DOS ain't dead

Trubo Oberon (Announce)

posted by rr  , Berlin, Germany, 08.07.2026, 21:24

User DosWorld asked to make you aware of his recent "self-hosting Oberon-07 compiler for 16-bit MS-DOS real mode".

From README.MD:

===== WHY THIS EXISTS =====

There is no free, modern, actively-usable Pascal-family compiler that targets (and works) 16-bit MS-DOS real mode. Borland stopped at Turbo Pascal 7 / Borland Pascal 7 in the early '90s and never open-sourced it. FreePascal — the natural place to look — has supported 16-bit i8086 code generation since around 2014, but it was always the neglected back corner of the project: undermaintained, thin on runtime support, and never treated as a first-class target the way its 32/64-bit backends are. I had been waiting since the late 1990s for a serious free 16-bit target from the Pascal world (i8086-msdos in FreePascal was the closest anyone got, decades after the fact), and it never became something you could really build on.

So this project doesn't try to be that. It picks Wirth's other, smaller language — Oberon-07, Pascal's own successor — and builds a compiler for it from scratch, purpose-built for 16-bit DOS real mode, with no inherited 32-bit assumptions to work around. The compiler, linker, dependency scanner, archive manager, and test tools are all written in Oberon-07 and compile themselves, on the target architecture (8086 real mode), from a single checked-in bootstrap binary. Feed it its own source and it reproduces itself byte-for-byte — a full fixpoint, verified on every change.

That means:

* No hidden C runtime. SYSTEM.MOD + a small SYS.ASM are the entire foundation.
* No 32-bit protected-mode escape hatch. Real segmented 8086 memory, real 64 KB segments, real far pointers.
* A compiler that could, in principle, have been built in 1987 — but with the discipline of zero-heap-leak, byte-reproducible modern engineering practice behind it.

===== HIGHLIGHTS =====

* Self-hosting, byte-stable. toc /ENTRY=Run TOC.MOD rebuilds the whole compiler in a single process; two consecutive generations are byte-identical. See TESTS/test_selfhost.sh.
* Zero heap leaks, guaranteed. Every compile and every link reports 0 leaked paragraphs — enforced by LeakGuard instrumentation and regression tests, not just hoped for.
* All-in-one driver. toc.exe is the dep-scanner, incremental compiler, and smart linker in one binary and one command — no makefiles required to build an Oberon program.
* Real DOS constraints, handled properly. Per-module 64 KB code segments, far pointers (segment:offset), a large memory model, EMS-backed temp files, and a linker that streams instead of holding everything in RAM.
* 272-row regression manifest plus DOS-side executable and unit-test suites — every codegen change is checked against real compiled/linked/run output, not just "it compiled."
* Turbo Debugger-compatible debug info. Compile with (*$D+*), link with /G, and get a Borland TDS/TDINFO v2.08 block appended straight onto the .EXE — inspect with the included tdinfo.exe.
* Linkable with external assembly. The linker consumes standard RDOFF2 object files, so hand-written assembly modules assembled with NASM, YASM, or MSA2 (-f rdf) can be linked directly alongside Oberon-compiled .rdf/.om modules — no C shim required.

(…) Read more at https://github.com/DosWorld/toc/

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Complete thread:

• Trubo Oberon - rr, 08.07.2026, 21:24 (Announce)