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

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Message-ID: <20080820123929.GA29972@x200.localdomain>
Date:	Wed, 20 Aug 2008 16:39:29 +0400
From:	adobriyan@...il.com
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

On Wed, Aug 20, 2008 at 03:31:53PM +0300, Boaz Harrosh 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.

See how kmalloc() works.

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