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=-8.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 54333C433DF for ; Thu, 25 Jun 2020 16:15:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A0422089D for ; Thu, 25 Jun 2020 16:15:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="QWdvdGQM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406004AbgFYQPM (ORCPT ); Thu, 25 Jun 2020 12:15:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389693AbgFYQPL (ORCPT ); Thu, 25 Jun 2020 12:15:11 -0400 Received: from mail-pg1-x544.google.com (mail-pg1-x544.google.com [IPv6:2607:f8b0:4864:20::544]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4AB46C08C5C1 for ; Thu, 25 Jun 2020 09:15:11 -0700 (PDT) Received: by mail-pg1-x544.google.com with SMTP id f3so3514869pgr.2 for ; Thu, 25 Jun 2020 09:15:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=no7YVr00DbKKQ+yaF/NLUAHDlIF83IoT6Cfe6Ue8Rsk=; b=QWdvdGQMKWLXFCj/e3uSXu3nIed+fEpI9sixMesz0lmaFvY+vhrbPQCL2sfOwX5Xtz dJOd7qtWZudwGhWJ+gbv1sxQvZIkuGk6XpJScPP6djHS3Gjtpwa7FrqRlou+lHRJtZZZ E6lOy4qOE0EckdWmFhkcLT54pDwlj99vXre4+ksDWSXwsjNcFMNF4qwlEGG8e1VqTFDQ xJh5VQeFsuhh9JPP5l68M979tHfFPP91RJEzeejy+3inJ6Ch9ZslROLlJkFXrp0dB7vi CJdzxgSmmDz68iPXfh2R8CxQ1kMKTk1lzBLXZYMYpViAqBc0if/psRGS2Bx8e3vIkdLC XavA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=no7YVr00DbKKQ+yaF/NLUAHDlIF83IoT6Cfe6Ue8Rsk=; b=iagJfwJK722b+HidV35jM/wNi/HTAKVS1V3PLIJeAPHxbBDwSxA4Q/DwdC92dWTVG0 m/lpvokWh5gGugKokZnOOWqCTijmyV0yngJhZvaLhmjTmLbxg33Wr7iqeUVCJfukbKC7 /pkdyuzg6cGxYGG0vjirCOAdJoijr5GwwLs8/yPpq0np89iLbjW/j4ji748syoxWicA0 laoHdBwgsZ33I2x/KmYKKQf+AAw3LH4yAabmwKGd+/YVf1ZXIWT9Y5tj+xRsb+5owlml fnkA1O6wDc3+rUxX5+hpvSh4ayL9xYmkKWXoWDPhn/xRvs961JmjsDsX3DZVlJX1Of64 StLw== X-Gm-Message-State: AOAM532p/hMyiTHLmw/GK9vjEVTUY2hgAiLaJe4Gm5Jc4TFZE1LzFSz9 Cqkl6ECreVVGm0bg7zDgNV3oWw== X-Google-Smtp-Source: ABdhPJwBA+f5YY24rFGe1FlZ0Pbcr47k53bKGlTrbuSqy24H60q+oFwTSxgIA7OapKwETcq0tJs/tw== X-Received: by 2002:a63:395:: with SMTP id 143mr23203113pgd.57.1593101710493; Thu, 25 Jun 2020 09:15:10 -0700 (PDT) Received: from google.com ([2620:15c:201:2:ce90:ab18:83b0:619]) by smtp.gmail.com with ESMTPSA id u12sm8450067pjy.37.2020.06.25.09.15.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Jun 2020 09:15:09 -0700 (PDT) Date: Thu, 25 Jun 2020 09:15:03 -0700 From: Sami Tolvanen To: Peter Zijlstra 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: <20200625161503.GB173089@google.com> References: <20200624203200.78870-1-samitolvanen@google.com> <20200624203200.78870-5-samitolvanen@google.com> <20200624212737.GV4817@hirez.programming.kicks-ass.net> <20200624214530.GA120457@google.com> <20200625074530.GW4817@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200625074530.GW4817@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 25, 2020 at 09:45:30AM +0200, Peter Zijlstra wrote: > 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? Yes. > 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 ? Sure, sounds good. arm64 uses -fpatchable-function-entry with clang, so we don't need recordmcount there. Sami