Cross-Compiling Hello World for DOS on macOS

Technically this should work for any platform that OpenWatcom 2 supports compiling binaries for. Some instructions are based on a post at retrocoding.net, and John Tsiombikas's post

Prerequisites

You should already have XCode / Command Line Tools, and Homebrew installed. To compile Open Watcom for DOS you will need DOSBox (I use DOSBox-X).

brew install --cask dosbox-x

Compiling Open Watcom v2

If this process is super annoying, I might make a custom homebrew tap to build and install Open Watcom

git clone https://github.com/open-watcom/open-watcom-v2
cp open-watcom-v2/setvars.sh custom_setvars.sh

Now, edit this setvars.sh file. My file looks like this:

#!/bin/zsh
export OWROOT="/Users/navanchauhan/Developer/8088Stuff/open-watcom-v2"
export OWTOOLS=CLANG
export OWDOCBUILD=0
export OWGUINOBUILD=0
export OWDISTRBUILD=0
export OWDOSBOX="/Applications/dosbox-x.app/Contents/MacOS/dosbox-x"
export OWOBJDIR=binbuildV01
. "$OWROOT/cmnvars.sh"
echo "OWROOT=$OWROOT"
cd "$OWROOT"

Note, your OWRTOOT is definitely going to be in a different location.

source ./custom_setvars.sh
./build.sh
./build.sh rel

This will build, and then copy everything to the rel directory inside open-watcom-v2 directory. Since I ran this on an Apple Silicon Mac, all the binaries for me are in the armo64 directory. You can now move everything inside the rel folder to another location, or create a simple script to init all variables whenever you want.

I like having a script called exportVarsForDOS.sh

#!/bin/zsh

export WATCOM=/Users/navanchauhan/Developer/8088Stuff/open-watcom-v2/rel
export PATH=$PATH:$WATCOM/armo64
export EDDAT=$WATCOM/eddat

# For DOS 8088/8086 development
export INCLUDE=$WATCOM/h
export LIB=$WATCOM/lib286 # You don't really need this

Then, when you need to load up these variables, you can simply run source exportVarsForDOS.sh or . exportVarsForDOS.sh

Hello World

Buliding without any Makefiles

Create a new file called example1.c

#include<stdio.h>

int main() {
    printf("Hello World!");
    return 0;
}

First we compile the code:

$ wcc example1.c
Open Watcom C x86 16-bit Optimizing Compiler
Version 2.0 beta Mar 15 2024 13:11:55
Copyright (c) 2002-2024 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1984-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See https://github.com/open-watcom/open-watcom-v2#readme for details.
example1.c: 7 lines, included 818, 0 warnings, 0 errors
Code size: 19

Then, link to make an executable:

$ wlink name example1.exe system dos file example1.o
Open Watcom Linker Version 2.0 beta Mar 15 2024 13:10:09
Copyright (c) 2002-2024 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1985-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See https://github.com/open-watcom/open-watcom-v2#readme for details.
loading object files
searching libraries
creating a DOS executable

If you want to test this executable, jump to the section titled Testing with DOSBox-X below.

Simple Makefile

obj = main.o hello.o
bin = tizts.com

CC = wcc
CFLAGS = -0
LD = wlink

$(bin): $(obj)
    $(LD) name $@ system dos file main.o file hello.o 

.c.o:
    $(CC) $(CFLAGS) $<

clean:
    rm $(obj) $(bin)

Where, main.c

void hello(void);

int main(void)
{
    hello();
    return 0;
}

and hello.c

/* hello.c */
#include <stdio.h>

void hello(void)
{
    printf("Hello!");
}

To compile into tizts.com simply run wmake

$ wmake
➜  simple-cpp wmake
Open Watcom Make Version 2.0 beta Mar 15 2024 13:10:16
Copyright (c) 2002-2024 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1988-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See https://github.com/open-watcom/open-watcom-v2#readme for details.
    wcc -0 main.c
Open Watcom C x86 16-bit Optimizing Compiler
Version 2.0 beta Mar 15 2024 13:11:55
Copyright (c) 2002-2024 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1984-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See https://github.com/open-watcom/open-watcom-v2#readme for details.
main.c(8): Warning! W138: No newline at end of file
main.c: 8 lines, included 53, 1 warnings, 0 errors
Code size: 12
    wcc -0 hello.c
Open Watcom C x86 16-bit Optimizing Compiler
Version 2.0 beta Mar 15 2024 13:11:55
Copyright (c) 2002-2024 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1984-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See https://github.com/open-watcom/open-watcom-v2#readme for details.
hello.c: 8 lines, included 818, 0 warnings, 0 errors
Code size: 17
    wlink name tizts.com system dos file main.o file hello.o
Open Watcom Linker Version 2.0 beta Mar 15 2024 13:10:09
Copyright (c) 2002-2024 The Open Watcom Contributors. All Rights Reserved.
Portions Copyright (c) 1985-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See https://github.com/open-watcom/open-watcom-v2#readme for details.
loading object files
searching libraries
creating a DOS executable

Using CMake

Create a file called CMakeLists.txt

project(hello)

set(SOURCES abc.c)

add_executable(hello ${SOURCES})

Where, abc.c is:

#include <stdio.h>

int main() {
    printf("Does this work?");
    return 0;
}

mkdir build
cd build

And build using CMake

cmake -DCMAKE_SYSTEM_NAME=DOS -DCMAKE_SYSTEM_PROCESSOR=I86 -DCMAKE_C_FLAGS="-0 -bt=dos -d0 -oaxt" -G "Watcom WMake" ../..

There you have it. Three different ways to compile a C program on a macOS device in 2024 that can run on an IBM PC 5150 (which was released in 1981!)

Testing with DOSBox-X

cp example1.exe ~/Downloads
/Applications/dosbox-x.app/Contents/MacOS/dosbox-x

In DOSBox-X we now mount the ~/Downloads folder as our C: drive

mount C ~/Downloads

Switch to the C drive

C:

Run the program:

example1

Running our program in DOSBox-X

My DOSBox setup might look slightly different than yours...

If you have scrolled this far, consider subscribing to my mailing list here. You can subscribe to either a specific type of post you are interested in, or subscribe to everything with the "Everything" list.