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 D9F76C432C0 for ; Fri, 29 Nov 2019 18:47:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B0A2D21736 for ; Fri, 29 Nov 2019 18:47:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727043AbfK2Sra (ORCPT ); Fri, 29 Nov 2019 13:47:30 -0500 Received: from gate.crashing.org ([63.228.1.57]:56566 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726909AbfK2Sra (ORCPT ); Fri, 29 Nov 2019 13:47:30 -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 xATIkxwn003148; Fri, 29 Nov 2019 12:47:00 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id xATIkw6Y003147; Fri, 29 Nov 2019 12:46:58 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 29 Nov 2019 12:46:58 -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: <20191129184658.GR9491@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> <20191127145958.GG9491@gate.crashing.org> <2072e066-1ffb-867e-60ec-04a6bb9075c1@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: <2072e066-1ffb-867e-60ec-04a6bb9075c1@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 Hi! On Wed, Nov 27, 2019 at 04:15:15PM +0100, Christophe Leroy wrote: > Le 27/11/2019 à 15:59, Segher Boessenkool a écrit : > >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). > > But the whole purpose of the patch is to inline the call to __do_irq() > in order to avoid the trampoline function. Yes, so you call __do_irq. You have to make sure that what you tell the compiler -- and what you *don't tell the compiler -- works with what the ABIs require, and what the called function expects and provides. > >That does not fix everything. The called function requires a specific > >value in r2 on entry. > > Euh ... but there is nothing like that when using existing > call_do_irq(). > How does GCC know that call_do_irq() has same TOC as __do_irq() ? The existing call_do_irq isn't C code. It doesn't do anything with r2, as far as I can see; __do_irq just gets whatever the caller of call_do_irq has. So I guess all the callers of call_do_irq have the correct r2 value always already? In that case everything Just Works. > >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 :-) > > Anyway it sees I reference it, as it is in input arguments. Isn't it > enough ? It is enough for some things, sure. But not all. 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 78B26C432C0 for ; Fri, 29 Nov 2019 18:49:38 +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 108BD21736 for ; Fri, 29 Nov 2019 18:49:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 108BD21736 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 47Pk7y39NczDrDD for ; Sat, 30 Nov 2019 05:49:34 +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 47Pk5J5ycnzDr9L for ; Sat, 30 Nov 2019 05:47:16 +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 xATIkxwn003148; Fri, 29 Nov 2019 12:47:00 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id xATIkw6Y003147; Fri, 29 Nov 2019 12:46:58 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 29 Nov 2019 12:46:58 -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: <20191129184658.GR9491@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> <20191127145958.GG9491@gate.crashing.org> <2072e066-1ffb-867e-60ec-04a6bb9075c1@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: <2072e066-1ffb-867e-60ec-04a6bb9075c1@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" Hi! On Wed, Nov 27, 2019 at 04:15:15PM +0100, Christophe Leroy wrote: > Le 27/11/2019 à 15:59, Segher Boessenkool a écrit : > >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). > > But the whole purpose of the patch is to inline the call to __do_irq() > in order to avoid the trampoline function. Yes, so you call __do_irq. You have to make sure that what you tell the compiler -- and what you *don't tell the compiler -- works with what the ABIs require, and what the called function expects and provides. > >That does not fix everything. The called function requires a specific > >value in r2 on entry. > > Euh ... but there is nothing like that when using existing > call_do_irq(). > How does GCC know that call_do_irq() has same TOC as __do_irq() ? The existing call_do_irq isn't C code. It doesn't do anything with r2, as far as I can see; __do_irq just gets whatever the caller of call_do_irq has. So I guess all the callers of call_do_irq have the correct r2 value always already? In that case everything Just Works. > >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 :-) > > Anyway it sees I reference it, as it is in input arguments. Isn't it > enough ? It is enough for some things, sure. But not all. Segher