From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA561C433F5 for ; Thu, 28 Oct 2021 13:35:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD8B7610F8 for ; Thu, 28 Oct 2021 13:35:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229945AbhJ1NiS (ORCPT ); Thu, 28 Oct 2021 09:38:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:40130 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229887AbhJ1NiR (ORCPT ); Thu, 28 Oct 2021 09:38:17 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AFF5261038; Thu, 28 Oct 2021 13:35:49 +0000 (UTC) Date: Thu, 28 Oct 2021 09:35:47 -0400 From: Steven Rostedt To: Christophe Leroy Cc: Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , Ingo Molnar , "Naveen N . Rao" , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, live-patching@vger.kernel.org Subject: Re: [PATCH v1 0/5] Implement livepatch on PPC32 Message-ID: <20211028093547.48c69dfe@gandalf.local.home> In-Reply-To: References: X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, 28 Oct 2021 14:24:00 +0200 Christophe Leroy wrote: > This series implements livepatch on PPC32. > > This is largely copied from what's done on PPC64. > > Christophe Leroy (5): > livepatch: Fix build failure on 32 bits processors > powerpc/ftrace: No need to read LR from stack in _mcount() > powerpc/ftrace: Add module_trampoline_target() for PPC32 > powerpc/ftrace: Activate HAVE_DYNAMIC_FTRACE_WITH_REGS on PPC32 > powerpc/ftrace: Add support for livepatch to PPC32 > > arch/powerpc/Kconfig | 2 +- > arch/powerpc/include/asm/livepatch.h | 4 +- > arch/powerpc/kernel/module_32.c | 33 +++++ > arch/powerpc/kernel/trace/ftrace.c | 53 +++----- > arch/powerpc/kernel/trace/ftrace_32.S | 187 ++++++++++++++++++++++++-- > kernel/livepatch/core.c | 4 +- > 6 files changed, 230 insertions(+), 53 deletions(-) > This is great that you are doing this, but I wonder if it would even be easier, and more efficient, if you could implement HAVE_DYNAMIC_FTRACE_WITH_ARGS? Then you don't need to save all regs for live kernel patching. And I am also working on function tracing with arguments with this too. That is, to call a generic ftrace callback, you need to save all the args that are stored in registers to prevent the callback from clobbering them. As live kernel patching only needs to have the arguments of the functions, you save time from having to save the other regs as well. The callbacks now have "struct ftrace_regs" instead of pt_regs, because it will allow non ftrace_regs_caller functions to access the arguments if it is supported. Look at how x86_64 implements this. It should be possible to do this for all other archs as well. Also note, by doing this, we can then get rid of the ftrace_graph_caller, and have function graph tracer be a function tracing callback, as it will allow ftrace_graph_caller to have access to the stack and the return as well. If you need any more help or information to do this, I'd be happy to assist you. Note, you can implement this first, (I looked over the patches and they seem fine) and then update both ppc64 and ppc32 to implement DYNAMIC_FTRACE_WITH_ARGS. Cheers, -- Steve