linux-kernel - Re: [PATCH v4 9/9] bug.h: Convert BUILD_BUG{,_ON} to use BUILD_BUG_ON

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Date:	Tue, 30 Oct 2012 18:02:32 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Borislav Petkov <bp@...en8.de>,
	Daniel Santos <daniel.santos@...ox.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	Joe Perches <joe@...ches.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-sparse@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v4 9/9] bug.h: Convert BUILD_BUG{,_ON} to use
 BUILD_BUG_ON_MSG

On Tue, Oct 30, 2012 at 08:19:05PM +0100, Borislav Petkov wrote:
> On Sun, Oct 28, 2012 at 03:57:15PM -0500, danielfsantos@....net wrote:
> > Remove duplicate code by converting BUILD_BUG and BUILD_BUG_ON to just
> > call BUILD_BUG_ON_MSG.  This not only reduces source code bloat, but
> > also prevents the possibility of code being changed for one macro and
> > not for the other (which was previously the case for BUILD_BUG and
> > BUILD_BUG_ON).
> > 
> > Signed-off-by: Daniel Santos <daniel.santos@...ox.com>
> > ---
> >  include/linux/bug.h |   17 +++--------------
> >  1 files changed, 3 insertions(+), 14 deletions(-)
> > 
> > diff --git a/include/linux/bug.h b/include/linux/bug.h
> > index 3bc1ddf..b58ba51 100644
> > --- a/include/linux/bug.h
> > +++ b/include/linux/bug.h
> > @@ -81,14 +81,8 @@ struct pt_regs;
> >  #ifndef __OPTIMIZE__
> >  #define BUILD_BUG_ON(condition) __compiletime_error_fallback(condition)
> >  #else
> > -#define BUILD_BUG_ON(condition)						\
> > -	do {								\
> > -		extern void __build_bug_on_failed(void)			\
> > -			__compiletime_error("BUILD_BUG_ON failed");	\
> > -		__compiletime_error_fallback(condition);		\
> > -		if (condition)						\
> > -			__build_bug_on_failed();			\
> > -	} while(0)
> > +#define BUILD_BUG_ON(condition) \
> > +	BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> 
> Concatenating "condition" might not be very informative in all cases.
> For example:
> 
> BUILD_BUG_ON(1);
> 
> Having __LINE__ is good enough IMHO.

While it doesn't always help, it may help sometimes.  Worst case,
BUILD_BUG_ON(1) gives you no less information than it did before; best
case, it gives you useful data.

- Josh Triplett
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