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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 E8366C04AAD for ; Tue, 7 May 2019 01:53:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C563A206BF for ; Tue, 7 May 2019 01:53:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726302AbfEGBx7 (ORCPT ); Mon, 6 May 2019 21:53:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:58306 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725994AbfEGBx6 (ORCPT ); Mon, 6 May 2019 21:53:58 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9F031206A3; Tue, 7 May 2019 01:53:54 +0000 (UTC) Date: Mon, 6 May 2019 21:53:53 -0400 From: Steven Rostedt To: Linus Torvalds Cc: Peter Zijlstra , Andy Lutomirski , Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , Andy Lutomirski , Nicolai Stange , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "the arch/x86 maintainers" , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , Shuah Khan , Konrad Rzeszutek Wilk , Tim Chen , Sebastian Andrzej Siewior , Mimi Zohar , Juergen Gross , Nick Desaulniers , Nayna Jain , Masahiro Yamada , Joerg Roedel , "open list:KERNEL SELFTEST FRAMEWORK" , stable , Masami Hiramatsu Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions Message-ID: <20190506215353.14a8ef78@oasis.local.home> In-Reply-To: References: <20190502181811.GY2623@hirez.programming.kicks-ass.net> <20190503092247.20cc1ff0@gandalf.local.home> <2045370D-38D8-406C-9E94-C1D483E232C9@amacapital.net> <20190506081951.GJ2606@hirez.programming.kicks-ass.net> <20190506095631.6f71ad7c@gandalf.local.home> <20190506130643.62c35eeb@gandalf.local.home> <20190506145745.17c59596@gandalf.local.home> <20190506162915.380993f9@gandalf.local.home> <20190506174511.2f8b696b@gandalf.local.home> <20190506210416.2489a659@oasis.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 May 2019 18:34:59 -0700 Linus Torvalds wrote: > On Mon, May 6, 2019 at 6:04 PM Steven Rostedt wrote: > > > > That iterator does something special for each individual record. All > > 40,000 of them. > > .. yes, but the 'int3' only happens for *one* of them at a time. > > Why would it bother with the other 39,999 calls? > > You could easily just look up the record at the int3 time, and just > use the record. Exactly the same way you use the one-at-a-time ones. > > Instead, you emulate a fake call to a function that *wouldn't* get > called, which now does the lookup there. That's the part I don't get. > Why are you emulating something else than what you'd be rewriting? > Ah, now I see what you are saying. Yes, I could pass in what it is suppose to call. But I was trying to use the same code for all the alternative solutions we were passing around, and this became the "default" case that would work with any int3_emulate_call implementation we came up with. That is, if we call ftrace_regs_caller() for any scenario it should work. Even if the call was suppose to be a nop, because in that case, all the ftrace_ops registered in the iterator would refuse to have their handler be called for that function. I sent you a single patch, but that was really just a diff of several applied patches against your unmodified tree. The last patch implements the ftrace code. And I had it this way because it should work for any of the implementations. I could modify it so that it picks what function to call when the int3 is triggered. I think all the solutions we are down to allow that now. Some of the early ideas had me call one function for all int3s due to trampolines and such. Also, I figured just calling ftrace_regs_caller() was simpler then having that int3 handler do the hash look ups to determine what handler it needs to call. -- Steve