syscalls.h: slightly reduce the jungles of macros

a) teach __MAP(num, m, <list of type/name pairs>) to take empty
list (with num being 0, of course)
b) fold types__... and args__... declaration and initialization into
SYSCALL_METADATA(num, ...), making their use conditional on num != 0.
That allows to use the SYSCALL_METADATA instead of its near-duplicate
in SYSCALL_DEFINE0.
c) make SYSCALL_METADATA expand to nothing in case if CONFIG_FTRACE_SYSCALLS
is not defined; that allows to make SYSCALL_DEFINE0 and SYSCALL_DEFINEx
definitions independent from CONFIG_FTRACE_SYSCALLS.
d) kill SYSCALL_DEFINE - no users left (SYSCALL_DEFINE[0-6] is, of course,
still alive and well).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/syscalls.h

@@ -87,6 +87,7 @@ struct sigaltstack;
  * of __MAP starting at the third one) is in the same format as
  * for SYSCALL_DEFINE<n>/COMPAT_SYSCALL_DEFINE<n>
  */
+#define __MAP0(m,...)
 #define __MAP1(m,t,a) m(t,a)
 #define __MAP2(m,t,a,...) m(t,a), __MAP1(m,__VA_ARGS__)
 #define __MAP3(m,t,a,...) m(t,a), __MAP2(m,__VA_ARGS__)
@@ -139,7 +140,13 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 	  __attribute__((section("_ftrace_events")))			\
 	*__event_exit_##sname = &event_exit_##sname;
 
-#define SYSCALL_METADATA(sname, nb)				\
+#define SYSCALL_METADATA(sname, nb, ...)			\
+	static const char *types_##sname[] = {			\
+		__MAP(nb,__SC_STR_TDECL,__VA_ARGS__)		\
+	};							\
+	static const char *args_##sname[] = {			\
+		__MAP(nb,__SC_STR_ADECL,__VA_ARGS__)		\
+	};							\
 	SYSCALL_TRACE_ENTER_EVENT(sname);			\
 	SYSCALL_TRACE_EXIT_EVENT(sname);			\
 	static struct syscall_metadata __used			\
@@ -147,8 +154,8 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 		.name 		= "sys"#sname,			\
 		.syscall_nr	= -1,	/* Filled in at boot */	\
 		.nb_args 	= nb,				\
-		.types		= types_##sname,		\
-		.args		= args_##sname,			\
+		.types		= nb ? types_##sname : NULL,	\
+		.args		= nb ? args_##sname : NULL,	\
 		.enter_event	= &event_enter_##sname,		\
 		.exit_event	= &event_exit_##sname,		\
 		.enter_fields	= LIST_HEAD_INIT(__syscall_meta_##sname.enter_fields), \
@@ -156,26 +163,13 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 	static struct syscall_metadata __used			\
 	  __attribute__((section("__syscalls_metadata")))	\
 	 *__p_syscall_meta_##sname = &__syscall_meta_##sname;
+#else
+#define SYSCALL_METADATA(sname, nb, ...)
+#endif
 
 #define SYSCALL_DEFINE0(sname)					\
-	SYSCALL_TRACE_ENTER_EVENT(_##sname);			\
-	SYSCALL_TRACE_EXIT_EVENT(_##sname);			\
-	static struct syscall_metadata __used			\
-	  __syscall_meta__##sname = {				\
-		.name 		= "sys_"#sname,			\
-		.syscall_nr	= -1,	/* Filled in at boot */	\
-		.nb_args 	= 0,				\
-		.enter_event	= &event_enter__##sname,	\
-		.exit_event	= &event_exit__##sname,		\
-		.enter_fields	= LIST_HEAD_INIT(__syscall_meta__##sname.enter_fields), \
-	};							\
-	static struct syscall_metadata __used			\
-	  __attribute__((section("__syscalls_metadata")))	\
-	 *__p_syscall_meta_##sname = &__syscall_meta__##sname;	\
+	SYSCALL_METADATA(_##sname, 0);				\
 	asmlinkage long sys_##sname(void)
-#else
-#define SYSCALL_DEFINE0(name)	   asmlinkage long sys_##name(void)
-#endif
 
 #define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
 #define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)
@@ -184,22 +178,9 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 #define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__)
 #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__)
 
-#ifdef CONFIG_FTRACE_SYSCALLS
 #define SYSCALL_DEFINEx(x, sname, ...)				\
-	static const char *types_##sname[] = {			\
-		__MAP(x,__SC_STR_TDECL,__VA_ARGS__)		\
-	};							\
-	static const char *args_##sname[] = {			\
-		__MAP(x,__SC_STR_ADECL,__VA_ARGS__)		\
-	};							\
-	SYSCALL_METADATA(sname, x);				\
+	SYSCALL_METADATA(sname, x, __VA_ARGS__)			\
 	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
-#else
-#define SYSCALL_DEFINEx(x, sname, ...)				\
-	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
-#endif
-
-#define SYSCALL_DEFINE(name) static inline long SYSC_##name
 
 #define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
 #define __SYSCALL_DEFINEx(x, name, ...)					\