Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753801AbaKZPlW (ORCPT ); Wed, 26 Nov 2014 10:41:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46169 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753663AbaKZPlS (ORCPT ); Wed, 26 Nov 2014 10:41:18 -0500 Date: Wed, 26 Nov 2014 09:40:42 -0600 From: Josh Poimboeuf To: Miroslav Benes Cc: Seth Jennings , Jiri Kosina , Vojtech Pavlik , Steven Rostedt , Petr Mladek , Christoph Hellwig , Greg KH , Andy Lutomirski , Masami Hiramatsu , live-patching@vger.kernel.org, x86@kernel.org, kpatch@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCHv4 2/3] kernel: add support for live patching Message-ID: <20141126154042.GB29079@treble.hsd1.ky.comcast.net> References: <1416935709-404-1-git-send-email-sjenning@redhat.com> <1416935709-404-3-git-send-email-sjenning@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Miroslav, Just addressing one of your comments below. I'll let Seth respond to the others :-) On Wed, Nov 26, 2014 at 03:19:17PM +0100, Miroslav Benes wrote: > > +/** > > + * struct klp_func - function structure for live patching > > + * @old_name: name of the function to be patched > > + * @new_func: pointer to the patched function code > > + * @old_addr: a hint conveying at what address the old function > > + * can be found (optional, vmlinux patches only) > > + */ > > +struct klp_func { > > + /* external */ > > + const char *old_name; > > + void *new_func; > > + /* > > + * The old_addr field is optional and can be used to resolve > > + * duplicate symbol names in the vmlinux object. If this > > + * information is not present, the symbol is located by name > > + * with kallsyms. If the name is not unique and old_addr is > > + * not provided, the patch application fails as there is no > > + * way to resolve the ambiguity. > > + */ > > + unsigned long old_addr; > > I wonder if we really need old_addr as an external field. I assume that > userspace tool in kpatch use it as a "hint" for kernel part and thus > kallsyms is not needed there (and it solves ambiguity problem as well). > But I am not sure if it is gonna be the same in upstream. When kernel is > randomized (CONFIG_RANDOMIZE_BASE is set to 'y', though default is 'n') > old_addr is not usable (and we throw it away in the code). Without > old_addr being set by the user we could spare some of code (calls to > klp_verify_vmlinux_symbol and such). Even with CONFIG_RANDOMIZE_BASE, the function offsets will be the same regardless of the base address. So we could still use old_addr to determine the offset. > So the question is whether future userspace tool in upstream would need it > and would use it. Please note that I do not mean it as a kpatch or kgraft > way to do things, I'm just not sure about old_addr being "public" and want > do discuss the options. > > The ambiguity of symbols was discussed in some other thread in lkml in > october (I guess) with no conclusion IIRC... We need to resolve ambiguity somehow, and old_addr is a way to do that. Do you have any other ideas? -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/