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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 0A0A7C0044C for ; Sat, 3 Nov 2018 17:33:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BA88A20843 for ; Sat, 3 Nov 2018 17:33:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA88A20843 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728741AbeKDCp2 (ORCPT ); Sat, 3 Nov 2018 22:45:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:38310 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726985AbeKDCp2 (ORCPT ); Sat, 3 Nov 2018 22:45:28 -0400 Received: from vmware.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (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 6896D204FD; Sat, 3 Nov 2018 17:33:31 +0000 (UTC) Date: Sat, 3 Nov 2018 13:33:29 -0400 From: Steven Rostedt To: Masami Hiramatsu Cc: Josh Poimboeuf , Aleksa Sarai , "Naveen N. Rao" , Anil S Keshavamurthy , "David S. Miller" , Jonathan Corbet , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Shuah Khan , Alexei Starovoitov , Daniel Borkmann , Brendan Gregg , Christian Brauner , Aleksa Sarai , netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v3 1/2] kretprobe: produce sane stack traces Message-ID: <20181103133329.2160bfd7@vmware.local.home> In-Reply-To: <20181103133021.6676708c@vmware.local.home> References: <20181101083551.3805-1-cyphar@cyphar.com> <20181101083551.3805-2-cyphar@cyphar.com> <20181101204720.6ed3fe37@vmware.local.home> <20181102050509.tw3dhvj5urudvtjl@yavin> <20181102065932.bdt4pubbrkvql4mp@yavin> <20181102091658.1bc979a4@gandalf.local.home> <20181102154325.bt6xoysl4xdl33wd@treble> <20181102121307.32e99414@gandalf.local.home> <20181103220012.55ecd97e671c43e4959c8b62@kernel.org> <20181103091341.3d32683e@vmware.local.home> <20181104013430.9d3e91b8ebbae7dcb6860ef1@kernel.org> <20181103133021.6676708c@vmware.local.home> X-Mailer: Claws Mail 3.15.1 (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 Sat, 3 Nov 2018 13:30:21 -0400 Steven Rostedt wrote: > What I was thinking was to store a count and the functions to be called: > > > [original_return_address] > [function_A] > [function_B] > [function_C] > [ 3 ] > > Then the trampoline that processes the return codes for ftrace (and > kretprobes and everyone else) can simply do: > > count = pop_shadow_stack(); > for (i = 0; i < count; i++) { > func = pop_shadow_stack(); > func(...); > } > return_address = pop_shadow_stack(); > > That way we only need to register a function to the return handler and > it will be called, without worrying about making trampolines. There > will just be a single trampoline that handles all the work. And since the most common case is a single function to call, instead of using a count, we can take advantage that kernel functions are negative numbers and do: [original_return_address] [function_A] ---- long count; count = pop_shadow_stack(); if (count < 0) { func = (void *)count; func(); } else { for (i = 0; i < count; i++) { [...] The unwinder will just need to know how to handle all this :-) -- Steve