Commit 56baeeba authored by Jackie Liu's avatar Jackie Liu Committed by Andrii Nakryiko
Browse files

libbpf: Use available_filter_functions_addrs with multi-kprobes 

Now that kernel provides a new available_filter_functions_addrs file
which can help us avoid the need to cross-validate
available_filter_functions and kallsyms, we can improve efficiency of
multi-attach kprobes. For example, on my device, the sample program [1]
of start time:

$ sudo ./funccount "tcp_*"

before   after
1.2s     1.0s

  [1]: https://github.com/JackieLiu1/ketones/tree/master/src/funccount



Signed-off-by: default avatarJackie Liu <liuyun01@kylinos.cn>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230705091209.3803873-2-liu.yun@linux.dev
parent 8a3fe76f

tools/lib/bpf/libbpf.c

+61 −1
Original line number Diff line number Diff line
@@ -10234,6 +10234,12 @@ static const char *tracefs_available_filter_functions(void) 
			     : TRACEFS"/available_filter_functions";

}



static const char *tracefs_available_filter_functions_addrs(void)

{

	return use_debugfs() ? DEBUGFS"/available_filter_functions_addrs"

			     : TRACEFS"/available_filter_functions_addrs";

}



static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,

					 const char *kfunc_name, size_t offset)

{
@@ -10650,6 +10656,57 @@ static int libbpf_available_kallsyms_parse(struct kprobe_multi_resolve *res) 
	return err;

}



static bool has_available_filter_functions_addrs(void)

{

	return access(tracefs_available_filter_functions_addrs(), R_OK) != -1;

}



static int libbpf_available_kprobes_parse(struct kprobe_multi_resolve *res)

{

	const char *available_path = tracefs_available_filter_functions_addrs();

	char sym_name[500];

	FILE *f;

	int ret, err = 0;

	unsigned long long sym_addr;



	f = fopen(available_path, "re");

	if (!f) {

		err = -errno;

		pr_warn("failed to open %s: %d\n", available_path, err);

		return err;

	}



	while (true) {

		ret = fscanf(f, "%llx %499s%*[^\n]\n", &sym_addr, sym_name);

		if (ret == EOF && feof(f))

			break;



		if (ret != 2) {

			pr_warn("failed to parse available_filter_functions_addrs entry: %d\n",

				ret);

			err = -EINVAL;

			goto cleanup;

		}



		if (!glob_match(sym_name, res->pattern))

			continue;



		err = libbpf_ensure_mem((void **)&res->addrs, &res->cap,

					sizeof(*res->addrs), res->cnt + 1);

		if (err)

			goto cleanup;



		res->addrs[res->cnt++] = (unsigned long)sym_addr;

	}



	if (res->cnt == 0)

		err = -ENOENT;



cleanup:

	fclose(f);

	return err;

}



struct bpf_link *

bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,

				      const char *pattern,
@@ -10686,6 +10743,9 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, 
		return libbpf_err_ptr(-EINVAL);



	if (pattern) {

		if (has_available_filter_functions_addrs())

			err = libbpf_available_kprobes_parse(&res);

		else

			err = libbpf_available_kallsyms_parse(&res);

		if (err)

			goto error;