ART: Add GetLoadedClasses support

Add support to retrieve all loaded classes. Use the standard
ClassLoader callback infrastructure.

Bug: 31684578
Test: m test-art-host-run-test-907-get-loaded-classes
Change-Id: Ifb33cae27dc32602bcd8fd930d3c7eda02598c26
diff --git a/test/907-get-loaded-classes/get_loaded_classes.cc b/test/907-get-loaded-classes/get_loaded_classes.cc
new file mode 100644
index 0000000..c0f7082
--- /dev/null
+++ b/test/907-get-loaded-classes/get_loaded_classes.cc
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "get_loaded_classes.h"
+
+#include <iostream>
+#include <pthread.h>
+#include <stdio.h>
+#include <vector>
+
+#include "base/macros.h"
+#include "jni.h"
+#include "openjdkjvmti/jvmti.h"
+#include "ScopedLocalRef.h"
+#include "ScopedUtfChars.h"
+
+#include "ti-agent/common_load.h"
+
+namespace art {
+namespace Test907GetLoadedClasses {
+
+static jstring GetClassName(JNIEnv* jni_env, jclass cls) {
+  ScopedLocalRef<jclass> class_class(jni_env, jni_env->GetObjectClass(cls));
+  jmethodID mid = jni_env->GetMethodID(class_class.get(), "getName", "()Ljava/lang/String;");
+  return reinterpret_cast<jstring>(jni_env->CallObjectMethod(cls, mid));
+}
+
+extern "C" JNIEXPORT jobjectArray JNICALL Java_Main_getLoadedClasses(
+    JNIEnv* env, jclass klass ATTRIBUTE_UNUSED) {
+  jint count = -1;
+  jclass* classes = nullptr;
+  jvmtiError result = jvmti_env->GetLoadedClasses(&count, &classes);
+  if (result != JVMTI_ERROR_NONE) {
+    char* err;
+    jvmti_env->GetErrorName(result, &err);
+    printf("Failure running GetLoadedClasses: %s\n", err);
+    return nullptr;
+  }
+
+  ScopedLocalRef<jclass> obj_class(env, env->FindClass("java/lang/String"));
+  if (obj_class.get() == nullptr) {
+    return nullptr;
+  }
+
+  jobjectArray ret = env->NewObjectArray(count, obj_class.get(), nullptr);
+  if (ret == nullptr) {
+    return ret;
+  }
+
+  for (size_t i = 0; i < static_cast<size_t>(count); ++i) {
+    jstring class_name = GetClassName(env, classes[i]);
+    env->SetObjectArrayElement(ret, static_cast<jint>(i), class_name);
+    env->DeleteLocalRef(class_name);
+  }
+
+  // Need to:
+  // 1) Free the local references.
+  // 2) Deallocate.
+  for (size_t i = 0; i < static_cast<size_t>(count); ++i) {
+    env->DeleteLocalRef(classes[i]);
+  }
+  jvmti_env->Deallocate(reinterpret_cast<unsigned char*>(classes));
+
+  return ret;
+}
+
+}  // namespace Test907GetLoadedClasses
+}  // namespace art