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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 "Strings.h"
#include "lld/Core/LLVM.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ELF.h"
namespace lld {
namespace elf {
class ArchiveFile;
class BitcodeFile;
class InputFile;
class LazyObjectFile;
template <class ELFT> class ObjectFile;
class OutputSection;
template <class ELFT> class SharedFile;
struct Symbol;
// The base class for real symbol classes.
class SymbolBody {
enum Kind {
DefinedRegularKind = DefinedFirst,
DefinedLast = DefinedCommonKind,
SymbolBody(Kind K) : SymbolKind(K) {}
Symbol *symbol();
const Symbol *symbol() const {
return const_cast<SymbolBody *>(this)->symbol();
Kind kind() const { return static_cast<Kind>(SymbolKind); }
bool isUndefined() const { return SymbolKind == UndefinedKind; }
bool isDefined() const { return SymbolKind <= DefinedLast; }
bool isCommon() const { return SymbolKind == DefinedCommonKind; }
bool isLazy() const {
return SymbolKind == LazyArchiveKind || SymbolKind == LazyObjectKind;
bool isShared() const { return SymbolKind == SharedKind; }
bool isInCurrentDSO() const { return !isUndefined() && !isShared(); }
bool isLocal() const { return IsLocal; }
bool isPreemptible() const;
StringRef getName() const { return Name; }
uint8_t getVisibility() const { return StOther & 0x3; }
void parseSymbolVersion();
bool isInGot() const { return GotIndex != -1U; }
bool isInPlt() const { return PltIndex != -1U; }
uint64_t getVA(int64_t Addend = 0) const;
uint64_t getGotOffset() const;
uint64_t getGotVA() const;
uint64_t getGotPltOffset() const;
uint64_t getGotPltVA() const;
uint64_t getPltVA() const;
template <class ELFT> typename ELFT::uint getSize() const;
OutputSection *getOutputSection() const;
// The file from which this symbol was created.
InputFile *File = nullptr;
uint32_t DynsymIndex = 0;
uint32_t GotIndex = -1;
uint32_t GotPltIndex = -1;
uint32_t PltIndex = -1;
uint32_t GlobalDynIndex = -1;
SymbolBody(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
uint8_t Type);
const unsigned SymbolKind : 8;
// True if the linker has to generate a copy relocation.
// For SharedSymbol only.
unsigned NeedsCopy : 1;
// True the symbol should point to its PLT entry.
// For SharedSymbol only.
unsigned NeedsPltAddr : 1;
// True if this is a local symbol.
unsigned IsLocal : 1;
// True if this symbol has an entry in the global part of MIPS GOT.
unsigned IsInGlobalMipsGot : 1;
// True if this symbol is referenced by 32-bit GOT relocations.
unsigned Is32BitMipsGot : 1;
// True if this symbol is in the Iplt sub-section of the Plt.
unsigned IsInIplt : 1;
// True if this symbol is in the Igot sub-section of the .got.plt or .got.
unsigned IsInIgot : 1;
// The following fields have the same meaning as the ELF symbol attributes.
uint8_t Type; // symbol type
uint8_t StOther; // st_other field value
// The Type field may also have this value. It means that we have not yet seen
// a non-Lazy symbol with this name, so we don't know what its type is. The
// Type field is normally set to this value for Lazy symbols unless we saw a
// weak undefined symbol first, in which case we need to remember the original
// symbol's type in order to check for TLS mismatches.
enum { UnknownType = 255 };
bool isSection() const { return Type == llvm::ELF::STT_SECTION; }
bool isTls() const { return Type == llvm::ELF::STT_TLS; }
bool isFunc() const { return Type == llvm::ELF::STT_FUNC; }
bool isGnuIFunc() const { return Type == llvm::ELF::STT_GNU_IFUNC; }
bool isObject() const { return Type == llvm::ELF::STT_OBJECT; }
bool isFile() const { return Type == llvm::ELF::STT_FILE; }
StringRefZ Name;
// The base class for any defined symbols.
class Defined : public SymbolBody {
Defined(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther, uint8_t Type);
static bool classof(const SymbolBody *S) { return S->isDefined(); }
class DefinedCommon : public Defined {
DefinedCommon(StringRef N, uint64_t Size, uint32_t Alignment, uint8_t StOther,
uint8_t Type, InputFile *File);
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 Offset;
// The maximum alignment we have seen for this symbol.
uint32_t Alignment;
uint64_t Size;
// Regular defined symbols read from object file symbol tables.
class DefinedRegular : public Defined {
DefinedRegular(StringRefZ Name, bool IsLocal, uint8_t StOther, uint8_t Type,
uint64_t Value, uint64_t Size, SectionBase *Section,
InputFile *File)
: Defined(SymbolBody::DefinedRegularKind, Name, IsLocal, StOther, Type),
Value(Value), Size(Size), Section(Section) {
this->File = File;
// Return true if the symbol is a PIC function.
template <class ELFT> bool isMipsPIC() const;
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::DefinedRegularKind;
uint64_t Value;
uint64_t Size;
SectionBase *Section;
class Undefined : public SymbolBody {
Undefined(StringRefZ Name, bool IsLocal, uint8_t StOther, uint8_t Type,
InputFile *F);
static bool classof(const SymbolBody *S) {
return S->kind() == UndefinedKind;
class SharedSymbol : public Defined {
static bool classof(const SymbolBody *S) {
return S->kind() == SymbolBody::SharedKind;
SharedSymbol(InputFile *File, StringRef Name, uint8_t StOther, uint8_t Type,
const void *ElfSym, const void *Verdef)
: Defined(SymbolBody::SharedKind, Name, /*IsLocal=*/false, StOther, Type),
Verdef(Verdef), ElfSym(ElfSym) {
// IFuncs defined in DSOs are treated as functions by the static linker.
if (isGnuIFunc())
Type = llvm::ELF::STT_FUNC;
this->File = File;
template <class ELFT> uint64_t getShndx() const {
return getSym<ELFT>().st_shndx;
template <class ELFT> uint64_t getValue() const {
return getSym<ELFT>().st_value;
template <class ELFT> uint64_t getSize() const {
return getSym<ELFT>().st_size;
template <class ELFT> uint32_t getAlignment() const;
// This field is a pointer to the symbol's version definition.
const void *Verdef;
// CopyRelSec and CopyRelSecOff are significant only when NeedsCopy is true.
InputSection *CopyRelSec;
uint64_t CopyRelSecOff;
template <class ELFT> const typename ELFT::Sym &getSym() const {
return *(const typename ELFT::Sym *)ElfSym;
const void *ElfSym;
// 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 {
static bool classof(const SymbolBody *S) { return S->isLazy(); }
// Returns an object file for this symbol, or a nullptr if the file
// was already returned.
InputFile *fetch();
Lazy(SymbolBody::Kind K, StringRef Name, uint8_t Type)
: SymbolBody(K, Name, /*IsLocal=*/false, llvm::ELF::STV_DEFAULT, Type) {}
// LazyArchive symbols represents symbols in archive files.
class LazyArchive : public Lazy {
LazyArchive(ArchiveFile &File, const llvm::object::Archive::Symbol S,
uint8_t Type);
static bool classof(const SymbolBody *S) {
return S->kind() == LazyArchiveKind;
ArchiveFile *file() { return (ArchiveFile *)this->File; }
InputFile *fetch();
const llvm::object::Archive::Symbol Sym;
// LazyObject symbols represents symbols in object files between
// --start-lib and --end-lib options.
class LazyObject : public Lazy {
LazyObject(StringRef Name, LazyObjectFile &File, uint8_t Type);
static bool classof(const SymbolBody *S) {
return S->kind() == LazyObjectKind;
LazyObjectFile *file() { return (LazyObjectFile *)this->File; }
InputFile *fetch();
// Some linker-generated symbols need to be created as
// DefinedRegular symbols.
struct ElfSym {
// __bss_start
static DefinedRegular *Bss;
// etext and _etext
static DefinedRegular *Etext1;
static DefinedRegular *Etext2;
// edata and _edata
static DefinedRegular *Edata1;
static DefinedRegular *Edata2;
// end and _end
static DefinedRegular *End1;
static DefinedRegular *End2;
// _gp, _gp_disp and __gnu_local_gp symbols. Only for MIPS.
static DefinedRegular *MipsGp;
static DefinedRegular *MipsGpDisp;
static DefinedRegular *MipsLocalGp;
// A real symbol object, SymbolBody, is usually stored within a Symbol. There's
// always one Symbol for each symbol name. The resolver updates the SymbolBody
// stored in the Body field of this object as it resolves symbols. Symbol also
// holds computed properties of symbol names.
struct Symbol {
// Symbol binding. This is on the Symbol to track changes during resolution.
// In particular:
// An undefined weak is still weak when it resolves to a shared library.
// An undefined weak will not fetch archive members, but we have to remember
// it is weak.
uint8_t Binding;
// Version definition index.
uint16_t VersionId;
// Symbol visibility. This is the computed minimum visibility of all
// observed non-DSO symbols.
unsigned Visibility : 2;
// True if the symbol was used for linking and thus need to be added to the
// output file's symbol table. This is true for all symbols except for
// unreferenced DSO symbols and bitcode symbols that are unreferenced except
// by other bitcode objects.
unsigned IsUsedInRegularObj : 1;
// If this flag is true and the symbol has protected or default visibility, it
// will appear in .dynsym. This flag is set by interposable DSO symbols in
// executables, by most symbols in DSOs and executables built with
// --export-dynamic, and by dynamic lists.
unsigned ExportDynamic : 1;
// True if this symbol is specified by --trace-symbol option.
unsigned Traced : 1;
// This symbol version was found in a version script.
unsigned InVersionScript : 1;
bool includeInDynsym() const;
uint8_t computeBinding() const;
bool isWeak() const { return Binding == llvm::ELF::STB_WEAK; }
// This field is used to store the Symbol's SymbolBody. This instantiation of
// AlignedCharArrayUnion gives us a struct with a char array field that is
// large and aligned enough to store any derived class of SymbolBody.
llvm::AlignedCharArrayUnion<DefinedCommon, DefinedRegular, Undefined,
SharedSymbol, LazyArchive, LazyObject>
SymbolBody *body() { return reinterpret_cast<SymbolBody *>(Body.buffer); }
const SymbolBody *body() const { return const_cast<Symbol *>(this)->body(); }
void printTraceSymbol(Symbol *Sym);
template <typename T, typename... ArgT>
void replaceBody(Symbol *S, ArgT &&... Arg) {
static_assert(sizeof(T) <= sizeof(S->Body), "Body too small");
static_assert(alignof(T) <= alignof(decltype(S->Body)),
"Body not aligned enough");
assert(static_cast<SymbolBody *>(static_cast<T *>(nullptr)) == nullptr &&
"Not a SymbolBody");
new (S->Body.buffer) T(std::forward<ArgT>(Arg)...);
// Print out a log message if --trace-symbol was specified.
// This is for debugging.
if (S->Traced)
inline Symbol *SymbolBody::symbol() {
return reinterpret_cast<Symbol *>(reinterpret_cast<char *>(this) -
offsetof(Symbol, Body));
} // namespace elf
std::string toString(const elf::SymbolBody &B);
} // namespace lld