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=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9FFF2C433DF for ; Thu, 25 Jun 2020 07:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7430620A8B for ; Thu, 25 Jun 2020 07:46:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MVs61XR8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390438AbgFYHq2 (ORCPT ); Thu, 25 Jun 2020 03:46:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41064 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390410AbgFYHq2 (ORCPT ); Thu, 25 Jun 2020 03:46:28 -0400 Received: from casper.infradead.org (unknown [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3A0F0C061573; Thu, 25 Jun 2020 00:46:28 -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=2aQ/V3CRB+JTPOL3qC/HxsWm+wJhkXGBtq9FiN50dxw=; b=MVs61XR8PHT2An2kAHFoVGpNaN L4hxfCHN0na+bXYcmoGM6fWmmaLm7d3p6PumUpigGZx4NET8Y22MadCNhuDD2tjz4bsAx+YeRr8US rO5Ph/sbzdu4v7rVC1aVaiLtBk178mbNOCE6uWemg8h/W8LV+TH9FVvH8ZqN2vdqTAt5dRcG3NIfV szFdqm0VJ59PkYZYpIY6zdlwCdeWCvhK56AovRtjFjyPn0yqF3yhfbzwmorhqV4KQ1ma6vlIdDuje xB9TwF6459hMixZkCdI6jdbxggiKReKLnIA3sI0gv2cMZe/rxoUPK9GVPLyTKxrBYihPvtqUYvTp7 UeOTNh3A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1joMZg-0007WT-Ba; Thu, 25 Jun 2020 07:45:32 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id E3B15304BAE; Thu, 25 Jun 2020 09:45:30 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D836B203CDC50; Thu, 25 Jun 2020 09:45:30 +0200 (CEST) Date: Thu, 25 Jun 2020 09:45:30 +0200 From: Peter Zijlstra To: Sami Tolvanen Cc: Steven Rostedt , Masahiro Yamada , Will Deacon , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 04/22] kbuild: lto: fix recordmcount Message-ID: <20200625074530.GW4817@hirez.programming.kicks-ass.net> References: <20200624203200.78870-1-samitolvanen@google.com> <20200624203200.78870-5-samitolvanen@google.com> <20200624212737.GV4817@hirez.programming.kicks-ass.net> <20200624214530.GA120457@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200624214530.GA120457@google.com> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, Jun 24, 2020 at 02:45:30PM -0700, Sami Tolvanen wrote: > On Wed, Jun 24, 2020 at 11:27:37PM +0200, Peter Zijlstra wrote: > > On Wed, Jun 24, 2020 at 01:31:42PM -0700, Sami Tolvanen wrote: > > > With LTO, LLVM bitcode won't be compiled into native code until > > > modpost_link. This change postpones calls to recordmcount until after > > > this step. > > > > > > In order to exclude specific functions from inspection, we add a new > > > code section .text..nomcount, which we tell recordmcount to ignore, and > > > a __nomcount attribute for moving functions to this section. > > > > I'm confused, you only add this to functions in ftrace itself, which is > > compiled with: > > > > KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS)) > > > > and so should not have mcount/fentry sites anyway. So what's the point > > of ignoring them further? > > > > This Changelog does not explain. > > Normally, recordmcount ignores each ftrace.o file, but since we are > running it on vmlinux.o, we need another way to stop it from looking > at references to mcount/fentry that are not calls. Here's a comment > from recordmcount.c: > > /* > * The file kernel/trace/ftrace.o references the mcount > * function but does not call it. Since ftrace.o should > * not be traced anyway, we just skip it. > */ > > But I agree, the commit message could use more defails. Also +Steven > for thoughts about this approach. Ah, is thi because recordmcount isn't smart enough to know the difference between "CALL $mcount" and any other RELA that has mcount? At least for x86_64 I can do a really quick take for a recordmcount pass in objtool, but I suppose you also need this for ARM64 ?