selftests/bpf: Add bpf_read_branch_records() selftest

Add a selftest to test:

* default bpf_read_branch_records() behavior
* BPF_F_GET_BRANCH_RECORDS_SIZE flag behavior
* error path on non branch record perf events
* using helper to write to stack
* using helper to write to global

On host with hardware counter support:

    # ./test_progs -t perf_branches
    #27/1 perf_branches_hw:OK
    #27/2 perf_branches_no_hw:OK
    #27 perf_branches:OK
    Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED

On host without hardware counter support (VM):

    # ./test_progs -t perf_branches
    #27/1 perf_branches_hw:OK
    #27/2 perf_branches_no_hw:OK
    #27 perf_branches:OK
    Summary: 1/2 PASSED, 1 SKIPPED, 0 FAILED

Also sync tools/include/uapi/linux/bpf.h.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200218030432.4600-3-dxu@dxuuu.xyz

1 files changed, 50 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_perf_branches.c b/tools/testing/selftests/bpf/progs/test_perf_branches.c
new file mode 100644
index 000000000000..0f7e27d97567
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_perf_branches.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+
+#include <stddef.h>
+#include <linux/ptrace.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_trace_helpers.h"
+
+int valid = 0;
+int required_size_out = 0;
+int written_stack_out = 0;
+int written_global_out = 0;
+
+struct {
+	__u64 _a;
+	__u64 _b;
+	__u64 _c;
+} fpbe[30] = {0};
+
+SEC("perf_event")
+int perf_branches(void *ctx)
+{
+	__u64 entries[4 * 3] = {0};
+	int required_size, written_stack, written_global;
+
+	/* write to stack */
+	written_stack = bpf_read_branch_records(ctx, entries, sizeof(entries), 0);
+	/* ignore spurious events */
+	if (!written_stack)
+		return 1;
+
+	/* get required size */
+	required_size = bpf_read_branch_records(ctx, NULL, 0,
+						BPF_F_GET_BRANCH_RECORDS_SIZE);
+
+	written_global = bpf_read_branch_records(ctx, fpbe, sizeof(fpbe), 0);
+	/* ignore spurious events */
+	if (!written_global)
+		return 1;
+
+	required_size_out = required_size;
+	written_stack_out = written_stack;
+	written_global_out = written_global;
+	valid = 1;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";