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Date: Tue, 26 May 2026 11:33:11 -0400
From: Steven Rostedt <rostedt@kernel.org>
To: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Linux trace kernel
 <linux-trace-kernel@vger.kernel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@efficios.com>, Mark Rutland <mark.rutland@arm.com>,
 Peter Zijlstra <peterz@infradead.org>, Namhyung Kim <namhyung@kernel.org>,
 Takaya Saeki <takayas@google.com>, Douglas Raillard
 <douglas.raillard@arm.com>, Tom Zanussi <zanussi@kernel.org>, Andrew Morton
 <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Ian
 Rogers <irogers@google.com>, Jiri Olsa <olsajiri@gmail.com>
Subject: Re: [PATCH v6] tracing/eprobes: Allow use of BTF names to
 dereference pointers
Message-ID: <20260526113311.18d1858e@gandalf.local.home>
In-Reply-To: <20260525235507.a81c565023258c63fc9201f4@kernel.org>
References: <20260521225033.56458336@fedora>
	<20260525235507.a81c565023258c63fc9201f4@kernel.org>
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On Mon, 25 May 2026 23:55:07 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> On Thu, 21 May 2026 22:50:33 -0400
> Steven Rostedt <rostedt@kernel.org> wrote:
> 
> > +static int handle_typecast(char *arg, struct fetch_insn **pcode,
> > +			   struct fetch_insn *end,
> > +			   struct traceprobe_parse_context *ctx)
> > +{
> > +	char *tmp;
> > +	int ret;
> > +
> > +	/* Currently this only works for eprobes */
> > +	if (!(ctx->flags & TPARG_FL_TEVENT)) {
> > +		trace_probe_log_err(ctx->offset, TYPECAST_NOT_EVENT);
> > +		return -EINVAL;
> > +	}
> > +
> > +	tmp = strchr(arg, ')');
> > +	if (!tmp) {
> > +		trace_probe_log_err(ctx->offset + strlen(arg),
> > +				    DEREF_OPEN_BRACE);
> > +		return -EINVAL;
> > +	}
> > +	*tmp = '\0';
> > +	ret = query_btf_struct(arg + 1, ctx);
> > +	*tmp = ')';  
> 
> BTW, is there any reason to recover this? The @arg is copied
> string, see traceprobe_parse_probe_arg_body().

Yeah I know. But it's just something I prefer to do to keep code more
robust. That is, don't leave side effects if you can help it. It likely
doesn't matter here, but I've always errored on the side of caution. ;-)

-- Steve