1 files changed, 65 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/prog_tests/legacy_printk.c b/tools/testing/selftests/bpf/prog_tests/legacy_printk.c
new file mode 100644
index 000000000000..ec6e45f2a644
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/legacy_printk.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include "test_legacy_printk.skel.h"
+
+static int execute_one_variant(bool legacy)
+{
+	struct test_legacy_printk *skel;
+	int err, zero = 0, my_pid = getpid(), res, map_fd;
+
+	skel = test_legacy_printk__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return -errno;
+
+	bpf_program__set_autoload(skel->progs.handle_legacy, legacy);
+	bpf_program__set_autoload(skel->progs.handle_modern, !legacy);
+
+	err = test_legacy_printk__load(skel);
+	/* no ASSERT_OK, we expect one of two variants can fail here */
+	if (err)
+		goto err_out;
+
+	if (legacy) {
+		map_fd = bpf_map__fd(skel->maps.my_pid_map);
+		err = bpf_map_update_elem(map_fd, &zero, &my_pid, BPF_ANY);
+		if (!ASSERT_OK(err, "my_pid_map_update"))
+			goto err_out;
+		err = bpf_map_lookup_elem(map_fd, &zero, &res);
+	} else {
+		skel->bss->my_pid_var = my_pid;
+	}
+
+	err = test_legacy_printk__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto err_out;
+
+	usleep(1); /* trigger */
+
+	if (legacy) {
+		map_fd = bpf_map__fd(skel->maps.res_map);
+		err = bpf_map_lookup_elem(map_fd, &zero, &res);
+		if (!ASSERT_OK(err, "res_map_lookup"))
+			goto err_out;
+	} else {
+		res = skel->bss->res_var;
+	}
+
+	if (!ASSERT_GT(res, 0, "res")) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+err_out:
+	test_legacy_printk__destroy(skel);
+	return err;
+}
+
+void test_legacy_printk(void)
+{
+	/* legacy variant should work everywhere */
+	ASSERT_OK(execute_one_variant(true /* legacy */), "legacy_case");
+
+	/* execute modern variant, can fail the load on old kernels */
+	execute_one_variant(false);
+}