linux-kernel - Re: [PATCH] BUILD_BUG_ON() should not use array type

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Message-ID: <20080829233815.GA3365@x200.localdomain>
Date:	Sat, 30 Aug 2008 03:38:15 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Beulich <jbeulich@...ell.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] BUILD_BUG_ON() should not use array type

> > +/* Force a compilation error if condition is constant and true */
> > +#define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)]))
> 
> MAYBE_BUILD_BUG_ON() hurts my brain.  It's doing:
> 
> 	if (__builtin_constant_p(expr))
> 		BUILD_BUG_ON(expr);
> 
> yes?  For inlined (or macro) callsites which can be used with constant
> or non-constant args.
> 
> It's tempting to just zap the one callsite and not add this at all,

Yes, please. There should be no maybes in kernel.

Imagine probabilistic BUG_ON(). Imagine probabilistic refcounting: maybe_get_net().

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