372 lines
13 KiB
C++
372 lines
13 KiB
C++
//===- Symbols.cpp --------------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "Symbols.h"
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#include "Error.h"
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#include "InputFiles.h"
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#include "InputSection.h"
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#include "OutputSections.h"
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#include "Target.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Config/config.h"
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#ifdef HAVE_CXXABI_H
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#include <cxxabi.h>
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#endif
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using namespace llvm;
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using namespace llvm::object;
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using namespace llvm::ELF;
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using namespace lld;
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using namespace lld::elf;
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template <class ELFT>
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static typename ELFT::uint getSymVA(const SymbolBody &Body,
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typename ELFT::uint &Addend) {
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typedef typename ELFT::uint uintX_t;
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switch (Body.kind()) {
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case SymbolBody::DefinedSyntheticKind: {
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auto &D = cast<DefinedSynthetic<ELFT>>(Body);
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if (D.Value == DefinedSynthetic<ELFT>::SectionEnd)
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return D.Section.getVA() + D.Section.getSize();
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return D.Section.getVA() + D.Value;
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}
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case SymbolBody::DefinedRegularKind: {
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auto &D = cast<DefinedRegular<ELFT>>(Body);
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InputSectionBase<ELFT> *SC = D.Section;
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// According to the ELF spec reference to a local symbol from outside
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// the group are not allowed. Unfortunately .eh_frame breaks that rule
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// and must be treated specially. For now we just replace the symbol with
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// 0.
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if (SC == &InputSection<ELFT>::Discarded)
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return 0;
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// This is an absolute symbol.
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if (!SC)
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return D.Value;
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uintX_t Offset = D.Value;
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if (D.isSection()) {
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Offset += Addend;
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Addend = 0;
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}
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uintX_t VA = SC->OutSec->getVA() + SC->getOffset(Offset);
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if (D.isTls())
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return VA - Out<ELFT>::TlsPhdr->p_vaddr;
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return VA;
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}
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case SymbolBody::DefinedCommonKind:
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return Out<ELFT>::Bss->getVA() + cast<DefinedCommon>(Body).OffsetInBss;
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case SymbolBody::SharedKind: {
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auto &SS = cast<SharedSymbol<ELFT>>(Body);
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if (!SS.NeedsCopyOrPltAddr)
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return 0;
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if (SS.isFunc())
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return Body.getPltVA<ELFT>();
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return Out<ELFT>::Bss->getVA() + SS.OffsetInBss;
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}
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case SymbolBody::UndefinedElfKind:
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case SymbolBody::UndefinedBitcodeKind:
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return 0;
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case SymbolBody::LazyKind:
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assert(Body.isUsedInRegularObj() && "lazy symbol reached writer");
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return 0;
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case SymbolBody::DefinedBitcodeKind:
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llvm_unreachable("should have been replaced");
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}
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llvm_unreachable("invalid symbol kind");
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}
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SymbolBody::SymbolBody(Kind K, uint32_t NameOffset, uint8_t StOther,
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uint8_t Type)
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: SymbolKind(K), Type(Type), Binding(STB_LOCAL), StOther(StOther),
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NameOffset(NameOffset) {
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init();
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}
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SymbolBody::SymbolBody(Kind K, StringRef Name, uint8_t Binding, uint8_t StOther,
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uint8_t Type)
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: SymbolKind(K), Type(Type), Binding(Binding), StOther(StOther),
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Name({Name.data(), Name.size()}) {
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assert(!isLocal());
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init();
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}
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void SymbolBody::init() {
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Kind K = kind();
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IsUsedInRegularObj = K == DefinedRegularKind || K == DefinedCommonKind ||
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K == DefinedSyntheticKind || K == UndefinedElfKind;
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CanKeepUndefined = false;
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MustBeInDynSym = false;
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NeedsCopyOrPltAddr = false;
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}
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// Returns true if a symbol can be replaced at load-time by a symbol
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// with the same name defined in other ELF executable or DSO.
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bool SymbolBody::isPreemptible() const {
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if (isLocal())
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return false;
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if (isShared())
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return true;
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if (isUndefined()) {
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if (!isWeak())
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return true;
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// Ideally the static linker should see a definition for every symbol, but
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// shared object are normally allowed to have undefined references that the
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// static linker never sees a definition for.
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if (Config->Shared)
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return true;
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// Otherwise, just resolve to 0.
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return false;
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}
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if (!Config->Shared)
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return false;
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if (getVisibility() != STV_DEFAULT)
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return false;
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if (Config->Bsymbolic || (Config->BsymbolicFunctions && isFunc()))
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return false;
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return true;
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}
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template <class ELFT>
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typename ELFT::uint SymbolBody::getVA(typename ELFT::uint Addend) const {
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typename ELFT::uint OutVA = getSymVA<ELFT>(*this, Addend);
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return OutVA + Addend;
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}
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template <class ELFT> typename ELFT::uint SymbolBody::getGotVA() const {
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return Out<ELFT>::Got->getVA() +
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(Out<ELFT>::Got->getMipsLocalEntriesNum() + GotIndex) *
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sizeof(typename ELFT::uint);
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}
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template <class ELFT> typename ELFT::uint SymbolBody::getGotPltVA() const {
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return Out<ELFT>::GotPlt->getVA() + GotPltIndex * sizeof(typename ELFT::uint);
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}
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template <class ELFT> typename ELFT::uint SymbolBody::getPltVA() const {
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return Out<ELFT>::Plt->getVA() + Target->PltZeroSize +
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PltIndex * Target->PltEntrySize;
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}
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template <class ELFT> typename ELFT::uint SymbolBody::getThunkVA() const {
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auto *D = cast<DefinedRegular<ELFT>>(this);
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auto *S = cast<InputSection<ELFT>>(D->Section);
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return S->OutSec->getVA() + S->OutSecOff + S->getThunkOff() +
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ThunkIndex * Target->ThunkSize;
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}
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template <class ELFT> typename ELFT::uint SymbolBody::getSize() const {
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if (const auto *C = dyn_cast<DefinedCommon>(this))
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return C->Size;
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if (const auto *DR = dyn_cast<DefinedRegular<ELFT>>(this))
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return DR->Size;
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if (const auto *S = dyn_cast<SharedSymbol<ELFT>>(this))
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return S->Sym.st_size;
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if (const auto *U = dyn_cast<UndefinedElf<ELFT>>(this))
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return U->Size;
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return 0;
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}
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static uint8_t getMinVisibility(uint8_t VA, uint8_t VB) {
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if (VA == STV_DEFAULT)
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return VB;
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if (VB == STV_DEFAULT)
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return VA;
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return std::min(VA, VB);
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}
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static int compareCommons(DefinedCommon *A, DefinedCommon *B) {
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if (Config->WarnCommon)
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warning("multiple common of " + A->getName());
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A->Alignment = B->Alignment = std::max(A->Alignment, B->Alignment);
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return A->Size < B->Size ? -1 : 1;
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}
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// Returns 1, 0 or -1 if this symbol should take precedence
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// over the Other, tie or lose, respectively.
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int SymbolBody::compare(SymbolBody *Other) {
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assert(!isLazy() && !Other->isLazy());
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std::tuple<bool, bool, bool> L(isDefined(), !isShared(), !isWeak());
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std::tuple<bool, bool, bool> R(Other->isDefined(), !Other->isShared(),
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!Other->isWeak());
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// Normalize
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if (L > R)
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return -Other->compare(this);
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uint8_t V = getMinVisibility(getVisibility(), Other->getVisibility());
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setVisibility(V);
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Other->setVisibility(V);
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if (IsUsedInRegularObj || Other->IsUsedInRegularObj)
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IsUsedInRegularObj = Other->IsUsedInRegularObj = true;
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// We want to export all symbols that exist both in the executable
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// and in DSOs, so that the symbols in the executable can interrupt
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// symbols in the DSO at runtime.
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if (isShared() != Other->isShared())
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if (isa<Defined>(isShared() ? Other : this)) {
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IsUsedInRegularObj = Other->IsUsedInRegularObj = true;
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MustBeInDynSym = Other->MustBeInDynSym = true;
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}
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if (L != R)
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return -1;
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if (!isDefined() || isShared() || isWeak())
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return 1;
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if (!isCommon() && !Other->isCommon())
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return 0;
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if (isCommon() && Other->isCommon())
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return compareCommons(cast<DefinedCommon>(this),
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cast<DefinedCommon>(Other));
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if (Config->WarnCommon)
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warning("common " + this->getName() + " is overridden");
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return isCommon() ? -1 : 1;
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}
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Defined::Defined(Kind K, StringRef Name, uint8_t Binding, uint8_t StOther,
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uint8_t Type)
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: SymbolBody(K, Name, Binding, StOther, Type) {}
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Defined::Defined(Kind K, uint32_t NameOffset, uint8_t StOther, uint8_t Type)
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: SymbolBody(K, NameOffset, StOther, Type) {}
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DefinedBitcode::DefinedBitcode(StringRef Name, bool IsWeak, uint8_t StOther)
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: Defined(DefinedBitcodeKind, Name, IsWeak ? STB_WEAK : STB_GLOBAL,
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StOther, 0 /* Type */) {}
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bool DefinedBitcode::classof(const SymbolBody *S) {
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return S->kind() == DefinedBitcodeKind;
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}
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UndefinedBitcode::UndefinedBitcode(StringRef N, bool IsWeak, uint8_t StOther)
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: SymbolBody(SymbolBody::UndefinedBitcodeKind, N,
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IsWeak ? STB_WEAK : STB_GLOBAL, StOther, 0 /* Type */) {}
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template <typename ELFT>
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UndefinedElf<ELFT>::UndefinedElf(StringRef N, const Elf_Sym &Sym)
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: SymbolBody(SymbolBody::UndefinedElfKind, N, Sym.getBinding(),
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Sym.st_other, Sym.getType()),
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Size(Sym.st_size) {}
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template <typename ELFT>
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UndefinedElf<ELFT>::UndefinedElf(StringRef Name, uint8_t Binding,
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uint8_t StOther, uint8_t Type,
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bool CanKeepUndefined)
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: SymbolBody(SymbolBody::UndefinedElfKind, Name, Binding, StOther, Type) {
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this->CanKeepUndefined = CanKeepUndefined;
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}
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template <typename ELFT>
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UndefinedElf<ELFT>::UndefinedElf(const Elf_Sym &Sym)
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: SymbolBody(SymbolBody::UndefinedElfKind, Sym.st_name, Sym.st_other,
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Sym.getType()),
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Size(Sym.st_size) {
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assert(Sym.getBinding() == STB_LOCAL);
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}
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template <typename ELFT>
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DefinedSynthetic<ELFT>::DefinedSynthetic(StringRef N, uintX_t Value,
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OutputSectionBase<ELFT> &Section,
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uint8_t StOther)
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: Defined(SymbolBody::DefinedSyntheticKind, N, STB_GLOBAL, StOther,
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0 /* Type */),
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Value(Value), Section(Section) {}
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DefinedCommon::DefinedCommon(StringRef N, uint64_t Size, uint64_t Alignment,
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uint8_t Binding, uint8_t StOther, uint8_t Type)
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: Defined(SymbolBody::DefinedCommonKind, N, Binding, StOther, Type),
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Alignment(Alignment), Size(Size) {}
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std::unique_ptr<InputFile> Lazy::getMember() {
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MemoryBufferRef MBRef = File->getMember(&Sym);
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// getMember returns an empty buffer if the member was already
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// read from the library.
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if (MBRef.getBuffer().empty())
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return std::unique_ptr<InputFile>(nullptr);
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return createObjectFile(MBRef, File->getName());
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}
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// Returns the demangled C++ symbol name for Name.
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std::string elf::demangle(StringRef Name) {
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#if !defined(HAVE_CXXABI_H)
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return Name;
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#else
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if (!Config->Demangle)
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return Name;
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// __cxa_demangle can be used to demangle strings other than symbol
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// names which do not necessarily start with "_Z". Name can be
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// either a C or C++ symbol. Don't call __cxa_demangle if the name
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// does not look like a C++ symbol name to avoid getting unexpected
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// result for a C symbol that happens to match a mangled type name.
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if (!Name.startswith("_Z"))
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return Name;
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char *Buf =
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abi::__cxa_demangle(Name.str().c_str(), nullptr, nullptr, nullptr);
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if (!Buf)
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return Name;
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std::string S(Buf);
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free(Buf);
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return S;
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#endif
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}
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template uint32_t SymbolBody::template getVA<ELF32LE>(uint32_t) const;
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template uint32_t SymbolBody::template getVA<ELF32BE>(uint32_t) const;
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template uint64_t SymbolBody::template getVA<ELF64LE>(uint64_t) const;
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template uint64_t SymbolBody::template getVA<ELF64BE>(uint64_t) const;
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template uint32_t SymbolBody::template getGotVA<ELF32LE>() const;
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template uint32_t SymbolBody::template getGotVA<ELF32BE>() const;
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template uint64_t SymbolBody::template getGotVA<ELF64LE>() const;
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template uint64_t SymbolBody::template getGotVA<ELF64BE>() const;
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template uint32_t SymbolBody::template getGotPltVA<ELF32LE>() const;
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template uint32_t SymbolBody::template getGotPltVA<ELF32BE>() const;
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template uint64_t SymbolBody::template getGotPltVA<ELF64LE>() const;
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template uint64_t SymbolBody::template getGotPltVA<ELF64BE>() const;
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template uint32_t SymbolBody::template getPltVA<ELF32LE>() const;
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template uint32_t SymbolBody::template getPltVA<ELF32BE>() const;
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template uint64_t SymbolBody::template getPltVA<ELF64LE>() const;
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template uint64_t SymbolBody::template getPltVA<ELF64BE>() const;
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template uint32_t SymbolBody::template getSize<ELF32LE>() const;
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template uint32_t SymbolBody::template getSize<ELF32BE>() const;
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template uint64_t SymbolBody::template getSize<ELF64LE>() const;
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template uint64_t SymbolBody::template getSize<ELF64BE>() const;
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template uint32_t SymbolBody::template getThunkVA<ELF32LE>() const;
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template uint32_t SymbolBody::template getThunkVA<ELF32BE>() const;
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template uint64_t SymbolBody::template getThunkVA<ELF64LE>() const;
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template uint64_t SymbolBody::template getThunkVA<ELF64BE>() const;
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template class elf::UndefinedElf<ELF32LE>;
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template class elf::UndefinedElf<ELF32BE>;
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template class elf::UndefinedElf<ELF64LE>;
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template class elf::UndefinedElf<ELF64BE>;
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template class elf::DefinedSynthetic<ELF32LE>;
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template class elf::DefinedSynthetic<ELF32BE>;
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template class elf::DefinedSynthetic<ELF64LE>;
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template class elf::DefinedSynthetic<ELF64BE>;
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