object file formats

[David Fokkema <fokkema at nat dot vu dot nl>]

Hi there!

I have a problem concerning object file formats. Because djgpp's linker 
doesn't support too many formats, I'm a bit limited when I try to 
interface asm with c. I use nasm v0.97 as assembler. The problem is that 
I want to write a loader and stub that to a 32bit c program. Because the 
loader executes from 16bit real mode (bootstrap) I can't use nasm's coff 
format since that doesn't support 16bit references. So I use Linux a.out 
format since djgpp seems to support that as i.386-a.out. The problem is 
that no external symbol used in the asm file is resolved in the output 
file. Jmps, calls etc. to c routines result in jmps and calls to 
0x00000000. When I declare external nonexisting symbols, ld doens't 
complain. I build some simple test files which are fully 32bit to test 
the differences between the coff and aout formats. Assembled using coff, 
ld outputs the correct file and complains if nonexisting symbols are 
used. Assembled using aout, every symbol is resolved as null. When I use 
objdump -i, I get error messages concerning an invalid header of the 
a.out object file format. Is this related to my problem? The test files I 
used are included in a zip file. Stub.asm is the correct stub for main.c. 
Makecoff.bat builds the binary using the coff format for stub.o and 
results in a correct output file, but unuseable as a loader. Makeaout.bat 
builds the same binary using the aout format for stub.o and results in an 
incorrect output file. Stub2.asm has a wrong symbol in it. Makec2.bat 
builds this using coff, and complains. Makea2.bat builds it using aout 
and doesn't complain. Objdump.out is my output for objdump -i and 
version.txt displays the versions I used. I compiled all using DOS. I 
hope you can help me out since it might be a bug in binutils. Of course, 
it could be something else.

Thanx in advance,

David Fokkema

E-mail: fokkema@nat.vu.nl

test.zip