[ITK-dev] Workaround for dynamic_cast on Mac OSX

[Isaiah Norton]

On Mon, Nov 14, 2016 at 8:47 PM, Sean McBride <sean at rogue-research.com>
wrote:

> On Thu, 10 Nov 2016 14:11:59 -0500, Marcus D. Hanwell said:
>
> >I would be interested in further details on which case or cases are
> >causing dynamic_cast to fail, and why using consistent symbol
> >visibility in the interfaces is not feasible/possible.
>
> I'm not really following this issue, but...
>
> Is this really a Mac OS X issue, or is it being conflated with clang?
> That is, does the issue happen with clang on linux for example?  Is it only
> Apple's fork or clang, or the open source one too?  Does it happen with gcc
> on Mac OS X?  etc.
>

The compiler ABI rules and behavior have not changed. What has changed is
that OS X linker fallbacks have been removed [1], and Slicer (and perhaps
ITK itself by default, I haven't spelunked the log) have set the default
symbol visibility to hidden, which means that (now-hidden) type_info
symbols are not coalesced across compilation unit boundaries.

I would recommend this summary of the issue from a libreoffice commit
message [2], as well as the summary linked in a previous message [3].
Recent libstdc++ have reinstated a strcmp fallback [4], so the issue is
unlikely to be encountered on most Linux distributions.


[1] On OS X, my understanding is that libc++ (cxxabi) was compiled with
"_LIBCXX_DYNAMIC_FALLBACK" until OS X 10.11, which causes a fallback to
strcmp comparison of the type_info name (10.11 still contains a program
name-based fallback for two Adobe products that Apple could not reasonably
break).
[2]
https://lists.freedesktop.org/archives/libreoffice-commits/2015-January/091572.html
[3] http://www.russellmcc.com/posts/2013-08-03-rtti.html
[4] https://gcc.gnu.org/ml/gcc-patches/2009-07/msg01239.html


>
> Cheers,
>
> --
> ____________________________________________________________
> Sean McBride, B. Eng                 sean at rogue-research.com
> Rogue Research                        www.rogue-research.com
> Mac Software Developer              Montréal, Québec, Canada
>
>
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