Name: rlT66838			Date: 05/03/2000


java version "1.3.0rc3"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0rc3-Z)
Java HotSpot(TM) Client VM (build 1.3.0rc3-Z, mixed mode)


I am working on an application that uses an embedded jvm, instantiated using
the JNI.  For the most part, this works great.  But, I am having difficulty when
I try to enable the remote debugging interface.  I'm using the "JPDA Connection
and Invocation" doc as a reference.

I can start up a java program with the "java.exe" executable and the appropriate
debug options and then attach the jdb debugger later from another shell.  That
works fine.  But, when I try to pass the same debug arguments to a JVM that I
create through the JNI, I get a crash every time in the JNI_CreateJavaVM
function.  If I remove the -Xrunjdwp argument, then the crash goes away.

I've included a simple test program that I wrote in Dev Studio to demonstrate
the problem.

I'm guessing that this should work.  Any help would be greatly appriciated!  It
would make my life much easier if I had a debugger.  I'm going to experiment
with jdk1.2.2 and see if I can get any further.

------

// TestJVM.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <jni.h>

#define OPTION_COUNT 5

int main(int argc, char* argv[])
{
    JavaVMInitArgs vm_args;
	JavaVMOption options[OPTION_COUNT];

	// Enable remote debugging
	//
	options[0].optionString = "-verbose:jni";
	options[1].optionString = "-Xdebug";
	options[2].optionString = "-Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n";

/* for use with classic VM
	options[3].optionString = "-Djava.compiler=NONE";
	options[4].optionString = "-Xnoagent";
	*/

	// Set up options to be passed to the virtual machine when it is
        // created.
	//
	vm_args.version = JNI_VERSION_1_2;
	vm_args.options = options;
	vm_args.nOptions = OPTION_COUNT;
	vm_args.ignoreUnrecognized = 1;

	// Create the virtual Machine
	//
	JNIEnv * jvmEnv = NULL;
	JavaVM * vm = NULL;
	jint ret = JNI_CreateJavaVM(&vm, (void **)&jvmEnv, &vm_args);

	return 0;
}
(Review ID: 104417) 

======================================================================

Name: tb29552			Date: 04/30/2001


java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0)
Java HotSpot(TM) Server VM (build 1.3.0, mixed mode)

Invoke JNI_CreateJavaVM with an option set to "-Xrunjdwp:help", this will cause
a SEG_FAULT in arguments.cpp, line 475, due to trying to write to a const char
*. You need to copy the option to a separate buffer or store the length of
"name" in a variable so you don't need to use strlen() to get it.
(Review ID: 123351)
======================================================================

Response from the submitter:


I just read the update in the bug.  I tried doing strdup's on my strings that I'm
passing as options so that I'm not using static strings anymore.  That did indeed
fix the crash.

I'm a little curious as to why the JVM would be writing over my option strings. I 
didn't do anything different than was suggested in the JNI docs that came with the
JDK 1.3.

I have not double checked to make sure that I can attach a debugger yet.  But if that
works, then I'm in business.

You may, at the very least, consider updating the docs.

My work flow for recreating the bug is that I compile the attached program, ran it, and it crashed (NT 4.0 and JDK 1.3).  I have an embedded JVM that I need to attach a debugger to. 
The crash was preventing that.  The tip in the bug update seems to make it possible.


// jnicrash.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <string.h>


#include <jni.h>

#define OPTION_COUNT 3

int main(int argc, char* argv[])
{    
	JavaVMInitArgs vm_args;
	JavaVMOption options[OPTION_COUNT];
				
/* 
                     // This version works

	// Enable remote debugging													
	//
	options[0].optionString = strdup( "-verbose:jni" );
	options[1].optionString = strdup( "-Xdebug" );
	options[2].optionString = strdup( "-Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n" );
*/
        // This version does not

	// Enable remote debugging													
	//
	options[0].optionString = "-verbose:jni";
	options[1].optionString = "-Xdebug";
	options[2].optionString = "-Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n";

	// Set up options to be passed to the virtual machine when it is
	// created.
	//
	vm_args.version = JNI_VERSION_1_2;
	vm_args.options = options;
	vm_args.nOptions = OPTION_COUNT;
	vm_args.ignoreUnrecognized = 1;

	// Create the virtual Machine
	//
	JNIEnv * jvmEnv = NULL;
	JavaVM * vm = NULL;
	jint ret = JNI_CreateJavaVM(&vm, (void **)&jvmEnv, &vm_args);

	return 0;
}


ranjith.mandala@Eng 2001-07-25