382 lines
12 KiB
C++
382 lines
12 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 "Strings.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "Writer.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Support/Path.h"
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#include <cstring>
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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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DefinedRegular *ElfSym::Bss;
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DefinedRegular *ElfSym::Etext1;
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DefinedRegular *ElfSym::Etext2;
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DefinedRegular *ElfSym::Edata1;
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DefinedRegular *ElfSym::Edata2;
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DefinedRegular *ElfSym::End1;
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DefinedRegular *ElfSym::End2;
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DefinedRegular *ElfSym::GlobalOffsetTable;
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DefinedRegular *ElfSym::MipsGp;
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DefinedRegular *ElfSym::MipsGpDisp;
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DefinedRegular *ElfSym::MipsLocalGp;
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static uint64_t getSymVA(const SymbolBody &Body, int64_t &Addend) {
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switch (Body.kind()) {
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case SymbolBody::DefinedRegularKind: {
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auto &D = cast<DefinedRegular>(Body);
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SectionBase *IS = D.Section;
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if (auto *ISB = dyn_cast_or_null<InputSectionBase>(IS))
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IS = ISB->Repl;
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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 (IS == &InputSection::Discarded)
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return 0;
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// This is an absolute symbol.
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if (!IS)
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return D.Value;
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uint64_t Offset = D.Value;
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// An object in an SHF_MERGE section might be referenced via a
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// section symbol (as a hack for reducing the number of local
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// symbols).
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// Depending on the addend, the reference via a section symbol
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// refers to a different object in the merge section.
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// Since the objects in the merge section are not necessarily
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// contiguous in the output, the addend can thus affect the final
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// VA in a non-linear way.
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// To make this work, we incorporate the addend into the section
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// offset (and zero out the addend for later processing) so that
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// we find the right object in the section.
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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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const OutputSection *OutSec = IS->getOutputSection();
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// In the typical case, this is actually very simple and boils
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// down to adding together 3 numbers:
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// 1. The address of the output section.
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// 2. The offset of the input section within the output section.
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// 3. The offset within the input section (this addition happens
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// inside InputSection::getOffset).
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//
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// If you understand the data structures involved with this next
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// line (and how they get built), then you have a pretty good
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// understanding of the linker.
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uint64_t VA = (OutSec ? OutSec->Addr : 0) + IS->getOffset(Offset);
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if (D.isTls() && !Config->Relocatable) {
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if (!Out::TlsPhdr)
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fatal(toString(D.getFile()) +
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" has an STT_TLS symbol but doesn't have an SHF_TLS section");
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return VA - Out::TlsPhdr->p_vaddr;
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}
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return VA;
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}
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case SymbolBody::DefinedCommonKind:
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if (!Config->DefineCommon)
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return 0;
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return InX::Common->getParent()->Addr + InX::Common->OutSecOff +
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cast<DefinedCommon>(Body).Offset;
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case SymbolBody::SharedKind: {
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auto &SS = cast<SharedSymbol>(Body);
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if (SS.CopyRelSec)
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return SS.CopyRelSec->getParent()->Addr + SS.CopyRelSec->OutSecOff +
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SS.CopyRelSecOff;
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if (SS.NeedsPltAddr)
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return Body.getPltVA();
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return 0;
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}
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case SymbolBody::UndefinedKind:
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return 0;
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case SymbolBody::LazyArchiveKind:
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case SymbolBody::LazyObjectKind:
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assert(Body.symbol()->IsUsedInRegularObj && "lazy symbol reached writer");
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return 0;
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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, StringRefZ Name, bool IsLocal, uint8_t StOther,
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uint8_t Type)
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: SymbolKind(K), NeedsPltAddr(false), IsLocal(IsLocal),
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IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
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IsInIgot(false), IsPreemptible(false), Type(Type), StOther(StOther),
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Name(Name) {}
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InputFile *SymbolBody::getFile() const {
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if (isLocal()) {
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const SectionBase *Sec = cast<DefinedRegular>(this)->Section;
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// Local absolute symbols actually have a file, but that is not currently
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// used. We could support that by having a mostly redundant InputFile in
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// SymbolBody, or having a special absolute section if needed.
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return Sec ? cast<InputSectionBase>(Sec)->File : nullptr;
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}
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return symbol()->File;
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}
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// Overwrites all attributes with Other's so that this symbol becomes
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// an alias to Other. This is useful for handling some options such as
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// --wrap.
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void SymbolBody::copy(SymbolBody *Other) {
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memcpy(symbol()->Body.buffer, Other->symbol()->Body.buffer,
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sizeof(Symbol::Body));
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}
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uint64_t SymbolBody::getVA(int64_t Addend) const {
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uint64_t OutVA = getSymVA(*this, Addend);
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return OutVA + Addend;
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}
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uint64_t SymbolBody::getGotVA() const {
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return InX::Got->getVA() + getGotOffset();
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}
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uint64_t SymbolBody::getGotOffset() const {
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return GotIndex * Target->GotEntrySize;
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}
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uint64_t SymbolBody::getGotPltVA() const {
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if (this->IsInIgot)
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return InX::IgotPlt->getVA() + getGotPltOffset();
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return InX::GotPlt->getVA() + getGotPltOffset();
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}
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uint64_t SymbolBody::getGotPltOffset() const {
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return GotPltIndex * Target->GotPltEntrySize;
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}
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uint64_t SymbolBody::getPltVA() const {
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if (this->IsInIplt)
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return InX::Iplt->getVA() + PltIndex * Target->PltEntrySize;
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return InX::Plt->getVA() + Target->PltHeaderSize +
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PltIndex * Target->PltEntrySize;
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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>(this))
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return DR->Size;
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if (const auto *S = dyn_cast<SharedSymbol>(this))
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return S->getSize<ELFT>();
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return 0;
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}
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OutputSection *SymbolBody::getOutputSection() const {
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if (auto *S = dyn_cast<DefinedRegular>(this)) {
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if (S->Section)
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return S->Section->getOutputSection();
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return nullptr;
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}
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if (auto *S = dyn_cast<SharedSymbol>(this)) {
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if (S->CopyRelSec)
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return S->CopyRelSec->getParent();
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return nullptr;
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}
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if (isa<DefinedCommon>(this)) {
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if (Config->DefineCommon)
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return InX::Common->getParent();
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return nullptr;
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}
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return nullptr;
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}
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// If a symbol name contains '@', the characters after that is
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// a symbol version name. This function parses that.
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void SymbolBody::parseSymbolVersion() {
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StringRef S = getName();
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size_t Pos = S.find('@');
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if (Pos == 0 || Pos == StringRef::npos)
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return;
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StringRef Verstr = S.substr(Pos + 1);
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if (Verstr.empty())
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return;
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// Truncate the symbol name so that it doesn't include the version string.
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Name = {S.data(), Pos};
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// If this is not in this DSO, it is not a definition.
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if (!isInCurrentDSO())
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return;
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// '@@' in a symbol name means the default version.
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// It is usually the most recent one.
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bool IsDefault = (Verstr[0] == '@');
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if (IsDefault)
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Verstr = Verstr.substr(1);
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for (VersionDefinition &Ver : Config->VersionDefinitions) {
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if (Ver.Name != Verstr)
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continue;
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if (IsDefault)
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symbol()->VersionId = Ver.Id;
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else
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symbol()->VersionId = Ver.Id | VERSYM_HIDDEN;
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return;
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}
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// It is an error if the specified version is not defined.
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// Usually version script is not provided when linking executable,
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// but we may still want to override a versioned symbol from DSO,
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// so we do not report error in this case.
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if (Config->Shared)
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error(toString(getFile()) + ": symbol " + S + " has undefined version " +
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Verstr);
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}
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Defined::Defined(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
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uint8_t Type)
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: SymbolBody(K, Name, IsLocal, StOther, Type) {}
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template <class ELFT> bool DefinedRegular::isMipsPIC() const {
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typedef typename ELFT::Ehdr Elf_Ehdr;
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if (!Section || !isFunc())
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return false;
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auto *Sec = cast<InputSectionBase>(Section);
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const Elf_Ehdr *Hdr = Sec->template getFile<ELFT>()->getObj().getHeader();
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return (this->StOther & STO_MIPS_MIPS16) == STO_MIPS_PIC ||
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(Hdr->e_flags & EF_MIPS_PIC);
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}
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Undefined::Undefined(StringRefZ Name, bool IsLocal, uint8_t StOther,
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uint8_t Type)
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: SymbolBody(SymbolBody::UndefinedKind, Name, IsLocal, StOther, Type) {}
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DefinedCommon::DefinedCommon(StringRef Name, uint64_t Size, uint32_t Alignment,
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uint8_t StOther, uint8_t Type)
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: Defined(SymbolBody::DefinedCommonKind, Name, /*IsLocal=*/false, StOther,
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Type),
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Live(!Config->GcSections), Alignment(Alignment), Size(Size) {}
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// If a shared symbol is referred via a copy relocation, its alignment
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// becomes part of the ABI. This function returns a symbol alignment.
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// Because symbols don't have alignment attributes, we need to infer that.
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template <class ELFT> uint32_t SharedSymbol::getAlignment() const {
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SharedFile<ELFT> *File = getFile<ELFT>();
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uint32_t SecAlign = File->getSection(getSym<ELFT>())->sh_addralign;
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uint64_t SymValue = getSym<ELFT>().st_value;
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uint32_t SymAlign = uint32_t(1) << countTrailingZeros(SymValue);
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return std::min(SecAlign, SymAlign);
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}
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InputFile *Lazy::fetch() {
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if (auto *S = dyn_cast<LazyArchive>(this))
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return S->fetch();
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return cast<LazyObject>(this)->fetch();
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}
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LazyArchive::LazyArchive(const llvm::object::Archive::Symbol S, uint8_t Type)
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: Lazy(LazyArchiveKind, S.getName(), Type), Sym(S) {}
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LazyObject::LazyObject(StringRef Name, uint8_t Type)
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: Lazy(LazyObjectKind, Name, Type) {}
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ArchiveFile *LazyArchive::getFile() {
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return cast<ArchiveFile>(SymbolBody::getFile());
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}
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InputFile *LazyArchive::fetch() {
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std::pair<MemoryBufferRef, uint64_t> MBInfo = getFile()->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 (MBInfo.first.getBuffer().empty())
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return nullptr;
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return createObjectFile(MBInfo.first, getFile()->getName(), MBInfo.second);
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}
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LazyObjFile *LazyObject::getFile() {
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return cast<LazyObjFile>(SymbolBody::getFile());
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}
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InputFile *LazyObject::fetch() { return getFile()->fetch(); }
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uint8_t Symbol::computeBinding() const {
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if (Config->Relocatable)
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return Binding;
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if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
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return STB_LOCAL;
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if (VersionId == VER_NDX_LOCAL && body()->isInCurrentDSO())
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return STB_LOCAL;
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if (Config->NoGnuUnique && Binding == STB_GNU_UNIQUE)
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return STB_GLOBAL;
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return Binding;
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}
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bool Symbol::includeInDynsym() const {
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if (computeBinding() == STB_LOCAL)
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return false;
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if (body()->isUndefined())
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return Config->Shared || !body()->symbol()->isWeak();
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return ExportDynamic || body()->isShared();
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}
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// Print out a log message for --trace-symbol.
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void elf::printTraceSymbol(Symbol *Sym) {
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SymbolBody *B = Sym->body();
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std::string S;
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if (B->isUndefined())
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S = ": reference to ";
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else if (B->isCommon())
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S = ": common definition of ";
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else
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S = ": definition of ";
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message(toString(Sym->File) + S + B->getName());
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}
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// Returns a symbol for an error message.
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std::string lld::toString(const SymbolBody &B) {
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if (Config->Demangle)
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if (Optional<std::string> S = demangle(B.getName()))
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return *S;
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return B.getName();
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}
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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 bool DefinedRegular::template isMipsPIC<ELF32LE>() const;
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template bool DefinedRegular::template isMipsPIC<ELF32BE>() const;
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template bool DefinedRegular::template isMipsPIC<ELF64LE>() const;
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template bool DefinedRegular::template isMipsPIC<ELF64BE>() const;
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template uint32_t SharedSymbol::template getAlignment<ELF32LE>() const;
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template uint32_t SharedSymbol::template getAlignment<ELF32BE>() const;
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template uint32_t SharedSymbol::template getAlignment<ELF64LE>() const;
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template uint32_t SharedSymbol::template getAlignment<ELF64BE>() const;
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