Re: [PATCHv2 bpf-next 0/8] bpf: Add kprobe multi link

[Andrii Nakryiko]

On Tue, Feb 22, 2022 at 9:06 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> hi,
> this patchset adds new link type BPF_TRACE_KPROBE_MULTI that attaches
> kprobe program through fprobe API [1] instroduced by Masami.
>
> The fprobe API allows to attach probe on multiple functions at once very
> fast, because it works on top of ftrace. On the other hand this limits
> the probe point to the function entry or return.
>
>
> With bpftrace support I see following attach speed:
>
>   # perf stat --null -r 5 ./src/bpftrace -e 'kprobe:x* { } i:ms:1 { exit(); } '
>   Attaching 2 probes...
>   Attaching 3342 functions
>   ...
>
>   1.4960 +- 0.0285 seconds time elapsed  ( +-  1.91% )
>
>
> v2 changes:
>   - based on latest fprobe changes [1]
>   - renaming the uapi interface to kprobe multi
>   - adding support for sort_r to pass user pointer for swap functions
>     and using that in cookie support to keep just single functions array
>   - moving new link to kernel/trace/bpf_trace.c file
>   - using single fprobe callback function for entry and exit
>   - using kvzalloc, libbpf_ensure_mem functions
>   - adding new k[ret]probe.multi sections instead of using current kprobe
>   - used glob_match from test_progs.c, added '?' matching
>   - move bpf_get_func_ip verifier inline change to seprate change
>   - couple of other minor fixes
>
>

I think it's shaping up pretty well. Great work, Jiri! Can't wait to
adopt this in retsnoop. See below about dependency on Masami's
patches.

> Also available at:
>   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   bpf/kprobe_multi
>
> thanks,
> jirka
>
>
> [1] https://lore.kernel.org/bpf/164458044634.586276.3261555265565111183.stgit@devnote2/

Masami, Jiri, Steven, what would be the logistics here? What's the
plan for getting this upstream? Any idea about timelines? I really
hope it won't take as long as it took for kretprobe stack trace
capturing fixes last year to land. Can we take Masami's changes
through bpf-next tree? If yes, Steven, can you please review and give
your acks? Thanks for understanding!

> ---
> Jiri Olsa (10):
>       lib/sort: Add priv pointer to swap function
>       bpf: Add multi kprobe link
>       bpf: Add bpf_get_func_ip kprobe helper for multi kprobe link
>       bpf: Add support to inline bpf_get_func_ip helper on x86
>       bpf: Add cookie support to programs attached with kprobe multi link
>       libbpf: Add libbpf_kallsyms_parse function
>       libbpf: Add bpf_link_create support for multi kprobes
>       libbpf: Add bpf_program__attach_kprobe_opts support for multi kprobes
>       selftest/bpf: Add kprobe_multi attach test
>       selftest/bpf: Add kprobe_multi test for bpf_cookie values
>
>  include/linux/bpf_types.h                                   |   1 +
>  include/linux/sort.h                                        |   4 +-
>  include/linux/trace_events.h                                |   6 ++
>  include/linux/types.h                                       |   1 +
>  include/uapi/linux/bpf.h                                    |  14 ++++
>  kernel/bpf/syscall.c                                        |  26 ++++++--
>  kernel/bpf/verifier.c                                       |  21 +++++-
>  kernel/trace/bpf_trace.c                                    | 331 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  lib/sort.c                                                  |  42 +++++++++---
>  tools/include/uapi/linux/bpf.h                              |  14 ++++
>  tools/lib/bpf/bpf.c                                         |   7 ++
>  tools/lib/bpf/bpf.h                                         |   9 ++-
>  tools/lib/bpf/libbpf.c                                      | 192 +++++++++++++++++++++++++++++++++++++++++++++--------
>  tools/lib/bpf/libbpf_internal.h                             |   5 ++
>  tools/testing/selftests/bpf/prog_tests/bpf_cookie.c         |  72 ++++++++++++++++++++
>  tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c  | 115 ++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/kprobe_multi.c            |  58 ++++++++++++++++
>  tools/testing/selftests/bpf/progs/kprobe_multi_bpf_cookie.c |  62 +++++++++++++++++
>  18 files changed, 930 insertions(+), 50 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
>  create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi.c
>  create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_bpf_cookie.c