starkernel: item 3.1 -- the Stadium cell and header

Punch list §25 item 3.1 complete. Defines StadiumPatronHeader and StadiumContinuationCell in new include/starkernel/vm/stadium.h, unioned as StadiumCell per §3's closed two-valued union. src/starkernel/vm/stadium.c added to Makefile.starkernel's LOADER_EXTRA_SRCS/KERNEL_EXTRA_SRCS so the header's compile-time size checks are actually compiled, not merely included by something that never builds. Discriminator ruled an external side bitmap (Captain Bob), not a header field -- amended into §3 and §23.3 before this code was written. Item 3.1 declares the bitmap's purpose/indexing in a comment only; allocating it is item 3.2's scope. Both cell shapes counted for real at exactly 64 bytes with zero compiler-inserted padding (three C99-portable negative-array-size assertions -- no _Static_assert, this project targets C99). Header matches §23.3's original 32+32 split unchanged, since the discriminator moving outside the cell left nothing to compete for that space. Continuation cell matches item 1.12's 4+60 figure unchanged for the same reason. Verified the size assertion is actually live: broke it to 63, confirmed the build failed with the expected negative-array-size error, restored it, confirmed a clean compile. Verified: three-architecture boot (amd64, aarch64, riscv64), all reaching ok> with identical dict_hash=0x3d4e1daf289da94f matching the item-2.2 baseline. Confirmed stadium.o present in both obj/loader/vm and obj/kernel/vm post-build on amd64, closing the gap the item-2.2 WIP exposed (an uncompiled header proves nothing). Left open, not fabricated: §23.4 #2 ("does a typical message fit in one cell") is unanswerable today -- no message patron struct exists anywhere in this tree yet. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
2026-08-04 14:55:30 -04:00
parent 05c9eba360
commit d55ec3241b
11 changed files with 31498 additions and 10 deletions
@@ -138,6 +138,16 @@ never reaped and never dispatched — it is floor space, accounted for in its ow
 > the Stadium, resolved and ranked exactly as any other patron. `contains` is a reference to
 > that residency, not a physical embedding of one patron's cells inside another's. See §8 for
 > what this wire is for and why it replaced a lock.
+>
+> **Amended by item 3.1 (2026-08-04) — the header/continuation discriminator is an
+> external side bitmap, not a header field.** A flat-array scan must tell a header cell
+> from a continuation cell before it knows which shape it is looking at. That rules out
+> folding a tag into either variant's own bytes: a continuation cell has no header fields
+> to place one in, and forcing a common leading tag byte into both shapes would eat into
+> the continuation cell's usable payload, contradicting §23.3's 60-byte figure. Ruled: one
+> bit per cell, in a bitmap kept outside the 64-byte cell array. Item 3.1 declares the
+> bitmap's purpose and indexing; item 3.2 (boot-time allocation) allocates it, since it is
+> Stadium-sized memory decided at boot alongside the cell array itself.

 **The code field is the entire type system.** A block's code field migrates. A message's
 delivers. A VM's ticks. The engine never asks what kind of thing it is holding; it
@@ -1899,13 +1909,14 @@ These are numbers to check against a real build, not derived truths.
 | Continuation cell | **undetermined** | see below — depends on an unsettled encoding |

 The four reserved bytes are deliberate rather than a rounding artefact. The fields above sum
-to 28; padding to 32 keeps the header a clean half-cell, leaves room for the
-header/continuation discriminator §3 now requires, and gives the `contains` wire item 1.1
-resolved to somewhere to live. Whether 4 bytes actually covers `contains` at whatever width
-gets chosen (it is an index, the same kind of quantity as `link`, currently sized at 4 bytes
-itself) is exactly the kind of thing item 3.1's real byte count settles, not this section —
-flagged here rather than assumed. Reserved space in a header that is expected to grow is
-cheaper than repacking one later.
+to 28; padding to 32 keeps the header a clean half-cell and gives the `contains` wire item
+1.1 resolved to somewhere to live — a 4-byte index, the same width as `link`. (The
+header/continuation discriminator does not compete for this space: item 3.1 ruled it an
+external side bitmap, not a header field — see §3's amendment.) Whether 4 bytes is the
+final byte count item 3.1 settles on for `contains`, or whether it can shrink, is exactly
+the kind of thing item 3.1's real byte count settles, not this section — flagged here
+rather than assumed. Reserved space in a header that is expected to grow is cheaper than
+repacking one later.

 256 KB per VM is comfortable against QEMU's `-m 1024`, and the outer Stadium's capacity
 (§20.5 #1) then follows from how many VMs the machine is willing to host.
@@ -2608,13 +2619,61 @@ document and committing that amendment as its own item.*

 *Blocked on Phase 0 complete, and on items 1.1–1.7 and 1.12.*

- [ ] **3.1 — Cell and header.** Define the entry with all eight wires (§3) — **nine if
+- [x] **3.1 — Cell and header.** Define the entry with all eight wires (§3) — **nine if
  item 1.1 resolves to a holder index.** Define both members of §3's closed two-valued
  union: patron header and continuation cell. Validate the 64-byte cell by counting real
  bytes; adjust and record if it does not fit.
  **Blocked on:** item 1.1 (may add a wire) and item 1.12 (the continuation-cell encoding —
  contiguous or linked — which sets the mass of every large patron and cannot be guessed).
  *Refs:* §3, §23.3, §23.4 #4.
+
+  > **DONE 2026-08-04.** `StadiumPatronHeader` and `StadiumContinuationCell` defined in the
+  > new `include/starkernel/vm/stadium.h`, unioned as `StadiumCell`; translation unit
+  > `src/starkernel/vm/stadium.c` added to `Makefile.starkernel`'s `LOADER_EXTRA_SRCS` /
+  > `KERNEL_EXTRA_SRCS` so the header actually gets compiled, not merely included by
+  > something that never builds.
+  >
+  > **Discriminator ruling, made before this item's code was written (Captain Bob's call):**
+  > the header/continuation discriminator is an external side bitmap, one bit per cell, kept
+  > outside the 64-byte cell array — not a header field. Amended into §3 and §23.3
+  > accordingly. Item 3.1 declares the bitmap's purpose and indexing contract in a comment;
+  > it does not allocate it — that is item 3.2's scope, since sizing depends on the memory
+  > budget item 3.2 works from.
+  >
+  > **Byte count, both counted for real, both exactly 64 with zero compiler-inserted
+  > padding** (verified via three C99-portable negative-array-size assertions, no
+  > `_Static_assert` — this project targets C99, not C11):
+  > - `StadiumPatronHeader`: `identity` u64(8) + `heat` u64(8) + `ttl` u32(4) + `link` u32(4)
+  >   + `contains` u32(4) + `mass` u16(2) + `flags` u8(1) + `behaviour` u8(1) +
+  >   `payload` u8[32] = 64. `pin` lives as bit 0 of `flags`, not its own field, matching
+  >   §3/§23.3. Fields ordered largest-to-smallest so every offset is already a multiple of
+  >   its own alignment and the 64-byte total is a multiple of the struct's 8-byte max
+  >   alignment — no padding, without resorting to a `packed` attribute (a GNU extension,
+  >   forbidden by CLAUDE.md's strict-ANSI-C99 rule).
+  >   Because the discriminator moved outside the cell, this matches §23.3's original
+  >   32-byte-header / 32-byte-inline-payload proposal exactly — no adjustment needed here,
+  >   unlike the continuation cell below.
+  > - `StadiumContinuationCell`: `next` u32(4) + `payload` u8[60] = 64, unchanged from
+  >   item 1.12's figure — the discriminator living outside the cell means neither variant's
+  >   byte budget was disturbed by it.
+  >
+  > **Assertion proven live, not just present:** temporarily changed the header check's
+  > expected size to 63, recompiled `stadium.c` standalone
+  > (`cc -std=c99 -Wall -Werror -Wextra -D__STARKERNEL__`), confirmed the build failed with
+  > `error: size of array 'stadium_header_size_check' is negative`, then restored it and
+  > confirmed a clean compile.
+  >
+  > **Regression: clean, and `stadium.o` confirmed present.** All three architectures boot to
+  > `ok>` with identical `dict_hash=0x3d4e1daf289da94f`, matching the item-2.2 baseline —
+  > amd64 (`logs/20260804-145132`), aarch64 (`logs/20260804-145232`), riscv64
+  > (`logs/20260804-145329`). `find build/<arch> -iname stadium*` confirmed
+  > `obj/loader/vm/stadium.o` and `obj/kernel/vm/stadium.o` both exist post-build, closing
+  > the gap the WIP on item 2.2 exposed: a header nothing compiles proves nothing.
+  >
+  > **Open, deferred honestly:** §23.4 #2 ("does a typical message still fit in one cell")
+  > remains unanswered — there is no message patron struct anywhere in this tree yet
+  > (messages are undesigned future work), so there is nothing concrete to check the 32-byte
+  > inline payload against. Not fabricated a number to close this; left open.
 - [ ] **3.2 — Boot-time allocation.** One global cell array, sized from the memory budget,
  before any VM exists. *Refs:* §6, §17.6, §22.3.
 - [ ] **3.3 — Behaviour enumeration and dispatch.** Closed tag set fixed at build time.
@@ -449,7 +449,8 @@ LOADER_EXTRA_SRCS := \
    $(KERNEL_SRC)/vm/vm_bootstrap.c \
    $(KERNEL_SRC)/vm/vm_runtime.c \
    $(KERNEL_SRC)/vm/alloc_kernel.c \
-    $(KERNEL_SRC)/vm/q48_stubs.c
+    $(KERNEL_SRC)/vm/q48_stubs.c \
+    $(KERNEL_SRC)/vm/stadium.c

 KERNEL_EXTRA_SRCS := $(LOADER_EXTRA_SRCS)

@@ -1,5 +1,5 @@
 # Capsule Block Manifest — Auto-generated
-<!-- Generated by mkcapsule --manifest  2026-08-04T17:50:45Z -->
+<!-- Generated by mkcapsule --manifest  2026-08-04T18:53:13Z -->
 <!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh.  -->
 <!-- Hand-written justifications and immutability notes live  -->
 <!-- in MANIFEST.md alongside this auto-generated index.      -->
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@@ -0,0 +1,59 @@
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+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  This file is part of the StarForth project.
+
+  Licensed under the StarForth License, Version 1.0 (the "License");
+  you may not use this file except in compliance with the License.
+
+  You may obtain a copy of the License at:
+      https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
+
+  This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  express or implied, including but not limited to the warranties of
+  merchantability, fitness for a particular purpose, and noninfringement.
+
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ */
+
+/**
+ * stadium.h - The Stadium cell and header (FABRIC.md §3, punch list item 3.1)
+ *
+ * A cell is one of exactly two things: a patron header, or a continuation
+ * cell owned by exactly one patron. The union is closed, two-valued, and
+ * fixed at build time -- not a type field. See FABRIC.md §3.
+ */
+
+#ifndef STARKERNEL_VM_STADIUM_H
+#define STARKERNEL_VM_STADIUM_H
+
+#ifdef __STARKERNEL__
+
+#include <stdint.h>
+
+#define STADIUM_CELL_BYTES 64
+
+/*
+ * StadiumPatronHeader - one member of the closed two-valued cell union
+ * (FABRIC.md §3). Nine wires: identity, heat, TTL, pin (a bit in `flags`),
+ * link, code field (`behaviour`), mass, payload, contains. `flags` bit 0 is
+ * `pin`; the remaining bits are reserved. `behaviour` is the closed code-field
+ * enumeration (§18.3) -- not yet defined, item 3.3's scope.
+ *
+ * Field order is largest-to-smallest so natural C99 alignment adds zero
+ * padding: every offset below is already a multiple of that field's own
+ * alignment, and the struct's total size (64) is a multiple of its max
+ * alignment (8), so no compiler inserts trailing padding either. Do not
+ * reorder without re-checking this holds on all three ISAs.
+ */
+typedef struct {
+    uint64_t identity;     /* offset 0  -- handle or name, never a content hash while resident (§24.4) */
+    uint64_t heat;         /* offset 8  -- Q48.16, conserved share of 1.0 (§19.1) */
+    uint32_t ttl;          /* offset 16 -- remaining lifetime; messages and ACLs only (§17.1) */
+    uint32_t link;         /* offset 20 -- index into the Stadium, not a pointer */
+    uint32_t contains;     /* offset 24 -- index of the patron held inside this one, or none (item 1.1) */
+    uint16_t mass;         /* offset 28 -- cells this patron occupies (§19.2) */
+    uint8_t  flags;        /* offset 30 -- bit 0 = pin; remaining bits reserved */
+    uint8_t  behaviour;    /* offset 31 -- code field, closed enumeration (§18.3) */
+    uint8_t  payload[32];  /* offset 32 -- inline payload, used when mass == 1 */
+} StadiumPatronHeader;
+
+/*
+ * StadiumContinuationCell - the other member of the union. Owned by exactly
+ * one patron header, chained by `next`. Never ranked, never reaped, never
+ * dispatched (§3) -- pure floor space, accounted for in its owner's mass.
+ */
+typedef struct {
+    uint32_t next;          /* offset 0 -- index of the next continuation cell, or none */
+    uint8_t  payload[60];   /* offset 4 */
+} StadiumContinuationCell;
+
+/*
+ * StadiumCell - the closed two-valued union itself (§3). Which member is
+ * valid for a given array slot is NOT stored in the cell -- FABRIC.md's item
+ * 3.1 amendment to §3 rules this an external side bitmap, one bit per cell,
+ * kept outside the cell array. Declared here as the indexing contract this
+ * type expects; item 3.2 (boot-time allocation) allocates the bitmap itself.
+ */
+typedef union {
+    StadiumPatronHeader     header;
+    StadiumContinuationCell continuation;
+} StadiumCell;
+
+/* C99-portable compile-time size assertions (no _Static_assert -- that's C11). */
+typedef char stadium_header_size_check[(sizeof(StadiumPatronHeader) == STADIUM_CELL_BYTES) ? 1 : -1];
+typedef char stadium_continuation_size_check[(sizeof(StadiumContinuationCell) == STADIUM_CELL_BYTES) ? 1 : -1];
+typedef char stadium_cell_size_check[(sizeof(StadiumCell) == STADIUM_CELL_BYTES) ? 1 : -1];
+
+#endif /* __STARKERNEL__ */
+
+#endif /* STARKERNEL_VM_STADIUM_H */
@@ -0,0 +1,33 @@
+/*
+  StarForth — Steady-State Virtual Machine Runtime
+
+  Copyright (c) 2023–2025 Robert A. James
+  All rights reserved.
+
+  This file is part of the StarForth project.
+
+  Licensed under the StarForth License, Version 1.0 (the "License");
+  you may not use this file except in compliance with the License.
+
+  You may obtain a copy of the License at:
+      https://github.com/star.4th@proton.me/StarForth/LICENSE.txt
+
+  This software is provided "AS IS", WITHOUT WARRANTY OF ANY KIND,
+  express or implied, including but not limited to the warranties of
+  merchantability, fitness for a particular purpose, and noninfringement.
+
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ */
+
+/**
+ * stadium.c - Translation unit for the Stadium cell definitions (item 3.1).
+ *
+ * Exists so stadium.h's compile-time size assertions are actually compiled
+ * on all three architectures, not merely included by something that never
+ * builds. No behavior yet -- item 3.2 onward adds the array, dispatch, and
+ * ranking.
+ */
+
+#include "starkernel/vm/stadium.h"