From: "Jan Beulich" <JBeulich@novell.com>
To: Hollis Blanchard <hollisb@us.ibm.com>
Cc: sfr@canb.auug.org.au, Rusty Russell <rusty@rustcorp.com.au>,
linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
linux-next@vger.kernel.org, akpm@linux-foundation.org,
linuxppc-dev@lists.ozlabs.org
Subject: Re: linux-next: tree build failure
Date: Mon, 05 Oct 2009 07:58:25 +0100 [thread overview]
Message-ID: <4AC9B5310200007800017EA1@vpn.id2.novell.com> (raw)
In-Reply-To: <1254498517.3839.17.camel@slab.beaverton.ibm.com>
[-- Attachment #1: Type: text/plain, Size: 745 bytes --]
>>> Hollis Blanchard <hollisb@us.ibm.com> 02.10.09 17:48 >>>
>On Wed, 2009-09-30 at 07:35 +0100, Jan Beulich wrote:
>> The one Rusty suggested the other day may help here. I don't like it
>> as a drop-in replacement for BUILD_BUG_ON() though (due to it
>> deferring the error generated to the linking stage), I'd rather view
>> this as an improvement to MAYBE_BUILD_BUG_ON() (which should
>> then be used here).
>
>Can you be more specific?
>
>I have no idea what Rusty suggested where. I can't even guess what
I'm attaching Rusty's response I was referring to.
>MAYBE_BUILD_BUG_ON() is supposed to do (sounds like a terrible name).
Agreed - but presumably better than just deleting the bogus instances
altogether...
Jan
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From: Rusty Russell <rusty@rustcorp.com.au>
To: "Jan Beulich" <JBeulich@novell.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix BUILD_BUG_ON() and a couple of bogus uses of it
Date: Wed, 23 Sep 2009 10:27:00 +0930
Message-ID: <200909231027.01006.rusty@rustcorp.com.au>
On Wed, 19 Aug 2009 01:29:25 am Jan Beulich wrote:
> gcc permitting variable length arrays makes the current construct
> used for BUILD_BUG_ON() useless, as that doesn't produce any diagnostic
> if the controlling expression isn't really constant. Instead, this
> patch makes it so that a bit field gets used here. Consequently, those
> uses where the condition isn't really constant now also need fixing.
>
> Note that in the gfp.h, kmemcheck.h, and virtio_config.h cases
> MAYBE_BUILD_BUG_ON() really just serves documentation purposes - even
> if the expression is compile time constant (__builtin_constant_p()
> yields true), the array is still deemed of variable length by gcc, and
> hence the whole expression doesn't have the intended effect.
>
> Signed-off-by: Jan Beulich <jbeulich@novell.com>
We used to use an undefined symbol here; diagnostics are worse but it catches
more stuff.
Perhaps a hybrid is the way to go?
#ifndef __OPTIMIZE__
#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
#else
/* If it's a constant, catch it at compile time, otherwise at link time. */
extern int __build_bug_on_failed;
#define BUILD_BUG_ON(condition) \
do { \
((void)sizeof(char[1 - 2*!!(condition)])); \
if (condition) __build_bug_on_failed = 1; \
} while(0)
#endif
Thanks,
Rusty.
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next prev parent reply other threads:[~2009-10-05 6:58 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-29 9:28 linux-next: tree build failure Jan Beulich
[not found] ` <4AC1E15502000078000516B5-Qfbpwmsw6RoS3W1tAdPHOtBPR1lH4CV8@public.gmane.org>
2009-09-29 9:51 ` roel kluin
[not found] ` <25e057c00909290251h55c0dc25o4ab1f2e84c920dca-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2009-09-30 6:29 ` Jan Beulich
2009-09-29 23:39 ` Hollis Blanchard
[not found] ` <1254267572.15622.1621.camel-yDUrRDS8jBVhsM67afOH+sxtgHpCUUYS@public.gmane.org>
2009-09-30 6:35 ` Jan Beulich
[not found] ` <4AC318450200007800017355-Qfbpwmsw6RoS3W1tAdPHOtBPR1lH4CV8@public.gmane.org>
2009-10-02 15:48 ` Hollis Blanchard
2009-10-05 6:58 ` Jan Beulich [this message]
2009-10-09 19:14 ` Hollis Blanchard
2009-10-14 22:57 ` Hollis Blanchard
2009-10-15 7:27 ` Jan Beulich
2009-10-19 18:19 ` Hollis Blanchard
2009-10-20 1:12 ` Rusty Russell
[not found] ` <200910201142.34006.rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
2009-10-20 1:29 ` Hollis Blanchard
2009-10-20 3:45 ` [PATCH] BUILD_BUG_ON: make it handle more cases Rusty Russell
2009-10-20 13:58 ` Américo Wang
2009-10-20 14:43 ` Alan Jenkins
[not found] ` <9b2b86520910200743h4e134cf8jd2860d42b3936597-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2009-10-23 1:50 ` Américo Wang
[not found] ` <200910201415.34361.rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
2009-10-22 21:04 ` Hollis Blanchard
2009-11-05 0:20 ` Stephen Rothwell
2009-11-05 6:28 ` Rusty Russell
[not found] ` <200911051658.36265.rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
2009-11-05 6:37 ` Rusty Russell
2009-11-05 6:38 ` Stephen Rothwell
[not found] ` <20091105173842.c94ba501.sfr-3FnU+UHB4dNDw9hX6IcOSA@public.gmane.org>
2009-11-06 6:30 ` Rusty Russell
2009-10-29 21:30 ` Hollis Blanchard
2009-11-05 6:01 ` Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2009-12-16 7:21 linux-next: tree build failure Stephen Rothwell
2009-12-16 9:02 ` Felipe Balbi
2009-12-16 10:10 ` Liam Girdwood
2009-10-01 3:19 Stephen Rothwell
2009-10-01 7:58 ` Jens Axboe
2009-10-01 10:41 ` Stephen Rothwell
2009-09-24 5:21 Stephen Rothwell
[not found] ` <20090924152102.8d7d40cf.sfr-3FnU+UHB4dNDw9hX6IcOSA@public.gmane.org>
2009-09-29 0:00 ` Hollis Blanchard
2009-08-17 8:39 Stephen Rothwell
2009-08-03 0:35 Stephen Rothwell
2009-08-03 1:01 ` NeilBrown
2009-08-03 1:30 ` Stephen Rothwell
2009-07-27 7:53 Stephen Rothwell
2009-07-27 9:21 ` Karsten Keil
2009-07-27 15:06 ` David Miller
2009-07-28 4:22 ` Stephen Rothwell
2009-04-07 3:41 Stephen Rothwell
2009-04-07 10:00 ` Mark Brown
2009-04-08 1:48 ` Takashi Iwai
2009-03-23 9:38 Stephen Rothwell
2009-03-23 22:27 ` Mauro Carvalho Chehab
2009-03-23 23:25 ` Stephen Rothwell
2009-03-05 7:41 Stephen Rothwell
2009-03-06 5:01 ` Rusty Russell
2009-01-16 5:37 Stephen Rothwell
2009-01-16 7:25 ` Peter Zijlstra
2009-01-16 9:03 ` Ingo Molnar
2009-01-16 10:39 ` Stephen Rothwell
2009-01-16 10:53 ` Ingo Molnar
2009-01-16 11:53 ` Stephen Rothwell
2009-01-16 12:32 ` Ingo Molnar
2008-11-28 10:04 Stephen Rothwell
2008-11-28 10:25 ` Takashi Iwai
2008-11-28 10:43 ` Stephen Rothwell
2008-11-28 17:23 ` Takashi Iwai
2008-10-21 8:30 Stephen Rothwell
2008-08-25 10:33 Stephen Rothwell
2008-08-25 16:36 ` Steven Rostedt
2008-06-30 14:35 Stephen Rothwell
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