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

From: Akira Yokosawa
Date: Tue Feb 26 2019 - 09:57:06 EST

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.

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