On Tue, 2006-10-03 at 02:56 +0200, Lionel Bouton wrote: > Here's an updated draft. I included most of your remarks and added some > notes on append-flags/filter-flags. I'll probably submit it to Ulrich > around the end of the week.
I surely hope you don't submit it to Ulrich if you want it to actually ever get in the GWN. Instead, you should submit it to [EMAIL PROTECTED] like the GWN tells you to do. =] Thanks, > --- Draft BEGIN --- > <section> > <title>CFLAGS</title> > <body> > > <p> > 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. > </p> > <p> > 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 : > <ul> > <li>nss_ldap stopped working with <c>-ffast-math</c> (reported to break > many packages changing with the actual gcc version)</li> > <li><c>-fvisibility-inlines-hidden</c> still breaks some code</li> > <li>if you used gcc-4.0, <c>-ftree-loop-linear</c> now breaks in > gcc-4.1(at least with mesa)</li> > <li>again for gcc-4.0 users, <c>-ftree-vectorize</c> is known to be > broken in gcc-4.1 (at least for x86 and ppc, amd64 users seem to be > safe)</li> > <li><c>-fforce-addr</c> and <c>-fweb</c> break regularly on x86 with > video libraries or graphic processing apps which use hand-optimised ASM</li> > </ul> > </p> > <p> > Users with unsupported CFLAGS (see the <uri > link='http://gentoo-wiki.com/CFLAGS_matrix'>CFLAGS matrix</uri> for > example) might want to return to safe CFLAGS (see <uri > link='http://gentoo-wiki.com/Safe_Cflags'>Safe CFLAGS</uri>) 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. > </p> > <p> > Notes: > <ul> > <li>The gcc man page contains warnings for some unsafe optimization > options. You should read it carefully when you experiment with CFLAGS or > upgrade GCC on a CFLAGS-customized Gentoo.</li> > <li>Some options that are unsafe in the system-wide CFLAGS might be > added automatically in some ebuilds if the developper deems them safe > (by redefining CFLAGS or using append-flags of the flag-o-matic eclass). > For example <c>-ffast-math</c> is added by the xmame/xmess ebuilds on > most architectures even if you don't put it in your CFLAGS.</li> > <li>You might get an idea of the stability issues of a specific > optimization option by running: <c>find /usr/portage -name '*.ebuild'| > xargs grep -- '-<your-risky-optimization-option>'</c>. It takes quite > some time, but might be enlightening: look for the 'filter-flags'.</li> > </ul> > </p> > </body> > </section> > --- Draft END --- > > Lionel -- Chris Gianelloni Release Engineering Strategic Lead Alpha/AMD64/x86 Architecture Teams Games Developer/Council Member/Foundation Trustee Gentoo Foundation
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