Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759011Ab1FVV6P (ORCPT ); Wed, 22 Jun 2011 17:58:15 -0400 Received: from mail-fx0-f46.google.com ([209.85.161.46]:53823 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758594Ab1FVV6O (ORCPT ); Wed, 22 Jun 2011 17:58:14 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=Is6OSFdJ9u3rTBRA6S52sMf6zsw9AlLypNdkbG9co6bv6nUNJbh4CHkf80VJ93+OZx BVcKb6ietgrnumiKvG/prOJKFd1FmrtMwpuSkBLyeuM+05vddE+UVkfzrTx/Zn5ay5vt cjb+l0pcLM+FBZCItQSWIV8xVcf7mNzpNEPeQ= MIME-Version: 1.0 In-Reply-To: References: <20110622132114.GA8656@dumpdata.com> Date: Wed, 22 Jun 2011 14:58:12 -0700 Message-ID: Subject: Re: code sections beyond .text skipped from alternatives_smp_module_add From: Deep Debroy To: Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, kraxel@redhat.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2643 Lines: 61 On Wed, Jun 22, 2011 at 10:27 AM, Deep Debroy wrote: > On Wed, Jun 22, 2011 at 6:21 AM, Konrad Rzeszutek Wilk > wrote: >>> > Looking at the code, in module_finalize for x86, only .text seems to >>> > be getting picked for the patching of lock prefixes while other >>> > sections such as .exit.text or .init.text are not. Is there a reason >>> > we skip the other *.text code sections from the lock patches? Would >>> + Gerd Hoffmann who introduced the SMP patching code below back in Jan >>> 2006 as part of 2.6.15. >> >> Whoa, long time ago. >> >>> >>> Any comments on why patching of smp_lock prefixes should be restricted >>> to .text and not other *.text code sections? >> >> It could be that at that time the .exit.text or .init.text did not exist. >> >> As in, the patching code just hasn't kept up. One way of checking that >> is just finding the ancient 2.6.15 code and seeing if there is any >> mention of those extra segments. >> > > Thanks Konrad. One slight correction: after rechecking the kernel > sources, it appears the smp lock prefix code first made it's > appearance in the official trees during 2.6.18. In any case, going > back even to 2.6.16 sources, layout_sections in module.c specially > handled .init prefixed sections from the rest i.e. core sections. > Further, the module struct in include/module/linux.h seems to have had > members such as init_text_size which suggests atleast .init.text did > exit back then as well. While I didn't find any crumbs in the code > that point to the existence of a .exit.text (besides a function > pointer called exit which most likely ended up in the .exit.text), the > ELF headers for Centos 5.6 kernel objects (which uses the 2.6.18 > kernel) typically have a .exit.text. > >> Do you have a patch to fix this? >> > > I can work on that. Just wanted to first make sure that there wasn't > any specific reason to avoid patching non .text sections. > > Thanks, > Deep > Some further digging through messages revealed a patch from Randy Dunlap in June 2006: "[PATCH] ignore smp_locks section warnings from init/exit code." Given this patch came in after the smp locking hotpatching mechanism was introduced, there may have been an assumption that instructions that results in entries in smp_locks relocations in the object file should not exist in the init/exit.text sections. Thanks, Deep -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/