About bfd in gdb

[libra]

Hello,all:

About the gdb source code, I have some questions.

I will use "ARM" for my example.

In the gdb source code architecture,when you build the gdb(ex: target=arm-efl)
,you can find that first you will build bfd and opcodes that the same as 
binutils, then build the gdb and sim.

My question is that :

Why we must build the bfd and opcodes parts that the same as in binutils (like 
archures.c reloc.c arm-dis.c and arm-opc.h and so on)

My idea is that :
We just need to build bfd inoder to recognize the input file format,then
i can use the gdb to connect to simulator(sim),after that, I can run my own 
program.

So, the aboved mentioned file (ex: arm-dis.c and arm-opc.h), why is those file 
must be built again. It seem does not be used in gdb.


                                                      thanks a lot!!