# SX VM Opcode Extension Mechanism

Mechanism in `hosts/ocaml/lib/` that lets language ports register specialized
bytecode opcodes without modifying the SX VM core. Direct prerequisite for
**erlang-on-sx Phase 9** (the BEAM analog) and a structural enabler for any
future language port that wants performance-critical opcodes.

Reference: `plans/erlang-on-sx.md` Phase 9, `plans/fed-sx-design.md` §17.5,
`hosts/ocaml/lib/sx_vm.ml` (current VM).

Status: **complete** on `loops/sx-vm-extensions` (Phases A-E landed
2026-05-14 / 2026-05-15). Ready for first real consumer
(`hosts/ocaml/lib/extensions/erlang.ml`, replacing the Phase 9b stub
dispatcher in `lib/erlang/vm/dispatcher.sx`).

---

## Goal

Allow language ports to register custom bytecode opcodes in the SX VM, with:

- **Zero overhead for core opcodes.** Existing opcodes (current ceiling 175,
  see `sx_vm.ml`) must dispatch identically. No regression for any existing
  language port or the core SX runtime.
- **One additional dispatch step for extension opcodes.** Acceptable cost; the
  win comes from avoiding the general CEK machinery.
- **Per-extension state slot.** Erlang's process scheduler, Haskell's thunk
  cache, etc. need somewhere to hang state alongside the VM.
- **Compiler awareness.** The bytecode compiler (`lib/compiler.sx`) must be
  able to emit extension opcodes by name, looked up against the registered
  set.
- **JIT compatibility.** Existing JIT (lazy lambda compilation) continues to
  work for code paths using only core opcodes. Extension opcodes are
  interpreted in v1; JITing them is a follow-up.

## Non-goals

- **Hot opcode reload.** Adding/replacing opcodes mid-runtime is not in
  scope. Extensions are compile-time additions to the OCaml binary. (If
  needed, that's a separate project.)
- **Per-instance opcode sets.** All running instances of the SX VM share
  the same opcode set determined at build time. Selective opcode loading
  per instance is out of scope.
- **Opcode hot-swap or supersession.** Once registered, opcodes are stable
  for the lifetime of the binary.
- **Language-port isolation at the dispatch layer.** Two language ports can
  see each other's opcodes (they share the dispatch table). Isolation is a
  build-time concern — don't compile in extensions you don't trust.

---

## Why now

The Erlang-on-SX Phase 9 work needs this. Without it, Phase 9b-9g (the actual
opcode implementations) have nowhere to plug in. The Erlang loop hit this
dependency as a Blocker (`0abf05ed`); this design is what unblocks it.

It also enables the **shared opcode pattern** discussed in `plans/fed-sx-
design.md` §17.5: opcodes Erlang Phase 9 produces that other ports could
plausibly use (pattern match, perform/handle, record access) get chiselled
out to `lib/guest/vm/` when a second port has an actual second use. Without
the extension mechanism, each port would have to fork the SX VM core or
modify shared dispatch — neither acceptable.

---

## Architectural overview

```
                ┌──────────────────────────────────────────┐
                │ SX VM core (hosts/ocaml/lib/sx_vm.ml)    │
                │                                            │
                │  ┌────────────────────────────────────┐  │
                │  │ Bytecode dispatch loop             │  │
                │  │                                     │  │
                │  │ match op with                       │  │
                │  │   | 1  (OP_CONST) -> ...           │  │
                │  │   | 2  (OP_NIL)   -> ...           │  │
                │  │   | ...                            │  │
                │  │   | 175 -> ... (last core opcode)  │  │
                │  │   | op when op >= 200 ->            │  │
                │  │       !extension_dispatch_ref op    │  │ ◄── new
                │  │       vm frame                      │  │
                │  └────────────────────────────────────┘  │
                │                                            │
                │  ┌────────────────────────────────────┐  │
                │  │ Extension registry                 │  │
                │  │   opcode_id -> handler             │  │ ◄── Phase B
                │  │   opcode_name -> opcode_id         │  │
                │  │   extension_state per extension    │  │
                │  └────────────────────────────────────┘  │
                └──────────────────────────────────────────┘
                                   ▲
                                   │ register at startup
                ┌──────────────────┴──────────────────────┐
                │ Extension modules                       │
                │  hosts/ocaml/lib/extensions/erlang.ml   │
                │  hosts/ocaml/lib/extensions/haskell.ml  │
                │  hosts/ocaml/lib/extensions/datalog.ml  │
                │  hosts/ocaml/lib/extensions/guest_vm.ml │ ◄── shared opcodes
                └─────────────────────────────────────────┘
```

### Opcode ID space partition

Current SX VM uses opcode IDs from 1 to 175 (per inspection of `sx_vm.ml`,
ceiling at OP_DEC = 175). We partition the 0-255 space:

| Range   | Use                                                              |
|---------|------------------------------------------------------------------|
| 0       | reserved / NOP                                                   |
| 1-199   | **core opcodes** — owned by the SX VM, locked schema             |
| 200-247 | **extension opcodes** — registered by extensions (ports + shared) |
| 248-255 | reserved for future expansion / multi-byte opcodes               |

This gives the core 24 free slots above the current 175 ceiling for future
core additions, and 48 slots for extensions. Erlang Phase 9 expects to need
fewer than 30 specialized opcodes, so this is comfortable headroom.

The plan originally proposed a finer split (`128-199` for `lib/guest/vm/`
shared, `200-247` for ports). That distinction is preserved at the **naming
level** (`guest_vm.OP_X` vs `erlang.OP_Y`) and policed by the registry
(duplicate IDs fail at startup), without consuming separate ID ranges. The
chiselling discipline (move an opcode to `guest_vm` when a second port uses
it) operates at the source level.

If we need more than 256 opcodes total, multi-byte opcodes (a leading 248-255
byte plus a second byte) extend the space without breaking the schema.

### Extension module signature

```ocaml
(* hosts/ocaml/lib/sx_vm_extension.ml *)

(** A handler for an extension opcode. Reads operands from bytecode,
    manipulates the VM stack, updates the frame's instruction pointer.
    May raise exceptions (which propagate via the existing VM error path). *)
type handler = vm -> frame -> unit

(** State an extension carries alongside the VM. Opaque to the VM core;
    extensions cast as needed. *)
type extension_state = ..

module type EXTENSION = sig
  (** Stable name for this extension (e.g. "erlang", "guest_vm"). *)
  val name : string

  (** Initialize per-instance state. Called once when the VM starts and the
      extension is loaded. *)
  val init : unit -> extension_state

  (** Opcodes this extension provides. Each is (opcode_id, opcode_name, handler).
      opcode_id must be in 200-247. Conflicts cause startup failure. *)
  val opcodes : extension_state -> (int * string * handler) list
end
```

### Registration and dispatch

```ocaml
(* hosts/ocaml/lib/sx_vm_extensions.ml *)

let extensions : (module EXTENSION) list ref = ref []
let states : (string, extension_state) Hashtbl.t = Hashtbl.create 8
let by_id : (int, handler) Hashtbl.t = Hashtbl.create 64
let by_name : (string, int) Hashtbl.t = Hashtbl.create 64

let register (m : (module EXTENSION)) =
  let module M = (val m) in
  let st = M.init () in
  Hashtbl.add states M.name st;
  List.iter (fun (id, name, h) ->
    if Hashtbl.mem by_id id then
      failwith (Printf.sprintf "Opcode %d (%s) already registered" id name);
    Hashtbl.add by_id id h;
    Hashtbl.add by_name name id
  ) (M.opcodes st);
  extensions := m :: !extensions

let dispatch op vm frame =
  match Hashtbl.find_opt by_id op with
  | Some handler -> handler vm frame
  | None -> raise (Invalid_opcode op)

let id_of_name name = Hashtbl.find_opt by_name name
let state_of_extension name = Hashtbl.find_opt states name
```

Phase B installs this dispatcher into `Sx_vm.extension_dispatch_ref` at
module init. Until then, the ref's default raises `Invalid_opcode op` for
any opcode ≥ 200, which is the Phase A test condition.

The dispatch path adds **one hashtable lookup per extension opcode**.
Acceptable cost — and Erlang's specialized opcodes win >100× over going
through the general CEK machine, so the overhead is negligible by comparison.

### Bytecode compiler integration

The compiler (`lib/compiler.sx`) needs to know extension opcode IDs to emit
them. New SX primitive exposed to the compiler:

```sx
(extension-opcode-id "erlang.OP_PATTERN_TUPLE_2") ; → 200, or nil if not loaded
```

When the compiler wants to emit a specialized opcode, it queries by name. If
the extension isn't loaded, the compiler falls back to the general path
(emit a `CALL_PRIM` or general SX `case`). This means a language port's
optimization is opt-in per build, and missing extensions degrade to slower
correct execution rather than failure.

Naming convention: `<extension-name>.OP_<NAME>`. So `erlang.OP_PATTERN_TUPLE_2`,
`guest_vm.OP_PERFORM`, etc.

### Per-extension state access

Some opcodes need state beyond the VM stack (Erlang's scheduler, mailbox
state, etc.). Extensions store state in their `init`-returned value, accessed
via `state_of_extension`:

```ocaml
let op_spawn vm frame =
  let st = Sx_vm_extensions.state_of_extension "erlang"
           |> Option.get
           |> Obj.magic in   (* extension casts to its known type *)
  let body = pop vm in
  let pid = Erlang_scheduler.spawn st body in
  push vm (pid_value pid);
  frame.ip <- frame.ip + 1
```

Shared scheduler state lives in the Erlang extension's state value. Other
extensions don't see it.

---

## Phase plan

Five sub-phases in dependency order. Each is testable in isolation.

### Phase A — Opcode ID partition + dispatch fallthrough

- [x] Define `exception Invalid_opcode of int` in `sx_vm.ml`.
- [x] Add `extension_dispatch_ref : (int -> vm -> frame -> unit) ref`
      whose default handler raises `Invalid_opcode op`. Forward-declared in
      the same style as the existing `jit_compile_ref`.
- [x] Add `| op when op >= 200 -> !extension_dispatch_ref op vm frame` arm
      in the dispatch loop, immediately before the catch-all.
- [x] Document the partition in a comment near the top of the opcode list.

**Tests:**
- All existing OCaml VM/CEK tests pass unchanged (zero regression for core).
- Constructed bytecode using opcode 200 raises `Invalid_opcode 200` when no
  extension is registered.

**Effort:** small. ~50 lines + tests.

### Phase B — Extension registry module

`hosts/ocaml/lib/sx_vm_extensions.ml` per the sketch above. Pure plumbing, no
opcodes yet. Phase B's module init installs the real `dispatch` into
`Sx_vm.extension_dispatch_ref`, replacing Phase A's stub.

- [x] `Sx_vm_extension` interface module (handler type, EXTENSION sig).
- [x] `Sx_vm_extensions` registry module (`register`, `dispatch`,
      `id_of_name`, `state_of_extension`).
- [x] Wire the registry's `dispatch` into `Sx_vm.extension_dispatch_ref` at
      module init.

**Tests:**
- Register a test extension with one opcode; dispatch finds it.
- Duplicate opcode-id registration fails at startup.
- `id_of_name` and `state_of_extension` lookups work.

**Effort:** small. ~150 lines + tests.

### Phase C — Compiler-side opcode lookup primitive

Expose `extension-opcode-id` as an SX primitive in `hosts/ocaml/lib/`. The
compiler in `lib/compiler.sx` can call it to emit extension opcodes by name.

Does not require any extension to actually exist — the primitive returns
`nil` for unknown names, and the compiler falls back.

- [x] Register `extension-opcode-id` in `sx_primitives.ml`.
- [x] Returns `Integer id` when registered, `Nil` otherwise.

**Tests:**
- Primitive returns nil for unknown name.
- After registering a test extension, primitive returns the registered ID.

**Effort:** small. Single primitive registration + compiler-side use docs.

### Phase D — Test extension demonstrating end-to-end flow

A dummy extension at `hosts/ocaml/lib/extensions/test_ext.ml` registering
one or two trivial opcodes (e.g. `OP_TEST_PUSH_42`, `OP_TEST_DOUBLE_TOS`).
Wired into the build, available when running tests.

Compiler test: write SX that triggers the test compiler-extension to emit
`OP_TEST_PUSH_42`, then verify the VM executes it correctly via
`bytecode-inspect` and `vm-trace`.

- [x] `test_ext.ml` registers two opcodes.
- [x] Wired into the build (extensions registered at startup).
- [x] Bytecode emission via name lookup produces the right ID.
- [x] `bytecode-inspect` shows the opcode by name.

**Tests:**
- Bytecode emission via name lookup produces the right ID.
- Execution produces the expected stack effect.
- `bytecode-inspect` shows the opcode by name.
- `vm-trace` correctly reports the extension opcode.

**Effort:** small. ~100 lines including build wiring.

### Phase E — JIT awareness (interpreted-only for v1)

The JIT (lazy lambda compilation) currently compiles based on opcode ranges.
Extension opcodes (≥200) should fall through to interpretation, not be
JIT-compiled in v1.

- [x] Mark extension opcodes as "interpret only" in the JIT pre-analysis.
- [x] Lambda containing only core opcodes JIT-compiles as before.
- [x] Lambda containing any extension opcode runs interpreted.

JITing extension opcodes is a follow-up project; v1 keeps the JIT scope
unchanged and just makes it correctly route mixed bytecode.

**Tests:**
- Lambda with only core opcodes: JIT-compiled, fast path.
- Lambda with extension opcode: interpreted, correct result.
- Mixed lambda: interpreted, correct result.

**Effort:** small-medium. Requires understanding the JIT's pre-analysis
(per `project_jit_compilation.md` memory: "Lazy JIT implemented: lambda
bodies compiled on first VM call, cached, failures sentinel-marked").
Extension-opcode detection becomes another reason to mark a lambda
"interpret-only."

---

## Acceptance criteria

1. **Phase A-D pass their test suites.**
2. **Zero regression on existing SX VM tests.** All language-port test
   suites currently passing on the architecture branch (Erlang 530+, Haskell
   285+, Datalog 276+, Smalltalk 625+, the SX core test suite, etc.) still
   pass.
3. **Test extension demonstrates the flow end-to-end.** SX source compiles
   via the compiler with a registered extension opcode, executes through the
   VM via the dispatch fallthrough, returns correct result.
4. **Documentation:** README in `hosts/ocaml/lib/extensions/` explaining the
   pattern, with a worked example (the test extension is the canonical one).

After acceptance, the Erlang-on-SX Phase 9 work in `lib/erlang/vm/` can use
this mechanism. The Erlang loop's Blocker for 9a is resolved.

---

## Risk and mitigation

**Risk: regression in core opcode dispatch.** A misplaced `match` arm could
break something. *Mitigation:* run every existing language-port conformance
suite before merging.

**Risk: opcode ID conflicts as more extensions land.** If Erlang Phase 9
claims IDs 200-220 and Haskell wants 215-235, we have a problem.
*Mitigation:* maintain a registry document at `hosts/ocaml/lib/extensions/
README.md` listing claimed ID ranges per extension. Convention: each
extension claims a contiguous block at first registration; collisions caught
at startup with a clear error.

**Risk: extension state types leak through `Obj.magic`.** The extension state
is type-erased in the registry. *Mitigation:* extensions cast in their own
opcode handlers, never expose state to other extensions or the VM core.
First-class modules / GADTs could add more type safety; deferred unless
this becomes a concrete pain point.

**Risk: extensions become a back door for kernel mutation.** An extension
opcode handler has full access to the VM. *Mitigation:* extensions are
build-time additions, not runtime; they're as trusted as the rest of the
binary. Operators audit at build time, not runtime. Same trust model as
any other compiled-in code.

**Risk: shared `lib/guest/vm/` opcodes evolve under different language
ports' needs.** *Mitigation:* the chiselling discipline (move to guest only
on second use) ensures the shared opcodes are tested against at least two
ports' actual usage before being considered stable.

---

## Open questions

To be resolved during implementation, not blocking design approval:

1. **Multi-byte opcode encoding.** If we need >256 opcodes total, the
   leading-byte 248-255 schema accommodates it. Do we need multi-byte at
   v1? Probably not — 48 extension opcodes is more than any single port
   should reasonably want.
2. **Extension ordering matters?** If two extensions register opcodes that
   read the same VM state, ordering of registration could matter for
   initialization. Probably not in practice; flag if it bites.
3. **Hot-reload of extensions.** Out of scope for v1 (per non-goals). If
   wanted later, the registry would need teardown + re-registration; the
   `gen_server` `code_change/3` model from Erlang Phase 7 is a precedent.
4. **Cross-extension opcode composition.** Can `guest_vm.OP_PERFORM` invoke
   `erlang.OP_RECEIVE_SCAN`? In principle yes — handlers can do anything.
   The interface is clean; the question is whether we want any conventions
   to keep ergonomics tractable. Defer until composition appears in
   practice.

---

## Implementation roadmap and sequencing

This is a sister workstream to `loops/erlang`. Driven by Erlang Phase 9.
Single bounded loop on `loops/sx-vm-extensions`, ~1-2 weeks.

Recommended sequencing (one phase per loop fire):

1. **Phase A** — dispatch fallthrough. Smallest viable change to `sx_vm.ml`.
2. **Phase B** — extension registry module.
3. **Phase C** — compiler-side opcode lookup primitive.
4. **Phase D** — test extension demonstrating end-to-end flow.
5. **Phase E** — JIT awareness (interpret-only routing).

After acceptance:

- **`hosts/ocaml/lib/extensions/erlang.ml`** becomes the *first real
  consumer* — written by whoever takes over from the Erlang loop's stub
  dispatcher in `lib/erlang/vm/dispatcher.sx`. That's the integration
  moment that closes the loop.

Estimated total effort: 1-2 weeks for one focused engineer with OCaml SX VM
familiarity.

---

## Relationship to other plans

- **`plans/erlang-on-sx.md` Phase 9:** unblocked by this work. Erlang loop
  develops opcodes against a stub dispatcher in `lib/erlang/vm/`; once this
  mechanism lands, swap stub for real registration via
  `hosts/ocaml/lib/extensions/erlang.ml`.
- **`plans/fed-sx-design.md` §17.5:** documents this as Layer-1 prerequisite.
  The shared-opcode discipline (lib/guest/vm/) is designed on top of this
  mechanism's namespace allocation.
- **Future language ports (Haskell, Datalog, Smalltalk perf phases):** will
  use the same mechanism. Each adds an extension module, claims an opcode
  range, registers handlers. The `lib/guest/vm/` opcodes get
  cross-referenced when the second port's needs justify chiselling.
- **JIT roadmap (per `project_jit_architecture.md` memory):** extension
  opcodes are interpreted in v1. JITing them is a logical follow-up but
  a separate project.

---

## Progress log

Newest first.

- **2026-05-15** — Phase E done. Loop complete (acceptance criteria
  1-4 all met). New `Sx_vm.bytecode_uses_extension_opcodes` walks
  bytecode operand-aware (CONST u16 indices, CALL_PRIM u16+u8,
  CLOSURE u16+dynamic upvalue descriptors) so values that happen to
  be ≥200 don't false-positive as extension opcodes. Wired into
  `jit_compile_lambda`: when the inner closure's bytecode contains
  any extension opcode, JIT returns None and the lambda runs
  interpreted via CEK (the dispatch fallthrough still routes
  extension opcodes through the registry — this just prevents the
  JIT from claiming ownership of code it can't optimise). 7 new
  foundation tests (`jit extension-opcode awareness` suite): pure
  core eligible, head/middle/post-CLOSURE detection, CONST + CALL_PRIM
  + CLOSURE-descriptor false-positive avoidance. +7 pass vs Phase D
  baseline (4833 vs 4826), 1111 pre-existing failures unchanged.
  Conformance suites green: erlang 530/530, haskell 285/285, datalog
  276/276, prolog 590/590, smalltalk 847/847, common-lisp 487/487,
  apl 562/562, js 148/148, forth 632/638 (pre-existing), tcl 3/4
  (pre-existing), ocaml-on-sx unit 607/607.

  Loop done. Hand-off: the Erlang loop's Phase 9b stub dispatcher in
  `lib/erlang/vm/dispatcher.sx` can now be replaced with a real
  `hosts/ocaml/lib/extensions/erlang.ml` consumer.

- **2026-05-15** — Phase D done. New `hosts/ocaml/lib/extensions/` subtree
  wired into the `sx` library via `(include_subdirs unqualified)`.
  `extensions/test_ext.ml` is the canonical worked example: two
  operand-less opcodes (`test_ext.OP_TEST_PUSH_42` = 220,
  `test_ext.OP_TEST_DOUBLE_TOS` = 221) carrying `TestExtState` (an
  invocation counter that exercises the per-extension state slot).
  `extensions/README.md` documents the registration pattern, opcode-ID
  range conventions, and naming rules.

  `Sx_vm.opcode_name` now consults `extension_opcode_name_ref` (forward
  ref) so disassembly shows extension opcodes by name instead of
  `UNKNOWN_n`. Registry maintains `name_of_id_table` (reverse of
  `by_name`) and installs the lookup at module init alongside the
  dispatch ref. 5 new foundation tests (`extensions/test_ext` suite):
  `extension-opcode-id` finds OP_TEST_PUSH_42, end-to-end bytecode runs
  to 84, disassemble shows opcode names, unregistered ext opcodes still
  fall back to UNKNOWN_n, per-extension state counter increments.
  +5 pass vs Phase C baseline (4826 vs 4821), 1111 pre-existing failures
  unchanged. Conformance suites green: erlang 530/530, haskell 285/285,
  datalog 276/276, prolog 590/590, smalltalk 847/847, common-lisp
  487/487, apl 562/562, js 148/148, forth 632/638 (pre-existing), tcl
  3/4 (pre-existing), ocaml-on-sx unit 607/607.

- **2026-05-15** — Phase C done. `extension-opcode-id` SX primitive
  registered from `sx_vm_extensions.ml` module init (avoids the
  `sx_primitives ↔ sx_vm` cycle by registering downstream of both).
  Accepts a string or symbol; returns `Integer id` for registered
  opcode names, `Nil` for unknown — so a missing extension at compile
  time degrades to a fallback rather than failure. 5 new foundation
  tests (`extension-opcode-id primitive` suite): registered lookup,
  unknown → nil, symbol arg, zero-arg rejection, integer-arg
  rejection. +5 pass vs Phase B baseline (4821 vs 4816), 1111
  pre-existing failures unchanged. Conformance suites green: erlang
  530/530, haskell 285/285, datalog 276/276, prolog 590/590, smalltalk
  847/847, common-lisp 487/487, apl 562/562, js 148/148, forth 632/638
  (pre-existing), tcl 3/4 (pre-existing), ocaml-on-sx unit 607/607.

- **2026-05-14** — Phase B done. Added `hosts/ocaml/lib/sx_vm_extension.ml`
  (interface: `handler` type, `extension_state` extensible variant,
  `EXTENSION` module type) and `sx_vm_extensions.ml` (registry: `register`,
  `dispatch`, `id_of_name`, `state_of_extension`, `_reset_for_tests`).
  `let () = install_dispatch ()` at module init replaces Phase A's stub
  with the real registry dispatch — Phase A behavior preserved (empty
  registry still raises `Invalid_opcode` for unregistered ops). Registry
  rejects opcode IDs outside 200-247, duplicate IDs, duplicate names, and
  duplicate extension names. 9 new foundation tests (`vm-extension-registry`
  suite): id_of_name resolve+miss, state_of_extension resolve+miss,
  end-to-end VM dispatch (push 42), opcode composition (push 42 → double
  → 84), duplicate-id / out-of-range / duplicate-name rejection. +9 pass
  vs Phase A baseline (4816 vs 4807), 1111 pre-existing failures unchanged.
  Conformance suites green: erlang 530/530, haskell 285/285, datalog
  276/276, prolog 590/590, smalltalk 847/847, common-lisp 487/487, apl
  562/562, js 148/148, forth 632/638 (pre-existing), tcl 3/4 (pre-existing),
  ocaml-on-sx unit 607/607.

- **2026-05-14** — Phase A done. Added `Invalid_opcode of int` exception,
  `extension_dispatch_ref` (default raises `Invalid_opcode op`), and the
  `| op when op >= 200 -> !extension_dispatch_ref op vm frame` arm before the
  catch-all in `sx_vm.ml`. Partition comment documents 1-199 core / 200-247
  extensions / 248-255 reserved (current core ceiling is OP_DEC = 175).
  4 new foundation tests (3 × Invalid_opcode for opcodes 200/224/247, 1 ×
  Eval_error for opcode 199 to pin the threshold). Foundation 64/64;
  full OCaml test suite +4 pass vs baseline (4807 vs 4803), 1111 pre-existing
  failures unchanged. Conformance suites green: erlang 530/530, haskell
  285/285, datalog 276/276, prolog 590/590, smalltalk 847/847, common-lisp
  305/305, apl 562/562, js 148/148, forth 632/638 (pre-existing), tcl 3/4
  (pre-existing), ocaml-on-sx unit 607/607. (Lua 0/16 and ocaml-conformance
  baseline programs not exercised — pre-existing scoreboard state and
  multi-hour runtime respectively.)

