From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755981AbYBSRiQ (ORCPT ); Tue, 19 Feb 2008 12:38:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753495AbYBSRiA (ORCPT ); Tue, 19 Feb 2008 12:38:00 -0500 Received: from terminus.zytor.com ([198.137.202.10]:54633 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752820AbYBSRh7 (ORCPT ); Tue, 19 Feb 2008 12:37:59 -0500 Message-ID: <47BB13ED.90705@zytor.com> Date: Tue, 19 Feb 2008 09:37:49 -0800 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: James Crosby CC: linux-kernel@vger.kernel.org Subject: Re: Ideal Architecture for Linux References: <146444620802190601t63ac667cpd41d834cc98d10df@mail.gmail.com> In-Reply-To: <146444620802190601t63ac667cpd41d834cc98d10df@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org James Crosby wrote: > A stack based architecture is best, it makes nested interrupts, and general > interruptibility very easy. If you mean stack-based register file, then that's *not* desirable; Linux depends on gcc which prefers a flat register file. 16 registers minimum. > Two hardware stack pointers, one for kernel stack and one for user mode > stack of each task, but maybe a third, interrupt stack. Don't necessarily have to be hardware registers, although it speed things up. Interrupt stacks are good. > At least two corresponding processor modes, a user mode with access only > to 'safe' instructions, and a privileged one that can do anything. But would > additional modes for interrupt handlers and system call handlers be > beneficial? Not in Linux. > I would also consider it a significant security problem if when a task enters > the kernel, kernel data is stored on the task's user-mode stack, since the > task could fish around beyond the end of its stack and sniff private data. (This > is, if I understand correctly, the reason ARM system mode is unused.) > > But on the other hand, if each task didn't need a separate kernel stack, then > there could be 4k or 8k less memory use per thread. No, it would just be in a different place. Linux will *NOT* accommodate this model. > Is it necessarily the case that the more similar to x86, the better Linux 'fits' > the architecture? No, the x86 is lacking quite a few key features. Linux would prefer to have address space numbers, instructions for user-space memory access in kernel mode, and a larger page size (4K is really too small for modern multi-gigabyte machines.) The design of the I/O infrastructure is another matter, too. -hpa