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Date: Sun, 25 Jun 2017 12:14:04 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Larry Finger <Larry.Finger@lwfinger.net>
Cc: LKML <linux-kernel@vger.kernel.org>,
 Thorsten Leemhuis <regressions@leemhuis.info>,
 linuxppc-dev@lists.ozlabs.org
Subject: Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to
 commit 3448890c32c3
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On Sun, Jun 25, 2017 at 10:53:58AM +0100, Al Viro wrote:
> On Sat, Jun 24, 2017 at 12:29:23PM -0500, Larry Finger wrote:
> 
> > I made a break through. If I turn off inline copy to/from users for 32-bit
> > ppc with the following patch, then the system boots:
> 
> OK...  So it's 4.6.3 miscompiling something - it is hardware-independent,
> reproduced in qemu.  I'd like to get more self-contained example of
> miscompile, though; should be done by tonight...

OK, it's the call in rw_copy_check_uvector(); with INLINE_COPY_FROM_USER
it's miscompiled by 4.6.3.  I hadn't looked through the generated code
yet; will do that after I grab some sleep.