Why argv is allways (NULL) in my execve system call monitor

I wrote lkm hook that monitor the execve system call it basically should print the parameter of the char ** argv .and i tried to print the argv but it didn't worked i must say that the filename parameter and the env variable were printed fine but when i print the argv the result is

(NULL)

when i run the ls -all command or any other programthis is my code

char argv[100];char **mid;asmlinkage long our_execl(struct pt_regs *tr){copy_from_user(mid,tr->cx,100);strncpy_from_user(argv,mid[1], 253);printk("%s\n",argv);}