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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 80457C433EF for ; Wed, 4 May 2022 12:44:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=mS8NPa1xcUouTlERHtqK66t4t19NyB4l84elHKmkQtM=; b=BOZF9mMh3OLRXE wYjmuygWpPl9kRWO7fJZjMXaDxpTUUdjfdCjU1+wH4q/3NUrDDBn5dDtVPX9zrXYq0yl7bGO7eFvz iNYESIl7lyhIYWUAqBER9JS2M4yhRIzLncDTrYfSsX+vWFs+YE/xZ9RG088MnotGlGi4E1SSTYjyT ioNdLQHgFIgzU0VmSZByYvtCgPszdL4Mi0SddR70p8q4uPt8wQc65b/np8K8NQF+SsHP0nkE/l9VA s7XiDgybr8AuDbXa5PBI1vU0cpw+zlZToG7CK/p2hdRtd9GFuoqEDK/V3InqXOFo6Peog2C5JIVAe 4i7YIMi7KEYt4ALs5/Dg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nmELz-00Aoiw-3m; Wed, 04 May 2022 12:43:39 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nmELt-00Aog7-Ri for linux-arm-kernel@lists.infradead.org; Wed, 04 May 2022 12:43:35 +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 5F0661042; Wed, 4 May 2022 05:43:30 -0700 (PDT) Received: from lakrids (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E24503FA50; Wed, 4 May 2022 05:43:28 -0700 (PDT) Date: Wed, 4 May 2022 13:43:26 +0100 From: Mark Rutland To: Steven Rostedt Cc: Wang ShaoBo , cj.chengjian@huawei.com, huawei.libin@huawei.com, xiexiuqi@huawei.com, liwei391@huawei.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, zengshun.wu@outlook.com Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Message-ID: References: <20220316100132.244849-1-bobo.shaobowang@huawei.com> <20220316100132.244849-4-bobo.shaobowang@huawei.com> <20220421100639.03c0d123@gandalf.local.home> <20220421114201.21228eeb@gandalf.local.home> <20220421130648.56b21951@gandalf.local.home> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220421130648.56b21951@gandalf.local.home> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220504_054334_005218_DE5ACD00 X-CRM114-Status: GOOD ( 23.85 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Apr 21, 2022 at 01:06:48PM -0400, Steven Rostedt wrote: > On Thu, 21 Apr 2022 17:27:40 +0100 > Mark Rutland wrote: > > > We can initialize the ops pointer to a default ops that does the whole > > __do_for_each_ftrace_ops() dance. > > OK, I think I understand now. What you are doing is instead of creating a > trampoline that has all the information in the trampoline, you add nops to > all the functions where you can place the information in the nops (before > the function), and then have the trampoline just read that information to > find the ops pointer as well as the function to call. FWIW, I had a go at mocking that up: https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/ftrace/per-callsite-ops Aside from some bodges required to ensure the patch site is suitably aligned (which I think can be cleaned up somewhat), I don't think it looks that bad. I wasn't sure how exactly to wire that up in the core code, so all the patch sites are initialized with a default ops that calls arch_ftrace_ops_list_func(), but it looks like it should be possible to wire that up in the core with some refactoring. > I guess you could have two trampolines as well. One that always calls the > list loop, and one that calls the data stored in front of the function that > was just called the trampoline. As it is always safe to call the loop > function, you could have the call call that trampoline first, set up the > specific data before the function, then call the trampoline that will read > it. I was thinking we could just patch the ops with a default ops that called the list loop, as my patches default them to. > And same thing for tear down. I wasn't sure how teardown was meant to work in general. When we want to remove an ops structure, or a trampoline, how do we ensure those are no longer in use before we remove them? I can see how we can synchronize the updates to the kernel text, but I couldn't spot how we handle a thread being in the middle of a trampoline. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel