samples/bpf: move common-purpose trace functions to selftests

There is no functionality change in this patch. The common-purpose
trace functions, including perf_event polling and ksym lookup,
are moved from trace_output_user.c and bpf_load.c to
selftests/bpf/trace_helpers.c so that these function can
be reused later in selftests.

Acked-by: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/tools/testing/selftests/bpf/trace_helpers.h b/tools/testing/selftests/bpf/trace_helpers.h
new file mode 100644
index 0000000..fe3eefd
--- /dev/null
+++ b/tools/testing/selftests/bpf/trace_helpers.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __TRACE_HELPER_H
+#define __TRACE_HELPER_H
+
+struct ksym {
+	long addr;
+	char *name;
+};
+
+int load_kallsyms(void);
+struct ksym *ksym_search(long key);
+
+typedef int (*perf_event_print_fn)(void *data, int size);
+
+/* return code for perf_event_print_fn */
+#define PERF_EVENT_DONE		0
+#define PERF_EVENT_ERROR	-1
+#define PERF_EVENT_CONT		-2
+
+int perf_event_mmap(int fd);
+/* return PERF_EVENT_DONE or PERF_EVENT_ERROR */
+int perf_event_poller(int fd, perf_event_print_fn output_fn);
+#endif