hi,
adding support to attach kprobe program through kprobe_multi link
in a session mode, which means:
- program is attached to both function entry and return
- entry program can decided if the return program gets executed
- entry program can share u64 cookie value with return program
The initial RFC for this was posted in [0] and later discussed more
and which ended up with the session idea [1]
Having entry together with return probe for given function is common
use case for tetragon, bpftrace and most likely for others.
At the moment if we want both entry and return probe to execute bpf
program we need to create two (entry and return probe) links. The link
for return probe creates extra entry probe to setup the return probe.
The extra entry probe execution could be omitted if we had a way to
use just single link for both entry and exit probe.
In addition the possibility to control the return program execution
and sharing data within entry and return probe allows for other use
cases.
Changes from last RFC version [1]:
- changed wrapper name to session
- changed flag to adding new attach type for session:
BPF_TRACE_KPROBE_MULTI_SESSION
it's more convenient wrt filtering on kfuncs setup and seems
to make more sense alltogether
- renamed bpf_kprobe_multi_is_return to bpf_session_is_return
- added bpf_session_cookie kfunc, which actually already works
on current fprobe implementation (not just fprobe-on-fgraph)
and it provides the shared data between entry/return probes [Andrii]
we could actually make the cookie size configurable.. thoughts?
(it's 8 bytes atm)
- better attach setup conditions changes [Andrii]
- I'm not including uprobes change atm, because it needs extra
uprobe change so I'll post it separately
Also available at:
https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
bpf/session_data
thanks,
jirka
[0] https://lore.kernel.org/bpf/20240207153550.856536-1-jolsa@xxxxxxxxxx/
[1] https://lore.kernel.org/bpf/20240228090242.4040210-1-jolsa@xxxxxxxxxx/
---
Jiri Olsa (7):
bpf: Add support for kprobe multi session attach
bpf: Add support for kprobe multi session context
bpf: Add support for kprobe multi session cookie
libbpf: Add support for kprobe multi session attach
libbpf: Add kprobe session attach type name to attach_type_name
selftests/bpf: Add kprobe multi session test
selftests/bpf: Add kprobe multi wrapper cookie test
include/uapi/linux/bpf.h | 1 +
kernel/bpf/btf.c | 3 +++
kernel/bpf/syscall.c | 7 +++++-
kernel/bpf/verifier.c | 7 ++++++
kernel/trace/bpf_trace.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------------
tools/include/uapi/linux/bpf.h | 1 +
tools/lib/bpf/bpf.c | 1 +
tools/lib/bpf/libbpf.c | 41 ++++++++++++++++++++++++++++++++--
tools/lib/bpf/libbpf.h | 4 +++-
tools/testing/selftests/bpf/bpf_kfuncs.h | 3 +++
tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
tools/testing/selftests/bpf/progs/kprobe_multi_session.c | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++
13 files changed, 396 insertions(+), 18 deletions(-)
create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_session.c
create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_session_cookie.c
