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Date: Tue, 19 May 2026 13:37:34 -0400
From: Steven Rostedt <rostedt@kernel.org>
To: LKML <linux-kernel@vger.kernel.org>, Linux trace kernel
 <linux-trace-kernel@vger.kernel.org>, bpf@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@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 v5] tracing/eprobes: Allow use of BTF names to
 dereference pointers
Message-ID: <20260519133734.2d3150df@fedora>
In-Reply-To: <20260519132830.3011a194@fedora>
References: <20260519130144.40e71a00@fedora>
	<20260519132830.3011a194@fedora>
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On Tue, 19 May 2026 13:28:30 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 19 May 2026 13:01:44 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > @@ -636,11 +694,12 @@ static int parse_btf_arg(char *varname,
> >  	struct fetch_insn *code = *pcode;
> >  	const struct btf_param *params;
> >  	const struct btf_type *type;
> > +	struct btf *btf = ctx_btf(ctx);
> >  	char *field = NULL;
> >  	int i, is_ptr, ret;
> >  	u32 tid;
> >  
> > -	if (WARN_ON_ONCE(!ctx->funcname))
> > +	if (WARN_ON_ONCE(!ctx->funcname && !(ctx->flags & TPARG_FL_TYPECAST)))
> >  		return -EINVAL;
> >  
> >  	is_ptr = split_next_field(varname, &field, ctx);
> > @@ -653,6 +712,14 @@ static int parse_btf_arg(char *varname,
> >  		return -EOPNOTSUPP;
> >  	}
> >  
> > +	if (ctx->flags & TPARG_FL_TEVENT) {
> > +		int ret;
> > +
> > +		ret = parse_trace_event(varname, code, ctx);
> > +		if (ret < 0)
> > +			return ret;

Actually, since typecasting is currently only for eprobes, I'm going to
shuffle the code around a bit to only have the TYPECAST affect TEVENT,
and do the jump to found_type from here.

-- Steve


> > +	}
> > +
> >  	if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) {
> >  		code->op = FETCH_OP_RETVAL;
> >  		/* Check whether the function return type is not void */
> > @@ -672,7 +739,7 @@ static int parse_btf_arg(char *varname,
> >  		return 0;
> >  	}
> >  
> > -	if (!ctx->btf) {
> > +	if (!btf) {
> >  		ret = query_btf_context(ctx);  
> 
> Oops, need a:
> 
> 		btf = ctx->btf;
> 
> here!
> 
> -- Steve
> 
> >  		if (ret < 0 || ctx->nr_params == 0) {
> >  			trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);