Hi, I was going through the file kernel/time.c and found the definition of 'gettimeofday' system call as follows. SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv, struct timezone __user *, tz) <--- NOTE THE COMMA between variable types and names. In syscalls.h I could find the needed macros for expanding the definition to its final form i.e., asmlinkage long sys_gettimeofday(struct timeval __user * tv, struct timezone __user *tz) [syscalls.h macros] #define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__) #define SYSCALL_DEFINEx(x, sname, ...) \ __SYSCALL_DEFINEx(x, sname, __VA_ARGS__) #define __SYSCALL_DEFINEx(x, name, ...) \ asmlinkage long sys##name(__SC_DECL##x(__VA_ARGS__)) #define __SC_DECL1(t1, a1) t1 a1 #define __SC_DECL2(t2, a2, ...) t2 a2, __SC_DECL1(__VA_ARGS__) [Question] Note the comma between the variable types and names in the original definition (e.g., "struct timeval __user *, tv" instead of "struct timeval __user *tv"). What is is the reason behind separating variable types and variable names using 'comma' and latter removing the comma character using _SC_DECLx macros? -- Thanks Sudheer