c++/3993: dynamic_cast<>() fails in simple test case w/ dynamic loading

[abramsh at acm dot org]

>Number:         3993
>Category:       c++
>Synopsis:       dynamic_cast<>() fails in simple test case w/ dynamic loading
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Aug 10 22:56:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Howard Abrams
>Release:        gcc version 3.0
>Organization:
>Environment:
Linux blah.voidstar.org 2.4.2-2 #1 Sun Apr 8 20:41:30 EDT 2001 i686 unknown
on i686-pc-linux-gnu
>Description:
When using "dlopen" to load a library, gcc seems to NOT merge
type_info symbols from the library. The result is dynamic
casts fail, as well as type_info::operator== for object that
they should not fail on. Below is simple source to reproduce
this problem.

Also note that on version 2.96 (Red Hat Linux 7.1 2.96-81)
(I know, you don't support that... ) this works fine.

>How-To-Repeat:
To reproduce this there are three small files. Compile with
the following two lines:

g++ -g -o test2.so -shared test2.cpp
g++ -g -o testcase test.cpp -ldl


The files are as follows:

classb.h
========
struct a
{
        virtual ~a() {}
};

struct b : public a
{
        virtual ~b() {}
};

test2.cpp
=========
#include <typeinfo>

#include "classb.h"

extern "C" {

a *getnewb() { return new b; }
const std::type_info &gettypeb() { return typeid( b ); }

}

test.cpp
========
#include <dlfcn.h>
#include <typeinfo>
#include <cassert>

#include "classb.h"

int main()
{
        a *(*func)(void);
        const std::type_info &(*type)(void);

        void *handle = dlopen( "test2.so", RTLD_NOW );
        func = (a *(*)(void))dlsym( handle, "getnewb" );
        type = (const std::type_info &(*)(void))dlsym( handle, "gettypeb" );

        a *a_ptr = (*func)();
        const std::type_info &t = (*type)();

        assert ( dynamic_cast<b*>( a_ptr ) );
        assert ( typeid( b ) == t );
}
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: