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=-2.2 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 ED0A7C432C0 for ; Wed, 27 Nov 2019 15:00:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB41C20665 for ; Wed, 27 Nov 2019 15:00:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727004AbfK0PAY (ORCPT ); Wed, 27 Nov 2019 10:00:24 -0500 Received: from gate.crashing.org ([63.228.1.57]:47841 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726514AbfK0PAY (ORCPT ); Wed, 27 Nov 2019 10:00:24 -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 xARF00sE025427; Wed, 27 Nov 2019 09:00:00 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id xARExxVi025420; Wed, 27 Nov 2019 08:59:59 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 27 Nov 2019 08:59:58 -0600 From: Segher Boessenkool To: Christophe Leroy Cc: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v4 2/2] powerpc/irq: inline call_do_irq() and call_do_softirq() Message-ID: <20191127145958.GG9491@gate.crashing.org> References: <5ca6639b7c1c21ee4b4138b7cfb31d6245c4195c.1570684298.git.christophe.leroy@c-s.fr> <877e3tbvsa.fsf@mpe.ellerman.id.au> <20191121101552.GR16031@gate.crashing.org> <87y2w49rgo.fsf@mpe.ellerman.id.au> <20191125142556.GU9491@gate.crashing.org> <5fdb1c92-8bf4-01ca-f81c-214870c33be3@c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5fdb1c92-8bf4-01ca-f81c-214870c33be3@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 Wed, Nov 27, 2019 at 02:50:30PM +0100, Christophe Leroy wrote: > So what do we do ? We just drop the "r2" clobber ? You have to make sure your asm code works for all ABIs. This is quite involved if you do a call to an external function. The compiler does *not* see this call, so you will have to make sure that all that the compiler and linker do will work, or prevent some of those things (say, inlining of the function containing the call). > Otherwise, to be on the safe side we can just save r2 in a local var > before the bl and restore it after. I guess it won't collapse CPU time > on a performant PPC64. That does not fix everything. The called function requires a specific value in r2 on entry. So all this needs verification. Hopefully you can get away with just not clobbering r2 (and not adding a nop after the bl), sure. But this needs to be checked. Changing control flow inside inline assembler always is problematic. Another problem in this case (on all ABIs) is that the compiler does not see you call __do_irq. Again, you can probably get away with that too, but :-) Segher 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=-2.2 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 036DEC432C3 for ; Wed, 27 Nov 2019 15:02:47 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6CF8820665 for ; Wed, 27 Nov 2019 15:02:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6CF8820665 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 47NPC63J5QzDqxM for ; Thu, 28 Nov 2019 02:02:42 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=permerror (SPF Permanent Error: Unknown mechanism found: ip:192.40.192.88/32) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 47NP8H1ZgVzDqvT for ; Thu, 28 Nov 2019 02:00:14 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id xARF00sE025427; Wed, 27 Nov 2019 09:00:00 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id xARExxVi025420; Wed, 27 Nov 2019 08:59:59 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 27 Nov 2019 08:59:58 -0600 From: Segher Boessenkool To: Christophe Leroy Subject: Re: [PATCH v4 2/2] powerpc/irq: inline call_do_irq() and call_do_softirq() Message-ID: <20191127145958.GG9491@gate.crashing.org> References: <5ca6639b7c1c21ee4b4138b7cfb31d6245c4195c.1570684298.git.christophe.leroy@c-s.fr> <877e3tbvsa.fsf@mpe.ellerman.id.au> <20191121101552.GR16031@gate.crashing.org> <87y2w49rgo.fsf@mpe.ellerman.id.au> <20191125142556.GU9491@gate.crashing.org> <5fdb1c92-8bf4-01ca-f81c-214870c33be3@c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5fdb1c92-8bf4-01ca-f81c-214870c33be3@c-s.fr> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras , linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Nov 27, 2019 at 02:50:30PM +0100, Christophe Leroy wrote: > So what do we do ? We just drop the "r2" clobber ? You have to make sure your asm code works for all ABIs. This is quite involved if you do a call to an external function. The compiler does *not* see this call, so you will have to make sure that all that the compiler and linker do will work, or prevent some of those things (say, inlining of the function containing the call). > Otherwise, to be on the safe side we can just save r2 in a local var > before the bl and restore it after. I guess it won't collapse CPU time > on a performant PPC64. That does not fix everything. The called function requires a specific value in r2 on entry. So all this needs verification. Hopefully you can get away with just not clobbering r2 (and not adding a nop after the bl), sure. But this needs to be checked. Changing control flow inside inline assembler always is problematic. Another problem in this case (on all ABIs) is that the compiler does not see you call __do_irq. Again, you can probably get away with that too, but :-) Segher