#in perlcall, you have to use ENTER,SAVETMPS, FREETMPS, LEAVE to free mortal variables
 dSP;

    ENTER;
    SAVETMPS;

    PUSHMARK(SP);
    EXTEND(SP, 2);
    PUSHs(sv_2mortal(newSVpv(a, 0)));
    PUSHs(sv_2mortal(newSViv(b)));
    PUTBACK;

    call_pv("LeftString", G_DISCARD);

    FREETMPS;
    LEAVE;

#in XS, you don't have to do that:
void
rpcb_gettime(host)
     char *host
   PREINIT:
     time_t  timep;
     bool_t  status;
   PPCODE:
     status = rpcb_gettime( host, &timep );
     EXTEND(SP, 2);
     PUSHs(sv_2mortal(newSViv(status)));
     PUSHs(sv_2mortal(newSViv(timep)));