tracing: add size checks for exported ftrace internal structures

The events exported by TRACE_EVENT are automated and are guaranteed
to be correct when used.

The internal ftrace structures on the other hand are more manually
exported. These require the ftrace maintainer to make sure they
are up to date.

This patch adds a size check to help flag when a type changes in
an internal ftrace data structure, and the update needs to be reflected
in the export.

If a export is incorrect, then the only harm is that the user space
tools will not know how to correctly read the internal structures of
ftrace.

[ Impact: help prevent inconsistent ftrace format print outs ]

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

kernel/trace/trace_events.c

@@ -381,8 +381,11 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	return cnt;
 }
 
+extern char *__bad_type_size(void);
+
 #undef FIELD
 #define FIELD(type, name)						\
+	sizeof(type) != sizeof(field.name) ? __bad_type_size() :	\
 	#type, "common_" #name, offsetof(typeof(field), name),		\
 		sizeof(field.name)
 

kernel/trace/trace_export.c

@@ -19,8 +19,12 @@
 #undef TRACE_STRUCT
 #define TRACE_STRUCT(args...) args
 
+extern void __bad_type_size(void);
+
 #undef TRACE_FIELD
 #define TRACE_FIELD(type, item, assign)					\
+	if (sizeof(type) != sizeof(field.item))				\
+		__bad_type_size();					\
 	ret = trace_seq_printf(s, "\tfield:" #type " " #item ";\t"	\
 			       "offset:%u;\tsize:%u;\n",		\
 			       (unsigned int)offsetof(typeof(field), item), \