Re: [PATCHv4 bpf-next 3/5] fprobe: Resolve symbols with ftrace_lookup_symbols

Masami Hiramatsu
2022-04-29T14:54:54Z

On Thu, 28 Apr 2022 22:12:05 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

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

This line is no more needed because get_ftrace_locations sorts the syms.
Except for that, this looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks!

>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> 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..aac63ca9c3d1 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;
> + /* ftrace_lookup_symbols 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 (!ftrace_lookup_symbols(syms, num, addrs))
> + return addrs;
>
> - addrs[i] = addr;
> - }
> -
> - return addrs;
> -
> -error:
> kfree(addrs);
> -
> return ERR_PTR(-ENOENT);
> }
>
> --
> 2.35.1
>

--
Masami Hiramatsu <mhiramat@kernel.org>