BFM-decomp/cookbook/C0337.md

§303 — MODULE ISLAND TABLES: DERIVE THE PADS AT BUILD TIME, PEEL NOTHING — THE §154-A/§260 "island-pads"/"island-blocked" WALLS DISSOLVE (P31 S62 T3a; byte-proven md_SC03_076 func_801F0A9C + func_801F0F28, sha 9a165e36…)

The shape. A module's rodata island (offset 0, [0x0, .rodata, md_X]) packs every switch's jump table in source order, each table followed by 0–n zero words; the island is bound to the main TU object, and every stub's .s carries its own table (+ its trailing pad) at the stub's position in the stream, while a matched body's cc1 emits .align 3 + $L + N entries — the real entries only. §260 peeled only END-adjacent tables into their own object; interior tables ("island-blocked") and padded tables ("island-pads") were refused: 16 + 9 fns in the S62 resolver stock alone.

The law: emission order == island order, so the object can emit the whole island in place. cc1 places each table at its function's position; INCLUDE_ASM'd .s blocks interleave in place; C const data (D_…:) lands where the source puts it. The ONLY missing bytes are the pads a matched body no longer supplies — and they are computable from the retail island. tools/jtbl_rodata_pads.py:

• is now table-aware: it acts only on an .align 3 that a $L label follows; const data (.align 2, D_…:, .byte), includes and string pools pass through untouched;
• takes trailing pads: token 0t1 = no leading pad, one zero word after the table (4t2 etc.);
• --derive <binary> --tu <tu> (modules; wired in the Makefile for every md_ object):* parses the maspsx stream's rodata items in order — .included .s blocks (span from their /* off vaddr */ comments, sized by directive when the comment carries no hex), C data objects (start = the address in the D_XXXXXXXX name, size from the directives), C tables — then walks the retail island: a .s span must start exactly at the running position, C data at its aligned address, and a C table takes lead 4 iff the retail word at the position is zero, N in-range code words, then trailing zeros up to the next anchor (or the next non-zero word); an anchorless stream (an isolated §260 object) is framed by its yaml .rodata piece. Any anchor miss refuses with the offset — a CARVE-DRIFT verdict AT BUILD TIME, attributable, never a silent shift.
• Nothing is stored (R33): no modules.mk spec, no yaml edit, no isolation — so nothing can drift (contrast §302: every S61 red was a stored carve spec drifting).

Gate side. harvest_verify._jtbl_prep_one: a module island wall now just leaves the splice in place ([jtbl] module island table … handled by --derive); the build judges. The old §260 peel stays valid for already-peeled pieces (--tu frames them).

Controls. Positive: the derive reproduces the hand-proven 0t1,0 and its filtered output is byte-identical to the stored-spec output. Negative: every module binary rebuilt through the derive stage must stay byte-identical (the S62 module sweep — count quoted in the phase log).