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=-4.1 required=3.0 tests=BAYES_00,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 026E3C433E4 for ; Wed, 22 Jul 2020 18:42:11 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 58A5E20737 for ; Wed, 22 Jul 2020 18:42:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="f2QZ2qti" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 58A5E20737 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-19416-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 20359 invoked by uid 550); 22 Jul 2020 18:42:03 -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 20339 invoked from network); 22 Jul 2020 18:42:02 -0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=DqMZf+NKxev5DHoTyVPRSIfA19GkA4kV6jf4PNYb+Nw=; b=f2QZ2qtibGlJEp42Nw1cOpOp54 xbjG6CyuAnifkHhoaLv3ELLYaPI+boJBEqUHwPU8IRo3DgqZB0dDkl95wHJ3Axyeoto9wfj7/AslF 9aPPV/YLLSrMT4llswvO23XJiYK29HD1OetvJXWSZcPxxR+MdkO8QvG++Vlqc/nBAoJhsojJbIiHo SI/70lKuy3BslY5UiNJn0bADWU41eswtFmSrIoBoLcUK+SyrYfBMQ5U6RrsOJxJAMH0reIgx8ltdR 3ypKp2jtlWDYKldYYGBc79YEfFgyCydN57+ohspjNE9DQ9wgkd6pv9IRLS98rE9bYGad90A2JdWZ2 ZzlpB7wg==; Date: Wed, 22 Jul 2020 20:41:37 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: Sami Tolvanen , 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, Josh Poimboeuf , mhelsley@vmware.com Subject: Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool Message-ID: <20200722184137.GP10769@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> <20200625074530.GW4817@hirez.programming.kicks-ass.net> <20200625161503.GB173089@google.com> <20200625200235.GQ4781@hirez.programming.kicks-ass.net> <20200625224042.GA169781@google.com> <20200626112931.GF4817@hirez.programming.kicks-ass.net> <20200722135542.41127cc4@oasis.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200722135542.41127cc4@oasis.local.home> On Wed, Jul 22, 2020 at 01:55:42PM -0400, Steven Rostedt wrote: > > Ha! it is trying to convert the "CALL __fentry__" into a NOP and not > > finding the CALL -- because objtool already made it a NOP... > > > > Weird, I thought recordmcount would also write NOPs, it certainly has > > code for that. I suppose we can use CC_USING_NOP_MCOUNT to avoid those, > > but I'd rather Steve explain this before I wreck things further. > > The reason for not having recordmcount insert all the nops, is because > x86 has more than one optimal nop which is determined by the machine it > runs on, and not at compile time. So we figured just updated it then. > > We can change it to be a nop on boot, and just modify it if it's not > the optimal nop already. Right, I throught that's what we'd be doing already, anyway: > That said, Andi Kleen added an option to gcc called -mnop-mcount which > will have gcc do both create the mcount section and convert the calls > into nops. When doing so, it defines CC_USING_NOP_MCOUNT which will > tell ftrace to expect the calls to already be converted. That seems like the much easier solution, then we can forget about recordmcount / objtool entirely for this.