You can't define your own method called debug() in your JNI code, because
the debug() function is already defined in libjvm.so.

jvm source code at:
{hotspot_ws}/src/share/vm/utilities/debug.cpp

This is not documented anywhere and could lead to a crash,
when you are trying to call your function called "debug()"
across c libraries.


How to reproduce:
=================
HelloJWorld.java
----------------
public class HelloJWorld
{
  private native void Hi();

  public static void main(String[] args) {
    new HelloJWorld().Hi();
  }

  static {
    System.loadLibrary("HelloCWorld");
  }
}

HelloJWorld.h (you can create it with javah HelloJWorld)
-------------
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class HelloJWorld */

#ifndef _Included_HelloJWorld
#define _Included_HelloJWorld
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class: HelloJWorld
 * Method: debug
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_HelloJWorld_debug
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif


HelloCWorld.c
-------------
#include <jni.h>
#include <stdio.h>
#include "HelloJWorld.h"

JNIEXPORT void JNICALL
Java_HelloJWorld_Hi(JNIEnv *env, jobject obj)
{
        debug(4, "Hello debug World!\n");
        return;
}


util.c (in ./util folder)
-------------------------
#include <stdio.h>
#include <sys/types.h>

int debug( int level, char *fmt, char *var)
{

        fprintf(stderr, "DEBUG:%d - %s %s\n", level, fmt, var);

}

Complete sourcecodes and Makefiles are attached to this bugreport.
If you compile them (with gcc and Java 1.4.2),
HelloJWorld.java file gets compiled to HelloJWorld.class file
HelloCWorld.c file gets compiled to libHelloCWorld.so library file
util.c file gets compiled to libutil.so library file

When you run above java program it crashes with the following log:
An unexpected exception has been detected in native code outside the VM.
Unexpected Signal : 10 occurred at PC=0xFF3C2BF0
Function=elf_rtbndr+0x20
Library=/usr/lib/ld.so.1

Current Java thread:
        at HelloJWorld.Hi(Native Method)
        at HelloJWorld.main(HelloJWorld.java:6)

Dynamic libraries:
0x10000 java
0xff370000 /usr/lib/libthread.so.1
0xff3a0000 /usr/lib/libdl.so.1
0xff280000 /usr/lib/libc.so.1
0xff350000 /usr/platform/SUNW,Ultra-60/lib/libc_psr.so.1
0xfec00000 /opt/java/j2sdk/j2sdk1.4.2/jre/lib/sparc/client/libjvm.so
0xff230000 /usr/lib/libCrun.so.1
0xff210000 /usr/lib/libsocket.so.1
0xff100000 /usr/lib/libnsl.so.1
0xff1d0000 /usr/lib/libm.so.1
0xff0e0000 /usr/lib/libsched.so.1
0xff260000 /usr/lib/libw.so.1
0xff0c0000 /usr/lib/libmp.so.2
0xff0a0000 /usr/lib/librt.so.1
0xff080000 /usr/lib/libaio.so.1
0xff060000 /usr/lib/libmd5.so.1
0xff030000 /usr/platform/SUNW,Ultra-60/lib/libmd5_psr.so.1
0xfebd0000 /opt/java/j2sdk/j2sdk1.4.2/jre/lib/sparc/native_threads/libhpi.so
0xfeb80000 /opt/java/j2sdk/j2sdk1.4.2/jre/lib/sparc/libverify.so
0xfeb30000 /opt/java/j2sdk/j2sdk1.4.2/jre/lib/sparc/libjava.so
0xfeb10000 /opt/java/j2sdk/j2sdk1.4.2/jre/lib/sparc/libzip.so
0xfe860000 /usr/lib/locale/en_US.ISO8859-1/en_US.ISO8859-1.so.2
0xfe3e0000 /net/cores/cores/CA_63639521/ori/jni/mydebug/libHelloCWorld.so

Heap at VM Abort:
Heap
 def new generation total 2112K, used 112K [0xf1800000, 0xf1a20000, 0xf1f10000)
  eden space 2048K, 5% used [0xf1800000, 0xf181c2a0, 0xf1a00000)
  from space 64K, 0% used [0xf1a00000, 0xf1a00000, 0xf1a10000)
  to space 64K, 0% used [0xf1a10000, 0xf1a10000, 0xf1a20000)
 tenured generation total 1408K, used 0K [0xf1f10000, 0xf2070000, 0xf5800000)
   the space 1408K, 0% used [0xf1f10000, 0xf1f10000, 0xf1f10200, 0xf2070000)
 compacting perm gen total 4096K, used 960K [0xf5800000, 0xf5c00000, 0xf9800000)
   the space 4096K, 23% used [0xf5800000, 0xf58f0220, 0xf58f0400, 0xf5c00000)

Local Time = Tue Aug 12 14:15:09 2003
Elapsed Time = 0
#
# The exception above was detected in native code outside the VM
#
# Java VM: Java HotSpot(TM) Client VM (1.4.2-b28 mixed mode)
#
# An error report file has been saved as hs_err_pid971.log.
# Please refer to the file for further information.
#
Abort


The same progam works fine if you rename the function name 'debug()' to 'debug1()' for example. Here is the output of the program with funtion name modified to 'debug1()':


#./run
DEBUG:4 -
Hello debug World!
Have a nice day!