SYSCALL3(_SysFDFlags, SYS_FDCTL) // int, int, int
SYSCALL1(_SysClose, SYS_CLOSE) // int
SYSCALL3(_SysRead, SYS_READ) // int, uint, void*
+SYSCALL5(_SysReadAt, SYS_READAT) // int, uint, uint64, void*
SYSCALL3(_SysWrite, SYS_WRITE) // int, uint, void*
+SYSCALL5(_SysWriteAt, SYS_WRITEAT) // int, uint, uint64, void*
SYSCALL4(_SysSeek, SYS_SEEK) // int, uint64_t, int
SYSCALL1(_SysTell, SYS_TELL) // int
SYSCALL3(_SysFInfo, SYS_FINFO) // int, void*, int