FULL PRODUCT VERSION :
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) 64-Bit Server VM (build 1.6.0-b105, mixed mode)

FULL OS VERSION :
Linux xyz 2.6.18-gentoo-r4 #1 SMP Sat Dec 16 17:13:55 CET 2006 x86_64 AMD Athlon(tm) 64 X2 Dual Core Processor 4400+ AuthenticAMD GNU/Linux

A DESCRIPTION OF THE PROBLEM :

Any application started with JDK 6 results in this:

#
# An unexpected error has been detected by Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00000030b242de54, pid=30743, tid=1090758992
#
# Java VM: Java HotSpot(TM) 64-Bit Server VM (1.6.0-b105 mixed mode)
# Problematic frame:
# C  [libc.so.6+0x2de54]  catgets+0x14
#
# An error report file with more information is saved as hs_err_pid30743.log
#
# If you would like to submit a bug report, please visit:
#   http://java.sun.com/webapps/bugreport/crash.jsp
#
Aborted

I found out, that console programs work (i.e. System.out.println("Hello 
World!") but everything that uses any Frames (GUI) does not work. I.e. the 
following program does not work with JDK 6:

import javax.swing.JFrame;

public class Test {

        public static void main(String[] args) {
                JFrame frame = new JFrame();
                frame.pack();
                frame.setVisible(true);
        }

}

I also managed to get JDK 6 working. Please see my forum entry at the gentoo 
forums: http://forums.gentoo.org/viewtopic-t-527808-highlight-.html 
(especially my reply). But it turned out, that it workes only 
occassionally.

I'm afraid I can not help you reproducing the problem, because just anything 
that uses Swing/AWT crashes. I'm completely re-installing my system. I hope 
the problem goes away with that.

I tried everything: recompiling my whole system, prelinking everything.. etc..

THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: Yes

THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Yes

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Execute any java app with frames.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Attached separatly

REPRODUCIBILITY :
This bug can be reproduced always.