[PATCH v3 2/2] selftests: Add test for overriding global data value before load

["Toke Høiland-Jørgensen" <toke@redhat.com>]

This extends the global_data test to also exercise the new
bpf_map__set_initial_value() function. The test simply overrides the global
data section with all zeroes, and checks that the new value makes it into
the kernel map on load.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 .../selftests/bpf/prog_tests/global_data.c    | 61 +++++++++++++++++++
 1 file changed, 61 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/global_data.c b/tools/testing/selftests/bpf/prog_tests/global_data.c
index c680926fce73..f018ce53a8d1 100644
--- a/tools/testing/selftests/bpf/prog_tests/global_data.c
+++ b/tools/testing/selftests/bpf/prog_tests/global_data.c
@@ -121,6 +121,65 @@ static void test_global_data_rdonly(struct bpf_object *obj, __u32 duration)
 	      "err %d errno %d\n", err, errno);
 }
 
+static void test_global_data_set_rdonly(__u32 duration)
+{
+	const char *file = "./test_global_data.o";
+	int err = -ENOMEM, map_fd, zero = 0;
+	__u8 *buff = NULL, *newval = NULL;
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	struct bpf_map *map;
+	size_t sz;
+
+	obj = bpf_object__open_file(file, NULL);
+	if (CHECK_FAIL(!obj))
+		return;
+	prog = bpf_program__next(NULL, obj);
+	if (CHECK_FAIL(!prog))
+		goto out;
+	err = bpf_program__set_sched_cls(prog);
+	if (CHECK_FAIL(err))
+		goto out;
+
+	map = bpf_object__find_map_by_name(obj, "test_glo.rodata");
+	if (CHECK_FAIL(!map || !bpf_map__is_internal(map)))
+		goto out;
+
+	sz = bpf_map__def(map)->value_size;
+	newval = malloc(sz);
+	if (CHECK_FAIL(!newval))
+		goto out;
+	memset(newval, 0, sz);
+
+	/* wrong size, should fail */
+	err = bpf_map__set_initial_value(map, newval, sz - 1);
+	if (CHECK(!err, "reject set initial value wrong size", "err %d\n", err))
+		goto out;
+
+	err = bpf_map__set_initial_value(map, newval, sz);
+	if (CHECK_FAIL(err))
+		goto out;
+
+	err = bpf_object__load(obj);
+	if (CHECK_FAIL(err))
+		goto out;
+
+	map_fd = bpf_map__fd(map);
+	if (CHECK_FAIL(map_fd < 0))
+		goto out;
+
+	buff = malloc(sz);
+	if (buff)
+		err = bpf_map_lookup_elem(map_fd, &zero, buff);
+	CHECK(!buff || err || memcmp(buff, newval, sz),
+	      "compare .rodata map data override",
+	      "err %d errno %d\n", err, errno);
+out:
+	free(buff);
+	free(newval);
+	bpf_object__close(obj);
+}
+
 void test_global_data(void)
 {
 	const char *file = "./test_global_data.o";
@@ -144,4 +203,6 @@ void test_global_data(void)
 	test_global_data_rdonly(obj, duration);
 
 	bpf_object__close(obj);
+
+	test_global_data_set_rdonly(duration);
 }
-- 
2.26.0