Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752781AbcLHNNk (ORCPT ); Thu, 8 Dec 2016 08:13:40 -0500 Received: from foss.arm.com ([217.140.101.70]:33026 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751577AbcLHNNh (ORCPT ); Thu, 8 Dec 2016 08:13:37 -0500 Date: Thu, 8 Dec 2016 13:12:32 +0000 From: Catalin Marinas To: Arnd Bergmann Cc: linux-doc@vger.kernel.org, szabolcs.nagy@arm.com, heiko.carstens@de.ibm.com, cmetcalf@ezchip.com, Yury Norov , philipp.tomsich@theobroma-systems.com, joseph@codesourcery.com, linux-arch@vger.kernel.org, zhouchengming1@huawei.com, Prasun.Kapoor@caviumnetworks.com, agraf@suse.de, geert@linux-m68k.org, kilobyte@angband.pl, manuel.montezelo@gmail.com, pinskia@gmail.com, linyongting@huawei.com, klimov.linux@gmail.com, broonie@kernel.org, bamvor.zhangjian@huawei.com, Bamvor Zhang Jian , linux-arm-kernel@lists.infradead.org, maxim.kuvyrkov@linaro.org, Nathan_Lynch@mentor.com, linux-kernel@vger.kernel.org, schwidefsky@de.ibm.com, davem@davemloft.net, christoph.muellner@theobroma-systems.com Subject: Re: [PATCH 16/18] arm64: ptrace: handle ptrace_request differently for aarch32 and ilp32 Message-ID: <20161208131232.GA15141@e104818-lin.cambridge.arm.com> References: <1477081997-4770-1-git-send-email-ynorov@caviumnetworks.com> <20161206062508.GA17835@yury-N73SV> <20161207165913.GD31779@e104818-lin.cambridge.arm.com> <3703608.GKr1zzErMk@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3703608.GKr1zzErMk@wuerfel> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2103 Lines: 50 On Wed, Dec 07, 2016 at 09:40:13PM +0100, Arnd Bergmann wrote: > On Wednesday, December 7, 2016 4:59:13 PM CET Catalin Marinas wrote: > > On Tue, Dec 06, 2016 at 11:55:08AM +0530, Yury Norov wrote: > > > On Mon, Dec 05, 2016 at 04:34:23PM +0000, Catalin Marinas wrote: > > > > On Fri, Oct 21, 2016 at 11:33:15PM +0300, Yury Norov wrote: > > > > > New aarch32 ptrace syscall handler is introduced to avoid run-time > > > > > detection of the task type. > > > > > > > > What's wrong with the run-time detection? If it's just to avoid a > > > > negligible overhead, I would rather keep the code simpler by avoiding > > > > duplicating the generic compat_sys_ptrace(). > > > > > > Nothing wrong. This is how Arnd asked me to do. You already asked this > > > question: http://lkml.iu.edu/hypermail/linux/kernel/1604.3/00930.html > > > > Hmm, I completely forgot about this ;). There is still an advantage to > > doing run-time checking if we avoid touching core code (less acks to > > gather and less code duplication). > > > > Let's see what Arnd says but the initial patch looked simpler. > > I don't currently have either version of the patch in my inbox > (the archive is on a different machine), but in general I'd still > think it's best to avoid the runtime check for aarch64-ilp32 > altogether. I'd have to look at the overall kernel source to > see if it's worth avoiding one or two instances though, or > if there are an overwhelming number of other checks that we > can't avoid at all. Just in case you haven't found them already, current version: https://marc.info/?l=linux-arm-kernel&m=147708276818318&w=2 Original version: https://patchwork.kernel.org/patch/7980521/ The old one looks more readable and given that ptrace is not really a fast path, I'm not two worried about run-time checks > Regarding ptrace, I notice that arch/tile doesn't even use > the compat entry point for its ilp32 user space on 64-bit > kernels, it just calls the regular 64-bit one. Would that > help here? I don't know whether it would work, we have incompatible siginfo_t on AArch64/ILP32. -- Catalin