Re: [RFC] ftrace: Add support to keep some functions out of ftrace

Jiri Olsa
2022-08-18T21:23:03Z

On Thu, Aug 18, 2022 at 04:50:24PM -0400, Steven Rostedt wrote:
> On Thu, 18 Aug 2022 22:27:07 +0200
> Jiri Olsa <olsajiri@gmail.com> wrote:
>
> > ok, so the problem with __attribute__((patchable_function_entry(5))) is that
> > it puts function address into __patchable_function_entries section, which is
> > one of ftrace locations source:
> >
> > #define MCOUNT_REC() . = ALIGN(8); \
> > __start_mcount_loc = .; \
> > KEEP(*(__mcount_loc)) \
> > KEEP(*(__patchable_function_entries)) \
> > __stop_mcount_loc = .; \
> > ...
> >
> >
> > it looks like __patchable_function_entries is used for other than x86 archs,
> > so we perhaps we could have x86 specific MCOUNT_REC macro just with
> > __mcount_loc section?
>
> So something like this:
>
> #ifdef CONFIG_X86
> # define NON_MCOUNT_PATCHABLE KEEP(*(__patchable_function_entries))
> # define MCOUNT_PATCHABLE
> #else
> # define NON_MCOUNT_PATCHABLE
> # define MCOUNT_PATCHABLE KEEP(*(__patchable_function_entries))
> #endif
>
> #define MCOUNT_REC() . = ALIGN(8); \
> __start_mcount_loc = .; \
> KEEP(*(__mcount_loc)) \
> MCOUNT_PATCHABLE \
> __stop_mcount_loc = .; \
> NON_MCOUNT_PATCHABLE \
> ...
>

is there a reason to keep NON_MCOUNT_PATCHABLE section for x86? otherwise LGTM

jirka