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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 E9CE4C433E0 for ; Thu, 25 Jun 2020 07:46:32 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 47DC620675 for ; Thu, 25 Jun 2020 07:46:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MVs61XR8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 47DC620675 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19159-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 30024 invoked by uid 550); 25 Jun 2020 07:46:23 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 29986 invoked from network); 25 Jun 2020 07:46:22 -0000 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==; 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> 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 ?