linux-kernel - Re: [PATCH v4 6/13] bug.h: Replace __linktime_error with __compiletime

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Message-ID: <4FE8BC69.7000104@att.net>
Date:	Mon, 25 Jun 2012 14:30:49 -0500
From:	Daniel Santos <danielfsantos@....net>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
CC:	Daniel Santos <daniel.santos@...ox.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Ingo Molnar <mingo@...nel.org>, Joe Perches <joe@...ches.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-doc@...r.kernel.org, linux-sparse@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Richard Weinberger <richard@....at>,
	Rob Landley <rob@...dley.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH v4 6/13] bug.h: Replace __linktime_error with __compiletime_error

On 06/25/2012 01:16 PM, Paul Gortmaker wrote:
>
> At a quick glance of the bug.h parts, I would think you need
> this commit _before_ #5 (that deleted __linktime_error) otherwise
> you'll have introduced a bisection build failure.  Or, alternatively
> you could combine #5 and #6 since they are clearly related, and
> their separation is more of a per-file CVS mentality than it is of
> any existence of distinct and separate/unrelated changesets.
>
> P.
Thanks, will do.

And after I thought about this more, I realized that both
__build_bug_failed and __build_bug_on_failed could just be declared
globally rather than being part of the macro. It may not be that big of
a deal, but it would reduce the size of pre-processed files at least
(something I look at a lot working with this patch set). But I'll let
you make the final call on that one

Oh, and as it turns out, adding the string-ized condition in the
BUILD_BUG_ON macro is useless (actually confusing) since gcc takes the
attributes of the first occurrence of an externed function in a
translation unit. Thus, the following code:

#include <linux/bug.h>
void func(void)
{
const int a = 0;
BUILD_BUG_ON(a == 1);
BUILD_BUG_ON(1) ;
}

would result in the error message:

call to ‘__build_bug_on_failed’ declared with attribute error:
BUILD_BUG_ON failed: a == 1

At least the line number is correct however. So my "declare a function
multiple times with with differing attributes" turns out to not work right.

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