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//===- Symbols.h ------------------------------------------------*- C++ -*-===//
// The LLVM Linker
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// All symbols are handled as SymbolBodies regardless of their types.
// This file defines various types of SymbolBodies.
#include "InputSection.h"
#include "lld/Core/LLVM.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ELF.h"
namespace lld {
namespace elf {
class ArchiveFile;
class InputFile;
class SymbolBody;
template <class ELFT> class ObjectFile;
template <class ELFT> class OutputSection;
template <class ELFT> class OutputSectionBase;
template <class ELFT> class SharedFile;
// Returns a demangled C++ symbol name. If Name is not a mangled
// name or the system does not provide __cxa_demangle function,
// it returns the unmodified string.
std::string demangle(StringRef Name);
// A real symbol object, SymbolBody, is usually accessed indirectly
// through a Symbol. There's always one Symbol for each symbol name.
// The resolver updates SymbolBody pointers as it resolves symbols.
struct Symbol {
SymbolBody *Body;
// The base class for real symbol classes.
class SymbolBody {
enum Kind {
DefinedRegularKind = DefinedFirst,
DefinedElfLast = SharedKind,
DefinedLast = DefinedSyntheticKind,
Kind kind() const { return static_cast<Kind>(SymbolKind); }
bool isWeak() const { return IsWeak; }
bool isUndefined() const {
return SymbolKind == UndefinedKind || SymbolKind == UndefinedElfKind;
bool isDefined() const { return SymbolKind <= DefinedLast; }
bool isCommon() const { return SymbolKind == DefinedCommonKind; }
bool isLazy() const { return SymbolKind == LazyKind; }
bool isShared() const { return SymbolKind == SharedKind; }
bool isLocal() const { return IsLocal; }
bool isUsedInRegularObj() const { return IsUsedInRegularObj; }
bool isPreemptible() const;
template <class ELFT> bool isGnuIfunc() const;
// Returns the symbol name.
StringRef getName() const { return Name; }
uint8_t getVisibility() const { return Visibility; }
unsigned DynsymIndex = 0;
uint32_t GlobalDynIndex = -1;
uint32_t GotIndex = -1;
uint32_t GotPltIndex = -1;
uint32_t PltIndex = -1;
bool hasGlobalDynIndex() { return GlobalDynIndex != uint32_t(-1); }
bool isInGot() const { return GotIndex != -1U; }
bool isInPlt() const { return PltIndex != -1U; }
template <class ELFT>
typename ELFT::uint getVA(typename ELFT::uint Addend = 0) const;
template <class ELFT> typename ELFT::uint getGotVA() const;
template <class ELFT> typename ELFT::uint getGotPltVA() const;
template <class ELFT> typename ELFT::uint getPltVA() const;
template <class ELFT> typename ELFT::uint getSize() const;
// A SymbolBody has a backreference to a Symbol. Originally they are
// doubly-linked. A backreference will never change. But the pointer
// in the Symbol may be mutated by the resolver. If you have a
// pointer P to a SymbolBody and are not sure whether the resolver
// has chosen the object among other objects having the same name,
// you can access P->Backref->Body to get the resolver's result.
void setBackref(Symbol *P) { Backref = P; }
SymbolBody &repl() { return Backref ? *Backref->Body : *this; }
Symbol *getSymbol() { return Backref; }
// Decides which symbol should "win" in the symbol table, this or
// the Other. Returns 1 if this wins, -1 if the Other wins, or 0 if
// they are duplicate (conflicting) symbols.
template <class ELFT> int compare(SymbolBody *Other);
SymbolBody(Kind K, StringRef Name, bool IsWeak, bool IsLocal,
uint8_t Visibility, uint8_t Type)
: SymbolKind(K), IsWeak(IsWeak), IsLocal(IsLocal), Visibility(Visibility),
MustBeInDynSym(false), NeedsCopyOrPltAddr(false), Name(Name) {
IsFunc = Type == llvm::ELF::STT_FUNC;
IsTls = Type == llvm::ELF::STT_TLS;
IsUsedInRegularObj = K != SharedKind && K != LazyKind;
const unsigned SymbolKind : 8;
unsigned IsWeak : 1;
unsigned IsLocal : 1;
unsigned Visibility : 2;
// True if the symbol was used for linking and thus need to be
// added to the output file's symbol table. It is usually true,
// but if it is a shared symbol that were not referenced by anyone,
// it can be false.
unsigned IsUsedInRegularObj : 1;
// If true, the symbol is added to .dynsym symbol table.
unsigned MustBeInDynSym : 1;
// True if the linker has to generate a copy relocation for this shared
// symbol or if the symbol should point to its plt entry.
unsigned NeedsCopyOrPltAddr : 1;
unsigned IsTls : 1;
unsigned IsFunc : 1;
StringRef Name;
Symbol *Backref = nullptr;
// The base class for any defined symbols.
class Defined : public SymbolBody {
Defined(Kind K, StringRef Name, bool IsWeak, bool IsLocal, uint8_t Visibility,
uint8_t Type);
static bool classof(const SymbolBody *S) { return S->isDefined(); }
// Any defined symbol from an ELF file.
template <class ELFT> class DefinedElf : public Defined {
typedef typename ELFT::Sym Elf_Sym;
DefinedElf(Kind K, StringRef N, const Elf_Sym &Sym)
: Defined(K, N, Sym.getBinding() == llvm::ELF::STB_WEAK,
Sym.getBinding() == llvm::ELF::STB_LOCAL, Sym.getVisibility(),
Sym(Sym) {}
const Elf_Sym &Sym;
static bool classof(const SymbolBody *S) {
return S->kind() <= DefinedElfLast;
class DefinedBitcode : public Defined {
DefinedBitcode(StringRef Name, bool IsWeak, uint8_t Visibility);
static bool classof(const SymbolBody *S);
class DefinedCommon : public Defined {
DefinedCommon(StringRef N, uint64_t Size, uint64_t Alignment, bool IsWeak,
uint8_t Visibility);
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedCommonKind;
// The output offset of this common symbol in the output bss. Computed by the
// writer.
uint64_t OffsetInBss;
// The maximum alignment we have seen for this symbol.
uint64_t Alignment;
uint64_t Size;
// Regular defined symbols read from object file symbol tables.
template <class ELFT> class DefinedRegular : public DefinedElf<ELFT> {
typedef typename ELFT::Sym Elf_Sym;
DefinedRegular(StringRef N, const Elf_Sym &Sym,
InputSectionBase<ELFT> *Section)
: DefinedElf<ELFT>(SymbolBody::DefinedRegularKind, N, Sym),
Section(Section ? Section->Repl : NullInputSection) {}
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedRegularKind;
// The input section this symbol belongs to. Notice that this is
// a reference to a pointer. We are using two levels of indirections
// because of ICF. If ICF decides two sections need to be merged, it
// manipulates this Section pointers so that they point to the same
// section. This is a bit tricky, so be careful to not be confused.
// If this is null, the symbol is an absolute symbol.
InputSectionBase<ELFT> *&Section;
static InputSectionBase<ELFT> *NullInputSection;
template <class ELFT>
InputSectionBase<ELFT> *DefinedRegular<ELFT>::NullInputSection;
// DefinedSynthetic is a class to represent linker-generated ELF symbols.
// The difference from the regular symbol is that DefinedSynthetic symbols
// don't belong to any input files or sections. Thus, its constructor
// takes an output section to calculate output VA, etc.
template <class ELFT> class DefinedSynthetic : public Defined {
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::uint uintX_t;
DefinedSynthetic(StringRef N, uintX_t Value, OutputSectionBase<ELFT> &Section,
uint8_t Visibility);
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedSyntheticKind;
uintX_t Value;
const OutputSectionBase<ELFT> &Section;
// Undefined symbol.
class Undefined : public SymbolBody {
typedef SymbolBody::Kind Kind;
bool CanKeepUndefined;
Undefined(Kind K, StringRef N, bool IsWeak, uint8_t Visibility, uint8_t Type);
Undefined(StringRef N, bool IsWeak, uint8_t Visibility,
bool CanKeepUndefined);
static bool classof(const SymbolBody *S) { return S->isUndefined(); }
bool canKeepUndefined() const { return CanKeepUndefined; }
template <class ELFT> class UndefinedElf : public Undefined {
typedef typename ELFT::Sym Elf_Sym;
UndefinedElf(StringRef N, const Elf_Sym &Sym);
const Elf_Sym &Sym;
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::UndefinedElfKind;
template <class ELFT> class SharedSymbol : public DefinedElf<ELFT> {
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::uint uintX_t;
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::SharedKind;
SharedSymbol(SharedFile<ELFT> *F, StringRef Name, const Elf_Sym &Sym)
: DefinedElf<ELFT>(SymbolBody::SharedKind, Name, Sym), File(F) {}
SharedFile<ELFT> *File;
// OffsetInBss is significant only when needsCopy() is true.
uintX_t OffsetInBss = 0;
bool needsCopy() const { return this->NeedsCopyOrPltAddr && !this->IsFunc; }
// This class represents a symbol defined in an archive file. It is
// created from an archive file header, and it knows how to load an
// object file from an archive to replace itself with a defined
// symbol. If the resolver finds both Undefined and Lazy for
// the same name, it will ask the Lazy to load a file.
class Lazy : public SymbolBody {
Lazy(ArchiveFile *F, const llvm::object::Archive::Symbol S)
: SymbolBody(LazyKind, S.getName(), false, false, llvm::ELF::STV_DEFAULT,
/* Type */ 0),
File(F), Sym(S) {}
static bool classof(const SymbolBody *S) { return S->kind() == LazyKind; }
// Returns an object file for this symbol, or a nullptr if the file
// was already returned.
std::unique_ptr<InputFile> getMember();
void setWeak() { IsWeak = true; }
void setUsedInRegularObj() { IsUsedInRegularObj = true; }
ArchiveFile *File;
const llvm::object::Archive::Symbol Sym;
// Some linker-generated symbols need to be created as
// DefinedRegular symbols, so they need Elf_Sym symbols.
// Here we allocate such Elf_Sym symbols statically.
template <class ELFT> struct ElfSym {
typedef typename ELFT::Sym Elf_Sym;
// Used to represent an undefined symbol which we don't want to add to the
// output file's symbol table. It has weak binding and can be substituted.
static Elf_Sym Ignored;
// The content for _etext and etext symbols.
static Elf_Sym Etext;
// The content for _edata and edata symbols.
static Elf_Sym Edata;
// The content for _end and end symbols.
static Elf_Sym End;
// The content for _gp symbol for MIPS target.
static Elf_Sym MipsGp;
// __rel_iplt_start/__rel_iplt_end for signaling
// where R_[*]_IRELATIVE relocations do live.
static Elf_Sym RelaIpltStart;
static Elf_Sym RelaIpltEnd;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::Ignored;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::Etext;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::Edata;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::End;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::MipsGp;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::RelaIpltStart;
template <class ELFT> typename ELFT::Sym ElfSym<ELFT>::RelaIpltEnd;
} // namespace elf
} // namespace lld