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

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Message-Id: <20190226142845.GK4072@linux.ibm.com>
Date:   Tue, 26 Feb 2019 06:28:45 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 02:49:06PM +0100, Peter Zijlstra wrote:
> On Tue, Feb 26, 2019 at 12:38:13PM +0100, Borislav Petkov wrote:
> > On Tue, Feb 26, 2019 at 12:30:08PM +0100, Peter Zijlstra wrote:
> > > When I used the argc variant, gcc-8 'works', but with s/argc/1/ it is
> > > still broken.
> > 
> > As requested on IRC:
> 
> What I asked was if you could get your GCC developer friends to have a
> look at this :-)

Yes, this all is a bit on the insane side from a kernel viewpoint.
But the paper you found does not impose this; it has instead been there
for about 20 years, back before C and C++ admitted to the existence
of concurrency.  But of course compilers are getting more aggressive,
and yes, some of the problems show up in single-threaded code.

The usual response is "then cast the pointers to intptr_t!" but of
course that breaks type checking.

There is an effort to claw back the concurrency pieces, and I would
be happy to run the resulting paper past you guys.

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?

							Thanx, Paul