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:

quoted

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.