3/28/2024 0 Comments Dosbox int 3 debugger![]() ![]() To use the DOS version of Flat Assembler, you’ll need an utility like CWSDPMI. The means that code can be rewritten in memory by the code it self. They can be mixed and data can be treated as code and vice versa. DOS does not require that code and data are separate. If you looked into Linux assembler (or any other) you might notice that the data segment is not marked out in code. The $ symbol is important and used by the printing function to know where the end of the string is. In this case it is a string och bytes that ends with a $ symbol. Leading to all kinds of weird random stuff. If not called, the bytes that follow will be executed as code. This tells DOS to step executing the code and return to the prompt. Then the function is called by setting AH to 9, DS:DX to the memory location where the bytes to print are and calling Interrupt Procedure 0x21. Because the offset is in the code segment, the data segment register needs to be set to the same value. We’re using the label “hello_world_string” (defined later) to refer to an offset in the code segment. ![]() In this example we are using a DOS function to print the code. This part is where the instructions for printing “Hello World” are. It will make sure we have a MZ header at the start of the file. This line tells Flat Assembler that we want a DOS-executable as output. If you want to debug it and step through the instructions one by one, type “debug hwex.exe”. Like this: mount f: C:\exampleĪnd when that is done, navigate to the new drive and run the executable. Type “mount”, followed by a letter and a colon and lastly the path to the folder you want to mount. It will create a new drive that will allow you to access the folders content. It can be done by calling the Mount command in the DOSBox prompt. But to access it in DOSBox, you’ll need to mount the folder where you saved it first. Now you have an executable that can be run and debugged in DOSBox. Select where to save the file and name it “hwex.exe”. In the menu, select “Run” and then “Compile”. Set data segment to same as code segmentĭb 'Hello World$' $ = end of string marker Once you have downloaded and installed the tools, start the Windows version of Flat Assembler and copy paste the code below in to the window. It gave a lot of insights into why Dune was programmed the way it was. (Contains references, but not a good place to start learning VGA programming I’m afraid.)Īlso a good read about Assembly programming is “ Zen of Assembly Language: Volume I, Knowledge” by Michael Abrash (Note: A volumn 2 was never published).
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