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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 1B699C5DF61 for ; Thu, 7 Nov 2019 04:41:14 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 D81472187F for ; Thu, 7 Nov 2019 04:41:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="UMxpadQM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D81472187F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=+1XP+7SlWox3qkfaZgEoYyQ8uz5FWYsFatZk7B3GsiQ=; b=UMxpadQMIqipO0sQE2R2ZyzAw 3/HrEGb9awQAA9An1K6epL/frD3GPO3enUgPlU4BmIHtfV9wRsUS42AC8+0cVJSkLcRgkY3+zPWWh CJjHP82bHGijz12TZYdGvC/kvhREsigSOT77fMA/AvKcluDWCugYcwG8/tkU/j4qKu6W8aFa1eZH9 z86EvVt3r+aj6y6lZ3XotrwVw39ynjWHCLHFOeHfVtV9B3nWS7QNGpkUxiOpY+IwujfM/C0gkOxbc 5mv0+HdMfcDIrExnMdyKFziJM/4FnayF1HUepx8Up+c0TX/r+jRhGatS683O3LShHMQ3eMXd2cpDa wd4y5NAGA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iSZbc-0005Aa-Tb; Thu, 07 Nov 2019 04:41:12 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iSZbZ-00059e-Kn for linux-arm-kernel@lists.infradead.org; Thu, 07 Nov 2019 04:41:11 +0000 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 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-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191106_204109_724706_F5421BF8 X-CRM114-Status: GOOD ( 17.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jthierry@redhat.com, linux-parisc@vger.kernel.org, peterz@infradead.org, catalin.marinas@arm.com, deller@gmx.de, jpoimboe@redhat.com, linux-kernel@vger.kernel.org, Steven Rostedt , James.Bottomley@HansenPartnership.com, takahiro.akashi@linaro.org, will@kernel.org, mingo@redhat.com, james.morse@arm.com, jeyu@kernel.org, svens@stackframe.org, duwe@suse.de, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel