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Hi, I just had an unpleasant experience with -ffast-math and GCC 4.1.1 |
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(it borked my LDAP authentication on several systems which worked with |
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the same CFLAGS as long as GCC 3.4.6 was used). |
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|
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There is a lot of material out there about CFLAGS and Gentoo (google |
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returns 387000 pages) but what's working for someone might not for |
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another. There are flags that work for a GCC version and most ebuilds |
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and don't work with another GCC version (my unfortunate experience) or |
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some ebuilds. Flag combination/architecture/LDFLAGS might be an issue too. |
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|
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There are already good resources (http://gentoo-wiki.com/CFLAGS_matrix |
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was mentioned to me by robbat2) but they may not be advertised enough. |
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I'd like to propose a paragraph to the GWN editor which presents some |
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gotchas and good references on the subject. |
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|
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Here's a draft for review. You're welcomed to expand on the subject. |
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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 -ffast-math</li> |
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<li>...</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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</body> |
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</section> |
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--- Draft END --- |
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|
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If possible, I'd like to expand the list of 3.4.6 -> 4.1.1 upgrade |
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problems which are linked to experimental CFLAGS. If you want to expand |
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the subject to cover other tuning/stability gotchas that recent updates |
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might have brought into the light, please feel free to do so. As English |
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is not my native tongue, feel free to spell check too. |
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|
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Cheers, |
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|
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Lionel. |
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-- |
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