tracing: Fix endianness bug in histogram trigger

At least on PA-RISC and s390 synthetic histogram triggers are failing
selftests because trace_event_raw_event_synth() always writes a 64 bit
values, but the reader expects a field->size sized value. On little endian
machines this doesn't hurt, but on big endian this makes the reader always
read zero values.

Link: http://lore.kernel.org/linux-trace-devel/20191218074427.96184-4-svens@linux.ibm.com

Cc: stable@vger.kernel.org
Fixes: 4b147936 ("tracing: Add support for 'synthetic' events")
Acked-by: NTom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: NSven Schnelle <svens@linux.ibm.com>
Signed-off-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -911,7 +911,26 @@ static notrace void trace_event_raw_event_synth(void *__data,
 			strscpy(str_field, str_val, STR_VAR_LEN_MAX);
 			n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
 		} else {
-			entry->fields[n_u64] = var_ref_vals[var_ref_idx + i];
+			struct synth_field *field = event->fields[i];
+			u64 val = var_ref_vals[var_ref_idx + i];
+
+			switch (field->size) {
+			case 1:
+				*(u8 *)&entry->fields[n_u64] = (u8)val;
+				break;
+
+			case 2:
+				*(u16 *)&entry->fields[n_u64] = (u16)val;
+				break;
+
+			case 4:
+				*(u32 *)&entry->fields[n_u64] = (u32)val;
+				break;
+
+			default:
+				entry->fields[n_u64] = val;
+				break;
+			}
 			n_u64++;
 		}
 	}