Hi all,
Thanks for the pointers to the source of the problem. Indeed it is related to
symbol visibility. For reference, I had to change Xcode's default settings as
follows:
GCC_SYMBOLS_PRIVATE_EXTERN = NO (Setting name in Xcode is "Symbols
Hidden by Default")
GCC_INLINES_ARE_PRIVATE_EXTERN = NO (Setting name in Xcode is "Inline
Methods Hidden")
and finally things work as expected on OS X. In my case I needed both for the
fix. For reference, this is with Clang/LLVM 4.2.1.
A thread on the Clang/LLVM mailing list indicates that there is a warning flag
which can be activated to alert to these kind of issues:
-Wweak-vtables
With the default Xcode settings (hiding symbols not explicitly exported) and
this warning activated, I got a lot of warnings like:
'ResetAnimationNodesVisitor' has no out-of-line virtual method
definitions; its vtable will be emitted in every translation unit
This is in spite of it clearly having a virtual method -- it would be more
helpful if the weak vtables check could have told me that the vtable was being
discarded by the symbol hiding, rather than not being created at all. A missing
(or weak) vtable would certainly prevent RTTI from working correctly.
Many thanks for the help with a rather obscure problem.
Regards,
Phil.
On 8/02/2013, at 8:40 AM, Robert Osfield <[email protected]> wrote:
> Hi Stephan,
>
> Thanks for the explanation, you learn something new everyday :-)
>
> Incompatibility like this I'd personally put down as a bug in the
> design/implementation rather than a "feature". I am curious why we
> haven't seen this particular issue more often. If the visibility of
> classes is hidden by default then we should be seeing these issues
> between OSG libs and applications all the time - for instance the code
> almost identical that that Philip is using is used in osgPresentation
> with it doing dynamic_cast<> on objects provided by the core osg lib.
>
> The question next is really what to do about the issue. Just document
> the bug and it's workaround - changing symbol visibility via compiler
> options or do we change the OSG itself so it by default doesn't hide
> visibility of symbols.
>
> Robert.
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