[ITK-dev] Workaround for dynamic_cast on Mac OSX

[Isaiah Norton]

Hi Matt,


> Here are the tests:
>   http://review.source.kitware.com/#/c/21755/

where reasonable export specification is added in both ITK and the
> client libraries. But, dynamic_cast fails on OSX:


The export changes in this merge request don't seem to be related to the
casts that are failing. A small change [1] allows all of the tests to pass.
Of course, many more export annotations would be required for general
applicability.

There is a compiler option that could potentially address the issue
"-fvisibility-ms-compat" -- see [2]. As mentioned on that page, these RTTI
type_info issues *also break exception handling*, so simply changing all of
the ITK `dynamic_cast` uses to a custom implementation will not fully
address the issue (I have encountered this a number of times in Slicer: ITK
exceptions thrown by dynamic libraries are incorrectly identified).

Alternatively, if there is concern about symbol bloat (I've seen some
threads to that effect related to SimpleITK) then a linker script could be
used to export all `_ZTN*` symbols.

Best,
Isaiah

[1]
```
diff --git a/Modules/Core/Common/include/itkImage.h
b/Modules/Core/Common/include/itkImage.h
index 2e601c2..9592957 100644
--- a/Modules/Core/Common/include/itkImage.h
+++ b/Modules/Core/Common/include/itkImage.h
@@ -72,7 +72,7 @@ namespace itk
  * \endwiki
  */
 template< typename TPixel, unsigned int VImageDimension = 2 >
-class Image:public ImageBase< VImageDimension >
+class ITK_ABI_EXPORT Image:public ImageBase< VImageDimension >
 {
 public:
   /** Standard class typedefs */
```

[2]
https://developer.apple.com/library/content/technotes/tn2185/_index.html#//apple_ref/doc/uid/DTS10004200-CH1-SUBSECTION2
and
https://developer.apple.com/library/content/technotes/tn2185/_index.html#//apple_ref/doc/uid/DTS10004200-CH1-SUBSECTION6


On Sat, Nov 12, 2016 at 12:01 AM, Matt McCormick <matt.mccormick at kitware.com
> wrote:

> Here are the tests:
>
>   http://review.source.kitware.com/#/c/21755/
>
> where reasonable export specification is added in both ITK and the
> client libraries. But, dynamic_cast fails on OSX:
>
>   https://open.cdash.org/testDetails.php?test=499059765&build=4637669
>
>
> Matt
>
> On Thu, Nov 10, 2016 at 3:21 PM, Johnson, Hans J <hans-johnson at uiowa.edu>
> wrote:
> > I agree with Marcus.  At least until it is very clear that not using
> dynamic_cast is the only solution to a broken compiler, I am very weary of
> “doing what works today”.
> >
> > Hans
> >
> >
> > --
> >
> >
> > On 11/10/16, 1:11 PM, "Insight-developers on behalf of Marcus D.
> Hanwell" <insight-developers-bounces at itk.org on behalf of
> marcus.hanwell at kitware.com> wrote:
> >
> >     On Tue, Nov 8, 2016 at 5:01 PM, Matt McCormick
> >     <matt.mccormick at kitware.com> wrote:
> >     > Hi folks,
> >     >
> >     > As we have wrestled with in Slicer, along with other applications
> >     > where ITK is used in multiple shared libraries, dynamic_cast can
> fail
> >     > on Mac OSX.
> >     >
> >     > I summarized the cause of the problem and steps for the proposed
> solution here:
> >     >
> >     >   https://issues.itk.org/jira/browse/ITK-3490
> >     >
> >     > Feedback is welcome. The effort is targeted for the ITK 4.11.0
> release.
> >     >
> >     From the issue it is not clear to me why you can't fix the symbol
> >     visibility issues, or which of these cases it causing the breakage.
> >     Reading the linked blog post it seems like Apple/Clang is doing the
> >     right thing, and C++ libraries must be careful to use consistent
> >     symbol visibility.
> >
> >     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.
> >
> >     Thanks,
> >
> >     Marcus
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