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Lionel Bouton wrote: |
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> Here's an updated draft. I included most of your remarks and added some |
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> notes on append-flags/filter-flags. I'll probably submit it to Ulrich |
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> around the end of the week. |
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> |
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> --- Draft BEGIN --- |
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> <section> |
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> <title>CFLAGS</title> |
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> <body> |
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> |
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> <p> |
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> Being able to tune the CFLAGS is part of one of the core principles of |
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> Gentoo: let the user be in control. Being in control brings both |
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> benefits and problems and CFLAGS tuning is not an exception. |
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> </p> |
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> <p> |
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> The recent upgrade to gcc-4.1.1 for x86 and amd64 users changed the |
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> landscape. Users that spent some time tuning their CFLAGS with gcc-3.4.6 |
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> might find out that an upgrade to gcc-4.1.1 leaves them with an unstable |
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> system. Example of this are : |
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> <ul> |
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> <li>nss_ldap stopped working with <c>-ffast-math</c> (reported to break |
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> many packages changing with the actual gcc version)</li> |
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> <li><c>-fvisibility-inlines-hidden</c> still breaks some code</li> |
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> <li>if you used gcc-4.0, <c>-ftree-loop-linear</c> now breaks in |
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> gcc-4.1(at least with mesa)</li> |
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> <li>again for gcc-4.0 users, <c>-ftree-vectorize</c> is known to be |
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> broken in gcc-4.1 (at least for x86 and ppc, amd64 users seem to be |
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> safe)</li> |
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> <li><c>-fforce-addr</c> and <c>-fweb</c> break regularly on x86 with |
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> video libraries or graphic processing apps which use hand-optimised ASM</li> |
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> </ul> |
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> </p> |
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> <p> |
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> Users with unsupported CFLAGS (see the <uri |
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> link='http://gentoo-wiki.com/CFLAGS_matrix'>CFLAGS matrix</uri> for |
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> example) might want to return to safe CFLAGS (see <uri |
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> link='http://gentoo-wiki.com/Safe_Cflags'>Safe CFLAGS</uri>) if recent |
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> updates caused them stability problems. On the other hand, more |
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> adventurous users might want to experiment with CFLAGS that didn't work |
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> properly with gcc-3.4.6... As always, the user is in control. |
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> </p> |
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> <p> |
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> Notes: |
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> <ul> |
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> <li>The gcc man page contains warnings for some unsafe optimization |
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> options. You should read it carefully when you experiment with CFLAGS or |
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> upgrade GCC on a CFLAGS-customized Gentoo.</li> |
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> <li>Some options that are unsafe in the system-wide CFLAGS might be |
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> added automatically in some ebuilds if the developper deems them safe |
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> (by redefining CFLAGS or using append-flags of the flag-o-matic eclass). |
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> For example <c>-ffast-math</c> is added by the xmame/xmess ebuilds on |
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> most architectures even if you don't put it in your CFLAGS.</li> |
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> <li>You might get an idea of the stability issues of a specific |
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> optimization option by running: <c>find /usr/portage -name '*.ebuild'| |
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> xargs grep -- '-<your-risky-optimization-option>'</c>. It takes quite |
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> some time, but might be enlightening: look for the 'filter-flags'.</li> |
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> </ul> |
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> </p> |
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> </body> |
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> </section> |
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> --- Draft END --- |
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> |
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> Lionel |
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Uh, Gentoo-wiki does not get linked. Period. Not in official Gentoo stuff -- the |
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wiki is not supported or endorsed by the developers. It's not remotely official, |
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and in fact contains a great deal of false and/or misleading information, which |
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is why you don't see it mentioned in any documentation (for example). |
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