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=-7.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,TVD_SUBJ_WIPE_DEBT,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 730B6C433E2 for ; Thu, 10 Sep 2020 08:17:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A6462067C for ; Thu, 10 Sep 2020 08:17:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728626AbgIJIQu (ORCPT ); Thu, 10 Sep 2020 04:16:50 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:46071 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729779AbgIJION (ORCPT ); Thu, 10 Sep 2020 04:14:13 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4BnBVJ36t0z9txjs; Thu, 10 Sep 2020 10:13:44 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id mLdPjtz4MI3T; Thu, 10 Sep 2020 10:13:44 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4BnBVJ24wQz9txjr; Thu, 10 Sep 2020 10:13:44 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 5C4A28B820; Thu, 10 Sep 2020 10:13:45 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id yqpTmoCr2JC9; Thu, 10 Sep 2020 10:13:45 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 71AD28B81D; Thu, 10 Sep 2020 10:13:43 +0200 (CEST) Subject: Re: remove the last set_fs() in common code, and remove it for x86 and powerpc v3 To: David Laight , 'Linus Torvalds' , Segher Boessenkool Cc: linux-arch , Kees Cook , the arch/x86 maintainers , Nick Desaulniers , Linux Kernel Mailing List , Christoph Hellwig , Luis Chamberlain , Al Viro , linux-fsdevel , linuxppc-dev , Alexey Dobriyan References: <20200903142242.925828-1-hch@lst.de> <20200903142803.GM1236603@ZenIV.linux.org.uk> <20200909184001.GB28786@gate.crashing.org> <3beb8b019e4a4f7b81fdb1bc68bd1e2d@AcuMS.aculab.com> From: Christophe Leroy Message-ID: <186a62fc-042c-d6ab-e7dc-e61b18945498@csgroup.eu> Date: Thu, 10 Sep 2020 10:13:42 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <3beb8b019e4a4f7b81fdb1bc68bd1e2d@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Le 10/09/2020 à 10:04, David Laight a écrit : > From: Linus Torvalds >> Sent: 09 September 2020 22:34 >> On Wed, Sep 9, 2020 at 11:42 AM Segher Boessenkool >> wrote: >>> >>> It will not work like this in GCC, no. The LLVM people know about that. >>> I do not know why they insist on pushing this, being incompatible and >>> everything. >> >> Umm. Since they'd be the ones supporting this, *gcc* would be the >> incompatible one, not clang. > > I had an 'interesting' idea. > > Can you use a local asm register variable as an input and output to > an 'asm volatile goto' statement? > > Well you can - but is it guaranteed to work :-) > With gcc at least it should work according to https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html They even explicitely tell: "The only supported use for this feature is to specify registers for input and output operands when calling Extended asm " Christophe