[PATCH] powerpc: Avoid panic during boot due to divide by zero in init_cache_info()

[David Laight]

From: Segher Boessenkool
> Sent: 06 March 2017 14:18
> On Mon, Mar 06, 2017 at 01:03:19PM +0100, Gabriel Paubert wrote:
> > > > > The PowerPC divw etc. instructions do not trap by themselves, but recent
> > > > > GCC inserts trap instructions on code paths that are always undefined
> > > > > behaviour (like, dividing by zero).
> > > >
> > > > Is it systematic or does it depend from, e.g., optimization levels?
> > >
> > > In this case it needs -fisolate-erroneous-paths-dereference which is
> > > default at -O2 and higher.
> >
> > Great, another optimization-dependent behaviour. :-(
> 
> It makes the "behaviour" for undefined behaviour *less* surprising.
> It does not change anything else: malformed programs stay malformed,
> correct programs do exactly what they did before, too.

Yep, 'undefined behaviour' is exactly that.
It doesn't mean 'undefined result', or 'maybe a signal'.
Wiping the disk and targeting the user with an ICBM are both valid.

	David