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

Sami Tolvanen
2020-09-30T16:06:13Z

On Tue, Sep 29, 2020 at 5:13 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue, 29 Sep 2020 14:46:08 -0700
> Sami Tolvanen <samitolvanen@google.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