Re: dlopen(), atexit() crash on FreeBSD (testcase included)

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On Mon, 31 Dec 2007 19:01:23 -0800
Tim Kientzle <[e-mail]> wrote:

> Markus Hoenicka wrote:
> > Alexander Kabaev writes:
> >  > As designed. atexit should not be used by shared objects that do
> >  > not expect themselves to live until actual exit() happens. ELF
> >  > provides proper _init/_fini sections to support shared object
> >  > initialization/destruction.
> >  >=20
> >=20
> > That is, the only real solution to this problem is to convince the
> > Firebird folks to remove their atexit() calls from the client
> > libraries?
>=20
> I suspect they never considered that their dynamic library
> might be used via dlopen()/dlclose().  The real question is
> whether they're interesting in supporting this model.
> If the Firebird folks aren't interested in having their
> library be accessible in that fashion, then you have
> little choice but to simply forgo unloading this particular
> library.
>=20
> It's a bit unfortunate that there is no standard way
> to remove an atexit() registration.  It would probably
> be easier to convince the Firebird folks to remove the
> registration as part of their cleanup routines (and
> you could then invoke those cleanup routines manually
> for that case).
>=20
> > Also, I'm wondering how other OSes handle this. I don't see this
> > code crash on Linux, contrary to its design as you say.
>=20
> I would be curious to see the results of running your
> sample program (with lots of extra fprint(stderr...)
> calls, of course) on Linux to see whether it calls the
> registered exit function at dlclose time or never.
>=20

Linux pulls hidden atexit symbol into every binary that uses it by
means of linking in libc_nonshared.a into every glibc consumer. Having
local function allows for reliable determination of who has called the
atexit function. Linux calls atexit entries at object unload time.

Solaris implements a libc callback from ld.so.1 to cleanup dangling
pointers from objects being unloaded. This resets sigaction entries,
atfork and atexit callbacks. Solaris calls atexit callback when removing
it too.

I guess we better follow the suit, if anyone wants to that. I prefer
Solaris approach myself, but see the reason for Linux one too.
--=20
Alexander Kabaev

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