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 S1754182Ab2EFSqq (ORCPT <rfc822;w@1wt.eu>);
	Sun, 6 May 2012 14:46:46 -0400
Received: from zeniv.linux.org.uk ([195.92.253.2]:35645 "EHLO
	ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754079Ab2EFSqp (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sun, 6 May 2012 14:46:45 -0400
Date: Sun, 6 May 2012 19:46:42 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH] broken TASK_SIZE for ia32_aout
Message-ID: <20120506184641.GW6871@ZenIV.linux.org.uk>
References: <20120506162000.GT6871@ZenIV.linux.org.uk>
 <CA+55aFzj3Ocjpnw3WdmKjp3oELwmXt=Zs2=fZuYy0TUyF4nXiA@mail.gmail.com>
 <20120506175451.GU6871@ZenIV.linux.org.uk>
 <4FA6BBD9.3040308@zytor.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4FA6BBD9.3040308@zytor.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sun, May 06, 2012 at 10:58:49AM -0700, H. Peter Anvin wrote:

> > What kind of semantics do we want?  "Thread property" one, set when we
> > set personality on execve(), or "syscall property", like e.g. x86 TIF_IRET
> > and TS_COMPAT?
> 
> It depends on the ABI properties of the platform.  The x86 compat ABI is
> that any task can issue a compat ABI request and get a compat ABI
> response (a 64-bit task can call int $0x80 for an ia32 syscall
> invocation, or use syscall with either an x86-64 or and x32 system call
> number.)  So is_compat_task() returns the current system call mode of
> the task, because that is what downstream users need.  One of the
> biggest users is the input subsystem, which earns the black mark for
> worst possible ABI design, and that definitely depends on the system
> call type being invoked.

Umm...  Let me restate that question: is there ever a case when it would
_not_ be a syscall property?  I.e. when both 64bit and 32bit syscalls are
possible for a given process *and* callers of is_compat_task() care about
the kind of process and not the kind of syscall?

Is e.g. sparc behaviour ("what kind of process it is, regardless of whether
we are issuing a 32bit or a 64bit syscall") correct?

Sure, on a platform where the possible kind of syscall is a function of
process' personality, a thread property can be a used to tell which
kind of syscall we are in.