Re: [PATCH v2 5/8] ftrace: Add swap_func to ftrace_process_locs()

On Mon, 26 Aug 2024 09:55:29 +0300
Mike Rapoport <[email protected]> wrote:

> From: Song Liu <[email protected]>
> 
> ftrace_process_locs sorts module mcount, which is inside RO memory. Add a
> ftrace_swap_func so that archs can use RO-memory-poke function to do the
> sorting.

Can you add the above as a comment above the ftrace_swap_func() function?

Thanks,

-- Steve

> 
> Signed-off-by: Song Liu <[email protected]>
> Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
> ---
>  include/linux/ftrace.h |  2 ++
>  kernel/trace/ftrace.c  | 13 ++++++++++++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index fd5e84d0ec47..b794dcb7cae8 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -1188,4 +1188,6 @@ unsigned long arch_syscall_addr(int nr);
>  
>  #endif /* CONFIG_FTRACE_SYSCALLS */
>  
> +void ftrace_swap_func(void *a, void *b, int n);
> +
>  #endif /* _LINUX_FTRACE_H */
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 4c28dd177ca6..9829979f3a46 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6989,6 +6989,17 @@ static void test_is_sorted(unsigned long *start,
> unsigned long count) }
>  #endif
>  
> +void __weak ftrace_swap_func(void *a, void *b, int n)
> +{
> +	unsigned long t;
> +
> +	WARN_ON_ONCE(n != sizeof(t));
> +
> +	t = *((unsigned long *)a);
> +	*(unsigned long *)a = *(unsigned long *)b;
> +	*(unsigned long *)b = t;
> +}
> +
>  static int ftrace_process_locs(struct module *mod,
>  			       unsigned long *start,
>  			       unsigned long *end)
> @@ -7016,7 +7027,7 @@ static int ftrace_process_locs(struct module *mod,
>  	 */
>  	if (!IS_ENABLED(CONFIG_BUILDTIME_MCOUNT_SORT) || mod) {
>  		sort(start, count, sizeof(*start),
> -		     ftrace_cmp_ips, NULL);
> +		     ftrace_cmp_ips, ftrace_swap_func);
>  	} else {
>  		test_is_sorted(start, count);
>  	}