Description of problem:
When building an application against an alternate build of glibc (with -Wl,--dynamic-linker and -Wl,-rpath) the debugger issues an odd auto-load safe-path warning that doesn't quite work nor is it correct.

Version-Release number of selected component (if applicable):
gdb-7.6.1-42.fc19.x86_64

How reproducible:
Always reproducible.

Steps to reproduce:
cat >> thread.c <<EOF
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *
myfunc (void *arg)
{
  printf ("myfunc!\n");
  return NULL;
}

int
main (void)
{
  pthread_t mythread;
  int ret;
  void *retval;

  ret = pthread_create (&mythread, NULL, myfunc, NULL);

  if (ret != 0)
    {
      printf ("FAIL: pthread_create failed with %d\n", ret);
      exit (1);
    }
  else
    ret = pthread_join (mythread, &retval);

  if (ret != 0)
    {
      printf ("FAIL: pthread_join failed with %d\n", ret);
      exit (1);
    }

  return 0;
}
EOF

# Use the normal linker script but without all the distro-specific SEARCH_DIR paths.

ld --verbose | tail -n +11 | sed -e 's,SEARCH_DIR.*,,g' -e 's,===.*,,g' > link.script

# Compile the object file.
gcc -c thread.c

# Link against the alternate glibc build.
ld -Map link.map -T link.script --build-id --no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker /home/carlos/build/glibc/elf/ld.so -o thread /home/carlos/build/glibc/csu/crt1.o /home/carlos/build/glibc/csu/crti.o /usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtbegin.o -L/home/carlos/build/glibc -L/home/carlos/build/glibc/dlfcn -L/home/carlos/build/glibc/nptl -L/home/carlos/build/glibc/nss -L/home/carlos/build/glibc/nptl_db -L/home/carlos/build/glibc/csu -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2 -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../.. --dynamic-linker=/home/carlos/build/glibc/elf/ld.so -rpath=/home/carlos/build/glibc:/home/carlos/build/glibc/dlfcn:/home/carlos/build/glibc/nptl:/home/carlos/build/glibc/nss:/home/carlos/build/glibc/nptl_db /home/carlos/build/glibc/elf/ld.so -lpthread /home/carlos/build/glibc/nptl/libpthread_nonshared.a ./thread.o -lgcc --as-needed -lgcc_s --no-as-needed -lc /home/carlos/build/glibc/libc_nonshared.a -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtend.o /home/carlos/build/glibc/csu/crtn.o

Actual results:

[carlos@koi tmp]$ gdb thread
GNU gdb (GDB) Fedora 7.6.1-42.fc19
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/carlos/support/2013-11-22/tmp/thread...done.
(gdb) 
(gdb) r
Starting program: /home/carlos/support/2013-11-22/tmp/thread 
warning: File "/home/carlos/build/glibc/nptl/libthread_db.so.1" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load:/usr/bin/mono-gdb.py".
To enable execution of this file add
	add-auto-load-safe-path /home/carlos/build/glibc/nptl/libthread_db.so.1
line to your configuration file "/home/carlos/.gdbinit".
To completely disable this security protection add
	set auto-load safe-path /
line to your configuration file "/home/carlos/.gdbinit".
For more information about this security protection see the
"Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:
	info "(gdb)Auto-loading safe path"
warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.
myfunc!
[Inferior 1 (process 27628) exited normally]
(gdb) 

# Note that /home/carlos/build/glibc/nptl/libthread_db.so.1 is actually the wrong path, it should be /home/carlos/build/glibc/nptl_db/libthread_db.so.1.

(gdb) add-auto-load-safe-path /home/carlos/build/glibc/nptl/libthread_db.so.1
(gdb) r
Starting program: /home/carlos/support/2013-11-22/tmp/thread 
warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.
myfunc!
[Inferior 1 (process 27748) exited normally]
(gdb) 

# So the recommendation doesn't work.

(gdb) set auto-load safe-path /
(gdb) r
Starting program: /home/carlos/support/2013-11-22/tmp/thread 
warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.
myfunc!
[Inferior 1 (process 27846) exited normally]
(gdb) 

# Completely disabling doesn't work either. What about the old preload trick?

[carlos@koi tmp]$ LD_PRELOAD=/home/carlos/build/glibc/nptl_db/libthread_db.so.1 gdb thread
GNU gdb (GDB) Fedora 7.6.1-42.fc19
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/carlos/support/2013-11-22/tmp/thread...done.
(gdb) r
Starting program: /home/carlos/support/2013-11-22/tmp/thread 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/home/carlos/build/glibc/nptl_db/libthread_db.so.1".
[New Thread 0x7ffff7608700 (LWP 27913)]
myfunc!
[Thread 0x7ffff7608700 (LWP 27913) exited]
[Inferior 1 (process 27909) exited normally]
(gdb) 

# OK, that works.

Expected results:

The auto-load safe-path warning should talk about /home/carlos/build/glibc/nptl_db/libthread_db.so.1, and it should be able to load that DSO without me needing to preload it.

I know this is a corner case, but I filed it anyways just to make the gdb team aware of the issues I saw while debuggin an alternate runtime.