linux-kernel - Re: [PATCH v4 06/29] tracing: move function tracer options to Kconfig

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Message-ID: <CABCJKud3S7pn8Ap3AkNRUUC4v8nMwOzM2_EwEB6+NFzDp5gppA@mail.gmail.com>
Date:   Wed, 30 Sep 2020 09:05:38 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.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>
Subject: Re: [PATCH v4 06/29] tracing: move function tracer options to Kconfig

On Tue, Sep 29, 2020 at 5:13 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 29 Sep 2020 14:46:08 -0700
> Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> > +++ b/kernel/trace/Kconfig
> > @@ -595,6 +595,22 @@ config FTRACE_MCOUNT_RECORD
> >       depends on DYNAMIC_FTRACE
> >       depends on HAVE_FTRACE_MCOUNT_RECORD
> >
> > +config FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY
> > +     bool
> > +     depends on FTRACE_MCOUNT_RECORD
> > +
> > +config FTRACE_MCOUNT_USE_CC
> > +     def_bool y
> > +     depends on $(cc-option,-mrecord-mcount)
>
> Does the above get executed at every build? Or does a make *config need
> to be done? If someone were to pass a .config to someone else that had
> a compiler that didn't support this, would it be changed if the person
> just did a make?

Yes, it's updated if you copy a .config and just run make. For
example, here's what happens when I create a config with gcc and then
build it with Clang:

$ make defconfig
...
$ ./scripts/config -e FUNCTION_TRACER -e DYNAMIC_FTRACE
$ make olddefconfig
...
$ grep MCOUNT_USE .config
CONFIG_FTRACE_MCOUNT_USE_CC=y
$ make CC=clang
scripts/kconfig/conf  --syncconfig Kconfig
...
^C
$ grep MCOUNT_USE .config
CONFIG_FTRACE_MCOUNT_USE_OBJTOOL=y

Sami