tracing: Fix number printing bug in print_synth_event()

Fix a varargs-related bug in print_synth_event() which resulted in
strange output and oopses on 32-bit x86 systems. The problem is that
trace_seq_printf() expects the varargs to match the format string, but
print_synth_event() was always passing u64 values regardless.  This
results in unspecified behavior when unpacking with va_arg() in
trace_seq_printf().

Add a function that takes the size into account when calling
trace_seq_printf().

Before:

  modprobe-1731  [003] ....   919.039758: gen_synth_test: next_pid_field=777(null)next_comm_field=hula hoops ts_ns=1000000 ts_ms=1000 cpu=3(null)my_string_field=thneed my_int_field=598(null)

After:

 insmod-1136  [001] ....    36.634590: gen_synth_test: next_pid_field=777 next_comm_field=hula hoops ts_ns=1000000 ts_ms=1000 cpu=1 my_string_field=thneed my_int_field=598

Link: http://lkml.kernel.org/r/a9b59eb515dbbd7d4abe53b347dccf7a8e285657.1581720155.git.zanussi@kernel.org

Reported-by: Steven Rostedt (VMware) <[email protected]>
Signed-off-by: Tom Zanussi <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

Author: Tom Zanussi

kernel/trace/trace_events_hist.c

@@ -820,6 +820,29 @@ static const char *synth_field_fmt(char *type)
 	return fmt;
 }
 
+static void print_synth_event_num_val(struct trace_seq *s,
+				      char *print_fmt, char *name,
+				      int size, u64 val, char *space)
+{
+	switch (size) {
+	case 1:
+		trace_seq_printf(s, print_fmt, name, (u8)val, space);
+		break;
+
+	case 2:
+		trace_seq_printf(s, print_fmt, name, (u16)val, space);
+		break;
+
+	case 4:
+		trace_seq_printf(s, print_fmt, name, (u32)val, space);
+		break;
+
+	default:
+		trace_seq_printf(s, print_fmt, name, val, space);
+		break;
+	}
+}
+
 static enum print_line_t print_synth_event(struct trace_iterator *iter,
 					   int flags,
 					   struct trace_event *event)
@@ -858,10 +881,13 @@ static enum print_line_t print_synth_event(struct trace_iterator *iter,
 		} else {
 			struct trace_print_flags __flags[] = {
 			    __def_gfpflag_names, {-1, NULL} };
+			char *space = (i == se->n_fields - 1 ? "" : " ");
 
-			trace_seq_printf(s, print_fmt, se->fields[i]->name,
-					 entry->fields[n_u64],
-					 i == se->n_fields - 1 ? "" : " ");
+			print_synth_event_num_val(s, print_fmt,
+						  se->fields[i]->name,
+						  se->fields[i]->size,
+						  entry->fields[n_u64],
+						  space);
 
 			if (strcmp(se->fields[i]->type, "gfp_t") == 0) {
 				trace_seq_puts(s, " (");