ELF: Extract a non-ELFT base class for VersionNeedSection.

[pcc]

Summary

We're going to need a separate VersionNeedSection for each partition, and
the partition data structure won't be templated.

With this the VersionTableSection class no longer needs ELFT, so detemplate it.

[ruiu]

I wonder if we can just get rid of ELFT from the class. At runtime we know endianess and word width, so in theory we can create a version table without ELFT. I'm not totally sure if this makes things easier to handle, but many classes are template with ELFT because they transitively use a ELFT-templated class. So removing ELFT from one class might allow us remove ELFT from more classes.

[pcc]

In D58808#1414591, @ruiu wrote:

I wonder if we can just get rid of ELFT from the class. At runtime we know endianess and word width, so in theory we can create a version table without ELFT. I'm not totally sure if this makes things easier to handle, but many classes are template with ELFT because they transitively use a ELFT-templated class. So removing ELFT from one class might allow us remove ELFT from more classes.

You mean from VersionNeedSection? Yes in theory, but now that createSyntheticSections is the only direct user of VersionNeedSection I think we'd also need to remove templating from RelocationSection, SymbolTableSection etc in order to detemplate anything else. And those classes are similar to VersionNeedSection in that they need to manipulate ELF data structures directly, so it's not clear that it's the right way to go.

That said, now that I've removed InX there does appear to be some low hanging fruit in finalizeSections() that can be detemplated. Let me see if I can send a patch.

[ruiu]

LGTM

lld/ELF/Driver.cpp

 #include "llvm/IR/RuntimeLibcalls.def"
 #undef HANDLE_LIBCALL
 };
 
 // Do actual linking. Note that when this function is called,
 // all linker scripts have already been parsed.
 template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   Target = getTarget();
-  InX<ELFT>::VerSym = nullptr;
-  InX<ELFT>::VerNeed = nullptr;
 
   Config->MaxPageSize = getMaxPageSize(Args);
   Config->ImageBase = getImageBase(Args);
 
   // If a -hash-style option was not given, set to a default value,
   // which varies depending on the target.
   if (!Args.hasArg(OPT_hash_style)) {
     if (Config->EMachine == EM_MIPS)

lld/ELF/SyntheticSections.h

 };
 
 // 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 {
 public:
   VersionTableSection();
   void finalizeContents() override;
   size_t getSize() const override;
   void writeTo(uint8_t *Buf) override;
   bool empty() const override;
 };
 
+class VersionNeedBaseSection : public SyntheticSection {
+protected:
+  // The next available version identifier.
+  unsigned NextIndex;
+
+public:
+  VersionNeedBaseSection();
+  virtual void addSymbol(Symbol *Sym) = 0;
+  virtual size_t getNeedNum() const = 0;
+};
+
 // 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 {
+template <class ELFT>
+class VersionNeedSection final : public VersionNeedBaseSection {
   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(Symbol *Sym);
+  void addSymbol(Symbol *Sym) override;
   void finalizeContents() override;
   void writeTo(uint8_t *Buf) override;
   size_t getSize() const override;
-  size_t getNeedNum() const { return Needed.size(); }
+  size_t getNeedNum() const override { return Needed.size(); }
   bool empty() const override;
 };
 
 // MergeSyntheticSection is a class that allows us to put mergeable sections
 // with different attributes in a single output sections. To do that
 // we put them into MergeSyntheticSection synthetic input sections which are
 // attached to regular output sections.
 class MergeSyntheticSection : public SyntheticSection {
struct InStruct {
   RelrBaseSection *RelrDyn;
   RelocationBaseSection *RelaPlt;
   RelocationBaseSection *RelaIplt;
   StringTableSection *ShStrTab;
   StringTableSection *StrTab;
   SymbolTableBaseSection *SymTab;
   SymtabShndxSection *SymTabShndx;
   VersionDefinitionSection *VerDef;
+  VersionNeedBaseSection *VerNeed;
+  VersionTableSection *VerSym;
 };
 
 extern InStruct In;
 
-template <class ELFT> struct InX {
-  static VersionTableSection<ELFT> *VerSym;
-  static VersionNeedSection<ELFT> *VerNeed;
-};
-
-template <class ELFT> VersionTableSection<ELFT> *InX<ELFT>::VerSym;
-template <class ELFT> VersionNeedSection<ELFT> *InX<ELFT>::VerNeed;
 } // namespace elf
 } // namespace lld
 
 #endif

lld/ELF/SyntheticSections.cpp

template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
 
   if (Symbol *B = Symtab->find(Config->Init))
     if (B->isDefined())
       addSym(DT_INIT, B);
   if (Symbol *B = Symtab->find(Config->Fini))
     if (B->isDefined())
       addSym(DT_FINI, B);
 
-  bool HasVerNeed = InX<ELFT>::VerNeed->getNeedNum() != 0;
+  bool HasVerNeed = In.VerNeed->getNeedNum() != 0;
   if (HasVerNeed || In.VerDef)
-    addInSec(DT_VERSYM, InX<ELFT>::VerSym);
+    addInSec(DT_VERSYM, In.VerSym);
   if (In.VerDef) {
     addInSec(DT_VERDEF, In.VerDef);
     addInt(DT_VERDEFNUM, getVerDefNum());
   }
   if (HasVerNeed) {
-    addInSec(DT_VERNEED, InX<ELFT>::VerNeed);
-    addInt(DT_VERNEEDNUM, InX<ELFT>::VerNeed->getNeedNum());
+    addInSec(DT_VERNEED, In.VerNeed);
+    addInt(DT_VERNEEDNUM, In.VerNeed->getNeedNum());
   }
 
   if (Config->EMachine == EM_MIPS) {
     addInt(DT_MIPS_RLD_VERSION, 1);
     addInt(DT_MIPS_FLAGS, RHF_NOTPOT);
     addInt(DT_MIPS_BASE_ADDRESS, Target->getImageBase());
     addInt(DT_MIPS_SYMTABNO, In.DynSymTab->getNumSymbols());
 
void VersionDefinitionSection::writeTo(uint8_t *Buf) {
   write32(Buf + 16, 0); // vd_next
 }
 
 size_t VersionDefinitionSection::getSize() const {
   return EntrySize * getVerDefNum();
 }
 
 // .gnu.version is a table where each entry is 2 byte long.
-template <class ELFT>
-VersionTableSection<ELFT>::VersionTableSection()
+VersionTableSection::VersionTableSection()
     : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
                        ".gnu.version") {
   this->Entsize = 2;
 }
 
-template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
+void VersionTableSection::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 = In.DynSymTab->getParent()->SectionIndex;
 }
 
-template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
+size_t VersionTableSection::getSize() const {
   return (In.DynSymTab->getSymbols().size() + 1) * 2;
 }
 
-template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
+void VersionTableSection::writeTo(uint8_t *Buf) {
   Buf += 2;
   for (const SymbolTableEntry &S : In.DynSymTab->getSymbols()) {
     write16(Buf, S.Sym->VersionId);
     Buf += 2;
   }
 }
 
-template <class ELFT> bool VersionTableSection<ELFT>::empty() const {
-  return !In.VerDef && InX<ELFT>::VerNeed->empty();
+bool VersionTableSection::empty() const {
+  return !In.VerDef && In.VerNeed->empty();
 }
 
-template <class ELFT>
-VersionNeedSection<ELFT>::VersionNeedSection()
+VersionNeedBaseSection::VersionNeedBaseSection()
     : 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 elf::RelrSection<ELF64LE>;
 template class elf::RelrSection<ELF64BE>;
 
 template class elf::SymbolTableSection<ELF32LE>;
 template class elf::SymbolTableSection<ELF32BE>;
 template class elf::SymbolTableSection<ELF64LE>;
 template class elf::SymbolTableSection<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>;

lld/ELF/Writer.cpp

if (Config->EMachine == EM_MIPS) {
     if (auto *Sec = MipsReginfoSection<ELFT>::create())
       Add(Sec);
   }
 
   if (Config->HasDynSymTab) {
     In.DynSymTab = make<SymbolTableSection<ELFT>>(*In.DynStrTab);
     Add(In.DynSymTab);
 
-    InX<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
-    Add(InX<ELFT>::VerSym);
+    In.VerSym = make<VersionTableSection>();
+    Add(In.VerSym);
 
     if (!Config->VersionDefinitions.empty()) {
       In.VerDef = make<VersionDefinitionSection>();
       Add(In.VerDef);
     }
 
-    InX<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
-    Add(InX<ELFT>::VerNeed);
+    In.VerNeed = make<VersionNeedSection<ELFT>>();
+    Add(In.VerNeed);
 
     if (Config->GnuHash) {
       In.GnuHashTab = make<GnuHashTableSection>();
       Add(In.GnuHashTab);
     }
 
     if (Config->SysvHash) {
       In.HashTab = make<HashTableSection>();
if (!includeInSymtab(*Sym))
       continue;
     if (In.SymTab)
       In.SymTab->addSymbol(Sym);
 
     if (Sym->includeInDynsym()) {
       In.DynSymTab->addSymbol(Sym);
       if (auto *File = dyn_cast_or_null<SharedFile<ELFT>>(Sym->File))
         if (File->IsNeeded && !Sym->isUndefined())
-          InX<ELFT>::VerNeed->addSymbol(Sym);
+          In.VerNeed->addSymbol(Sym);
     }
   }
 
   // Do not proceed if there was an undefined symbol.
   if (errorCount())
     return;
 
   if (In.MipsGot)
template <class ELFT> void Writer<ELFT>::finalizeSections() {
   finalizeSynthetic(In.GotPlt);
   finalizeSynthetic(In.RelaDyn);
   finalizeSynthetic(In.RelrDyn);
   finalizeSynthetic(In.RelaIplt);
   finalizeSynthetic(In.RelaPlt);
   finalizeSynthetic(In.Plt);
   finalizeSynthetic(In.Iplt);
   finalizeSynthetic(In.EhFrameHdr);
-  finalizeSynthetic(InX<ELFT>::VerSym);
-  finalizeSynthetic(InX<ELFT>::VerNeed);
+  finalizeSynthetic(In.VerSym);
+  finalizeSynthetic(In.VerNeed);
   finalizeSynthetic(In.Dynamic);
 
   if (!Script->HasSectionsCommand && !Config->Relocatable)
     fixSectionAlignments();
 
   // After link order processing .ARM.exidx sections can be deduplicated, which
   // needs to be resolved before any other address dependent operation.
   resolveShfLinkOrder();