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: 4b147936fa509 ("tracing: Add support for 'synthetic' events")
Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f49d1a3..f62de5f 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/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++;
                }
        }