tracing/probes: Add more typecast features [LWN.net]

From:		"Masami Hiramatsu (Google)" <mhiramat-AT-kernel.org>
To:		Steven Rostedt <rostedt-AT-goodmis.org>, Mathieu Desnoyers <mathieu.desnoyers-AT-efficios.com>
Subject:		[PATCH v3 0/7] tracing/probes: Add more typecast features
Date:		Sun, 14 Jun 2026 23:53:22 +0900
Message-ID:		<178144880282.159464.16882854283219530040.stgit@devnote2>
Cc:		Jonathan Corbet <corbet-AT-lwn.net>, Shuah Khan <skhan-AT-linuxfoundation.org>, Masami Hiramatsu <mhiramat-AT-kernel.org>, linux-kernel-AT-vger.kernel.org, linux-trace-kernel-AT-vger.kernel.org, linux-doc-AT-vger.kernel.org, linux-kselftest-AT-vger.kernel.org
Archive-link:		Article

Hi,

Here is the 3rd version of series to introduce more typecast features
to probe events. The previous version is here:

 https://lore.kernel.org/all/178105268094.21760.1366824993...

In this version, I fixed various problems Sashiko reviewed and add new
test cases.

Steve introduced BTF typecast feature for eprobe[1].
This series extends it and add more options:

1. Expanding BTF typecast to kprobe and fprobe.
   (currently only function entry/exit)

2. Introduce container_of like typecast. This adds a "assigned
   member" option to the typecast.

   (STRUCT,MEMBER)VAR->ANOTHER_MEMBER

   This casts VAR to STRUCT type but the VAR is as the address
   of STRUCT.MEMBER. In C, it is:

   container_of(VAR, STRUCT, MEMBER)->ANOTHER_MEMBER

3. Support nested typecast, e.g.

   (STRUCT)((STRUCT2)VAR->MEMBER2)->MEMBER

   the nest level must be smaller than 3.

4. Add $current variable to point "current" task_struct.
   This is useful with typecast, e.g.

   (task_struct)$current->pid

5. per-cpu dereference support.

   Intrdouce this_cpu_read(VAR) and this_cpu_ptr(VAR) to
   access per-cpu data on the current CPU (accessing other CPU
   data is not stable, because it can be changed.)

   You can access the member of per-cpu data structure using
   typecast like:

   (STRUCT)this_cpu_ptr(VAR)->MEMBER


And added a test script to test part of them.

[1] https://lore.kernel.org/all/20260601130746.2139d926@ganda...


---

Masami Hiramatsu (Google) (7):
      tracing/events: Fix to check the simple_tsk_fn creation
      tracing/probes: Support typecast for various probe events
      tracing/probes: Support nested typecast
      tracing/probes: Support field specifier option for typecast
      tracing/probes: Add $current variable support
      tracing/probes: Add this_cpu_read() and this_cpu_ptr() dereference method to fetcharg
      tracing/probes: Add a new testcase for BTF typecasts


 Documentation/trace/eprobetrace.rst                |    9 
 Documentation/trace/fprobetrace.rst                |   10 
 Documentation/trace/kprobetrace.rst                |   11 +
 kernel/trace/trace.c                               |    6 
 kernel/trace/trace_probe.c                         |  413 +++++++++++++++-----
 kernel/trace/trace_probe.h                         |   19 +
 kernel/trace/trace_probe_tmpl.h                    |   33 +-
 samples/trace_events/trace-events-sample.c         |   45 ++
 samples/trace_events/trace-events-sample.h         |   34 ++
 .../ftrace/test.d/dynevent/btf_probe_event.tc      |   51 ++
 .../ftrace/test.d/dynevent/fprobe_syntax_errors.tc |    9 
 .../ftrace/test.d/kprobe/kprobe_syntax_errors.tc   |    9 
 .../ftrace/test.d/kprobe/uprobe_syntax_errors.tc   |    5 
 13 files changed, 540 insertions(+), 114 deletions(-)
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/btf_probe_event.tc

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>