From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF32DC43381 for ; Fri, 8 Mar 2019 19:53:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BA58020857 for ; Fri, 8 Mar 2019 19:53:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726987AbfCHTxM (ORCPT ); Fri, 8 Mar 2019 14:53:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54216 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726258AbfCHTxI (ORCPT ); Fri, 8 Mar 2019 14:53:08 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4F76B3092659; Fri, 8 Mar 2019 19:53:08 +0000 (UTC) Received: from treble (ovpn-120-61.rdu2.redhat.com [10.10.120.61]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1C8905D704; Fri, 8 Mar 2019 19:53:04 +0000 (UTC) Date: Fri, 8 Mar 2019 13:53:02 -0600 From: Josh Poimboeuf To: Peter Zijlstra Cc: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com, julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net, mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com, valentin.schneider@arm.com, brgerst@gmail.com, luto@kernel.org, bp@alien8.de, dvlasenk@redhat.com, linux-kernel@vger.kernel.org, dvyukov@google.com, rostedt@goodmis.org Subject: Re: [PATCH 03/20] x86/uaccess: Move copy_user_handle_tail into asm Message-ID: <20190308195302.popw53eqeoozg53r@treble> References: <20190307114511.870090179@infradead.org> <20190307115159.349746915@infradead.org> <20190308185321.jukfavqk6pl3ifev@treble> <20190308194835.GD32494@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190308194835.GD32494@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Fri, 08 Mar 2019 19:53:08 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 08, 2019 at 08:48:35PM +0100, Peter Zijlstra wrote: > On Fri, Mar 08, 2019 at 12:53:21PM -0600, Josh Poimboeuf wrote: > > On Thu, Mar 07, 2019 at 12:45:14PM +0100, Peter Zijlstra wrote: > > > /* > > > + * Try to copy last bytes and clear the rest if needed. > > > + * Since protection fault in copy_from/to_user is not a normal situation, > > > + * it is not necessary to optimize tail handling. > > > + * > > > + * Input: > > > + * rdi destination > > > + * rsi source > > > + * rdx count > > > + * > > > + * Output: > > > + * eax uncopied bytes or 0 if successful. > > > + */ > > > +ALIGN; > > > +copy_user_handle_tail: > > > + movl %edx,%ecx > > > +1: rep movsb > > > +2: mov %ecx,%eax > > > + ASM_CLAC > > > + ret > > > + > > > + _ASM_EXTABLE_UA(1b, 2b) > > > +ENDPROC(copy_user_handle_tail) > > > > This is an unstructured piece of code rather than a callable function, > > END would probably be more appropriate. Or maybe it should just be a > > local label (.Lcopy_user_handle_tail) because I don't think the > > alignment and ELF symbol size are even needed. > > ENDPROC makes it STT_FUNC and gets us stricter AC tests. How so? I would have thought the opposite. Doesn't objtool only follow a jump if its destination is to a non-function? Otherwise it's considered a sibling call. -- Josh