Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3

[Al Viro]

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.