pthread function in testing print weird messages to stderr

["Britton Kerin" <bkerin@fastmail.fm>]

This minimal program, test_threads.c:

   #include <assert.h>
   #include <pthread.h>
   #include <stdio.h>
   #include <stdlib.h>

   int thread_return;

   void *
   thread_function (void *arg)
   {
     int idx;
     for ( idx = 0 ; idx < 3 ; idx++ ) {
       sleep (1);
       printf ("thread_arg: %d\n", *((int *)arg));
     }

     thread_return = 42;

     pthread_exit (&thread_return);
   }


   int
   main (void)
   {
     int thread_arg = 2;
     pthread_t thread;
   
     int return_code;

     //  pthread_attr_t thread_attrs;
     //  return_code = pthread_attr_init (&thread_attrs);
    
     return_code = pthread_create (&thread, NULL, thread_function, 
				(void *) &thread_arg);
     assert (return_code == 0);

     int **return_location;
     return_code = pthread_join (thread, (void **) return_location);
     assert (return_code == 0);
 
     printf ("thread_return: %d\n", **return_location);

     return 0;
   }

Compiled this way:

   gcc -Wall -D_REENTRANT test_threads.c -lpthread -o test

without any errors or warnings, produces this output when run:

   thread_arg: 2
   thread_arg: 2
   thread_arg: 2
   thread_return: 42
         1581:
         1581:     runtime linker statistics:
         1581:                final number of relocations: 139
         1581:     final number of relocations from cache: 7

with the latter four lines being on stderr.  Is there some debugging
information that didn't get turned off or something?  I guess this 
might be a libc bug report?

Uncommenting the lines that set up the thread_attrs structure and
passing a pointer to it to pthread_create insteal of NULL as the 
second argument yields a different weird output:

   thread_arg: 2
   thread_arg: 2
   thread_arg: 2
   thread_return: 42
      1598:     binding file /lib/tls/libpthread.so.0 to
      /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
      1598:     binding file /lib/libgcc_s.so.1 to /lib/tls/libc.so.6:
      normal symbol `__cxa_finalize' [GLIBC_2.1.3]

Any clues as to what is going on here would be greatly appreciated.

Thanks,
Britton
-- 
  Britton Kerin
  bkerin@fastmail.fm