selftests/bpf: Test BPF_MAP_TYPE_PROG_ARRAY static initialization

Add testcase for BPF_MAP_TYPE_PROG_ARRAY static initialization.
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211128141633.502339-3-hengqi.chen@gmail.com

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

+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2021 Hengqi Chen */
+
+#include <test_progs.h>
+#include "test_prog_array_init.skel.h"
+
+void test_prog_array_init(void)
+{
+	struct test_prog_array_init *skel;
+	int err;
+
+	skel = test_prog_array_init__open();
+	if (!ASSERT_OK_PTR(skel, "could not open BPF object"))
+		return;
+
+	skel->rodata->my_pid = getpid();
+
+	err = test_prog_array_init__load(skel);
+	if (!ASSERT_OK(err, "could not load BPF object"))
+		goto cleanup;
+
+	skel->links.entry = bpf_program__attach_raw_tracepoint(skel->progs.entry, "sys_enter");
+	if (!ASSERT_OK_PTR(skel->links.entry, "could not attach BPF program"))
+		goto cleanup;
+
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->value, 42, "unexpected value");
+
+cleanup:
+	test_prog_array_init__destroy(skel);
+}

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

+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2021 Hengqi Chen */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+const volatile pid_t my_pid = 0;
+int value = 0;
+
+SEC("raw_tp/sys_enter")
+int tailcall_1(void *ctx)
+{
+	value = 42;
+	return 0;
+}
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 2);
+	__uint(key_size, sizeof(__u32));
+	__array(values, int (void *));
+} prog_array_init SEC(".maps") = {
+	.values = {
+		[1] = (void *)&tailcall_1,
+	},
+};
+
+SEC("raw_tp/sys_enter")
+int entry(void *ctx)
+{
+	pid_t pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid != my_pid)
+		return 0;
+
+	bpf_tail_call(ctx, &prog_array_init, 1);
+	return 0;
+}