What happened in this cleanup procedure?

Posted on 1998-06-13
Medium Priority
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?

Question by:whluk
  • 2
LVL 22

Accepted Solution

nietod earned 200 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.
LVL 22

Expert Comment

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.

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.

624 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question