linux-kernel - [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

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Message-ID:  <168657113778.3038017.12245893750241701312.stgit@mhiramat.roam.corp.google.com>
Date:   Mon, 12 Jun 2023 20:58:57 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     linux-trace-kernel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        mhiramat@...nel.org, Florent Revest <revest@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org,
        Bagas Sanjaya <bagasdotme@...il.com>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

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

To hide the first dummy 'data' argument on the tracepoint probe events,
the BTF argument array was modified (skip the first argument for tracepoint),
but the '$arg*' meta argument parser missed that.

Fix to increment the argument index if it is tracepoint probe. And decrement
the index when searching the type of the argument.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 kernel/trace/trace_probe.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 473e1c43bc57..643aa3a51d5a 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -456,7 +456,10 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
 
 		if (name && !strcmp(name, varname)) {
 			code->op = FETCH_OP_ARG;
-			code->param = i;
+			if (ctx->flags & TPARG_FL_TPOINT)
+				code->param = i + 1;
+			else
+				code->param = i;
 			return 0;
 		}
 	}
@@ -470,8 +473,11 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
 	struct btf *btf = traceprobe_get_btf();
 	const char *typestr = NULL;
 
-	if (btf && ctx->params)
+	if (btf && ctx->params) {
+		if (ctx->flags & TPARG_FL_TPOINT)
+			arg_idx--;
 		typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
+	}
 
 	return find_fetch_type(typestr, ctx->flags);
 }