From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031473AbXD3JSU (ORCPT ); Mon, 30 Apr 2007 05:18:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031478AbXD3JSU (ORCPT ); Mon, 30 Apr 2007 05:18:20 -0400 Received: from caramon.arm.linux.org.uk ([217.147.92.249]:4486 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031467AbXD3JSS (ORCPT ); Mon, 30 Apr 2007 05:18:18 -0400 Date: Mon, 30 Apr 2007 10:18:09 +0100 From: Russell King To: Christoph Hellwig , Roland McGrath , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: utrace comments Message-ID: <20070430091808.GA11345@flint.arm.linux.org.uk> Mail-Followup-To: Christoph Hellwig , Roland McGrath , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20061127165138.GA2991@lst.de> <20070430040213.BF9901801A4@magilla.sf.frob.com> <20070430090840.GB31397@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070430090840.GB31397@infradead.org> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 30, 2007 at 10:08:40AM +0100, Christoph Hellwig wrote: > Btw, is there a fundamental reason why an architecture would not support > single-stepping except for a transition period of porting, i.e. are there > real hardware limitation in any of our ports? Roland's idea of single-stepping is that it *must* be supported by hardware for utrace to use it. There are a number of architectures which can only do single-stepping by modifying the text of the program being single stepped. ARM is one such example. As such, even when utrace is complete, some architectures will never support in-kernel single step with utrace. I believe Roland's idea is to have single step supported on these via some vapourware userspace library. My biggest worry is that the architectures which do not support hardware single stepping are seen by many people as "minority architectures" which "don't really matter" and as such making support for a feature such a special case will probably result in the feature effectively being unavailable on those architectures. As such I have zero motivation to continue my forrey into utrace from a couple of months ago. I'd also like to see utrace become *optional* for architectures to support, rather than as it currently stands as a *mandatory* requirement when merged. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: