#Value.pm   (no package declaration)
sub getValue 
{
...  
}
1;

#MainModule.pm
package MainModule
{
   use ExtraModule;
   ExtraModule::doSomething();

   require Value;
   $x = 'getValue';
   &$x();   #does not work at all

}

#ExtraModule.pm
package ExtraModule
{
    sub doSomething()
    {
       require Value;
       $x = 'getValue';
       &$x();   #works fine
    }
}