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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 4E063C47254 for ; Tue, 5 May 2020 15:33:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3368220838 for ; Tue, 5 May 2020 15:33:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730359AbgEEPdR (ORCPT ); Tue, 5 May 2020 11:33:17 -0400 Received: from gate.crashing.org ([63.228.1.57]:42699 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730346AbgEEPdP (ORCPT ); Tue, 5 May 2020 11:33:15 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 045FWkQB009965; Tue, 5 May 2020 10:32:46 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 045FWjVS009961; Tue, 5 May 2020 10:32:45 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 5 May 2020 10:32:45 -0500 From: Segher Boessenkool To: Michael Ellerman Cc: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , npiggin@gmail.com, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto' Message-ID: <20200505153245.GN31009@gate.crashing.org> References: <23e680624680a9a5405f4b88740d2596d4b17c26.1587143308.git.christophe.leroy@c-s.fr> <87sggecv81.fsf@mpe.ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sggecv81.fsf@mpe.ellerman.id.au> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! On Wed, May 06, 2020 at 12:27:58AM +1000, Michael Ellerman wrote: > Christophe Leroy writes: > > unsafe_put_user() is designed to take benefit of 'asm goto'. > > > > Instead of using the standard __put_user() approach and branch > > based on the returned error, use 'asm goto' and make the > > exception code branch directly to the error label. There is > > no code anymore in the fixup section. > > > > This change significantly simplifies functions using > > unsafe_put_user() > > > ... > > > > Signed-off-by: Christophe Leroy > > --- > > arch/powerpc/include/asm/uaccess.h | 61 +++++++++++++++++++++++++----- > > 1 file changed, 52 insertions(+), 9 deletions(-) > > > > diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h > > index 9cc9c106ae2a..9365b59495a2 100644 > > --- a/arch/powerpc/include/asm/uaccess.h > > +++ b/arch/powerpc/include/asm/uaccess.h > > @@ -196,6 +193,52 @@ do { \ > > }) > > > > > > +#define __put_user_asm_goto(x, addr, label, op) \ > > + asm volatile goto( \ > > + "1: " op "%U1%X1 %0,%1 # put_user\n" \ > > + EX_TABLE(1b, %l2) \ > > + : \ > > + : "r" (x), "m<>" (*addr) \ > > The "m<>" here is breaking GCC 4.6.3, which we allegedly still support. [ You shouldn't use 4.6.3, there has been 4.6.4 since a while. And 4.6 is nine years old now. Most projects do not support < 4.8 anymore, on any architecture. ] > Plain "m" works, how much does the "<>" affect code gen in practice? > > A quick diff here shows no difference from removing "<>". It will make it impossible to use update-form instructions here. That probably does not matter much at all, in this case. If you remove the "<>" constraints, also remove the "%Un" output modifier? Segher