From owner-svn-src-all@freebsd.org Tue Dec 29 23:22:53 2015 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 07978A5461C; Tue, 29 Dec 2015 23:22:53 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id DCA6419C2; Tue, 29 Dec 2015 23:22:52 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from ralph.baldwin.cx (c-73-231-226-104.hsd1.ca.comcast.net [73.231.226.104]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 0CA95B93E; Tue, 29 Dec 2015 18:22:51 -0500 (EST) From: John Baldwin To: Ian Lepore Cc: Warner Losh , src-committers , svn-src-head@freebsd.org, svn-src-all@freebsd.org, Warner Losh Subject: Re: svn commit: r292809 - head/lib/libc/stdio Date: Tue, 29 Dec 2015 15:22:32 -0800 Message-ID: <4400685.QN9T0cbN9C@ralph.baldwin.cx> User-Agent: KMail/4.14.3 (FreeBSD/10.2-STABLE; KDE/4.14.3; amd64; ; ) In-Reply-To: <1451429489.1369.35.camel@freebsd.org> References: <201512272304.tBRN4C5D034464@repo.freebsd.org> <2345870.SHMMVrpc1D@ralph.baldwin.cx> <1451429489.1369.35.camel@freebsd.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Tue, 29 Dec 2015 18:22:51 -0500 (EST) X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 29 Dec 2015 23:22:53 -0000 On Tuesday, December 29, 2015 03:51:29 PM Ian Lepore wrote: > On Tue, 2015-12-29 at 11:37 -0800, John Baldwin wrote: > > On Monday, December 28, 2015 01:01:26 PM Warner Losh wrote: > > > I'll look at that, but I don't think posix_memalign is the right > > > way to go. > > > The alignment of FILE is more strict than posix_memalign will > > > return. Ian's > > > idea of __alignof__ is the way to go. We allocate them in one block > > > on > > > purpose for performance, and posix_memalign would be a one at a > > > time affair. > > > > posix_memalign gives you whatever alignment you ask for. Using > > __alignof__ > > to determine the alignment instead of hardcoding sizeof(int64_t) > > would > > certainly be an improvement. If you move the glue after the FILE > > objects > > then you can use posix_memalign() directly as so: > > > > void *mem; > > int error; > > > > error = posix_memalign(&mem, MAX(ALIGNBYTES, > > __alignof__(mbstate_t)), > > n * sizeof(FILE) + sizeof(*g)); > > if (error) > > return (NULL); > > p = (FILE *)mem; > > g = (struct glue *)(p + n); > > g->next = NULL; > > g->niobs = n; > > g->iobs = p; > > ... > > > > (This presumes that the requested alignment of 'struct glue' is less > > than > > the alignment needed by FILE which should be true.) > > > > If there's going to be an assumption that __alignof__(glue) <= > __alignof__(FILE), it might be nice to have a static_assert() of that > to prevent a future time bomb similar to the one that exploded on arm > when it turned out the opposite assumption was wrong. A static assert seems sensible, yes. -- John Baldwin