C 언어 컴파일 에러가 나왔는데 이해하기가 힘들어요

root@ilya:/home/ilya/tools# gcc password.c
/usr/bin/ld: /tmp/ccoYZ8ot.o: in function `main':
password.c:(.text+0x24): undefined reference to `passwordU'
collect2: error: ld returned 1 exit status
root@ilya:/home/ilya/tools#
 
 
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
 
#define CRU 1
#define RMU 2
#define BUU 3
#define MFU 4
 
#define CREATE_USER 3, 1
#define REMOVE_USER 2, 2
#define BACK_UP_USER 2, 3
#define MODIFY_USER 2, 4
 
typedef struct UserLinkList
{
    struct userStruct* next;
    struct userStruct* prev;
}UserLinkList;
 
 
struct userStruct
{
    char name[30];
    int user_id;
    int userPassword;
    int limeitDay;
    UserLinkList link;
    int authority;
};
 
int passwordU(int args, ...);
struct userStruct* createU(struct userStruct* rootUser);
 
int main()
{
    struct userStruct rootUser;
    passwordU(3, 1, &rootUser, 1);
}
 
int passswordU(int args, ...)
{
    struct userStruct* rootUser;
    int flag;
    va_list ap;
    va_start(ap, args);
    flag = va_arg(ap, int);
 
    struct userStruct* new_user;
    rootUser = va_arg(ap, struct userStruct*);
    if (flag == CRU)
    {
        new_user = createU(rootUser);
        new_user->authority = va_arg(ap, int);
    }
    else if (flag == RMU)
    {
    }
    else if (flag == BUU)
    {
    }
    else if (flag == MFU)
    {
    }
    else
    {
        return -1;
    }
    va_end(ap);
    return 0;
}
 
struct userStruct* createU(struct userStruct* rootUser)
{
    size_t uS_size = sizeof(struct userStruct);
    struct userStruct* new_user;
    struct userStruct* perv_user = rootUser;
    struct userStruct* next_user = rootUser;
    new_user = (struct userStruct*)malloc(uS_size);
 
    while (1)
    {
        if (next_user->link.next == 0)
        {
            next_user->link.next = new_user;
            new_user->link.prev = next_user;
            break;
        }
        next_user = perv_user->link.next;
        perv_user = next_user;
    }
    return 0;
}