[MAJOR BUG] g++ 2.95.x generates invalid code for KDE 3.3.0

[Thiago Macieira]

Hello,

I hope I am not making a fool of myself, if this turns out to be something 
else than I've determined.

But anyways, this is a serious problem. 

The attached program is a simple test-case showing the problem. It mimics 
the hierarchy leading to KNetwork::KStreamSocket and, thence, to 
KNetwork::KBufferedSocket. The latter is being used already in Kopete code 
as released with KDE 3.3.0, as well as Konversation.

As reported in bug #87548, Kopete crashes as it tries to connect. Valgrind 
log shows the function KNetwork::KSocketBase::mutex() returns 0x10 instead 
of the proper address for a QMutex. That can only happen if KSocketBase's d 
pointer is NULL -- which again isn't possible since it is initialised in 
KSocketBase's only constructor.

Suspecting compiler bug, I created the attached code that mimics the real 
inheritance hierarchy (which is quite complex, including a virtual base). 
The code crashes as well, with the exact same symptom as that reported in 
bug #87548. What's more, g++ 3.3- and 3.4-compiled code does *not* crash. I 
tracked the bug down to a pointer adjustment for 'this', as I had suspected 
in the bug report.

After this lengthy explanation, here goes:

1) can anyone else confirm my conclusion (i.e., that it is a compiler bug)?

2) if not so, where's the error?

3) if so, what do we do now?
Kopete and Konversation, as released, do not work when compiled with g++ 
2.95.4. Current libkdecore therefore contains faulty code.

3.a) Is there a more updated version than g++ 2.95.4, which fixes the bug?

3.b) If not, Is there a way to modify the code so as not to trigger this g++ 
bug?
If this involves redesigning the hierarchy, it'll have to be inside 
#if/#endif.

3.c) If not, we will have to drop compatibility for g++ 2.95.x a lot sooner 
than expected.

-- 
  Thiago Macieira  -  Registered Linux user #65028
   thiago (AT) macieira (DOT) info
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