[PATCH 2/2] selftests/bpf: Add test for bpf_rdtsc

[Tero Kristo <tero.kristo@linux.intel.com>]

Add selftest for bpf_rdtsc() which reads the TSC (Time Stamp Counter) on
x86_64 architectures. The test reads the TSC from both userspace and the
BPF program, and verifies the TSC values are in incremental order as
expected. The test is automatically skipped on architectures that do not
support the feature.

Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
---
 .../selftests/bpf/prog_tests/test_rdtsc.c     | 67 +++++++++++++++++++
 .../testing/selftests/bpf/progs/test_rdtsc.c  | 21 ++++++
 2 files changed, 88 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_rdtsc.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_rdtsc.c

diff --git a/tools/testing/selftests/bpf/prog_tests/test_rdtsc.c b/tools/testing/selftests/bpf/prog_tests/test_rdtsc.c
new file mode 100644
index 000000000000..2b26deb5b35a
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/test_rdtsc.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2023 Intel Corporation */
+
+#include "test_progs.h"
+#include "test_rdtsc.skel.h"
+
+#ifdef __x86_64__
+
+static inline u64 _rdtsc(void)
+{
+	u32 low, high;
+
+	__asm__ __volatile__("rdtscp" : "=a" (low), "=d" (high));
+	return ((u64)high << 32) | low;
+}
+
+static int rdtsc(struct test_rdtsc *skel)
+{
+	int err, prog_fd;
+	u64 user_c1, user_c2;
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+
+	err = test_rdtsc__attach(skel);
+	if (!ASSERT_OK(err, "test_rdtsc_attach"))
+		return err;
+
+	user_c1 = _rdtsc();
+
+	prog_fd = bpf_program__fd(skel->progs.test1);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+
+	user_c2 = _rdtsc();
+
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(topts.retval, 0, "test_run");
+
+	test_rdtsc__detach(skel);
+
+	ASSERT_GE(skel->bss->c1, user_c1, "bpf c1 > user c1");
+	ASSERT_GE(user_c2, skel->bss->c2, "user c2 > bpf c2");
+	ASSERT_GE(skel->bss->c2, user_c1, "bpf c2 > bpf c1");
+	ASSERT_GE(user_c2, user_c1, "user c2 > user c1");
+
+	return 0;
+}
+#endif
+
+void test_rdtsc(void)
+{
+#ifdef __x86_64__
+	struct test_rdtsc *skel;
+	int err;
+
+	skel = test_rdtsc__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_rdtsc_skel_load"))
+		goto cleanup;
+	err = rdtsc(skel);
+	ASSERT_OK(err, "rdtsc");
+
+cleanup:
+	test_rdtsc__destroy(skel);
+#else
+	printf("%s:SKIP:bpf_rdtsc() kfunc not supported\n", __func__);
+	test__skip();
+#endif
+}
diff --git a/tools/testing/selftests/bpf/progs/test_rdtsc.c b/tools/testing/selftests/bpf/progs/test_rdtsc.c
new file mode 100644
index 000000000000..14776b83bd3e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_rdtsc.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2023 Intel Corporation */
+#include <linux/bpf.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+__u64 c1;
+__u64 c2;
+
+extern __u64 bpf_rdtsc(void) __ksym;
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG2(test1, int, a)
+{
+	c1 = bpf_rdtsc();
+	c2 = bpf_rdtsc();
+
+	return 0;
+}
-- 
2.25.1