output = sv_newmortal();
output_len = 8;
if (!SvUPGRADE(output, SVt_PV))
(void)SvUPGRADE(output, SVt_PV);
croak("cannot use output argument as lvalue");
perl_des_crypt(input, SvGROW(output, output_len), (i32 *)ks, enc_flag);