044b98dcc4
RTTI at vtable[-1] names the class .?AVSilphScriptPhase@silph@@ and the next class's COL at 0x820A8680 terminates the table at 113 entries. The earlier ">=200 slots" reading used a bad terminator -- scanning for a non-code word runs straight into the next vtable. Cross-check: the 147 built-in stubs use 109 distinct slots, min 0 max 110. The next vtable is .?AVSilphScriptPhaseDemo@silph@@, also 113 slots, overriding 109 of them with mostly one shared stub -- a cut-down phase. That explains why sub_822710D0 has two callers: sub_82263408 and sub_82275800 are the two classes' Update, both slot 111. Both "unread spawner callers" are placed: sub_82264058 is slot 0 of SilphScriptPhase and sub_82273910 is slot 0 of the Demo class -- the two destructors. Also records a negative: the Stage%02d construction site I proposed last iteration does not exist (no stage format string among the 43 short %d strings; no precomputed name hash anywhere), so the stage-index lead cannot be settled that way. Docs only; artefacts byte-identical.
147 lines
6.8 KiB
Markdown
147 lines
6.8 KiB
Markdown
# ✅ How a built-in's result reaches a condition — the operand chain
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The previous iteration named the branches and stated plainly that this was still
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missing: *"naming the branch does not by itself give the clear condition — that
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needs the operand chain feeding each compare."* It is read now, and it closes.
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## ⚠️ First: the corpus already had half of it, and I had written the stale file
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[`isl-bytecode.md`](isl-bytecode.md) — which **owns** the opcode table — already
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named ops 21–24 (`push.i` / `push.f` / `pop.i` / `pop.f`) and ops 13–18 as the
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six branches. My own [`isl-branches.md`](isl-branches.md), written one iteration
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earlier, said `op23` and `op21` were unread. **The stale file was mine.**
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Verified rather than assumed, from the thunks and handlers:
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| op | moves | verified by |
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|---|---|---|
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| 21 `push.i` | `[phase+168]` → deque at `phase+44` | thunk: `addi r4,r30,168` / `addi r3,r30,44` |
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| 22 `push.f` | `[phase+184]` → deque at `phase+64` | thunk: `addi r4,r30,184` / `addi r3,r30,64` |
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| 23 `pop.i` | → `[phase+168]` | handler `0x82271C30`, only r3-offset touched is **168** |
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| 24 `pop.f` | → `[phase+184]` | handler `0x82271CB8`, only r3-offset touched is **184** |
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With `isl-bytecode.md`'s operand-kind table (`special[0] = [phase+164]`,
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`special[1] = [phase+168]`), `pop.i` lands in **`special[1]`**.
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## ✅ The built-in table is a thin dispatch layer over a vtable
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Each of the 147 entries is a **stub**, not an implementation. The stub resolves
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the `local[]` argument base and tail-calls a fixed slot of the `ScriptPhase`
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vtable at `[phase+0]`:
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```
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82272DFC addi r3, r31, 20 ; local[] base
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82272E00 bl 0x82454A40 ; resolve
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82272E04 lwz r11, 0(r31) ; the vptr
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82272E10 lwz r11, 184(r11) ; <- fixed slot, one per built-in
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82272E14 b 0x822724F0 ; mtspr CTR / bcctrl, then return 0
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```
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Measured over all 147:
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| | count |
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|---|---|
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| dispatched through a `ScriptPhase` vtable slot | **112** |
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| write `[phase+164]` (`special[0]`) inline in the stub | 17 |
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| write `[phase+184]` inline | 0 |
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**Every named predicate is in the vtable group** — `unit_state` 184,
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`unit_alive` 188, `hp_pct_test` 64, `dist_lt` 56, `unit_hp_pct` 256,
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`is_engaged` 252, `group_ratio_pct` 196, `timer_elapsed` 372,
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`player_gauge0/1_test` 396/400 — which is the control: the split is not
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arbitrary, it separates engine queries from script-local bookkeeping.
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## ✅ The vtable is at `0x820A84BC`, derived self-checkingly
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Not guessed from a stride — the trap this corpus already paid for. Derived from
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a **known implementation**:
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1. `isl-bytecode.md` documents built-in **39** `MARK_LAST_PHASE` as `[phase+300] = 2`.
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2. The function `0x8226B498` is exactly `addi r11,r0,2 ; stw r11,300(r3) ; blr`.
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3. It appears as a data word at exactly **one** address: `0x820A8570`.
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4. Built-in 39's stub uses slot **180** → base = `0x820A8570 − 180` = **`0x820A84BC`**.
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**The check, which was not used in the derivation:** built-in **40**
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`mark_not_last` (`[phase+300] = 1`) uses slot **176**, so the base predicts
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`0x820A84A8`… and slot 176 holds `0x8226B4A8`, which is
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`addi r11,r0,1 ; stw r11,300(r3) ; blr` — the `= 1` stub sitting immediately
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after the `= 2` one. Predicted and confirmed.
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**Third, independent:** the database's own `vptr_writes` lists
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`0x820A84BC` as a vtable, written at `0x82261B80`.
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## ✅ And the result lands in `special[0]`
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`unit_state` is slot 184 → **`0x8226ADF0`**. It indexes `[phase+324]` — the unit
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array `isl-builtins.md` already documents — by `local[4]`, reads the record, and
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writes its answer to **`[phase+164]` = `special[0]`** at both its normal exit
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(`0x8226AEC4`) and its early exit (`0x8226AF48`).
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That completes the chain, and the phase-3 poll loop now reads end to end:
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```
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call unit_state(ADT308) ; result -> special[0]
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pop.i ; special[1] <- the pushed comparand
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cmp.i special[0], special[1]
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beq -> 0xFEB4 ; loop back while they are equal
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```
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**A built-in's return value is `special[0]`; the comparand is popped into
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`special[1]`; the compare and branch do the rest.** That is the shape of every
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clear condition in the corpus.
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## 🟡 Not settled
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* **The other 111 vtable slots are not read.** The base is now known, so each is
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a lookup rather than a search — but knowing where `hp_pct_test` lives is not
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the same as having read it.
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* **Which comparand each site pushes.** The loop above compares against whatever
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`push.i` put on the deque; recovering that per site needs the push tracked
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through the decode, which `isl.py` does not do.
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* **The 35 non-vtable built-ins**, and `op21`/`op22`'s generic deque helpers
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(`0x82175C20`, `0x82274BA0`), were not read — only their arguments.
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* ~~**The vtable's length.**~~ ✅ **SETTLED (2026-08-27): 113 slots (0…112).**
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## ✅ (2026-08-27) The class is `silph::SilphScriptPhase`, the vtable is 113 slots, and there is a SECOND one
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The MSVC RTTI locator sits at `vtable[-1]`. At **`0x820A84B8`** it is `0x8210DDC0`,
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whose type descriptor `0x8289CD18` spells **`.?AVSilphScriptPhase@silph@@`** — so
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the class is named, not inferred.
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The vtable **ends at `0x820A867C`, 113 entries**. The terminator is not "a
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non-code word" — a scan on that rule runs straight past the end, which is why an
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earlier pass reported "≥200 slots, no non-code word in the first 200". The real
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terminator is **the next class's COL**: `0x820A8680` holds `0x8210DD74`, and a
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second vtable begins at `0x820A8684`.
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**Cross-check, independent of the RTTI:** the 147 built-in stubs between them
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reference **109 distinct slots, minimum 0, maximum 110** — every one inside
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0…112. A wrong length would have stubs pointing past the end.
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### The second class: `silph::SilphScriptPhaseDemo`
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`0x8210DD74` → type descriptor `0x8289CCC0` = **`.?AVSilphScriptPhaseDemo@silph@@`**,
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vtable at `0x820A8684`, **also 113 slots**. It **overrides 109 of the 113**, and
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the overwhelming majority point at a single shared stub, `0x8226C160`. So the Demo
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phase implements almost none of the script surface — it keeps a handful of real
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methods (slot 15 → `sub_82391BA8`, slot 111 `Update` → `sub_82275800`,
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slot 112 → `sub_8237EF08`) and stubs the rest.
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🔑 That explains a loose end from [isl-timers](isl-timers.md): the stopwatch
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advance `sub_822710D0` has **two** callers, `sub_82263408` and `sub_82275800`.
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They are the two classes' `Update` methods — same slot 111, base and derived.
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### And both "unread spawner callers" are placed
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`isl-coroutine-spawner.md` lists `sub_82273910` and `sub_82264058` as unread
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callers of the spawner. They are a **matched pair**:
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| | slot | class |
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| `sub_82264058` | **0** | `SilphScriptPhase` |
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| `sub_82273910` | **0** | `SilphScriptPhaseDemo` |
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Slot 0 in this ABI is the scalar deleting destructor, so these are the two
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classes' teardown paths — not two separate mysteries. 🟡 *Why* a destructor
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reaches the spawner is not read here.
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