From: Andrii Nakryiko <andriin@fb.com>
Date: Tue, 7 Jul 2020 18:53:16 -0700
Subject: selftests/bpf: Add test relying only on CO-RE and no recent kernel
 features
Patch-mainline: v5.9-rc1
Git-commit: fcda189a5133b6fe50eb63d1062a15be4df9e3de
References: bsc#1177028

Add a test that relies on CO-RE, but doesn't expect any of the recent
features, not available on old kernels. This is useful for Travis CI tests
running against very old kernels (e.g., libbpf has 4.9 kernel testing now), to
verify that CO-RE still works, even if kernel itself doesn't support BTF yet,
as long as there is .BTF embedded into vmlinux image by pahole. Given most of
CO-RE doesn't require any kernel awareness of BTF, it is a useful test to
validate that libbpf's BTF sanitization is working well even with ancient
kernels.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200708015318.3827358-5-andriin@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/testing/selftests/bpf/prog_tests/core_retro.c |   33 ++++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_core_retro.c |   30 ++++++++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/core_retro.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_core_retro.c

--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/core_retro.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+#define _GNU_SOURCE
+#include <test_progs.h>
+#include "test_core_retro.skel.h"
+
+void test_core_retro(void)
+{
+	int err, zero = 0, res, duration = 0;
+	struct test_core_retro *skel;
+
+	/* load program */
+	skel = test_core_retro__open_and_load();
+	if (CHECK(!skel, "skel_load", "skeleton open/load failed\n"))
+		goto out_close;
+
+	/* attach probe */
+	err = test_core_retro__attach(skel);
+	if (CHECK(err, "attach_kprobe", "err %d\n", err))
+		goto out_close;
+
+	/* trigger */
+	usleep(1);
+
+	err = bpf_map_lookup_elem(bpf_map__fd(skel->maps.results), &zero, &res);
+	if (CHECK(err, "map_lookup", "failed to lookup result: %d\n", errno))
+		goto out_close;
+
+	CHECK(res != getpid(), "pid_check", "got %d != exp %d\n", res, getpid());
+
+out_close:
+	test_core_retro__destroy(skel);
+}
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_core_retro.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+
+struct task_struct {
+	int tgid;
+} __attribute__((preserve_access_index));
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} results SEC(".maps");
+
+SEC("tp/raw_syscalls/sys_enter")
+int handle_sys_enter(void *ctx)
+{
+	struct task_struct *task = (void *)bpf_get_current_task();
+	int tgid = BPF_CORE_READ(task, tgid);
+	int zero = 0;
+
+	bpf_map_update_elem(&results, &zero, &tgid, 0);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";