From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934310AbcKJPgM (ORCPT ); Thu, 10 Nov 2016 10:36:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48854 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933690AbcKJPgK (ORCPT ); Thu, 10 Nov 2016 10:36:10 -0500 Date: Thu, 10 Nov 2016 09:36:08 -0600 From: Josh Poimboeuf To: live-patching@vger.kernel.org Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 0/2] livepatch: patch creation tooling proposal Message-ID: <20161110153608.jsxlygej4r3ux42g@treble> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 10 Nov 2016 15:36:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 27, 2016 at 09:35:48AM -0500, Josh Poimboeuf wrote: > So here's my proposal: use the existing kernel build infrastructure. If > klp relocations are needed, manually specify them with a new > klp_module_reloc struct and corresponding KLP_MODULE_RELOC macro. Then > run a post-processing tool called klp-convert which converts those > klp_module_reloc structs into the sections, relocations, and symbols > needed by the klp runtime code. I think the biggest blocker for this approach is detecting gcc optimizations which break function ABI, i.e. Miroslav's presentation: http://www.linuxplumbersconf.org/2016/ocw//system/presentations/3573/original/pres_gcc.pdf Right now we have no way of finding all such cases. I think our options are: 1) Find a way for gcc to report when function ABI has been broken; 2) Disable all gcc optimizations which can break function ABI. Not sure if this is even possible, but if so, we'd need to quantify the performance impact. (Note we might be able to leave some options enabled if they result in a function name change (e.g., -fpartial-inlining, -fipa-sra, -fipa-cp)); or 3) Stay with the status quo (kpatch-build?), since it has detection of such optimizations "built in". Does anybody want to take ownership of this patch set and/or try to explore the options further? I don't have any more bandwidth right now (mainly due to the consistency model and porting objtool to DWARF). -- Josh