Re: [PATCH] mips: avoid explicit UB in assignment of mips_io_port_base

From: Nick Desaulniers <ndesaulniers@google.com>
To: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>,
	James Hogan <jhogan@kernel.org>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Eli Friedman <efriedma@quicinc.com>,
	Hassan Naveed <hnaveed@wavecomp.com>,
	Stephen Kitt <steve@sk2.org>,
	Serge Semin <fancer.lancer@gmail.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	"regehr@cs.utah.edu" <regehr@cs.utah.edu>,
	Philip Reames <listmail@philipreames.com>,
	Alexander Potapenko <glider@google.com>,
	Alistair Delva <adelva@google.com>,
	"Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [PATCH] mips: avoid explicit UB in assignment of mips_io_port_base
Date: Mon, 26 Aug 2019 10:31:09 -0700	[thread overview]
Message-ID: <CAKwvOdmWS0_5haTdS67Sh0YjrUwfVOhLCwEXCO7vj6X1gXmCqQ@mail.gmail.com> (raw)
In-Reply-To: <20190824141213.svzmdr3pxdaqssuj@pburton-laptop>

On Sat, Aug 24, 2019 at 7:12 AM Paul Burton <paul.burton@mips.com> wrote:
>
> Hi Nick,
>
> On Fri, Aug 23, 2019 at 10:16:04AM -0700, Nick Desaulniers wrote:
> > On Tue, Aug 20, 2019 at 10:15 AM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > > Hi Paul,
> > > Bumping this thread; we'd really like to be able to boot test another
> > > ISA in our CI.  This lone patch is affecting our ability to boot.  Can
> > > you please pick it up?
> > > https://lore.kernel.org/lkml/20190729211014.39333-1-ndesaulniers@google.com/
> >
> > Hi Paul,
> > Following up with this link that explains the undefined behavior issue more:
> > https://wiki.sei.cmu.edu/confluence/display/c/EXP05-C.+Do+not+cast+away+a+const+qualification
> > Please reconsider accepting this patch.
>
> Sorry, it's been a crazy few months & I'm currently away awaiting my
> father's funeral so I'm working through a backlog & catching up on
> things.

That's an extremely tough hand to be dealt.  Got it myself a week
before I turned 20.  Technically, (spoiler) everyone is eventually
dealt it; not that that or really anything else can ever truly provide
solace despite the common refrain "time heals all wounds" (Narrator:
it doesn't).  Depending on where you are in life it can really really
destabilize things.  I wrote this blog post
(https://nickdesaulniers.github.io/blog/2013/04/29/the-persistence-of-memory/)
that I'm not too proud of at a time I now realize that I was still
kind of a state of shock (even years later).  I also found it very
difficult to accept advice from others who didn't share the experience
of losing a parent.

No one would fault you for asking your co-maintainers to handle more
maintainer responsibilities for a while.  I hope you can find a friend
to commiserate with over beers.  I owe you one.

>
> It will be a shame to lose the optimization opportunities const offers
> us, but it is an ugly hack & so I'm OK with applying this. It's likely
> to affect older machines more than newer ones (which tend to use less or
> no I/O port access) so I'm not too worried about the impact, but if we
> find it matters we can always try the fixmap approach I suggested
> previously.
>
> Thanks,
>     Paul

-- 
Thanks,
~Nick Desaulniers