[RFC,bpf-next,0/2] libbpf: Add support for dynamic tracepoint

Message

Yafang Shao Jan. 5, 2025, 12:44 p.m. UTC

Dynamic tracepoints can be created using tools like perf-probe, debugfs, or
similar. For example:

- perf probe
  $ perf probe -a 'tcp_listendrop sk'
  $ ls /sys/kernel/debug/tracing/events/probe/tcp_listendrop/
  enable  filter  format  hist  id  trigger

- debugfs
  $ echo 'p:myprobe kernel_clone' >> /sys/kernel/debug/tracing/kprobe_events
  $ ls /sys/kernel/debug/tracing/events/kprobes/myprobe/
  enable  filter  format  hist  id  trigger

While these dynamic tracepoints are functional, they cannot be easily
attached to BPF programs. For instance, attempting to use them with
bpftrace results in the following error:

  $ bpftrace -e 'tracepoint:probe:tcp_listendrop {print(comm)}'
  Attaching 1 probe...
  ioctl(PERF_EVENT_IOC_SET_BPF): Invalid argument
  ERROR: Error attaching probe: tracepoint:probe:tcp_listendrop

The issue lies in how these dynamic tracepoints are implemented: despite
being exposed as tracepoints, they remain kprobe events internally. As a
result, loading them as a tracepoint program fails. Instead, they must be
loaded as kprobe programs but attached as tracepoints.

This patchset addresses the limitation, enabling seamless attachment of
such tracepoints with BPF. It simplifies tracing inlined kernel functions
using BPF.
 
Yafang Shao (2):
  libbpf: Add support for dynamic tracepoint
  selftests/bpf: Add selftest for dynamic tracepoint

 tools/lib/bpf/libbpf.c                        |  3 +
 .../bpf/prog_tests/test_dynamic_tp.c          | 64 +++++++++++++++++++
 .../testing/selftests/bpf/progs/dynamic_tp.c  | 27 ++++++++
 3 files changed, 94 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_dynamic_tp.c
 create mode 100644 tools/testing/selftests/bpf/progs/dynamic_tp.c