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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 2B2CCC2D0CE for ; Fri, 24 Jan 2020 08:58:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F270D20709 for ; Fri, 24 Jan 2020 08:58:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729946AbgAXI6u (ORCPT ); Fri, 24 Jan 2020 03:58:50 -0500 Received: from gate.crashing.org ([63.228.1.57]:42470 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725887AbgAXI6t (ORCPT ); Fri, 24 Jan 2020 03:58:49 -0500 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 00O8wVx7016348; Fri, 24 Jan 2020 02:58:31 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 00O8wU1T016347; Fri, 24 Jan 2020 02:58:30 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 24 Jan 2020 02:58:30 -0600 From: Segher Boessenkool To: Christophe Leroy Cc: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] powerpc/irq: don't use current_stack_pointer() in check_stack_overflow() Message-ID: <20200124085830.GT3191@gate.crashing.org> References: <87d0b9iez3.fsf@mpe.ellerman.id.au> <74cb4227-1a24-6fe1-2df4-3d4b069453c4@c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <74cb4227-1a24-6fe1-2df4-3d4b069453c4@c-s.fr> 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 On Fri, Jan 24, 2020 at 07:03:36AM +0000, Christophe Leroy wrote: > >Le 24/01/2020 à 06:46, Michael Ellerman a écrit : > >> > >>If I do this it seems to work, but feels a little dicey: > >> > >>    asm ("" : "=r" (r1)); > >>    sp = r1 & (THREAD_SIZE - 1); > > > > > >Or we could do add in asm/reg.h what we have in boot/reg.h: > > > >register void *__stack_pointer asm("r1"); > >#define get_sp()    (__stack_pointer) > > > >And use get_sp() > > > > It works, and I guess doing it this way is acceptable as it's exactly > what's done for current in asm/current.h with register r2. That is a *global* register variable. That works. We still need to document a bit better what it does exactly, but this is the expected use case, so that will work. > Now I (still) get: > > sp = get_sp() & (THREAD_SIZE - 1); > b9c: 54 24 04 fe clrlwi r4,r1,19 > if (unlikely(sp < 2048)) { > ba4: 2f 84 07 ff cmpwi cr7,r4,2047 > > Allthough GCC 8.1 what doing exactly the same with the form CLANG don't > like: > > register unsigned long r1 asm("r1"); > long sp = r1 & (THREAD_SIZE - 1); > b84: 54 24 04 fe clrlwi r4,r1,19 > if (unlikely(sp < 2048)) { > b8c: 2f 84 07 ff cmpwi cr7,r4,2047 Sure, if it did what you expected, things will usually work out fine ;-) (Pity that the compiler didn't come up with rlwinm. r4,r1,0,19,20 bne bad Or are the low bits of r4 used later again?) Segher