screen broken on Slackware-current?

Dear All,
     I am running Slackware-current (32-bit) and have not been able to run
screen (the screen manager program) for some time now.  It fails with

$ screen
Bad tty '/dev/pts/0'

Digging into the source, the problem is in CheckTtyname() in tty.c
which calls the realpath() function on the pty device name which
returns a NULL pointer result for the canonicalized pathname.

The problem is not related to the target being a device special file
as the following demo code (largely copied from CheckTtyname() in
tty.c) reproduces,

/tmp/screen-4.3.1$ cat tomdeb.c
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <errno.h>

int main(int argc, char **argv) {
  char *tty;
  {
    char * real;
    char resolved_path[PATH_MAX];
    errno=0;

    tty = argv[1];

    printf ("argv[1]=\"%s\"\n", argv[1]);

    printf ("PATH_MAX=%d\n", PATH_MAX);

    real = realpath(tty,resolved_path);
    perror ("call1");
    printf ("tty=\"%s\" real=\"%s\" resolved_path=\"%s\"\n", tty, real, resolved_path);

    real = realpath(tty, NULL);
    perror ("call2");
    printf ("tty=\"%s\" real=\"%s\"\n", tty, real);
    if (!real) {
      printf ("returning -1\n");
      return -1;
    }

    free(real);
    return 0;
  }
}

/tmp/screen-4.3.1$ cc -Wall -o tomdeb tomdeb.c
/tmp/screen-4.3.1$ ./tomdeb $PWD/tomdeb.c
argv[1]="/tmp/screen-4.3.1/tomdeb.c"
PATH_MAX=4096
call1: Success
tty="/tmp/screen-4.3.1/tomdeb.c" real="/tmp/screen-4.3.1/tomdeb.c" resolved_path="/tmp/screen-4.3.1/tomdeb.c"
call2: Invalid argument
tty="/tmp/screen-4.3.1/tomdeb.c" real="(null)"
returning -1


The first call to realpath() returns the expected result but the
second call which is as used in CheckTtyname() in tty.c returns a NULL
pointer.  According to the man page,

> char *realpath(const char *path, char *resolved_path);
>
> If resolved_path is specified as NULL, then realpath() uses malloc(3)
> to allocate a buffer of up to PATH_MAX bytes to hold the resolved
> pathname, and returns a pointer to this buffer.

The man page also reports,

> EINVAL path is NULL.  (In glibc versions before 2.3, this error is
> also returned if resolved_path is NULL.)

Slackware-current is using glibc-2.21.

I also tried the demo code on an old Slackware 11.1 system which has
glibc-2.5 and it displays the same fault but screen works.  Checking
the screen-4.0.3 source code (the version installed on my
Slackware-11.1 system) reveals it does not use realpath().  Finally I
tried the demo code on SLC5 & SLC6 (based on RHEL5 & RHEL6) systems
where both calls return the correct results.

Does anyone else have this problem with screen on their
Slackware-current systems?  Googling the error did now show much of
interest...

I am running a 3.18.11 kernel.

Regards
Tom Crane

Ps. Also posted to alt.os.linux.slackware
-- 
Tom Crane, Dept. Physics, Royal Holloway, University of London, Egham Hill,
Egham, Surrey, TW20 0EX, England. 
Email:  T dot Crane at rhul dot ac dot uk
Fax:    +44 (0) 1784 472794