best place for xstrdup

As suggested by Bruce Mojiman I'm working on
substitute some strdup not checked with xstrdup.

I seen that in the backend source tree there is no
xstrdup ( there is one in bin/psql tree) ,
I wrote it and inserted temporarelly in
backend/utils/mmgr/aset.c

I don't know exactly how work the error report
mechanism sso before to submit a wrong implementation
this was what I wrote:

char *xstrdup(const char *string)
{
char * ret_value;

if ( !string ) {
elog(ERROR, "xstrdup called with a NULL pointer");
}

ret_value = strdup( string );

if ( !ret_value ) {
ereport(FATAL,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("strdup out of memory")));
}

return ret_value;
}

if this implementation is ok where is the best place ?

Regards
Gaetano Mendola