从JNI jclass确定Java类的大小 [英] determine Java class size from JNI jclass

问题描述

我正在使用JNI分析某些程序.我只是想知道，在获得jclass引用之后，如何找到基础类的大小?

I'm using JNI to analyze some program. I just wonder, after get jclass reference, how it is possible to find the size of the underlying class ?

例如: class cls = env-> FindClass("Lee/Boehm/Test");

for example: class cls = env->FindClass("Lee/Boehm/Test");

从这里我如何评估热点堆中Lee.Boehm.Test类的大小?

from here how can i evaluate the size of the class Lee.Boehm.Test inside hotspot's heap ?

谢谢 勃姆

推荐答案

去这里

agent.c

#include <stdlib.h>
#include "jvmti.h"

jvmtiEnv *globalJVMTIInterface;

JNIEXPORT jlong JNICALL Java_util_Util_getObjectSize
  (JNIEnv *jni_env , jclass class , jobject object) {

    jlong objectSize;

     (*globalJVMTIInterface)->GetObjectSize(globalJVMTIInterface, object, &objectSize);

     return objectSize;
}

JNIEXPORT jint JNICALL
Agent_OnLoad(JavaVM * jvm, char *options, void *reserved)
{

  jint returnCode = (*jvm)->GetEnv(jvm, (void **) &globalJVMTIInterface,
      JVMTI_VERSION_1_0);

  if (returnCode != JNI_OK)
    {
      fprintf(stderr,
          "The version of JVMTI requested (1.0) is not supported by this JVM.\n");
      return JVMTI_ERROR_UNSUPPORTED_VERSION;
    }

  return JVMTI_ERROR_NONE;
}

和./util/Util.java

and ./util/Util.java

package util;

public class Util {
    public static final native long getObjectSize(Object obj);
}

和Test.java

and Test.java

public class Test {

   public static void main(String[] args) {

      System.out.println(util.Util.getObjectSize(new String()));

   }

}

gcc -I/opt/ibm-jdk-bin-1.6.0.9/include -shared -fPIC -o libagent.so agent.c

gcc -I/opt/ibm-jdk-bin-1.6.0.9/include -shared -fPIC -o libagent.so agent.c

java -agentpath:./libagent.so测试

java -agentpath:./libagent.so Test

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