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

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Date:   Tue, 26 Feb 2019 12:38:13 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        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>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo

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:

$ gcc --version
gcc (SUSE Linux) 4.8.5
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cat ptr.c
#include <stdio.h>
#include <string.h>
int y = 2, x = 1;
int main (int argc, char **argv) {
        int *p = &x + 1;
        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);

$ gcc -O2 -fno-strict-aliasing  -o ptr ptr.c ; ./ptr
p=0x601044 q=0x601044
x=1 y=2 *p=11 *q=2

-- 
Regards/Gruss,
    Boris.

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