thanks for spotting the typo. it still failed to compile and it still fails at the assembler stage. many of the assembler messages are :

8(%rdi)' is not a valid 32 bit base/index expression
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yet i am on a 64b opteron. all the perl packages are 64b. could it be that another flag is needed to tell the assembler this?

anyway, the XS file is :

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "INLINE.h"

void inc_refcnt(SV * sv ) {
    SvREFCNT_inc(sv);
}
SV * get_refcnt(SV * sv) {
    return newSVuv(svREFCNT(sv));
}


MODULE = exp_pl_aa05    PACKAGE = main  
PROTOTYPES: DISABLE

void
inc_refcnt (sv)
        SV *    sv
        PREINIT:
        I32* temp;
        PPCODE:
        temp = PL_markstack_ptr++;
        inc_refcnt(sv);
        if (PL_markstack_ptr != temp) {
          /* truly void, because dXSARGS not invoked */
          PL_markstack_ptr = temp;
          XSRETURN_EMPTY; /* return empty stack */
        }
        /* must have used dXSARGS; list context implied */
        return; /* assume stack size is correct */

SV *
get_refcnt (sv)
        SV *    sv
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the resulting C code is :

/*
 * This file was generated automatically by xsubpp version 1.9508 from
+ the 
 * contents of exp_pl_aa05.xs. Do not edit this file, edit exp_pl_aa05
+.xs instead.
 *
 *      ANY CHANGES MADE HERE WILL BE LOST! 
 *
 */

#line 1 "exp_pl_aa05.xs"
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include "INLINE.h"

void inc_refcnt(SV * sv ) {
    SvREFCNT_inc(sv);
}
SV * get_refcnt(SV * sv) {
    return newSVuv(svREFCNT(sv));
}


#line 24 "exp_pl_aa05.c"
XS(XS_main_inc_refcnt)
{
    dXSARGS;
    if (items != 1)
        Perl_croak(aTHX_ "Usage: main::inc_refcnt(sv)");
    SP -= items;
    {
        SV *    sv = ST(0);
#line 23 "exp_pl_aa05.xs"
        I32* temp;
#line 35 "exp_pl_aa05.c"
#line 25 "exp_pl_aa05.xs"
        temp = PL_markstack_ptr++;
        inc_refcnt(sv);
        if (PL_markstack_ptr != temp) {
          /* truly void, because dXSARGS not invoked */
          PL_markstack_ptr = temp;
          XSRETURN_EMPTY; /* return empty stack */
        }
        /* must have used dXSARGS; list context implied */
        return; /* assume stack size is correct */
#line 46 "exp_pl_aa05.c"
        PUTBACK;
        return;
    }
}

XS(XS_main_get_refcnt)
{
    dXSARGS;
    if (items != 1)
        Perl_croak(aTHX_ "Usage: main::get_refcnt(sv)");
    {
        SV *    sv = ST(0);
        SV *    RETVAL;

        RETVAL = get_refcnt(sv);
        ST(0) = RETVAL;
        sv_2mortal(ST(0));
    }
    XSRETURN(1);
}

#ifdef __cplusplus
extern "C"
#endif
XS(boot_exp_pl_aa05)
{
    dXSARGS;
    char* file = __FILE__;

    XS_VERSION_BOOTCHECK ;

        newXS("main::inc_refcnt", XS_main_inc_refcnt, file);
        newXS("main::get_refcnt", XS_main_get_refcnt, file);
    XSRETURN_YES;
}
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