#define SYS_fork 1
#define SYS_exit 2
#define SYS_wait 3
#define SYS_pipe 5
#define SYS_write 6
#define SYS_read 7
#define SYS_close 8
#define SYS_block 9
#define SYS_kill 10
#define SYS_exec 13
#define SYS_open 14
#define SYS_mknod 15
#define SYS_unlink 16
#define SYS_fstat 17
#define SYS_link 18
#define SYS_mkdir 19
#define SYS_chdir 20