Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Thu, 6 Feb 2020 23:18:31 -0500
To:     Larry Finger <Larry.Finger@lwfinger.net>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Ville =?utf-8?B?U3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Tom Anderson <thomasanderson@google.com>,
        Hans Verkuil <hansverk@cisco.com>,
        Manasi Navare <manasi.d.navare@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: Error building v5.5-git on PowerPC32 - bisected to commit
 7befe621ff81
Message-ID: <20200207041831.GA3091628@rani.riverdale.lan>
References: <0fb64c98-57c2-b988-051c-6ba0e460ad37@lwfinger.net>
 <20200206231211.GA2976063@rani.riverdale.lan>
 <20200206233325.GA3036478@rani.riverdale.lan>
 <cda542ae-e0ea-a9bc-53bc-8e91e06d254d@lwfinger.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <cda542ae-e0ea-a9bc-53bc-8e91e06d254d@lwfinger.net>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Feb 06, 2020 at 06:29:42PM -0600, Larry Finger wrote:
> On 2/6/20 5:33 PM, Arvind Sankar wrote:
> > On Thu, Feb 06, 2020 at 06:12:13PM -0500, Arvind Sankar wrote:
> >> On Thu, Feb 06, 2020 at 04:46:52PM -0600, Larry Finger wrote:
> >>> When building post V5.5 on my PowerBook G4 Aluminum, the build failed with the
> >>> following error:
> >>
> >> It's not that the attributes are wrong. The problem is that BUILD_BUG_ON
> >> requires a compile-time evaluatable condition. gcc-4.6 is apparently not
> >> good enough at optimizing to reduce that expression to a constant,
> >> though it was able to do it with the array accesses.
> > 
> > Should have noted, it fails on x86 too with gcc-4.6.4, not specific to PPC.
> 
> What pre-processor test would be correct to skip the test for gcc4?
> 
> Larry
> 

I think the patch you bisected to is broken. It should not use
BUILD_BUG_ON with a condition that is not obviously compile-time
evaluatable.