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<h1 id="cross-compiling-hello-world-for-dos-on-macos">Cross-Compiling Hello World for DOS on macOS</h1>
<p>Technically this should work for any platform that OpenWatcom 2 supports compiling binaries for. Some instructions are based on <a rel="noopener" target="_blank" href="https://retrocoding.net/openwatcom-gateway-to-ancient-world-of-x86">a post at retrocoding.net</a>,
and <a rel="noopener" target="_blank" href="http://nuclear.mutantstargoat.com/articles/retrocoding/dos01-setup/#hello-world-program">John Tsiombikas's post</a></p>
<h2 id="prerequisites">Prerequisites</h2>
<p>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).</p>
<div class="codehilite">
<pre><span></span><code>brew<span class="w"> </span>install<span class="w"> </span>--cask<span class="w"> </span>dosbox-x
</code></pre>
</div>
<h2 id="compiling-open-watcom-v2">Compiling Open Watcom v2</h2>
<p><em>If this process is super annoying, I might make a custom homebrew tap to build and install Open Watcom</em></p>
<div class="codehilite">
<pre><span></span><code>git<span class="w"> </span>clone<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2
cp<span class="w"> </span>open-watcom-v2/setvars.sh<span class="w"> </span>custom_setvars.sh
</code></pre>
</div>
<p>Now, edit this <code>setvars.sh</code> file. My file looks like this:</p>
<div class="codehilite">
<pre><span></span><code><span class="ch">#!/bin/zsh</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">OWROOT</span><span class="o">=</span><span class="s2">"/Users/navanchauhan/Developer/8088Stuff/open-watcom-v2"</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">OWTOOLS</span><span class="o">=</span>CLANG
<span class="nb">export</span><span class="w"> </span><span class="nv">OWDOCBUILD</span><span class="o">=</span><span class="m">0</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">OWGUINOBUILD</span><span class="o">=</span><span class="m">0</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">OWDISTRBUILD</span><span class="o">=</span><span class="m">0</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">OWDOSBOX</span><span class="o">=</span><span class="s2">"/Applications/dosbox-x.app/Contents/MacOS/dosbox-x"</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">OWOBJDIR</span><span class="o">=</span>binbuildV01
.<span class="w"> </span><span class="s2">"</span><span class="nv">$OWROOT</span><span class="s2">/cmnvars.sh"</span>
<span class="nb">echo</span><span class="w"> </span><span class="s2">"OWROOT=</span><span class="nv">$OWROOT</span><span class="s2">"</span>
<span class="nb">cd</span><span class="w"> </span><span class="s2">"</span><span class="nv">$OWROOT</span><span class="s2">"</span>
</code></pre>
</div>
<p>Note, your <code>OWRTOOT</code> is definitely going to be in a different location.</p>
<div class="codehilite">
<pre><span></span><code><span class="nb">source</span><span class="w"> </span>./custom_setvars.sh
./build.sh
./build.sh<span class="w"> </span>rel
</code></pre>
</div>
<p>This will build, and then copy everything to the <code>rel</code> directory inside <code>open-watcom-v2</code> directory. Since I ran this on an Apple Silicon Mac,
all the binaries for me are in the <code>armo64</code> directory. You can now move everything inside the rel folder to another location, or create a simple
script to init all variables whenever you want.</p>
<p>I like having a script called <code>exportVarsForDOS.sh</code> </p>
<div class="codehilite">
<pre><span></span><code><span class="ch">#!/bin/zsh</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">WATCOM</span><span class="o">=</span>/Users/navanchauhan/Developer/8088Stuff/open-watcom-v2/rel
<span class="nb">export</span><span class="w"> </span><span class="nv">PATH</span><span class="o">=</span><span class="nv">$PATH</span>:<span class="nv">$WATCOM</span>/armo64
<span class="nb">export</span><span class="w"> </span><span class="nv">EDDAT</span><span class="o">=</span><span class="nv">$WATCOM</span>/eddat
<span class="c1"># For DOS 8088/8086 development</span>
<span class="nb">export</span><span class="w"> </span><span class="nv">INCLUDE</span><span class="o">=</span><span class="nv">$WATCOM</span>/h
<span class="nb">export</span><span class="w"> </span><span class="nv">LIB</span><span class="o">=</span><span class="nv">$WATCOM</span>/lib286<span class="w"> </span><span class="c1"># You don't really need this</span>
</code></pre>
</div>
<p>Then, when you need to load up these variables, you can simply run <code>source exportVarsForDOS.sh</code> or <code>. exportVarsForDOS.sh</code></p>
<h2 id="hello-world">Hello World</h2>
<h3 id="buliding-without-any-makefiles">Buliding without any Makefiles</h3>
<p>Create a new file called <code>example1.c</code></p>
<div class="codehilite">
<pre><span></span><code><span class="cp">#include</span><span class="cpf"><stdio.h></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Hello World!"</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</code></pre>
</div>
<p>First we compile the code:</p>
<div class="codehilite">
<pre><span></span><code>$<span class="w"> </span>wcc<span class="w"> </span>example1.c
Open<span class="w"> </span>Watcom<span class="w"> </span>C<span class="w"> </span>x86<span class="w"> </span><span class="m">16</span>-bit<span class="w"> </span>Optimizing<span class="w"> </span>Compiler
Version<span class="w"> </span><span class="m">2</span>.0<span class="w"> </span>beta<span class="w"> </span>Mar<span class="w"> </span><span class="m">15</span><span class="w"> </span><span class="m">2024</span><span class="w"> </span><span class="m">13</span>:11:55
Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">2002</span>-2024<span class="w"> </span>The<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Contributors.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Portions<span class="w"> </span>Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">1984</span>-2002<span class="w"> </span>Sybase,<span class="w"> </span>Inc.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Source<span class="w"> </span>code<span class="w"> </span>is<span class="w"> </span>available<span class="w"> </span>under<span class="w"> </span>the<span class="w"> </span>Sybase<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Public<span class="w"> </span>License.
See<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2#readme<span class="w"> </span><span class="k">for</span><span class="w"> </span>details.
example1.c:<span class="w"> </span><span class="m">7</span><span class="w"> </span>lines,<span class="w"> </span>included<span class="w"> </span><span class="m">818</span>,<span class="w"> </span><span class="m">0</span><span class="w"> </span>warnings,<span class="w"> </span><span class="m">0</span><span class="w"> </span>errors
Code<span class="w"> </span>size:<span class="w"> </span><span class="m">19</span>
</code></pre>
</div>
<p>Then, link to make an executable:</p>
<div class="codehilite">
<pre><span></span><code>$<span class="w"> </span>wlink<span class="w"> </span>name<span class="w"> </span>example1.exe<span class="w"> </span>system<span class="w"> </span>dos<span class="w"> </span>file<span class="w"> </span>example1.o
Open<span class="w"> </span>Watcom<span class="w"> </span>Linker<span class="w"> </span>Version<span class="w"> </span><span class="m">2</span>.0<span class="w"> </span>beta<span class="w"> </span>Mar<span class="w"> </span><span class="m">15</span><span class="w"> </span><span class="m">2024</span><span class="w"> </span><span class="m">13</span>:10:09
Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">2002</span>-2024<span class="w"> </span>The<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Contributors.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Portions<span class="w"> </span>Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">1985</span>-2002<span class="w"> </span>Sybase,<span class="w"> </span>Inc.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Source<span class="w"> </span>code<span class="w"> </span>is<span class="w"> </span>available<span class="w"> </span>under<span class="w"> </span>the<span class="w"> </span>Sybase<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Public<span class="w"> </span>License.
See<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2#readme<span class="w"> </span><span class="k">for</span><span class="w"> </span>details.
loading<span class="w"> </span>object<span class="w"> </span>files
searching<span class="w"> </span>libraries
creating<span class="w"> </span>a<span class="w"> </span>DOS<span class="w"> </span>executable<span class="w"> </span>
</code></pre>
</div>
<p>If you want to test this executable, jump to the section titled <code>Testing with DOSBox-X</code> below.</p>
<h3 id="simple-makefile">Simple Makefile</h3>
<div class="codehilite">
<pre><span></span><code><span class="nv">obj</span><span class="w"> </span><span class="o">=</span><span class="w"> </span>main.o<span class="w"> </span>hello.o
<span class="nv">bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span>tizts.com
<span class="nv">CC</span><span class="w"> </span><span class="o">=</span><span class="w"> </span>wcc
<span class="nv">CFLAGS</span><span class="w"> </span><span class="o">=</span><span class="w"> </span>-0
<span class="nv">LD</span><span class="w"> </span><span class="o">=</span><span class="w"> </span>wlink
<span class="nf">$(bin)</span><span class="o">:</span><span class="w"> </span><span class="k">$(</span><span class="nv">obj</span><span class="k">)</span>
<span class="w"> </span><span class="k">$(</span>LD<span class="k">)</span><span class="w"> </span>name<span class="w"> </span><span class="nv">$@</span><span class="w"> </span>system<span class="w"> </span>dos<span class="w"> </span>file<span class="w"> </span>main.o<span class="w"> </span>file<span class="w"> </span>hello.o<span class="w"> </span>
<span class="nf">.c.o</span><span class="o">:</span>
<span class="w"> </span><span class="k">$(</span>CC<span class="k">)</span><span class="w"> </span><span class="k">$(</span>CFLAGS<span class="k">)</span><span class="w"> </span>$<
<span class="nf">clean</span><span class="o">:</span>
<span class="w"> </span>rm<span class="w"> </span><span class="k">$(</span>obj<span class="k">)</span><span class="w"> </span><span class="k">$(</span>bin<span class="k">)</span>
</code></pre>
</div>
<p>Where, <code>main.c</code></p>
<div class="codehilite">
<pre><span></span><code><span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">hello</span><span class="p">();</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</code></pre>
</div>
<p>and <code>hello.c</code></p>
<div class="codehilite">
<pre><span></span><code><span class="cm">/* hello.c */</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><stdio.h></span>
<span class="kt">void</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Hello!"</span><span class="p">);</span>
<span class="p">}</span>
</code></pre>
</div>
<p>To compile into <code>tizts.com</code> simply run <code>wmake</code></p>
<div class="codehilite">
<pre><span></span><code>$<span class="w"> </span>wmake
➜<span class="w"> </span>simple-cpp<span class="w"> </span>wmake
Open<span class="w"> </span>Watcom<span class="w"> </span>Make<span class="w"> </span>Version<span class="w"> </span><span class="m">2</span>.0<span class="w"> </span>beta<span class="w"> </span>Mar<span class="w"> </span><span class="m">15</span><span class="w"> </span><span class="m">2024</span><span class="w"> </span><span class="m">13</span>:10:16
Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">2002</span>-2024<span class="w"> </span>The<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Contributors.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Portions<span class="w"> </span>Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">1988</span>-2002<span class="w"> </span>Sybase,<span class="w"> </span>Inc.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Source<span class="w"> </span>code<span class="w"> </span>is<span class="w"> </span>available<span class="w"> </span>under<span class="w"> </span>the<span class="w"> </span>Sybase<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Public<span class="w"> </span>License.
See<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2#readme<span class="w"> </span><span class="k">for</span><span class="w"> </span>details.
<span class="w"> </span>wcc<span class="w"> </span>-0<span class="w"> </span>main.c
Open<span class="w"> </span>Watcom<span class="w"> </span>C<span class="w"> </span>x86<span class="w"> </span><span class="m">16</span>-bit<span class="w"> </span>Optimizing<span class="w"> </span>Compiler
Version<span class="w"> </span><span class="m">2</span>.0<span class="w"> </span>beta<span class="w"> </span>Mar<span class="w"> </span><span class="m">15</span><span class="w"> </span><span class="m">2024</span><span class="w"> </span><span class="m">13</span>:11:55
Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">2002</span>-2024<span class="w"> </span>The<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Contributors.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Portions<span class="w"> </span>Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">1984</span>-2002<span class="w"> </span>Sybase,<span class="w"> </span>Inc.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Source<span class="w"> </span>code<span class="w"> </span>is<span class="w"> </span>available<span class="w"> </span>under<span class="w"> </span>the<span class="w"> </span>Sybase<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Public<span class="w"> </span>License.
See<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2#readme<span class="w"> </span><span class="k">for</span><span class="w"> </span>details.
main.c<span class="o">(</span><span class="m">8</span><span class="o">)</span>:<span class="w"> </span>Warning!<span class="w"> </span>W138:<span class="w"> </span>No<span class="w"> </span>newline<span class="w"> </span>at<span class="w"> </span>end<span class="w"> </span>of<span class="w"> </span>file
main.c:<span class="w"> </span><span class="m">8</span><span class="w"> </span>lines,<span class="w"> </span>included<span class="w"> </span><span class="m">53</span>,<span class="w"> </span><span class="m">1</span><span class="w"> </span>warnings,<span class="w"> </span><span class="m">0</span><span class="w"> </span>errors
Code<span class="w"> </span>size:<span class="w"> </span><span class="m">12</span>
<span class="w"> </span>wcc<span class="w"> </span>-0<span class="w"> </span>hello.c
Open<span class="w"> </span>Watcom<span class="w"> </span>C<span class="w"> </span>x86<span class="w"> </span><span class="m">16</span>-bit<span class="w"> </span>Optimizing<span class="w"> </span>Compiler
Version<span class="w"> </span><span class="m">2</span>.0<span class="w"> </span>beta<span class="w"> </span>Mar<span class="w"> </span><span class="m">15</span><span class="w"> </span><span class="m">2024</span><span class="w"> </span><span class="m">13</span>:11:55
Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">2002</span>-2024<span class="w"> </span>The<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Contributors.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Portions<span class="w"> </span>Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">1984</span>-2002<span class="w"> </span>Sybase,<span class="w"> </span>Inc.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Source<span class="w"> </span>code<span class="w"> </span>is<span class="w"> </span>available<span class="w"> </span>under<span class="w"> </span>the<span class="w"> </span>Sybase<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Public<span class="w"> </span>License.
See<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2#readme<span class="w"> </span><span class="k">for</span><span class="w"> </span>details.
hello.c:<span class="w"> </span><span class="m">8</span><span class="w"> </span>lines,<span class="w"> </span>included<span class="w"> </span><span class="m">818</span>,<span class="w"> </span><span class="m">0</span><span class="w"> </span>warnings,<span class="w"> </span><span class="m">0</span><span class="w"> </span>errors
Code<span class="w"> </span>size:<span class="w"> </span><span class="m">17</span>
<span class="w"> </span>wlink<span class="w"> </span>name<span class="w"> </span>tizts.com<span class="w"> </span>system<span class="w"> </span>dos<span class="w"> </span>file<span class="w"> </span>main.o<span class="w"> </span>file<span class="w"> </span>hello.o
Open<span class="w"> </span>Watcom<span class="w"> </span>Linker<span class="w"> </span>Version<span class="w"> </span><span class="m">2</span>.0<span class="w"> </span>beta<span class="w"> </span>Mar<span class="w"> </span><span class="m">15</span><span class="w"> </span><span class="m">2024</span><span class="w"> </span><span class="m">13</span>:10:09
Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">2002</span>-2024<span class="w"> </span>The<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Contributors.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Portions<span class="w"> </span>Copyright<span class="w"> </span><span class="o">(</span>c<span class="o">)</span><span class="w"> </span><span class="m">1985</span>-2002<span class="w"> </span>Sybase,<span class="w"> </span>Inc.<span class="w"> </span>All<span class="w"> </span>Rights<span class="w"> </span>Reserved.
Source<span class="w"> </span>code<span class="w"> </span>is<span class="w"> </span>available<span class="w"> </span>under<span class="w"> </span>the<span class="w"> </span>Sybase<span class="w"> </span>Open<span class="w"> </span>Watcom<span class="w"> </span>Public<span class="w"> </span>License.
See<span class="w"> </span>https://github.com/open-watcom/open-watcom-v2#readme<span class="w"> </span><span class="k">for</span><span class="w"> </span>details.
loading<span class="w"> </span>object<span class="w"> </span>files
searching<span class="w"> </span>libraries
creating<span class="w"> </span>a<span class="w"> </span>DOS<span class="w"> </span>executable
</code></pre>
</div>
<h3 id="using-cmake">Using CMake</h3>
<p>Create a file called <code>CMakeLists.txt</code></p>
<div class="codehilite">
<pre><span></span><code><span class="nb">project</span><span class="p">(</span><span class="s">hello</span><span class="p">)</span>
<span class="nb">set</span><span class="p">(</span><span class="s">SOURCES</span><span class="w"> </span><span class="s">abc.c</span><span class="p">)</span>
<span class="nb">add_executable</span><span class="p">(</span><span class="s">hello</span><span class="w"> </span><span class="o">${</span><span class="nv">SOURCES</span><span class="o">}</span><span class="p">)</span>
</code></pre>
</div>
<p>Where, <code>abc.c</code> is:</p>
<div class="codehilite">
<pre><span></span><code><span class="cp">#include</span><span class="w"> </span><span class="cpf"><stdio.h></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">printf</span><span class="p">(</span><span class="s">"Does this work?"</span><span class="p">);</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</code></pre>
</div>
<div class="codehilite">
<pre><span></span><code>mkdir<span class="w"> </span>build
<span class="nb">cd</span><span class="w"> </span>build
</code></pre>
</div>
<p>And build using CMake</p>
<pre><code>cmake -DCMAKE_SYSTEM_NAME=DOS -DCMAKE_SYSTEM_PROCESSOR=I86 -DCMAKE_C_FLAGS="-0 -bt=dos -d0 -oaxt" -G "Watcom WMake" ../..
</code></pre>
<p>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!)</p>
<h2 id="testing-with-dosbox-x">Testing with DOSBox-X</h2>
<div class="codehilite">
<pre><span></span><code>cp<span class="w"> </span>example1.exe<span class="w"> </span>~/Downloads
/Applications/dosbox-x.app/Contents/MacOS/dosbox-x
</code></pre>
</div>
<p>In DOSBox-X we now mount the <code>~/Downloads</code> folder as our <code>C:</code> drive</p>
<pre><code>mount C ~/Downloads
</code></pre>
<p>Switch to the C drive</p>
<pre><code>C:
</code></pre>
<p>Run the program:</p>
<pre><code>example1
</code></pre>
<p><img src="/assets/posts/dosbox/hello-world.png" alt="Running our program in DOSBox-X" /></p>
<p><em>My DOSBox setup might look slightly different than yours...</em></p>
</div>
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