selftests/bpf: Add union argument tests using fexit programs

Add test coverage for union argument support using fexit programs:

* 8B union argument - verify that the verifier accepts it and that fexit
  programs can trace such functions.
* 16B union argument - verify that the verifier accepts it and that
  fexit programs can access the argument, which is passed using two
  registers.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20250919044110.23729-3-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/tracing_struct.c b/tools/testing/selftests/bpf/progs/tracing_struct.c
index c435a3a8328a..d460732e2023 100644
--- a/tools/testing/selftests/bpf/progs/tracing_struct.c
+++ b/tools/testing/selftests/bpf/progs/tracing_struct.c
@@ -18,6 +18,18 @@ struct bpf_testmod_struct_arg_3 {
 	int b[];
 };
 
+union bpf_testmod_union_arg_1 {
+	char a;
+	short b;
+	struct bpf_testmod_struct_arg_1 arg;
+};
+
+union bpf_testmod_union_arg_2 {
+	int a;
+	long b;
+	struct bpf_testmod_struct_arg_2 arg;
+};
+
 long t1_a_a, t1_a_b, t1_b, t1_c, t1_ret, t1_nregs;
 __u64 t1_reg0, t1_reg1, t1_reg2, t1_reg3;
 long t2_a, t2_b_a, t2_b_b, t2_c, t2_ret;
@@ -26,6 +38,9 @@ long t4_a_a, t4_b, t4_c, t4_d, t4_e_a, t4_e_b, t4_ret;
 long t5_ret;
 int t6;
 
+long ut1_a_a, ut1_b, ut1_c;
+long ut2_a, ut2_b_a, ut2_b_b;
+
 SEC("fentry/bpf_testmod_test_struct_arg_1")
 int BPF_PROG2(test_struct_arg_1, struct bpf_testmod_struct_arg_2, a, int, b, int, c)
 {
@@ -130,4 +145,22 @@ int BPF_PROG2(test_struct_arg_11, struct bpf_testmod_struct_arg_3 *, a)
 	return 0;
 }
 
+SEC("fexit/bpf_testmod_test_union_arg_1")
+int BPF_PROG2(test_union_arg_1, union bpf_testmod_union_arg_1, a, int, b, int, c)
+{
+	ut1_a_a = a.arg.a;
+	ut1_b = b;
+	ut1_c = c;
+	return 0;
+}
+
+SEC("fexit/bpf_testmod_test_union_arg_2")
+int BPF_PROG2(test_union_arg_2, int, a, union bpf_testmod_union_arg_2, b)
+{
+	ut2_a = a;
+	ut2_b_a = b.arg.a;
+	ut2_b_b = b.arg.b;
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";