linux-kernel - Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo

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Date:   Tue, 26 Feb 2019 15:47:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo

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.