Tuesday, October 27, 2009

16-bit Assembly Compilation in 64-bit Windows 7

I'm taking Computer Organization and Architecture this semester, and as part of the class I need to write/compile some assembly programs. Unfortunately, due to the age of the class, all of the example code & what we're being taught is with respect to 16-bit DOS programs. So I was in the unusual situation of needing to compile code that won't run in my current OS (Windows 7 Professional-64bit).

After experimenting a while, I got the following setup to work:

1. Installed Visual Studio 2008 & all associated updates
2. Downloaded & extracted a 16-bit compatible linker using a VM running XP (any box running XP will be able to extract it)
3. Created a folder for the assembly programming, made sure the link.exe from (2) was inside the folder.
4. Created a batch file (compile.bat) to automate the compile/linking process:
//start batch file
"C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\bin\ml.exe" /omf /Bllink16 /Zm %1.asm
LINK.EXE %1.obj,%1.exe,nul.map,.lib,nul.def
//end batch file
5. Begin writing programs. To compile, simply type "compile helloworld" (WITHOUT the .asm)
For example, here's a sample run of a famous program:
//begin console
c:\Assembly>compile hello

c:\Assembly>"C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\bin\ml.exe" /
omf /Bllink16 /Zm hello.asm
Microsoft (R) Macro Assembler Version 9.00.21022.08
Copyright (C) Microsoft Corporation. All rights reserved.

Assembling: hello.asm

c:\Assembly>LINK.EXE hello.obj,hello.exe,nul.map,.lib,nul.def

Microsoft (R) Segmented Executable Linker Version 5.60.339 Dec 5 1994
Copyright (C) Microsoft Corp 1984-1993. All rights reserved.
//end console
6. Finally, to test the compiled programs I run them inside a DOSBox instance (as Win7-64 doesn't run 16-bit programs).
//begin console
Hello, World!
//end console

Hopefully this helps someone running into the same issues I did.

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