Message-ID: <20251217095445.218428-1-dongml2@chinatelecom.cn>
Date: Wed, 17 Dec 2025 17:54:36 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
	andrii@...nel.org
Cc: davem@...emloft.net,
	dsahern@...nel.org,
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Subject: [PATCH bpf-next v4 0/9] bpf: tracing session supporting

Hi, all.

In this version, I combined Alexei and Andrii's advice, which makes the
architecture specific code much simpler.

Sometimes, we need to hook both the entry and exit of a function with
TRACING. Therefore, we need define a FENTRY and a FEXIT for the target
function, which is not convenient.

Therefore, we add a tracing session support for TRACING. Generally
speaking, it's similar to kprobe session, which can hook both the entry
and exit of a function with a single BPF program. Session cookie is also
supported with the kfunc bpf_fsession_cookie(). In order to limit the
stack usage, we limit the maximum number of cookies to 4.

The kfunc bpf_fsession_is_return() and bpf_fsession_cookie() are both
inlined in the verifier.

We allow the usage of bpf_get_func_ret() to get the return value in the
fentry of the tracing session, as it will always get "0", which is safe
enough and is OK. Maybe we can prohibit the usage of bpf_get_func_ret()
in the fentry in verifier, which can make the architecture specific code
simpler.

The fsession stuff is arch related, so the -EOPNOTSUPP will be returned if
it is not supported yet by the arch. In this series, we only support
x86_64. And later, other arch will be implemented.

Changes since v3:
* instead of adding a new hlist to progs_hlist in trampoline, add the bpf
  program to both the fentry hlist and the fexit hlist.
* introduce the 2nd patch to reuse the nr_args field in the stack to
  store all the information we need(except the session cookies).
* limit the maximum number of cookies to 4.
* remove the logic to skip fexit if the fentry return non-zero.

Changes since v2:
* squeeze some patches:
  - the 2 patches for the kfunc bpf_tracing_is_exit() and
    bpf_fsession_cookie() are merged into the second patch.
  - the testcases for fsession are also squeezed.

* fix the CI error by move the testcase for bpf_get_func_ip to
  fsession_test.c

Changes since v1:
* session cookie support.
  In this version, session cookie is implemented, and the kfunc
  bpf_fsession_cookie() is added.

* restructure the layout of the stack.
  In this version, the session stuff that stored in the stack is changed,
  and we locate them after the return value to not break
  bpf_get_func_ip().

* testcase enhancement.
  Some nits in the testcase that suggested by Jiri is fixed. Meanwhile,
  the testcase for get_func_ip and session cookie is added too.

Menglong Dong (9):
  bpf: add tracing session support
  bpf: use last 8-bits for the nr_args in trampoline
  bpf: add the kfunc bpf_fsession_is_return
  bpf: add the kfunc bpf_fsession_cookie
  bpf,x86: introduce emit_st_r0_imm64() for trampoline
  bpf,x86: add tracing session supporting for x86_64
  libbpf: add support for tracing session
  selftests/bpf: add testcases for tracing session
  selftests/bpf: test fsession mixed with fentry and fexit

 arch/x86/net/bpf_jit_comp.c                   |  47 +++-
 include/linux/bpf.h                           |  39 +++
 include/uapi/linux/bpf.h                      |   1 +
 kernel/bpf/btf.c                              |   2 +
 kernel/bpf/syscall.c                          |  18 +-
 kernel/bpf/trampoline.c                       |  50 +++-
 kernel/bpf/verifier.c                         |  75 ++++--
 kernel/trace/bpf_trace.c                      |  56 ++++-
 net/bpf/test_run.c                            |   1 +
 net/core/bpf_sk_storage.c                     |   1 +
 tools/bpf/bpftool/common.c                    |   1 +
 tools/include/uapi/linux/bpf.h                |   1 +
 tools/lib/bpf/bpf.c                           |   2 +
 tools/lib/bpf/libbpf.c                        |   3 +
 .../selftests/bpf/prog_tests/fsession_test.c  |  90 +++++++
 .../bpf/prog_tests/tracing_failure.c          |   2 +-
 .../selftests/bpf/progs/fsession_test.c       | 226 ++++++++++++++++++
 17 files changed, 571 insertions(+), 44 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/fsession_test.c
 create mode 100644 tools/testing/selftests/bpf/progs/fsession_test.c

-- 
2.52.0

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