From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

When tracing a dynamic string field for a synthetic event, the offset
calculation for where to write the next event can use struct_size() to
find what the current size of the structure is.

This simplifies the code and makes it less error prone.

Link: https://lkml.kernel.org/r/20230117152235.698632147@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_events_synth.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 67592eed0be8..9f79cd689b79 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -416,8 +416,7 @@ static unsigned int trace_string(struct synth_trace_event *entry,
 	if (is_dynamic) {
 		u32 data_offset;
 
-		data_offset = offsetof(typeof(*entry), fields);
-		data_offset += event->n_u64 * sizeof(u64);
+		data_offset = struct_size(entry, fields, event->n_u64);
 		data_offset += data_size;
 
 		len = kern_fetch_store_strlen((unsigned long)str_val);
-- 
2.39.0