Re: [PATCH bpf-next 12/16] selftests/bpf: add selftest for multi-prog sections and bpf-to-bpf calls

Add a selftest excercising bpf-to-bpf subprogram calls, as well as multiple
entry-point BPF programs per section. Also make sure that BPF CO-RE works for
such set ups both for sub-programs and for multi-entry sections.

Signed-off-by: Andrii Nakryiko <redacted>
---
 .../selftests/bpf/prog_tests/subprogs.c       | 31 +++++++
 .../selftests/bpf/progs/test_subprogs.c       | 92 +++++++++++++++++++
 2 files changed, 123 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs.c

diff --git a/tools/testing/selftests/bpf/prog_tests/subprogs.c b/tools/testing/selftests/bpf/prog_tests/subprogs.c
new file mode 100644
index 000000000000..a00abf58c037
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/subprogs.c

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+#include <test_progs.h>
+#include <time.h>
+#include "test_subprogs.skel.h"
+
+static int duration;
+
+void test_subprogs(void)
+{
+       struct test_subprogs *skel;
+       int err;
+
+       skel = test_subprogs__open_and_load();
+       if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+               return;
+
+       err = test_subprogs__attach(skel);
+       if (CHECK(err, "skel_attach", "failed to attach skeleton: %d\n", err))
+               goto cleanup;
+
+       usleep(1);
+
+       CHECK(skel->bss->res1 != 12, "res1", "got %d, exp %d\n", skel->bss->res1, 12);
+       CHECK(skel->bss->res2 != 17, "res2", "got %d, exp %d\n", skel->bss->res2, 17);
+       CHECK(skel->bss->res3 != 19, "res3", "got %d, exp %d\n", skel->bss->res3, 19);
+       CHECK(skel->bss->res4 != 36, "res4", "got %d, exp %d\n", skel->bss->res4, 36);
+