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Index > DOS > Working with segments in MZ executable

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Trinitek



Joined: 06 Nov 2011
Posts: 257
Trinitek
Alright guys, I'm having a bit of trouble here. My COM program got so big that I had to switch over to the MZ format, and there's only one problem with that.

Code:
format MZ
heap 0
entry Main:Start

segment Main use16
Start:
push Data     ;apparently you can't do this. Sad
pop DS
;...rest of the code

segment Data use16
text_string DB "Here's some data.",0    


The problem is that I need to get the segment value of Data into DS. How do I go about doing that? What's the syntax for doing something like that?

Thanks.
Post 08 Dec 2011, 02:08
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freecrac



Joined: 19 Oct 2011
Posts: 117
Location: Germany Hamburg
freecrac
Trinitek wrote:
Alright guys, I'm having a bit of trouble here. My COM program got so big that I had to switch over to the MZ format, and there's only one problem with that.

Code:
format MZ
heap 0
entry Main:Start

segment Main use16
Start:
push Data     ;apparently you can't do this. Sad
pop DS
;...rest of the code

segment Data use16
text_string DB "Here's some data.",0    


The problem is that I need to get the segment value of Data into DS. How do I go about doing that? What's the syntax for doing something like that?

Thanks.

With searching for "mov data flat assembler" it is easy to find an answer, because the second result pointed to this thread: http://board.flatassembler.net/topic.php?t=12588

Dirk
Post 08 Dec 2011, 03:45
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Trinitek



Joined: 06 Nov 2011
Posts: 257
Trinitek
freecrac wrote:
Trinitek wrote:
Alright guys, I'm having a bit of trouble here. My COM program got so big that I had to switch over to the MZ format, and there's only one problem with that.

Code:
format MZ
heap 0
entry Main:Start

segment Main use16
Start:
push Data     ;apparently you can't do this. Sad
pop DS
;...rest of the code

segment Data use16
text_string DB "Here's some data.",0    


The problem is that I need to get the segment value of Data into DS. How do I go about doing that? What's the syntax for doing something like that?

Thanks.

With searching for "mov data flat assembler" it is easy to find an answer, because the second result pointed to this thread: http://board.flatassembler.net/topic.php?t=12588

Dirk


I had searched before I posted, but apparently I wasn't using the right keywords. Wink Thanks a lot!

Now for one more question: I can't directly push the segment Data into the stack like how I have it written in my example? Not that it's a problem, but I'd like to know for future reference.
Post 08 Dec 2011, 03:56
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freecrac



Joined: 19 Oct 2011
Posts: 117
Location: Germany Hamburg
freecrac
Trinitek wrote:
Now for one more question: I can't directly push the segment Data into the stack like how I have it written in my example? Not that it's a problem, but I'd like to know for future reference.

mov ax, Data
mov ds, ax

push ax ; only if you need

Dirk
Post 08 Dec 2011, 05:04
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7802
Location: Kraków, Poland
Tomasz Grysztar
Trinitek wrote:
Now for one more question: I can't directly push the segment Data into the stack like how I have it written in my example? Not that it's a problem, but I'd like to know for future reference.
You can directly push the segment value, the problem here is that you use a reserved keyword "data", which for fasm means something different. Just rename the segment to avoid this problem:
Code:
format MZ
heap 0 
entry Main:Start 

segment Main use16 
Start: 
push DataSeg
pop DS 

segment DataSeg use16
text_string DB "Here's some data.",0    
Post 08 Dec 2011, 06:43
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freecrac



Joined: 19 Oct 2011
Posts: 117
Location: Germany Hamburg
freecrac
Tomasz Grysztar wrote:
You can directly push the segment value, the problem here is that you use a reserved keyword "data", which for fasm means something different. Just rename the segment to avoid this problem:

Ah, good to know how to solve this problem.

Quote:

Code:
format MZ
heap 0 
entry Main:Start 

segment Main use16 
Start: 
push DataSeg
pop DS 

segment DataSeg use16
text_string DB "Here's some data.",0    

But i think only for to store a segment address into a segment register we did not need to access the stack. I think it is often better to use only register for to do this instead, to prevent a slow ram access to the stack.

Dirk
Post 08 Dec 2011, 10:41
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AsmGuru62



Joined: 28 Jan 2004
Posts: 1419
Location: Toronto, Canada
AsmGuru62
So, how exactly the COM got big? Just curious, because, there are a lot of memory there if I recall - about 550K which laid out AFTER the COM image ends (CS + 64Kb is where it begins). You can plan it as you go. Load files there or whatever. Do you have a lot of strings? You can load strings from a file. etc.

If all I assume is false, then just your code must have got to over 64Kb - very impressive! How much time you coded it?
Post 08 Dec 2011, 15:12
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Trinitek



Joined: 06 Nov 2011
Posts: 257
Trinitek
AsmGuru62 wrote:
So, how exactly the COM got big? Just curious, because, there are a lot of memory there if I recall - about 550K which laid out AFTER the COM image ends (CS + 64Kb is where it begins). You can plan it as you go. Load files there or whatever.


I wasn't aware at the time that I could do this. I'll have to look into it sometime...

Quote:
Do you have a lot of strings? You can load strings from a file. etc.


I'm working with a bitmap image that takes up about 65,000 bytes. I also have a few text strings thrown in there as well. I kept going over the memory limit by only a few bytes which kept cutting off the last few pixels on the image when it writes it to the screen and I couldn't optimize the code any further to try to get it to fit.

But now that I've switched over to the MZ model, there aren't any problems now. Everything is working like it's supposed to. Smile
Post 10 Dec 2011, 18:53
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AsmGuru62



Joined: 28 Jan 2004
Posts: 1419
Location: Toronto, Canada
AsmGuru62
Cool stuff!
Post 11 Dec 2011, 00:49
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