tracing: Restore the const qualifier for field names and types definition

Restore the const qualifier in field's name and type parameters of
trace_define_field that was lost while solving a conflict.

Fields names and types are defined as builtin constant strings in
static TRACE_EVENTs. But kprobes allocates these dynamically.

That said, we still want to always pass these strings as const char *
in trace_define_fields() to avoid any further accidental writes on
the pointed strings.

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>

include/linux/ftrace_event.h

@@ -148,9 +148,9 @@ enum {
 };
 
 extern int trace_define_common_fields(struct ftrace_event_call *call);
-extern int trace_define_field(struct ftrace_event_call *call, char *type,
+extern int trace_define_field(struct ftrace_event_call *call, const char *type,
-			      char *name, int offset, int size, int is_signed,
+			      const char *name, int offset, int size,
-			      int filter_type);
+			      int is_signed, int filter_type);
 extern int trace_add_event_call(struct ftrace_event_call *call);
 extern void trace_remove_event_call(struct ftrace_event_call *call);
 

kernel/trace/trace_events.c

@@ -27,8 +27,8 @@ DEFINE_MUTEX(event_mutex);
 
 LIST_HEAD(ftrace_events);
 
-int trace_define_field(struct ftrace_event_call *call, char *type,
+int trace_define_field(struct ftrace_event_call *call, const char *type,
-		       char *name, int offset, int size, int is_signed,
+		       const char *name, int offset, int size, int is_signed,
 		       int filter_type)
 {
 	struct ftrace_event_field *field;

kernel/trace/trace_syscalls.c

@@ -193,8 +193,8 @@ int syscall_enter_define_fields(struct ftrace_event_call *call)
 		return ret;
 
 	for (i = 0; i < meta->nb_args; i++) {
-		ret = trace_define_field(call, (char *)meta->types[i],
+		ret = trace_define_field(call, meta->types[i],
-					 (char *)meta->args[i], offset,
+					 meta->args[i], offset,
 					 sizeof(unsigned long), 0,
 					 FILTER_OTHER);
 		offset += sizeof(unsigned long);