From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sami Tolvanen <samitolvanen@google.com>
Subject: Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool
Date: Mon, 20 Jul 2020 09:52:37 -0700
Message-ID: <CABCJKucDrS9wNZLjtmN5qMbZBTHLvB1Z7WqTwT3b11-K4kNcyg@mail.gmail.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>
 <20200625161503.GB173089@google.com> <20200625200235.GQ4781@hirez.programming.kicks-ass.net>
 <20200625224042.GA169781@google.com> <20200626112931.GF4817@hirez.programming.kicks-ass.net>
 <CABCJKucSM7gqWmUtiBPbr208wB0pc25afJXc6yBQzJDZf4LSWA@mail.gmail.com>
 <20200717133645.7816c0b6@oasis.local.home> <CABCJKuda0AFCZ-1J2NTLc-M0xax007a9u-fzOoxmU2z60jvzbA@mail.gmail.com>
 <20200717140545.6f008208@oasis.local.home>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Return-path: <linux-arch-owner@vger.kernel.org>
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50254 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1728930AbgGTQwu (ORCPT
        <rfc822;linux-arch@vger.kernel.org>); Mon, 20 Jul 2020 12:52:50 -0400
Received: from mail-ej1-x644.google.com (mail-ej1-x644.google.com [IPv6:2a00:1450:4864:20::644])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2317DC0619D5
        for <linux-arch@vger.kernel.org>; Mon, 20 Jul 2020 09:52:50 -0700 (PDT)
Received: by mail-ej1-x644.google.com with SMTP id y10so18811975eje.1
        for <linux-arch@vger.kernel.org>; Mon, 20 Jul 2020 09:52:50 -0700 (PDT)
In-Reply-To: <20200717140545.6f008208@oasis.local.home>
Sender: linux-arch-owner@vger.kernel.org
List-ID: <linux-arch.vger.kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Masahiro Yamada <masahiroy@kernel.org>, Will Deacon <will@kernel.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Paul E. McKenney" <paulmck@kernel.org>, Kees Cook <keescook@chromium.org>, Nick Desaulniers <ndesaulniers@google.com>, clang-built-linux <clang-built-linux@googlegroups.com>, Kernel Hardening <kernel-hardening@lists.openwall.com>, linux-arch <linux-arch@vger.kernel.org>, linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, linux-kbuild <linux-kbuild@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, linux-pci@vger.kernel.org, X86 ML <x86@kernel.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Matt Helsley <mhelsley@vmware.com>

On Fri, Jul 17, 2020 at 11:05 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Fri, 17 Jul 2020 10:47:51 -0700
> Sami Tolvanen <samitolvanen@google.com> wrote:
>
> > > Someone just submitted a patch for arm64 for this:
> > >
> > > https://lore.kernel.org/r/20200717143338.19302-1-gregory.herrero@oracle.com
> > >
> > > Is that what you want?
> >
> > That looks like the same issue, but we need to fix this on x86 instead.
>
> Does x86 have a way to differentiate between the two that record mcount
> can check?

I'm not sure if looking at the relocation alone is sufficient on x86,
we might also have to decode the instruction, which is what objtool
does. Did you have any thoughts on Peter's patch, or my initial
suggestion, which adds a __nomcount attribute to affected functions?

Sami