[PATCH] tracing: Pretty-print enum parameters in function arguments

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

From: Donglin Peng <pengdonglin@xiaomi.com>

Currently, print_function_args() prints enum parameter values
in decimal format, reducing trace log readability.

Use BTF information to resolve enum parameters and print their
symbolic names (where available). This improves readability by
showing meaningful identifiers instead of raw numbers.

Before:
  mod_memcg_lruvec_state(lruvec=0xffff..., idx=5, val=320)

After:
  mod_memcg_lruvec_state(lruvec=0xffff..., idx=5 [NR_SLAB_RECLAIMABLE_B], val=320)

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Donglin Peng <pengdonglin@xiaomi.com>
---
v2:
 - Iterate btf_enum members directly with a for loop,
   replacing the for_each_enum macro helper.
---
 kernel/trace/trace_output.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index cc2d3306bb60..548e3cd06b04 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 *enums;
 	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 +755,15 @@ void print_function_args(struct trace_seq *s, unsigned long *args,
 			break;
 		case BTF_KIND_ENUM:
 			trace_seq_printf(s, "%ld", arg);
+			enums = btf_enum(t);
+			for (i = 0; i < btf_vlen(t); i++) {
+				if (arg == enums[i].val) {
+					trace_seq_printf(s, " [%s]",
+							 btf_name_by_offset(btf,
+							 enums[i].name_off));
+					break;
+				}
+			}
 			break;
 		default:
 			/* This does not handle complex arguments */
-- 
2.34.1