selftests/bpf: Ensure libbpf skip all-zeros fields of struct_ops maps.

A new version of a type may have additional fields that do not exist in
older versions. Previously, libbpf would reject struct_ops maps with a new
version containing extra fields when running on a machine with an old
kernel. However, we have updated libbpf to ignore these fields if their
values are all zeros or null in order to provide backward compatibility.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240313214139.685112-3-thinker.li@gmail.com

1 files changed, 15 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/progs/struct_ops_module.c b/tools/testing/selftests/bpf/progs/struct_ops_module.c
index 026cabfa7f1f..86e1e50c5531 100644
--- a/tools/testing/selftests/bpf/progs/struct_ops_module.c
+++ b/tools/testing/selftests/bpf/progs/struct_ops_module.c
@@ -23,7 +23,7 @@ void BPF_PROG(test_2, int a, int b)
 	test_2_result = a + b;
 }
 
-SEC("struct_ops/test_3")
+SEC("?struct_ops/test_3")
 int BPF_PROG(test_3, int a, int b)
 {
 	test_2_result = a + b + 3;
@@ -54,3 +54,17 @@ struct bpf_testmod_ops___v2 testmod_2 = {
 	.test_1 = (void *)test_1,
 	.test_2 = (void *)test_2_v2,
 };
+
+struct bpf_testmod_ops___zeroed {
+	int (*test_1)(void);
+	void (*test_2)(int a, int b);
+	int (*test_maybe_null)(int dummy, struct task_struct *task);
+	void (*zeroed_op)(int a, int b);
+	int zeroed;
+};
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops___zeroed testmod_zeroed = {
+	.test_1 = (void *)test_1,
+	.test_2 = (void *)test_2_v2,
+};