Syscalls: When can I use "cond_syscall()" macro?

Hello, friends!! How are you?! Im studing the linux kernel, to be part of the community!! Anyone know where/when can I use the con_syscall() macro?! And another question: Where are the file "unistd_32.h"?! I'm not founding it in the "arch/x86/include/asm/" directory!! []'s Peace. -- Atenciosamente, Gustavo da Silva gustavodasilva@gmail.com