DOS ain't dead

a.out (Developers)

posted by boeckmann, Aachen, Germany, 13.10.2025, 19:45

> Oh - I also see in my code that I have:
>
> mov cx, offset DGROUP:_edata
>
> My initial reaction is - how on earth does this work? That's an incomplete
> address. In large/huge memory model, how does a.out carry the required
> information to know that I just want the offset portion?
>
> If that's not magic, I don't know what is.

If objdump works on this, it may give you some insight, especially if it is able to dump the relocation entries. Which a.out flavor exactly do the tools you use emit? To my knowledge, there are many variations of the a.out format. Without knowing the EXACT a.out variant, one can only guess:

Technically it should not take much to make this work. In the relocation table, there is most likely a section or symbol relative offset fixup for this, and DGROUP may map for example to the a.out initialized data section or a symbol. Segment fixups should be harder, as the a.out specifications I skimmed over do not seem to have support for this...

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Complete thread:

a.out - kerravon, 13.10.2025, 16:03
- a.out - kerravon, 13.10.2025, 16:22
  - a.out - kerravon, 13.10.2025, 16:24
  - a.out - boeckmann, 13.10.2025, 19:45