symbols visibility + inline virtual desctructors => dynamic_cast<DOMElement>
failure in user code
-------------------------------------------------------------------------------------------------
Key: XERCESC-1550
URL: http://issues.apache.org/jira/browse/XERCESC-1550
Project: Xerces-C++
Type: Bug
Components: Build
Versions: 2.7.0
Environment: OSX GCC 4.0
Reporter: Miklos Fazekas
We have a code like this:
XMLTest.cpp:
DOMNodeList* nodes = doc->getElementsByTagName(L("TABLE"));
if ( int i=nodes->getLength() == 1 )
{
DOMNode* att_node = nodes->item(0);
DOMElement* att_element = dynamic_cast<DOMElement*>(att_node);
printf ("Element:%d\n", att_element);
}
On OSX when we use symbols visibility attrbiutes, the dynamic_cast returns 0.
The issue seems to be the following:
1. There is two RTTI entries generated for the class. [According to C++ the
RTTI is generated at the place of the implementation of first virtual function.]
2. One RTTI entry is marked with visibility("hidden") and found in usercode.
The other one is marked with visibility("default").
3. It seems that if there's an RTTI marked as "hidden" the dynamic_cast can't
work. Quote from http://gcc.gnu.org/wiki/Visibility :
" Symbol visibility is "default" by default but if it encounters just one
definition with it hidden - just one - that typeinfo symbol becomes permanently
hidden (remember the C++ standard's ODR - one definition rule). "
class CDOM_EXPORT DOMElement: public DOMNode {
public:
...
virtual ~DOMElement() {};
...
}
Possible fixes:
a.) Implement the destructor in a C++ file, compiled into xerces c++. This
would avoid multiple RTTI .
b.) set CDOM_EXPORT to visibility("default") even when it's used from the user
code.
We choose a.) as it seems to be a nicer solution.
[By the way i do not see why symbols visibility of GCC should work that crappy
with dynamic_cast, but there's not too much i could do there.]
References:
http://gcc.gnu.org/wiki/Visibility
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