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

From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	Alan Stern <stern@rowland.harvard.edu>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	Akira Yokosawa <akiyks@gmail.com>,
	Daniel Lustig <dlustig@nvidia.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo
Date: Tue, 26 Feb 2019 12:25:21 +0100	[thread overview]
Message-ID: <20190226112521.GH32534@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190226112133.GG32534@hirez.programming.kicks-ass.net>

On Tue, Feb 26, 2019 at 12:21:33PM +0100, Peter Zijlstra wrote:

> Also; we need to find a GCC person to find/give us a knob to kill this
> entire class of nonsense. This is just horrible broken shit:
> 
> 
> ~/tmp# gcc -O2 -fno-strict-aliasing  -o ptr ptr.c ; ./ptr
> p=0x5635dd3d5034 q=0x5635dd3d5034
> x=1 y=2 *p=11 *q=2
> ~/tmp# cat ptr.c
> #include <stdio.h>
> #include <string.h>
> int y = 2, x = 1;
> int main (int argc, char **argv) {
> 	int *p = &x + argc;

damn; wrong version; that should've been: s/argc/1/
same result though.

> 	int *q = &y;
> 	printf("p=%p q=%p\n", p, q);
> 	if (!memcmp(&p, &q, sizeof(p))) {
> 		*p = 11;
> 		printf("x=%d y=%d *p=%d *q=%d\n", x, y, *p, *q);
> 	}
> }