2022-04-29 13:39:12

by Jiri Olsa

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

Using ftrace_lookup_symbols to speed up symbols lookup
in register_fprobe_syms API.

This requires syms array to be alphabetically sorted.

Signed-off-by: Jiri Olsa <[email protected]>
---
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

2022-05-01 08:20:42

by Masami Hiramatsu

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

On Thu, 28 Apr 2022 22:12:05 +0200
Jiri Olsa <[email protected]> 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 <[email protected]>

Thanks!

>
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
> 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 <[email protected]>