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To: gentoo-dev@g.o
From: Lionel Bouton <lionel-dev@...>
Subject: Re: [RFC] CFLAGS paragraph for the GWN
Date: Sun, 01 Oct 2006 00:42:34 +0200
Mike Frysinger wrote the following on 30.09.2006 23:48 :
> [...]
> `man gcc` always seemed fine to me
>
> in fact, lets read the -ffast-math section:
>        -ffast-math
>            This option should never be turned on by any -O option since it can
>            result in incorrect output for programs which depend on an exact
>            implementation of IEEE or ISO rules/specifications for math func-
>            tions.
>
> this flag is never safe to use in CFLAGS
>
>   

Indeed, I'll add a reminder to adventurous users to check `man gcc` (I
believe I added fast-math following an example somewhere on the web
instead of checking the man page).

>> link='http://gentoo-wiki.com/CFLAGS_matrix'
>>     
>
> no way will our documentation link to gentoo-wiki.com
>
>   

The GWN paragraph is mainly a 'heads-up' kind of thing, no more. Don't
confuse the GuideXML extract with an official documentation extract, GWN
uses GuideXML too :-)

>> If possible, I'd like to expand the list of 3.4.6 -> 4.1.1 upgrade
>> problems which are linked to experimental CFLAGS
>>     
>
> i find maintaining a list of "safe" CFLAGS on a per-gcc basis to be a waste of 
> time ... but that's just me
>   

That's not the idea. The main idea is to remind people that playing with
CFLAGS is allowed, as long as you remember to revert to safe CFLAGS
before reporting bugs.
As I wasted one dev time by forgetting to check my CFLAGS, I merely
thought that maybe this wasn't a common reflex for other users too
(fast-math was the only unsafe flag I used, I'm pretty conservative and
simply was mistaken because roughly 2 years ago I didn't check the
proper source of information: the man page). Maybe very few bug reports
are caused by inadequate CFLAGS. If my problem is an uncommon exception
I won't press the matter further, there would be no point to do so.

I'll wait and see if other devs are aware of common CFLAGS gotchas
plaguing bugzilla.

Lionel.
-- 
gentoo-dev@g.o mailing list


Replies:
Re: [RFC] CFLAGS paragraph for the GWN
-- Ryan Hill
References:
[RFC] CFLAGS paragraph for the GWN
-- Lionel Bouton
Re: [RFC] CFLAGS paragraph for the GWN
-- Mike Frysinger
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Updated Jun 17, 2009

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