llvm-project/lld/ELF/Symbols.cpp

274 lines
7.9 KiB
C++

//===- Symbols.cpp --------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Symbols.h"
#include "InputFiles.h"
#include "InputSection.h"
#include "OutputSections.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "Writer.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Strings.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Path.h"
#include <cstring>
using namespace llvm;
using namespace llvm::object;
using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf;
Defined *ElfSym::Bss;
Defined *ElfSym::Etext1;
Defined *ElfSym::Etext2;
Defined *ElfSym::Edata1;
Defined *ElfSym::Edata2;
Defined *ElfSym::End1;
Defined *ElfSym::End2;
Defined *ElfSym::GlobalOffsetTable;
Defined *ElfSym::MipsGp;
Defined *ElfSym::MipsGpDisp;
Defined *ElfSym::MipsLocalGp;
Defined *ElfSym::RelaIpltEnd;
static uint64_t getSymVA(const Symbol &Sym, int64_t &Addend) {
switch (Sym.kind()) {
case Symbol::DefinedKind: {
auto &D = cast<Defined>(Sym);
SectionBase *IS = D.Section;
// According to the ELF spec reference to a local symbol from outside
// the group are not allowed. Unfortunately .eh_frame breaks that rule
// and must be treated specially. For now we just replace the symbol with
// 0.
if (IS == &InputSection::Discarded)
return 0;
// This is an absolute symbol.
if (!IS)
return D.Value;
IS = IS->Repl;
uint64_t Offset = D.Value;
// An object in an SHF_MERGE section might be referenced via a
// section symbol (as a hack for reducing the number of local
// symbols).
// Depending on the addend, the reference via a section symbol
// refers to a different object in the merge section.
// Since the objects in the merge section are not necessarily
// contiguous in the output, the addend can thus affect the final
// VA in a non-linear way.
// To make this work, we incorporate the addend into the section
// offset (and zero out the addend for later processing) so that
// we find the right object in the section.
if (D.isSection()) {
Offset += Addend;
Addend = 0;
}
// In the typical case, this is actually very simple and boils
// down to adding together 3 numbers:
// 1. The address of the output section.
// 2. The offset of the input section within the output section.
// 3. The offset within the input section (this addition happens
// inside InputSection::getOffset).
//
// If you understand the data structures involved with this next
// line (and how they get built), then you have a pretty good
// understanding of the linker.
uint64_t VA = IS->getVA(Offset);
if (D.isTls() && !Config->Relocatable) {
if (!Out::TlsPhdr)
fatal(toString(D.File) +
" has an STT_TLS symbol but doesn't have an SHF_TLS section");
return VA - Out::TlsPhdr->p_vaddr;
}
return VA;
}
case Symbol::SharedKind:
case Symbol::UndefinedKind:
return 0;
case Symbol::LazyArchiveKind:
case Symbol::LazyObjectKind:
llvm_unreachable("lazy symbol reached writer");
}
llvm_unreachable("invalid symbol kind");
}
uint64_t Symbol::getVA(int64_t Addend) const {
uint64_t OutVA = getSymVA(*this, Addend);
return OutVA + Addend;
}
uint64_t Symbol::getGotVA() const { return InX::Got->getVA() + getGotOffset(); }
uint64_t Symbol::getGotOffset() const {
return GotIndex * Target->GotEntrySize;
}
uint64_t Symbol::getGotPltVA() const {
if (this->IsInIgot)
return InX::IgotPlt->getVA() + getGotPltOffset();
return InX::GotPlt->getVA() + getGotPltOffset();
}
uint64_t Symbol::getGotPltOffset() const {
if (IsInIgot)
return PltIndex * Target->GotPltEntrySize;
return (PltIndex + Target->GotPltHeaderEntriesNum) * Target->GotPltEntrySize;
}
uint64_t Symbol::getPltVA() const {
if (this->IsInIplt)
return InX::Iplt->getVA() + PltIndex * Target->PltEntrySize;
return InX::Plt->getVA() + Target->getPltEntryOffset(PltIndex);
}
uint64_t Symbol::getPltOffset() const {
assert(!this->IsInIplt);
return Target->getPltEntryOffset(PltIndex);
}
uint64_t Symbol::getSize() const {
if (const auto *DR = dyn_cast<Defined>(this))
return DR->Size;
if (const auto *S = dyn_cast<SharedSymbol>(this))
return S->Size;
return 0;
}
OutputSection *Symbol::getOutputSection() const {
if (auto *S = dyn_cast<Defined>(this)) {
if (auto *Sec = S->Section)
return Sec->Repl->getOutputSection();
return nullptr;
}
return nullptr;
}
// If a symbol name contains '@', the characters after that is
// a symbol version name. This function parses that.
void Symbol::parseSymbolVersion() {
StringRef S = getName();
size_t Pos = S.find('@');
if (Pos == 0 || Pos == StringRef::npos)
return;
StringRef Verstr = S.substr(Pos + 1);
if (Verstr.empty())
return;
// Truncate the symbol name so that it doesn't include the version string.
NameSize = Pos;
// If this is not in this DSO, it is not a definition.
if (!isDefined())
return;
// '@@' in a symbol name means the default version.
// It is usually the most recent one.
bool IsDefault = (Verstr[0] == '@');
if (IsDefault)
Verstr = Verstr.substr(1);
for (VersionDefinition &Ver : Config->VersionDefinitions) {
if (Ver.Name != Verstr)
continue;
if (IsDefault)
VersionId = Ver.Id;
else
VersionId = Ver.Id | VERSYM_HIDDEN;
return;
}
// It is an error if the specified version is not defined.
// Usually version script is not provided when linking executable,
// but we may still want to override a versioned symbol from DSO,
// so we do not report error in this case.
if (Config->Shared)
error(toString(File) + ": symbol " + S + " has undefined version " +
Verstr);
}
InputFile *LazyArchive::fetch() { return cast<ArchiveFile>(File)->fetch(Sym); }
uint8_t Symbol::computeBinding() const {
if (Config->Relocatable)
return Binding;
if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
return STB_LOCAL;
if (VersionId == VER_NDX_LOCAL && isDefined())
return STB_LOCAL;
if (!Config->GnuUnique && Binding == STB_GNU_UNIQUE)
return STB_GLOBAL;
return Binding;
}
bool Symbol::includeInDynsym() const {
if (!Config->HasDynSymTab)
return false;
if (computeBinding() == STB_LOCAL)
return false;
if (!isDefined())
return true;
return ExportDynamic;
}
// Print out a log message for --trace-symbol.
void elf::printTraceSymbol(Symbol *Sym) {
std::string S;
if (Sym->isUndefined())
S = ": reference to ";
else if (Sym->isLazy())
S = ": lazy definition of ";
else if (Sym->isShared())
S = ": shared definition of ";
else if (dyn_cast_or_null<BssSection>(cast<Defined>(Sym)->Section))
S = ": common definition of ";
else
S = ": definition of ";
message(toString(Sym->File) + S + Sym->getName());
}
void elf::warnUnorderableSymbol(const Symbol *Sym) {
if (!Config->WarnSymbolOrdering)
return;
const InputFile *File = Sym->File;
auto *D = dyn_cast<Defined>(Sym);
auto Warn = [&](StringRef S) { warn(toString(File) + S + Sym->getName()); };
if (Sym->isUndefined())
Warn(": unable to order undefined symbol: ");
else if (Sym->isShared())
Warn(": unable to order shared symbol: ");
else if (D && !D->Section)
Warn(": unable to order absolute symbol: ");
else if (D && isa<OutputSection>(D->Section))
Warn(": unable to order synthetic symbol: ");
else if (D && !D->Section->Repl->Live)
Warn(": unable to order discarded symbol: ");
}
// Returns a symbol for an error message.
std::string lld::toString(const Symbol &B) {
if (Config->Demangle)
if (Optional<std::string> S = demangleItanium(B.getName()))
return *S;
return B.getName();
}