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

From: Paul E. McKenney
Date: Tue Feb 26 2019 - 10:40:08 EST

On Tue, Feb 26, 2019 at 03:47:30PM +0100, Peter Zijlstra wrote:
> 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.

My understanding is that their goal is better analysis of pointer
aliasing, and that this case is a side effect.

Thanx, Paul