macro: introduce COUNT_ARGS() macro

move COUNT_ARGS() macro from apparmor to generic header and extend it
to count till twelve.

COUNT() was an alternative name for this logic, but it's used for
different purpose in many other places.

Similarly for CONCATENATE() macro.

Suggested-by: Linus Torvalds <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>

include/linux/kernel.h

···
 #define swap(a, b) \
 	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
 
+/* This counts to 12. Any more, it will return 13th argument. */
+#define __COUNT_ARGS(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _n, X...) _n
+#define COUNT_ARGS(X...) __COUNT_ARGS(, ##X, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+
+#define __CONCAT(a, b) a ## b
+#define CONCATENATE(a, b) __CONCAT(a, b)
+
 /**
  * container_of - cast a member of a structure out to the containing structure
  * @ptr:	the pointer to the member.

security/apparmor/include/path.h

···
 
 DECLARE_PER_CPU(struct aa_buffers, aa_buffers);
 
-#define COUNT_ARGS(X...) COUNT_ARGS_HELPER(, ##X, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
-#define COUNT_ARGS_HELPER(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, n, X...) n
-#define CONCAT(X, Y) X ## Y
-#define CONCAT_AFTER(X, Y) CONCAT(X, Y)
-
 #define ASSIGN(FN, X, N) ((X) = FN(N))
 #define EVAL1(FN, X) ASSIGN(FN, X, 0) /*X = FN(0)*/
 #define EVAL2(FN, X, Y...) do { ASSIGN(FN, X, 1);  EVAL1(FN, Y); } while (0)
-#define EVAL(FN, X...) CONCAT_AFTER(EVAL, COUNT_ARGS(X))(FN, X)
+#define EVAL(FN, X...) CONCATENATE(EVAL, COUNT_ARGS(X))(FN, X)
 
 #define for_each_cpu_buffer(I) for ((I) = 0; (I) < MAX_PATH_BUFFERS; (I)++)