linux-kernel - Re: Error building v5.5-git on PowerPC32

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Date:   Thu, 6 Feb 2020 23:18:31 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Larry Finger <Larry.Finger@...inger.net>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Tom Anderson <thomasanderson@...gle.com>,
        Hans Verkuil <hansverk@...co.com>,
        Manasi Navare <manasi.d.navare@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Error building v5.5-git on PowerPC32 - bisected to commit
 7befe621ff81

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.