linux-kernel - Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool

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Date:   Mon, 20 Jul 2020 09:52:37 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
        X86 ML <x86@...nel.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
        Matt Helsley <mhelsley@...are.com>
Subject: Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool

On Fri, Jul 17, 2020 at 11:05 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Fri, 17 Jul 2020 10:47:51 -0700
> Sami Tolvanen <samitolvanen@...gle.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