linux-kernel - Re: [PATCH v2] byteswap: try to avoid __builtin_constant

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Message-Id: <20160502163225.8b00a5ef7170a0f2533438e9@linux-foundation.org>
Date:	Mon, 2 May 2016 16:32:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, jpoimboe@...hat.com,
	Martin Jambor <mjambor@...e.cz>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Thomas Graf <tgraf@...g.ch>,
	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Himanshu Madhani <himanshu.madhani@...gic.com>,
	Dept-Eng QLA2xxx Upstream <qla2xxx-upstream@...gic.com>,
	Jan Hubicka <hubicka@....cz>
Subject: Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug

On Tue, 03 May 2016 01:10:16 +0200 Arnd Bergmann <arnd@...db.de> wrote:

> On Monday 02 May 2016 16:02:18 Andrew Morton wrote:
> > On Mon, 02 May 2016 23:48:19 +0200 Arnd Bergmann <arnd@...db.de> wrote:
> > 
> > > This is another attempt to avoid a regression in wwn_to_u64() after
> > > that started using get_unaligned_be64(), which in turn ran into a
> > > bug on gcc-4.9 through 6.1.
> > 
> > I'm still getting a couple screenfuls of things like
> > 
> > net/tipc/name_distr.c: In function 'tipc_named_process_backlog':
> > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 3 has type 'unsigned int'
> > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 4 has type 'unsigned int'
> > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 5 has type 'unsigned int'
> > net/tipc/name_distr.c:330: warning: format '%u' expects type 'unsigned int', but argument 7 has type 'unsigned int'
> 
> I've built a few thousand kernels (arm32 with gcc-6.1) with the patch applied,
> but didn't see this one. What target architecture and compiler version produced
> this? Does it go away if you add a (__u32) cast? I don't even know what the
> warning is trying to tell me.

heh, I didn't actually read it.

Hopefully we can write this off as a gcc-4.4.4 glitch. 4.8.4 is OK.