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Load jar and execute class method from JVMTI + JNI
#include <jvmti.h>
#include <cstring>
#include <iostream>
void debug(char* msg...){
// printf(msg);
}
int loadJar(JNIEnv *jni){
debug("loading jar...\n");
const char* javaNetUrlClassName = "java/net/URL";
char* jarPath = (char*) "file://hello-world-library.jar";
jclass urlClass = jni->FindClass(javaNetUrlClassName);
if(urlClass == NULL){
char msg[50];
sprintf(msg, "couldn't find class: %s\n", javaNetUrlClassName);
jni->FatalError((char *) msg);
}
debug("urlClass created\n");
jmethodID urlConstructor = jni->GetMethodID(urlClass, "<init>", "(Ljava/lang/String;)V");
jstring jarPathJString = jni->NewStringUTF(jarPath);
jobject url = jni->NewObject(urlClass, urlConstructor, jarPathJString);
jni->ReleaseStringUTFChars(jarPathJString, NULL);
if(url == NULL){
jni->FatalError("Couldn't create URL object");
}
debug("jar url created\n");
jobjectArray urls = jni->NewObjectArray(1, jni->FindClass(javaNetUrlClassName), NULL);
jni->SetObjectArrayElement(urls, 0, url);
jclass classLoaderClass = jni->FindClass("java/net/URLClassLoader");
jmethodID constructor = jni->GetMethodID(classLoaderClass, "<init>", "([Ljava/net/URL;)V");
jobject classLoader = jni->NewObject(classLoaderClass, constructor, urls);
debug("classloader created \n");
jclass clazz = jni->FindClass("java/lang/Class");
jmethodID classForNameMethod = jni->GetStaticMethodID(clazz, "forName", "(Ljava/lang/String;ZLjava/lang/ClassLoader;)Ljava/lang/Class;");
if(classForNameMethod == NULL){
jni->FatalError("Class.forName(String,boolean,java.lang.ClassLoader)java.lang.Class method not found\n");
}
char *jarInitClass = "samepackage.Calculator";
jstring classToLoad = jni->NewStringUTF(jarInitClass);
jclass jarClass = (jclass) jni->CallStaticObjectMethod(clazz, classForNameMethod, classToLoad, true, classLoader);
jni->ReleaseStringUTFChars(classToLoad, NULL);
if(jarClass == NULL){
printf("jarClass found %s\n", jarClass);
char msg[100];
sprintf(msg, "jar init class not found: %s\n", jarInitClass);
jni->FatalError((char *) msg);
}
jmethodID mainMethod = jni->GetStaticMethodID(jarClass, "sum", "(II)I");
jint result = jni->CallStaticIntMethod(jarClass, mainMethod, 15, 8);
printf("loaded jar and executed: %d\n", result);
}
void JNICALL vmInitCallback(jvmtiEnv *jvmtiEnv, JNIEnv* jniEnv, jthread thread){
printf("callback called \n");
loadJar(jniEnv);
}
JNIEXPORT jint JNICALL
Agent_OnAttach(JavaVM *jvm, char *options, void *reserved) {
printf("on attach options=%s\n", options);
jvmtiEnv *jvmti = NULL;
jint result = jvm->GetEnv((void **) &jvmti, JVMTI_VERSION_1_1);
if (result != JNI_OK) {
printf("ERROR: Unable to access JVMTI! %d\n", result);
}
JNIEnv *jni;
jint r = jvm->GetEnv((void **) &jni, JNI_VERSION_1_6);
if (r != JNI_OK) {
printf("couldn't get JNI env %d", r);
return r;
}
loadJar(jni);
return JNI_OK;
}
JNIEXPORT jint JNICALL
Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) {
printf("on load options=%s\n", options);
static jvmtiEnv *jvmti = NULL;
jint result = jvm->GetEnv((void **) &jvmti, JVMTI_VERSION_1_1);
if (result != JNI_OK) {
printf("ERROR: Unable to access JVMTI! %d\n", result);
}
jvmtiEventCallbacks callbacks;
memset(&callbacks, 0, sizeof(callbacks));
callbacks.VMInit = &vmInitCallback;
jvmti->SetEventCallbacks(&callbacks, sizeof(callbacks));
jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_VM_INIT, NULL);
std::cout << "I'm a native Agent!!!\n";
return JNI_OK;
}
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