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

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Message-Id: <20190226150427.GM4072@linux.ibm.com>
Date:   Tue, 26 Feb 2019 07:04:27 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Akira Yokosawa <akiyks@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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>,
        Daniel Lustig <dlustig@...dia.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo

On Tue, Feb 26, 2019 at 11:56:57PM +0900, Akira Yokosawa wrote:
> Hi Paul,
> 
> On Tue, 26 Feb 2019 06:28:45 -0800, Paul E. McKenney wrote:
> > 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.
> 
> By "it", do you mean the concept of "pointer provenance"?
> 
> I'm asking because the paper's header reads:
> 
>         "ISO/IEC JTC1/SC22/WG14 N2311, 2018-11-09"
> 
> Just wanted to make sure.

This paper introduces neither pointer provenance nor indeterminate-on-free,
but rather proposes modification.  These things have been around for a
few decades.

							Thanx, Paul

>         Thanks, Akira
> 
> >                  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
> > 
>