From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7702 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: trouble spots for atomic access Date: Tue, 19 May 2015 15:57:00 +0200 Message-ID: <1432043820.27572.26.camel@inria.fr> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-ybwYPz7CMP8TkHRnvl5F" X-Trace: ger.gmane.org 1432043845 31261 80.91.229.3 (19 May 2015 13:57:25 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 19 May 2015 13:57:25 +0000 (UTC) To: musl Original-X-From: musl-return-7714-gllmg-musl=m.gmane.org@lists.openwall.com Tue May 19 15:57:24 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.12.9-1+b1 Xref: news.gmane.org gmane.linux.lib.musl.general:7702 Archived-At: --=-ybwYPz7CMP8TkHRnvl5F Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello, by forcing the compiler to detect consistency checks for=20 atomics as I mentioned earlier, I detected 5 trouble spots. The first four are relatively clear: - a_and and a_or interfaces on i386 and friends are not consistent with the remaining archs. They have `volatile void*` for the arguments and then do a gratuitous cast to `int*`. As far as I can see just using `volatile int*` as for the other archs works fine. - pthread_once_t should always be volatile - pthread_spinlock_t should always be volatile - pthread_barrier needs atomic increment The fifth troubles me a bit. It concerns __timedwait and __timedwait_cp. These both are mostly used with a first argument addr that is atomic. This makes sense, since addr then is passed to a call to futex, which internally might do some atomic operations. Now there is one call that doesn't pass something that is otherwise seen as atomic, namely line 14 in pthread_join.c. It reads as while ((tmp =3D t->tid)) __timedwait_cp(&t->tid, tmp, 0, 0, 0); So is the task id here to be seen as atomic, or not? Will updates to that field that are not atomic (and maybe optimized in some sort) be able to mess up the futex call? Thanks Jens --=20 :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt :: --=-ybwYPz7CMP8TkHRnvl5F Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEABECAAYFAlVbQSwACgkQD9PoadrVN+I6RgCfURcPQ/YzBCR0xlSJgz2j+oIW 6QEAnjDAUxrJ5UGMBsvknoQDkmZBD8mh =uDBy -----END PGP SIGNATURE----- --=-ybwYPz7CMP8TkHRnvl5F--