oberonc is a self-hosted Oberon-07 compiler targeting MS-DOS real-mode large memory model (CS≠DS≠SS). It produces RDOFF2 object files and .om archive libraries, linked into DOS MZ executables. The entire toolchain runs natively on MS-DOS and under the xt emulator on Linux/macOS.

Self-hosting (2026-06-09): The compiler is written in Oberon and compiles itself. boot/oc.exe (a checked-in MS-DOS binary) seeds the build. From there, the compiler rebuilds itself and all tools from Oberon source. The self-hosting regression test (tests/test_selfhost.sh) verifies boot/oc.exe → src/oc/*.Mod → oc1.exe and then oc1.exe → oc2.exe are byte-identical.

• Full Oberon-07 subset with practical extensions (see "Language extensions" below).
• RDOFF2 code generation with smart linking — only reachable modules are emitted.
• x87 FPU support: REAL (32-bit) and LONGREAL (64-bit) arithmetic, comparison, conversion.
• LONGINT (32-bit signed integers) with helpers for multiplication, division, and modulus.
• SET type (16-bit): literals, ranges, set operators, IN membership test.
• Constant expression folding for CONST declarations, ARRAY dims, CASE labels.
• FAR/NEAR procedure calling conventions with procedural variables.
• Nested procedures (no uplevel access — inner procs see only globals, imports, own params).
• Dynamic allocation: NEW/DISPOSE with typed and sized variants; ADDRESS far pointers.
• Forward and self-referential POINTER TO RECORD types within a TYPE section.
• SYSTEM intrinsics: MOVE, FILL, ADR, SEG, OFS, PTR, LSL, LSR, ASR, ROR; PORTOUT/PORTIN.
• EXTERNAL procedure declarations (body provided by an external .rdf at link time).
• $L directive to pack hand-assembled .rdf files into .om archives.
• $M directive to declare stack and heap sizes.
• $R directive to enable/disable array bounds checking.
• Dead-code/unused-symbol warnings (non-fatal, stderr).
• All-in-one oc.exe: dep-scan + incremental compile + smart link in one binary.

• // single-line comments.
• INLINE(byte, ...) as a statement: emits raw bytes inside a regular procedure body.
• (*$L path.rdf*) / //$L path.rdf — include extra .rdf in .om archive.
• (*$M stack, min, max*) — stack and heap size hints.
• (*$R+*) / (*$R-*) — enable/disable array bounds checks.
• FAR / NEAR modifiers on PROCEDURE declarations and types.
• EXTERNAL modifier on PROCEDURE declarations.
• VAR name without : type (typeless VAR parameter — callee receives ADDRESS).
• ADDRESS built-in type (4-byte far pointer, any segment).
• FLOAT(x) synonym for REAL(x); ENTIER(x) synonym for FLOOR(x).
• ARRAY m, n OF T multi-dimensional array sugar (up to 7 dims).
• Named integer constants as array dimensions.
• NEW(p, n) sized allocation (n is a runtime byte-count expression).
• Implicit INTEGER→REAL/LONGREAL coercion in binary expressions.

oberonc/
  boot/         Bootstrap MS-DOS binaries (immutable — never modified by make)
    oc.exe        All-in-one compiler/linker/dep-scan
    olib.exe      Archive manager
  src/          Oberon source for all tools
    oc/           Compiler + linker (Main, Parser, Link, …)
    olib/         Archive manager source
    tools/        Test tools (rdfgrep.Mod)
  src-lib/      Oberon library sources + SYSTEM assembly
  lib/          Compiled library output (OBERON.OM after make)
  tests/        Test suite (MANIFEST.TSV, T*.Mod, testall.Mod, …)
  docs/         Grammar, ABI, build and test reference
  CLAUDE.md     Developer guide for Claude Code sessions
  MANUAL.MD     Programmer manual: dialect, ABI, calling conventions

Requirements:

• GNU make
• xt DOS emulator (required for all compilation — runs boot/oc.exe and bin/oc.exe)

Build:

make          # boot/oc.exe → stdlib → bin/oc.exe → bin/olib.exe → tools → OBERON.OM
make test     # full clean + rebuild + run 247 manifest tests (host-side, fast)
make testall  # full DOS-side suite via xt: manifest + Section 17/18 (~9 min)

Compile a module (via xt):

xt run --max=50000000 -c . bin/oc.exe -L lib Hello.Mod

Compile + link to executable:

xt run --max=50000000 -c . bin/oc.exe -L lib -entry Run Hello.Mod hello.exe
xt run --max=5000000 hello.exe

Use on real MS-DOS:

SET OBERON_LIB=C:\lib
oc.exe Hello.Mod
oc.exe -entry Run Hello.Mod hello.exe

VAR parameters pass a 4-byte far address; open-array formals use a 6-byte slot {offset, segment, LEN}.

DOS real-mode large model: CS≠DS≠SS. The linker places all modules' data in one combined DS, code groups in their own CS paragraphs, and the stack in a separate SS. SYSTEM.ADR returns a full far ADDRESS (segment:offset) for any variable form; locals use SS, globals use DS.

247-row manifest test suite plus Section 17 executable tests and Section 18 unit tests.

• MANUAL.MD — programmer manual: dialect, ABI, calling conventions, open arrays
• docs/oberon07.ebnf — authoritative grammar
• docs/oberon-language.md — type sizes, ABI, naming, FAR/NEAR, module init
• docs/implementation-rules.md — DOS/portability rules
• docs/build.md — detailed build instructions and oc.exe usage
• docs/tests.md — all test information: how to run, add, and interpret tests
• docs/xt.md — xt emulator reference
• docs/rdoff2-spec.md — RDOFF2 format specification

Public domain. See LICENSE.TXT.