Cannot get simple shellcode runner to work

I'm just trying to execute shellcode directly from the command line. I send a simple 0x90 NOP and get a segmentation fault?

root@server:~# gcc shellcode.c -o shellrun -fno-stack-protector

root@server:~# ./shellrun `perl -e 'print "\x90"'`
Segmentation fault (core dumped)

root@server:~# more shellcode.c
int main(int argc, char *argv[])
{
        (*(void(*)())argv[1])();
        return 0;
}