From owner-freebsd-current@FreeBSD.ORG Wed Feb 18 22:45:59 2009 Return-Path: Delivered-To: current@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B10E51065676; Wed, 18 Feb 2009 22:45:59 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from harmony.bsdimp.com (bsdimp.com [199.45.160.85]) by mx1.freebsd.org (Postfix) with ESMTP id 6D7238FC1A; Wed, 18 Feb 2009 22:45:59 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from localhost (localhost [127.0.0.1]) by harmony.bsdimp.com (8.14.2/8.14.1) with ESMTP id n1IMi5Yb062162; Wed, 18 Feb 2009 15:44:05 -0700 (MST) (envelope-from imp@bsdimp.com) Date: Wed, 18 Feb 2009 15:44:14 -0700 (MST) Message-Id: <20090218.154414.-1283372409.imp@bsdimp.com> To: bms@incunabulum.net From: "M. Warner Losh" In-Reply-To: <499C8396.2020000@incunabulum.net> References: <20090218.120514.831271136.imp@bsdimp.com> <499C8396.2020000@incunabulum.net> X-Mailer: Mew version 5.2 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: xcllnt@mac.com, mips@FreeBSD.org, tinderbox@FreeBSD.org, current@FreeBSD.org Subject: Re: [head tinderbox] failure on mips/mips X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 18 Feb 2009 22:46:01 -0000 In message: <499C8396.2020000@incunabulum.net> Bruce Simpson writes: : M. Warner Losh wrote: : > ... : > : The point being that programmers *do* code with certain : > : assumptions and as soon as those assumptions don't hold on : > : a platform, you end up worse off. My thoughts for MIPS n32 : > : are to make it behave like any "normal" 32-bit strong- : > : alignment platform to avoid 1) a large number of runtime : > : alignment faults -- which are a bigger performance bottleneck : > : than forcing 64-bit integrals to be accessed with 2 32-bit : > : accesses : > : : FWIW, Linux use a type-length-value protocol for the netlink routing : socket, so alignment issues of this kind are shifted around (forgive the : pun). FreeBSD does too for the most part, but it is only at the inter-message level, not intra-message. : > It also turns out that in this case, a simple (void *) is safe and : > causes no issues because that time_t isn't accessed... It does give : > one time to pause and think about it. : > : : Yes, the void * cast works around the issue for now, but doesn't offer : any guarantees that we are doing the right thing on strict alignment : architectures. : If the alignment *is* invalid, then we take the hit. Right. The compiler doesn't check it, but I just did and things are fine given the fields accessed. But its that last bit that's the problem... I also have changed the offending line in my tree to be u_long instead of time_t since that is a better match to the protocol, and also gives us 168 years of uptime before there's an issue. Warner