I try to write simple c++ program that calls aarch64 assembly function. But when I try to link it i get this error:

usr/bin/ld: /tmp/ccQFRHpO.o: in function `read_file(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
main.cpp:(.text+0x1a4): undefined reference to `Distance(int, int, int, int)'
collect2: error: ld returned 1 exit status 

I know that this problem was posted many times, but I couldn’t fine solution for my case. There seems to be no mismatch function names.

Commands I run:

as odl.s -o odl.o

g++ main.cpp odl.o -o main

Content of my files:

main.cpp :

#include "functions.h"

using namespace std;

dane *glowa;

int main(int argc, char *argv[]){

    if(argc < 2)
        return 1;

    glowa = read_file("dane/" + string(argv[1]));


    return 0;
}

functions.h :

#include<omp.h>
#include<fstream>
#include<math.h>
#include<iostream>
#include<string>
#include<vector>

extern double Distance(int a, int b, int c, int d);

struct dane{
    double czas;
    unsigned char liczba_rdzeni;
    double *tablica;
};

dane* read_file(std::string file_name){

    dane *glowa = new dane;
    glowa->liczba_rdzeni = 1;

    std::vector<int> xy;
    int a;

        std::fstream in;
    in.open(file_name, std::ios::in);
    
    while (in>>a)
        xy.push_back(a);
    

    in.close();

    glowa->tablica = new double[(xy.size()/2)*(xy.size()/2)];

    for(int i = 0; i < (xy.size()/2); i += 2)
        for(int j = 0; j < (xy.size()/2); j += 2){

            if(j == i)
                glowa->tablica [i*(xy.size()/2)+j] = 0;
            else
                glowa->tablica [i*(xy.size()/2)+j] = Distance(xy[i], xy[i+1], xy[j], xy[j+1]);

        }


    return glowa;
}

odl.s :

global Distance
.section .text

Distance:
    add x0, x0, x2
    add x1, x1, x3
    mul x1, x1, x1
    madd x0, x1, x0, x0
    scvtf d0, x0
    fsqrt d0, d0
    ret