question regarding SYSCALL macros
dhylands at gmail.com
Fri Apr 29 16:30:13 EDT 2011
On Thu, Apr 28, 2011 at 3:16 AM, Sudheer Divakaran
<inbox1.sudheer at gmail.com> wrote:
> 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__)
> 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?
Some of the other macros, like SC_CAST1
#define __SC_CAST1(t1, a1) (t1) a1
need the type to be separated from the argument.
Shuswap, BC, Canada
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