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:		[RFC PATCH 0/7] tracing/probes: Add more typecast features
Date:		Mon, 08 Jun 2026 23:24:16 +0900
Message-ID:		<178092865666.163648.10457567771536160909.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 a series of patches to introduce more typecast features
to probe events, which includes 1. expanding BTF typecast to
fprobe and kprobe events, 2. introducing container_of like typecst
option, 3. supporting nested typecast, 4. adding $current special
variable support, 5. adding per-cpu dereference support, 6. adding
a testcase to check typecasts.

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.

   +CPU(VAR) is the same as this_cpu_read(VAR), and
   +PCPU(VAR) is the same as this_cpu_ptr(VAR).
   Also, "this_cpu_ptr(VAR)" is available. This is good
   with nesting expression.

   (STRUCT)(this_cpu_ptr(VAR))->MEMBER

   (However, it might be better to allow a special way to omit
    parentheses for thi_cpu_ptr())

And added a test script to test part of them.

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


---

Masami Hiramatsu (Google) (7):
      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 +CPU() and +PCPU() dereference method to fetcharg
      tracing/probes: Support reserved this_cpu_ptr() method
      tracing/probes: Add a new testcase for BTF typecasts


 Documentation/trace/eprobetrace.rst                |   11 +
 Documentation/trace/fprobetrace.rst                |   11 +
 Documentation/trace/kprobetrace.rst                |   12 +
 kernel/trace/trace.c                               |    6 
 kernel/trace/trace_probe.c                         |  312 +++++++++++++++-----
 kernel/trace/trace_probe.h                         |   12 +
 kernel/trace/trace_probe_tmpl.h                    |   33 ++
 samples/trace_events/trace-events-sample.c         |   38 ++
 samples/trace_events/trace-events-sample.h         |   34 ++
 .../ftrace/test.d/dynevent/btf_probe_event.tc      |   52 +++
 10 files changed, 422 insertions(+), 99 deletions(-)
 create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/btf_probe_event.tc

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