An example program to understand the Calling Convention used for 64-bit Binaries.

sum.c

#include <stdio.h>

int sum(int, int, int, int);

int main(int argc, char **argv)
{
    int result = 0;
    result = sum(1,2,3,4);
   
    printf("The sum is: %d\n", result);
   
    return 0;
}

int sum(int a, int b, int c, int d)
{
    int e = 0;
    e = a + b + c + d;
    return e;
}