From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755653AbdCWNZD (ORCPT ); Thu, 23 Mar 2017 09:25:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59954 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750952AbdCWNZC (ORCPT ); Thu, 23 Mar 2017 09:25:02 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 1491061D1D Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jpoimboe@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 1491061D1D Date: Thu, 23 Mar 2017 08:24:58 -0500 From: Josh Poimboeuf To: Ingo Molnar Cc: Jiri Slaby , Pavel Machek , mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, Boris Ostrovsky , Juergen Gross , xen-devel@lists.xenproject.org, "Rafael J. Wysocki" , Len Brown , linux-pm@vger.kernel.org Subject: Re: [PATCH v2 02/10] x86: assembly, FUNC_START for fn, DATA_START for data Message-ID: <20170323132458.wuil6uvri4o2kyom@treble> References: <9ea5e137-61f9-dccc-bb9d-ac3ff86e5867@suse.cz> <20170320123222.15453-1-jslaby@suse.cz> <20170320123222.15453-2-jslaby@suse.cz> <20170321140840.GA23311@amd> <20170322072557.GA13904@gmail.com> <20170322074616.GA10809@gmail.com> <20170322141123.opss3u4gpupqgl2q@treble> <20170323073819.GA14258@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170323073819.GA14258@gmail.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 23 Mar 2017 13:25:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 23, 2017 at 08:38:20AM +0100, Ingo Molnar wrote: > > * Josh Poimboeuf wrote: > > > On Wed, Mar 22, 2017 at 08:46:16AM +0100, Ingo Molnar wrote: > > > > > > * Jiri Slaby wrote: > > > > > > > On 03/22/2017, 08:25 AM, Ingo Molnar wrote: > > > > > > > > > > * Pavel Machek wrote: > > > > > > > > > >> Hi! > > > > >> > > > > >>> -ENTRY(saved_rbp) .quad 0 > > > > >>> -ENTRY(saved_rsi) .quad 0 > > > > >>> -ENTRY(saved_rdi) .quad 0 > > > > >>> -ENTRY(saved_rbx) .quad 0 > > > > >>> +SYM_DATA_START(saved_rbp) .quad 0 > > > > >>> +SYM_DATA_START(saved_rsi) .quad 0 > > > > >>> +SYM_DATA_START(saved_rdi) .quad 0 > > > > >>> +SYM_DATA_START(saved_rbx) .quad 0 > > > > >> > > > > >> Does it make sense to call it SYM_DATA_*START* when there's no > > > > >> corresponding end? > > > > > > > > > > That looks like a bug - I think we should strive for them to always be in pairs. > > > > > > > > > > Jiri, Josh, could objtool help here perhaps, to detect 'non-terminated' > > > > > SYM_*_START() uses? This could be done by emitting debug data into a special > > > > > section and then analyzing that section for unpaired entries. The section can be > > > > > discarded in the final link, it won't show up in the kernel image. > > > > > > > > It should be easier than that. No introduction of other info needed -- > > > > every global symbol without a ".type" or ".size" (i.e. SYM_*_END) should > > > > be a bug now. > > > > > > I'm all for that! > > > > It would be easy to add this checking to objtool since it already reads > > the symbol table. The hard part is figuring out the logistics. :-) > > > > - Should the warnings be on by default? > > Yes, if objtool is running. Keep it simple. > > > - Part of the "objtool check" command or something else? > > Yes - I think it's still within the 'object file check' functionality. > > > - Separate config option or just include it with > > CONFIG_STACK_VALIDATION? > > Yeah, but I'd rename CONFIG_STACK_VALIDATION to CONFIG_OBJ_VALIDATION or such. As > I predicted early on, objtool will go beyond stack checking! ;-) > > > - Should all asm files be checked, including those currently skipped by > > objtool with OBJECT_FILES_NON_STANDARD? > > The symbol syntax check should definitely be for all files, yes. That all sounds reasonable. I'll work something up. > Could we perhaps emit 'non-standard stack frames' information into the .o itself > (via a flag or a special section?), so that objtool can decide on its own whether > to complain about any weirdnesses there? For the OBJECT_FILES_NON_STANDARD case, where the whole file is "special", we can just provide a flag to "objtool check" to tell it to skip stack checking for that file, but still do the symbol checks. > > > Can we detect double ends as well - i.e. do a build check of the full syntax of > > > these symbol definition primitives? > > > > Detecting double ends would be a little trickier. The second SYM_*_END > > supersedes the first, so that information isn't in the ELF symbol table. > > Indeed. > > > We could use a special section to annotate all the macro uses and have > > objtool do the checking, similar to what you suggested earlier. > > That might be useful for other purposes as well - such as the non-standard stack > frame annotations? To start with we can try going without all the special sections (other than the SYM_END double end check). If we end up finding another case which isn't covered then we can always add the special sections later. -- Josh