Re: [PATCH v7 00/10] tracing/probes: Add more typecast features

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

On Tue, 23 Jun 2026 10:44:10 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> Hi,
> 
> Here is the 7th version of series to introduce more typecast features
> to probe events. The previous version is here:
> 
>  https://lore.kernel.org/all/178201238795.570818.15573963115625446598.stgit@devnote2/
> 
> In this version, I added 2 new fix and cleanup patches and update
> according to Sashiko's review. [1/10] is a long-lived issue about
> @+FOFFS, which was wrongly adding offset twice. [2/10] is a clean
> up patch for renaming fetch_op name (good to dump it). 
> This is applicable against probes/core branch on linux-trace tree.

I'll take the first 2 patches to probes/core, since those
are obvious fix and cleanup.

Thanks,

> 
> 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 fetcharg dump feature (for debug) and updated test scripts
> to test part of them.
> 
> Thanks,
> 
> ---
> base-commit: 3ec75d0067f30eb5e0730f033766d6ab2feca7ae
> 
> Masami Hiramatsu (Google) (10):
>       tracing/probes: Fix double addition of offset for @+FOFFSET
>       tracing/probes: Rename FETCH_OP_DATA to FETCH_OP_IMMSTR
>       tracing/probes: Support dumping fetcharg program for debugging dynamic events
>       tracing/probes: Support typecast for various probe events
>       tracing/probes: Support nested typecast
>       tracing/probes: Type casting always involves nested calls
>       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/Kconfig                               |   11 
>  kernel/trace/trace.c                               |    8 
>  kernel/trace/trace_eprobe.c                        |    2 
>  kernel/trace/trace_fprobe.c                        |    2 
>  kernel/trace/trace_kprobe.c                        |    2 
>  kernel/trace/trace_probe.c                         |  582 ++++++++++++++++----
>  kernel/trace/trace_probe.h                         |   98 ++-
>  kernel/trace/trace_probe_tmpl.h                    |   27 +
>  kernel/trace/trace_uprobe.c                        |    3 
>  samples/trace_events/trace-events-sample.c         |   40 +
>  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 |   11 
>  .../ftrace/test.d/kprobe/kprobe_syntax_errors.tc   |   11 
>  .../ftrace/test.d/kprobe/uprobe_syntax_errors.tc   |    5 
>  18 files changed, 756 insertions(+), 161 deletions(-)
>  create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/btf_probe_event.tc
> 
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>


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