No gcj 64 bit compilation support? What the?

I am compiling Java source code in Mandriva 2011 64 bit,
and default mode runs happily.

The -m32 mode behaves as expected.

However, when I try

gcj Test.java --main=Test -m64 -o Test.bin

 I get the error:

jc1: sorry, unimplemented: 64-bit mode not compiled in

If my linux is 64 bit and if I omit -m64 and let it proceed,
will gcj compile into 64 bit by default?
 
 
> This error means that your gcj compiler was built without support for
> x86 64-bit mode.
> 
> Ian

Then why is this, if my compiler is on a 64 bit operating system with
64 bit hardware?  Shouldn't it compile to 64 bit files anyway?
Isn't the operating system really doing this by default? Is this my reply really accurate?
If not, why not? Where can I find simple instructions to build gcj
to compile 64 bit optimised executable files?