On Thu, Sep 2, 2021 at 9:58 AM Song Liu <songliubraving@xxxxxx> wrote:
>
> Introduce bpf_get_branch_snapshot(), which allows tracing pogram to get
> branch trace from hardware (e.g. Intel LBR). To use the feature, the
> user need to create perf_event with proper branch_record filtering
> on each cpu, and then calls bpf_get_branch_snapshot in the bpf function.
> On Intel CPUs, VLBR event (raw event 0x1b00) can be use for this.
>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> ---
> include/uapi/linux/bpf.h | 22 ++++++++++++++++++++++
> kernel/bpf/trampoline.c | 3 ++-
> kernel/trace/bpf_trace.c | 33 +++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 22 ++++++++++++++++++++++
> 4 files changed, 79 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 791f31dd0abee..c986e6fad5bc0 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -4877,6 +4877,27 @@ union bpf_attr {
> * Get the struct pt_regs associated with **task**.
> * Return
> * A pointer to struct pt_regs.
> + *
> + * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
> + * Description
> + * Get branch trace from hardware engines like Intel LBR. The
> + * branch trace is taken soon after the trigger point of the
> + * BPF program, so it may contain some entries after the
This part is a leftover from previous design, so not relevant anymore?
> + * trigger point. The user need to filter these entries
> + * accordingly.
> + *
> + * The data is stored as struct perf_branch_entry into output
> + * buffer *entries*. *size* is the size of *entries* in bytes.
> + * *flags* is reserved for now and must be zero.
> + *
> + * Return
> + * On success, number of bytes written to *buf*. On error, a
> + * negative value.
> + *
> + * **-EINVAL** if arguments invalid or **size** not a multiple
> + * of **sizeof**\ (**struct perf_branch_entry**\ ).
> + *
> + * **-ENOENT** if architecture does not support branch records.
[...]
