Re: [PATCH v13 11/12] tracing/wprobe: Support BTF typecast in fetchargs

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

Allow BTF typecast syntax (STRUCT)FETCHARG->MEMBER in wprobe event
fetchargs. Previously, handle_typecast() rejected any probe context
that was not a function entry/return or tracepoint event probe.

Wprobe events use $addr (the accessed address) and $value (the value
at that address). By enabling BTF typecast, users can now cast these
to a concrete struct type and access its fields directly. For example:

  echo 'w:watch rw@0:8 dflag=(dentry)$addr->d_flags' >> dynamic_events

With a set_wprobe trigger pointing the watchpoint at a dentry address,
the resulting trace shows d_flags being accessed at that location.

Note that $addr and $value are restricted to kernel-space memory,
which is consistent with the existing TPARG_FL_KERNEL flag used when
parsing wprobe fetchargs.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/178739053919.1520941.17662338993878200834.stgit@devnote2?part=11