From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751826AbdB1Tfs (ORCPT ); Tue, 28 Feb 2017 14:35:48 -0500 Received: from prod-mail-xrelay08.akamai.com ([96.6.114.112]:17233 "EHLO prod-mail-xrelay08.akamai.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751499AbdB1Tfm (ORCPT ); Tue, 28 Feb 2017 14:35:42 -0500 Subject: Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes To: David Daney , Steven Rostedt , Sachin Sant References: <1488221364-13905-1-git-send-email-jbaron@akamai.com> <93219edf-0f6d-5cc7-309c-c998f16fe7ac@akamai.com> <20170227160601.5b79a1fe@gandalf.local.home> <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com> <20170227170911.2280ca3e@gandalf.local.home> <7fa95eea-20be-611c-2b63-fca600779465@caviumnetworks.com> <20170227173630.57fff459@gandalf.local.home> <7bd72716-feea-073f-741c-04212ebd0802@caviumnetworks.com> <68fe24ea-7795-24d8-211b-9d8a50affe9f@akamai.com> <510FF566-011D-4199-86F7-2BB4DBF36434@linux.vnet.ibm.com> <20170228112144.65455de5@gandalf.local.home> <1de00727-de97-f887-78bd-dd49131cdf61@akamai.com> <999e2c3f-698c-703c-67a9-26aea3c97dc0@caviumnetworks.com> Cc: linux-mips@linux-mips.org, Chris Metcalf , Michael Ellerman , Russell King , Ralf Baechle , LKML , Rabin Vincent , Paul Mackerras , Anton Blanchard , linuxppc-dev@lists.ozlabs.org, Ingo Molnar , linux-arm-kernel@lists.infradead.org, Zhigang Lu From: Jason Baron Message-ID: <542488db-5c59-afa5-6d1d-a437c87bc613@akamai.com> Date: Tue, 28 Feb 2017 14:34:52 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/28/2017 02:22 PM, David Daney wrote: > On 02/28/2017 11:05 AM, David Daney wrote: >> On 02/28/2017 10:39 AM, Jason Baron wrote: >>> > [...] >>>> I suspect that the alignment of the __jump_table section in the .ko >>>> files is not correct, and you are seeing some sort of problem due to >>>> that. >>>> >>>> >>> >>> Hi, >>> >>> Yes, if you look at the trace that Sachin sent the module being loaded >>> that does the WARN_ON() is nfsd.ko. >>> >>> That module from Sachin's trace has: >>> >>> [31] __jump_table PROGBITS 0000000000000000 03fd77 0000c0 >>> 18 WAM 0 0 1 >> >> The problem is then the section alignment (last column) for power. >> >> On mips with no patches applied, we get: >> >> [17] __jump_table PROGBITS 0000000000000000 00d2c0 000048 >> 00 WA 0 0 8 >> >> Look, proper alignment! >> >> The question I have is why do the power ".llong" and ".long" assembler >> directives not force section alignment? Is there an alternative that >> could be used that would result in the proper alignment? Would ".word" >> work? >> >> If not, then I would say patch only power with your balign thing. 8-byte >> alignment for 64-bit kernel, 4-byte alignment for 32-bit kernel >> > > I think the proper fix is either: > > A) Modify scripts/module-common.lds to force __jump_table alignment for > all architectures. > > B) Add arch/powerpc/kernel/module.lds to force __jump_table alignment > for powerpc only. > > David. > > Ok, I can try adding it to the linger script. FWIW, here is my before and after with the .balign thing for the nfsd.ko module on powperc (using a cross-compiler): before: [31] __jump_table PROGBITS 0000000000000000 03ee3e 0000f0 00 WA 0 0 1 after: [31] __jump_table PROGBITS 0000000000000000 03ee40 0000f0 00 WA 0 0 4 Thanks, -Jason > >> >>> >>> So its not the size but rather the start offset '03fd77', that is the >>> problem here. That is what the WARN_ON triggers on, that the start of >>> the table is not 4-byte aligned. >>> >>> Using a ppc cross-compiler and the ENTSIZE patch that line does not >>> change, however if I use the initial patch posted in this thread, the >>> start does align to 4-bytes and thus the warning goes away, as Sachin >>> verified. In fact, without the patch I found several modules that don't >>> start at the proper alignment, however with the patch that started this >>> thread they were all properly aligned. >>> >>> In terms of the '.balign' causing holes, we originally added the >>> '_ASM_ALIGN' to x86 for precisely this reason. See commit: >>> ef64789 jump label: Add _ASM_ALIGN for x86 and x86_64 and discussion. >>> >>> In addition, we have a lot of runtime with the .balign in the tree and >>> I'm not aware of any holes in the table. I think the code would blow up >>> pretty badly if there were. >>> >>> A number of arches were already using the '.balign', and the patch I >>> proposed simply added it to remaining ones, now that we added a >>> WARN_ON() to catch this condition. >>> >>> Thanks, >>> >>> -Jason >>> >>> >>> >>> >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >