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 S1752634AbdJRNRy (ORCPT <rfc822;w@1wt.eu>);
        Wed, 18 Oct 2017 09:17:54 -0400
Received: from mail-wm0-f67.google.com ([74.125.82.67]:56421 "EHLO
        mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1750782AbdJRNRv (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 18 Oct 2017 09:17:51 -0400
X-Google-Smtp-Source: ABhQp+Rh2lQczD5xNVIKDmXpa4pXhGye/An8hQKQgpBJqj/eHKCuk3+YIU6ugwQdUY70KKkNOqOz3w==
Date: Wed, 18 Oct 2017 15:17:47 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, luto@kernel.org,
        brgerst@gmail.com
Subject: Re: [PATCH] x86, syscalls: use SYSCALL_DEFINE() macros for
 sys_modify_ldt()
Message-ID: <20171018131747.xwte4c3oc5gt7yc5@gmail.com>
References: <20171017192231.72C327B4@viggo.jf.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171017192231.72C327B4@viggo.jf.intel.com>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Dave Hansen <dave.hansen@linux.intel.com> wrote:

> 
> We do not have tracepoints for sys_modify_ldt() because we define
> it directly instead of using the normal SYSCALL_DEFINEx() macros.
> 
> However, there is a reason sys_modify_ldt() does not use the macros:
> it has an 'int' return type instead of 'unsigned long'.  This is
> a bug, but it's a bug cemented in the ABI.
> 
> What does this mean?  If we return -EINVAL from a function that
> returns 'int', we have 0x00000000ffffffea in %rax.  But, if we
> return -EINVAL from a function returning 'unsigned long', we end
> up with 0xffffffffffffffea in %rax, which is wrong.
> 
> To work around this and maintain the 'int' behavior while using
> the SYSCALL_DEFINEx() macros, so we add a cast to 'unsigned int'
> in both implementations of sys_modify_ldt().
> 
> Cc: x86@kernel.org
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Brian Gerst <brgerst@gmail.com>

I have added your:

  Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>

let me know if that's OK.

Thanks,

	Ingo