How to relocate for COFF object files?

[David Lin]

Dear all:
 
There is a question encountered.
 

While handing COFF object file generated by gcc, 

I have to retrieve the executable portion 

(such as text section, data section and bss section) 
from object file,
and make the executable portion REALLY 
executable 
so that it could be insert into the system and 
can be executed.
 
That is, I am working similiarly to the linker 
ld.
 
The most difficult part of my work is 
relocation.
 
Here comes the question
How do bytes needed relocation in object file differ 
from others?
The structure defined for relocation 
entries leaves a field r_symndx to the symbol index it referring 
to,
and leaves another field r_type to 
indicate how it relocates.
Do all kind of types need 
relocation?
or how does the relocation be performed?
 
For the arm-coff case, the value of r_type might be 
defined in coff-arm.c

(bintuils/bfd/coff-arm.c)
such as ARM_8, ARM_16, ARM_32, etc.
Several values is defined in internal.h
(binutils/include/coff/internal.h)
such as R_DIR16, R_DIR32, R_IMAGEBASE, R_RELBYTE, R_RELWORD 
and R_RELLONG, etc.
I am confued that which class of values indicates the arm-coff 
r_type.
For an unconfirmed suggestion, bytes needing relocation with its r_type is 
R_RELLONG
(case in m68k )
 
Is there any place could I find the answer?
 
David