selftests/bpf: add testcases for fsession

Add testcases for BPF_TRACE_FSESSION. The function arguments and return
value are tested both in the entry and exit. And the kfunc
bpf_session_is_ret() is also tested.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Link: https://lore.kernel.org/r/20260124062008.8657-11-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 ChinaTelecom */
+#include <test_progs.h>
+#include "fsession_test.skel.h"
+
+static int check_result(struct fsession_test *skel)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	int err, prog_fd;
+
+	/* Trigger test function calls */
+	prog_fd = bpf_program__fd(skel->progs.test1);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	if (!ASSERT_OK(err, "test_run_opts err"))
+		return err;
+	if (!ASSERT_OK(topts.retval, "test_run_opts retval"))
+		return topts.retval;
+
+	for (int i = 0; i < sizeof(*skel->bss) / sizeof(__u64); i++) {
+		if (!ASSERT_EQ(((__u64 *)skel->bss)[i], 1, "test_result"))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void test_fsession_basic(void)
+{
+	struct fsession_test *skel = NULL;
+	int err;
+
+	skel = fsession_test__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "fsession_test__open_and_load"))
+		goto cleanup;
+
+	err = fsession_test__attach(skel);
+	if (!ASSERT_OK(err, "fsession_attach"))
+		goto cleanup;
+
+	check_result(skel);
+cleanup:
+	fsession_test__destroy(skel);
+}
+
+static void test_fsession_reattach(void)
+{
+	struct fsession_test *skel = NULL;
+	int err;
+
+	skel = fsession_test__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "fsession_test__open_and_load"))
+		goto cleanup;
+
+	/* first attach */
+	err = fsession_test__attach(skel);
+	if (!ASSERT_OK(err, "fsession_first_attach"))
+		goto cleanup;
+
+	if (check_result(skel))
+		goto cleanup;
+
+	/* detach */
+	fsession_test__detach(skel);
+
+	/* reset counters */
+	memset(skel->bss, 0, sizeof(*skel->bss));
+
+	/* second attach */
+	err = fsession_test__attach(skel);
+	if (!ASSERT_OK(err, "fsession_second_attach"))
+		goto cleanup;
+
+	if (check_result(skel))
+		goto cleanup;
+
+cleanup:
+	fsession_test__destroy(skel);
+}
+
+void test_fsession_test(void)
+{
+#if !defined(__x86_64__)
+	test__skip();
+	return;
+#endif
+	if (test__start_subtest("fsession_test"))
+		test_fsession_basic();
+	if (test__start_subtest("fsession_reattach"))
+		test_fsession_reattach();
+}

tools/testing/selftests/bpf/progs/fsession_test.c

@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 ChinaTelecom */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u64 test1_entry_result = 0;
+__u64 test1_exit_result = 0;
+
+SEC("fsession/bpf_fentry_test1")
+int BPF_PROG(test1, int a, int ret)
+{
+	bool is_exit = bpf_session_is_return(ctx);
+
+	if (!is_exit) {
+		test1_entry_result = a == 1 && ret == 0;
+		return 0;
+	}
+
+	test1_exit_result = a == 1 && ret == 2;
+	return 0;
+}
+
+__u64 test2_entry_result = 0;
+__u64 test2_exit_result = 0;
+
+SEC("fsession/bpf_fentry_test3")
+int BPF_PROG(test2, char a, int b, __u64 c, int ret)
+{
+	bool is_exit = bpf_session_is_return(ctx);
+
+	if (!is_exit) {
+		test2_entry_result = a == 4 && b == 5 && c == 6 && ret == 0;
+		return 0;
+	}
+
+	test2_exit_result = a == 4 && b == 5 && c == 6 && ret == 15;
+	return 0;
+}
+
+__u64 test3_entry_result = 0;
+__u64 test3_exit_result = 0;
+
+SEC("fsession/bpf_fentry_test4")
+int BPF_PROG(test3, void *a, char b, int c, __u64 d, int ret)
+{
+	bool is_exit = bpf_session_is_return(ctx);
+
+	if (!is_exit) {
+		test3_entry_result = a == (void *)7 && b == 8 && c == 9 && d == 10 && ret == 0;
+		return 0;
+	}
+
+	test3_exit_result = a == (void *)7 && b == 8 && c == 9 && d == 10 && ret == 34;
+	return 0;
+}
+
+__u64 test4_entry_result = 0;
+__u64 test4_exit_result = 0;
+
+SEC("fsession/bpf_fentry_test5")
+int BPF_PROG(test4, __u64 a, void *b, short c, int d, __u64 e, int ret)
+{
+	bool is_exit = bpf_session_is_return(ctx);
+
+	if (!is_exit) {
+		test4_entry_result = a == 11 && b == (void *)12 && c == 13 && d == 14 &&
+			e == 15 && ret == 0;
+		return 0;
+	}
+
+	test4_exit_result = a == 11 && b == (void *)12 && c == 13 && d == 14 &&
+		e == 15 && ret == 65;
+	return 0;
+}
+
+__u64 test5_entry_result = 0;
+__u64 test5_exit_result = 0;
+
+SEC("fsession/bpf_fentry_test7")
+int BPF_PROG(test5, struct bpf_fentry_test_t *arg, int ret)
+{
+	bool is_exit = bpf_session_is_return(ctx);
+
+	if (!is_exit) {
+		if (!arg)
+			test5_entry_result = ret == 0;
+		return 0;
+	}
+
+	if (!arg)
+		test5_exit_result = 1;
+	return 0;
+}
+