From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S2992671AbcB0X0f (ORCPT <rfc822;w@1wt.eu>);
	Sat, 27 Feb 2016 18:26:35 -0500
Received: from ozlabs.org ([103.22.144.67]:55518 "EHLO ozlabs.org"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S2992556AbcB0X0e (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Sat, 27 Feb 2016 18:26:34 -0500
Date: Sun, 28 Feb 2016 10:26:29 +1100
From: Stephen Rothwell <sfr@canb.auug.org.au>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dave Hansen <dave@sr71.net>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel@vger.kernel.org, dave.hansen@linux.intel.com,
        akpm@linux-foundation.org, tglx@linutronix.de, mingo@elte.hu,
        peterz@infradead.org, linux-next@vger.kernel.org, deller@gmx.de
Subject: Re: [PATCH] x86, pkeys: fix siginfo ABI breakage from new field
Message-ID: <20160228102629.0ef4ef4f@canb.auug.org.au>
In-Reply-To: <9E8119F8-1F37-4084-AE31-34CA6DE8C15E@zytor.com>
References: <20160226173427.54A6949F@viggo.jf.intel.com>
	<6C5C3B9B-CAD6-4010-9A3E-AFFF7E13FAE3@zytor.com>
	<20160227091013.6e0606d1@canb.auug.org.au>
	<20160227114154.GA16200@gmail.com>
	<56D1F61C.5050308@sr71.net>
	<9E8119F8-1F37-4084-AE31-34CA6DE8C15E@zytor.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi H.,

On Sat, 27 Feb 2016 11:35:08 -0800 "H. Peter Anvin" <hpa@zytor.com> wrote:
>
> On February 27, 2016 11:16:44 AM PST, Dave Hansen <dave@sr71.net> wrote:
> >On 02/27/2016 03:41 AM, Ingo Molnar wrote:  
> >> * Stephen Rothwell <sfr@canb.auug.org.au> wrote:  
> >>> > On Fri, 26 Feb 2016 09:44:00 -0800 "H. Peter Anvin"  
> ><hpa@zytor.com> wrote:  
> >>>> > > __u64 is okay, "unsigned long" is really messy in the presence  
> >of 32-on-64 bit ABIs...  
> >>> > 
> >>> > Yeah, but unfortunately, any 64 bit scalar type here will change  
> >the  
> >>> > alignment of the enclosing unions on (some) 32 bit platforms and  
> >thus  
> >>> > break the ABI.  
> >> Then a different solution has to be found.  
> >
> >I've acked Stephen's initial patch changing the 'u64' to an 'int'.  x86
> >only needs 4 bits, and in the remote chance that a future
> >implementation
> >needed more space, we could easily add a second 32-bit field "_pkey_hi"
> >or something that wouldn't have the alignment issues of a true 64-bit
> >type.
> >
> >How should we get Stephen's patch in to the tip tree?  
> 
> u32?

It would have to be __u32, but we already use int and unsigned int
extensively in the siginfo structure (which are both always assumed to
be 32 bits).  So "unsigned int" probably makes most sense.

I will submit that patch - with Dave's Ack.
-- 
Cheers,
Stephen Rothwell