Bringing Ada to SunOS 4

When I started the path of creating a group of cohesive and utilitarian packages for SunOS 4, I decided earlier on that I wanted GNU-GNAT to be a centerpiece of it along with all the other tools we come to expect on a modern Unix server.

From my previous experience adding GNAT to my Solaris LSE, I knew there was some challenge and the first order of business was to FIND an Ada compiler. The reason is simple: one needs Ada to compile GNAT. It needs itself.

The story says that long ago the first releases of GNAT used a commercial Ada compiler to create the first build of GNAT, and from there it compiled itself.

So I turned to Google, then the Internet Archive, came out dry! Not a mention of GNAT anywhere in SunOS. (I’ll later discover why).

Then I figured it should be in one of the old CDs from Walnut Creek Inc. or a SunSite mirror. Nothing! The earliest Ada compiler I knew about was gnat-3.15p for Solaris 2.5.1.

So I pivoted to try cross-compiling. I knew it was a thing, but I had never attempted such a thing. Armed with the source code of gnat-3.15p and gcc 2.8.1, I could not find good instructions on the internet of how to build Ada on GCC; probably lost like so many things from that time.

I did my best. The first thing was to get /usr/lib, /usr/include, and /usr/kvm (this one I learned about later from SunOS) and make them available for the cross-compiler. I put them under /opt/cross.

Then one is supposed to copy Ada into the GCC folder, similar to how g++ is built under 2.8.1, which I had done recently when I started LSE for SunOS 4.

After 5 days of fighting with it, I gave up, resigned to not having Ada, and concentrated on building the LSE MVP.

When LSE for SunOS was almost ready, I decided to try a second time building GNAT. This time I decided not to start until I could locate some kind of document explaining how to build it, to avoid falling in the same trap.

Finding the document proved difficult. But oh… RTFM!!! It was right there in front of my eyes the whole time. The source of Ada did have instructions for compiling Ada under GCC 2.8.1!

Looking back at my previous attempt, the one thing I missed is that unlike g++, one needs to patch GCC to get it to integrate with GNAT.

The Cross-Compiler

At first I didn’t really understand what a cross-compiler is. One figures it’s just a flag when compiling like gcc -target=SunOS right? Nope!

In essence, what is done is to build a new compiler stack that is a binary of your build systemâin my case, Solaris 2.5.1 on an Ultra 60âbut it “thinks” it is running on your target platform, SunOS 4.1.4 on a v7 CPU. I’ll link the SunOS objects and libraries.

Once I had GCC, Ada, and its companions, then it was time to build Ada. It was actually a painful process because I learned gnat-3.15p does not build cleanly in SunOS 4. Looking back, it makes sense why I was not able to find any binaries! Here comes lsecompat and my experience building shims (adding missing functionality to vintage platforms).

The other problem I had was that as I was building and had a missing cross-compiler binary, I had to retarget, build the binary, and then clean up my working folder from ELF binaries to build the tool for SunOS (a.out).

This went on for some time. I even created a script to find and blast out bad objects.

for obj in *.o; do
  [ -f "$obj" ] || continue
  # Check if object is NOT SPARC architecture
  file "$obj"
  if  file "$obj" | ggrep  "ELF" >/dev/null 2>&1; then
    echo "=== Recompiling non-SPARC object: $obj ==="
    base="${obj%.o}"

    # Check for Ada source file (.adb) or C source file (.c)
    if [ -f "${base}.adb" ]; then
      ../xgcc -B../ -c -g -O2 -gnatg -gnatp -gnatws -I. -Irts -I.. -I../config "${base}.adb" -o "$obj"
    elif [ -f "${base}.c" ]; then
      ../xgcc -B../ -c -g -O2 -I. -I.. -I../config "${base}.c" -o "$obj"
    elif [ -f "a-${base}.c" ]; then
      ../xgcc -B../ -c -g -O2 -I. -I.. -I../config "a-${base}.c" -o "$obj"
    fi
  fi
done

Because a make all or something like that did not work for me during cross-compiling, I did it the try, fail, and fix way.

I copied my binaries and attempted building my Ada demo, which is a contact database with disk-based indexes. I needed among others the driver (gcc, cc1 Ada-aware) and gnatmake.

Once I got everything working, I created a wrapper shell to make it work with my target folder /usr/local/lse prefix. I could have rebuilt GNAT again now from SunOS, but why? My cross-compiled binaries work just fine.

To showcase the compiler stack in action meetups, I set up the demo to trigger a fresh build cycle via gnatmake on menu actions-giving older SPARC hardware a proper workout.

SunOS 4.1.4 ISAM Disk Sub-Engine Demo

I created a gnat-3.15p-SunOS-4.1.x.tar.gz that should be dropped on /usr/local/lse along with this document and a bundle with my cross-compiler, in case somebody needs to use it. Probably not useful to anybody, but I cannot see the future, so better keep it around.

Luis Enrique Limon, Oct 17, 2026

The Cross-Compiler#

The Cross-Compiler