blob: 3fffb15ff14be025fe5aac19da15cbab18edd10a [file] [log] [blame]
//===- 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 "Target.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Config/config.h"
#include <cxxabi.h>
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf;
template <class ELFT>
static typename ELFT::uint getSymVA(const SymbolBody &Body,
typename ELFT::uint &Addend) {
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::uint uintX_t;
switch (Body.kind()) {
case SymbolBody::DefinedSyntheticKind: {
auto &D = cast<DefinedSynthetic<ELFT>>(Body);
return D.Section.getVA() + D.Value;
case SymbolBody::DefinedRegularKind: {
auto &D = cast<DefinedRegular<ELFT>>(Body);
InputSectionBase<ELFT> *SC = D.Section;
// This is an absolute symbol.
if (!SC)
return D.Sym.st_value;
const Elf_Sym &Sym = D.Sym;
uintX_t Offset = Sym.st_value;
if (Sym.getType() == STT_SECTION) {
Offset += Addend;
Addend = 0;
uintX_t VA = SC->OutSec->getVA() + SC->getOffset(Offset);
if (Sym.getType() == STT_TLS)
return VA - Out<ELFT>::TlsPhdr->p_vaddr;
return VA;
case SymbolBody::DefinedCommonKind:
return Out<ELFT>::Bss->getVA() + cast<DefinedCommon>(Body).OffsetInBss;
case SymbolBody::SharedKind: {
auto &SS = cast<SharedSymbol<ELFT>>(Body);
if (!SS.NeedsCopyOrPltAddr)
return 0;
if (SS.IsFunc)
return Body.getPltVA<ELFT>();
return Out<ELFT>::Bss->getVA() + SS.OffsetInBss;
case SymbolBody::UndefinedElfKind:
case SymbolBody::UndefinedKind:
return 0;
case SymbolBody::LazyKind:
assert(Body.isUsedInRegularObj() && "lazy symbol reached writer");
return 0;
case SymbolBody::DefinedBitcodeKind:
llvm_unreachable("should have been replaced");
llvm_unreachable("invalid symbol kind");
// 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;
if (isShared())
return true;
if (isUndefined()) {
if (!isWeak())
return true;
// Ideally the static linker should see a definition for every symbol, but
// shared object are normally allowed to have undefined references that the
// static linker never sees a definition for.
if (Config->Shared)
return true;
// Otherwise, just resolve to 0.
return false;
if (!Config->Shared)
return false;
if (getVisibility() != STV_DEFAULT)
return false;
if (Config->Bsymbolic || (Config->BsymbolicFunctions && IsFunc))
return false;
return true;
template <class ELFT> bool SymbolBody::isGnuIfunc() const {
if (auto *D = dyn_cast<DefinedElf<ELFT>>(this))
return D->Sym.getType() == STT_GNU_IFUNC;
return false;
template <class ELFT>
typename ELFT::uint SymbolBody::getVA(typename ELFT::uint Addend) const {
typename ELFT::uint OutVA = getSymVA<ELFT>(*this, Addend);
return OutVA + Addend;
template <class ELFT> typename ELFT::uint SymbolBody::getGotVA() const {
return Out<ELFT>::Got->getVA() +
(Out<ELFT>::Got->getMipsLocalEntriesNum() + GotIndex) *
sizeof(typename ELFT::uint);
template <class ELFT> typename ELFT::uint SymbolBody::getGotPltVA() const {
return Out<ELFT>::GotPlt->getVA() + GotPltIndex * sizeof(typename ELFT::uint);
template <class ELFT> typename ELFT::uint SymbolBody::getPltVA() const {
return Out<ELFT>::Plt->getVA() + Target->PltZeroSize +
PltIndex * Target->PltEntrySize;
template <class ELFT> typename ELFT::uint SymbolBody::getSize() const {
if (auto *B = dyn_cast<DefinedElf<ELFT>>(this))
return B->Sym.st_size;
return 0;
static uint8_t getMinVisibility(uint8_t VA, uint8_t VB) {
return VB;
return VA;
return std::min(VA, VB);
static int compareCommons(DefinedCommon *A, DefinedCommon *B) {
if (Config->WarnCommon)
warning("multiple common of " + A->getName());
A->Alignment = B->Alignment = std::max(A->Alignment, B->Alignment);
if (A->Size < B->Size)
return -1;
return 1;
// Returns 1, 0 or -1 if this symbol should take precedence
// over the Other, tie or lose, respectively.
template <class ELFT> int SymbolBody::compare(SymbolBody *Other) {
assert(!isLazy() && !Other->isLazy());
std::tuple<bool, bool, bool> L(isDefined(), !isShared(), !isWeak());
std::tuple<bool, bool, bool> R(Other->isDefined(), !Other->isShared(),
// Normalize
if (L > R)
return -Other->compare<ELFT>(this);
Visibility = Other->Visibility =
getMinVisibility(Visibility, Other->Visibility);
if (IsUsedInRegularObj || Other->IsUsedInRegularObj)
IsUsedInRegularObj = Other->IsUsedInRegularObj = true;
// We want to export all symbols that exist both in the executable
// and in DSOs, so that the symbols in the executable can interrupt
// symbols in the DSO at runtime.
if (isShared() != Other->isShared())
if (isa<DefinedRegular<ELFT>>(isShared() ? Other : this))
MustBeInDynSym = Other->MustBeInDynSym = true;
if (L != R)
return -1;
if (!isDefined() || isShared() || isWeak())
return 1;
if (!isCommon() && !Other->isCommon())
return 0;
if (isCommon() && Other->isCommon())
return compareCommons(cast<DefinedCommon>(this),
if (Config->WarnCommon)
warning("common " + this->getName() + " is overridden");
return isCommon() ? -1 : 1;
Defined::Defined(Kind K, StringRef Name, bool IsWeak, bool IsLocal,
uint8_t Visibility, uint8_t Type)
: SymbolBody(K, Name, IsWeak, IsLocal, Visibility, Type) {}
DefinedBitcode::DefinedBitcode(StringRef Name, bool IsWeak, uint8_t Visibility)
: Defined(DefinedBitcodeKind, Name, IsWeak, false, Visibility,
0 /* Type */) {}
bool DefinedBitcode::classof(const SymbolBody *S) {
return S->kind() == DefinedBitcodeKind;
Undefined::Undefined(SymbolBody::Kind K, StringRef N, bool IsWeak,
uint8_t Visibility, uint8_t Type)
: SymbolBody(K, N, IsWeak, false, Visibility, Type),
CanKeepUndefined(false) {}
Undefined::Undefined(StringRef N, bool IsWeak, uint8_t Visibility,
bool CanKeepUndefined)
: Undefined(SymbolBody::UndefinedKind, N, IsWeak, Visibility, 0 /* Type */) {
this->CanKeepUndefined = CanKeepUndefined;
template <typename ELFT>
UndefinedElf<ELFT>::UndefinedElf(StringRef N, const Elf_Sym &Sym)
: Undefined(SymbolBody::UndefinedElfKind, N,
Sym.getBinding() == llvm::ELF::STB_WEAK, Sym.getVisibility(),
Sym(Sym) {}
template <typename ELFT>
DefinedSynthetic<ELFT>::DefinedSynthetic(StringRef N, uintX_t Value,
OutputSectionBase<ELFT> &Section,
uint8_t Visibility)
: Defined(SymbolBody::DefinedSyntheticKind, N, false, false, Visibility,
0 /* Type */),
Value(Value), Section(Section) {}
DefinedCommon::DefinedCommon(StringRef N, uint64_t Size, uint64_t Alignment,
bool IsWeak, uint8_t Visibility)
: Defined(SymbolBody::DefinedCommonKind, N, IsWeak, false, Visibility,
0 /* Type */),
Alignment(Alignment), Size(Size) {}
std::unique_ptr<InputFile> Lazy::getMember() {
MemoryBufferRef MBRef = File->getMember(&Sym);
// getMember returns an empty buffer if the member was already
// read from the library.
if (MBRef.getBuffer().empty())
return std::unique_ptr<InputFile>(nullptr);
return createObjectFile(MBRef, File->getName());
// Returns the demangled C++ symbol name for Name.
std::string elf::demangle(StringRef Name) {
#if !defined(HAVE_CXXABI_H)
return Name;
if (!Config->Demangle)
return Name;
// __cxa_demangle can be used to demangle strings other than symbol
// names which do not necessarily start with "_Z". Name can be
// either a C or C++ symbol. Don't call __cxa_demangle if the name
// does not look like a C++ symbol name to avoid getting unexpected
// result for a C symbol that happens to match a mangled type name.
if (!Name.startswith("_Z"))
return Name;
char *Buf =
abi::__cxa_demangle(Name.str().c_str(), nullptr, nullptr, nullptr);
if (!Buf)
return Name;
std::string S(Buf);
return S;
template bool SymbolBody::template isGnuIfunc<ELF32LE>() const;
template bool SymbolBody::template isGnuIfunc<ELF32BE>() const;
template bool SymbolBody::template isGnuIfunc<ELF64LE>() const;
template bool SymbolBody::template isGnuIfunc<ELF64BE>() const;
template uint32_t SymbolBody::template getVA<ELF32LE>(uint32_t) const;
template uint32_t SymbolBody::template getVA<ELF32BE>(uint32_t) const;
template uint64_t SymbolBody::template getVA<ELF64LE>(uint64_t) const;
template uint64_t SymbolBody::template getVA<ELF64BE>(uint64_t) const;
template uint32_t SymbolBody::template getGotVA<ELF32LE>() const;
template uint32_t SymbolBody::template getGotVA<ELF32BE>() const;
template uint64_t SymbolBody::template getGotVA<ELF64LE>() const;
template uint64_t SymbolBody::template getGotVA<ELF64BE>() const;
template uint32_t SymbolBody::template getGotPltVA<ELF32LE>() const;
template uint32_t SymbolBody::template getGotPltVA<ELF32BE>() const;
template uint64_t SymbolBody::template getGotPltVA<ELF64LE>() const;
template uint64_t SymbolBody::template getGotPltVA<ELF64BE>() const;
template uint32_t SymbolBody::template getPltVA<ELF32LE>() const;
template uint32_t SymbolBody::template getPltVA<ELF32BE>() const;
template uint64_t SymbolBody::template getPltVA<ELF64LE>() const;
template uint64_t SymbolBody::template getPltVA<ELF64BE>() const;
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 int SymbolBody::compare<ELF32LE>(SymbolBody *Other);
template int SymbolBody::compare<ELF32BE>(SymbolBody *Other);
template int SymbolBody::compare<ELF64LE>(SymbolBody *Other);
template int SymbolBody::compare<ELF64BE>(SymbolBody *Other);
template class elf::UndefinedElf<ELF32LE>;
template class elf::UndefinedElf<ELF32BE>;
template class elf::UndefinedElf<ELF64LE>;
template class elf::UndefinedElf<ELF64BE>;
template class elf::DefinedSynthetic<ELF32LE>;
template class elf::DefinedSynthetic<ELF32BE>;
template class elf::DefinedSynthetic<ELF64LE>;
template class elf::DefinedSynthetic<ELF64BE>;