specify entry point of a c/c++ program instead of main

no_main.c

#include <stdio.h>
#include <stdlib.h>

/*extern "C"*/ int sum(int a, int b)
{
    return 2 * a + 3 * b;
}

/*extern "C"*/ int entry()
{
    printf("this is call from function test\n");
    printf("result of sum(1,2) = %d\n", sum(1,2));
    exit(0);
}

//int main()
//{
//    printf("this is call from function main\n");
//    return 0;
//}

// compile command
// gcc -fPIE -nostartfiles no_main.c -Wl,-eentry -o no_main
or
// gcc -fPIE -nostartfiles -e entry no_main.c -o no_main