GCJ (and IRC) questions.

[Bryce McKinlay]

Troy Wu wrote:

>Hello, everyone.
>
>I'm having some trouble with GCJ.  Is there an IRC channel where 
>developers (and other knowledgable folks) hang out?  Also an IRC 
>newbie....
>  
>
irc.oftc.net #gcj

>I'm a new user to GCJ.  I'm getting unusual compiler messages.  Let me try 
>to break down my problem:
>
>	The command:
>
>gcj -g -fPIC --main=tacular.gui.Graphics `find . -name "*.o"` -L/usr/X11/lib64 -lX11
>
>	The resultant error(s):
>
>./cni/Globals.o(.gnu.linkonce.d.DW.ref.__gxx_personality_v0+0x0): In 
>function `runtime_init()':
>/raid/troy/tacular/cni/Globals.cc:24: undefined reference to 
>`__gxx_personality_v0'
>./cni/NativeGraphics.o(.text+0x11): In function 
>`tacular::gui::NativeGraphics::NativeGraphics[not-in-charge]()':
>/raid/troy/tacular/cni/NativeGraphics.cc:31: undefined reference to 
>`tacular::gui::Graphics::Graphics[not-in-charge]()'
>./cni/NativeGraphics.o(.text+0x1c):/raid/troy/tacular/cni/NativeGraphics.cc:31: 
>undefined reference to `vtable for tacular::gui::NativeGraphics'
>./cni/NativeGraphics.o(.text+0xad): In function 
>`tacular::gui::NativeGraphics::NativeGraphics[in-charge]()':
>/raid/troy/tacular/cni/NativeGraphics.cc:31: undefined reference to 
>`tacular::gui::Graphics::Graphics[not-in-charge]()'
>./cni/NativeGraphics.o(.text+0xb8):/raid/troy/tacular/cni/NativeGraphics.cc:31: 
>undefined reference to `vtable for tacular::gui::NativeGraphics'
>collect2: ld returned 1 exit status
>make: *** [final] Error 1
>
>-------------------------------------------------------------------------
>
>It's enough to boggle the mind!
>
>I don't know what the first thing is (the __gxx_personality_v0+0x0).  The 
>second set of errors seems to say that the vtable for a class is busted.  
>The third set of errors seems to say that vtable for the same class is 
>busted.
>
>What in the world are these 2 functions:
>
>	tacular::gui::NativeGraphics::NativeGraphics[in-charge]()
>	tacular::gui::NativeGraphics::NativeGraphics[not-in-charge]()
>
>Are these ctors?  Is G++ doing something weird with Java ctors using GCJ?
>  
>

Yes, it looks like something strange is going on here. Java (CNI) 
classes, unlike real C++ classes, should not distinguish between 
in-charge and not-in-charge constructors. If you could post a small test 
case which shows the error, it should help to diagnose the problem.

>Relevant info:
>
>	* Using a dual-proc opteron machine running SuSE-9.2 (2.6.5)
>
>	* Using GCJ 3.3.3
>
>	* Graphics is an abstract class defined in Java, compiled with
>	  GCJ.
>
>	* NativeGraphics is a concrete class (extending Graphics) written
>	  in C++, compiled with g++.
>  
>

I presume you've read the CNI documentation, but note that 
NativeGraphics needs to be declared in Java, then the "native" methods 
implemented in C++ against the header file built with gcjh. Failing to 
do this means your native class would not be declared "extern Java", and 
that would also cause the undefined reference to __gxx_personality_v0 error.

Regards

Bryce