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

[Jiri Olsa]

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@xxxxxxxxx> 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