Make sure that const-class linkage is preserved.
After calling loadClass() on the initiating loader, insert
the Class to the ClassTable. Check that the returned class
has the correct name and that the ClassTable does not yet
contain a different Class for the same name. If either check
fails, follow the RI behavior for parallel capable class
loaders, i.e. throw NoClassDefFoundError for name mismatch
(with more descriptive message than RI) or return the Class
already present in the ClassTable. This ensures that the
const-class instruction for a given name always gives the
same result as the first time it succeeded for the same
initiating loader, even for non-well-behaved loader.
Inserting the Class to the ClassTable is also a necessary
step for changing to hash-based dex cache type array when
the DexCache will not necessarily keep the Class and
therefore the defining loader alive while the initiating
loader stays alive, so the ClassTable entry is necessary
to keep the dependecy.
Add tests that a const-class instruction always returns the
same Class<?> as it returned the first time, i.e. when it
was "linked", even for class loaders that are not
well-behaved, even if the dex cache type array is cleared.
Also test the edge cases, i.e. NoClassDefFoundError and
returning old entry from ClassTable when already inserted
by another thread.
Bug: 30627598
Test: 626-const-class-linking
Test: m test-art-host
Change-Id: Ie9b721464b4e9a5dcce8df8095548e983bba1fe8
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 4905514..d34d348 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -1941,13 +1941,36 @@
void Visit(ObjPtr<mirror::ClassLoader> class_loader)
REQUIRES_SHARED(Locks::classlinker_classes_lock_, Locks::mutator_lock_) OVERRIDE {
ClassTable* const class_table = class_loader->GetClassTable();
- if (!done_ && class_table != nullptr && !class_table->Visit(*visitor_)) {
- // If the visitor ClassTable returns false it means that we don't need to continue.
- done_ = true;
+ if (!done_ && class_table != nullptr) {
+ DefiningClassLoaderFilterVisitor visitor(class_loader, visitor_);
+ if (!class_table->Visit(visitor)) {
+ // If the visitor ClassTable returns false it means that we don't need to continue.
+ done_ = true;
+ }
}
}
private:
+ // Class visitor that limits the class visits from a ClassTable to the classes with
+ // the provided defining class loader. This filter is used to avoid multiple visits
+ // of the same class which can be recorded for multiple initiating class loaders.
+ class DefiningClassLoaderFilterVisitor : public ClassVisitor {
+ public:
+ DefiningClassLoaderFilterVisitor(ObjPtr<mirror::ClassLoader> defining_class_loader,
+ ClassVisitor* visitor)
+ : defining_class_loader_(defining_class_loader), visitor_(visitor) { }
+
+ bool operator()(ObjPtr<mirror::Class> klass) OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_) {
+ if (klass->GetClassLoader() != defining_class_loader_) {
+ return true;
+ }
+ return (*visitor_)(klass);
+ }
+
+ ObjPtr<mirror::ClassLoader> const defining_class_loader_;
+ ClassVisitor* const visitor_;
+ };
+
ClassVisitor* const visitor_;
// If done is true then we don't need to do any more visiting.
bool done_;
@@ -2532,56 +2555,109 @@
}
} else {
ScopedObjectAccessUnchecked soa(self);
- ObjPtr<mirror::Class> cp_klass;
- if (FindClassInBaseDexClassLoader(soa, self, descriptor, hash, class_loader, &cp_klass)) {
- // The chain was understood. So the value in cp_klass is either the class we were looking
- // for, or not found.
- if (cp_klass != nullptr) {
- return cp_klass.Ptr();
- }
- // TODO: We handle the boot classpath loader in FindClassInBaseDexClassLoader. Try to unify
- // this and the branch above. TODO: throw the right exception here.
+ ObjPtr<mirror::Class> result_ptr;
+ bool descriptor_equals;
+ bool known_hierarchy =
+ FindClassInBaseDexClassLoader(soa, self, descriptor, hash, class_loader, &result_ptr);
+ if (result_ptr != nullptr) {
+ // The chain was understood and we found the class. We still need to add the class to
+ // the class table to protect from racy programs that can try and redefine the path list
+ // which would change the Class<?> returned for subsequent evaluation of const-class.
+ DCHECK(known_hierarchy);
+ DCHECK(result_ptr->DescriptorEquals(descriptor));
+ descriptor_equals = true;
+ } else {
+ // Either the chain wasn't understood or the class wasn't found.
+ //
+ // If the chain was understood and but we did not find the class, let the Java-side
+ // rediscover all this and throw the exception with the right stack trace. Note that
+ // the Java-side could still succeed for racy programs if another thread is actively
+ // modifying the class loader's path list.
- // We'll let the Java-side rediscover all this and throw the exception with the right stack
- // trace.
- }
-
- if (Runtime::Current()->IsAotCompiler()) {
- // Oops, compile-time, can't run actual class-loader code.
- ObjPtr<mirror::Throwable> pre_allocated = Runtime::Current()->GetPreAllocatedNoClassDefFoundError();
- self->SetException(pre_allocated);
- return nullptr;
- }
-
- ScopedLocalRef<jobject> class_loader_object(soa.Env(),
- soa.AddLocalReference<jobject>(class_loader.Get()));
- std::string class_name_string(DescriptorToDot(descriptor));
- ScopedLocalRef<jobject> result(soa.Env(), nullptr);
- {
- ScopedThreadStateChange tsc(self, kNative);
- ScopedLocalRef<jobject> class_name_object(soa.Env(),
- soa.Env()->NewStringUTF(class_name_string.c_str()));
- if (class_name_object.get() == nullptr) {
- DCHECK(self->IsExceptionPending()); // OOME.
+ if (Runtime::Current()->IsAotCompiler()) {
+ // Oops, compile-time, can't run actual class-loader code.
+ ObjPtr<mirror::Throwable> pre_allocated =
+ Runtime::Current()->GetPreAllocatedNoClassDefFoundError();
+ self->SetException(pre_allocated);
return nullptr;
}
- CHECK(class_loader_object.get() != nullptr);
- result.reset(soa.Env()->CallObjectMethod(class_loader_object.get(),
- WellKnownClasses::java_lang_ClassLoader_loadClass,
- class_name_object.get()));
+
+ ScopedLocalRef<jobject> class_loader_object(
+ soa.Env(), soa.AddLocalReference<jobject>(class_loader.Get()));
+ std::string class_name_string(DescriptorToDot(descriptor));
+ ScopedLocalRef<jobject> result(soa.Env(), nullptr);
+ {
+ ScopedThreadStateChange tsc(self, kNative);
+ ScopedLocalRef<jobject> class_name_object(
+ soa.Env(), soa.Env()->NewStringUTF(class_name_string.c_str()));
+ if (class_name_object.get() == nullptr) {
+ DCHECK(self->IsExceptionPending()); // OOME.
+ return nullptr;
+ }
+ CHECK(class_loader_object.get() != nullptr);
+ result.reset(soa.Env()->CallObjectMethod(class_loader_object.get(),
+ WellKnownClasses::java_lang_ClassLoader_loadClass,
+ class_name_object.get()));
+ }
+ if (self->IsExceptionPending()) {
+ // If the ClassLoader threw, pass that exception up.
+ // However, to comply with the RI behavior, first check if another thread succeeded.
+ result_ptr = LookupClass(self, descriptor, hash, class_loader.Get());
+ if (result_ptr != nullptr && result_ptr->IsResolved()) {
+ self->ClearException();
+ return result_ptr.Ptr();
+ }
+ return nullptr;
+ } else if (result.get() == nullptr) {
+ // broken loader - throw NPE to be compatible with Dalvik
+ ThrowNullPointerException(StringPrintf("ClassLoader.loadClass returned null for %s",
+ class_name_string.c_str()).c_str());
+ return nullptr;
+ }
+ result_ptr = soa.Decode<mirror::Class>(result.get());
+ // Check the name of the returned class.
+ descriptor_equals = result_ptr->DescriptorEquals(descriptor);
}
- if (self->IsExceptionPending()) {
- // If the ClassLoader threw, pass that exception up.
- return nullptr;
- } else if (result.get() == nullptr) {
- // broken loader - throw NPE to be compatible with Dalvik
- ThrowNullPointerException(StringPrintf("ClassLoader.loadClass returned null for %s",
- class_name_string.c_str()).c_str());
- return nullptr;
- } else {
- // success, return mirror::Class*
- return soa.Decode<mirror::Class>(result.get()).Ptr();
+
+ // Try to insert the class to the class table, checking for mismatch.
+ ObjPtr<mirror::Class> old;
+ {
+ ReaderMutexLock mu(self, *Locks::classlinker_classes_lock_);
+ ClassTable* const class_table = InsertClassTableForClassLoader(class_loader.Get());
+ old = class_table->Lookup(descriptor, hash);
+ if (old == nullptr) {
+ old = result_ptr; // For the comparison below, after releasing the lock.
+ if (descriptor_equals) {
+ class_table->InsertWithHash(result_ptr.Ptr(), hash);
+ Runtime::Current()->GetHeap()->WriteBarrierEveryFieldOf(class_loader.Get());
+ } // else throw below, after releasing the lock.
+ }
}
+ if (UNLIKELY(old != result_ptr)) {
+ // Return `old` (even if `!descriptor_equals`) to mimic the RI behavior for parallel
+ // capable class loaders. (All class loaders are considered parallel capable on Android.)
+ mirror::Class* loader_class = class_loader->GetClass();
+ const char* loader_class_name =
+ loader_class->GetDexFile().StringByTypeIdx(loader_class->GetDexTypeIndex());
+ LOG(WARNING) << "Initiating class loader of type " << DescriptorToDot(loader_class_name)
+ << " is not well-behaved; it a returned different Class for racing loadClass(\""
+ << DescriptorToDot(descriptor) << "\").";
+ return old.Ptr();
+ }
+ if (UNLIKELY(!descriptor_equals)) {
+ std::string result_storage;
+ const char* result_name = result_ptr->GetDescriptor(&result_storage);
+ std::string loader_storage;
+ const char* loader_class_name = class_loader->GetClass()->GetDescriptor(&loader_storage);
+ ThrowNoClassDefFoundError(
+ "Initiating class loader of type %s returned class %s instead of %s.",
+ DescriptorToDot(loader_class_name).c_str(),
+ DescriptorToDot(result_name).c_str(),
+ DescriptorToDot(descriptor).c_str());
+ return nullptr;
+ }
+ // success, return mirror::Class*
+ return result_ptr.Ptr();
}
UNREACHABLE();
}
@@ -3662,12 +3738,6 @@
Runtime::Current()->GetHeap()->WriteBarrierEveryFieldOf(klass);
}
-bool ClassLinker::RemoveClass(const char* descriptor, ObjPtr<mirror::ClassLoader> class_loader) {
- WriterMutexLock mu(Thread::Current(), *Locks::classlinker_classes_lock_);
- ClassTable* const class_table = ClassTableForClassLoader(class_loader);
- return class_table != nullptr && class_table->Remove(descriptor);
-}
-
mirror::Class* ClassLinker::LookupClass(Thread* self,
const char* descriptor,
size_t hash,