Convert EhOutputSection to be a synthetic section

[• rafael]

Summary

With this we complete the transition out of special output sections, and with the previous patches it should be possible to merge OutputSectionBase and OuputSection.

[ruiu]

LGTM

ELF/Writer.cpp

1095

Can you add why?

[• espindola]

296023

ELF/InputSection.h

 namespace lld {
 namespace elf {
 
 class DefinedCommon;
 class SymbolBody;
 struct SectionPiece;
 
 template <class ELFT> class DefinedRegular;
+template <class ELFT> class EhFrameSection;
 template <class ELFT> class MergeSyntheticSection;
 template <class ELFT> class ObjectFile;
 template <class ELFT> class OutputSection;
 class OutputSectionBase;
 
 // This corresponds to a section of an input file.
 class InputSectionBase {
 public:
public:
   EhInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header, StringRef Name);
   static bool classof(const InputSectionBase *S);
   void split();
   template <class RelTy> void split(ArrayRef<RelTy> Rels);
 
   // Splittable sections are handled as a sequence of data
   // rather than a single large blob of data.
   std::vector<EhSectionPiece> Pieces;
+  EhFrameSection<ELFT> *EHSec = nullptr;
 };
 
 // This corresponds to a non SHF_MERGE section of an input file.
 class InputSection : public InputSectionBase {
 public:
   InputSection();
   InputSection(uint64_t Flags, uint32_t Type, uint64_t Addralign,
                ArrayRef<uint8_t> Data, StringRef Name, Kind K = Regular);

ELF/InputSection.cpp

uint64_t InputSectionBase::getOffset(uint64_t Offset) const {
   }
   llvm_unreachable("invalid section kind");
 }
 
 template <class ELFT>
 OutputSectionBase *InputSectionBase::getOutputSection() const {
   if (auto *MS = dyn_cast<MergeInputSection<ELFT>>(this))
     return MS->MergeSec ? MS->MergeSec->OutSec : nullptr;
+  if (auto *EH = dyn_cast<EhInputSection<ELFT>>(this))
+    return EH->EHSec->OutSec;
   return OutSec;
 }
 
 // Uncompress section contents. Note that this function is called
 // from parallel_for_each, so it must be thread-safe.
 template <class ELFT> void InputSectionBase::uncompress() {
   Decompressor Dec = check(Decompressor::create(
       Name, toStringRef(Data), ELFT::TargetEndianness == llvm::support::little,
void InputSectionBase::relocate(uint8_t *Buf, uint8_t *BufEnd) {
 
   typedef typename ELFT::uint uintX_t;
   const unsigned Bits = sizeof(uintX_t) * 8;
   for (const Relocation &Rel : Relocations) {
     uintX_t Offset = getOffset<ELFT>(Rel.Offset);
     uint8_t *BufLoc = Buf + Offset;
     uint32_t Type = Rel.Type;
 
-    uintX_t AddrLoc = OutSec->Addr + Offset;
+    uintX_t AddrLoc = getOutputSection<ELFT>()->Addr + Offset;
     RelExpr Expr = Rel.Expr;
     uint64_t TargetVA = SignExtend64<Bits>(
         getRelocTargetVA<ELFT>(Type, Rel.Addend, AddrLoc, *Rel.Sym, Expr));
 
     switch (Expr) {
     case R_RELAX_GOT_PC:
     case R_RELAX_GOT_PC_NOPIC:
       Target->relaxGot(BufLoc, TargetVA);

ELF/OutputSections.h

static bool classof(const OutputSectionBase *B) {
     return B->getKind() == Regular;
   }
   std::vector<InputSection *> Sections;
 
   // Location in the output buffer.
   uint8_t *Loc = nullptr;
 };
 
-struct CieRecord {
-  EhSectionPiece *Piece = nullptr;
-  std::vector<EhSectionPiece *> FdePieces;
-};
-
-// Output section for .eh_frame.
-template <class ELFT> class EhOutputSection final : public OutputSectionBase {
-  typedef typename ELFT::uint uintX_t;
-  typedef typename ELFT::Shdr Elf_Shdr;
-  typedef typename ELFT::Rel Elf_Rel;
-  typedef typename ELFT::Rela Elf_Rela;
-
-public:
-  EhOutputSection();
-  void writeTo(uint8_t *Buf) override;
-  void finalize() override;
-  bool empty() const { return Sections.empty(); }
-  void forEachInputSection(std::function<void(InputSectionBase *)> F) override;
-
-  void addSection(InputSectionBase *S) override;
-  Kind getKind() const override { return EHFrame; }
-  static bool classof(const OutputSectionBase *B) {
-    return B->getKind() == EHFrame;
-  }
-
-  size_t NumFdes = 0;
-
-private:
-  template <class RelTy>
-  void addSectionAux(EhInputSection<ELFT> *S, llvm::ArrayRef<RelTy> Rels);
-
-  template <class RelTy>
-  CieRecord *addCie(EhSectionPiece &Piece, ArrayRef<RelTy> Rels);
-
-  template <class RelTy>
-  bool isFdeLive(EhSectionPiece &Piece, ArrayRef<RelTy> Rels);
-
-  uintX_t getFdePc(uint8_t *Buf, size_t Off, uint8_t Enc);
-
-  std::vector<EhInputSection<ELFT> *> Sections;
-  std::vector<CieRecord *> Cies;
-
-  // CIE records are uniquified by their contents and personality functions.
-  llvm::DenseMap<std::pair<ArrayRef<uint8_t>, SymbolBody *>, CieRecord> CieMap;
-};
-
 // All output sections that are hadnled by the linker specially are
 // globally accessible. Writer initializes them, so don't use them
 // until Writer is initialized.
 template <class ELFT> struct Out {
   typedef typename ELFT::uint uintX_t;
   typedef typename ELFT::Phdr Elf_Phdr;
 
   static uint8_t First;
-  static EhOutputSection<ELFT> *EhFrame;
   static OutputSection<ELFT> *Bss;
   static OutputSection<ELFT> *BssRelRo;
   static OutputSectionBase *Opd;
   static uint8_t *OpdBuf;
   static PhdrEntry *TlsPhdr;
   static OutputSectionBase *DebugInfo;
   static OutputSectionBase *ElfHeader;
   static OutputSectionBase *ProgramHeaders;

 
 template <class ELFT> uint64_t getHeaderSize() {
   if (Config->OFormatBinary)
     return 0;
   return Out<ELFT>::ElfHeader->Size + Out<ELFT>::ProgramHeaders->Size;
 }
 
 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>::BssRelRo;
 template <class ELFT> OutputSectionBase *Out<ELFT>::Opd;
 template <class ELFT> uint8_t *Out<ELFT>::OpdBuf;
 template <class ELFT> PhdrEntry *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
 } // namespace lld
 
 
 #endif

ELF/OutputSections.cpp

 //===- OutputSections.cpp -------------------------------------------------===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "OutputSections.h"
 #include "Config.h"
-#include "EhFrame.h"
 #include "LinkerScript.h"
 #include "Memory.h"
 #include "Strings.h"
 #include "SymbolTable.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "Threads.h"
 #include "llvm/Support/Dwarf.h"
template <class ELFT> void OutputSection<ELFT>::writeTo(uint8_t *Buf) {
   forEach(Sections.begin(), Sections.end(), Fn);
 
   // Linker scripts may have BYTE()-family commands with which you
   // can write arbitrary bytes to the output. Process them if any.
   Script<ELFT>::X->writeDataBytes(this->Name, Buf);
 }
 
 template <class ELFT>
-EhOutputSection<ELFT>::EhOutputSection()
-    : OutputSectionBase(".eh_frame", SHT_PROGBITS, SHF_ALLOC) {}
-
-template <class ELFT>
-void EhOutputSection<ELFT>::forEachInputSection(
-    std::function<void(InputSectionBase *)> F) {
-  for (EhInputSection<ELFT> *S : Sections)
-    F(S);
-}
-
-// 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 *EhOutputSection<ELFT>::addCie(EhSectionPiece &Piece,
-                                         ArrayRef<RelTy> Rels) {
-  auto *Sec = cast<EhInputSection<ELFT>>(Piece.ID);
-  const endianness E = ELFT::TargetEndianness;
-  if (read32<E>(Piece.data().data() + 4) != 0)
-    fatal(toString(Sec) + ": CIE expected at beginning of .eh_frame");
-
-  SymbolBody *Personality = nullptr;
-  unsigned FirstRelI = Piece.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 *Cie = &CieMap[{Piece.data(), Personality}];
-
-  // If not found, create a new one.
-  if (Cie->Piece == nullptr) {
-    Cie->Piece = &Piece;
-    Cies.push_back(Cie);
-  }
-  return Cie;
-}
-
-// There is one FDE per function. Returns true if a given FDE
-// points to a live function.
-template <class ELFT>
-template <class RelTy>
-bool EhOutputSection<ELFT>::isFdeLive(EhSectionPiece &Piece,
-                                      ArrayRef<RelTy> Rels) {
-  auto *Sec = cast<EhInputSection<ELFT>>(Piece.ID);
-  unsigned FirstRelI = Piece.FirstRelocation;
-  if (FirstRelI == (unsigned)-1)
-    return false;
-  const RelTy &Rel = Rels[FirstRelI];
-  SymbolBody &B = Sec->template getFile<ELFT>()->getRelocTargetSym(Rel);
-  auto *D = dyn_cast<DefinedRegular<ELFT>>(&B);
-  if (!D || !D->Section)
-    return false;
-  InputSectionBase *Target = D->Section->Repl;
-  return Target && Target->Live;
-}
-
-// .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 EhOutputSection<ELFT>::addSectionAux(EhInputSection<ELFT> *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 *Cie = OffsetToCie[CieOffset];
-    if (!Cie)
-      fatal(toString(Sec) + ": invalid CIE reference");
-
-    if (!isFdeLive(Piece, Rels))
-      continue;
-    Cie->FdePieces.push_back(&Piece);
-    NumFdes++;
-  }
-}
-
-template <class ELFT>
-void EhOutputSection<ELFT>::addSection(InputSectionBase *C) {
-  auto *Sec = cast<EhInputSection<ELFT>>(C);
-  Sec->OutSec = this;
-  this->updateAlignment(Sec->Alignment);
-  Sections.push_back(Sec);
-
-  // .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();
-  if (Sec->Pieces.empty())
-    return;
-
-  if (Sec->NumRelocations) {
-    if (Sec->AreRelocsRela)
-      addSectionAux(Sec, Sec->template relas<ELFT>());
-    else
-      addSectionAux(Sec, Sec->template rels<ELFT>());
-    return;
-  }
-  addSectionAux(Sec, makeArrayRef<Elf_Rela>(nullptr, nullptr));
-}
-
-template <class ELFT>
-static void writeCieFde(uint8_t *Buf, ArrayRef<uint8_t> D) {
-  memcpy(Buf, D.data(), D.size());
-
-  // Fix the size field. -4 since size does not include the size field itself.
-  const endianness E = ELFT::TargetEndianness;
-  write32<E>(Buf, alignTo(D.size(), sizeof(typename ELFT::uint)) - 4);
-}
-
-template <class ELFT> void EhOutputSection<ELFT>::finalize() {
-  if (this->Size)
-    return; // Already finalized.
-
-  size_t Off = 0;
-  for (CieRecord *Cie : Cies) {
-    Cie->Piece->OutputOff = Off;
-    Off += alignTo(Cie->Piece->size(), sizeof(uintX_t));
-
-    for (EhSectionPiece *Fde : Cie->FdePieces) {
-      Fde->OutputOff = Off;
-      Off += alignTo(Fde->size(), sizeof(uintX_t));
-    }
-  }
-  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>
-typename ELFT::uint EhOutputSection<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 + this->Addr + Off;
-  fatal("unknown FDE size relative encoding");
-}
-
-template <class ELFT> void EhOutputSection<ELFT>::writeTo(uint8_t *Buf) {
-  const endianness E = ELFT::TargetEndianness;
-  for (CieRecord *Cie : Cies) {
-    size_t CieOffset = Cie->Piece->OutputOff;
-    writeCieFde<ELFT>(Buf + CieOffset, Cie->Piece->data());
-
-    for (EhSectionPiece *Fde : Cie->FdePieces) {
-      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<ELFT> *S : Sections)
-    S->template relocate<ELFT>(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 *Cie : Cies) {
-      uint8_t Enc = getFdeEncoding<ELFT>(Cie->Piece);
-      for (SectionPiece *Fde : Cie->FdePieces) {
-        uintX_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
-        uintX_t FdeVA = this->Addr + Fde->OutputOff;
-        In<ELFT>::EhFrameHdr->addFde(Pc, FdeVA);
-      }
-    }
-  }
-}
-
-template <class ELFT>
 static typename ELFT::uint getOutFlags(InputSectionBase *S) {
   return S->Flags & ~SHF_GROUP & ~SHF_COMPRESSED;
 }
 
 template <class ELFT>
 static SectionKey createKey(InputSectionBase *C, StringRef OutsecName) {
   //  The ELF spec just says
   // ----------------------------------------------------------------
if (Sec->Type != IS->Type) {
       else
         error("Section has different type from others with the same name " +
               toString(IS));
     }
     Sec->Flags |= Flags;
   } else {
     uint32_t Type = IS->Type;
     if (IS->kind() == InputSectionBase::EHFrame) {
-      Out<ELFT>::EhFrame->addSection(IS);
+      In<ELFT>::EhFrame->addSection(IS);
       return;
     }
     Sec = make<OutputSection<ELFT>>(Key.Name, Type, Flags);
     OutputSections.push_back(Sec);
   }
 
   Sec->addSection(IS);
 }

 template void OutputSectionBase::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
 template void OutputSectionBase::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
 
 template class OutputSection<ELF32LE>;
 template class OutputSection<ELF32BE>;
 template class OutputSection<ELF64LE>;
 template class OutputSection<ELF64BE>;
 
-template class EhOutputSection<ELF32LE>;
-template class EhOutputSection<ELF32BE>;
-template class EhOutputSection<ELF64LE>;
-template class EhOutputSection<ELF64BE>;
-
 template class OutputSectionFactory<ELF32LE>;
 template class OutputSectionFactory<ELF32BE>;
 template class OutputSectionFactory<ELF64LE>;
 template class OutputSectionFactory<ELF64BE>;
 }
 }

ELF/Relocations.h

 #ifndef LLD_ELF_RELOCATIONS_H
 #define LLD_ELF_RELOCATIONS_H
 
 #include "lld/Core/LLVM.h"
 
 namespace lld {
 namespace elf {
 class SymbolBody;
-class InputSectionData;
 class InputSection;
 class InputSectionBase;
 class OutputSectionBase;
 
 // List of target-independent relocation types. Relocations read
 // from files are converted to these types so that the main code
 // doesn't have to know about architecture-specific details.
 enum RelExpr {

ELF/SyntheticSections.h

 // using linker scripts just like other input sections from regular
 // files.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLD_ELF_SYNTHETIC_SECTION_H
 #define LLD_ELF_SYNTHETIC_SECTION_H
 
+#include "EhFrame.h"
 #include "GdbIndex.h"
 #include "InputSection.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/MC/StringTableBuilder.h"
 
 namespace lld {
 namespace elf {
 
uintX_t getVA() const {
     return this->OutSec ? this->OutSec->Addr + this->OutSecOff : 0;
   }
 
   static bool classof(const InputSectionBase *D) {
     return D->kind() == InputSectionBase::Synthetic;
   }
 };
 
+struct CieRecord {
+  EhSectionPiece *Piece = nullptr;
+  std::vector<EhSectionPiece *> FdePieces;
+};
+
+// Section for .eh_frame.
+template <class ELFT>
+class EhFrameSection final : public SyntheticSection<ELFT> {
+  typedef typename ELFT::uint uintX_t;
+  typedef typename ELFT::Shdr Elf_Shdr;
+  typedef typename ELFT::Rel Elf_Rel;
+  typedef typename ELFT::Rela Elf_Rela;
+
+  void updateAlignment(uint64_t Val) {
+    if (Val > this->Alignment)
+      this->Alignment = Val;
+  }
+
+public:
+  EhFrameSection();
+  void writeTo(uint8_t *Buf) override;
+  void finalize() override;
+  bool empty() const override { return Sections.empty(); }
+  size_t getSize() const override { return Size; }
+
+  void addSection(InputSectionBase *S);
+
+  size_t NumFdes = 0;
+
+private:
+  uint64_t Size = 0;
+  template <class RelTy>
+  void addSectionAux(EhInputSection<ELFT> *S, llvm::ArrayRef<RelTy> Rels);
+
+  template <class RelTy>
+  CieRecord *addCie(EhSectionPiece &Piece, ArrayRef<RelTy> Rels);
+
+  template <class RelTy>
+  bool isFdeLive(EhSectionPiece &Piece, ArrayRef<RelTy> Rels);
+
+  uintX_t getFdePc(uint8_t *Buf, size_t Off, uint8_t Enc);
+
+  std::vector<EhInputSection<ELFT> *> Sections;
+  std::vector<CieRecord *> Cies;
+
+  // CIE records are uniquified by their contents and personality functions.
+  llvm::DenseMap<std::pair<ArrayRef<uint8_t>, SymbolBody *>, CieRecord> CieMap;
+};
+
 template <class ELFT> class GotSection final : public SyntheticSection<ELFT> {
   typedef typename ELFT::uint uintX_t;
 
 public:
   GotSection();
   void writeTo(uint8_t *Buf) override;
   size_t getSize() const override { return Size; }
   void finalize() override;
template <class ELFT> struct In {
   static InputSection *Common;
   static DynamicSection<ELFT> *Dynamic;
   static StringTableSection<ELFT> *DynStrTab;
   static SymbolTableSection<ELFT> *DynSymTab;
   static EhFrameHeader<ELFT> *EhFrameHdr;
   static GnuHashTableSection<ELFT> *GnuHashTab;
   static GdbIndexSection<ELFT> *GdbIndex;
   static GotSection<ELFT> *Got;
+  static EhFrameSection<ELFT> *EhFrame;
   static MipsGotSection<ELFT> *MipsGot;
   static GotPltSection<ELFT> *GotPlt;
   static IgotPltSection<ELFT> *IgotPlt;
   static HashTableSection<ELFT> *HashTab;
   static InputSection *Interp;
   static MipsRldMapSection<ELFT> *MipsRldMap;
   static PltSection<ELFT> *Plt;
   static PltSection<ELFT> *Iplt;

 template <class ELFT> InputSection *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> EhFrameSection<ELFT> *In<ELFT>::EhFrame;
 template <class ELFT> MipsGotSection<ELFT> *In<ELFT>::MipsGot;
 template <class ELFT> GotPltSection<ELFT> *In<ELFT>::GotPlt;
 template <class ELFT> IgotPltSection<ELFT> *In<ELFT>::IgotPlt;
 template <class ELFT> HashTableSection<ELFT> *In<ELFT>::HashTab;
 template <class ELFT> InputSection *In<ELFT>::Interp;
 template <class ELFT> MipsRldMapSection<ELFT> *In<ELFT>::MipsRldMap;
 template <class ELFT> PltSection<ELFT> *In<ELFT>::Plt;
 template <class ELFT> PltSection<ELFT> *In<ELFT>::Iplt;

ELF/SyntheticSections.cpp

case BuildIdKind::Hexstring:
     memcpy(HashBuf, Config->BuildIdVector.data(), Config->BuildIdVector.size());
     break;
   default:
     llvm_unreachable("unknown BuildIdKind");
   }
 }
 
 template <class ELFT>
+EhFrameSection<ELFT>::EhFrameSection()
+    : SyntheticSection<ELFT>(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 &Piece,
+                                        ArrayRef<RelTy> Rels) {
+  auto *Sec = cast<EhInputSection<ELFT>>(Piece.ID);
+  const endianness E = ELFT::TargetEndianness;
+  if (read32<E>(Piece.data().data() + 4) != 0)
+    fatal(toString(Sec) + ": CIE expected at beginning of .eh_frame");
+
+  SymbolBody *Personality = nullptr;
+  unsigned FirstRelI = Piece.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 *Cie = &CieMap[{Piece.data(), Personality}];
+
+  // If not found, create a new one.
+  if (Cie->Piece == nullptr) {
+    Cie->Piece = &Piece;
+    Cies.push_back(Cie);
+  }
+  return Cie;
+}
+
+// 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 &Piece,
+                                     ArrayRef<RelTy> Rels) {
+  auto *Sec = cast<EhInputSection<ELFT>>(Piece.ID);
+  unsigned FirstRelI = Piece.FirstRelocation;
+  if (FirstRelI == (unsigned)-1)
+    return false;
+  const RelTy &Rel = Rels[FirstRelI];
+  SymbolBody &B = Sec->template getFile<ELFT>()->getRelocTargetSym(Rel);
+  auto *D = dyn_cast<DefinedRegular<ELFT>>(&B);
+  if (!D || !D->Section)
+    return false;
+  InputSectionBase *Target = D->Section->Repl;
+  return Target && Target->Live;
+}
+
+// .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<ELFT> *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 *Cie = OffsetToCie[CieOffset];
+    if (!Cie)
+      fatal(toString(Sec) + ": invalid CIE reference");
+
+    if (!isFdeLive(Piece, Rels))
+      continue;
+    Cie->FdePieces.push_back(&Piece);
+    NumFdes++;
+  }
+}
+
+template <class ELFT>
+void EhFrameSection<ELFT>::addSection(InputSectionBase *C) {
+  auto *Sec = cast<EhInputSection<ELFT>>(C);
+  Sec->EHSec = this;
+  updateAlignment(Sec->Alignment);
+  Sections.push_back(Sec);
+
+  // .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();
+  if (Sec->Pieces.empty())
+    return;
+
+  if (Sec->NumRelocations) {
+    if (Sec->AreRelocsRela)
+      addSectionAux(Sec, Sec->template relas<ELFT>());
+    else
+      addSectionAux(Sec, Sec->template rels<ELFT>());
+    return;
+  }
+  addSectionAux(Sec, makeArrayRef<Elf_Rela>(nullptr, nullptr));
+}
+
+template <class ELFT>
+static void writeCieFde(uint8_t *Buf, ArrayRef<uint8_t> D) {
+  memcpy(Buf, D.data(), D.size());
+
+  // Fix the size field. -4 since size does not include the size field itself.
+  const endianness E = ELFT::TargetEndianness;
+  write32<E>(Buf, alignTo(D.size(), sizeof(typename ELFT::uint)) - 4);
+}
+
+template <class ELFT> void EhFrameSection<ELFT>::finalize() {
+  if (this->Size)
+    return; // Already finalized.
+
+  size_t Off = 0;
+  for (CieRecord *Cie : Cies) {
+    Cie->Piece->OutputOff = Off;
+    Off += alignTo(Cie->Piece->size(), sizeof(uintX_t));
+
+    for (EhSectionPiece *Fde : Cie->FdePieces) {
+      Fde->OutputOff = Off;
+      Off += alignTo(Fde->size(), sizeof(uintX_t));
+    }
+  }
+  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>
+typename ELFT::uint 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 + this->OutSec->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 *Cie : Cies) {
+    size_t CieOffset = Cie->Piece->OutputOff;
+    writeCieFde<ELFT>(Buf + CieOffset, Cie->Piece->data());
+
+    for (EhSectionPiece *Fde : Cie->FdePieces) {
+      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<ELFT> *S : Sections)
+    S->template relocate<ELFT>(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 *Cie : Cies) {
+      uint8_t Enc = getFdeEncoding<ELFT>(Cie->Piece);
+      for (SectionPiece *Fde : Cie->FdePieces) {
+        uintX_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
+        uintX_t FdeVA = this->OutSec->Addr + Fde->OutputOff;
+        In<ELFT>::EhFrameHdr->addFde(Pc, FdeVA);
+      }
+    }
+  }
+}
+
+template <class ELFT>
 GotSection<ELFT>::GotSection()
     : SyntheticSection<ELFT>(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
                              Target->GotEntrySize, ".got") {}
 
 template <class ELFT> void GotSection<ELFT>::addEntry(SymbolBody &Sym) {
   Sym.GotIndex = NumEntries;
   ++NumEntries;
 }
template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
   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, Out<ELFT>::EhFrame->Addr - this->getVA() - 4);
+  write32<E>(Buf + 4, In<ELFT>::EhFrame->OutSec->Addr - this->getVA() - 4);
   write32<E>(Buf + 8, Fdes.size());
   Buf += 12;
 
   uintX_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 + Out<ELFT>::EhFrame->NumFdes * 8;
+  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 Out<ELFT>::EhFrame->empty();
+  return In<ELFT>::EhFrame->empty();
 }
 
 template <class ELFT>
 VersionDefinitionSection<ELFT>::VersionDefinitionSection()
     : SyntheticSection<ELFT>(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
                              ".gnu.version_d") {}
 
 static StringRef getFileDefName() {

 template class elf::ARMExidxSentinelSection<ELF32BE>;
 template class elf::ARMExidxSentinelSection<ELF64LE>;
 template class elf::ARMExidxSentinelSection<ELF64BE>;
 
 template class elf::ThunkSection<ELF32LE>;
 template class elf::ThunkSection<ELF32BE>;
 template class elf::ThunkSection<ELF64LE>;
 template class elf::ThunkSection<ELF64BE>;
+
+template class elf::EhFrameSection<ELF32LE>;
+template class elf::EhFrameSection<ELF32BE>;
+template class elf::EhFrameSection<ELF64LE>;
+template class elf::EhFrameSection<ELF64BE>;

ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
 
   // Create singleton output sections.
   Out<ELFT>::Bss =
       make<OutputSection<ELFT>>(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
   Out<ELFT>::BssRelRo = make<OutputSection<ELFT>>(".bss.rel.ro", 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>::RelaDyn = make<RelocationSection<ELFT>>(
       Config->Rela ? ".rela.dyn" : ".rel.dyn", Config->ZCombreloc);
   In<ELFT>::ShStrTab = make<StringTableSection<ELFT>>(".shstrtab", false);
 
   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));
template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
   In<ELFT>::Iplt = make<PltSection<ELFT>>(0);
   Add(In<ELFT>::Iplt);
 
   if (Config->EhFrameHdr) {
     In<ELFT>::EhFrameHdr = make<EhFrameHeader<ELFT>>();
     Add(In<ELFT>::EhFrameHdr);
   }
 
+  if (!Config->Relocatable) {
+    In<ELFT>::EhFrame = make<EhFrameSection<ELFT>>();
+    Add(In<ELFT>::EhFrame);
+  }
+
   if (In<ELFT>::SymTab)
     Add(In<ELFT>::SymTab);
   Add(In<ELFT>::ShStrTab);
   if (In<ELFT>::StrTab)
     Add(In<ELFT>::StrTab);
 }
 
 template <class ELFT>
template <class ELFT> void Writer<ELFT>::finalizeSections() {
   // Even the author of gold doesn't remember why gold behaves that way.
   // https://sourceware.org/ml/binutils/2002-03/msg00360.html
   if (In<ELFT>::DynSymTab)
     addRegular<ELFT>("_DYNAMIC", In<ELFT>::Dynamic, 0);
 
   // Define __rel[a]_iplt_{start,end} symbols if needed.
   addRelIpltSymbols();
 
-  if (!Out<ELFT>::EhFrame->empty()) {
-    OutputSections.push_back(Out<ELFT>::EhFrame);
-    Out<ELFT>::EhFrame->finalize();
-  }
+  // This has to be before the relocation scan.
+  finalizeSynthetic<ELFT>({In<ELFT>::EhFrame});
 
   // Scan relocations. This must be done after every symbol is declared so that
   // we can correctly decide if a dynamic relocation is needed.
   forEachRelSec(scanRelocations<ELFT>);
 
   if (In<ELFT>::Plt && !In<ELFT>::Plt->empty())
     In<ELFT>::Plt->addSymbols();
   if (In<ELFT>::Iplt && !In<ELFT>::Iplt->empty())
template <class ELFT> std::vector<PhdrEntry> Writer<ELFT>::createPhdrs() {
   PhdrEntry RelRo(PT_GNU_RELRO, PF_R);
   for (OutputSectionBase *Sec : OutputSections)
     if (needsPtLoad<ELFT>(Sec) && isRelroSection<ELFT>(Sec))
       RelRo.add(Sec);
   if (RelRo.First)
     Ret.push_back(std::move(RelRo));
 
   // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
-  if (!Out<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr)
+  if (!In<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr)
     AddHdr(PT_GNU_EH_FRAME, In<ELFT>::EhFrameHdr->OutSec->getPhdrFlags())
         ->add(In<ELFT>::EhFrameHdr->OutSec);
 
   // PT_OPENBSD_RANDOMIZE specifies the location and size of a part of the
   // memory image of the program that must be filled with random data before any
   // code in the object is executed.
   if (OutputSectionBase *Sec = findSection(".openbsd.randomdata"))
     AddHdr(PT_OPENBSD_RANDOMIZE, Sec->getPhdrFlags())->add(Sec);
template <class ELFT> void Writer<ELFT>::writeSections() {
 
   for (OutputSectionBase *Sec : OutputSections)
     if (Sec != Out<ELFT>::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
         Sec->Type != SHT_RELA)
       Sec->writeTo(Buf + Sec->Offset);
 
   // The .eh_frame_hdr depends on .eh_frame section contents, therefore
   // it should be written after .eh_frame is written.
-  if (!Out<ELFT>::EhFrame->empty() && EhFrameHdr)
+  if (EhFrameHdr)
     EhFrameHdr->writeTo(Buf + EhFrameHdr->Offset);
 }
 
 template <class ELFT> void Writer<ELFT>::writeBuildId() {
   if (!In<ELFT>::BuildId || !In<ELFT>::BuildId->OutSec)
     return;
 
   // Compute a hash of all sections of the output file.

test/ELF/map-file.s

 bar:
 .long bar - .
 .long zed - .
 local:
 .comm   common,4,16
 
 // CHECK:      Address          Size             Align Out     In      File    Symbol
 // CHECK-NEXT: 0000000000200158 0000000000000030     8 .eh_frame
+// CHECK-NEXT: 0000000000200158 0000000000000030     8         .eh_frame
 // CHECK-NEXT: 0000000000201000 0000000000000015     4 .text
 // CHECK-NEXT: 0000000000201000 000000000000000e     4         .text
 // CHECK-NEXT: 0000000000201000 000000000000000e     4                 {{.*}}{{/|\\}}map-file.s.tmp1.o
 // CHECK-NEXT: 000000000020100e 0000000000000000     0                         local
 // CHECK-NEXT: 0000000000201005 0000000000000000     0                         f(int)
 // CHECK-NEXT: 0000000000201000 0000000000000000     0                         _start
 // CHECK-NEXT: 0000000000201010 0000000000000002     4                 {{.*}}{{/|\\}}map-file.s.tmp2.o
 // CHECK-NEXT: 0000000000201010 0000000000000000     0                         foo