From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7654 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: Deduplicating atomics written in terms of CAS Date: Sun, 17 May 2015 09:37:19 +0200 Message-ID: <1431848239.11628.3.camel@inria.fr> References: <20150517045536.GA25046@brightrain.aerifal.cx> <20150517061430.GL17573@brightrain.aerifal.cx> 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="=-gvCvTaqNnuKtpMYhQrxY" X-Trace: ger.gmane.org 1431848257 25943 80.91.229.3 (17 May 2015 07:37:37 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 17 May 2015 07:37:37 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7666-gllmg-musl=m.gmane.org@lists.openwall.com Sun May 17 09:37:37 2015 Return-path: Envelope-to: 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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:7654 Archived-At: --=-gvCvTaqNnuKtpMYhQrxY Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Am Sonntag, den 17.05.2015, 02:14 -0400 schrieb Rich Felker: > - a_and_64/a_or_64 (malloc only; these are misnamed too) I should have checked the use before my last mail. They are definitively misnamed. Both uses of them look ok concerning atomicity, only one of the a_and or a_or calls triggers. The only object (mal.binmap) to which this is applied is in fact volatile, so it must actually be reloaded all the time it is used. But in line 352 the code uses another assumption, then, that 64 bit loads always are atomic. I don't see why this should hold in general. We already have a similar assumption for 32 bit int all over the place, and I am not too happy with such "silent" assumption. For 64 bit, this assumption looks wrong to me. I would be much happier by using explicit atomic types and atomic load functions or macros everywhere. For normal builds these could be dummy types made to resolve to the actual code that we have, now. But this would allow to have hardening builds, that check for consistency of all atomic accesses. 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 :: --=-gvCvTaqNnuKtpMYhQrxY 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 iEYEABECAAYFAlVYRS8ACgkQD9PoadrVN+KPBwCfcKG41PY91uU84MFVp81gVmH2 2g8AoICgCpULX9ZrmNCTmiDTeYCqwTie =6wUX -----END PGP SIGNATURE----- --=-gvCvTaqNnuKtpMYhQrxY--