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What happened in this cleanup procedure?

Posted on 1998-06-13
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Last Modified: 2011-08-18
Dear All,
     I've got a C program which also contains assembly code.
The 'C' program first calls an assembly routine that does mode setting job. The program have to gain access to a data segment, so I did this mov ax, seg_b and mov ds, ax at the beginning.but when I add these statments into the assembly routine,then there comes some problems concerning the cleanup procedure. If I deleted them, the program works fine.
Why did this happen?

Jacky
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Question by:whluk
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nietod earned 50 total points
ID: 1165830
The code expects that DS will still be pointing to the segment it originally was.  Just restore the original DS when you are done with the assembly and you will be fine.
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by:nietod
ID: 1165831
I believe that many 16 bit compilers assume that DS will always point to a segment called _TEXT.  I'm not sure of the details about that, though.  Your best bet is to save and restore DS and ES around any procedure that messes with it.  You also might need to save and restore SI and DI, some compilers assume they will not change as well.
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