[PATCH 2/2] tracing: resolve enum names for function arguments via BTF

[Donglin Peng <dolinux.peng@gmail.com>]

From: Donglin Peng <pengdonglin@xiaomi.com>

Use BTF to print symbolic names for enum-type function arguments,
improving trace readability.

Before:
count_memcg_events(memcg=0xffff..., idx=20, count=0x1) {

After:
count_memcg_events(memcg=0xffff..., idx=20 [PGFAULT], count=0x1) {

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: linux-trace-kernel@vger.kernel.org
Signed-off-by: Donglin Peng <pengdonglin@xiaomi.com>
---
 kernel/trace/trace_output.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index cc2d3306bb60..c395f768c3b8 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -695,12 +695,13 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 {
 	const struct btf_param *param;
 	const struct btf_type *t;
+	const struct btf_enum *enump;
 	const char *param_name;
 	char name[KSYM_NAME_LEN];
 	unsigned long arg;
 	struct btf *btf;
 	s32 tid, nr = 0;
-	int a, p, x;
+	int a, p, x, i;
 	u16 encode;
 
 	trace_seq_printf(s, "(");
@@ -754,6 +755,14 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 			break;
 		case BTF_KIND_ENUM:
 			trace_seq_printf(s, "%ld", arg);
+			for_each_enum(i, t, enump) {
+				if (arg == enump->val) {
+					trace_seq_printf(s, " [%s]",
+							 btf_name_by_offset(btf,
+							 enump->name_off));
+					break;
+				}
+			}
 			break;
 		default:
 			/* This does not handle complex arguments */
-- 
2.34.1