#ifdef HAS_PROCSELFEXE
/* This is a function so that we don't hold on to MAXPATHLEN
   bytes of stack longer than necessary
 */
STATIC void
S_procself_val(pTHX_ SV *sv, const char *arg0)
{
    char buf[MAXPATHLEN];
    int len = readlink(PROCSELFEXE_PATH, buf, sizeof(buf) - 1);

    /* On Playstation2 Linux V1.0 (kernel 2.2.1) readlink(/proc/self/exe)
       includes a spurious NUL which will cause $^X to fail in system
       or backticks (this will prevent extensions from being built and
       many tests from working). readlink is not meant to add a NUL.
       Normal readlink works fine.
     */
    if (len > 0 && buf[len-1] == '\0') {
      len--;
    }

    /* FreeBSD's implementation is acknowledged to be imperfect, sometimes
       returning the text "unknown" from the readlink rather than the path
       to the executable (or returning an error from the readlink).  Any valid
       path has a '/' in it somewhere, so use that to validate the result.
       See http://www.freebsd.org/cgi/query-pr.cgi?pr=35703
    */
    if (len > 0 && memchr(buf, '/', len)) {
        sv_setpvn(sv,buf,len);
    }
    else {
        sv_setpv(sv,arg0);
    }
}
#endif /* HAS_PROCSELFEXE */

STATIC void
S_set_caret_X(pTHX) {
    dVAR;
    GV* tmpgv = gv_fetchpvs("\030", GV_ADD|GV_NOTQUAL, SVt_PV); /* $^X */
    if (tmpgv) {
#ifdef HAS_PROCSELFEXE
        S_procself_val(aTHX_ GvSV(tmpgv), PL_origargv[0]);
#else
#ifdef OS2
        sv_setpv(GvSVn(tmpgv), os2_execname(aTHX));
#else
        sv_setpv(GvSVn(tmpgv),PL_origargv[0]);
#endif
#endif
    }
}