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

[Steven Rostedt]

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		    \
   ...

??

-- Steve