Date: Thu, 5 Oct 2006 23:50:27 GMT From: Alexander Kabaev <kabaev@gmail.com> To: freebsd-threads@FreeBSD.org Subject: Re: threads/103975: Implicit loading/unloading of libpthread.so may crash user processes Message-ID: <200610052350.k95NoRVM021255@freefall.freebsd.org>
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The following reply was made to PR threads/103975; it has been noted by GNATS. From: Alexander Kabaev <kabaev@gmail.com> To: John Baldwin <john@baldwin.cx> Cc: freebsd-threads@freebsd.org, Takahiro <takahiro.kurosawa@gmail.com>, freebsd-gnats-submit@freebsd.org, KUROSAWA@freebsd.org Subject: Re: threads/103975: Implicit loading/unloading of libpthread.so may crash user processes Date: Thu, 5 Oct 2006 19:47:56 -0400 --Sig_olRQb9w73LRMGWxv5Pd0njU Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 5 Oct 2006 09:06:20 -0400 John Baldwin <john@baldwin.cx> wrote: >=20 > Actually, I wonder if it should be allowed to unload at all. On 4.x > at work we ran into an issue with the linuxthreads library loading, > setting _is_threaded, then unloading with a malloc() occurring during > the destructors resolving a _spinlock() weak symbol, then after the > libraries were completely unloaded, the next malloc() blew up when > _spinlock() pointed off into space. Hmm, this specific condition is > handled I think since __isthreaded in 6.x libpthread isn't set until > you do pthread_create() which at that point means a symbol is > resolved, and the library won't be unloaded (I think). Hmm, maybe > not since that doesn't guarantee that libc depends on libpthread > (that is what keeps it from being unloaded IIRC). So, maybe when the > library sets __isthreaded it should call one of the libc functions > (like malloc) to force one of the weak symbols to be resolved so it > isn't unloaded. >=20 > > To fix the problem, a function that has __attribute__((destructor)) > > in libpthread should probably be implemented in order to recover > > the initial state before unloading. >=20 > I'm not sure you can recover the state actually, hence why I think > maybe we should make it so that libpthread doesn't unload once it has > been loaded. >=20 > --=20 > John Baldwin Linux does not allow pthread library to be unloaded presumably because of reasons like this. From readelf -a /compat/linux/lib/libpthread.so.0: 0x6ffffffb (FLAGS_1) Flags: NODELETE INITFIRST Infortunately, rtld does not implement NODELETE and INITFIRST. Both are addressed in my patch that I am yet to commit. --=20 Alexander Kabaev --Sig_olRQb9w73LRMGWxv5Pd0njU Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQFFJZmvQ6z1jMm+XZYRAkaKAJ9/bV9FU6UgIVbE7QZAhBLKD7rg5ACeMjGr 1DVtUSKdDtw5N2PFrbduuwc= =+av7 -----END PGP SIGNATURE----- --Sig_olRQb9w73LRMGWxv5Pd0njU--
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