From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946551AbdKRIdy convert rfc822-to-8bit (ORCPT ); Sat, 18 Nov 2017 03:33:54 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:39810 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1946537AbdKRIdq (ORCPT ); Sat, 18 Nov 2017 03:33:46 -0500 Date: Sat, 18 Nov 2017 14:03:36 +0530 From: "Naveen N. Rao" Subject: Re: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call To: Josh Poimboeuf , Kamalesh Babulal Cc: Balbir Singh , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, live-patching@vger.kernel.org, Michael Ellerman References: <20171114092910.20399-1-kamalesh@linux.vnet.ibm.com> <20171114092910.20399-3-kamalesh@linux.vnet.ibm.com> <1510654928.8xrjtkjm8m.naveen@linux.ibm.com> <20171114155323.3sjxx3eykinnl2ea@treble> <1510737417.g8rnjuztlf.naveen@linux.ibm.com> <20171116012628.6ajxlychto365sf6@treble> <1510837263.5d3ac8knzo.naveen@linux.ibm.com> <20171116174537.duz4x6vfzhp44lfh@treble> <2094a573-d236-e1b7-6f4d-47049f3d0dfb@linux.vnet.ibm.com> In-Reply-To: <2094a573-d236-e1b7-6f4d-47049f3d0dfb@linux.vnet.ibm.com> User-Agent: astroid/0.10.2 (https://github.com/astroidmail/astroid) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8BIT X-TM-AS-GCONF: 00 x-cbid: 17111808-0008-0000-0000-000004ACDEB5 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17111808-0009-0000-0000-00001E3F9C52 Message-Id: <1510992250.emxjvilqnz.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-18_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1711180122 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kamalesh Babulal wrote: > On Thursday 16 November 2017 11:15 PM, Josh Poimboeuf wrote: >> On Thu, Nov 16, 2017 at 06:39:03PM +0530, Naveen N. Rao wrote: >>> Josh Poimboeuf wrote: >>>> On Wed, Nov 15, 2017 at 02:58:33PM +0530, Naveen N. Rao wrote: >>>>>> +int instr_is_link_branch(unsigned int instr) >>>>>> +{ >>>>>> + return (instr_is_branch_iform(instr) || instr_is_branch_bform(instr)) && >>>>>> + (instr & BRANCH_SET_LINK); >>>>>> +} >>>>>> + >>>>> >>>>> Nitpicking here, but since we're not considering the other branch forms, >>>>> perhaps this can be renamed to instr_is_link_relative_branch() (or maybe >>>>> instr_is_relative_branch_link()), just so we're clear :) >>>> >>>> My understanding is that the absolute/relative bit isn't a "form", but >>>> rather a bit that can be set for either the b-form (conditional) or the >>>> i-form (unconditional). And the above function isn't checking the >>>> absolute bit, so it isn't necessarily a relative branch. Or did I miss >>>> something? >>> >>> Ah, good point. I was coming from the fact that we are only considering the >>> i-form and b-form branches and not the lr/ctr/tar based branches, which are >>> always absolute branches, but can also set the link register. >> >> Hm, RISC is more complicated than I realized ;-) As long as 'RISC' gets people to take a look ;D >> >>> Thinking about this more, aren't we only interested in relative branches >>> here (for relocations), so can we actually filter out the absolute branches? >>> Something like this? >>> >>> int instr_is_relative_branch_link(unsigned int instr) >>> { >>> return ((instr_is_branch_iform(instr) || instr_is_branch_bform(instr)) && >>> !(instr & BRANCH_ABSOLUTE) && (instr & BRANCH_SET_LINK)); >> >> Yeah, makes sense to me. Here's another try (also untested). If this >> looks ok, Kamalesh would you mind testing again? Thanks. That looks good to me. Acked-by: Naveen N. Rao >> >> ----8<---- >> >> From: Josh Poimboeuf >> Subject: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call >> >> When attempting to load a livepatch module, I got the following error: >> >> module_64: patch_module: Expect noop after relocate, got 3c820000 >> >> The error was triggered by the following code in >> unregister_netdevice_queue(): >> >> 14c: 00 00 00 48 b 14c >> 14c: R_PPC64_REL24 net_set_todo >> 150: 00 00 82 3c addis r4,r2,0 >> >> GCC didn't insert a nop after the branch to net_set_todo() because it's >> a sibling call, so it never returns. The nop isn't needed after the >> branch in that case. >> >> Signed-off-by: Josh Poimboeuf > > Reviewed-and-tested-by: Kamalesh Babulal Thanks, Kamalesh! - Naveen