quick little CNI question

Sat Apr 1 00:00:00 GMT 2000

Glenn Chambers <GChambers@provsol.com> writes:
> Has anyone looked at whether the new C++ ABI that is being put together
> will remove the need for any sort of lookup?

It won't require any lookup - but then that has always been the case
for C++. However, C++ uses (at least used) multiple vtbale pointers
per objects, and "adjustment" of the this pointer. This violates the
JVM spec. I believe it is possible for a JVM to work around that,
but it means that the actual data representation differs in
important ways from the JVMs model. Specifically, you can't use
a simple interpreter without verification.
I mentioned the issue on the gcc mailing list - perhaps C++ could
use teh same data representation as Java in this respect, or at
least people should bear the java needs in mind. However, I
don't think that is going to happen. For one thing the expectations
for C++ is different than for Java, so using gcj's constant-time
lookup may not make sense for C++. In any case, it is not a
critical problem. We can always (and should someday) fix g++ so
that it knows about Java interfaces (field-less abstract classes that
have the Java property but don't inherit from Object), and can
generate the correct sequence for Java interface calls. There is
nothing fundamentally difficult with this; it's just a bit of a
pain, and other things have higher priority.
-- 
	--Per Bothner
per@bothner.com http://www.bothner.com/~per/