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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 9C353C433E0 for ; Fri, 7 Aug 2020 02:44:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 80ABD2073B for ; Fri, 7 Aug 2020 02:44:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="MPMsNyeT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726388AbgHGCor (ORCPT ); Thu, 6 Aug 2020 22:44:47 -0400 Received: from bilbo.ozlabs.org ([203.11.71.1]:42129 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726058AbgHGCop (ORCPT ); Thu, 6 Aug 2020 22:44:45 -0400 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4BN8pM1JlRz9sSG; Fri, 7 Aug 2020 12:44:43 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1596768284; bh=FZuIxnPjJkYxCWMXw2mxcRhOKtZPN4eNLc1MN/Gupm4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=MPMsNyeTn9a8d9v3fgyBEE07kO0XqO2/i5FfHbv9CyGV1GB8vH5IhwduGCenlTyPB ZYSTBZwtvBB0vFIwr9kUfvEI14D2YJ+gHaFR6FA0sPDvCvxxFpFSONBUyKuBg6bQrl U9VW0RJcVFHSTynki4Fz+vwmS8SG1pYoKBL8wXe5ZlwAHzfgPoLNq0GieUdNAoZ+BB aCj1+BSpCjXIY8vLjuh8Fnr9vMoJ/8a5RLgie/8bnzElqwrwFdXKgkTjYYEeC4F4J3 Mq7Rofv/RlSpKFLB5N2LIsV4DPkQotvYf740maIf3gyM1ZynE1dEGGcRvdpomw+GSx P0t+HR6XtxnGA== From: Michael Ellerman To: Segher Boessenkool Cc: Christophe Leroy , Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , nathanl@linux.ibm.com, linux-arch@vger.kernel.org, arnd@arndb.de, linux-kernel@vger.kernel.org, Tulio Magno Quites Machado Filho , luto@kernel.org, tglx@linutronix.de, vincenzo.frascino@arm.com, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v8 5/8] powerpc/vdso: Prepare for switching VDSO to generic C implementation. In-Reply-To: <20200806183316.GV6753@gate.crashing.org> References: <2a67c333893454868bbfda773ba4b01c20272a5d.1588079622.git.christophe.leroy@c-s.fr> <878sflvbad.fsf@mpe.ellerman.id.au> <65fd7823-cc9d-c05a-0816-c34882b5d55a@csgroup.eu> <87wo2dy5in.fsf@mpe.ellerman.id.au> <20200805133505.GN6753@gate.crashing.org> <87r1sky1hm.fsf@mpe.ellerman.id.au> <20200806183316.GV6753@gate.crashing.org> Date: Fri, 07 Aug 2020 12:44:42 +1000 Message-ID: <87mu37xjhh.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Segher Boessenkool writes: > On Thu, Aug 06, 2020 at 12:03:33PM +1000, Michael Ellerman wrote: >> Segher Boessenkool writes: >> > On Wed, Aug 05, 2020 at 04:24:16PM +1000, Michael Ellerman wrote: >> >> Christophe Leroy writes: >> >> > Indeed, 32-bit doesn't have a redzone, so I believe it needs a stack >> >> > frame whenever it has anything to same. > > ^^^ > >> >> > fbb60: 94 21 ff e0 stwu r1,-32(r1) >> > >> > This is the *only* place where you can use a negative offset from r1: >> > in the stwu to extend the stack (set up a new stack frame, or make the >> > current one bigger). >> >> (You're talking about 32-bit code here right?) > > The "SYSV" ELF binding, yeah, which is used for 32-bit on Linux (give or > take, ho hum). > > The ABIs that have a red zone are much nicer here (but less simple) :-) Yep, just checking I wasn't misunderstanding your comment about negative offsets. >> >> At the same time it's much safer for us to just save/restore r2, and >> >> probably in the noise performance wise. >> > >> > If you want a function to be able to work with ABI-compliant code safely >> > (in all cases), you'll have to make it itself ABI-compliant as well, >> > yes :-) >> >> True. Except this is the VDSO which has previously been a bit wild west >> as far as ABI goes :) > > It could get away with many things because it was guaranteed to be a > leaf function. Some of those things even violate the ABIs, but you can > get away with it easily, much reduced scope. Now if this is generated > code, violating the rules will catch up with you sooner rather than > later ;-) Agreed. cheers 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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 D52E2C433E0 for ; Fri, 7 Aug 2020 02:47:48 +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 8C84D21744 for ; Fri, 7 Aug 2020 02:47:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="MPMsNyeT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C84D21744 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BN8st2r1fzDqvw for ; Fri, 7 Aug 2020 12:47:46 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BN8pN3DvkzDqNR for ; Fri, 7 Aug 2020 12:44:44 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=MPMsNyeT; dkim-atps=neutral Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4BN8pM1JlRz9sSG; Fri, 7 Aug 2020 12:44:43 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1596768284; bh=FZuIxnPjJkYxCWMXw2mxcRhOKtZPN4eNLc1MN/Gupm4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=MPMsNyeTn9a8d9v3fgyBEE07kO0XqO2/i5FfHbv9CyGV1GB8vH5IhwduGCenlTyPB ZYSTBZwtvBB0vFIwr9kUfvEI14D2YJ+gHaFR6FA0sPDvCvxxFpFSONBUyKuBg6bQrl U9VW0RJcVFHSTynki4Fz+vwmS8SG1pYoKBL8wXe5ZlwAHzfgPoLNq0GieUdNAoZ+BB aCj1+BSpCjXIY8vLjuh8Fnr9vMoJ/8a5RLgie/8bnzElqwrwFdXKgkTjYYEeC4F4J3 Mq7Rofv/RlSpKFLB5N2LIsV4DPkQotvYf740maIf3gyM1ZynE1dEGGcRvdpomw+GSx P0t+HR6XtxnGA== From: Michael Ellerman To: Segher Boessenkool Subject: Re: [PATCH v8 5/8] powerpc/vdso: Prepare for switching VDSO to generic C implementation. In-Reply-To: <20200806183316.GV6753@gate.crashing.org> References: <2a67c333893454868bbfda773ba4b01c20272a5d.1588079622.git.christophe.leroy@c-s.fr> <878sflvbad.fsf@mpe.ellerman.id.au> <65fd7823-cc9d-c05a-0816-c34882b5d55a@csgroup.eu> <87wo2dy5in.fsf@mpe.ellerman.id.au> <20200805133505.GN6753@gate.crashing.org> <87r1sky1hm.fsf@mpe.ellerman.id.au> <20200806183316.GV6753@gate.crashing.org> Date: Fri, 07 Aug 2020 12:44:42 +1000 Message-ID: <87mu37xjhh.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain 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: Christophe Leroy , nathanl@linux.ibm.com, arnd@arndb.de, linux-kernel@vger.kernel.org, Tulio Magno Quites Machado Filho , Paul Mackerras , luto@kernel.org, linux-arch@vger.kernel.org, tglx@linutronix.de, vincenzo.frascino@arm.com, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Segher Boessenkool writes: > On Thu, Aug 06, 2020 at 12:03:33PM +1000, Michael Ellerman wrote: >> Segher Boessenkool writes: >> > On Wed, Aug 05, 2020 at 04:24:16PM +1000, Michael Ellerman wrote: >> >> Christophe Leroy writes: >> >> > Indeed, 32-bit doesn't have a redzone, so I believe it needs a stack >> >> > frame whenever it has anything to same. > > ^^^ > >> >> > fbb60: 94 21 ff e0 stwu r1,-32(r1) >> > >> > This is the *only* place where you can use a negative offset from r1: >> > in the stwu to extend the stack (set up a new stack frame, or make the >> > current one bigger). >> >> (You're talking about 32-bit code here right?) > > The "SYSV" ELF binding, yeah, which is used for 32-bit on Linux (give or > take, ho hum). > > The ABIs that have a red zone are much nicer here (but less simple) :-) Yep, just checking I wasn't misunderstanding your comment about negative offsets. >> >> At the same time it's much safer for us to just save/restore r2, and >> >> probably in the noise performance wise. >> > >> > If you want a function to be able to work with ABI-compliant code safely >> > (in all cases), you'll have to make it itself ABI-compliant as well, >> > yes :-) >> >> True. Except this is the VDSO which has previously been a bit wild west >> as far as ABI goes :) > > It could get away with many things because it was guaranteed to be a > leaf function. Some of those things even violate the ABIs, but you can > get away with it easily, much reduced scope. Now if this is generated > code, violating the rules will catch up with you sooner rather than > later ;-) Agreed. cheers