Your code is just defining the subroutines within the A namespace. You could use caller to return the namespace in which you want the subroutine exported.

sub build_funcs {
    my $package = caller;
    foreach ('A', 'B', 'C') {
        eval  "
        print \"building $_ func\\n\";
        sub $package\::${_}_func {
            print \"$_ func called\\n\";
        }
        ";
        push @EXPORT, "${_}func";
    }
}
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Of course, you could also use AutoLoader in combination with @ISA in your test script to have an AUTOLOAD that creates the subroutine for you. Also, on a side note, don't get in the habit of calling subroutines as &sub unless you know why you're doing it. Instead use sub(). Read perldoc perlsub for more information about it. I hope this helps you with your problem.