GDB X Postgresql 8 - Failed to read a valid object file image from memory

Hi!

I tried to use GDB with postgresql 8 and I didnt have success.
Can you help me?
I tried like as I did in postgresql 7.4
I run configure like this: ./configure --prefix=/usr/local/pgsql8
--enable-debug --enable-cassert --enable-depend
After, I run "make", "make install", "initdb"
After this, I tried run gdb, but I dont enter in backend.
See this:
postgres(at)debian:/home/anacrl$ gdb postgres
GNU gdb 6.8
Copyright (C) 2008 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 "i686-pc-linux-gnu"...
(gdb) run
Starting program: /usr/local/pgsql8/bin/postgres
Failed to read a valid object file image from memory.
LOG: database system was shut down at 2008-05-01 22:56:41 BRT
LOG: database system is ready to accept connections
LOG: autovacuum launcher started

So, I think that have something wrong (Failed to read a valid object file
image from memory).
Can you help me?
I tried run psql and attached process pid too, but no success. :-(

Thanks,
Ana Carolina