// Versions are usually assigned to symbols using version scripts,
// but there's another way to assign versions to symbols.
// If a symbol name contains '@', the string after it is not
// actually a part of the symbol name but specifies a version.
// This function takes care of it.
template <class ELFT> void SymbolTable<ELFT>::scanSymbolVersions() {
if (Config->VersionDefinitions.empty())
return;
int MaxVersionLen = getMaxVersionLen();
// Unfortunately there's no way other than iterating over all
// symbols to look for '@' characters in symbol names.
// So this is inherently slow. A good news is that we do this
// only when versions have been defined.
for (Symbol *Sym : SymVector) {
// Symbol versions for exported symbols are by nature
// only for defined global symbols.
SymbolBody *B = Sym->body();
if (!B->isDefined())
continue;
uint8_t Visibility = B->getVisibility();
if (Visibility != STV_DEFAULT && Visibility != STV_PROTECTED)
continue;
// Look for '@' in the symbol name.
StringRef Name;
uint16_t Version;
std::tie(Name, Version) = getSymbolVersion(B, MaxVersionLen);
if (Name.empty())
continue;
B->setName(Name);
Sym->VersionId = Version;
}
}
// This is the main function of the garbage collector.
// Starting from GC-root sections, this function visits all reachable
// sections to set their "Live" bits.
template <class ELFT> void elf::markLive(SymbolTable<ELFT> *Symtab) {
SmallVector<InputSection<ELFT> *, 256> Q;
auto Enqueue = [&](InputSectionBase<ELFT> *Sec) {
if (!Sec || Sec->Live)
return;
Sec->Live = true;
if (InputSection<ELFT> *S = dyn_cast<InputSection<ELFT>>(Sec))
Q.push_back(S);
};
auto MarkSymbol = [&](SymbolBody *Sym) {
if (Sym)
if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&Sym->repl()))
Enqueue(D->Section);
};
// Add GC root symbols.
MarkSymbol(Config->EntrySym);
MarkSymbol(Symtab->find(Config->Init));
MarkSymbol(Symtab->find(Config->Fini));
for (StringRef S : Config->Undefined)
MarkSymbol(Symtab->find(S));
// Preserve externally-visible symbols if the symbols defined by this
// file can interrupt other ELF file's symbols at runtime.
if (Config->Shared || Config->ExportDynamic) {
for (const std::pair<StringRef, Symbol *> &P : Symtab->getSymbols()) {
SymbolBody *B = P.second->Body;
if (B->getVisibility() == STV_DEFAULT)
MarkSymbol(B);
}
}
// Preserve special sections and those which are specified in linker
// script KEEP command.
for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab->getObjectFiles())
for (InputSectionBase<ELFT> *Sec : F->getSections())
if (Sec && Sec != &InputSection<ELFT>::Discarded)
if (isReserved(Sec) || Script->shouldKeep<ELFT>(Sec))
Enqueue(Sec);
// Mark all reachable sections.
while (!Q.empty())
forEachSuccessor<ELFT>(Q.pop_back_val(), Enqueue);
}