Commit 9edaafad authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
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selftests/bpf: Fix kprobe_multi_bench_attach test failure with LTO kernel 



In my locally build clang LTO kernel (enabling CONFIG_LTO and
CONFIG_LTO_CLANG_THIN), kprobe_multi_bench_attach/kernel subtest
failed like:
  test_kprobe_multi_bench_attach:PASS:get_syms 0 nsec
  test_kprobe_multi_bench_attach:PASS:kprobe_multi_empty__open_and_load 0 nsec
  libbpf: prog 'test_kprobe_empty': failed to attach: No such process
  test_kprobe_multi_bench_attach:FAIL:bpf_program__attach_kprobe_multi_opts unexpected error: -3
  #117/1   kprobe_multi_bench_attach/kernel:FAIL

There are multiple symbols in /sys/kernel/debug/tracing/available_filter_functions
are renamed in /proc/kallsyms due to cross file inlining. One example is for
  static function __access_remote_vm in mm/memory.c.
In a non-LTO kernel, we have the following call stack:
  ptrace_access_vm (global, kernel/ptrace.c)
    access_remote_vm (global, mm/memory.c)
      __access_remote_vm (static, mm/memory.c)

With LTO kernel, it is possible that access_remote_vm() is inlined by
ptrace_access_vm(). So we end up with the following call stack:
  ptrace_access_vm (global, kernel/ptrace.c)
    __access_remote_vm (static, mm/memory.c)
The compiler renames __access_remote_vm to __access_remote_vm.llvm.<hash>
to prevent potential name collision.

The kernel bpf_kprobe_multi_link_attach() and ftrace_lookup_symbols() try
to find addresses based on /proc/kallsyms, hence the current test failed
with LTO kenrel.

This patch consulted /proc/kallsyms to find the corresponding entries
for the ksym and this solved the issue.

Signed-off-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240326041518.1199758-1-yonghong.song@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent d1f02581

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

+48 −14
Original line number Diff line number Diff line
@@ -367,15 +367,49 @@ static bool skip_entry(char *name) 
	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
@@ -408,7 +442,14 @@ static int get_syms(char ***symsp, size_t *cntp, bool kernel) 
		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;
@@ -421,8 +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;
@@ -432,11 +472,8 @@ 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;

}
@@ -472,7 +509,7 @@ 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, i;

	size_t cnt = 0;



	if (!ASSERT_OK(get_syms(&syms, &cnt, kernel), "get_syms"))

		return;
@@ -488,12 +525,9 @@ static void test_kprobe_multi_bench_attach(bool kernel) 


cleanup:

	kprobe_multi_empty__destroy(skel);

	if (syms) {

		for (i = 0; i < cnt; i++)

			free(syms[i]);

	if (syms)

		free(syms);

}

}



static void test_attach_override(void)

{