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 54B4EC5DF60 for ; Thu, 7 Nov 2019 04:41:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2913E2187F for ; Thu, 7 Nov 2019 04:41:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733066AbfKGElC (ORCPT ); Wed, 6 Nov 2019 23:41:02 -0500 Received: from foss.arm.com ([217.140.110.172]:49702 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726935AbfKGElC (ORCPT ); Wed, 6 Nov 2019 23:41:02 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 069AE7A7; Wed, 6 Nov 2019 20:41:01 -0800 (PST) Received: from [10.162.42.33] (a075563-lin.blr.arm.com [10.162.42.33]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 430353F71A; Wed, 6 Nov 2019 20:40:56 -0800 (PST) Subject: Re: [PATCHv2 1/8] ftrace: add ftrace_init_nop() To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, Steven Rostedt , linux-kernel@vger.kernel.org, catalin.marinas@arm.com, deller@gmx.de, duwe@suse.de, James.Bottomley@HansenPartnership.com, james.morse@arm.com, jeyu@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com, linux-parisc@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, svens@stackframe.org, takahiro.akashi@linaro.org, will@kernel.org References: <20191029165832.33606-1-mark.rutland@arm.com> <20191029165832.33606-2-mark.rutland@arm.com> <20191104133657.GE45140@lakrids.cambridge.arm.com> <8e68de1f-f961-752d-9c07-ce41ce624d35@arm.com> <20191106141530.GC50610@lakrids.cambridge.arm.com> From: Amit Kachhap Message-ID: <77ba9a77-7971-77b6-c3f9-e3e0adf6cf54@arm.com> Date: Thu, 7 Nov 2019 10:10:52 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20191106141530.GC50610@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org On 11/6/19 7:45 PM, Mark Rutland wrote: > On Tue, Nov 05, 2019 at 12:17:26PM +0530, Amit Kachhap wrote: >> On 11/4/19 7:06 PM, Mark Rutland wrote: >>> On Sat, Nov 02, 2019 at 05:49:00PM +0530, Amit Daniel Kachhap wrote: >>>> On 10/29/19 10:28 PM, Mark Rutland wrote: >>>>> +/** >>>>> + * ftrace_init_nop - initialize a nop call site >>>>> + * @mod: module structure if called by module load initialization >>>>> + * @rec: the call site record (e.g. mcount/fentry) >>>>> + * >>>>> + * This is a very sensitive operation and great care needs >>>>> + * to be taken by the arch. The operation should carefully >>>>> + * read the location, check to see if what is read is indeed >>>>> + * what we expect it to be, and then on success of the compare, >>>>> + * it should write to the location. >>>>> + * >>>>> + * The code segment at @rec->ip should contain the contents created by >>>>> + * the compiler >>>> Nit: Will it be better to write it as "@rec->ip should store the adjusted >>>> ftrace entry address of the call site" or something like that. >>> >>> This was the specific wording requested by Steve, and it's trying to >>> describe the instructions at rec->ip, rather than the value of rec->ip, >>> so I think it's better to leave this as-is. >> ok Its fine this way too. Actually from the comment, I could not understand >> which one of the compiler contents this points to as in this case there are >> 2 nops. > > We can't say what the compiler contents will be. An architecture may use > this callback if it's using mcount, mfentry, patchable-function-entry, > or some other mechanism we're not aware of today. Depending on the > architecture and mechanism, the callsite could contain a number of > distinct things. > > All the comment is trying to say is that when ftrace_init_nop() is > called, the callsite has not been modified in any way since being > compiled, so we can expect the contents to be whatever the compiler > generated. ok. Your details seems reasonable. Thanks, Amit Daniel > > Thanks, > Mark. >