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

[Akira Yokosawa]

On Tue, 26 Feb 2019 07:04:27 -0800, Paul E. McKenney wrote:
> 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.

Got it!

        Thank, Akira
> 
> 							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
>>>
>>
>