Re: [PATCHv2 bpf-next 2/4] fprobe: Resolve symbols with kallsyms_lookup_names

[Masami Hiramatsu]

Hi Jiri,

On Mon, 18 Apr 2022 14:48:32 +0200
Jiri Olsa <jolsa@xxxxxxxxxx> wrote:

> Using kallsyms_lookup_names to speed up symbols lookup
> in register_fprobe_syms API.
> 
> This requires syms array to be alphabetically sorted.

This looks good to me. But we may need to update this for changing
the function name "kallsyms_lookup_names()". I think "ftrace_lookup_sorted_syms()"
will be better to understand.
What would you think?

Thank you,

> 
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  kernel/trace/fprobe.c | 32 ++++++++++++--------------------
>  1 file changed, 12 insertions(+), 20 deletions(-)
> 
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index 89d9f994ebb0..6419501a0036 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -85,39 +85,31 @@ static void fprobe_exit_handler(struct rethook_node *rh, void *data,
>  }
>  NOKPROBE_SYMBOL(fprobe_exit_handler);
>  
> +static int symbols_cmp(const void *a, const void *b)
> +{
> +	const char **str_a = (const char **) a;
> +	const char **str_b = (const char **) b;
> +
> +	return strcmp(*str_a, *str_b);
> +}
> +
>  /* Convert ftrace location address from symbols */
>  static unsigned long *get_ftrace_locations(const char **syms, int num)
>  {
> -	unsigned long addr, size;
>  	unsigned long *addrs;
> -	int i;
>  
>  	/* Convert symbols to symbol address */
>  	addrs = kcalloc(num, sizeof(*addrs), GFP_KERNEL);
>  	if (!addrs)
>  		return ERR_PTR(-ENOMEM);
>  
> -	for (i = 0; i < num; i++) {
> -		addr = kallsyms_lookup_name(syms[i]);
> -		if (!addr)	/* Maybe wrong symbol */
> -			goto error;
> -
> -		/* Convert symbol address to ftrace location. */
> -		if (!kallsyms_lookup_size_offset(addr, &size, NULL) || !size)
> -			goto error;
> +	/* kallsyms_lookup_names expects sorted symbols */
> +	sort(syms, num, sizeof(*syms), symbols_cmp, NULL);
>  
> -		addr = ftrace_location_range(addr, addr + size - 1);
> -		if (!addr) /* No dynamic ftrace there. */
> -			goto error;
> +	if (!kallsyms_lookup_names(syms, num, addrs))
> +		return addrs;
>  
> -		addrs[i] = addr;
> -	}
> -
> -	return addrs;
> -
> -error:
>  	kfree(addrs);
> -
>  	return ERR_PTR(-ENOENT);
>  }
>  
> -- 
> 2.35.1
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>