From owner-freebsd-current@FreeBSD.ORG Thu Nov 1 07:34:06 2007 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3150F16A418 for ; Thu, 1 Nov 2007 07:34:06 +0000 (UTC) (envelope-from yaraghchi@gmail.com) Received: from nz-out-0506.google.com (nz-out-0506.google.com [64.233.162.226]) by mx1.freebsd.org (Postfix) with ESMTP id E50A613C49D for ; Thu, 1 Nov 2007 07:34:05 +0000 (UTC) (envelope-from yaraghchi@gmail.com) Received: by nz-out-0506.google.com with SMTP id l8so307287nzf for ; Thu, 01 Nov 2007 00:34:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; bh=i9krYrGRkQkFVkWgmw89LVQpe7wVa41QwpI4gpkQ5BU=; b=ADMBX3PQWa8pMMapJPz7WOdPHvghPq5QeH/2bigD4r5+l0qrc0vGJUPtq83emSDspgJm6iO/LNTudG8xRnreAlwklcv6qNH2alq8qLaZEdZihb+RxiIos5U2L2nsCiCZev6mQpuj4QXmw1sPbcIFvHXHLlMmDUFehDSJTGSLJIE= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=Un34e9dkG2OUsvLqstj0gIsQ/hnf1A5uAbQ1lgp5ImUk6eSBVfMOrd6m7IQ4+Kxl3qNDuZEsJTQcsFZ9GTqHnuwhhJMMbmVYMdIKjdsvs4L1V6i0UUsBN9vlgmrpp99bmKDjdO6FpqVrn4vvjw5/d6AaYi1TC839fDozvAWAOAk= Received: by 10.142.165.9 with SMTP id n9mr27716wfe.1193902046902; Thu, 01 Nov 2007 00:27:26 -0700 (PDT) Received: by 10.143.158.18 with HTTP; Thu, 1 Nov 2007 00:27:26 -0700 (PDT) Message-ID: <25f52a3d0711010027t6b124227gfbddcada12b16e24@mail.gmail.com> Date: Thu, 1 Nov 2007 08:27:26 +0100 From: "Stephan F. Yaraghchi" Sender: yaraghchi@gmail.com To: "Kris Kennaway" In-Reply-To: <4728F43A.1030500@FreeBSD.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <25f52a3d0710300732x425f0c45vde1a29361096c018@mail.gmail.com> <47284E4F.5030008@FreeBSD.org> <25f52a3d0710310303w7138bf5ds92698f1b6af2f655@mail.gmail.com> <4728F43A.1030500@FreeBSD.org> X-Google-Sender-Auth: aff41aada20abbf1 Cc: freebsd-current@freebsd.org Subject: Re: loader breaks with -O2 optimizations 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: Thu, 01 Nov 2007 07:34:06 -0000 On 10/31/07, Kris Kennaway wrote: > Stephan F. Yaraghchi wrote: > > On 10/31/07, Kris Kennaway wrote: > >> Stephan F. Yaraghchi wrote: > >>> After making world on a freshly installed 7.0-BETA1 > >>> the system does not boot anymore due to a broken loader: > >>> > >>> > >>> FreeBSD/i386 bootstrap loader, Revision 1.1 > >>> (root@bigblue, Tue Oct 30 11:26:32 CET 2007) > >>> Can't work out which disk we are booting from. > >>> Guessed BIOS device 0xffffffff not found by probes defaulting to disk0: > >>> > >>> panic: free: guard1 fail@ 0x6ded4 from > >>> /usr/src/sys/boot/i386/loader/../../common/module.c:959 > >>> > >>> --> Press a key on the console to reboot <-- > >>> > >>> > >>> I found out that the following line in my make.conf causes > >>> the problem: > >>> > >>> CFLAGS= -O2 -funroll-loops -pipe > >>> > >>> > >>> After changing down to -O1 and making /usr/src/sys/boot again > >>> the systems behaves properly at boot. > >>> > >>> Is this behavior intended? > >> Maybe, what happens if you use just -O2 -pipe? -funroll-loops is not an > >> appropriate thing to be using globally anyway, unless your intention is > >> to randomly make some code slower. > >> > >> Kris > >> > > > > Hi Kris, > > > > I tried all possible combinations of these switches -- only -O2 led to > > the described > > behaviour. > > Presumably you mean -O2 -funroll-loops, not -O2. Or are you saying the > latter also breaks the loader? > > > Anyway, it's very interesting to hear that adding these optimizations > > to make.conf > > is not recommended, even that -funroll-loops is possibly slowing down > > certain code. > > > > I'm sure many people use it since it's a common tuning tip found on the web. > > I read about it in Dru Lavigne's "BSD Hacks" (O'Reilly)... > > Yes, unfortunately it's bogus advice. What does she say this option is > good for? > > Kris > Hi Kris, you are right: It's the combination of both that causes loader to break. Oliver suggested the defaults (-O2 -fno-strict-aliasing -pipe) and it works. By the way: "BSD Hacks" is a collection of hacks compiled by Dru. Hack #69 deals with tuning and is authored by Avleen Vig. It says: "The -funroll-loops saves one CPU register that would otherwise be tied up in tracking the iteration of the loop, but at the expense of making a slightly larger binary." -- Stephan www.deine-stimme-gegen-armut.de