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 1GTlxl-0003J7-Aa for garchives@archives.gentoo.org; Sat, 30 Sep 2006 21:01:33 +0000 Received: from robin.gentoo.org (localhost [127.0.0.1]) by robin.gentoo.org (8.13.8/8.13.6) with SMTP id k8UL0auw026063; Sat, 30 Sep 2006 21:00:36 GMT Received: from citycable.ch (mail.alinto.citycable.ch [85.218.0.111]) by robin.gentoo.org (8.13.8/8.13.6) with SMTP id k8UKwaON028494 for ; Sat, 30 Sep 2006 20:58:36 GMT Received: (qmail 19487 invoked by uid 64); 30 Sep 2006 20:58:35 -0000 Received: from dominique.michel@citycable.ch by alinto.net (uvscan: v4.4.00/v4863. Clean); 30 Sep 2006 20:58:35 -0000 Received: from unknown (HELO localhost) (dominique.michel@citycable.ch@85.218.2.234) by smtp.alinto.citycable.ch with SMTP; 30 Sep 2006 20:58:35 -0000 Date: Sat, 30 Sep 2006 22:58:27 +0200 From: Dominique Michel To: gentoo-dev@lists.gentoo.org Subject: Re: [gentoo-dev] [RFC] CFLAGS paragraph for the GWN Message-ID: <20060930225827.725ae31d@localhost> In-Reply-To: <451ED52E.5030407@bouton.name> References: <451ED52E.5030407@bouton.name> X-Mailer: Sylpheed-Claws 2.4.0 (GTK+ 2.8.19; i686-pc-linux-gnu) Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAJFBMVEXy8ubtkoXo7+b1+fbN cGKCeWDtamweFA8eMkmKPkPtvcWRoqyV0Pn7AAACbElEQVQ4jXXTMWvbQBQA4MOlizsdXEXp KAi09mKcLZ0EJxONDRJVkikg9AtqTm63gtHDmVJs1GsnC0JiaTMJGN2f67uzznJb+gZj9PFO 7717IqdtvCAmem4bxMLp/2BEyEBF1+U/0H8uhI6rv+BVLNrY/gH9T0L8yAxk2yMY3YuZxDCn TY/gpBByyTGktIcZOIvFjPNJmqYJDwrx3cIoBrE0zzG4FF8tfBAwM+DonKCYWjgROZ6Upjcm 5Qje58JAmlKKGfIAjzaDUuogZBY2Bjg14eDbywMIqZvwqgqFBcVFB0seYONLb00ZZlh4p0F6 FHNoUMyKAzxowJSQTyj+XloYs3MN3GeMpzyYSTMshLM00ODpWlPp4SDbqs4cViDcGAgmlK/a PsaOg7DvIQ3wzANMqB/iQW/XTkoTLO6XhSeHUoQKe+NLjyY/Ldx7CW2D4WTYhZ3V0GP64RpP Q/E66IUWMLj3+nDn4w2ejMACyXFeHZy6ETcZehc49bv1GQ/0bazNuzm97mDkhnoie9i30WYM w/YCnYT7Fx308s98n0IT//Jod1+aOzdzYXLVbftol+PC+REG3u+0AxdEtuSMB6G+DLGwMH4E vXGmJn8VCLM9LhmrOAMQYt5Wi/DFgIC52iFkUzMpDVmjAaDZRGC+JGwDqzJ/G5fUUcWZAaE7 YfvPLYtIU1Wb4A2IeS7uDMgcIFutiCr766qGfKHyuxvTIERKXVNSN27lDgCuBuojlpxIyJV6 ritS1uWWuHF2Ww7qcIKbqEFVNbmtmm3vGSCHbVXjikrY3SpVxwQWw2aIjwG+ueXTJDmHeK6a HfwGyU5ZSlGeSRQAAAAASUVORK5CYII= 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 Content-Type: text/plain; charset=UTF-8 X-aduser: dominique.michel@citycable.ch/85.218.2.234 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by robin.gentoo.org id k8UL0awp026063 X-Archives-Salt: 8a9ebd3c-0940-445b-a115-0b5de266e860 X-Archives-Hash: c8f99bf3063683670c970c9c94a85f1e Le Sat, 30 Sep 2006 22:35:58 +0200, Lionel Bouton a =C3=A9crit : > 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). >=20 > 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 t= oo. >=20 > 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. >=20 > Here's a draft for review. You're welcomed to expand on the subject. >=20 > --- Draft BEGIN --- >
> CFLAGS > >=20 >

> 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 unstabl= e > system. Example of this are : >

    >
  • nss_ldap stopped working with -ffast-math
    • >
  • ...
    • >
>

>

> Users with unsupported CFLAGS (see the link=3D'http://gentoo-wiki.com/CFLAGS_matrix'>CFLAGS matrix for > example) might want to return to safe CFLAGS (see link=3D'http://gentoo-wiki.com/Safe_Cflags'>Safe CFLAGS) if recen= t > 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 --- >=20 > 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 Englis= h > is not my native tongue, feel free to spell check too. >=20 > Cheers, >=20 > Lionel. My personal experience with other CFLAGS as the ones in the handbook is a= t gcc-4.1.1 have a better optimisation with the default gentoo CFLAGS. Even with -O2, the result is a faster system, and -O3 seam to be safer with ma= th related applications as with gcc-3.4.*. But in the other hand, other flags seam to be more problematic as with gcc-3.4.*. And the new optimisations flags as the vectorisation flags are= not easy to use, because the result depend on the code of the program. They c= an or not brake the code, and when the program run well, they can make it faste= r or slower. All depend of the size and complexity of the loops. And I thin= k also of the arch. So my conclusion is: For system flags, just keep the default, and if you want to experiment, d= o profiling for each single program you want to optimize. Cheers, Dominique --=20 Dominique Michel --=20 gentoo-dev@gentoo.org mailing list