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https://github.com/RGBCube/serenity
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LibELF: Cache consecutive lookups for the same symbol
This reduces the startup time of LibWeb by 10%, and eliminates 156'000 of the total 481'000 global symbol lookups during a self-test run.
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9a07ac0b6a
commit
1adf06c9f0
3 changed files with 31 additions and 6 deletions
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@ -209,8 +209,9 @@ void DynamicLoader::do_main_relocations()
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{
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do_relr_relocations();
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Optional<DynamicLoader::CachedLookupResult> cached_result;
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m_dynamic_object->relocation_section().for_each_relocation([&](DynamicObject::Relocation const& relocation) {
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switch (do_direct_relocation(relocation, ShouldInitializeWeak::No, ShouldCallIfuncResolver::No)) {
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switch (do_direct_relocation(relocation, cached_result, ShouldInitializeWeak::No, ShouldCallIfuncResolver::No)) {
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case RelocationResult::Failed:
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dbgln("Loader.so: {} unresolved symbol '{}'", m_filepath, relocation.symbol().name());
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VERIFY_NOT_REACHED();
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@ -281,8 +282,9 @@ Result<NonnullRefPtr<DynamicObject>, DlErrorMessage> DynamicLoader::load_stage_3
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VERIFY(result == RelocationResult::Success);
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}
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Optional<DynamicLoader::CachedLookupResult> cached_result;
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for (auto const& relocation : m_direct_ifunc_relocations) {
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auto result = do_direct_relocation(relocation, ShouldInitializeWeak::No, ShouldCallIfuncResolver::Yes);
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auto result = do_direct_relocation(relocation, cached_result, ShouldInitializeWeak::No, ShouldCallIfuncResolver::Yes);
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VERIFY(result == RelocationResult::Success);
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}
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@ -321,8 +323,9 @@ void DynamicLoader::load_stage_4()
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void DynamicLoader::do_lazy_relocations()
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{
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Optional<DynamicLoader::CachedLookupResult> cached_result;
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for (auto const& relocation : m_unresolved_relocations) {
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if (auto res = do_direct_relocation(relocation, ShouldInitializeWeak::Yes, ShouldCallIfuncResolver::Yes); res != RelocationResult::Success) {
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if (auto res = do_direct_relocation(relocation, cached_result, ShouldInitializeWeak::Yes, ShouldCallIfuncResolver::Yes); res != RelocationResult::Success) {
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dbgln("Loader.so: {} unresolved symbol '{}'", m_filepath, relocation.symbol().name());
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VERIFY_NOT_REACHED();
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}
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@ -522,7 +525,10 @@ void DynamicLoader::load_program_headers()
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}
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}
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DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObject::Relocation const& relocation, ShouldInitializeWeak should_initialize_weak, ShouldCallIfuncResolver should_call_ifunc_resolver)
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DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObject::Relocation const& relocation,
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Optional<DynamicLoader::CachedLookupResult>& cached_result,
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ShouldInitializeWeak should_initialize_weak,
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ShouldCallIfuncResolver should_call_ifunc_resolver)
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{
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FlatPtr* patch_ptr = nullptr;
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if (is_dynamic())
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@ -534,12 +540,21 @@ DynamicLoader::RelocationResult DynamicLoader::do_direct_relocation(DynamicObjec
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return VirtualAddress { reinterpret_cast<DynamicObject::IfuncResolver>(address.get())() };
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};
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auto lookup_symbol = [&](DynamicObject::Symbol const& symbol) {
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// The static linker sorts relocations by the referenced symbol. Especially when vtables
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// in large inheritance hierarchies are involved, there might be tens of references to
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// the same symbol. We can avoid redundant lookups by keeping track of the previous result.
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if (!cached_result.has_value() || !cached_result.value().symbol.definitely_equals(symbol))
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cached_result = DynamicLoader::CachedLookupResult { symbol, DynamicLoader::lookup_symbol(symbol) };
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return cached_result.value().result;
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};
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struct ResolvedTLSSymbol {
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DynamicObject const& dynamic_object;
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FlatPtr value;
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};
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auto resolve_tls_symbol = [](DynamicObject::Relocation const& relocation) -> Optional<ResolvedTLSSymbol> {
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auto resolve_tls_symbol = [&](DynamicObject::Relocation const& relocation) -> Optional<ResolvedTLSSymbol> {
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if (relocation.symbol_index() == 0)
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return ResolvedTLSSymbol { relocation.dynamic_object(), 0 };
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