linux-kernel - Re: [PATCH] debug: fix BUILD_BUG_ON() for non-constant expressions

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Message-ID: <20080821121748.GA3384@elte.hu>
Date:	Thu, 21 Aug 2008 14:17:48 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH] debug: fix BUILD_BUG_ON() for non-constant expressions


* Boaz Harrosh <bharrosh@...asas.com> wrote:

> Ingo Molnar wrote:
> > * Boaz Harrosh <bharrosh@...asas.com> wrote:
> > 
> >> If the user of virtio_has_feature() must pass a compile-time constant 
> >> then it must be converted to a MACRO, and then the BUILD_BUG_ON will 
> >> work. Or it should be changed to a BUG_ON() if fbit is a runtime 
> >> variable.
> > 
> 
> The use of __builtin_constant_p in inline functions is broken. This is 
> because it will give different results depending on the -O level used. 
> So I think that using it in the Kernel with inlines is plain broken. 
> And should be discouraged.

ok - that's convincing, so your approach is superior to my hack on 
multiple levels.

Could you please (re-)send your patch(es) with a changelog, etc., so 
that i can apply it and drop my patches?

Thanks,

	Ingo
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