tracing: Fix double CPP substitution in TRACE_EVENT_FN

TRACE_EVENT_FN relays on TRACE_EVENT by reprocessing its parameters
into the ftrace events CPP macro. This leads to a double substitution
in some cases.

For example, a bad consequence is a format always prefixed by
"%s, %s\n" for every TRACE_EVENT_FN based events.

Eg:
	cat /debug/tracing/events/syscalls/sys_enter/format
	[...]
	print fmt: "%s, %s\n", "\"NR %ld (%lx, %lx, %lx, %lx, %lx, %lx)\"",\
	"REC->id, REC->args[0], REC->args[1], REC->args[2], REC->args[3],\
	REC->args[4], REC->args[5]"

This creates a failure in post-processing tools such as perf trace or
trace-cmd.

Then drop this double substitution and replace it by a new __cpparg()
macro that relays CPP arguments containing commas.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Josh Stone <jistone@redhat.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Jason Baron <jbaron@redhat.com>
LKML-Reference: <1251413406-6704-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/trace/ftrace.h

@@ -45,14 +45,15 @@
 	};							\
 	static struct ftrace_event_call event_##name
 
+#undef __cpparg
+#define __cpparg(arg...) arg
+
 /* Callbacks are meaningless to ftrace. */
 #undef TRACE_EVENT_FN
-#define TRACE_EVENT_FN(name, proto, args, tstruct,		\
-		assign, print, reg, unreg)			\
-	TRACE_EVENT(name, TP_PROTO(proto), TP_ARGS(args),	\
-		TP_STRUCT__entry(tstruct),			\
-		TP_fast_assign(assign),				\
-		TP_printk(print))
+#define TRACE_EVENT_FN(name, proto, args, tstruct,			\
+		assign, print, reg, unreg)				\
+	TRACE_EVENT(name, __cpparg(proto), __cpparg(args),		\
+		__cpparg(tstruct), __cpparg(assign), __cpparg(print))	\
 
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)