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Date: Wed, 20 Aug 2008 16:39:29 +0400
To: Boaz Harrosh <bharrosh@panasas.com>
Cc: Ingo Molnar <mingo@elte.hu>, Rusty Russell <rusty@rustcorp.com.au>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [PATCH] debug: fix BUILD_BUG_ON() for non-constant expressions
Message-ID: <20080820123929.GA29972@x200.localdomain>
References: <20080816100948.GB19926@martell.zuzino.mipt.ru> <alpine.LFD.1.10.0808170936260.3324@nehalem.linux-foundation.org> <20080817173319.GA2450@elte.hu> <200808181109.43203.rusty@rustcorp.com.au> <20080818075459.GH30694@elte.hu> <48A9472F.908@panasas.com> <20080819133422.GA24369@elte.hu> <48AAF5F7.6040709@panasas.com> <20080820105922.GC18524@elte.hu> <48AC0EB9.3080708@panasas.com>
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From: adobriyan@gmail.com
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On Wed, Aug 20, 2008 at 03:31:53PM +0300, Boaz Harrosh wrote:
> Ingo Molnar wrote:
> > * Boaz Harrosh <bharrosh@panasas.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.