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/progs/test_prog_array_init.c

@@ -0,0 +1,39 @@
+/* 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;
+}