[ELF] Refactor PltSection and IPltSection into PltSection [NFC]

Much of the code in PltSection and IPltSection is similar, we identify
the IPlt by a HeaderSize of 0 and alter our behaviour in the member
functions appropriately:
-Iplt does not have a header
-Iplt always follows after the Plt
    
Differential Revision: https://reviews.llvm.org/D29664

llvm-svn: 294579

lld/ELF/SyntheticSections.cpp

@@ -1434,19 +1434,23 @@ template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
 }
 
 template <class ELFT>
-PltSection<ELFT>::PltSection()
+PltSection<ELFT>::PltSection(size_t S)
     : SyntheticSection<ELFT>(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16,
-                             ".plt") {}
+                             ".plt"),
+      HeaderSize(S) {}
 
 template <class ELFT> void PltSection<ELFT>::writeTo(uint8_t *Buf) {
-  // At beginning of PLT, we have code to call the dynamic linker
-  // to resolve dynsyms at runtime. Write such code.
-  Target->writePltHeader(Buf);
-  size_t Off = Target->PltHeaderSize;
+  // 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;
+    unsigned RelOff = I.second + PltOff;
     uint64_t Got = B->getGotPltVA<ELFT>();
     uint64_t Plt = this->getVA() + Off;
     Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
@@ -1456,61 +1460,34 @@ template <class ELFT> void PltSection<ELFT>::writeTo(uint8_t *Buf) {
 
 template <class ELFT> void PltSection<ELFT>::addEntry(SymbolBody &Sym) {
   Sym.PltIndex = Entries.size();
-  unsigned RelOff = In<ELFT>::RelaPlt->getRelocOffset();
+  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));
 }
 
 template <class ELFT> size_t PltSection<ELFT>::getSize() const {
-  return Target->PltHeaderSize + Entries.size() * Target->PltEntrySize;
+  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
 template <class ELFT> void PltSection<ELFT>::addSymbols() {
-  Target->addPltHeaderSymbols(this);
-  size_t Off = Target->PltHeaderSize;
+  // 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;
   }
 }
 
-template <class ELFT>
-IpltSection<ELFT>::IpltSection()
-    : SyntheticSection<ELFT>(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16,
-                             ".plt") {}
-
-template <class ELFT> void IpltSection<ELFT>::writeTo(uint8_t *Buf) {
-  // The IRelative relocations do not support lazy binding so no header is
-  // needed
-  size_t Off = 0;
-  for (auto &I : Entries) {
-    const SymbolBody *B = I.first;
-    unsigned RelOff = I.second + In<ELFT>::Plt->getSize();
-    uint64_t Got = B->getGotPltVA<ELFT>();
-    uint64_t Plt = this->getVA() + Off;
-    Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
-    Off += Target->PltEntrySize;
-  }
-}
-
-template <class ELFT> void IpltSection<ELFT>::addEntry(SymbolBody &Sym) {
-  Sym.PltIndex = Entries.size();
-  Sym.IsInIplt = true;
-  unsigned RelOff = In<ELFT>::RelaIplt->getRelocOffset();
-  Entries.push_back(std::make_pair(&Sym, RelOff));
-}
-
-template <class ELFT> size_t IpltSection<ELFT>::getSize() const {
-  return Entries.size() * Target->PltEntrySize;
-}
-
-template <class ELFT> void IpltSection<ELFT>::addSymbols() {
-  size_t Off = 0;
-  for (size_t I = 0; I < Entries.size(); ++I) {
-    Target->addPltSymbols(this, Off);
-    Off += Target->PltEntrySize;
-  }
+template <class ELFT> unsigned PltSection<ELFT>::getPltRelocOff() const {
+  return (HeaderSize == 0) ? In<ELFT>::Plt->getSize() : 0;
 }
 
 template <class ELFT>
@@ -2118,11 +2095,6 @@ template class elf::PltSection<ELF32BE>;
 template class elf::PltSection<ELF64LE>;
 template class elf::PltSection<ELF64BE>;
 
-template class elf::IpltSection<ELF32LE>;
-template class elf::IpltSection<ELF32BE>;
-template class elf::IpltSection<ELF64LE>;
-template class elf::IpltSection<ELF64BE>;
-
 template class elf::GdbIndexSection<ELF32LE>;
 template class elf::GdbIndexSection<ELF32BE>;
 template class elf::GdbIndexSection<ELF64LE>;

lld/ELF/SyntheticSections.h

@@ -234,7 +234,7 @@ private:
   std::vector<const SymbolBody *> Entries;
 };
 
-// The IgotPltSection is a Got associated with the IpltSection for GNU Ifunc
+// The IgotPltSection is a Got associated with the PltSection for GNU Ifunc
 // Symbols that will be relocated by Target->IRelativeRel.
 // On most Targets the IgotPltSection will immediately follow the GotPltSection
 // on ARM the IgotPltSection will immediately follow the GotSection.
@@ -461,25 +461,13 @@ private:
   size_t Size = 0;
 };
 
-template <class ELFT> class PltSection final : public SyntheticSection<ELFT> {
+// The PltSection is used for both the Plt and Iplt. The former always has a
+// header as its first entry that is used at run-time to resolve lazy binding.
+// The latter is used for GNU Ifunc symbols, that will be subject to a
+// Target->IRelativeRel.
+template <class ELFT> class PltSection : public SyntheticSection<ELFT> {
 public:
-  PltSection();
-  void writeTo(uint8_t *Buf) override;
-  size_t getSize() const override;
-  void addEntry(SymbolBody &Sym);
-  bool empty() const override { return Entries.empty(); }
-  void addSymbols();
-
-private:
-  std::vector<std::pair<const SymbolBody *, unsigned>> Entries;
-};
-
-// The IpltSection is a variant of Plt for recording entries for GNU Ifunc
-// symbols that will be subject to a Target->IRelativeRel
-// The IpltSection immediately follows the Plt section in the Output Section
-template <class ELFT> class IpltSection final : public SyntheticSection<ELFT> {
-public:
-  IpltSection();
+  PltSection(size_t HeaderSize);
   void writeTo(uint8_t *Buf) override;
   size_t getSize() const override;
   void addEntry(SymbolBody &Sym);
@@ -487,7 +475,12 @@ public:
   void addSymbols();
 
 private:
+  void writeHeader(uint8_t *Buf){};
+  void addHeaderSymbols(){};
+  unsigned getPltRelocOff() const;
   std::vector<std::pair<const SymbolBody *, unsigned>> Entries;
+  // Iplt always has HeaderSize of 0, the Plt HeaderSize is always non-zero
+  size_t HeaderSize;
 };
 
 template <class ELFT>
@@ -777,7 +770,7 @@ template <class ELFT> struct In {
   static InputSection<ELFT> *Interp;
   static MipsRldMapSection<ELFT> *MipsRldMap;
   static PltSection<ELFT> *Plt;
-  static IpltSection<ELFT> *Iplt;
+  static PltSection<ELFT> *Iplt;
   static RelocationSection<ELFT> *RelaDyn;
   static RelocationSection<ELFT> *RelaPlt;
   static RelocationSection<ELFT> *RelaIplt;
@@ -806,7 +799,7 @@ template <class ELFT> HashTableSection<ELFT> *In<ELFT>::HashTab;
 template <class ELFT> InputSection<ELFT> *In<ELFT>::Interp;
 template <class ELFT> MipsRldMapSection<ELFT> *In<ELFT>::MipsRldMap;
 template <class ELFT> PltSection<ELFT> *In<ELFT>::Plt;
-template <class ELFT> IpltSection<ELFT> *In<ELFT>::Iplt;
+template <class ELFT> PltSection<ELFT> *In<ELFT>::Iplt;
 template <class ELFT> RelocationSection<ELFT> *In<ELFT>::RelaDyn;
 template <class ELFT> RelocationSection<ELFT> *In<ELFT>::RelaPlt;
 template <class ELFT> RelocationSection<ELFT> *In<ELFT>::RelaIplt;

lld/ELF/Writer.cpp

@@ -426,9 +426,9 @@ template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
       false /*Sort*/);
   Add(In<ELFT>::RelaIplt);
 
-  In<ELFT>::Plt = make<PltSection<ELFT>>();
+  In<ELFT>::Plt = make<PltSection<ELFT>>(Target->PltHeaderSize);
   Add(In<ELFT>::Plt);
-  In<ELFT>::Iplt = make<IpltSection<ELFT>>();
+  In<ELFT>::Iplt = make<PltSection<ELFT>>(0);
   Add(In<ELFT>::Iplt);
 
   if (Config->EhFrameHdr) {