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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E54CCC433FE for ; Tue, 22 Mar 2022 07:55:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229689AbiCVH4p (ORCPT ); Tue, 22 Mar 2022 03:56:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54100 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229658AbiCVH4n (ORCPT ); Tue, 22 Mar 2022 03:56:43 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2FDFB59A40; Tue, 22 Mar 2022 00:55:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=BUf3kZEhqxCYRgicSzuUVNrLLp1FfVYato9rwoVBC/A=; b=O+Zv4B0vlsCDbWFJ84XG3F5o8D RT+3EoQ0TsekqJC3795MFOV9qhuOcNyw/s+L+MUEPHWKVdBjzh5beSxy5HP13T2ne05fzJTnHs/0b cg/yf8IXB4SVIiGrruz6sNPtvOVSDtNXuOycVdAPDmNXCR5NXR4Kt3mKwojOboE7Bgx7+1cT2oZXF udfX7pfRZHsJGg5nQN30gL58gKSoP/XvtLDzApstF11bM3W0shVP6JhLYRUVIAL687pJulOT1S9m/ WF7vA/WpJcjg+UodjUaEQLoqGSKkTUj3yEuzSKq18XBO82ftaIp0hYJFUY2/WpZ7EyEkV6R7yC7HL vZXmYnkg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nWZM0-00BOBw-5g; Tue, 22 Mar 2022 07:54:56 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8C61F3001CD; Tue, 22 Mar 2022 08:54:55 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 746922015B283; Tue, 22 Mar 2022 08:54:55 +0100 (CET) Date: Tue, 22 Mar 2022 08:54:55 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: Stephen Rothwell , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Linux Kernel Mailing List , Linux Next Mailing List , mhiramat@kernel.org, ast@kernel.org, hjl.tools@gmail.com, rick.p.edgecombe@intel.com, rppt@kernel.org, linux-toolchains@vger.kernel.org, Andrew.Cooper3@citrix.com, ndesaulniers@google.com Subject: Re: linux-next: build warnings after merge of the tip tree Message-ID: References: <20220321112805.1393f9b9@gandalf.local.home> <20220321121209.3b95e406@gandalf.local.home> <20220321121549.1c8588c5@gandalf.local.home> <20220321124551.3d73660b@gandalf.local.home> <20220321125419.0a20415c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220321125419.0a20415c@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 21, 2022 at 12:54:19PM -0400, Steven Rostedt wrote: > On Mon, 21 Mar 2022 17:50:50 +0100 > Peter Zijlstra wrote: > > > > This also assumes that we need to trace everything that is marked. I > > > mentioned in another email, what do we do if we only trace funcA? > > > > Like I said later on; if we inhibit tail-calls to notrace, this goes > > away. > > Please no. The number of "notrace" functions is increasing to the point > that it's starting to make function tracing useless in a lot of > circumstances. I've already lost my ability to see when user space goes > into the kernel (which I have to hack up custom coding to enable again). I really can't follow the argument there, nor on IRC. Suppose: notrace func_B() { ... } func_A() { ... return func_B(); } then inhibiting tail calls would end up looking like: func_A: call __fentry__ ... call func_B call __fexit__ ret Then A is fully traced, B is invisible, as per spec. What is the problem? The problem you initially had, of doing a tail-call into a notrace, was that the __fexit__ call went missing, because notrace will obviously not have that. But that's avoided by inhibiting all tail-calls between notrace and !notrace functions (note that notrace must also not tail-call !notrace). Your worry seems to stem about loosing visiblilty of !notrace functions, but AFAICT that doesn't happen.