RE: [PATCH v5 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot

[John Fastabend <john.fastabend@gmail.com>]

Song Liu wrote:
> This test uses bpf_get_branch_snapshot from a fexit program. The test uses
> a target function (bpf_testmod_loop_test) and compares the record against
> kallsyms. If there isn't enough record matching kallsyms, the test fails.
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  19 +++-
>  .../selftests/bpf/prog_tests/core_reloc.c     |  14 +--
>  .../bpf/prog_tests/get_branch_snapshot.c      | 100 ++++++++++++++++++
>  .../selftests/bpf/prog_tests/module_attach.c  |  39 -------
>  .../selftests/bpf/progs/get_branch_snapshot.c |  40 +++++++
>  tools/testing/selftests/bpf/test_progs.c      |  39 +++++++
>  tools/testing/selftests/bpf/test_progs.h      |   2 +
>  tools/testing/selftests/bpf/trace_helpers.c   |  37 +++++++
>  tools/testing/selftests/bpf/trace_helpers.h   |   5 +
>  9 files changed, 243 insertions(+), 52 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
>  create mode 100644 tools/testing/selftests/bpf/progs/get_branch_snapshot.c
> 

[...]

> diff --git a/tools/testing/selftests/bpf/progs/get_branch_snapshot.c b/tools/testing/selftests/bpf/progs/get_branch_snapshot.c
> new file mode 100644
> index 0000000000000..a1b139888048c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/get_branch_snapshot.c
> @@ -0,0 +1,40 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2021 Facebook */
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +__u64 test1_hits = 0;
> +__u64 address_low = 0;
> +__u64 address_high = 0;
> +int wasted_entries = 0;
> +long total_entries = 0;
> +
> +#define ENTRY_CNT 32
> +struct perf_branch_entry entries[ENTRY_CNT] = {};

It looks like perf_branch_entry has never changed, but it could grow?
Then size check in helper would fail. I'm not sure its worth it, but
this could be done with CO-RE so the size is correct even if the
struct grows.

> +
> +static inline bool in_range(__u64 val)
> +{
> +	return (val >= address_low) && (val < address_high);
> +}
> +
> +SEC("fexit/bpf_testmod_loop_test")
> +int BPF_PROG(test1, int n, int ret)
> +{
> +	long i;
> +
> +	total_entries = bpf_get_branch_snapshot(entries, sizeof(entries), 0);
> +	total_entries /= sizeof(struct perf_branch_entry);
> +
> +	for (i = 0; i < ENTRY_CNT; i++) {
> +		if (i >= total_entries)
> +			break;
> +		if (in_range(entries[i].from) && in_range(entries[i].to))
> +			test1_hits++;
> +		else if (!test1_hits)
> +			wasted_entries++;
> +	}
> +	return 0;
> +}

Other than small comment LGTM.

Acked-by: John Fastabend <john.fastabend@gmail.com>