Linux Kernel system call macro magic 1: syscall arguments

s1.c

#define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__)

#define SYSCALL_DEFINEx(x, name, ...)                   \
    static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))

#define __SC_DECL(t, a) t a
#define __SC_ARGS(t, a) a

#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__)
#define __MAP4(m,t,a,...) m(t,a), __MAP3(m,__VA_ARGS__)
#define __MAP5(m,t,a,...) m(t,a), __MAP4(m,__VA_ARGS__)
#define __MAP6(m,t,a,...) m(t,a), __MAP5(m,__VA_ARGS__)
#define __MAP(n,...) __MAP##n(__VA_ARGS__)

SYSCALL_DEFINE2(add, int, a, int, b){
    return a + b;

}

// real call isn't in Linux Kernel. it's just my practice.
                                                                                                                                   
#define REAL_CALL(x, name, ... ) \
    real_##SYSC_##name(__MAP(x,__SC_ARGS,__VA_ARGS__));

REAL_CALL(2, add, int, a, int, b)

s1.i

# 1 "s1.c"                                                                                                                         
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<command-line>" 2
# 1 "s1.c"
# 19 "s1.c"
static inline long SYSC_add(int a, int b){
    return a + b;

}






real_SYSC_add(a, b);

use techinique from /include/linux/syscall.h