From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3yf7YT2hYjzDrSP for ; Sat, 18 Nov 2017 19:33:48 +1100 (AEDT) Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vAI8Uvf2101246 for ; Sat, 18 Nov 2017 03:33:46 -0500 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2eaehc5s33-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sat, 18 Nov 2017 03:33:45 -0500 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 18 Nov 2017 08:33:43 -0000 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Message-Id: <1510992250.emxjvilqnz.naveen@linux.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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(inst= r)) && >>>>>> + (instr & BRANCH_SET_LINK); >>>>>> +} >>>>>> + >>>>> >>>>> Nitpicking here, but since we're not considering the other branch for= ms, >>>>> perhaps this can be renamed to instr_is_link_relative_branch() (or ma= ybe >>>>> 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 th= e >>>> i-form (unconditional). And the above function isn't checking the >>>> absolute bit, so it isn't necessarily a relative branch. Or did I mis= s >>>> 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 branche= s >>> here (for relocations), so can we actually filter out the absolute bran= ches? >>> 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 s= ibling 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 >=20 > Reviewed-and-tested-by: Kamalesh Babulal Thanks, Kamalesh! - Naveen =