BC ABI (was "Re: [fedora-java] Re: Java OpenGL on FC4")

[Andrew Haley]

John M. Gabriele writes:
 > 
 > 
 > --- Andrew Haley <aph at redhat.com> wrote:
 > 
 > > John M. Gabriele writes:
 > >  > 
 > >  > 
 > >  > --- Bryce McKinlay <mckinlay at redhat.com> wrote:
 > >  > 
 > >  > > John M. Gabriele wrote:
 > >  > > 
 > >  > > >Thanks for the reply Bryce. I used much of it to update the
 > >  > > >beginning of:
 > >  > > >http://gcc.gnu.org/wiki/How%20to%20BC%20compile%20with%20GCJ
 > >  > > >  
 > >  > > >
 > >  > > 
 > >  > > Great, thanks for doing this.
 > >  > 
 > >  > NP. :) I'm updating it as we go.
 > >  > 
 > >  > > 
 > >  > > >It sounds like, to be able to mix interpreted and natively
 > >  > > >compiled code at runtime, you need to have compiled your .jars
 > >  > > >with the -findirect-dispatch option, right?
 > >  > > >  
 > >  > > >
 > >  > > 
 > >  > > If you want to be able to call interpreted code from native code, yes.
 > >  > 
 > >  > So, we're talking about my natively compiled binary loading and
 > >  > using some regular old .jar file full of .class files...
 > >  > 
 > >  > I don't get it. As I'm understanding it, if the natively compiled code
 > >  > makes use of ClassLoader.defineClass(), it should just work right off the
 > >  > bat without the native code having been built with -findirect-dispatch,
 > >  > since when it tries to read a bytecode stream from the jar, it'll
 > >  > find it there. No fuss, no muss, right?
 > > 
 > > Right, that's true.  And that will work.  However, if your compiled
 > > program does something like
 > > 
 > >    foo.bar();
 > > 
 > > where foo *only* exists in bytecode -- has never been gcj-compiled --
 > > then that will *not* work.
 > 
 > *Only* exists in bytecode (if I'm understanding what you mean) is
 > just fine -- since that's what ClassLoader.defineClass() expects,
 > correct? My native code still knows how to deal with bytecode...
 > 
 > Hmm. Maybe I'm not understanding what you mean by only existing
 > in bytecode...
 > 
 > Is foo an instance of a class defined in the mystuff.jar file?

Yes.  Unless you are using indirect dispatch, the run-time dynamic
linker (i.e. that used by the OS for loading C programs) of your OS
will try to link against a shared object file and will fail if it
isn't there.  The gcj runtime doesn't even get consulted.

Andrew.