Symbol visibility

[DÃniel Varga <vargad88 at gmail dot com>]

Hi,
I try to understand symbol visibility better. The GCC Wiki
(http://gcc.gnu.org/wiki/Visibility) has a section about "Problems
with C++ exceptions". According to GCC Wiki it is possible the have
_runtime_ error because of not exported exceptions. Runtime errors
without compile time error/warning is quite dangerous so I tried to
understand the problem better. I made some experiments but I still
can't reproduce it. Any ideas how to reproduce the problem?

The Wiki mentions three library using each other, so I made three small library.

I run the following commands:

Exception class without vtable (works as expected):

    make
    ./dsouser

Exception class with vtable but it does not exported (does not even compile):

    make HAS_VIRTUAL=1

Exception class exported vtable (works as expected):

    make HAS_VIRTUAL=1 EXCEPTION_VISIBLE=1
    ./dsouser

Makefile:

    CXX=g++-4.7.1
    CFLAGS=-ggdb -O0 -fvisibility=hidden
    ifdef EXCEPTION_VISIBLE
      CFLAGS+=-DEXCEPTION_VISIBLE
    endif
    ifdef HAS_VIRTUAL
      CFLAGS+=-DHAS_VIRTUAL
    endif
    all: dsouser

    libmydso.so: mydso.cpp mydso.h
	    $(CXX) $(CFLAGS) -fPIC -shared -Wl,-soname,$@ -o $@ $<

    libmydso2.so: mydso2.cpp mydso.h mydso2.h libmydso.so
	    $(CXX) $(CFLAGS) -L.  -fPIC -shared -Wl,-soname,$@ -o $@ $< -lmydso

    libmydso3.so: mydso3.cpp mydso.h mydso2.h mydso3.h libmydso2.so
	    $(CXX) $(CFLAGS) -L.  -fPIC -shared -Wl,-soname,$@ -o $@ $<
-lmydso -lmydso2

    dsouser: dsouser.cpp libmydso3.so
	    $(CXX) $< $(CFLAGS) -L. -o $@ -lmydso -lmydso2 -lmydso3

    clean:
	    rm -f *.so *.o dsouser

    .PHONY: all clean

mydso.h:

    #ifndef DSO_H_INCLUDED
    #define DSO_H_INCLUDED
    #include <exception>
    #define SYMBOL_VISIBLE __attribute__ ((visibility ("default")))
    namespace dso
    {
      class
    #ifdef EXCEPTION_VISIBLE
        SYMBOL_VISIBLE
    #endif
        MyException : public std::exception
      {
      public:
    #ifdef HAS_VIRTUAL
        virtual void dump();
    #endif
        void SYMBOL_VISIBLE foo();
      };
    }
    #endif

mydso.cpp:

    #include <iostream>
    #include "mydso.h"
    namespace dso
    {

    #ifdef HAS_VIRTUAL
    void MyException::dump()
    {
    }
    #endif

    void MyException::foo()
    {
    #ifdef HAS_VIRTUAL
      dump();
    #endif
    }

    }

mydso2.h:

    #ifndef DSO2_H_INCLUDED
    #define DSO2_H_INCLUDED
    #define SYMBOL_VISIBLE __attribute__ ((visibility ("default")))
    namespace dso2
    {
      void SYMBOL_VISIBLE some_func();
    }
    #endif

mydso2.cpp:

    #include <iostream>
    #include "mydso.h"
    #include "mydso2.h"
    namespace dso2
    {
      void some_func()
      {
        throw dso::MyException();
      }
    }

mydso3.h:

    #ifndef DSO3_H_INCLUDED
    #define DSO3_H_INCLUDED
    #define SYMBOL_VISIBLE __attribute__ ((visibility ("default")))
    namespace dso3
    {
      void SYMBOL_VISIBLE some_func();
    }
    #endif

mydso3.cpp:

    #include <iostream>

    #include "mydso2.h"
    #include "mydso3.h"

    #include <iostream>

    namespace dso3
    {

      void some_func()
      {
        try
        {
          dso2::some_func();
        } catch (std::exception e)
        {
          std::cout << "Got exception\n";
        }
      }

    }

dsouser.cpp:

    #include <iostream>
    #include "mydso3.h"
    int main()
    {
      dso3::some_func();
      return 0;
    }


Thanks,
Dani