[PATCH v6 bpf-next 3/3] selftests/bpf: Add testcases for tailcall hierarchy fixing

Leon Hwang
2024-07-14T12:39:26Z

Add some test cases to confirm the tailcall hierarchy issue has been fixed.

On x64, the selftests result is:

cd tools/testing/selftests/bpf && ./test_progs -t tailcalls
327/18 tailcalls/tailcall_bpf2bpf_hierarchy_1:OK
327/19 tailcalls/tailcall_bpf2bpf_hierarchy_fentry:OK
327/20 tailcalls/tailcall_bpf2bpf_hierarchy_fexit:OK
327/21 tailcalls/tailcall_bpf2bpf_hierarchy_fentry_fexit:OK
327/22 tailcalls/tailcall_bpf2bpf_hierarchy_fentry_entry:OK
327/23 tailcalls/tailcall_bpf2bpf_hierarchy_2:OK
327/24 tailcalls/tailcall_bpf2bpf_hierarchy_3:OK
327 tailcalls:OK
Summary: 1/24 PASSED, 0 SKIPPED, 0 FAILED

On arm64, the selftests result is:

cd tools/testing/selftests/bpf && ./test_progs -t tailcalls
327/18 tailcalls/tailcall_bpf2bpf_hierarchy_1:OK
327/19 tailcalls/tailcall_bpf2bpf_hierarchy_fentry:OK
327/20 tailcalls/tailcall_bpf2bpf_hierarchy_fexit:OK
327/21 tailcalls/tailcall_bpf2bpf_hierarchy_fentry_fexit:OK
327/22 tailcalls/tailcall_bpf2bpf_hierarchy_fentry_entry:OK
327/23 tailcalls/tailcall_bpf2bpf_hierarchy_2:OK
327/24 tailcalls/tailcall_bpf2bpf_hierarchy_3:OK
327 tailcalls:OK
Summary: 1/24 PASSED, 0 SKIPPED, 0 FAILED

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
---
.../selftests/bpf/prog_tests/tailcalls.c | 320 ++++++++++++++++++
.../bpf/progs/tailcall_bpf2bpf_hierarchy1.c | 34 ++
.../bpf/progs/tailcall_bpf2bpf_hierarchy2.c | 70 ++++
.../bpf/progs/tailcall_bpf2bpf_hierarchy3.c | 62 ++++
.../progs/tailcall_bpf2bpf_hierarchy_fentry.c | 35 ++
tools/testing/selftests/bpf/progs/tc_dummy.c | 12 +
6 files changed, 533 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy1.c
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy3.c
create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy_fentry.c
create mode 100644 tools/testing/selftests/bpf/progs/tc_dummy.c

diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
index 59993fc9c0d7e..e01fabb8cc415 100644
--- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c
+++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
@@ -3,6 +3,8 @@
#include <test_progs.h>
#include <network_helpers.h>
#include "tailcall_poke.skel.h"
+#include "tailcall_bpf2bpf_hierarchy2.skel.h"
+#include "tailcall_bpf2bpf_hierarchy3.skel.h"

/* test_tailcall_1 checks basic functionality by patching multiple locations
@@ -1187,6 +1189,312 @@ static void test_tailcall_poke(void)
tailcall_poke__destroy(call);
}

+static void test_tailcall_hierarchy_count(const char *which, bool test_fentry,
+ bool test_fexit,
+ bool test_fentry_entry)
+{
+ int err, map_fd, prog_fd, main_data_fd, fentry_data_fd, fexit_data_fd, i, val;
+ struct bpf_object *obj = NULL, *fentry_obj = NULL, *fexit_obj = NULL;
+ struct bpf_link *fentry_link = NULL, *fexit_link = NULL;
+ struct bpf_program *prog, *fentry_prog;
+ struct bpf_map *prog_array, *data_map;
+ int fentry_prog_fd;
+ char buff[128] = {};
+
+ LIBBPF_OPTS(bpf_test_run_opts, topts,
+ .data_in = buff,
+ .data_size_in = sizeof(buff),
+ .repeat = 1,
+ );
+
+ err = bpf_prog_test_load(which, BPF_PROG_TYPE_SCHED_CLS, &obj,
+ &prog_fd);
+ if (!ASSERT_OK(err, "load obj"))
+ return;
+
+ prog = bpf_object__find_program_by_name(obj, "entry");
+ if (!ASSERT_OK_PTR(prog, "find entry prog"))
+ goto out;
+
+ prog_fd = bpf_program__fd(prog);
+ if (!ASSERT_GE(prog_fd, 0, "prog_fd"))
+ goto out;
+
+ if (test_fentry_entry) {
+ fentry_obj = bpf_object__open_file("tailcall_bpf2bpf_hierarchy_fentry.bpf.o",
+ NULL);
+ if (!ASSERT_OK_PTR(fentry_obj, "open fentry_obj file"))
+ goto out;
+
+ fentry_prog = bpf_object__find_program_by_name(fentry_obj,
+ "fentry");
+ if (!ASSERT_OK_PTR(prog, "find fentry prog"))
+ goto out;
+
+ err = bpf_program__set_attach_target(fentry_prog, prog_fd,
+ "entry");
+ if (!ASSERT_OK(err, "set_attach_target entry"))
+ goto out;
+
+ err = bpf_object__load(fentry_obj);
+ if (!ASSERT_OK(err, "load fentry_obj"))
+ goto out;
+
+ fentry_link = bpf_program__attach_trace(fentry_prog);
+ if (!ASSERT_OK_PTR(fentry_link, "attach_trace"))
+ goto out;
+
+ fentry_prog_fd = bpf_program__fd(fentry_prog);
+ if (!ASSERT_GE(fentry_prog_fd, 0, "fentry_prog_fd"))
+ goto out;
+
+ prog_array = bpf_object__find_map_by_name(fentry_obj, "jmp_table");
+ if (!ASSERT_OK_PTR(prog_array, "find jmp_table"))
+ goto out;
+
+ map_fd = bpf_map__fd(prog_array);
+ if (!ASSERT_GE(map_fd, 0, "map_fd"))
+ goto out;
+
+ i = 0;
+ err = bpf_map_update_elem(map_fd, &i, &fentry_prog_fd, BPF_ANY);
+ if (!ASSERT_OK(err, "update jmp_table"))
+ goto out;
+
+ data_map = bpf_object__find_map_by_name(fentry_obj, ".bss");
+ if (!ASSERT_FALSE(!data_map || !bpf_map__is_internal(data_map),
+ "find data_map"))
+ goto out;
+
+ } else {
+ prog_array = bpf_object__find_map_by_name(obj, "jmp_table");
+ if (!ASSERT_OK_PTR(prog_array, "find jmp_table"))
+ goto out;
+
+ map_fd = bpf_map__fd(prog_array);
+ if (!ASSERT_GE(map_fd, 0, "map_fd"))
+ goto out;
+
+ i = 0;
+ err = bpf_map_update_elem(map_fd, &i, &prog_fd, BPF_ANY);
+ if (!ASSERT_OK(err, "update jmp_table"))
+ goto out;
+
+ data_map = bpf_object__find_map_by_name(obj, ".bss");
+ if (!ASSERT_FALSE(!data_map || !bpf_map__is_internal(data_map),
+ "find data_map"))
+ goto out;
+ }
+
+ if (test_fentry) {
+ fentry_obj = bpf_object__open_file("tailcall_bpf2bpf_fentry.bpf.o",
+ NULL);
+ if (!ASSERT_OK_PTR(fentry_obj, "open fentry_obj file"))
+ goto out;
+
+ prog = bpf_object__find_program_by_name(fentry_obj, "fentry");
+ if (!ASSERT_OK_PTR(prog, "find fentry prog"))
+ goto out;
+
+ err = bpf_program__set_attach_target(prog, prog_fd,
+ "subprog_tail");
+ if (!ASSERT_OK(err, "set_attach_target subprog_tail"))
+ goto out;
+
+ err = bpf_object__load(fentry_obj);
+ if (!ASSERT_OK(err, "load fentry_obj"))
+ goto out;
+
+ fentry_link = bpf_program__attach_trace(prog);
+ if (!ASSERT_OK_PTR(fentry_link, "attach_trace"))
+ goto out;
+ }
+
+ if (test_fexit) {
+ fexit_obj = bpf_object__open_file("tailcall_bpf2bpf_fexit.bpf.o",
+ NULL);
+ if (!ASSERT_OK_PTR(fexit_obj, "open fexit_obj file"))
+ goto out;
+
+ prog = bpf_object__find_program_by_name(fexit_obj, "fexit");
+ if (!ASSERT_OK_PTR(prog, "find fexit prog"))
+ goto out;
+
+ err = bpf_program__set_attach_target(prog, prog_fd,
+ "subprog_tail");
+ if (!ASSERT_OK(err, "set_attach_target subprog_tail"))
+ goto out;
+
+ err = bpf_object__load(fexit_obj);
+ if (!ASSERT_OK(err, "load fexit_obj"))
+ goto out;
+
+ fexit_link = bpf_program__attach_trace(prog);
+ if (!ASSERT_OK_PTR(fexit_link, "attach_trace"))
+ goto out;
+ }
+
+ err = bpf_prog_test_run_opts(prog_fd, &topts);
+ ASSERT_OK(err, "tailcall");
+ ASSERT_EQ(topts.retval, 1, "tailcall retval");
+
+ main_data_fd = bpf_map__fd(data_map);
+ if (!ASSERT_GE(main_data_fd, 0, "main_data_fd"))
+ goto out;
+
+ i = 0;
+ err = bpf_map_lookup_elem(main_data_fd, &i, &val);
+ ASSERT_OK(err, "tailcall count");
+ ASSERT_EQ(val, 34, "tailcall count");
+
+ if (test_fentry) {
+ data_map = bpf_object__find_map_by_name(fentry_obj, ".bss");
+ if (!ASSERT_FALSE(!data_map || !bpf_map__is_internal(data_map),
+ "find tailcall_bpf2bpf_fentry.bss map"))
+ goto out;
+
+ fentry_data_fd = bpf_map__fd(data_map);
+ if (!ASSERT_GE(fentry_data_fd, 0,
+ "find tailcall_bpf2bpf_fentry.bss map fd"))
+ goto out;
+
+ i = 0;
+ err = bpf_map_lookup_elem(fentry_data_fd, &i, &val);
+ ASSERT_OK(err, "fentry count");
+ ASSERT_EQ(val, 68, "fentry count");
+ }
+
+ if (test_fexit) {
+ data_map = bpf_object__find_map_by_name(fexit_obj, ".bss");
+ if (!ASSERT_FALSE(!data_map || !bpf_map__is_internal(data_map),
+ "find tailcall_bpf2bpf_fexit.bss map"))
+ goto out;
+
+ fexit_data_fd = bpf_map__fd(data_map);
+ if (!ASSERT_GE(fexit_data_fd, 0,
+ "find tailcall_bpf2bpf_fexit.bss map fd"))
+ goto out;
+
+ i = 0;
+ err = bpf_map_lookup_elem(fexit_data_fd, &i, &val);
+ ASSERT_OK(err, "fexit count");
+ ASSERT_EQ(val, 68, "fexit count");
+ }
+
+ i = 0;
+ err = bpf_map_delete_elem(map_fd, &i);
+ if (!ASSERT_OK(err, "delete_elem from jmp_table"))
+ goto out;
+
+ err = bpf_prog_test_run_opts(prog_fd, &topts);
+ ASSERT_OK(err, "tailcall");
+ ASSERT_EQ(topts.retval, 1, "tailcall retval");
+
+ i = 0;
+ err = bpf_map_lookup_elem(main_data_fd, &i, &val);
+ ASSERT_OK(err, "tailcall count");
+ ASSERT_EQ(val, 35, "tailcall count");
+
+ if (test_fentry) {
+ i = 0;
+ err = bpf_map_lookup_elem(fentry_data_fd, &i, &val);
+ ASSERT_OK(err, "fentry count");
+ ASSERT_EQ(val, 70, "fentry count");
+ }
+
+ if (test_fexit) {
+ i = 0;
+ err = bpf_map_lookup_elem(fexit_data_fd, &i, &val);
+ ASSERT_OK(err, "fexit count");
+ ASSERT_EQ(val, 70, "fexit count");
+ }
+
+out:
+ bpf_link__destroy(fentry_link);
+ bpf_link__destroy(fexit_link);
+ bpf_object__close(fentry_obj);
+ bpf_object__close(fexit_obj);
+ bpf_object__close(obj);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_1 checks that the count value of the tail
+ * call limit enforcement matches with expectations when tailcalls are preceded
+ * with two bpf2bpf calls.
+ *
+ * subprog --tailcall-> entry
+ * entry <
+ * subprog --tailcall-> entry
+ */
+static void test_tailcall_bpf2bpf_hierarchy_1(void)
+{
+ test_tailcall_hierarchy_count("tailcall_bpf2bpf_hierarchy1.bpf.o",
+ false, false, false);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_fentry checks that the count value of the
+ * tail call limit enforcement matches with expectations when tailcalls are
+ * preceded with two bpf2bpf calls, and the two subprogs are traced by fentry.
+ */
+static void test_tailcall_bpf2bpf_hierarchy_fentry(void)
+{
+ test_tailcall_hierarchy_count("tailcall_bpf2bpf_hierarchy1.bpf.o",
+ true, false, false);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_fexit checks that the count value of the tail
+ * call limit enforcement matches with expectations when tailcalls are preceded
+ * with two bpf2bpf calls, and the two subprogs are traced by fexit.
+ */
+static void test_tailcall_bpf2bpf_hierarchy_fexit(void)
+{
+ test_tailcall_hierarchy_count("tailcall_bpf2bpf_hierarchy1.bpf.o",
+ false, true, false);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_fentry_fexit checks that the count value of
+ * the tail call limit enforcement matches with expectations when tailcalls are
+ * preceded with two bpf2bpf calls, and the two subprogs are traced by both
+ * fentry and fexit.
+ */
+static void test_tailcall_bpf2bpf_hierarchy_fentry_fexit(void)
+{
+ test_tailcall_hierarchy_count("tailcall_bpf2bpf_hierarchy1.bpf.o",
+ true, true, false);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_fentry_entry checks that the count value of
+ * the tail call limit enforcement matches with expectations when tailcalls are
+ * preceded with two bpf2bpf calls in fentry.
+ */
+static void test_tailcall_bpf2bpf_hierarchy_fentry_entry(void)
+{
+ test_tailcall_hierarchy_count("tc_dummy.bpf.o", false, false, true);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_2 checks that the count value of the tail
+ * call limit enforcement matches with expectations:
+ *
+ * subprog_tail0 --tailcall-> classifier_0 -> subprog_tail0
+ * entry <
+ * subprog_tail1 --tailcall-> classifier_1 -> subprog_tail1
+ */
+static void test_tailcall_bpf2bpf_hierarchy_2(void)
+{
+ RUN_TESTS(tailcall_bpf2bpf_hierarchy2);
+}
+
+/* test_tailcall_bpf2bpf_hierarchy_3 checks that the count value of the tail
+ * call limit enforcement matches with expectations:
+ *
+ * subprog with jmp_table0 to classifier_0
+ * entry --tailcall-> classifier_0 <
+ * subprog with jmp_table1 to classifier_0
+ */
+static void test_tailcall_bpf2bpf_hierarchy_3(void)
+{
+ RUN_TESTS(tailcall_bpf2bpf_hierarchy3);
+}
+
void test_tailcalls(void)
{
if (test__start_subtest("tailcall_1"))
@@ -1223,4 +1531,16 @@ void test_tailcalls(void)
test_tailcall_bpf2bpf_fentry_entry();
if (test__start_subtest("tailcall_poke"))
test_tailcall_poke();
+ if (test__start_subtest("tailcall_bpf2bpf_hierarchy_1"))
+ test_tailcall_bpf2bpf_hierarchy_1();
+ if (test__start_subtest("tailcall_bpf2bpf_hierarchy_fentry"))
+ test_tailcall_bpf2bpf_hierarchy_fentry();
+ if (test__start_subtest("tailcall_bpf2bpf_hierarchy_fexit"))
+ test_tailcall_bpf2bpf_hierarchy_fexit();
+ if (test__start_subtest("tailcall_bpf2bpf_hierarchy_fentry_fexit"))
+ test_tailcall_bpf2bpf_hierarchy_fentry_fexit();
+ if (test__start_subtest("tailcall_bpf2bpf_hierarchy_fentry_entry"))
+ test_tailcall_bpf2bpf_hierarchy_fentry_entry();
+ test_tailcall_bpf2bpf_hierarchy_2();
+ test_tailcall_bpf2bpf_hierarchy_3();
}
diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy1.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy1.c
new file mode 100644
index 0000000000000..327ca395e8601
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy1.c
@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_legacy.h"
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+ __uint(max_entries, 1);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(__u32));
+} jmp_table SEC(".maps");
+
+int count = 0;
+
+static __noinline
+int subprog_tail(struct __sk_buff *skb)
+{
+ bpf_tail_call_static(skb, &jmp_table, 0);
+ return 0;
+}
+
+SEC("tc")
+int entry(struct __sk_buff *skb)
+{
+ int ret = 1;
+
+ count++;
+ subprog_tail(skb);
+ subprog_tail(skb);
+
+ return ret;
+}
+
+char __license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c
new file mode 100644
index 0000000000000..37604b0b97aff
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+int classifier_0(struct __sk_buff *skb);
+int classifier_1(struct __sk_buff *skb);
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+ __uint(max_entries, 2);
+ __uint(key_size, sizeof(__u32));
+ __array(values, void (void));
+} jmp_table SEC(".maps") = {
+ .values = {
+ [0] = (void *) &classifier_0,
+ [1] = (void *) &classifier_1,
+ },
+};
+
+int count0 = 0;
+int count1 = 0;
+
+static __noinline
+int subprog_tail0(struct __sk_buff *skb)
+{
+ bpf_tail_call_static(skb, &jmp_table, 0);
+ return 0;
+}
+
+__auxiliary
+SEC("tc")
+int classifier_0(struct __sk_buff *skb)
+{
+ count0++;
+ subprog_tail0(skb);
+ return 0;
+}
+
+static __noinline
+int subprog_tail1(struct __sk_buff *skb)
+{
+ bpf_tail_call_static(skb, &jmp_table, 1);
+ return 0;
+}
+
+__auxiliary
+SEC("tc")
+int classifier_1(struct __sk_buff *skb)
+{
+ count1++;
+ subprog_tail1(skb);
+ return 0;
+}
+
+__success
+__retval(33)
+SEC("tc")
+int tailcall_bpf2bpf_hierarchy_2(struct __sk_buff *skb)
+{
+ volatile int ret = 0;
+
+ subprog_tail0(skb);
+ subprog_tail1(skb);
+
+ asm volatile (""::"r+"(ret));
+ return (count1 << 16) | count0;
+}
+
+char __license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy3.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy3.c
new file mode 100644
index 0000000000000..0cdbb781fcbc5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy3.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+int classifier_0(struct __sk_buff *skb);
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+ __uint(max_entries, 1);
+ __uint(key_size, sizeof(__u32));
+ __array(values, void (void));
+} jmp_table0 SEC(".maps") = {
+ .values = {
+ [0] = (void *) &classifier_0,
+ },
+};
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+ __uint(max_entries, 1);
+ __uint(key_size, sizeof(__u32));
+ __array(values, void (void));
+} jmp_table1 SEC(".maps") = {
+ .values = {
+ [0] = (void *) &classifier_0,
+ },
+};
+
+int count = 0;
+
+static __noinline
+int subprog_tail(struct __sk_buff *skb, void *jmp_table)
+{
+ bpf_tail_call_static(skb, jmp_table, 0);
+ return 0;
+}
+
+__auxiliary
+SEC("tc")
+int classifier_0(struct __sk_buff *skb)
+{
+ count++;
+ subprog_tail(skb, &jmp_table0);
+ subprog_tail(skb, &jmp_table1);
+ return count;
+}
+
+__success
+__retval(33)
+SEC("tc")
+int tailcall_bpf2bpf_hierarchy_3(struct __sk_buff *skb)
+{
+ volatile int ret = 0;
+
+ bpf_tail_call_static(skb, &jmp_table0, 0);
+
+ asm volatile (""::"r+"(ret));
+ return ret;
+}
+
+char __license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy_fentry.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy_fentry.c
new file mode 100644
index 0000000000000..c87f9ca982d3e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy_fentry.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Leon Hwang */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+ __uint(max_entries, 1);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(__u32));
+} jmp_table SEC(".maps");
+
+int count = 0;
+
+static __noinline
+int subprog_tail(void *ctx)
+{
+ bpf_tail_call_static(ctx, &jmp_table, 0);
+ return 0;
+}
+
+SEC("fentry/dummy")
+int BPF_PROG(fentry, struct sk_buff *skb)
+{
+ count++;
+ subprog_tail(ctx);
+ subprog_tail(ctx);
+
+ return 0;
+}
+
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/tc_dummy.c b/tools/testing/selftests/bpf/progs/tc_dummy.c
new file mode 100644
index 0000000000000..69a3d0dc87879
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tc_dummy.c
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_legacy.h"
+
+SEC("tc")
+int entry(struct __sk_buff *skb)
+{
+ return 1;
+}
+
+char __license[] SEC("license") = "GPL";
--
2.44.0