c++/2786: erroneous pointer returned by dynamic cast

[laurent.morel@isr.thomson-csf.com]

>Number:         2786
>Category:       c++
>Synopsis:       erroneous pointer returned by dynamic cast
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 08 23:46:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Laurent Morel
>Release:        unknown-1.0
>Organization:
>Environment:
tmp>cat /etc/mandrake-release
Linux Mandrake release 7.2 (Odyssey) for i586 
tmp>gcc -v
Reading specs from /usr/lib/gcc-lib/i586-mandrake-linux/2.95.3/specs
gcc version 2.95.3 19991030 (prerelease)
>Description:
I'm using g++ on GNU/Linux, Mandrake 7.2 distribution.
I've got a problem with a dynamic_cast operator call.

In the case that the result is not NULL, I have a result pointer 
shifted by a 4 bytes offset compared to the originally
allocated object.
It occurs when one of the ancestors classes has no virtual function.
>How-To-Repeat:
cf attached file
>Fix:
make sure that all ancestor classes has at least a
virtual function, for instance : declare all destructors
as virtual
>Release-Note:
>Audit-Trail:
>Unformatted:
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