SV* my_sv = newSViv(12345);
XPUSHs(my_sv);

##</code><code>##

SPAGAIN;
ENTER;
SAVETMPS;
PUSHMARK(SP);

call_pv( "a_perl_sub_that_return_something", some_flags );

SV* return = POPs;

FREETMPS;
LEAVE;