gdb with postgres

Hi,
I was using gdb to debug postgres. In order to debug the backend of
running query, I start postgres first and use "select * from
pg_backend_pid()" to ask for backend pid. Then I start gdb in another bash
window with "gdb postgres" and attach the pid obtained above and set the
breakpoint. Then I run the query from the first window. However, the
debugging precess which is shown below is not going to the breakpoint. I
tried many different breakpoints, but it always start from the 305
client_read_ended().

GNU gdb 6.6
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "sparc-sun-solaris2.10"...
(gdb) b qp_add_paths_to_joinrel
Breakpoint 1 at 0x1a6744: file joinpath.c, line 67.
(gdb) attach 23903
Attaching to program `/usrlocal/pgsql/bin/postgres', process 23903
Retry #1:
Retry #2:
Retry #3:
Retry #4:
[New LWP 1]
0xff0cbaa4 in _rt_boot () from /usr/lib/ld.so.1
(gdb) n
Single stepping until exit from function _rt_boot,
which has no line number information.
secure_read (port=0x4a7760, ptr=0x455948, len=8192) at be-secure.c:305
305 client_read_ended();
(gdb) n
pq_recvbuf () at pqcomm.c:767
767 if (r < 0)
(gdb) n
769 if (errno == EINTR)
(gdb) n
782 if (r == 0)
(gdb) n
788 return EOF;
(gdb) n
791 PqRecvLength += r;
(gdb)

Any one know what is going wrong? BTW, as you can see, the system is
solaris.

--
Best Regards
Huang Qi Victor