Exceptions across binary boundary

Question

I know, this question has been asked quite some times, however I can't find a solution for my problem.

I have the following situation:

   A
  / \
 /   \
B <-- C

• A is a shared library which contains the class EException
• B and C link against A
• C is a shared library as well
• B dynamically loads C at runtime

At some point C throws an instance of EException:

void doSometing() {
    throw EException("test-message");
}

in B I would like to catch this exception:

try {
    doSomething();
} catch (const EException& ex) {
    // Not reached
} catch (...) {
    // Not reached
}

but as mentioned in the code, neither one of the catch clauses get called. Instead the thread, this code is executed in, gets aborted.

I tried the following things:

• The visibility attribute of EException is set to "default" when compiling A
• The EException header file contains declarations only
• I am using the linker option -fvisibility=hidden in A, B and C
• I am using the linker option -E in C

Using nm I get for A:

0000000000066260 T EException::EException(QString const&)
0000000000066306 T EException::EException(EException const&)
00000000000661d0 T EException::EException() 
0000000000066260 T EException::EException(QString const&) 
0000000000066306 T EException::EException(EException const&) 
00000000000661d0 T EException::EException() 
00000000000664de T EException::~EException()
000000000006641e T EException::~EException() 
000000000006641e T EException::~EException() 
00000000000663b6 T EException::operator=(EException const&)
<...>
000000000028de40 V typeinfo for EException
000000000028dd80 V typeinfo for EException*
000000000007342b V typeinfo name for EException
0000000000072ab7 V typeinfo name for EException*
000000000028de00 V vtable for EException

for B:

U EException::EException(QString const&)
U EException::~EException()
<...>
0000000000726f60 V typeinfo for EException

and for C:

U EException::EException(QString const&)
U EException::~EException()
<...>
U typeinfo for EException

Could the problem be, that B uses its own typeinfo of EException, while C uses the one provided by A? How would I fix this?

My environment:

• gcc 4.6.3 on x86_64-linux-gnu
• using Qt

Thank you for your help!

Answer 1

I had similar problems with gcc < 4.5 with RTTI symbols used across shared library boundaries, but not with gcc 4.6. However, you might still find the following information useful.

As already mentioned, the vtable (containing an entry to the typeinfo object) for EException seems to be duplicated in some translation units which was definitely a problem with gcc < 4.5 (well, it is an issue of libsupc++, as far as I know, not merging the type_info objects). Anchoring the vtable of EException by defining a virtual out-of-line destructor (it must be the first virtual function declaration in the header) in A did the trick for me.

Posting the complete header file for EException might also be helpful.