lld/ELF/InputSection.cpp - toolchain/llvm-project - Gitiles

 //===- InputSection.cpp ---------------------------------------------------===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//

 #include "InputSection.h"
 #include "Config.h"
 #include "Error.h"
 #include "InputFiles.h"
 #include "OutputSections.h"
 #include "Target.h"

 #include "llvm/Support/Endian.h"

 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
 using namespace llvm::support::endian;

 using namespace lld;
 using namespace lld::elf;

 template <class ELFT>
 InputSectionBase<ELFT>::InputSectionBase(ObjectFile<ELFT> *File,
                                          const Elf_Shdr *Header,
                                          Kind SectionKind)
     : Header(Header), File(File), SectionKind(SectionKind), Repl(this) {
   // The garbage collector sets sections' Live bits.
   // If GC is disabled, all sections are considered live by default.
   Live = !Config->GcSections;

   // The ELF spec states that a value of 0 means the section has
   // no alignment constraits.
   Align = std::max<uintX_t>(Header->sh_addralign, 1);
 }

 template <class ELFT> StringRef InputSectionBase<ELFT>::getSectionName() const {
   return check(File->getObj().getSectionName(this->Header));
 }

 template <class ELFT>
 ArrayRef<uint8_t> InputSectionBase<ELFT>::getSectionData() const {
   return check(this->File->getObj().getSectionContents(this->Header));
 }

 template <class ELFT>
 typename ELFFile<ELFT>::uintX_t
 InputSectionBase<ELFT>::getOffset(uintX_t Offset) {
   switch (SectionKind) {
   case Regular:
     return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
   case EHFrame:
     return cast<EHInputSection<ELFT>>(this)->getOffset(Offset);
   case Merge:
     return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
   case MipsReginfo:
     // MIPS .reginfo sections are consumed by the linker,
     // so it should never be copied to output.
     llvm_unreachable("MIPS .reginfo reached writeTo().");
   }
   llvm_unreachable("invalid section kind");
 }

 template <class ELFT>
 typename ELFFile<ELFT>::uintX_t
 InputSectionBase<ELFT>::getOffset(const Elf_Sym &Sym) {
   return getOffset(Sym.st_value);
 }

 // Returns a section that Rel relocation is pointing to.
 template <class ELFT>
 InputSectionBase<ELFT> *
 InputSectionBase<ELFT>::getRelocTarget(const Elf_Rel &Rel) const {
   // Global symbol
   uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
   SymbolBody &B = File->getSymbolBody(SymIndex).repl();
   InputSectionBase<ELFT> *S = nullptr;
   if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&B))
     S = D->Section;
   if (S)
     return S->Repl;
   return nullptr;
 }

 template <class ELFT>
 InputSectionBase<ELFT> *
 InputSectionBase<ELFT>::getRelocTarget(const Elf_Rela &Rel) const {
   return getRelocTarget(reinterpret_cast<const Elf_Rel &>(Rel));
 }

 template <class ELFT>
 InputSection<ELFT>::InputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header)
     : InputSectionBase<ELFT>(F, Header, Base::Regular) {}

 template <class ELFT>
 bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
   return S->SectionKind == Base::Regular;
 }

 template <class ELFT>
 InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() {
   assert(this->Header->sh_type == SHT_RELA || this->Header->sh_type == SHT_REL);
   ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections();
   return Sections[this->Header->sh_info];
 }

 // This is used for -r. We can't use memcpy to copy relocations because we need
 // to update symbol table offset and section index for each relocation. So we
 // copy relocations one by one.
 template <class ELFT>
 template <bool isRela>
 void InputSection<ELFT>::copyRelocations(uint8_t *Buf,
                                          RelIteratorRange<isRela> Rels) {
   typedef Elf_Rel_Impl<ELFT, isRela> RelType;
   InputSectionBase<ELFT> *RelocatedSection = getRelocatedSection();

   for (const RelType &Rel : Rels) {
     uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
     uint32_t Type = Rel.getType(Config->Mips64EL);
     SymbolBody &Body = this->File->getSymbolBody(SymIndex).repl();

     RelType *P = reinterpret_cast<RelType *>(Buf);
     Buf += sizeof(RelType);

     P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
     P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL);
   }
 }

 static uint32_t getMipsPairedRelocType(uint32_t Type) {
   if (Config->EMachine != EM_MIPS)
     return R_MIPS_NONE;
   switch (Type) {
   case R_MIPS_HI16:
     return R_MIPS_LO16;
   case R_MIPS_PCHI16:
     return R_MIPS_PCLO16;
   case R_MICROMIPS_HI16:
     return R_MICROMIPS_LO16;
   default:
     return R_MIPS_NONE;
   }
 }

 template <class ELFT>
 template <bool isRela>
 uint8_t *
 InputSectionBase<ELFT>::findMipsPairedReloc(uint8_t *Buf, uint32_t SymIndex,
                                             uint32_t Type,
                                             RelIteratorRange<isRela> Rels) {
   // Some MIPS relocations use addend calculated from addend of the relocation
   // itself and addend of paired relocation. ABI requires to compute such
   // combined addend in case of REL relocation record format only.
   // See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
   if (isRela || Type == R_MIPS_NONE)
     return nullptr;
   for (const auto &RI : Rels) {
     if (RI.getType(Config->Mips64EL) != Type)
       continue;
     if (RI.getSymbol(Config->Mips64EL) != SymIndex)
       continue;
     uintX_t Offset = getOffset(RI.r_offset);
     if (Offset == (uintX_t)-1)
       return nullptr;
     return Buf + Offset;
   }
   return nullptr;
 }

 template <class ELFT>
 template <bool isRela>
 void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd,
                                       RelIteratorRange<isRela> Rels) {
   typedef Elf_Rel_Impl<ELFT, isRela> RelType;
   size_t Num = Rels.end() - Rels.begin();
   for (size_t I = 0; I < Num; ++I) {
     const RelType &RI = *(Rels.begin() + I);
     uintX_t Offset = getOffset(RI.r_offset);
     if (Offset == (uintX_t)-1)
       continue;

     uintX_t A = getAddend<ELFT>(RI);
     uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
     uint32_t Type = RI.getType(Config->Mips64EL);
     uint8_t *BufLoc = Buf + Offset;
     uintX_t AddrLoc = OutSec->getVA() + Offset;
     auto NextRelocs = llvm::make_range(&RI, Rels.end());

     if (Target->pointsToLocalDynamicGotEntry(Type) &&
         !Target->canRelaxTls(Type, nullptr)) {
       Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
                           Out<ELFT>::Got->getTlsIndexVA() + A);
       continue;
     }

     SymbolBody &Body = File->getSymbolBody(SymIndex).repl();

     if (Target->canRelaxTls(Type, &Body)) {
       uintX_t SymVA;
       if (Target->needsGot(Type, Body))
         SymVA = Body.getGotVA<ELFT>();
       else
         SymVA = Body.getVA<ELFT>();
       // By optimizing TLS relocations, it is sometimes needed to skip
       // relocations that immediately follow TLS relocations. This function
       // knows how many slots we need to skip.
       I += Target->relaxTls(BufLoc, BufEnd, Type, AddrLoc, SymVA, Body);
       continue;
     }

     // PPC64 has a special relocation representing the TOC base pointer
     // that does not have a corresponding symbol.
     if (Config->EMachine == EM_PPC64 && RI.getType(false) == R_PPC64_TOC) {
       uintX_t SymVA = getPPC64TocBase() + A;
       Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA, 0);
       continue;
     }

     if (Target->isTlsGlobalDynamicRel(Type) &&
         !Target->canRelaxTls(Type, &Body)) {
       Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
                           Out<ELFT>::Got->getGlobalDynAddr(Body) + A);
       continue;
     }

     uintX_t SymVA = Body.getVA<ELFT>(A);
     bool CBP = canBePreempted(Body);
     uint8_t *PairedLoc = nullptr;

     if (Target->needsPlt<ELFT>(Type, Body)) {
       SymVA = Body.getPltVA<ELFT>() + A;
     } else if (Target->needsGot(Type, Body)) {
       if (Config->EMachine == EM_MIPS && !CBP) {
         if (Body.isLocal()) {
           // R_MIPS_GOT16 relocation against local symbol requires index of
           // a local GOT entry which contains page address corresponds
           // to sum of the symbol address and addend. The addend in that case
           // is calculated using addends from R_MIPS_GOT16 and paired
           // R_MIPS_LO16 relocations.
           const endianness E = ELFT::TargetEndianness;
           uint8_t *LowLoc =
               findMipsPairedReloc(Buf, SymIndex, R_MIPS_LO16, NextRelocs);
           uint64_t AHL = read32<E>(BufLoc) << 16;
           if (LowLoc)
             AHL += SignExtend64<16>(read32<E>(LowLoc));
           SymVA = Out<ELFT>::Got->getMipsLocalPageAddr(SymVA + AHL);
         } else {
           // For non-local symbols GOT entries should contain their full
           // addresses. But if such symbol cannot be preempted, we do not
           // have to put them into the "global" part of GOT and use dynamic
           // linker to determine their actual addresses. That is why we
           // create GOT entries for them in the "local" part of GOT.
           SymVA = Out<ELFT>::Got->getMipsLocalFullAddr(Body) + A;
         }
       } else {
         SymVA = Body.getGotVA<ELFT>() + A;
       }
       if (Body.IsTls)
         Type = Target->getTlsGotRel(Type);
     } else if (Target->isSizeRel(Type) && CBP) {
       // A SIZE relocation is supposed to set a symbol size, but if a symbol
       // can be preempted, the size at runtime may be different than link time.
       // If that's the case, we leave the field alone rather than filling it
       // with a possibly incorrect value.
       continue;
     } else if (Config->EMachine == EM_MIPS) {
       if (Type == R_MIPS_HI16 && &Body == Config->MipsGpDisp) {
         SymVA = getMipsGpAddr<ELFT>() - AddrLoc + A;
       } else if (Type == R_MIPS_LO16 && &Body == Config->MipsGpDisp) {
         SymVA = getMipsGpAddr<ELFT>() - AddrLoc + 4 + A;
       } else if (&Body == Config->MipsLocalGp) {
         SymVA = getMipsGpAddr<ELFT>() + A;
       } else if (Type == R_MIPS_GPREL16 || Type == R_MIPS_GPREL32) {
         // We need to adjust SymVA value in case of R_MIPS_GPREL16/32
         // relocations because they use the following expression to calculate
         // the relocation's result for local symbol: S + A + GP0 - G.
         SymVA += File->getMipsGp0();
       } else {
         PairedLoc = findMipsPairedReloc(
             Buf, SymIndex, getMipsPairedRelocType(Type), NextRelocs);
       }
     } else if (!Target->needsCopyRel<ELFT>(Type, Body) && CBP) {
       continue;
     }
     uintX_t Size = Body.getSize<ELFT>();
     Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA, Size + A,
                         PairedLoc);
   }
 }

 template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
   if (this->Header->sh_type == SHT_NOBITS)
     return;
   // Copy section contents from source object file to output file.
   ArrayRef<uint8_t> Data = this->getSectionData();
   ELFFile<ELFT> &EObj = this->File->getObj();

   // That happens with -r. In that case we need fix the relocation position and
   // target. No relocations are applied.
   if (this->Header->sh_type == SHT_RELA) {
     this->copyRelocations(Buf + OutSecOff, EObj.relas(this->Header));
     return;
   }
   if (this->Header->sh_type == SHT_REL) {
     this->copyRelocations(Buf + OutSecOff, EObj.rels(this->Header));
     return;
   }

   memcpy(Buf + OutSecOff, Data.data(), Data.size());

   uint8_t *BufEnd = Buf + OutSecOff + Data.size();
   // Iterate over all relocation sections that apply to this section.
   for (const Elf_Shdr *RelSec : this->RelocSections) {
     if (RelSec->sh_type == SHT_RELA)
       this->relocate(Buf, BufEnd, EObj.relas(RelSec));
     else
       this->relocate(Buf, BufEnd, EObj.rels(RelSec));
   }
 }

 template <class ELFT>
 void InputSection<ELFT>::replace(InputSection<ELFT> *Other) {
   this->Align = std::max(this->Align, Other->Align);
   Other->Repl = this->Repl;
   Other->Live = false;
 }

 template <class ELFT>
 SplitInputSection<ELFT>::SplitInputSection(
     ObjectFile<ELFT> *File, const Elf_Shdr *Header,
     typename InputSectionBase<ELFT>::Kind SectionKind)
     : InputSectionBase<ELFT>(File, Header, SectionKind) {}

 template <class ELFT>
 EHInputSection<ELFT>::EHInputSection(ObjectFile<ELFT> *F,
                                      const Elf_Shdr *Header)
     : SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::EHFrame) {
   // Mark .eh_frame sections as live by default because there are
   // usually no relocations that point to .eh_frames. Otherwise,
   // the garbage collector would drop all .eh_frame sections.
   this->Live = true;
 }

 template <class ELFT>
 bool EHInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
   return S->SectionKind == InputSectionBase<ELFT>::EHFrame;
 }

 template <class ELFT>
 typename EHInputSection<ELFT>::uintX_t
 EHInputSection<ELFT>::getOffset(uintX_t Offset) {
   // The file crtbeginT.o has relocations pointing to the start of an empty
   // .eh_frame that is known to be the first in the link. It does that to
   // identify the start of the output .eh_frame. Handle this special case.
   if (this->getSectionHdr()->sh_size == 0)
     return Offset;
   std::pair<uintX_t, uintX_t> *I = this->getRangeAndSize(Offset).first;
   uintX_t Base = I->second;
   if (Base == uintX_t(-1))
     return -1; // Not in the output

   uintX_t Addend = Offset - I->first;
   return Base + Addend;
 }

 template <class ELFT>
 MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
                                            const Elf_Shdr *Header)
     : SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {}

 template <class ELFT>
 bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
   return S->SectionKind == InputSectionBase<ELFT>::Merge;
 }

 template <class ELFT>
 std::pair<std::pair<typename ELFFile<ELFT>::uintX_t,
                     typename ELFFile<ELFT>::uintX_t> *,
           typename ELFFile<ELFT>::uintX_t>
 SplitInputSection<ELFT>::getRangeAndSize(uintX_t Offset) {
   ArrayRef<uint8_t> D = this->getSectionData();
   StringRef Data((const char *)D.data(), D.size());
   uintX_t Size = Data.size();
   if (Offset >= Size)
     fatal("entry is past the end of the section");

   // Find the element this offset points to.
   auto I = std::upper_bound(
       Offsets.begin(), Offsets.end(), Offset,
       [](const uintX_t &A, const std::pair<uintX_t, uintX_t> &B) {
         return A < B.first;
       });
   uintX_t End = I == Offsets.end() ? Data.size() : I->first;
   --I;
   return std::make_pair(&*I, End);
 }

 template <class ELFT>
 typename MergeInputSection<ELFT>::uintX_t
 MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
   std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
       this->getRangeAndSize(Offset);
   std::pair<uintX_t, uintX_t> *I = T.first;
   uintX_t End = T.second;
   uintX_t Start = I->first;

   // Compute the Addend and if the Base is cached, return.
   uintX_t Addend = Offset - Start;
   uintX_t &Base = I->second;
   if (Base != uintX_t(-1))
     return Base + Addend;

   // Map the base to the offset in the output section and cache it.
   ArrayRef<uint8_t> D = this->getSectionData();
   StringRef Data((const char *)D.data(), D.size());
   StringRef Entry = Data.substr(Start, End - Start);
   Base =
       static_cast<MergeOutputSection<ELFT> *>(this->OutSec)->getOffset(Entry);
   return Base + Addend;
 }

 template <class ELFT>
 MipsReginfoInputSection<ELFT>::MipsReginfoInputSection(ObjectFile<ELFT> *F,
                                                        const Elf_Shdr *Hdr)
     : InputSectionBase<ELFT>(F, Hdr, InputSectionBase<ELFT>::MipsReginfo) {
   // Initialize this->Reginfo.
   ArrayRef<uint8_t> D = this->getSectionData();
   if (D.size() != sizeof(Elf_Mips_RegInfo<ELFT>))
     fatal("invalid size of .reginfo section");
   Reginfo = reinterpret_cast<const Elf_Mips_RegInfo<ELFT> *>(D.data());
 }

 template <class ELFT>
 bool MipsReginfoInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
   return S->SectionKind == InputSectionBase<ELFT>::MipsReginfo;
 }

 template class elf::InputSectionBase<ELF32LE>;
 template class elf::InputSectionBase<ELF32BE>;
 template class elf::InputSectionBase<ELF64LE>;
 template class elf::InputSectionBase<ELF64BE>;

 template class elf::InputSection<ELF32LE>;
 template class elf::InputSection<ELF32BE>;
 template class elf::InputSection<ELF64LE>;
 template class elf::InputSection<ELF64BE>;

 template class elf::EHInputSection<ELF32LE>;
 template class elf::EHInputSection<ELF32BE>;
 template class elf::EHInputSection<ELF64LE>;
 template class elf::EHInputSection<ELF64BE>;

 template class elf::MergeInputSection<ELF32LE>;
 template class elf::MergeInputSection<ELF32BE>;
 template class elf::MergeInputSection<ELF64LE>;
 template class elf::MergeInputSection<ELF64BE>;

 template class elf::MipsReginfoInputSection<ELF32LE>;
 template class elf::MipsReginfoInputSection<ELF32BE>;
 template class elf::MipsReginfoInputSection<ELF64LE>;
 template class elf::MipsReginfoInputSection<ELF64BE>;
	//===- InputSection.cpp ---------------------------------------------------===//
	//
	// The LLVM Linker
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//

	#include "InputSection.h"
	#include "Config.h"
	#include "Error.h"
	#include "InputFiles.h"
	#include "OutputSections.h"
	#include "Target.h"

	#include "llvm/Support/Endian.h"

	using namespace llvm;
	using namespace llvm::ELF;
	using namespace llvm::object;
	using namespace llvm::support::endian;

	using namespace lld;
	using namespace lld::elf;

	template <class ELFT>
	InputSectionBase<ELFT>::InputSectionBase(ObjectFile<ELFT> *File,
	const Elf_Shdr *Header,
	Kind SectionKind)
	: Header(Header), File(File), SectionKind(SectionKind), Repl(this) {
	// The garbage collector sets sections' Live bits.
	// If GC is disabled, all sections are considered live by default.
	Live = !Config->GcSections;

	// The ELF spec states that a value of 0 means the section has
	// no alignment constraits.
	Align = std::max<uintX_t>(Header->sh_addralign, 1);
	}

	template <class ELFT> StringRef InputSectionBase<ELFT>::getSectionName() const {
	return check(File->getObj().getSectionName(this->Header));
	}

	template <class ELFT>
	ArrayRef<uint8_t> InputSectionBase<ELFT>::getSectionData() const {
	return check(this->File->getObj().getSectionContents(this->Header));
	}

	template <class ELFT>
	typename ELFFile<ELFT>::uintX_t
	InputSectionBase<ELFT>::getOffset(uintX_t Offset) {
	switch (SectionKind) {
	case Regular:
	return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
	case EHFrame:
	return cast<EHInputSection<ELFT>>(this)->getOffset(Offset);
	case Merge:
	return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
	case MipsReginfo:
	// MIPS .reginfo sections are consumed by the linker,
	// so it should never be copied to output.
	llvm_unreachable("MIPS .reginfo reached writeTo().");
	}
	llvm_unreachable("invalid section kind");
	}

	template <class ELFT>
	typename ELFFile<ELFT>::uintX_t
	InputSectionBase<ELFT>::getOffset(const Elf_Sym &Sym) {
	return getOffset(Sym.st_value);
	}

	// Returns a section that Rel relocation is pointing to.
	template <class ELFT>
	InputSectionBase<ELFT> *
	InputSectionBase<ELFT>::getRelocTarget(const Elf_Rel &Rel) const {
	// Global symbol
	uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
	SymbolBody &B = File->getSymbolBody(SymIndex).repl();
	InputSectionBase<ELFT> *S = nullptr;
	if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&B))
	S = D->Section;
	if (S)
	return S->Repl;
	return nullptr;
	}

	template <class ELFT>
	InputSectionBase<ELFT> *
	InputSectionBase<ELFT>::getRelocTarget(const Elf_Rela &Rel) const {
	return getRelocTarget(reinterpret_cast<const Elf_Rel &>(Rel));
	}

	template <class ELFT>
	InputSection<ELFT>::InputSection(ObjectFile<ELFT> F, const Elf_Shdr Header)
	: InputSectionBase<ELFT>(F, Header, Base::Regular) {}

	template <class ELFT>
	bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
	return S->SectionKind == Base::Regular;
	}

	template <class ELFT>
	InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() {
	assert(this->Header->sh_type == SHT_RELA \|\| this->Header->sh_type == SHT_REL);
	ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections();
	return Sections[this->Header->sh_info];
	}

	// This is used for -r. We can't use memcpy to copy relocations because we need
	// to update symbol table offset and section index for each relocation. So we
	// copy relocations one by one.
	template <class ELFT>
	template <bool isRela>
	void InputSection<ELFT>::copyRelocations(uint8_t *Buf,
	RelIteratorRange<isRela> Rels) {
	typedef Elf_Rel_Impl<ELFT, isRela> RelType;
	InputSectionBase<ELFT> *RelocatedSection = getRelocatedSection();

	for (const RelType &Rel : Rels) {
	uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
	uint32_t Type = Rel.getType(Config->Mips64EL);
	SymbolBody &Body = this->File->getSymbolBody(SymIndex).repl();

	RelType P = reinterpret_cast<RelType >(Buf);
	Buf += sizeof(RelType);

	P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
	P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL);
	}
	}

	static uint32_t getMipsPairedRelocType(uint32_t Type) {
	if (Config->EMachine != EM_MIPS)
	return R_MIPS_NONE;
	switch (Type) {
	case R_MIPS_HI16:
	return R_MIPS_LO16;
	case R_MIPS_PCHI16:
	return R_MIPS_PCLO16;
	case R_MICROMIPS_HI16:
	return R_MICROMIPS_LO16;
	default:
	return R_MIPS_NONE;
	}
	}

	template <class ELFT>
	template <bool isRela>
	uint8_t *
	InputSectionBase<ELFT>::findMipsPairedReloc(uint8_t *Buf, uint32_t SymIndex,
	uint32_t Type,
	RelIteratorRange<isRela> Rels) {
	// Some MIPS relocations use addend calculated from addend of the relocation
	// itself and addend of paired relocation. ABI requires to compute such
	// combined addend in case of REL relocation record format only.
	// See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
	if (isRela \|\| Type == R_MIPS_NONE)
	return nullptr;
	for (const auto &RI : Rels) {
	if (RI.getType(Config->Mips64EL) != Type)
	continue;
	if (RI.getSymbol(Config->Mips64EL) != SymIndex)
	continue;
	uintX_t Offset = getOffset(RI.r_offset);
	if (Offset == (uintX_t)-1)
	return nullptr;
	return Buf + Offset;
	}
	return nullptr;
	}

	template <class ELFT>
	template <bool isRela>
	void InputSectionBase<ELFT>::relocate(uint8_t Buf, uint8_t BufEnd,
	RelIteratorRange<isRela> Rels) {
	typedef Elf_Rel_Impl<ELFT, isRela> RelType;
	size_t Num = Rels.end() - Rels.begin();
	for (size_t I = 0; I < Num; ++I) {
	const RelType &RI = *(Rels.begin() + I);
	uintX_t Offset = getOffset(RI.r_offset);
	if (Offset == (uintX_t)-1)
	continue;

	uintX_t A = getAddend<ELFT>(RI);
	uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
	uint32_t Type = RI.getType(Config->Mips64EL);
	uint8_t *BufLoc = Buf + Offset;
	uintX_t AddrLoc = OutSec->getVA() + Offset;
	auto NextRelocs = llvm::make_range(&RI, Rels.end());

	if (Target->pointsToLocalDynamicGotEntry(Type) &&
	!Target->canRelaxTls(Type, nullptr)) {
	Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
	Out<ELFT>::Got->getTlsIndexVA() + A);
	continue;
	}

	SymbolBody &Body = File->getSymbolBody(SymIndex).repl();

	if (Target->canRelaxTls(Type, &Body)) {
	uintX_t SymVA;
	if (Target->needsGot(Type, Body))
	SymVA = Body.getGotVA<ELFT>();
	else
	SymVA = Body.getVA<ELFT>();
	// By optimizing TLS relocations, it is sometimes needed to skip
	// relocations that immediately follow TLS relocations. This function
	// knows how many slots we need to skip.
	I += Target->relaxTls(BufLoc, BufEnd, Type, AddrLoc, SymVA, Body);
	continue;
	}

	// PPC64 has a special relocation representing the TOC base pointer
	// that does not have a corresponding symbol.
	if (Config->EMachine == EM_PPC64 && RI.getType(false) == R_PPC64_TOC) {
	uintX_t SymVA = getPPC64TocBase() + A;
	Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA, 0);
	continue;
	}

	if (Target->isTlsGlobalDynamicRel(Type) &&
	!Target->canRelaxTls(Type, &Body)) {
	Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
	Out<ELFT>::Got->getGlobalDynAddr(Body) + A);
	continue;
	}

	uintX_t SymVA = Body.getVA<ELFT>(A);
	bool CBP = canBePreempted(Body);
	uint8_t *PairedLoc = nullptr;

	if (Target->needsPlt<ELFT>(Type, Body)) {
	SymVA = Body.getPltVA<ELFT>() + A;
	} else if (Target->needsGot(Type, Body)) {
	if (Config->EMachine == EM_MIPS && !CBP) {
	if (Body.isLocal()) {
	// R_MIPS_GOT16 relocation against local symbol requires index of
	// a local GOT entry which contains page address corresponds
	// to sum of the symbol address and addend. The addend in that case
	// is calculated using addends from R_MIPS_GOT16 and paired
	// R_MIPS_LO16 relocations.
	const endianness E = ELFT::TargetEndianness;
	uint8_t *LowLoc =
	findMipsPairedReloc(Buf, SymIndex, R_MIPS_LO16, NextRelocs);
	uint64_t AHL = read32<E>(BufLoc) << 16;
	if (LowLoc)
	AHL += SignExtend64<16>(read32<E>(LowLoc));
	SymVA = Out<ELFT>::Got->getMipsLocalPageAddr(SymVA + AHL);
	} else {
	// For non-local symbols GOT entries should contain their full
	// addresses. But if such symbol cannot be preempted, we do not
	// have to put them into the "global" part of GOT and use dynamic
	// linker to determine their actual addresses. That is why we
	// create GOT entries for them in the "local" part of GOT.
	SymVA = Out<ELFT>::Got->getMipsLocalFullAddr(Body) + A;
	}
	} else {
	SymVA = Body.getGotVA<ELFT>() + A;
	}
	if (Body.IsTls)
	Type = Target->getTlsGotRel(Type);
	} else if (Target->isSizeRel(Type) && CBP) {
	// A SIZE relocation is supposed to set a symbol size, but if a symbol
	// can be preempted, the size at runtime may be different than link time.
	// If that's the case, we leave the field alone rather than filling it
	// with a possibly incorrect value.
	continue;
	} else if (Config->EMachine == EM_MIPS) {
	if (Type == R_MIPS_HI16 && &Body == Config->MipsGpDisp) {
	SymVA = getMipsGpAddr<ELFT>() - AddrLoc + A;
	} else if (Type == R_MIPS_LO16 && &Body == Config->MipsGpDisp) {
	SymVA = getMipsGpAddr<ELFT>() - AddrLoc + 4 + A;
	} else if (&Body == Config->MipsLocalGp) {
	SymVA = getMipsGpAddr<ELFT>() + A;
	} else if (Type == R_MIPS_GPREL16 \|\| Type == R_MIPS_GPREL32) {
	// We need to adjust SymVA value in case of R_MIPS_GPREL16/32
	// relocations because they use the following expression to calculate
	// the relocation's result for local symbol: S + A + GP0 - G.
	SymVA += File->getMipsGp0();
	} else {
	PairedLoc = findMipsPairedReloc(
	Buf, SymIndex, getMipsPairedRelocType(Type), NextRelocs);
	}
	} else if (!Target->needsCopyRel<ELFT>(Type, Body) && CBP) {
	continue;
	}
	uintX_t Size = Body.getSize<ELFT>();
	Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA, Size + A,
	PairedLoc);
	}
	}

	template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
	if (this->Header->sh_type == SHT_NOBITS)
	return;
	// Copy section contents from source object file to output file.
	ArrayRef<uint8_t> Data = this->getSectionData();
	ELFFile<ELFT> &EObj = this->File->getObj();

	// That happens with -r. In that case we need fix the relocation position and
	// target. No relocations are applied.
	if (this->Header->sh_type == SHT_RELA) {
	this->copyRelocations(Buf + OutSecOff, EObj.relas(this->Header));
	return;
	}
	if (this->Header->sh_type == SHT_REL) {
	this->copyRelocations(Buf + OutSecOff, EObj.rels(this->Header));
	return;
	}

	memcpy(Buf + OutSecOff, Data.data(), Data.size());

	uint8_t *BufEnd = Buf + OutSecOff + Data.size();
	// Iterate over all relocation sections that apply to this section.
	for (const Elf_Shdr *RelSec : this->RelocSections) {
	if (RelSec->sh_type == SHT_RELA)
	this->relocate(Buf, BufEnd, EObj.relas(RelSec));
	else
	this->relocate(Buf, BufEnd, EObj.rels(RelSec));
	}
	}

	template <class ELFT>
	void InputSection<ELFT>::replace(InputSection<ELFT> *Other) {
	this->Align = std::max(this->Align, Other->Align);
	Other->Repl = this->Repl;
	Other->Live = false;
	}

	template <class ELFT>
	SplitInputSection<ELFT>::SplitInputSection(
	ObjectFile<ELFT> File, const Elf_Shdr Header,
	typename InputSectionBase<ELFT>::Kind SectionKind)
	: InputSectionBase<ELFT>(File, Header, SectionKind) {}

	template <class ELFT>
	EHInputSection<ELFT>::EHInputSection(ObjectFile<ELFT> *F,
	const Elf_Shdr *Header)
	: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::EHFrame) {
	// Mark .eh_frame sections as live by default because there are
	// usually no relocations that point to .eh_frames. Otherwise,
	// the garbage collector would drop all .eh_frame sections.
	this->Live = true;
	}

	template <class ELFT>
	bool EHInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
	return S->SectionKind == InputSectionBase<ELFT>::EHFrame;
	}

	template <class ELFT>
	typename EHInputSection<ELFT>::uintX_t
	EHInputSection<ELFT>::getOffset(uintX_t Offset) {
	// The file crtbeginT.o has relocations pointing to the start of an empty
	// .eh_frame that is known to be the first in the link. It does that to
	// identify the start of the output .eh_frame. Handle this special case.
	if (this->getSectionHdr()->sh_size == 0)
	return Offset;
	std::pair<uintX_t, uintX_t> *I = this->getRangeAndSize(Offset).first;
	uintX_t Base = I->second;
	if (Base == uintX_t(-1))
	return -1; // Not in the output

	uintX_t Addend = Offset - I->first;
	return Base + Addend;
	}

	template <class ELFT>
	MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
	const Elf_Shdr *Header)
	: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {}

	template <class ELFT>
	bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
	return S->SectionKind == InputSectionBase<ELFT>::Merge;
	}

	template <class ELFT>
	std::pair<std::pair<typename ELFFile<ELFT>::uintX_t,
	typename ELFFile<ELFT>::uintX_t> *,
	typename ELFFile<ELFT>::uintX_t>
	SplitInputSection<ELFT>::getRangeAndSize(uintX_t Offset) {
	ArrayRef<uint8_t> D = this->getSectionData();
	StringRef Data((const char *)D.data(), D.size());
	uintX_t Size = Data.size();
	if (Offset >= Size)
	fatal("entry is past the end of the section");

	// Find the element this offset points to.
	auto I = std::upper_bound(
	Offsets.begin(), Offsets.end(), Offset,
	[](const uintX_t &A, const std::pair<uintX_t, uintX_t> &B) {
	return A < B.first;
	});
	uintX_t End = I == Offsets.end() ? Data.size() : I->first;
	--I;
	return std::make_pair(&*I, End);
	}

	template <class ELFT>
	typename MergeInputSection<ELFT>::uintX_t
	MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
	std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
	this->getRangeAndSize(Offset);
	std::pair<uintX_t, uintX_t> *I = T.first;
	uintX_t End = T.second;
	uintX_t Start = I->first;

	// Compute the Addend and if the Base is cached, return.
	uintX_t Addend = Offset - Start;
	uintX_t &Base = I->second;
	if (Base != uintX_t(-1))
	return Base + Addend;

	// Map the base to the offset in the output section and cache it.
	ArrayRef<uint8_t> D = this->getSectionData();
	StringRef Data((const char *)D.data(), D.size());
	StringRef Entry = Data.substr(Start, End - Start);
	Base =
	static_cast<MergeOutputSection<ELFT> *>(this->OutSec)->getOffset(Entry);
	return Base + Addend;
	}

	template <class ELFT>
	MipsReginfoInputSection<ELFT>::MipsReginfoInputSection(ObjectFile<ELFT> *F,
	const Elf_Shdr *Hdr)
	: InputSectionBase<ELFT>(F, Hdr, InputSectionBase<ELFT>::MipsReginfo) {
	// Initialize this->Reginfo.
	ArrayRef<uint8_t> D = this->getSectionData();
	if (D.size() != sizeof(Elf_Mips_RegInfo<ELFT>))
	fatal("invalid size of .reginfo section");
	Reginfo = reinterpret_cast<const Elf_Mips_RegInfo<ELFT> *>(D.data());
	}

	template <class ELFT>
	bool MipsReginfoInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
	return S->SectionKind == InputSectionBase<ELFT>::MipsReginfo;
	}

	template class elf::InputSectionBase<ELF32LE>;
	template class elf::InputSectionBase<ELF32BE>;
	template class elf::InputSectionBase<ELF64LE>;
	template class elf::InputSectionBase<ELF64BE>;

	template class elf::InputSection<ELF32LE>;
	template class elf::InputSection<ELF32BE>;
	template class elf::InputSection<ELF64LE>;
	template class elf::InputSection<ELF64BE>;

	template class elf::EHInputSection<ELF32LE>;
	template class elf::EHInputSection<ELF32BE>;
	template class elf::EHInputSection<ELF64LE>;
	template class elf::EHInputSection<ELF64BE>;

	template class elf::MergeInputSection<ELF32LE>;
	template class elf::MergeInputSection<ELF32BE>;
	template class elf::MergeInputSection<ELF64LE>;
	template class elf::MergeInputSection<ELF64BE>;

	template class elf::MipsReginfoInputSection<ELF32LE>;
	template class elf::MipsReginfoInputSection<ELF32BE>;
	template class elf::MipsReginfoInputSection<ELF64LE>;
	template class elf::MipsReginfoInputSection<ELF64BE>;