From mboxrd@z Thu Jan  1 00:00:00 1970
From: Josh Triplett <josh@joshtriplett.org>
Subject: Re: [PATCH 8/10] bug.h: Make BUILD_BUG_ON generate compile-time error
Date: Sun, 30 Sep 2012 17:26:49 -0700
Message-ID: <20121001002649.GB16784@leaf>
References: <1348874411-28288-1-git-send-email-daniel.santos@pobox.com>
 <1348874411-28288-9-git-send-email-daniel.santos@pobox.com>
 <20120929003239.GA14293@jtriplet-mobl1>
 <50664E30.7050809@att.net>
 <20120929025506.GA3183@leaf>
 <5068D5BD.1000802@att.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: QUOTED-PRINTABLE
Return-path: <linux-sparse-owner@vger.kernel.org>
Received: from relay4-d.mail.gandi.net ([217.70.183.196]:37671 "EHLO
	relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751132Ab2JAA05 convert rfc822-to-8bit (ORCPT
	<rfc822;linux-sparse@vger.kernel.org>);
	Sun, 30 Sep 2012 20:26:57 -0400
Content-Disposition: inline
In-Reply-To: <5068D5BD.1000802@att.net>
Sender: linux-sparse-owner@vger.kernel.org
List-Id: linux-sparse@vger.kernel.org
To: Daniel Santos <daniel.santos@pobox.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Andi Kleen <ak@linux.intel.com>, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Christopher Li <sparse@chrisli.org>, David Daney <david.daney@cavium.com>, David Howells <dhowells@redhat.com>, Joe Perches <joe@perches.com>, Konstantin Khlebnikov <khlebnikov@openvz.org>, linux-sparse@vger.kernel.org, Michel Lespinasse <walken@google.com>, Paul Gortmaker <paul.gortmaker@windriver.com>, Pavel Pisa <pisa@cmp.felk.cvut.cz>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Steven Rostedt <rostedt@goodmis.org>

On Sun, Sep 30, 2012 at 06:29:01PM -0500, Daniel Santos wrote:
> On 09/28/2012 09:55 PM, Josh Triplett wrote:
> > Assuming you don't call BUILD_BUG_ON_MSG more than once per line:
> >
> > /tmp$ cat test.c
> > #define BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line) \
> >     do { \
> >         extern void __build_bug_on_failed_ ## line (void) __attribu=
te__((error(msg))); \
> >         if (cond) \
> >             __build_bug_on_failed_ ## line(); \
> >     } while (0)
> >
> > #define BUILD_BUG_ON_MSG_INTERNAL(cond, msg, line) BUILD_BUG_ON_MSG=
_INTERNAL2(cond, msg, line)
> > #define BUILD_BUG_ON_MSG(cond, msg) BUILD_BUG_ON_MSG_INTERNAL(cond,=
 msg, __LINE__)
> >
> > void f(void)
> > {
> >     BUILD_BUG_ON_MSG(0, "test 1");
> >     BUILD_BUG_ON_MSG(1, "test 2");
> >     BUILD_BUG_ON_MSG(0, "test 3");
> >     BUILD_BUG_ON_MSG(1, "test 4");
> > }
> > /tmp$ gcc -c test.c
> > test.c: In function =E2=80=98f=E2=80=99:
> > test.c:14:119: error: call to =E2=80=98__build_bug_on_failed_14=E2=80=
=99 declared with attribute error: test 2
> > test.c:16:119: error: call to =E2=80=98__build_bug_on_failed_16=E2=80=
=99 declared with attribute error: test 4
> Thanks! This is very nice!  I've done a little more research and
> discovered that there's also a __COUNTER__ macro that is available
> in gcc 4.3+.  Before I realized that it was only available in gcc
> 4.3, I wrote this little macro:
>=20
> #define _CONCAT1(a, b) a##b
> #define CONCAT(a, b) _CONCAT1(a, b)
>=20
> #ifdef __COUNTER__
> # define UNIQUIFY(prefix) CONCAT(prefix, __COUNTER__)
> #else
> # define UNIQUIFY(prefix) CONCAT(prefix, __LINE__)
> #endif
>=20
> However, this could lead to code might compile on gcc 4.3+, but
> not compile prior, so this is bad, right?

Yes, as long as Linux continues to support prior GCC versions (currentl=
y
anything 3.2 or newer), I'd suggest sticking with __LINE__ so that it
consistently breaks if you use more than one BUILD_BUG_ON_MSG per line.

Good to know that __COUNTER__ exists, though.

Also, the name BUILD_BUG_ON_MSG seems wrong to me somehow; I keep
parsing it as though something about the message causes the build bug.

- Josh Triplett
--
To unsubscribe from this list: send the line "unsubscribe linux-sparse"=
 in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html