Re: Plans for ABI migration

[Andi Kleen <ak at suse dot de>]

Joe Buck <jbuck@racerx.synopsys.com> writes:

> Bernardo Innocenti writes:
> > did the steering comitee already set a roadmap to ease the
> > migration from the old C++ ABI (gcc 2.9x) to the new one
> > (gcc 3.x)?
> 
> No, because there is nothing special about an ABI change with a
> major release of the compiler.  Some background:
> 
> In the past, the C++ ABI broke with every major release.  egcs 1.0
> was different from 2.7.x.  egcs 1.1 was different from egcs 1.0.
> gcc 2.95 was different from egcs 1.1.  Red Hat's "2.96" is

In my experience egcs 1.0 / egcs 1.1 / 2.95 were not really incompatible
for "basic C++" (no exceptions, no RTTI, no STL, minor use of the C++
standard library, no multiple inheritance). Most C++ programs (e.g. Qt) 
only seem to use a similar subset so it wasn't that a big a problem 
to e.g. link an older Qt to a egcs 1.1 program. IIRC e.g. the changes
between 1.1 and 2.95 were only in some rather obscure parts.

With gcc 3 that will change though because the vtables are completely 
different and I guess a better migration strategy would make sense.

At least please make sure that it fails at link time, not with strange
crashes.

-Andi