Re: dlopen(), atexit() SEGV in NetBSD

[Byron Servies <bservies%pacang.com@localhost>]

On Jul 8, 2009, at 2:03 AM, Channa wrote:

> Hi,
>
> 2009/7/8 Thor Lancelot Simon <tls%panix.com@localhost>:
> > On Wed, Jul 08, 2009 at 01:10:50PM +0530, Channa wrote:
> > > Hi,
> > > I am facing some issue with atexit handler in NetBSD.
> > > The procedure to reproduce the problem i have explained below:
> > [...]
> > > Because after a dlopened library that calls atexit() the  
> > > libexample.so
> > > is dlclosed, an executable can't
> > > access a registered handler in the library and causes SEGV.
> >
> > Well, of course it does.  The documentation is quite clear:
> >
> >     dlclose() unlinks and removes the object referred to by handle  
> > from the
> >     process address space.
>
> Yes but while calling fini functions in the dynamic linker , the
> __cxa_finalize is called during that time the atexit() handlers
> registered in the library can be called?
>
> Or is there a method to unregister the atexit() handlers registered
> while dlclose()?

There is not.

This is why it is normal to use some sort of session handle when  
designing libraries that can be loaded and unloaded instead of library- 
internal state that needs to be cleaned up with an exit handler.   
Something like:

        int mylib_open (void **handle, args);
        int mylib_close (void *handle);
        int mylib_funcA(void *handle, .args);

and so on.  It can easily be argued that this is a failing in libc  
(and I believe it is), but those arguments are pointless: it is the  
way things are on all unix-like OS's and does not appear to be  
changing any time soon.

HTH,

Byron