Merge branch 'bpf-fix-a-couple-of-test-failures-with-lto-kernel'

Yonghong Song says:

====================
bpf: Fix a couple of test failures with LTO kernel

With a LTO kernel built with clang, with one of earlier version of kernel,
I encountered two test failures, ksyms and kprobe_multi_bench_attach/kernel.
Now with latest bpf-next, only kprobe_multi_bench_attach/kernel failed.
But it is possible in the future ksyms selftest may fail again.

Both test failures are due to static variable/function renaming
due to cross-file inlining. For Ksyms failure, the solution is
to strip .llvm.<hash> suffixes for symbols in /proc/kallsyms before
comparing against the ksym in bpf program.
For kprobe_multi_bench_attach/kernel failure, the solution is
to either provide names in /proc/kallsyms to the kernel or
ignore those names who have .llvm.<hash> suffix since the kernel
sym name comparison is against /proc/kallsyms.

Please see each individual patches for details.

Changelogs:
  v2 -> v3:
    - no need to check config file, directly so strstr with '.llvm.'.
    - for kprobe_multi_bench with syms, instead of skipping the syms,
      consult /proc/kallyms to find corresponding names.
    - add a test with populating addrs to the kernel for kprobe
      multi attach.
  v1 -> v2:
    - Let libbpf handle .llvm.<hash suffixes since it may impact
      bpf program ksym.
====================

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Alexei Starovoitov

tools/lib/bpf/libbpf.c

@@ -1970,6 +1970,20 @@ static struct extern_desc *find_extern_by_name(const struct bpf_object *obj,
 	return NULL;
 }
 
+static struct extern_desc *find_extern_by_name_with_len(const struct bpf_object *obj,
+							const void *name, int len)
+{
+	const char *ext_name;
+	int i;
+
+	for (i = 0; i < obj->nr_extern; i++) {
+		ext_name = obj->externs[i].name;
+		if (strlen(ext_name) == len && strncmp(ext_name, name, len) == 0)
+			return &obj->externs[i];
+	}
+	return NULL;
+}
+
 static int set_kcfg_value_tri(struct extern_desc *ext, void *ext_val,
 			      char value)
 {
@@ -7986,7 +8000,10 @@ static int bpf_object__sanitize_maps(struct bpf_object *obj)
 	return 0;
 }
 
-int libbpf_kallsyms_parse(kallsyms_cb_t cb, void *ctx)
+typedef int (*kallsyms_cb_t)(unsigned long long sym_addr, char sym_type,
+			     const char *sym_name, void *ctx);
+
+static int libbpf_kallsyms_parse(kallsyms_cb_t cb, void *ctx)
 {
 	char sym_type, sym_name[500];
 	unsigned long long sym_addr;
@@ -8026,8 +8043,13 @@ static int kallsyms_cb(unsigned long long sym_addr, char sym_type,
 	struct bpf_object *obj = ctx;
 	const struct btf_type *t;
 	struct extern_desc *ext;
+	char *res;
 
-	ext = find_extern_by_name(obj, sym_name);
+	res = strstr(sym_name, ".llvm.");
+	if (sym_type == 'd' && res)
+		ext = find_extern_by_name_with_len(obj, sym_name, res - sym_name);
+	else
+		ext = find_extern_by_name(obj, sym_name);
 	if (!ext || ext->type != EXT_KSYM)
 		return 0;
 

tools/lib/bpf/libbpf_internal.h

@@ -518,11 +518,6 @@ int btf_ext_visit_str_offs(struct btf_ext *btf_ext, str_off_visit_fn visit, void
 __s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,
 				 __u32 kind);
 
-typedef int (*kallsyms_cb_t)(unsigned long long sym_addr, char sym_type,
-			     const char *sym_name, void *ctx);
-
-int libbpf_kallsyms_parse(kallsyms_cb_t cb, void *arg);
-
 /* handle direct returned errors */
 static inline int libbpf_err(int ret)
 {

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c

@@ -336,15 +336,80 @@ static bool symbol_equal(long key1, long key2, void *ctx __maybe_unused)
 	return strcmp((const char *) key1, (const char *) key2) == 0;
 }
 
+static bool is_invalid_entry(char *buf, bool kernel)
+{
+	if (kernel && strchr(buf, '['))
+		return true;
+	if (!kernel && !strchr(buf, '['))
+		return true;
+	return false;
+}
+
+static bool skip_entry(char *name)
+{
+	/*
+	 * We attach to almost all kernel functions and some of them
+	 * will cause 'suspicious RCU usage' when fprobe is attached
+	 * to them. Filter out the current culprits - arch_cpu_idle
+	 * default_idle and rcu_* functions.
+	 */
+	if (!strcmp(name, "arch_cpu_idle"))
+		return true;
+	if (!strcmp(name, "default_idle"))
+		return true;
+	if (!strncmp(name, "rcu_", 4))
+		return true;
+	if (!strcmp(name, "bpf_dispatcher_xdp_func"))
+		return true;
+	if (!strncmp(name, "__ftrace_invalid_address__",
+		     sizeof("__ftrace_invalid_address__") - 1))
+		return true;
+	return false;
+}
+
+/* Do comparision by ignoring '.llvm.<hash>' suffixes. */
+static int compare_name(const char *name1, const char *name2)
+{
+	const char *res1, *res2;
+	int len1, len2;
+
+	res1 = strstr(name1, ".llvm.");
+	res2 = strstr(name2, ".llvm.");
+	len1 = res1 ? res1 - name1 : strlen(name1);
+	len2 = res2 ? res2 - name2 : strlen(name2);
+
+	if (len1 == len2)
+		return strncmp(name1, name2, len1);
+	if (len1 < len2)
+		return strncmp(name1, name2, len1) <= 0 ? -1 : 1;
+	return strncmp(name1, name2, len2) >= 0 ? 1 : -1;
+}
+
+static int load_kallsyms_compare(const void *p1, const void *p2)
+{
+	return compare_name(((const struct ksym *)p1)->name, ((const struct ksym *)p2)->name);
+}
+
+static int search_kallsyms_compare(const void *p1, const struct ksym *p2)
+{
+	return compare_name(p1, p2->name);
+}
+
 static int get_syms(char ***symsp, size_t *cntp, bool kernel)
 {
-	size_t cap = 0, cnt = 0, i;
-	char *name = NULL, **syms = NULL;
+	size_t cap = 0, cnt = 0;
+	char *name = NULL, *ksym_name, **syms = NULL;
 	struct hashmap *map;
+	struct ksyms *ksyms;
+	struct ksym *ks;
 	char buf[256];
 	FILE *f;
 	int err = 0;
 
+	ksyms = load_kallsyms_custom_local(load_kallsyms_compare);
+	if (!ASSERT_OK_PTR(ksyms, "load_kallsyms_custom_local"))
+		return -EINVAL;
+
 	/*
 	 * The available_filter_functions contains many duplicates,
 	 * but other than that all symbols are usable in kprobe multi
@@ -368,33 +433,23 @@ static int get_syms(char ***symsp, size_t *cntp, bool kernel)
 	}
 
 	while (fgets(buf, sizeof(buf), f)) {
-		if (kernel && strchr(buf, '['))
-			continue;
-		if (!kernel && !strchr(buf, '['))
+		if (is_invalid_entry(buf, kernel))
 			continue;
 
 		free(name);
 		if (sscanf(buf, "%ms$*[^\n]\n", &name) != 1)
 			continue;
-		/*
-		 * We attach to almost all kernel functions and some of them
-		 * will cause 'suspicious RCU usage' when fprobe is attached
-		 * to them. Filter out the current culprits - arch_cpu_idle
-		 * default_idle and rcu_* functions.
-		 */
-		if (!strcmp(name, "arch_cpu_idle"))
-			continue;
-		if (!strcmp(name, "default_idle"))
-			continue;
-		if (!strncmp(name, "rcu_", 4))
-			continue;
-		if (!strcmp(name, "bpf_dispatcher_xdp_func"))
-			continue;
-		if (!strncmp(name, "__ftrace_invalid_address__",
-			     sizeof("__ftrace_invalid_address__") - 1))
+		if (skip_entry(name))
 			continue;
 
-		err = hashmap__add(map, name, 0);
+		ks = search_kallsyms_custom_local(ksyms, name, search_kallsyms_compare);
+		if (!ks) {
+			err = -EINVAL;
+			goto error;
+		}
+
+		ksym_name = ks->name;
+		err = hashmap__add(map, ksym_name, 0);
 		if (err == -EEXIST) {
 			err = 0;
 			continue;
@@ -407,8 +462,7 @@ static int get_syms(char ***symsp, size_t *cntp, bool kernel)
 		if (err)
 			goto error;
 
-		syms[cnt++] = name;
-		name = NULL;
+		syms[cnt++] = ksym_name;
 	}
 
 	*symsp = syms;
@@ -418,42 +472,88 @@ static int get_syms(char ***symsp, size_t *cntp, bool kernel)
 	free(name);
 	fclose(f);
 	hashmap__free(map);
-	if (err) {
-		for (i = 0; i < cnt; i++)
-			free(syms[i]);
+	if (err)
 		free(syms);
+	return err;
+}
+
+static int get_addrs(unsigned long **addrsp, size_t *cntp, bool kernel)
+{
+	unsigned long *addr, *addrs, *tmp_addrs;
+	int err = 0, max_cnt, inc_cnt;
+	char *name = NULL;
+	size_t cnt = 0;
+	char buf[256];
+	FILE *f;
+
+	if (access("/sys/kernel/tracing/trace", F_OK) == 0)
+		f = fopen("/sys/kernel/tracing/available_filter_functions_addrs", "r");
+	else
+		f = fopen("/sys/kernel/debug/tracing/available_filter_functions_addrs", "r");
+
+	if (!f)
+		return -ENOENT;
+
+	/* In my local setup, the number of entries is 50k+ so Let us initially
+	 * allocate space to hold 64k entries. If 64k is not enough, incrementally
+	 * increase 1k each time.
+	 */
+	max_cnt = 65536;
+	inc_cnt = 1024;
+	addrs = malloc(max_cnt * sizeof(long));
+	if (addrs == NULL) {
+		err = -ENOMEM;
+		goto error;
 	}
+
+	while (fgets(buf, sizeof(buf), f)) {
+		if (is_invalid_entry(buf, kernel))
+			continue;
+
+		free(name);
+		if (sscanf(buf, "%p %ms$*[^\n]\n", &addr, &name) != 2)
+			continue;
+		if (skip_entry(name))
+			continue;
+
+		if (cnt == max_cnt) {
+			max_cnt += inc_cnt;
+			tmp_addrs = realloc(addrs, max_cnt);
+			if (!tmp_addrs) {
+				err = -ENOMEM;
+				goto error;
+			}
+			addrs = tmp_addrs;
+		}
+
+		addrs[cnt++] = (unsigned long)addr;
+	}
+
+	*addrsp = addrs;
+	*cntp = cnt;
+
+error:
+	free(name);
+	fclose(f);
+	if (err)
+		free(addrs);
 	return err;
 }
 
-static void test_kprobe_multi_bench_attach(bool kernel)
+static void do_bench_test(struct kprobe_multi_empty *skel, struct bpf_kprobe_multi_opts *opts)
 {
-	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
-	struct kprobe_multi_empty *skel = NULL;
 	long attach_start_ns, attach_end_ns;
 	long detach_start_ns, detach_end_ns;
 	double attach_delta, detach_delta;
 	struct bpf_link *link = NULL;
-	char **syms = NULL;
-	size_t cnt = 0, i;
-
-	if (!ASSERT_OK(get_syms(&syms, &cnt, kernel), "get_syms"))
-		return;
-
-	skel = kprobe_multi_empty__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "kprobe_multi_empty__open_and_load"))
-		goto cleanup;
-
-	opts.syms = (const char **) syms;
-	opts.cnt = cnt;
 
 	attach_start_ns = get_time_ns();
 	link = bpf_program__attach_kprobe_multi_opts(skel->progs.test_kprobe_empty,
-						     NULL, &opts);
+						     NULL, opts);
 	attach_end_ns = get_time_ns();
 
 	if (!ASSERT_OK_PTR(link, "bpf_program__attach_kprobe_multi_opts"))
-		goto cleanup;
+		return;
 
 	detach_start_ns = get_time_ns();
 	bpf_link__destroy(link);
@@ -462,17 +562,65 @@ static void test_kprobe_multi_bench_attach(bool kernel)
 	attach_delta = (attach_end_ns - attach_start_ns) / 1000000000.0;
 	detach_delta = (detach_end_ns - detach_start_ns) / 1000000000.0;
 
-	printf("%s: found %lu functions\n", __func__, cnt);
+	printf("%s: found %lu functions\n", __func__, opts->cnt);
 	printf("%s: attached in %7.3lfs\n", __func__, attach_delta);
 	printf("%s: detached in %7.3lfs\n", __func__, detach_delta);
+}
+
+static void test_kprobe_multi_bench_attach(bool kernel)
+{
+	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+	struct kprobe_multi_empty *skel = NULL;
+	char **syms = NULL;
+	size_t cnt = 0;
+
+	if (!ASSERT_OK(get_syms(&syms, &cnt, kernel), "get_syms"))
+		return;
+
+	skel = kprobe_multi_empty__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "kprobe_multi_empty__open_and_load"))
+		goto cleanup;
+
+	opts.syms = (const char **) syms;
+	opts.cnt = cnt;
+
+	do_bench_test(skel, &opts);
 
 cleanup:
 	kprobe_multi_empty__destroy(skel);
-	if (syms) {
-		for (i = 0; i < cnt; i++)
-			free(syms[i]);
+	if (syms)
 		free(syms);
+}
+
+static void test_kprobe_multi_bench_attach_addr(bool kernel)
+{
+	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+	struct kprobe_multi_empty *skel = NULL;
+	unsigned long *addrs = NULL;
+	size_t cnt = 0;
+	int err;
+
+	err = get_addrs(&addrs, &cnt, kernel);
+	if (err == -ENOENT) {
+		test__skip();
+		return;
 	}
+
+	if (!ASSERT_OK(err, "get_addrs"))
+		return;
+
+	skel = kprobe_multi_empty__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "kprobe_multi_empty__open_and_load"))
+		goto cleanup;
+
+	opts.addrs = addrs;
+	opts.cnt = cnt;
+
+	do_bench_test(skel, &opts);
+
+cleanup:
+	kprobe_multi_empty__destroy(skel);
+	free(addrs);
 }
 
 static void test_attach_override(void)
@@ -515,6 +663,10 @@ void serial_test_kprobe_multi_bench_attach(void)
 		test_kprobe_multi_bench_attach(true);
 	if (test__start_subtest("modules"))
 		test_kprobe_multi_bench_attach(false);
+	if (test__start_subtest("kernel"))
+		test_kprobe_multi_bench_attach_addr(true);
+	if (test__start_subtest("modules"))
+		test_kprobe_multi_bench_attach_addr(false);
 }
 
 void test_kprobe_multi_test(void)