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Mail Archives: djgpp/2002/04/15/11:15:08

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From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Another GAS problem
Date: 15 Apr 2002 15:13:21 GMT
Organization: Aachen University of Technology (RWTH)
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Jacky Luk <luckie AT netvigator DOT com> wrote:

>    I have posted on this question in this arena before. In GAS, how
> do u load the segment address into ES when dealing with BIOS
> interrupts like the 13h ?

Most of the time you don't, because the graphics BIOS can't use the
internal memory space of your 32bit app anyway, even if you do pass it
the right selector.  Int 13h is 16bit by nature, and simply doesn't
understand 32bit addresses.  If you're *sure* your 'bootbuffer' really
is in the first 1MB of real memory, you could use symbolic assembler
calculation to split it into segment and offset and use those.

>  movw bootbuffer, %bx  <--- I knew this one already
>                                              movw -4(%ebp), %ebx

Then you know this one incorrectly, I think.  -4(%epb) is an address
somewhere on the stack, whereas you want to access a *global* variable
named 'bootbuffer' and defined elsewhere in your assembly source.

>  movw .data, %es  <-- but what about this?

This doesn't exist, because GAS doesn't know anything about segments.
It's a 32bit flat world it assumes.

-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.

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