linux-kernel - Re: [PATCH] BUILD_BUG

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Message-Id: <200808162055.45136.rusty@rustcorp.com.au>
Date:	Sat, 16 Aug 2008 20:55:44 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	torvalds@...l.org, akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] BUILD_BUG_ON sucks

On Saturday 16 August 2008 20:09:48 Alexey Dobriyan wrote:
> BUILD_BUG_ON should have never existed -- BUG_ON could upgrade itself to
> compile-breaking version if compiler has enough information and this is
> what patch does.
>
> The only downside is that one can't write BUG_ON(1) anymore.

Interesting idea, but I've come to actually like the semantic explicitness of 
BUILD_BUG_ON.  There's a difference between "we should never get here" 
and "this should never exist".

But maybe I just like it because we have it.  At very least BUILD_BUG_ON 
should definitely compile-barf on a non-constant expr, and vice versa for 
BUG_ON().

Note that BUG_ON() is a hack caused by lack of attribute((cold)).  "if (x) 
BUG()" is clearer, and possible in the long run as people upgrade compilers.

Cheers,
Rusty.
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