ELF/Symbols.cpp - lld - Git at Google

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

 #include "Symbols.h"
 #include "Error.h"
 #include "InputFiles.h"
 #include "InputSection.h"
 #include "OutputSections.h"
 #include "Strings.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "Writer.h"

 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Path.h"
 #include <cstring>

 using namespace llvm;
 using namespace llvm::object;
 using namespace llvm::ELF;

 using namespace lld;
 using namespace lld::elf;

 DefinedRegular *ElfSym::Bss;
 DefinedRegular *ElfSym::Etext1;
 DefinedRegular *ElfSym::Etext2;
 DefinedRegular *ElfSym::Edata1;
 DefinedRegular *ElfSym::Edata2;
 DefinedRegular *ElfSym::End1;
 DefinedRegular *ElfSym::End2;
 DefinedRegular *ElfSym::GlobalOffsetTable;
 DefinedRegular *ElfSym::MipsGp;
 DefinedRegular *ElfSym::MipsGpDisp;
 DefinedRegular *ElfSym::MipsLocalGp;

 static uint64_t getSymVA(const SymbolBody &Body, int64_t &Addend) {
   switch (Body.kind()) {
   case SymbolBody::DefinedRegularKind: {
     auto &D = cast<DefinedRegular>(Body);
     SectionBase *IS = D.Section;
     if (auto *ISB = dyn_cast_or_null<InputSectionBase>(IS))
       IS = ISB->Repl;

     // According to the ELF spec reference to a local symbol from outside
     // the group are not allowed. Unfortunately .eh_frame breaks that rule
     // and must be treated specially. For now we just replace the symbol with
     // 0.
     if (IS == &InputSection::Discarded)
       return 0;

     // This is an absolute symbol.
     if (!IS)
       return D.Value;

     uint64_t Offset = D.Value;

     // An object in an SHF_MERGE section might be referenced via a
     // section symbol (as a hack for reducing the number of local
     // symbols).
     // Depending on the addend, the reference via a section symbol
     // refers to a different object in the merge section.
     // Since the objects in the merge section are not necessarily
     // contiguous in the output, the addend can thus affect the final
     // VA in a non-linear way.
     // To make this work, we incorporate the addend into the section
     // offset (and zero out the addend for later processing) so that
     // we find the right object in the section.
     if (D.isSection()) {
       Offset += Addend;
       Addend = 0;
     }

     const OutputSection *OutSec = IS->getOutputSection();

     // In the typical case, this is actually very simple and boils
     // down to adding together 3 numbers:
     // 1. The address of the output section.
     // 2. The offset of the input section within the output section.
     // 3. The offset within the input section (this addition happens
     //    inside InputSection::getOffset).
     //
     // If you understand the data structures involved with this next
     // line (and how they get built), then you have a pretty good
     // understanding of the linker.
     uint64_t VA = (OutSec ? OutSec->Addr : 0) + IS->getOffset(Offset);

     if (D.isTls() && !Config->Relocatable) {
       if (!Out::TlsPhdr)
         fatal(toString(D.File) +
               " has an STT_TLS symbol but doesn't have an SHF_TLS section");
       return VA - Out::TlsPhdr->p_vaddr;
     }
     return VA;
   }
   case SymbolBody::DefinedCommonKind:
     if (!Config->DefineCommon)
       return 0;
     return InX::Common->getParent()->Addr + InX::Common->OutSecOff +
            cast<DefinedCommon>(Body).Offset;
   case SymbolBody::SharedKind: {
     auto &SS = cast<SharedSymbol>(Body);
     if (SS.NeedsCopy)
       return SS.CopyRelSec->getParent()->Addr + SS.CopyRelSec->OutSecOff +
              SS.CopyRelSecOff;
     if (SS.NeedsPltAddr)
       return Body.getPltVA();
     return 0;
   }
   case SymbolBody::UndefinedKind:
     return 0;
   case SymbolBody::LazyArchiveKind:
   case SymbolBody::LazyObjectKind:
     assert(Body.symbol()->IsUsedInRegularObj && "lazy symbol reached writer");
     return 0;
   }
   llvm_unreachable("invalid symbol kind");
 }

 SymbolBody::SymbolBody(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
                        uint8_t Type)
     : SymbolKind(K), NeedsCopy(false), NeedsPltAddr(false), IsLocal(IsLocal),
       IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
       IsInIgot(false), Type(Type), StOther(StOther), Name(Name) {}

 // Returns true if a symbol can be replaced at load-time by a symbol
 // with the same name defined in other ELF executable or DSO.
 bool SymbolBody::isPreemptible() const {
   if (isLocal())
     return false;

   // Shared symbols resolve to the definition in the DSO. The exceptions are
   // symbols with copy relocations (which resolve to .bss) or preempt plt
   // entries (which resolve to that plt entry).
   if (isShared())
     return !NeedsCopy && !NeedsPltAddr;

   // That's all that can be preempted in a non-DSO.
   if (!Config->Shared)
     return false;

   // Only symbols that appear in dynsym can be preempted.
   if (!symbol()->includeInDynsym())
     return false;

   // Only default visibility symbols can be preempted.
   if (symbol()->Visibility != STV_DEFAULT)
     return false;

   // -Bsymbolic means that definitions are not preempted.
   if (Config->Bsymbolic || (Config->BsymbolicFunctions && isFunc()))
     return !isDefined();
   return true;
 }

 // Overwrites all attributes with Other's so that this symbol becomes
 // an alias to Other. This is useful for handling some options such as
 // --wrap.
 void SymbolBody::copy(SymbolBody *Other) {
   memcpy(symbol()->Body.buffer, Other->symbol()->Body.buffer,
          sizeof(Symbol::Body));
 }

 uint64_t SymbolBody::getVA(int64_t Addend) const {
   uint64_t OutVA = getSymVA(*this, Addend);
   return OutVA + Addend;
 }

 uint64_t SymbolBody::getGotVA() const {
   return InX::Got->getVA() + getGotOffset();
 }

 uint64_t SymbolBody::getGotOffset() const {
   return GotIndex * Target->GotEntrySize;
 }

 uint64_t SymbolBody::getGotPltVA() const {
   if (this->IsInIgot)
     return InX::IgotPlt->getVA() + getGotPltOffset();
   return InX::GotPlt->getVA() + getGotPltOffset();
 }

 uint64_t SymbolBody::getGotPltOffset() const {
   return GotPltIndex * Target->GotPltEntrySize;
 }

 uint64_t SymbolBody::getPltVA() const {
   if (this->IsInIplt)
     return InX::Iplt->getVA() + PltIndex * Target->PltEntrySize;
   return InX::Plt->getVA() + Target->PltHeaderSize +
          PltIndex * Target->PltEntrySize;
 }

 template <class ELFT> typename ELFT::uint SymbolBody::getSize() const {
   if (const auto *C = dyn_cast<DefinedCommon>(this))
     return C->Size;
   if (const auto *DR = dyn_cast<DefinedRegular>(this))
     return DR->Size;
   if (const auto *S = dyn_cast<SharedSymbol>(this))
     return S->getSize<ELFT>();
   return 0;
 }

 OutputSection *SymbolBody::getOutputSection() const {
   if (auto *S = dyn_cast<DefinedRegular>(this)) {
     if (S->Section)
       return S->Section->getOutputSection();
     return nullptr;
   }

   if (auto *S = dyn_cast<SharedSymbol>(this)) {
     if (S->NeedsCopy)
       return S->CopyRelSec->getParent();
     return nullptr;
   }

   if (isa<DefinedCommon>(this)) {
     if (Config->DefineCommon)
       return InX::Common->getParent();
     return nullptr;
   }

   return nullptr;
 }

 // If a symbol name contains '@', the characters after that is
 // a symbol version name. This function parses that.
 void SymbolBody::parseSymbolVersion() {
   StringRef S = getName();
   size_t Pos = S.find('@');
   if (Pos == 0 || Pos == StringRef::npos)
     return;
   StringRef Verstr = S.substr(Pos + 1);
   if (Verstr.empty())
     return;

   // Truncate the symbol name so that it doesn't include the version string.
   Name = {S.data(), Pos};

   // If this is not in this DSO, it is not a definition.
   if (!isInCurrentDSO())
     return;

   // '@@' in a symbol name means the default version.
   // It is usually the most recent one.
   bool IsDefault = (Verstr[0] == '@');
   if (IsDefault)
     Verstr = Verstr.substr(1);

   for (VersionDefinition &Ver : Config->VersionDefinitions) {
     if (Ver.Name != Verstr)
       continue;

     if (IsDefault)
       symbol()->VersionId = Ver.Id;
     else
       symbol()->VersionId = Ver.Id | VERSYM_HIDDEN;
     return;
   }

   // It is an error if the specified version is not defined.
   // Usually version script is not provided when linking executable,
   // but we may still want to override a versioned symbol from DSO,
   // so we do not report error in this case.
   if (Config->Shared)
     error(toString(File) + ": symbol " + S + " has undefined version " +
           Verstr);
 }

 Defined::Defined(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
                  uint8_t Type)
     : SymbolBody(K, Name, IsLocal, StOther, Type) {}

 template <class ELFT> bool DefinedRegular::isMipsPIC() const {
   typedef typename ELFT::Ehdr Elf_Ehdr;
   if (!Section || !isFunc())
     return false;

   auto *Sec = cast<InputSectionBase>(Section);
   const Elf_Ehdr *Hdr = Sec->template getFile<ELFT>()->getObj().getHeader();
   return (this->StOther & STO_MIPS_MIPS16) == STO_MIPS_PIC ||
          (Hdr->e_flags & EF_MIPS_PIC);
 }

 Undefined::Undefined(StringRefZ Name, bool IsLocal, uint8_t StOther,
                      uint8_t Type, InputFile *File)
     : SymbolBody(SymbolBody::UndefinedKind, Name, IsLocal, StOther, Type) {
   this->File = File;
 }

 DefinedCommon::DefinedCommon(StringRef Name, uint64_t Size, uint32_t Alignment,
                              uint8_t StOther, uint8_t Type, InputFile *File)
     : Defined(SymbolBody::DefinedCommonKind, Name, /*IsLocal=*/false, StOther,
               Type),
       Alignment(Alignment), Size(Size) {
   this->File = File;
 }

 // If a shared symbol is referred via a copy relocation, its alignment
 // becomes part of the ABI. This function returns a symbol alignment.
 // Because symbols don't have alignment attributes, we need to infer that.
 template <class ELFT> uint32_t SharedSymbol::getAlignment() const {
   auto *File = cast<SharedFile<ELFT>>(this->File);
   uint32_t SecAlign = File->getSection(getSym<ELFT>())->sh_addralign;
   uint64_t SymValue = getSym<ELFT>().st_value;
   uint32_t SymAlign = uint32_t(1) << countTrailingZeros(SymValue);
   return std::min(SecAlign, SymAlign);
 }

 InputFile *Lazy::fetch() {
   if (auto *S = dyn_cast<LazyArchive>(this))
     return S->fetch();
   return cast<LazyObject>(this)->fetch();
 }

 LazyArchive::LazyArchive(ArchiveFile &File,
                          const llvm::object::Archive::Symbol S, uint8_t Type)
     : Lazy(LazyArchiveKind, S.getName(), Type), Sym(S) {
   this->File = &File;
 }

 LazyObject::LazyObject(StringRef Name, LazyObjectFile &File, uint8_t Type)
     : Lazy(LazyObjectKind, Name, Type) {
   this->File = &File;
 }

 InputFile *LazyArchive::fetch() {
   std::pair<MemoryBufferRef, uint64_t> MBInfo = file()->getMember(&Sym);

   // getMember returns an empty buffer if the member was already
   // read from the library.
   if (MBInfo.first.getBuffer().empty())
     return nullptr;
   return createObjectFile(MBInfo.first, file()->getName(), MBInfo.second);
 }

 InputFile *LazyObject::fetch() { return file()->fetch(); }

 uint8_t Symbol::computeBinding() const {
   if (Config->Relocatable)
     return Binding;
   if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
     return STB_LOCAL;
   if (VersionId == VER_NDX_LOCAL && body()->isInCurrentDSO())
     return STB_LOCAL;
   if (Config->NoGnuUnique && Binding == STB_GNU_UNIQUE)
     return STB_GLOBAL;
   return Binding;
 }

 bool Symbol::includeInDynsym() const {
   if (computeBinding() == STB_LOCAL)
     return false;
   return ExportDynamic || body()->isShared() ||
          (body()->isUndefined() && Config->Shared);
 }

 // Print out a log message for --trace-symbol.
 void elf::printTraceSymbol(Symbol *Sym) {
   SymbolBody *B = Sym->body();
   std::string S;
   if (B->isUndefined())
     S = ": reference to ";
   else if (B->isCommon())
     S = ": common definition of ";
   else
     S = ": definition of ";

   message(toString(B->File) + S + B->getName());
 }

 // Returns a symbol for an error message.
 std::string lld::toString(const SymbolBody &B) {
   if (Config->Demangle)
     if (Optional<std::string> S = demangle(B.getName()))
       return *S;
   return B.getName();
 }

 template uint32_t SymbolBody::template getSize<ELF32LE>() const;
 template uint32_t SymbolBody::template getSize<ELF32BE>() const;
 template uint64_t SymbolBody::template getSize<ELF64LE>() const;
 template uint64_t SymbolBody::template getSize<ELF64BE>() const;

 template bool DefinedRegular::template isMipsPIC<ELF32LE>() const;
 template bool DefinedRegular::template isMipsPIC<ELF32BE>() const;
 template bool DefinedRegular::template isMipsPIC<ELF64LE>() const;
 template bool DefinedRegular::template isMipsPIC<ELF64BE>() const;

 template uint32_t SharedSymbol::template getAlignment<ELF32LE>() const;
 template uint32_t SharedSymbol::template getAlignment<ELF32BE>() const;
 template uint32_t SharedSymbol::template getAlignment<ELF64LE>() const;
 template uint32_t SharedSymbol::template getAlignment<ELF64BE>() const;
	//===- Symbols.cpp --------------------------------------------------------===//
	//
	// The LLVM Linker
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//

	#include "Symbols.h"
	#include "Error.h"
	#include "InputFiles.h"
	#include "InputSection.h"
	#include "OutputSections.h"
	#include "Strings.h"
	#include "SyntheticSections.h"
	#include "Target.h"
	#include "Writer.h"

	#include "llvm/ADT/STLExtras.h"
	#include "llvm/Support/Path.h"
	#include <cstring>

	using namespace llvm;
	using namespace llvm::object;
	using namespace llvm::ELF;

	using namespace lld;
	using namespace lld::elf;

	DefinedRegular *ElfSym::Bss;
	DefinedRegular *ElfSym::Etext1;
	DefinedRegular *ElfSym::Etext2;
	DefinedRegular *ElfSym::Edata1;
	DefinedRegular *ElfSym::Edata2;
	DefinedRegular *ElfSym::End1;
	DefinedRegular *ElfSym::End2;
	DefinedRegular *ElfSym::GlobalOffsetTable;
	DefinedRegular *ElfSym::MipsGp;
	DefinedRegular *ElfSym::MipsGpDisp;
	DefinedRegular *ElfSym::MipsLocalGp;

	static uint64_t getSymVA(const SymbolBody &Body, int64_t &Addend) {
	switch (Body.kind()) {
	case SymbolBody::DefinedRegularKind: {
	auto &D = cast<DefinedRegular>(Body);
	SectionBase *IS = D.Section;
	if (auto *ISB = dyn_cast_or_null<InputSectionBase>(IS))
	IS = ISB->Repl;

	// According to the ELF spec reference to a local symbol from outside
	// the group are not allowed. Unfortunately .eh_frame breaks that rule
	// and must be treated specially. For now we just replace the symbol with
	// 0.
	if (IS == &InputSection::Discarded)
	return 0;

	// This is an absolute symbol.
	if (!IS)
	return D.Value;

	uint64_t Offset = D.Value;

	// An object in an SHF_MERGE section might be referenced via a
	// section symbol (as a hack for reducing the number of local
	// symbols).
	// Depending on the addend, the reference via a section symbol
	// refers to a different object in the merge section.
	// Since the objects in the merge section are not necessarily
	// contiguous in the output, the addend can thus affect the final
	// VA in a non-linear way.
	// To make this work, we incorporate the addend into the section
	// offset (and zero out the addend for later processing) so that
	// we find the right object in the section.
	if (D.isSection()) {
	Offset += Addend;
	Addend = 0;
	}

	const OutputSection *OutSec = IS->getOutputSection();

	// In the typical case, this is actually very simple and boils
	// down to adding together 3 numbers:
	// 1. The address of the output section.
	// 2. The offset of the input section within the output section.
	// 3. The offset within the input section (this addition happens
	// inside InputSection::getOffset).
	//
	// If you understand the data structures involved with this next
	// line (and how they get built), then you have a pretty good
	// understanding of the linker.
	uint64_t VA = (OutSec ? OutSec->Addr : 0) + IS->getOffset(Offset);

	if (D.isTls() && !Config->Relocatable) {
	if (!Out::TlsPhdr)
	fatal(toString(D.File) +
	" has an STT_TLS symbol but doesn't have an SHF_TLS section");
	return VA - Out::TlsPhdr->p_vaddr;
	}
	return VA;
	}
	case SymbolBody::DefinedCommonKind:
	if (!Config->DefineCommon)
	return 0;
	return InX::Common->getParent()->Addr + InX::Common->OutSecOff +
	cast<DefinedCommon>(Body).Offset;
	case SymbolBody::SharedKind: {
	auto &SS = cast<SharedSymbol>(Body);
	if (SS.NeedsCopy)
	return SS.CopyRelSec->getParent()->Addr + SS.CopyRelSec->OutSecOff +
	SS.CopyRelSecOff;
	if (SS.NeedsPltAddr)
	return Body.getPltVA();
	return 0;
	}
	case SymbolBody::UndefinedKind:
	return 0;
	case SymbolBody::LazyArchiveKind:
	case SymbolBody::LazyObjectKind:
	assert(Body.symbol()->IsUsedInRegularObj && "lazy symbol reached writer");
	return 0;
	}
	llvm_unreachable("invalid symbol kind");
	}

	SymbolBody::SymbolBody(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
	uint8_t Type)
	: SymbolKind(K), NeedsCopy(false), NeedsPltAddr(false), IsLocal(IsLocal),
	IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
	IsInIgot(false), Type(Type), StOther(StOther), Name(Name) {}

	// Returns true if a symbol can be replaced at load-time by a symbol
	// with the same name defined in other ELF executable or DSO.
	bool SymbolBody::isPreemptible() const {
	if (isLocal())
	return false;

	// Shared symbols resolve to the definition in the DSO. The exceptions are
	// symbols with copy relocations (which resolve to .bss) or preempt plt
	// entries (which resolve to that plt entry).
	if (isShared())
	return !NeedsCopy && !NeedsPltAddr;

	// That's all that can be preempted in a non-DSO.
	if (!Config->Shared)
	return false;

	// Only symbols that appear in dynsym can be preempted.
	if (!symbol()->includeInDynsym())
	return false;

	// Only default visibility symbols can be preempted.
	if (symbol()->Visibility != STV_DEFAULT)
	return false;

	// -Bsymbolic means that definitions are not preempted.
	if (Config->Bsymbolic \|\| (Config->BsymbolicFunctions && isFunc()))
	return !isDefined();
	return true;
	}

	// Overwrites all attributes with Other's so that this symbol becomes
	// an alias to Other. This is useful for handling some options such as
	// --wrap.
	void SymbolBody::copy(SymbolBody *Other) {
	memcpy(symbol()->Body.buffer, Other->symbol()->Body.buffer,
	sizeof(Symbol::Body));
	}

	uint64_t SymbolBody::getVA(int64_t Addend) const {
	uint64_t OutVA = getSymVA(*this, Addend);
	return OutVA + Addend;
	}

	uint64_t SymbolBody::getGotVA() const {
	return InX::Got->getVA() + getGotOffset();
	}

	uint64_t SymbolBody::getGotOffset() const {
	return GotIndex * Target->GotEntrySize;
	}

	uint64_t SymbolBody::getGotPltVA() const {
	if (this->IsInIgot)
	return InX::IgotPlt->getVA() + getGotPltOffset();
	return InX::GotPlt->getVA() + getGotPltOffset();
	}

	uint64_t SymbolBody::getGotPltOffset() const {
	return GotPltIndex * Target->GotPltEntrySize;
	}

	uint64_t SymbolBody::getPltVA() const {
	if (this->IsInIplt)
	return InX::Iplt->getVA() + PltIndex * Target->PltEntrySize;
	return InX::Plt->getVA() + Target->PltHeaderSize +
	PltIndex * Target->PltEntrySize;
	}

	template <class ELFT> typename ELFT::uint SymbolBody::getSize() const {
	if (const auto *C = dyn_cast<DefinedCommon>(this))
	return C->Size;
	if (const auto *DR = dyn_cast<DefinedRegular>(this))
	return DR->Size;
	if (const auto *S = dyn_cast<SharedSymbol>(this))
	return S->getSize<ELFT>();
	return 0;
	}

	OutputSection *SymbolBody::getOutputSection() const {
	if (auto *S = dyn_cast<DefinedRegular>(this)) {
	if (S->Section)
	return S->Section->getOutputSection();
	return nullptr;
	}

	if (auto *S = dyn_cast<SharedSymbol>(this)) {
	if (S->NeedsCopy)
	return S->CopyRelSec->getParent();
	return nullptr;
	}

	if (isa<DefinedCommon>(this)) {
	if (Config->DefineCommon)
	return InX::Common->getParent();
	return nullptr;
	}

	return nullptr;
	}

	// If a symbol name contains '@', the characters after that is
	// a symbol version name. This function parses that.
	void SymbolBody::parseSymbolVersion() {
	StringRef S = getName();
	size_t Pos = S.find('@');
	if (Pos == 0 \|\| Pos == StringRef::npos)
	return;
	StringRef Verstr = S.substr(Pos + 1);
	if (Verstr.empty())
	return;

	// Truncate the symbol name so that it doesn't include the version string.
	Name = {S.data(), Pos};

	// If this is not in this DSO, it is not a definition.
	if (!isInCurrentDSO())
	return;

	// '@@' in a symbol name means the default version.
	// It is usually the most recent one.
	bool IsDefault = (Verstr[0] == '@');
	if (IsDefault)
	Verstr = Verstr.substr(1);

	for (VersionDefinition &Ver : Config->VersionDefinitions) {
	if (Ver.Name != Verstr)
	continue;

	if (IsDefault)
	symbol()->VersionId = Ver.Id;
	else
	symbol()->VersionId = Ver.Id \| VERSYM_HIDDEN;
	return;
	}

	// It is an error if the specified version is not defined.
	// Usually version script is not provided when linking executable,
	// but we may still want to override a versioned symbol from DSO,
	// so we do not report error in this case.
	if (Config->Shared)
	error(toString(File) + ": symbol " + S + " has undefined version " +
	Verstr);
	}

	Defined::Defined(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
	uint8_t Type)
	: SymbolBody(K, Name, IsLocal, StOther, Type) {}

	template <class ELFT> bool DefinedRegular::isMipsPIC() const {
	typedef typename ELFT::Ehdr Elf_Ehdr;
	if (!Section \|\| !isFunc())
	return false;

	auto *Sec = cast<InputSectionBase>(Section);
	const Elf_Ehdr *Hdr = Sec->template getFile<ELFT>()->getObj().getHeader();
	return (this->StOther & STO_MIPS_MIPS16) == STO_MIPS_PIC \|\|
	(Hdr->e_flags & EF_MIPS_PIC);
	}

	Undefined::Undefined(StringRefZ Name, bool IsLocal, uint8_t StOther,
	uint8_t Type, InputFile *File)
	: SymbolBody(SymbolBody::UndefinedKind, Name, IsLocal, StOther, Type) {
	this->File = File;
	}

	DefinedCommon::DefinedCommon(StringRef Name, uint64_t Size, uint32_t Alignment,
	uint8_t StOther, uint8_t Type, InputFile *File)
	: Defined(SymbolBody::DefinedCommonKind, Name, /IsLocal=/false, StOther,
	Type),
	Alignment(Alignment), Size(Size) {
	this->File = File;
	}

	// If a shared symbol is referred via a copy relocation, its alignment
	// becomes part of the ABI. This function returns a symbol alignment.
	// Because symbols don't have alignment attributes, we need to infer that.
	template <class ELFT> uint32_t SharedSymbol::getAlignment() const {
	auto *File = cast<SharedFile<ELFT>>(this->File);
	uint32_t SecAlign = File->getSection(getSym<ELFT>())->sh_addralign;
	uint64_t SymValue = getSym<ELFT>().st_value;
	uint32_t SymAlign = uint32_t(1) << countTrailingZeros(SymValue);
	return std::min(SecAlign, SymAlign);
	}

	InputFile *Lazy::fetch() {
	if (auto *S = dyn_cast<LazyArchive>(this))
	return S->fetch();
	return cast<LazyObject>(this)->fetch();
	}

	LazyArchive::LazyArchive(ArchiveFile &File,
	const llvm::object::Archive::Symbol S, uint8_t Type)
	: Lazy(LazyArchiveKind, S.getName(), Type), Sym(S) {
	this->File = &File;
	}

	LazyObject::LazyObject(StringRef Name, LazyObjectFile &File, uint8_t Type)
	: Lazy(LazyObjectKind, Name, Type) {
	this->File = &File;
	}

	InputFile *LazyArchive::fetch() {
	std::pair<MemoryBufferRef, uint64_t> MBInfo = file()->getMember(&Sym);

	// getMember returns an empty buffer if the member was already
	// read from the library.
	if (MBInfo.first.getBuffer().empty())
	return nullptr;
	return createObjectFile(MBInfo.first, file()->getName(), MBInfo.second);
	}

	InputFile *LazyObject::fetch() { return file()->fetch(); }

	uint8_t Symbol::computeBinding() const {
	if (Config->Relocatable)
	return Binding;
	if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
	return STB_LOCAL;
	if (VersionId == VER_NDX_LOCAL && body()->isInCurrentDSO())
	return STB_LOCAL;
	if (Config->NoGnuUnique && Binding == STB_GNU_UNIQUE)
	return STB_GLOBAL;
	return Binding;
	}

	bool Symbol::includeInDynsym() const {
	if (computeBinding() == STB_LOCAL)
	return false;
	return ExportDynamic \|\| body()->isShared() \|\|
	(body()->isUndefined() && Config->Shared);
	}

	// Print out a log message for --trace-symbol.
	void elf::printTraceSymbol(Symbol *Sym) {
	SymbolBody *B = Sym->body();
	std::string S;
	if (B->isUndefined())
	S = ": reference to ";
	else if (B->isCommon())
	S = ": common definition of ";
	else
	S = ": definition of ";

	message(toString(B->File) + S + B->getName());
	}

	// Returns a symbol for an error message.
	std::string lld::toString(const SymbolBody &B) {
	if (Config->Demangle)
	if (Optional<std::string> S = demangle(B.getName()))
	return *S;
	return B.getName();
	}

	template uint32_t SymbolBody::template getSize<ELF32LE>() const;
	template uint32_t SymbolBody::template getSize<ELF32BE>() const;
	template uint64_t SymbolBody::template getSize<ELF64LE>() const;
	template uint64_t SymbolBody::template getSize<ELF64BE>() const;

	template bool DefinedRegular::template isMipsPIC<ELF32LE>() const;
	template bool DefinedRegular::template isMipsPIC<ELF32BE>() const;
	template bool DefinedRegular::template isMipsPIC<ELF64LE>() const;
	template bool DefinedRegular::template isMipsPIC<ELF64BE>() const;

	template uint32_t SharedSymbol::template getAlignment<ELF32LE>() const;
	template uint32_t SharedSymbol::template getAlignment<ELF32BE>() const;
	template uint32_t SharedSymbol::template getAlignment<ELF64LE>() const;
	template uint32_t SharedSymbol::template getAlignment<ELF64BE>() const;