputSectionBase {
-  typedef typename ELFT::Verneed Elf_Verneed;
-  typedef typename ELFT::Vernaux Elf_Vernaux;
-
-  // A vector of shared files that need Elf_Verneed data structures and the
-  // string table offsets of their sonames.
-  std::vector<std::pair<SharedFile<ELFT> *, size_t>> Needed;
-
-  // The next available version identifier.
-  unsigned NextIndex;
-
-public:
-  VersionNeedSection();
-  void addSymbol(SharedSymbol<ELFT> *SS);
-  void finalize() override;
-  void writeTo(uint8_t *Buf) override;
-  size_t getNeedNum() const { return Needed.size(); }
-  Kind getKind() const override { return VersNeed; }
-  static bool classof(const OutputSectionBase *B) {
-    return B->getKind() == VersNeed;
-  }
-};
-
 template <class ELFT> class OutputSection final : public OutputSectionBase {
 
 public:
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::Rel Elf_Rel;
   typedef typename ELFT::Rela Elf_Rela;
   typedef typename ELFT::uint uintX_t;
template <class ELFT> struct Out {
   typedef typename ELFT::Phdr Elf_Phdr;
 
   static uint8_t First;
   static EhOutputSection<ELFT> *EhFrame;
   static OutputSection<ELFT> *Bss;
   static OutputSection<ELFT> *MipsRldMap;
   static OutputSectionBase *Opd;
   static uint8_t *OpdBuf;
-  static VersionDefinitionSection<ELFT> *VerDef;
-  static VersionTableSection<ELFT> *VerSym;
-  static VersionNeedSection<ELFT> *VerNeed;
   static Elf_Phdr *TlsPhdr;
   static OutputSectionBase *DebugInfo;
   static OutputSectionBase *ElfHeader;
   static OutputSectionBase *ProgramHeaders;
   static OutputSectionBase *PreinitArray;
   static OutputSectionBase *InitArray;
   static OutputSectionBase *FiniArray;
 };

 }
 
 template <class ELFT> uint8_t Out<ELFT>::First;
 template <class ELFT> EhOutputSection<ELFT> *Out<ELFT>::EhFrame;
 template <class ELFT> OutputSection<ELFT> *Out<ELFT>::Bss;
 template <class ELFT> OutputSection<ELFT> *Out<ELFT>::MipsRldMap;
 template <class ELFT> OutputSectionBase *Out<ELFT>::Opd;
 template <class ELFT> uint8_t *Out<ELFT>::OpdBuf;
-template <class ELFT> VersionDefinitionSection<ELFT> *Out<ELFT>::VerDef;
-template <class ELFT> VersionTableSection<ELFT> *Out<ELFT>::VerSym;
-template <class ELFT> VersionNeedSection<ELFT> *Out<ELFT>::VerNeed;
 template <class ELFT> typename ELFT::Phdr *Out<ELFT>::TlsPhdr;
 template <class ELFT> OutputSectionBase *Out<ELFT>::DebugInfo;
 template <class ELFT> OutputSectionBase *Out<ELFT>::ElfHeader;
 template <class ELFT> OutputSectionBase *Out<ELFT>::ProgramHeaders;
 template <class ELFT> OutputSectionBase *Out<ELFT>::PreinitArray;
 template <class ELFT> OutputSectionBase *Out<ELFT>::InitArray;
 template <class ELFT> OutputSectionBase *Out<ELFT>::FiniArray;
 } // namespace elf

ELF/OutputSections.cpp

void OutputSectionBase::writeHeaderTo(typename ELFT::Shdr *Shdr) {
   Shdr->sh_flags = Flags;
   Shdr->sh_info = Info;
   Shdr->sh_link = Link;
   Shdr->sh_addr = Addr;
   Shdr->sh_size = Size;
   Shdr->sh_name = ShName;
 }
 
-// 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>
 void EhFrameHeader<ELFT>::addFde(uint32_t Pc, uint32_t FdeVA) {
   Fdes.push_back({Pc, FdeVA});
 }
 
 template <class ELFT> static uint64_t getEntsize(uint32_t Type) {
   switch (Type) {
   case SHT_RELA:
template <class ELFT> void MergeOutputSection<ELFT>::finalize() {
   if (shouldTailMerge())
     for (MergeInputSection<ELFT> *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));
 }
 
 template <class ELFT>
-VersionDefinitionSection<ELFT>::VersionDefinitionSection()
-    : OutputSectionBase(".gnu.version_d", SHT_GNU_verdef, SHF_ALLOC) {
-  this->Addralign = sizeof(uint32_t);
-}
-
-static StringRef getFileDefName() {
-  if (!Config->SoName.empty())
-    return Config->SoName;
-  return Config->OutputFile;
-}
-
-template <class ELFT> void VersionDefinitionSection<ELFT>::finalize() {
-  FileDefNameOff = In<ELFT>::DynStrTab->addString(getFileDefName());
-  for (VersionDefinition &V : Config->VersionDefinitions)
-    V.NameOff = In<ELFT>::DynStrTab->addString(V.Name);
-
-  this->Size = (sizeof(Elf_Verdef) + sizeof(Elf_Verdaux)) * getVerDefNum();
-  this->Link = In<ELFT>::DynStrTab->OutSec->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
-  this->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>
-VersionTableSection<ELFT>::VersionTableSection()
-    : OutputSectionBase(".gnu.version", SHT_GNU_versym, SHF_ALLOC) {
-  this->Addralign = sizeof(uint16_t);
-}
-
-template <class ELFT> void VersionTableSection<ELFT>::finalize() {
-  this->Size =
-      sizeof(Elf_Versym) * (In<ELFT>::DynSymTab->getSymbols().size() + 1);
-  this->Entsize = sizeof(Elf_Versym);
-  // 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.
-  this->Link = In<ELFT>::DynSymTab->OutSec->SectionIndex;
-}
-
-template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
-  auto *OutVersym = reinterpret_cast<Elf_Versym *>(Buf) + 1;
-  for (const SymbolTableEntry &S : In<ELFT>::DynSymTab->getSymbols()) {
-    OutVersym->vs_index = S.Symbol->symbol()->VersionId;
-    ++OutVersym;
-  }
-}
-
-template <class ELFT>
-VersionNeedSection<ELFT>::VersionNeedSection()
-    : OutputSectionBase(".gnu.version_r", SHT_GNU_verneed, SHF_ALLOC) {
-  this->Addralign = sizeof(uint32_t);
-
-  // 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<ELFT> *SS) {
-  if (!SS->Verdef) {
-    SS->symbol()->VersionId = VER_NDX_GLOBAL;
-    return;
-  }
-  SharedFile<ELFT> *F = SS->file();
-  // 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 (F->VerdefMap.empty())
-    Needed.push_back({F, In<ELFT>::DynStrTab->addString(F->getSoName())});
-  typename SharedFile<ELFT>::NeededVer &NV = F->VerdefMap[SS->Verdef];
-  // 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 = In<ELFT>::DynStrTab->addString(
-        SS->file()->getStringTable().data() + SS->Verdef->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>::finalize() {
-  this->Link = In<ELFT>::DynStrTab->OutSec->SectionIndex;
-  this->Info = Needed.size();
-  unsigned Size = Needed.size() * sizeof(Elf_Verneed);
-  for (std::pair<SharedFile<ELFT> *, size_t> &P : Needed)
-    Size += P.first->VerdefMap.size() * sizeof(Elf_Vernaux);
-  this->Size = Size;
-}
-
-template <class ELFT>
 static typename ELFT::uint getOutFlags(InputSectionBase<ELFT> *S) {
   return S->Flags & ~SHF_GROUP & ~SHF_COMPRESSED;
 }
 
 template <class ELFT>
 static SectionKey<ELFT::Is64Bits> createKey(InputSectionBase<ELFT> *C,
                                             StringRef OutsecName) {
   typedef typename ELFT::uint uintX_t;

 template class EhOutputSection<ELF64LE>;
 template class EhOutputSection<ELF64BE>;
 
 template class MergeOutputSection<ELF32LE>;
 template class MergeOutputSection<ELF32BE>;
 template class MergeOutputSection<ELF64LE>;
 template class MergeOutputSection<ELF64BE>;
 
-template class VersionTableSection<ELF32LE>;
-template class VersionTableSection<ELF32BE>;
-template class VersionTableSection<ELF64LE>;
-template class VersionTableSection<ELF64BE>;
-
-template class VersionNeedSection<ELF32LE>;
-template class VersionNeedSection<ELF32BE>;
-template class VersionNeedSection<ELF64LE>;
-template class VersionNeedSection<ELF64BE>;
-
-template class VersionDefinitionSection<ELF32LE>;
-template class VersionDefinitionSection<ELF32BE>;
-template class VersionDefinitionSection<ELF64LE>;
-template class VersionDefinitionSection<ELF64BE>;
-
 template class OutputSectionFactory<ELF32LE>;
 template class OutputSectionFactory<ELF32BE>;
 template class OutputSectionFactory<ELF64LE>;
 template class OutputSectionFactory<ELF64BE>;
 }
 }

ELF/SyntheticSections.h

private:
   struct FdeData {
     uint32_t Pc;
     uint32_t FdeVA;
   };
 
   std::vector<FdeData> Fdes;
 };
 
+// For more information about .gnu.version and .gnu.version_r see:
+// https://www.akkadia.org/drepper/symbol-versioning
+
+// The .gnu.version_d section which has a section type of SHT_GNU_verdef shall
+// contain symbol version definitions. The number of entries in this section
+// shall be contained in the DT_VERDEFNUM entry of the .dynamic section.
+// The section shall contain an array of Elf_Verdef structures, optionally
+// followed by an array of Elf_Verdaux structures.
+template <class ELFT>
+class VersionDefinitionSection final : public SyntheticSection<ELFT> {
+  typedef typename ELFT::Verdef Elf_Verdef;
+  typedef typename ELFT::Verdaux Elf_Verdaux;
+
+public:
+  VersionDefinitionSection();
+  void finalize() override;
+  size_t getSize() const override;
+  void writeTo(uint8_t *Buf) override;
+
+private:
+  void writeOne(uint8_t *Buf, uint32_t Index, StringRef Name, size_t NameOff);
+
+  unsigned FileDefNameOff;
+};
+
+// The .gnu.version section specifies the required version of each symbol in the
+// dynamic symbol table. It contains one Elf_Versym for each dynamic symbol
+// table entry. An Elf_Versym is just a 16-bit integer that refers to a version
+// identifier defined in the either .gnu.version_r or .gnu.version_d section.
+// The values 0 and 1 are reserved. All other values are used for versions in
+// the own object or in any of the dependencies.
+template <class ELFT>
+class VersionTableSection final : public SyntheticSection<ELFT> {
+  typedef typename ELFT::Versym Elf_Versym;
+
+public:
+  VersionTableSection();
+  void finalize() override;
+  size_t getSize() const override;
+  void writeTo(uint8_t *Buf) override;
+};
+
+// The .gnu.version_r section defines the version identifiers used by
+// .gnu.version. It contains a linked list of Elf_Verneed data structures. Each
+// Elf_Verneed specifies the version requirements for a single DSO, and contains
+// a reference to a linked list of Elf_Vernaux data structures which define the
+// mapping from version identifiers to version names.
+template <class ELFT>
+class VersionNeedSection final : public SyntheticSection<ELFT> {
+  typedef typename ELFT::Verneed Elf_Verneed;
+  typedef typename ELFT::Vernaux Elf_Vernaux;
+
+  // A vector of shared files that need Elf_Verneed data structures and the
+  // string table offsets of their sonames.
+  std::vector<std::pair<SharedFile<ELFT> *, size_t>> Needed;
+
+  // The next available version identifier.
+  unsigned NextIndex;
+
+public:
+  VersionNeedSection();
+  void addSymbol(SharedSymbol<ELFT> *SS);
+  void finalize() override;
+  void writeTo(uint8_t *Buf) override;
+  size_t getSize() const override;
+  size_t getNeedNum() const { return Needed.size(); }
+};
+
 template <class ELFT> InputSection<ELFT> *createCommonSection();
 template <class ELFT> InputSection<ELFT> *createInterpSection();
 template <class ELFT> MergeInputSection<ELFT> *createCommentSection();
 
 // Linker generated sections which can be used as inputs.
 template <class ELFT> struct In {
   static BuildIdSection<ELFT> *BuildId;
   static InputSection<ELFT> *Common;
template <class ELFT> struct In {
   static MipsOptionsSection<ELFT> *MipsOptions;
   static MipsReginfoSection<ELFT> *MipsReginfo;
   static PltSection<ELFT> *Plt;
   static RelocationSection<ELFT> *RelaDyn;
   static RelocationSection<ELFT> *RelaPlt;
   static StringTableSection<ELFT> *ShStrTab;
   static StringTableSection<ELFT> *StrTab;
   static SymbolTableSection<ELFT> *SymTab;
+  static VersionDefinitionSection<ELFT> *VerDef;
+  static VersionTableSection<ELFT> *VerSym;
+  static VersionNeedSection<ELFT> *VerNeed;
 };
 
 template <class ELFT> BuildIdSection<ELFT> *In<ELFT>::BuildId;
 template <class ELFT> InputSection<ELFT> *In<ELFT>::Common;
 template <class ELFT> DynamicSection<ELFT> *In<ELFT>::Dynamic;
 template <class ELFT> StringTableSection<ELFT> *In<ELFT>::DynStrTab;
 template <class ELFT> SymbolTableSection<ELFT> *In<ELFT>::DynSymTab;
 template <class ELFT> EhFrameHeader<ELFT> *In<ELFT>::EhFrameHdr;
 template <class ELFT> GdbIndexSection<ELFT> *In<ELFT>::GdbIndex;
 template <class ELFT> GnuHashTableSection<ELFT> *In<ELFT>::GnuHashTab;
 template <class ELFT> GotSection<ELFT> *In<ELFT>::Got;
 template <class ELFT> MipsGotSection<ELFT> *In<ELFT>::MipsGot;
 template <class ELFT> GotPltSection<ELFT> *In<ELFT>::GotPlt;
 template <class ELFT> HashTableSection<ELFT> *In<ELFT>::HashTab;
 template <class ELFT> InputSection<ELFT> *In<ELFT>::Interp;
 template <class ELFT> MipsAbiFlagsSection<ELFT> *In<ELFT>::MipsAbiFlags;
 template <class ELFT> MipsOptionsSection<ELFT> *In<ELFT>::MipsOptions;
 template <class ELFT> MipsReginfoSection<ELFT> *In<ELFT>::MipsReginfo;
 template <class ELFT> PltSection<ELFT> *In<ELFT>::Plt;
 template <class ELFT> RelocationSection<ELFT> *In<ELFT>::RelaDyn;
 template <class ELFT> RelocationSection<ELFT> *In<ELFT>::RelaPlt;
 template <class ELFT> StringTableSection<ELFT> *In<ELFT>::ShStrTab;
 template <class ELFT> StringTableSection<ELFT> *In<ELFT>::StrTab;
 template <class ELFT> SymbolTableSection<ELFT> *In<ELFT>::SymTab;
+template <class ELFT> VersionDefinitionSection<ELFT> *In<ELFT>::VerDef;
+template <class ELFT> VersionTableSection<ELFT> *In<ELFT>::VerSym;
+template <class ELFT> VersionNeedSection<ELFT> *In<ELFT>::VerNeed;
 } // namespace elf
 } // namespace lld
 
 #endif

ELF/SyntheticSections.cpp

template <class ELFT> void StringTableSection<ELFT>::writeTo(uint8_t *Buf) {
   // ELF string tables start with NUL byte, so advance the pointer by one.
   ++Buf;
   for (StringRef S : Strings) {
     memcpy(Buf, S.data(), S.size());
     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<ELFT>(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC,
                              sizeof(uintX_t), ".dynamic") {
   this->Entsize = ELFT::Is64Bits ? 16 : 8;
   // .dynamic section is not writable on MIPS.
if (Out<ELFT>::FiniArray) {
     add({DT_FINI_ARRAYSZ, Out<ELFT>::FiniArray, Entry::SecSize});
   }
 
   if (SymbolBody *B = Symtab<ELFT>::X->find(Config->Init))
     add({DT_INIT, B});
   if (SymbolBody *B = Symtab<ELFT>::X->find(Config->Fini))
     add({DT_FINI, B});
 
-  bool HasVerNeed = Out<ELFT>::VerNeed->getNeedNum() != 0;
-  if (HasVerNeed || Out<ELFT>::VerDef)
-    add({DT_VERSYM, Out<ELFT>::VerSym});
-  if (Out<ELFT>::VerDef) {
-    add({DT_VERDEF, Out<ELFT>::VerDef});
+  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, Out<ELFT>::VerNeed});
-    add({DT_VERNEEDNUM, Out<ELFT>::VerNeed->getNeedNum()});
+    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, In<ELFT>::DynSymTab->getNumSymbols()});
     add({DT_MIPS_LOCAL_GOTNO, In<ELFT>::MipsGot->getLocalEntriesNum()});
template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
   }
 }
 
 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 + Out<ELFT>::EhFrame->NumFdes * 8;
 }
 
+template <class ELFT>
+VersionDefinitionSection<ELFT>::VersionDefinitionSection()
+    : SyntheticSection<ELFT>(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>::finalize() {
+  FileDefNameOff = In<ELFT>::DynStrTab->addString(getFileDefName());
+  for (VersionDefinition &V : Config->VersionDefinitions)
+    V.NameOff = In<ELFT>::DynStrTab->addString(V.Name);
+
+  this->OutSec->Link = this->Link = In<ELFT>::DynStrTab->OutSec->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
+  this->OutSec->Info = this->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<ELFT>(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
+                             ".gnu.version") {}
+
+template <class ELFT> void VersionTableSection<ELFT>::finalize() {
+  this->OutSec->Entsize = this->Entsize = sizeof(Elf_Versym);
+  // 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.
+  this->OutSec->Link = this->Link = In<ELFT>::DynSymTab->OutSec->SectionIndex;
+}
+
+template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
+  return sizeof(Elf_Versym) * (In<ELFT>::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 : In<ELFT>::DynSymTab->getSymbols()) {
+    OutVersym->vs_index = S.Symbol->symbol()->VersionId;
+    ++OutVersym;
+  }
+}
+
+template <class ELFT>
+VersionNeedSection<ELFT>::VersionNeedSection()
+    : SyntheticSection<ELFT>(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<ELFT> *SS) {
+  if (!SS->Verdef) {
+    SS->symbol()->VersionId = VER_NDX_GLOBAL;
+    return;
+  }
+  SharedFile<ELFT> *F = SS->file();
+  // 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 (F->VerdefMap.empty())
+    Needed.push_back({F, In<ELFT>::DynStrTab->addString(F->getSoName())});
+  typename SharedFile<ELFT>::NeededVer &NV = F->VerdefMap[SS->Verdef];
+  // 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 = In<ELFT>::DynStrTab->addString(
+        SS->file()->getStringTable().data() + SS->Verdef->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>::finalize() {
+  this->OutSec->Link = this->Link = In<ELFT>::DynStrTab->OutSec->SectionIndex;
+  this->OutSec->Info = this->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 InputSection<ELF32LE> *elf::createCommonSection();
 template InputSection<ELF32BE> *elf::createCommonSection();
 template InputSection<ELF64LE> *elf::createCommonSection();
 template InputSection<ELF64BE> *elf::createCommonSection();
 
 template InputSection<ELF32LE> *elf::createInterpSection();
 template InputSection<ELF32BE> *elf::createInterpSection();
 template InputSection<ELF64LE> *elf::createInterpSection();

 template class elf::GdbIndexSection<ELF32BE>;
 template class elf::GdbIndexSection<ELF64LE>;
 template class elf::GdbIndexSection<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>;

ELF/Writer.cpp

Out<ELFT>::Bss =
       make<OutputSection<ELFT>>(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
   In<ELFT>::DynStrTab = make<StringTableSection<ELFT>>(".dynstr", true);
   In<ELFT>::Dynamic = make<DynamicSection<ELFT>>();
   Out<ELFT>::EhFrame = make<EhOutputSection<ELFT>>();
   In<ELFT>::Plt = make<PltSection<ELFT>>();
   In<ELFT>::RelaDyn = make<RelocationSection<ELFT>>(
       Config->Rela ? ".rela.dyn" : ".rel.dyn", Config->ZCombreloc);
   In<ELFT>::ShStrTab = make<StringTableSection<ELFT>>(".shstrtab", false);
-  Out<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
-  Out<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
+  In<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
+  In<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
 
   Out<ELFT>::ElfHeader = make<OutputSectionBase>("", 0, SHF_ALLOC);
   Out<ELFT>::ElfHeader->Size = sizeof(Elf_Ehdr);
   Out<ELFT>::ProgramHeaders = make<OutputSectionBase>("", 0, SHF_ALLOC);
   Out<ELFT>::ProgramHeaders->updateAlignment(sizeof(uintX_t));
 
   if (needsInterpSection<ELFT>()) {
     In<ELFT>::Interp = createInterpSection<ELFT>();
if (Config->EMachine == EM_MIPS && !Config->Shared) {
     // See "Dynamic section" in Chapter 5 in the following document:
     // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
     Out<ELFT>::MipsRldMap = make<OutputSection<ELFT>>(".rld_map", SHT_PROGBITS,
                                                       SHF_ALLOC | SHF_WRITE);
     Out<ELFT>::MipsRldMap->Size = sizeof(uintX_t);
     Out<ELFT>::MipsRldMap->updateAlignment(sizeof(uintX_t));
   }
   if (!Config->VersionDefinitions.empty())
-    Out<ELFT>::VerDef = make<VersionDefinitionSection<ELFT>>();
+    In<ELFT>::VerDef = make<VersionDefinitionSection<ELFT>>();
 
   // Initialize linker generated sections
   if (!Config->Relocatable)
     Symtab<ELFT>::X->Sections.push_back(createCommentSection<ELFT>());
 
   if (Config->BuildId == BuildIdKind::Fast)
     In<ELFT>::BuildId = make<BuildIdFastHash<ELFT>>();
   else if (Config->BuildId == BuildIdKind::Md5)
if (!includeInSymtab<ELFT>(*Body))
       continue;
     if (In<ELFT>::SymTab)
       In<ELFT>::SymTab->addSymbol(Body);
 
     if (In<ELFT>::DynSymTab && S->includeInDynsym()) {
       In<ELFT>::DynSymTab->addSymbol(Body);
       if (auto *SS = dyn_cast<SharedSymbol<ELFT>>(Body))
         if (SS->file()->isNeeded())
-          Out<ELFT>::VerNeed->addSymbol(SS);
+          In<ELFT>::VerNeed->addSymbol(SS);
     }
   }
 
   // Do not proceed if there was an undefined symbol.
   if (HasError)
     return;
 
   // So far we have added sections from input object files.
template <class ELFT> void Writer<ELFT>::finalizeSections() {
   // Fill other section headers. The dynamic table is finalized
   // at the end because some tags like RELSZ depend on result
   // of finalizing other sections.
   for (OutputSectionBase *Sec : OutputSections)
     Sec->finalize();
 
   // Dynamic section must be the last one in this list and dynamic
   // symbol table section (DynSymTab) must be the first one.
-  finalizeSynthetic<ELFT>({In<ELFT>::DynSymTab, In<ELFT>::GnuHashTab,
-                           In<ELFT>::HashTab, In<ELFT>::SymTab,
-                           In<ELFT>::ShStrTab, In<ELFT>::StrTab,
-                           In<ELFT>::DynStrTab, In<ELFT>::GdbIndex,
-                           In<ELFT>::Got, In<ELFT>::MipsGot, In<ELFT>::GotPlt,
-                           In<ELFT>::RelaDyn, In<ELFT>::RelaPlt, In<ELFT>::Plt,
-                           In<ELFT>::EhFrameHdr, In<ELFT>::Dynamic});
+  finalizeSynthetic<ELFT>(
+      {In<ELFT>::DynSymTab, In<ELFT>::GnuHashTab, In<ELFT>::HashTab,
+       In<ELFT>::SymTab, In<ELFT>::ShStrTab, In<ELFT>::StrTab,
+       In<ELFT>::DynStrTab, In<ELFT>::GdbIndex, In<ELFT>::Got,
+       In<ELFT>::MipsGot, In<ELFT>::GotPlt, In<ELFT>::RelaDyn,
+       In<ELFT>::RelaPlt, In<ELFT>::Plt, In<ELFT>::EhFrameHdr, In<ELFT>::VerDef,
+       In<ELFT>::VerSym, In<ELFT>::VerNeed, In<ELFT>::Dynamic});
 }
 
 template <class ELFT> bool Writer<ELFT>::needsGot() {
   // We add the .got section to the result for dynamic MIPS target because
   // its address and properties are mentioned in the .dynamic section.
   if (Config->EMachine == EM_MIPS)
     return !Config->Relocatable;
 
template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
   if (In<ELFT>::GdbIndex && Out<ELFT>::DebugInfo)
     addInputSec(In<ELFT>::GdbIndex);
   addInputSec(In<ELFT>::SymTab);
   addInputSec(In<ELFT>::ShStrTab);
   addInputSec(In<ELFT>::StrTab);
   if (In<ELFT>::DynSymTab) {
     addInputSec(In<ELFT>::DynSymTab);
 
-    bool HasVerNeed = Out<ELFT>::VerNeed->getNeedNum() != 0;
-    if (Out<ELFT>::VerDef || HasVerNeed)
-      Add(Out<ELFT>::VerSym);
-    Add(Out<ELFT>::VerDef);
+    bool HasVerNeed = In<ELFT>::VerNeed->getNeedNum() != 0;
+    if (In<ELFT>::VerDef || HasVerNeed)
+      addInputSec(In<ELFT>::VerSym);
+    addInputSec(In<ELFT>::VerDef);
     if (HasVerNeed)
-      Add(Out<ELFT>::VerNeed);
+      addInputSec(In<ELFT>::VerNeed);
 
     addInputSec(In<ELFT>::GnuHashTab);
     addInputSec(In<ELFT>::HashTab);
     addInputSec(In<ELFT>::Dynamic);
     addInputSec(In<ELFT>::DynStrTab);
     if (In<ELFT>::RelaDyn->hasRelocs())
       addInputSec(In<ELFT>::RelaDyn);
     Add(Out<ELFT>::MipsRldMap);