CFLAGS

From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists.gentoo.org ([140.105.134.102] helo=robin.gentoo.org) by nuthatch.gentoo.org with esmtp (Exim 4.60) (envelope-from ) id 1GTpRA-0004qj-HD for garchives@archives.gentoo.org; Sun, 01 Oct 2006 00:44:08 +0000 Received: from robin.gentoo.org (localhost [127.0.0.1]) by robin.gentoo.org (8.13.8/8.13.6) with SMTP id k910gBE7018148; Sun, 1 Oct 2006 00:42:11 GMT Received: from py-out-1112.google.com (py-out-1112.google.com [64.233.166.180]) by robin.gentoo.org (8.13.8/8.13.6) with ESMTP id k910cDYk027022 for ; Sun, 1 Oct 2006 00:38:14 GMT Received: by py-out-1112.google.com with SMTP id d42so1489143pyd for ; Sat, 30 Sep 2006 17:38:14 -0700 (PDT) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:user-agent:mime-version:to:subject:references:in-reply-to:content-type:content-transfer-encoding; b=twYD6qTw4wrzOKobGvuquPruDRjUD78bF/FhhHZuQYzX0iVDraGScyRPaOZRjztLrnyLUsC4LevFMZ1hX6x8usuhhQVr5aCrm9FrMMVAT4X3td6/wh1s52XdiYAOd+PurfFaTfYCIUW39KPgHQNdycMG7JbcGiOtBt19fnhbyU4= Received: by 10.35.60.16 with SMTP id n16mr3966840pyk; Sat, 30 Sep 2006 17:38:13 -0700 (PDT) Received: from ?192.168.0.5? ( [211.31.12.195]) by mx.gmail.com with ESMTP id 10sm242193nzo.2006.09.30.17.38.11; Sat, 30 Sep 2006 17:38:12 -0700 (PDT) Message-ID: <451F0DE3.7090209@gmail.com> Date: Sun, 01 Oct 2006 10:37:55 +1000 From: George Prowse User-Agent: Thunderbird 1.5.0.7 (Windows/20060909) Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-dev@gentoo.org Reply-to: gentoo-dev@lists.gentoo.org MIME-Version: 1.0 To: gentoo-dev@lists.gentoo.org Subject: Re: [gentoo-dev] [RFC] CFLAGS paragraph for the GWN References: <451ED52E.5030407@bouton.name> In-Reply-To: <451ED52E.5030407@bouton.name> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Archives-Salt: e41d7f54-b33b-45da-9f99-caff0e5e899b X-Archives-Hash: 56a1ee7a5fba87190f42a15cf930fd2a Lionel Bouton wrote: > Hi, I just had an unpleasant experience with -ffast-math and GCC 4.1.1 > (it borked my LDAP authentication on several systems which worked with > the same CFLAGS as long as GCC 3.4.6 was used). > > There is a lot of material out there about CFLAGS and Gentoo (google > returns 387000 pages) but what's working for someone might not for > another. There are flags that work for a GCC version and most ebuilds > and don't work with another GCC version (my unfortunate experience) or > some ebuilds. Flag combination/architecture/LDFLAGS might be an issue too. > > There are already good resources (http://gentoo-wiki.com/CFLAGS_matrix > was mentioned to me by robbat2) but they may not be advertised enough. > I'd like to propose a paragraph to the GWN editor which presents some > gotchas and good references on the subject. > > Here's a draft for review. You're welcomed to expand on the subject. > > --- Draft BEGIN --- >

> CFLAGS > > >

> Being able to tune the CFLAGS is part of one of the core principles of > Gentoo: let the user be in control. Being in control brings both > benefits and problems and CFLAGS tuning is not an exception. >

> The recent upgrade to gcc-4.1.1 for x86 and amd64 users changed the > landscape. Users that spent some time tuning their CFLAGS with gcc-3.4.6 > might find out that an upgrade to gcc-4.1.1 leaves them with an unstable > system. Example of this are : >

nss_ldap stopped working with -ffast-math
...

> Users with unsupported CFLAGS (see the link='http://gentoo-wiki.com/CFLAGS_matrix'>CFLAGS matrix for > example) might want to return to safe CFLAGS (see link='http://gentoo-wiki.com/Safe_Cflags'>Safe CFLAGS) if recent > updates caused them stability problems. On the other hand, more > adventurous users might want to experiment with CFLAGS that didn't work > properly with gcc-3.4.6... As always, the user is in control. >

> >

> --- Draft END --- > > If possible, I'd like to expand the list of 3.4.6 -> 4.1.1 upgrade > problems which are linked to experimental CFLAGS. If you want to expand > the subject to cover other tuning/stability gotchas that recent updates > might have brought into the light, please feel free to do so. As English > is not my native tongue, feel free to spell check too. > > Cheers, > > Lionel. > I agree in principle because it would stop people using stupid CFLAGS. It should have an information section and a "use this CFLAG and dont ask us for help" section:

Good Compiler Flag

-floop-optimize Enables safe loop optimisation and is enabled in most -O$

Bad Compiler flag

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