[PATCH v2 1/2] libbpf: kprobe.multi: cross filter using available_filter_functions and kallsyms

[PATCH v2 1/2] libbpf: kprobe.multi: cross filter using available_filter_functions and kallsyms

[Jackie Liu]

From: Jackie Liu <liuyun01@kylinos.cn>

When using regular expression matching with "kprobe multi", it scans all
the functions under "/proc/kallsyms" that can be matched. However, not all
of them can be traced by kprobe.multi. If any one of the functions fails
to be traced, it will result in the failure of all functions. The best
approach is to filter out the functions that cannot be traced to ensure
proper tracking of the functions.

Suggested-by: Jiri Olsa <jolsa@kernel.org>
Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
---
 tools/lib/bpf/libbpf.c | 122 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 109 insertions(+), 13 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 214f828ece6b..8ea13de02c67 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10224,6 +10224,12 @@ static const char *tracefs_uprobe_events(void)
 	return use_debugfs() ? DEBUGFS"/uprobe_events" : TRACEFS"/uprobe_events";
 }
 
+static const char *tracefs_available_filter_functions(void)
+{
+	return use_debugfs() ? DEBUGFS"/available_filter_functions" :
+			       TRACEFS"/available_filter_functions";
+}
+
 static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
 					 const char *kfunc_name, size_t offset)
 {
@@ -10539,23 +10545,113 @@ struct kprobe_multi_resolve {
 	size_t cnt;
 };
 
-static int
-resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
-			const char *sym_name, void *ctx)
+static int qsort_compare_function(const void *a, const void *b)
 {
-	struct kprobe_multi_resolve *res = ctx;
-	int err;
+	return strcmp(*(const char **)a, *(const char **)b);
+}
 
-	if (!glob_match(sym_name, res->pattern))
-		return 0;
+static int bsearch_compare_function(const void *a, const void *b)
+{
+	return strcmp((const char *)a, *(const char **)b);
+}
 
-	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(unsigned long),
-				res->cnt + 1);
-	if (err)
+static int libbpf_available_kallsyms_parse(struct kprobe_multi_resolve *res)
+{
+	char sym_name[256];
+	const char *available_functions_file = tracefs_available_filter_functions();
+	FILE *f;
+	int err = 0, ret, i;
+	struct function_info {
+		const char **syms;
+		size_t cap;
+		size_t cnt;
+	} infos = {};
+
+	f = fopen(available_functions_file, "r");
+	if (!f) {
+		err = -errno;
+		pr_warn("failed to open %s\n", available_functions_file);
 		return err;
+	}
 
-	res->addrs[res->cnt++] = (unsigned long) sym_addr;
-	return 0;
+	while (true) {
+		char *name;
+
+		ret = fscanf(f, "%s%*[^\n]\n", sym_name);
+		if (ret == EOF && feof(f))
+			break;
+
+		if (ret != 1) {
+			pr_warn("failed to read available function file entry: %d\n",
+				ret);
+			err = -EINVAL;
+			goto cleanup;
+		}
+
+		if (!glob_match(sym_name, res->pattern))
+			continue;
+
+		err = libbpf_ensure_mem((void **)&infos.syms, &infos.cap,
+					sizeof(void *), infos.cnt + 1);
+		if (err)
+			goto cleanup;
+
+		name = strdup(sym_name);
+		if (!name) {
+			err = -errno;
+			goto cleanup;
+		}
+
+		infos.syms[infos.cnt++] = name;
+	}
+	fclose(f);
+
+	/* sort available functions */
+	qsort(infos.syms, infos.cnt, sizeof(void *), qsort_compare_function);
+
+	f = fopen("/proc/kallsyms", "r");
+	if (!f) {
+		err = -errno;
+		pr_warn("failed to open /proc/kallsyms\n");
+		goto free_infos;
+	}
+
+	while (true) {
+		unsigned long long sym_addr;
+
+		ret = fscanf(f, "%llx %*c %499s%*[^\n]\n", &sym_addr, sym_name);
+		if (ret == EOF && feof(f))
+			break;
+
+		if (ret != 2) {
+			pr_warn("failed to read kallsyms entry: %d\n", ret);
+			err = -EINVAL;
+			break;
+		}
+
+		if (!glob_match(sym_name, res->pattern))
+			continue;
+
+		if (!bsearch(&sym_name, infos.syms, infos.cnt, sizeof(void *),
+			     bsearch_compare_function))
+			continue;
+
+		err = libbpf_ensure_mem((void **)&res->addrs, &res->cap,
+					sizeof(unsigned long), res->cnt + 1);
+		if (err)
+			break;
+
+		res->addrs[res->cnt++] = (unsigned long)sym_addr;
+	}
+
+cleanup:
+	fclose(f);
+free_infos:
+	for (i = 0; i < infos.cnt; i++)
+		free((char *)infos.syms[i]);
+	free(infos.syms);
+
+	return err;
 }
 
 struct bpf_link *
@@ -10594,7 +10690,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
 		return libbpf_err_ptr(-EINVAL);
 
 	if (pattern) {
-		err = libbpf_kallsyms_parse(resolve_kprobe_multi_cb, &res);
+		err = libbpf_available_kallsyms_parse(&res);
 		if (err)
 			goto error;
 		if (!res.cnt) {
-- 
2.25.1

[PATCH v2 2/2] libbpf: kprobe.multi: Filter with available_filter_functions_addrs

[Jackie Liu]

From: Jackie Liu <liuyun01@kylinos.cn>

Now, we provide a new available_filter_functions_addrs interface, which can
help us not need to cross-validate available_filter_functions and kallsyms,
which can effectively improve efficiency. 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: Jackie Liu <liuyun01@kylinos.cn>
---
 tools/lib/bpf/libbpf.c | 58 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 8ea13de02c67..1ec861ad52a6 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10230,6 +10230,12 @@ 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)
 {
@@ -10654,6 +10660,53 @@ 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)
+{
+	char sym_name[256];
+	FILE *f;
+	int ret, err = 0;
+	unsigned long long sym_addr;
+	const char *available_path = tracefs_available_filter_functions_addrs();
+
+	f = fopen(available_path, "r");
+	if (!f) {
+		err = -errno;
+		pr_warn("failed to open %s.\n", available_path);
+		return err;
+	}
+
+	while (true) {
+		ret = fscanf(f, "%llx %s%*[^\n]\n", &sym_addr, sym_name);
+		if (ret == EOF && feof(f))
+			break;
+
+		if (ret != 2) {
+			pr_warn("failed to read available kprobe entry: %d\n",
+				ret);
+			err = -EINVAL;
+			break;
+		}
+
+		if (!glob_match(sym_name, res->pattern))
+			continue;
+
+		err = libbpf_ensure_mem((void **) &res->addrs, &res->cap,
+					sizeof(unsigned long), res->cnt + 1);
+		if (err)
+			break;
+
+		res->addrs[res->cnt++] = (unsigned long) sym_addr;
+	}
+
+	fclose(f);
+	return err;
+}
+
 struct bpf_link *
 bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
 				      const char *pattern,
@@ -10690,7 +10743,10 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
 		return libbpf_err_ptr(-EINVAL);
 
 	if (pattern) {
-		err = libbpf_available_kallsyms_parse(&res);
+		if (has_available_filter_functions_addrs())
+			err = libbpf_available_kprobes_parse(&res);
+		else
+			err = libbpf_available_kallsyms_parse(&res);
 		if (err)
 			goto error;
 		if (!res.cnt) {
-- 
2.25.1

Re: [PATCH v2 1/2] libbpf: kprobe.multi: cross filter using available_filter_functions and kallsyms

[kernel test robot]

Hi Jackie,

kernel test robot noticed the following build errors:

[auto build test ERROR on bpf-next/master]
[also build test ERROR on bpf/master linus/master v6.4 next-20230630]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Jackie-Liu/libbpf-kprobe-multi-Filter-with-available_filter_functions_addrs/20230701-161010
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link:    https://lore.kernel.org/r/20230701080817.1768865-1-liu.yun%40linux.dev
patch subject: [PATCH v2 1/2] libbpf: kprobe.multi: cross filter using available_filter_functions and kallsyms
config: x86_64-buildonly-randconfig-r001-20230702 (https://download.01.org/0day-ci/archive/20230703/202307030355.TdXOHklM-lkp@intel.com/config)
compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project.git 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
reproduce: (https://download.01.org/0day-ci/archive/20230703/202307030355.TdXOHklM-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202307030355.TdXOHklM-lkp@intel.com/

All errors (new ones prefixed by >>):

>> libbpf.c:10626:57: error: 'fscanf' may overflow; destination buffer in argument 4 has size 256, but the corresponding specifier may require size 500 [-Werror,-Wfortify-source]
                   ret = fscanf(f, "%llx %*c %499s%*[^\n]\n", &sym_addr, sym_name);
                                                                         ^
   1 error generated.
   make[5]: *** [tools/build/Makefile.build:97: tools/bpf/resolve_btfids/libbpf/staticobjs/libbpf.o] Error 1
   make[5]: *** Waiting for unfinished jobs....
   make[4]: *** [Makefile:157: tools/bpf/resolve_btfids/libbpf/staticobjs/libbpf-in.o] Error 2
   make[3]: *** [Makefile:63: tools/bpf/resolve_btfids//libbpf/libbpf.a] Error 2
   make[2]: *** [Makefile:76: bpf/resolve_btfids] Error 2 shuffle=967315254
   make[1]: *** [Makefile:1446: tools/bpf/resolve_btfids] Error 2 shuffle=967315254
   make[1]: Target 'prepare' not remade because of errors.
   make: *** [Makefile:226: __sub-make] Error 2 shuffle=967315254
   make: Target 'prepare' not remade because of errors.

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki