From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760709AbcBYNbj (ORCPT ); Thu, 25 Feb 2016 08:31:39 -0500 Received: from verein.lst.de ([213.95.11.211]:48387 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760290AbcBYNbh (ORCPT ); Thu, 25 Feb 2016 08:31:37 -0500 Date: Thu, 25 Feb 2016 14:31:33 +0100 From: Torsten Duwe To: Balbir Singh Cc: Michael Ellerman , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, kamalesh@linux.vnet.ibm.com, pmladek@suse.com, jeyu@redhat.com, jkosina@suse.cz, live-patching@vger.kernel.org, mbenes@suse.cz Subject: Re: [PATCH 03/12] powerpc/module: Create a special stub for ftrace_caller() Message-ID: <20160225133133.GE21932@lst.de> References: <1456324115-21144-1-git-send-email-mpe@ellerman.id.au> <1456324115-21144-3-git-send-email-mpe@ellerman.id.au> <56CE4616.9080100@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56CE4616.9080100@gmail.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 25, 2016 at 11:08:54AM +1100, Balbir Singh wrote: > How about some comments on r2 > r2 is still pointing to the module's toc, will be saved by ftrace_caller and restored by the instruction following bl ftrace_caller (after patching _mcount/nop) To be precise: ftrace_caller needs to save _and_ restore r2 in case of -mprofile-kernel. > > + /* Stub uses address relative to kernel_toc */ > > + reladdr = (unsigned long)ftrace_caller - get_paca()->kernel_toc; kernel_toc is a compile time constant; do you really want to look it up in memory at runtime each time? It's a bit tricky to get the +- 0x8000 right OTOH... I wrote: extern unsigned long __toc_start; reladdr = addr - ((unsigned long)(&__toc_start) + 0x8000UL); looks a bit odd, but evaluates to a constant for ftrace_caller. Either way is fine with me: Signed-off-by: Torsten Duwe Reviewed-by: Torsten Duwe > Reviewed-by: Balbir Singh Torsten