Add new function in pam_syslog.c

Question

My code uses Pam library for user authentication. When the there is a failure to login. I would need to print syslog message in a specific format, instead of the current syslog format in the function pam_vsyslog of libpam library.

I intend to write a new function that would write syslog in my required format.

Below are definitions : in file pam_ext.h

extern void PAM_FORMAT((printf, 3, 0)) PAM_NONNULL((3))
pam_kniwx_vsyslog (const pam_handle_t *pamh, int priority,
             const char *fmt, va_list args);

extern void PAM_FORMAT((printf, 3, 4)) PAM_NONNULL((3))
pam_kniwx_syslog (const pam_handle_t *pamh, int priority, const char *fmt, ...);

Implementation: libpam/libpam/pam_syslog.c


pam_kniwx_vsyslog (const pam_handle_t *pamh, int priority,
             const char *fmt, va_list args)
{
  char *msgbuf2 = NULL;
  int save_errno = errno;

  
  errno = save_errno;
  if (vasprintf (&msgbuf2, fmt, args) < 0)
    {
      syslog (LOG_AUTHPRIV|LOG_ERR, "vasprintf: %m");
      _pam_drop (msgbuf1);
      return;
    }

  errno = save_errno;
  syslog (LOG_AUTHPRIV|priority, "%s", msgbuf2);

  _pam_drop (msgbuf2);
}

void
pam_kniwx_syslog (const pam_handle_t *pamh, int priority,
            const char *fmt, ...)
{
  va_list args;

  va_start (args, fmt);
  pam_kniwx_vsyslog (pamh, priority, fmt, args);
  va_end (args);
}

In case of authentication failure I would like to invoke pam_kniwx_syslog from libpam/modules/pam_unix/support.c function :

pam_kniwx_syslog(pamh, LOG_NOTICE,
"authentication failure; "
"logname=%s uid=%d euid=%d "
tty=%s ruser=%s rhost=%s "
"%s%s",
new->name, new->uid, new->euid,
tty ? (const char *)tty : "",
ruser ? (const char *)ruser : "",
rhost ? (const char *)rhost : "",
new->user && new->user[0] != '\0')
? " user=" : "",
new->user
);

With this change When I compile the code, I seem to run into undefined reference in spite having the definitions and the header file inclusion.

/usr/src/debug/libpam/1.3.0-r5/libpam-1.3.0/modules/pam_unix/../../../../../../../../libpam/modules/pam_unix/support.c:850: undefined reference to `pam_kniwx_syslog'
collect2: error: ld returned 1 exit status
 Makefile:799: recipe for target 'pam_unix.la' failed
 make[3]: *** [pam_unix.la] Error 1
make[3]: Leaving directory  

Any help to resolve the issue is much appreciated.