From: ams AT ludd DOT luth DOT se (Martin Str|mberg)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: How to change Executable format to my own?
Date: 9 Jul 1999 22:02:36 GMT
Organization: University of Lulea, Sweden
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Christopher Nelson (paradox AT gye DOT satnet DOT net) wrote:
: >Sorry, I don't understand.  How can two sections begin at the same
: >address (zero)?
: 
: 
: intel x86 architecture allows using segment registers for separate data,
: code, stack, and 2 extra segments.  each segment may have it's own base, so
: in a fully segmented architecture, it's completely allowable to have data
: AND code a 0.
: 
: alternatively, for DJGPP programs used as boot-loaders, or for operating
: systems, you can have the compiler stick stuff where it wants to, then
: subtract the data segment base to assume a base of 0.  from there it is
: simply neccessary to properly initizlise the DS segment selector properly,
: and you have 0-based data.  since code is already at 0, you can just stick
: it in another similiar, but code-marked, segment.

But it's run in protected mode so the segments are selectors. Now
different selectors can point to diffent places, but if you point them
both at base=0, and expect code at address 0 not interfere with data
at address 0, I think you're misstaken. But I'm not an assembly guy,
so I could be wrong. Please correct me if so.


Skunk Anansie, Paranoid & Sunburnt,

								MartinS