By the way, you don't need to pass references.

sub_from_xs(my $num, my $str);
[download]

void
sub_from_xs(SV *num, SV *str)
    PREINIT:
        int nx;
        char *sx;
    CODE:
        nx = get_nx();
        sx = get_sx();

        sv_setiv_mg(num, nx);
        sv_setpv_mg(str, sx);
[download]

But I would personally prefer to see this function return a two element list.

my ($num, $str) = sub_from_xs();
[download]

void
sub_from_xs()
    PREINIT:
        int nx;
        char *sx;
    PPCODE:
        nx = get_nx();
        sx = get_sx();

        EXTEND(SP, 2);
        PUSHs(sv_2mortal(newSViv(nx)));
        PUSHs(sv_2mortal(newSVpv(sx, 0)));
[download]