gcc 3.0.1 & C++ ABI issues

[Nathan Sidwell <nathan at codesourcery dot com>]

Guys,
Stefan has emailed me, regarding the state of 3.0.1 wrt KDE. Here's my
summary

As PR 3909 shows, there are still issues with virtual inheritance. Stefan
has tested the patch which I posted for that, which although fixing 3909,
(http://gcc.gnu.org/ml/gcc-patches/2001-08/msg00045.html) does not fix the
problems in KDE's aRTs package. I think we should not apply that patch,
because it is incomplete anyway -- the only reason I posted it was to fix
KDE, which it fails to do.

As it's now the 5th August, I do not think we will have a KDEable compiler
with 3.0.1. The patch set from which I extracted 3909's fix is still
incomplete and I am unlikely to have time to work on it until late August.
Once I'm happy with that patch set, I'll see if KDE starts working with it.

There are some outstanding empty class issues. Jason had some queries with
the patch I posted (http://gcc.gnu.org/ml/gcc-patches/2001-08/msg00002.html)
concerning copying empty classes. Have you had time to consider my
response?

There appears to be something strange with passing empty classes by value
(http://gcc.gnu.org/ml/gcc-bugs/2001-08/msg00136.html). In spite of
the subject, this is nothing to do with multiple inheritance. The ABI doc
specifies (3.1.1), that value parameters need to be passed by reference
if they have a non-trivial copy ctor or dtor. At first glance we appear
to only check the former. So, although we're consistent, we're at variance
from the spec.

There appears to be a problem with thunks and sj-lj exception handling,
which is reported in http://gcc.gnu.org/ml/gcc-bugs/2001-08/msg00061.html.
Our long term goal is to eliminate sj-lj exceptions (right?), but that
doesn't help for now. (I don't know if this is a 2.95 regression)

nathan
-- 
Dr Nathan Sidwell   ::   http://www.codesourcery.com   ::   CodeSourcery LLC
         'But that's a lie.' - 'Yes it is. What's your point?'
nathan@codesourcery.com : http://www.cs.bris.ac.uk/~nathan/ : nathan@acm.org