From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo
Date: Tue, 26 Feb 2019 07:39:57 -0800
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>, Andrea Parri <andrea.parri@amarulasolutions.com>, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Alan Stern <stern@rowland.harvard.edu>, Will Deacon <will.deacon@arm.com>, Boqun Feng <boqun.feng@gmail.com>, Nicholas Piggin <npiggin@gmail.com>, David Howells <dhowells@redhat.com>, Jade Alglave <j.alglave@ucl.ac.uk>, Luc Maranget <luc.maranget@inria.fr>, Akira Yokosawa <akiyks@gmail.com>, Daniel Lustig <dlustig@nvidia.com>
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On Tue, Feb 26, 2019 at 03:47:30PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 26, 2019 at 06:28:45AM -0800, Paul E. McKenney wrote:
> > I must confess to not being all that sympathetic to code that takes
> > advantage of happenstance stack-frame layout.  Is there some reason
> > we need that?
> 
> Not that I'm aware; but if it gets this 'obvious' case wrong, I worry
> what else it gets wrong.
> 
> At the very least we should get this fixed and compile a kernel with the
> fixed compiler to see what (if anything) changes in the generated code
> and analyse the changes (if any) to make sure we were ok (or not).
> 
> I mean; yes that example is UB, but the result is also clearly batshit
> insane.

My understanding is that their goal is better analysis of pointer
aliasing, and that this case is a side effect.

							Thanx, Paul