agent.c

#include <string.h>

#include "jni.h"
#include "jvmti.h"

/*
  public class java.lang.ref.MyWeakReference extends java.lang.ref.WeakReference {};
*/
jbyte MyWeakReference_bytes[] = { 
  -54,  -2, -70, -66,   0,   0,   0,  49,   0,   5,   1,   0,  29, 106,  97, 118,
   97,  47, 108,  97, 110, 103,  47, 114, 101, 102,  47,  77, 121,  87, 101,  97,
  107,  82, 101, 102, 101, 114, 101, 110,  99, 101,   7,   0,   1,   1,   0,  27,
  106,  97, 118,  97,  47, 108,  97, 110, 103,  47, 114, 101, 102,  47,  87, 101,
   97, 107,  82, 101, 102, 101, 114, 101, 110,  99, 101,   7,   0,   3,   0,   1,
    0,   2,   0,   4,   0,   0,   0,   0,   0,   0,   0,   0
};
jsize MyWeakReference_len = 0x5C;

void JNICALL callback_ClassFileLoadHook_transform(jvmtiEnv *jvmti, JNIEnv* env,
  jclass class_being_redefined, jobject loader, const char* name,
  jobject protection_domain, jint class_data_len, const unsigned char* class_data,
  jint* new_class_data_len, unsigned char** new_class_data) {

  if (name && !strcmp(name, "java/lang/System")) {
    (*env)->DefineClass(env, "java/lang/ref/MyWeakReference", NULL, MyWeakReference_bytes, MyWeakReference_len);
  }
}

JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *vm, char *options, void *reserved) {
  jvmtiEventCallbacks callbacks;
  jvmtiCapabilities caps;
  jvmtiEnv *jvmti;

  (*vm)->GetEnv(vm, (void **)&jvmti, JVMTI_VERSION_9);

  memset(&caps, 0, sizeof(caps));
  memset(&callbacks, 0, sizeof(callbacks));

  caps.can_generate_early_vmstart = 1;
  caps.can_generate_all_class_hook_events = 1;
  caps.can_generate_early_class_hook_events = 1;

  callbacks.ClassFileLoadHook = &callback_ClassFileLoadHook_transform;

  (*jvmti)->AddCapabilities(jvmti, &caps);  
  (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks));
  (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, JVMTI_EVENT_CLASS_FILE_LOAD_HOOK, NULL);

  return 0;
}

MiscTest9.java

package app1;

import java.lang.ref.WeakReference;

public class MiscTest9 {
  public static void main(String[] args) throws Exception {
    WeakReference<?> weak = new WeakReference<>(new MiscTest9());

    boolean present = true;
    while (present) {
      System.out.println("Running GC");
      System.gc();
      present = weak.get() != null;
    }
  }
}

output

C:\XWork\Misc9>\Work\jvm\jdk-9-ea+160-jigsaw\bin\java -agentpath:c:\XWork\MinAgent\MinAgent\x64\Debug\MinAgent.dll -cp target\classes app1.MiscTest9
Running GC
Running GC
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x000000007224be47, pid=11252, tid=12148
#
# JRE version: Java(TM) SE Runtime Environment (9.0+160) (build 9-ea+160-jigsaw-nightly-h6207-20170316)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (9-ea+160-jigsaw-nightly-h6207-20170316, mixed mode, tiered, compressed oops, g1 gc, windows-amd64)
# Problematic frame:
# V  [jvm.dll+0x2abe47]  UpdateRSOopClosure::do_oop+0x47
#
# No core dump will be written. Minidumps are not enabled by default on client versions of Windows
#
# An error report file with more information is saved as:
# C:\XWork\Misc9\hs_err_pid11252.log
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
#