forked from OSchip/llvm-project
640 lines
20 KiB
C++
640 lines
20 KiB
C++
//===- Symbols.cpp --------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "Symbols.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 "SyntheticSections.h"
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#include "Target.h"
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#include "Writer.h"
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#include "lld/Common/ErrorHandler.h"
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#include "lld/Common/Strings.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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Defined *ElfSym::Bss;
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Defined *ElfSym::Etext1;
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Defined *ElfSym::Etext2;
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Defined *ElfSym::Edata1;
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Defined *ElfSym::Edata2;
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Defined *ElfSym::End1;
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Defined *ElfSym::End2;
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Defined *ElfSym::GlobalOffsetTable;
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Defined *ElfSym::MipsGp;
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Defined *ElfSym::MipsGpDisp;
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Defined *ElfSym::MipsLocalGp;
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Defined *ElfSym::RelaIpltStart;
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Defined *ElfSym::RelaIpltEnd;
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Defined *ElfSym::RISCVGlobalPointer;
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Defined *ElfSym::TlsModuleBase;
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static uint64_t getSymVA(const Symbol &Sym, int64_t &Addend) {
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switch (Sym.kind()) {
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case Symbol::DefinedKind: {
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auto &D = cast<Defined>(Sym);
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SectionBase *IS = D.Section;
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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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assert(IS != &InputSection::Discarded);
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IS = IS->Repl;
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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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// 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 = IS->getVA(Offset);
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// MIPS relocatable files can mix regular and microMIPS code.
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// Linker needs to distinguish such code. To do so microMIPS
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// symbols has the `STO_MIPS_MICROMIPS` flag in the `st_other`
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// field. Unfortunately, the `MIPS::relocateOne()` method has
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// a symbol value only. To pass type of the symbol (regular/microMIPS)
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// to that routine as well as other places where we write
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// a symbol value as-is (.dynamic section, `Elf_Ehdr::e_entry`
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// field etc) do the same trick as compiler uses to mark microMIPS
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// for CPU - set the less-significant bit.
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if (Config->EMachine == EM_MIPS && isMicroMips() &&
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((Sym.StOther & STO_MIPS_MICROMIPS) || Sym.NeedsPltAddr))
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VA |= 1;
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if (D.isTls() && !Config->Relocatable) {
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// Use the address of the TLS segment's first section rather than the
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// segment's address, because segment addresses aren't initialized until
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// after sections are finalized. (e.g. Measuring the size of .rela.dyn
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// for Android relocation packing requires knowing TLS symbol addresses
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// during section finalization.)
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if (!Out::TlsPhdr || !Out::TlsPhdr->FirstSec)
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fatal(toString(D.File) +
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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->FirstSec->Addr;
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}
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return VA;
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}
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case Symbol::SharedKind:
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case Symbol::UndefinedKind:
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return 0;
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case Symbol::LazyArchiveKind:
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case Symbol::LazyObjectKind:
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assert(Sym.IsUsedInRegularObj && "lazy symbol reached writer");
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return 0;
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case Symbol::CommonKind:
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llvm_unreachable("common symbol reached writer");
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case Symbol::PlaceholderKind:
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llvm_unreachable("placeholder symbol reached writer");
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}
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llvm_unreachable("invalid symbol kind");
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}
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uint64_t Symbol::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 Symbol::getGotVA() const {
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if (GotInIgot)
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return In.IgotPlt->getVA() + getGotPltOffset();
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return In.Got->getVA() + getGotOffset();
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}
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uint64_t Symbol::getGotOffset() const { return GotIndex * Config->Wordsize; }
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uint64_t Symbol::getGotPltVA() const {
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if (IsInIplt)
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return In.IgotPlt->getVA() + getGotPltOffset();
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return In.GotPlt->getVA() + getGotPltOffset();
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}
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uint64_t Symbol::getGotPltOffset() const {
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if (IsInIplt)
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return PltIndex * Config->Wordsize;
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return (PltIndex + Target->GotPltHeaderEntriesNum) * Config->Wordsize;
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}
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uint64_t Symbol::getPPC64LongBranchOffset() const {
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assert(PPC64BranchltIndex != 0xffff);
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return PPC64BranchltIndex * Config->Wordsize;
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}
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uint64_t Symbol::getPltVA() const {
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PltSection *Plt = IsInIplt ? In.Iplt : In.Plt;
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uint64_t OutVA =
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Plt->getVA() + Plt->HeaderSize + PltIndex * Target->PltEntrySize;
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// While linking microMIPS code PLT code are always microMIPS
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// code. Set the less-significant bit to track that fact.
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// See detailed comment in the `getSymVA` function.
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if (Config->EMachine == EM_MIPS && isMicroMips())
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OutVA |= 1;
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return OutVA;
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}
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uint64_t Symbol::getPPC64LongBranchTableVA() const {
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assert(PPC64BranchltIndex != 0xffff);
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return In.PPC64LongBranchTarget->getVA() +
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PPC64BranchltIndex * Config->Wordsize;
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}
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uint64_t Symbol::getSize() const {
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if (const auto *DR = dyn_cast<Defined>(this))
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return DR->Size;
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return cast<SharedSymbol>(this)->Size;
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}
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OutputSection *Symbol::getOutputSection() const {
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if (auto *S = dyn_cast<Defined>(this)) {
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if (auto *Sec = S->Section)
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return Sec->Repl->getOutputSection();
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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 Symbol::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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NameSize = Pos;
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// If this is not in this DSO, it is not a definition.
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if (!isDefined())
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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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VersionId = Ver.Id;
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else
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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. We also do not error
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// if the symbol has a local version as it won't be in the dynamic
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// symbol table.
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if (Config->Shared && VersionId != VER_NDX_LOCAL)
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error(toString(File) + ": symbol " + S + " has undefined version " +
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Verstr);
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}
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void Symbol::fetch() const {
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if (auto *Sym = dyn_cast<LazyArchive>(this)) {
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cast<ArchiveFile>(Sym->File)->fetch(Sym->Sym);
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return;
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}
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if (auto *Sym = dyn_cast<LazyObject>(this)) {
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dyn_cast<LazyObjFile>(Sym->File)->fetch();
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return;
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}
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llvm_unreachable("Symbol::fetch() is called on a non-lazy symbol");
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}
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MemoryBufferRef LazyArchive::getMemberBuffer() {
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Archive::Child C = CHECK(
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Sym.getMember(), "could not get the member for symbol " + Sym.getName());
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return CHECK(C.getMemoryBufferRef(),
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"could not get the buffer for the member defining symbol " +
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Sym.getName());
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}
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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 && isDefined() && !IsPreemptible)
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return STB_LOCAL;
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if (!Config->GnuUnique && 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 (!Config->HasDynSymTab)
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return false;
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if (computeBinding() == STB_LOCAL)
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return false;
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// If a PIE binary was not linked against any shared libraries, then we can
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// safely drop weak undef symbols from .dynsym.
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if (isUndefWeak() && Config->Pie && SharedFiles.empty())
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return false;
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if (!isDefined())
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return true;
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return ExportDynamic;
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}
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// Print out a log message for --trace-symbol.
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void elf::printTraceSymbol(const Symbol *Sym) {
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std::string S;
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if (Sym->isUndefined())
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S = ": reference to ";
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else if (Sym->isLazy())
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S = ": lazy definition of ";
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else if (Sym->isShared())
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S = ": shared definition of ";
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else if (Sym->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 + Sym->getName());
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}
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void elf::maybeWarnUnorderableSymbol(const Symbol *Sym) {
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if (!Config->WarnSymbolOrdering)
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return;
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// If UnresolvedPolicy::Ignore is used, no "undefined symbol" error/warning
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// is emitted. It makes sense to not warn on undefined symbols.
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//
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// Note, ld.bfd --symbol-ordering-file= does not warn on undefined symbols,
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// but we don't have to be compatible here.
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if (Sym->isUndefined() &&
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Config->UnresolvedSymbols == UnresolvedPolicy::Ignore)
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return;
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const InputFile *File = Sym->File;
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auto *D = dyn_cast<Defined>(Sym);
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auto Warn = [&](StringRef S) { warn(toString(File) + S + Sym->getName()); };
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if (Sym->isUndefined())
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Warn(": unable to order undefined symbol: ");
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else if (Sym->isShared())
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Warn(": unable to order shared symbol: ");
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else if (D && !D->Section)
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Warn(": unable to order absolute symbol: ");
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else if (D && isa<OutputSection>(D->Section))
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Warn(": unable to order synthetic symbol: ");
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else if (D && !D->Section->Repl->isLive())
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Warn(": unable to order discarded symbol: ");
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}
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// Returns a symbol for an error message.
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std::string lld::toString(const Symbol &B) {
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if (Config->Demangle)
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if (Optional<std::string> S = demangleItanium(B.getName()))
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return *S;
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return B.getName();
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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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// Merge symbol properties.
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//
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// When we have many symbols of the same name, we choose one of them,
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// and that's the result of symbol resolution. However, symbols that
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// were not chosen still affect some symbol properties.
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void Symbol::mergeProperties(const Symbol &Other) {
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if (Other.ExportDynamic)
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ExportDynamic = true;
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if (Other.IsUsedInRegularObj)
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IsUsedInRegularObj = true;
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// DSO symbols do not affect visibility in the output.
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if (!Other.isShared())
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Visibility = getMinVisibility(Visibility, Other.Visibility);
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}
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void Symbol::resolve(const Symbol &Other) {
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mergeProperties(Other);
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if (isPlaceholder()) {
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replace(Other);
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return;
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}
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switch (Other.kind()) {
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case Symbol::UndefinedKind:
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resolveUndefined(cast<Undefined>(Other));
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break;
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case Symbol::CommonKind:
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resolveCommon(cast<CommonSymbol>(Other));
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break;
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case Symbol::DefinedKind:
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resolveDefined(cast<Defined>(Other));
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break;
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case Symbol::LazyArchiveKind:
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resolveLazy(cast<LazyArchive>(Other));
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break;
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case Symbol::LazyObjectKind:
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resolveLazy(cast<LazyObject>(Other));
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break;
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case Symbol::SharedKind:
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resolveShared(cast<SharedSymbol>(Other));
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break;
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case Symbol::PlaceholderKind:
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llvm_unreachable("bad symbol kind");
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}
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}
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void Symbol::resolveUndefined(const Undefined &Other) {
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// An undefined symbol with non default visibility must be satisfied
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// in the same DSO.
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//
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// If this is a non-weak defined symbol in a discarded section, override the
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// existing undefined symbol for better error message later.
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if ((isShared() && Other.Visibility != STV_DEFAULT) ||
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(isUndefined() && Other.Binding != STB_WEAK && Other.DiscardedSecIdx)) {
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replace(Other);
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return;
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}
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if (Traced)
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printTraceSymbol(&Other);
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if (isShared() || isLazy() || (isUndefined() && Other.Binding != STB_WEAK))
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Binding = Other.Binding;
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if (isLazy()) {
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// An undefined weak will not fetch archive members. See comment on Lazy in
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// Symbols.h for the details.
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if (Other.Binding == STB_WEAK) {
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Type = Other.Type;
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return;
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}
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// Do extra check for --warn-backrefs.
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//
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// --warn-backrefs is an option to prevent an undefined reference from
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// fetching an archive member written earlier in the command line. It can be
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// used to keep compatibility with GNU linkers to some degree.
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// I'll explain the feature and why you may find it useful in this comment.
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//
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// lld's symbol resolution semantics is more relaxed than traditional Unix
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// linkers. For example,
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//
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// ld.lld foo.a bar.o
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//
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// succeeds even if bar.o contains an undefined symbol that has to be
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// resolved by some object file in foo.a. Traditional Unix linkers don't
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// allow this kind of backward reference, as they visit each file only once
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// from left to right in the command line while resolving all undefined
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// symbols at the moment of visiting.
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//
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// In the above case, since there's no undefined symbol when a linker visits
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// foo.a, no files are pulled out from foo.a, and because the linker forgets
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// about foo.a after visiting, it can't resolve undefined symbols in bar.o
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// that could have been resolved otherwise.
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//
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// That lld accepts more relaxed form means that (besides it'd make more
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// sense) you can accidentally write a command line or a build file that
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// works only with lld, even if you have a plan to distribute it to wider
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// users who may be using GNU linkers. With --warn-backrefs, you can detect
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// a library order that doesn't work with other Unix linkers.
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//
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// The option is also useful to detect cyclic dependencies between static
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// archives. Again, lld accepts
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//
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// ld.lld foo.a bar.a
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//
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// even if foo.a and bar.a depend on each other. With --warn-backrefs, it is
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// handled as an error.
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//
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// Here is how the option works. We assign a group ID to each file. A file
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// with a smaller group ID can pull out object files from an archive file
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// with an equal or greater group ID. Otherwise, it is a reverse dependency
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// and an error.
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//
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// A file outside --{start,end}-group gets a fresh ID when instantiated. All
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// files within the same --{start,end}-group get the same group ID. E.g.
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//
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// ld.lld A B --start-group C D --end-group E
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//
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// A forms group 0. B form group 1. C and D (including their member object
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// files) form group 2. E forms group 3. I think that you can see how this
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// group assignment rule simulates the traditional linker's semantics.
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bool Backref = Config->WarnBackrefs && Other.File &&
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File->GroupId < Other.File->GroupId;
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fetch();
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// We don't report backward references to weak symbols as they can be
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// overridden later.
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if (Backref && !isWeak())
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warn("backward reference detected: " + Other.getName() + " in " +
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toString(Other.File) + " refers to " + toString(File));
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}
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}
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// Using .symver foo,foo@@VER unfortunately creates two symbols: foo and
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// foo@@VER. We want to effectively ignore foo, so give precedence to
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// foo@@VER.
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// FIXME: If users can transition to using
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// .symver foo,foo@@@VER
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// we can delete this hack.
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static int compareVersion(StringRef A, StringRef B) {
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bool X = A.contains("@@");
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bool Y = B.contains("@@");
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if (!X && Y)
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return 1;
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if (X && !Y)
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return -1;
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return 0;
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}
|
|
|
|
// Compare two symbols. Return 1 if the new symbol should win, -1 if
|
|
// the new symbol should lose, or 0 if there is a conflict.
|
|
int Symbol::compare(const Symbol *Other) const {
|
|
assert(Other->isDefined() || Other->isCommon());
|
|
|
|
if (!isDefined() && !isCommon())
|
|
return 1;
|
|
|
|
if (int Cmp = compareVersion(getName(), Other->getName()))
|
|
return Cmp;
|
|
|
|
if (Other->isWeak())
|
|
return -1;
|
|
|
|
if (isWeak())
|
|
return 1;
|
|
|
|
if (isCommon() && Other->isCommon()) {
|
|
if (Config->WarnCommon)
|
|
warn("multiple common of " + getName());
|
|
return 0;
|
|
}
|
|
|
|
if (isCommon()) {
|
|
if (Config->WarnCommon)
|
|
warn("common " + getName() + " is overridden");
|
|
return 1;
|
|
}
|
|
|
|
if (Other->isCommon()) {
|
|
if (Config->WarnCommon)
|
|
warn("common " + getName() + " is overridden");
|
|
return -1;
|
|
}
|
|
|
|
auto *OldSym = cast<Defined>(this);
|
|
auto *NewSym = cast<Defined>(Other);
|
|
|
|
if (Other->File && isa<BitcodeFile>(Other->File))
|
|
return 0;
|
|
|
|
if (!OldSym->Section && !NewSym->Section && OldSym->Value == NewSym->Value &&
|
|
NewSym->Binding == STB_GLOBAL)
|
|
return -1;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static void reportDuplicate(Symbol *Sym, InputFile *NewFile,
|
|
InputSectionBase *ErrSec, uint64_t ErrOffset) {
|
|
if (Config->AllowMultipleDefinition)
|
|
return;
|
|
|
|
Defined *D = cast<Defined>(Sym);
|
|
if (!D->Section || !ErrSec) {
|
|
error("duplicate symbol: " + toString(*Sym) + "\n>>> defined in " +
|
|
toString(Sym->File) + "\n>>> defined in " + toString(NewFile));
|
|
return;
|
|
}
|
|
|
|
// Construct and print an error message in the form of:
|
|
//
|
|
// ld.lld: error: duplicate symbol: foo
|
|
// >>> defined at bar.c:30
|
|
// >>> bar.o (/home/alice/src/bar.o)
|
|
// >>> defined at baz.c:563
|
|
// >>> baz.o in archive libbaz.a
|
|
auto *Sec1 = cast<InputSectionBase>(D->Section);
|
|
std::string Src1 = Sec1->getSrcMsg(*Sym, D->Value);
|
|
std::string Obj1 = Sec1->getObjMsg(D->Value);
|
|
std::string Src2 = ErrSec->getSrcMsg(*Sym, ErrOffset);
|
|
std::string Obj2 = ErrSec->getObjMsg(ErrOffset);
|
|
|
|
std::string Msg = "duplicate symbol: " + toString(*Sym) + "\n>>> defined at ";
|
|
if (!Src1.empty())
|
|
Msg += Src1 + "\n>>> ";
|
|
Msg += Obj1 + "\n>>> defined at ";
|
|
if (!Src2.empty())
|
|
Msg += Src2 + "\n>>> ";
|
|
Msg += Obj2;
|
|
error(Msg);
|
|
}
|
|
|
|
void Symbol::resolveCommon(const CommonSymbol &Other) {
|
|
int Cmp = compare(&Other);
|
|
if (Cmp < 0)
|
|
return;
|
|
|
|
if (Cmp > 0) {
|
|
replace(Other);
|
|
return;
|
|
}
|
|
|
|
CommonSymbol *OldSym = cast<CommonSymbol>(this);
|
|
|
|
OldSym->Alignment = std::max(OldSym->Alignment, Other.Alignment);
|
|
if (OldSym->Size < Other.Size) {
|
|
OldSym->File = Other.File;
|
|
OldSym->Size = Other.Size;
|
|
}
|
|
}
|
|
|
|
void Symbol::resolveDefined(const Defined &Other) {
|
|
int Cmp = compare(&Other);
|
|
if (Cmp > 0)
|
|
replace(Other);
|
|
else if (Cmp == 0)
|
|
reportDuplicate(this, Other.File,
|
|
dyn_cast_or_null<InputSectionBase>(Other.Section),
|
|
Other.Value);
|
|
}
|
|
|
|
template <class LazyT> void Symbol::resolveLazy(const LazyT &Other) {
|
|
if (!isUndefined())
|
|
return;
|
|
|
|
// An undefined weak will not fetch archive members. See comment on Lazy in
|
|
// Symbols.h for the details.
|
|
if (isWeak()) {
|
|
uint8_t Ty = Type;
|
|
replace(Other);
|
|
Type = Ty;
|
|
Binding = STB_WEAK;
|
|
return;
|
|
}
|
|
|
|
Other.fetch();
|
|
}
|
|
|
|
void Symbol::resolveShared(const SharedSymbol &Other) {
|
|
if (Visibility == STV_DEFAULT && (isUndefined() || isLazy())) {
|
|
// An undefined symbol with non default visibility must be satisfied
|
|
// in the same DSO.
|
|
uint8_t Bind = Binding;
|
|
replace(Other);
|
|
Binding = Bind;
|
|
}
|
|
}
|