Audit-059 round 19 isolated the round-18 worker fault: the four silph::
WorkerCtx worker bodies all execute the sequence
lwz r3, 44(rN) ; r3 = [ctx+0x2C] — sub-object pointer
lwz r11, 0(r3) ; r11 = sub-object vtable
lwz r11, 60(r11) ; r11 = sub-object vtable[15]
mtctr r11
bctrl
Ours left [ctx+0x2C] NULL → PC=0 fault on first virtual dispatch. Round 19
recommended materialising a sub-object whose vtable points entirely at an
existing trivial-return stub so workers idle live, returning NULL work,
without crashing.
Changes (silph_synth.rs only, +63/-6):
- Grow SILPH_CTX_SIZE 0x500 → 0x800 to embed sub-object at +0x300 and a
32-slot sub-vtable at +0x500 in the same heap_alloc.
- After ctx header init, write sub-object pointer at [ctx+0x2C], the XEX-
resident wrapper constant 0xBE568F00 (round-7 finding) at [ctx+0x30],
and leave [ctx+0x28] NULL (matches canary first-fire snapshot).
- Populate every slot of the 32-entry sub-vtable with VA 0x8216CAA4, the
first 4-byte-aligned standalone `li r3, 0; blr` stub located by a fresh
PE-text scan (preceded by a `blr` terminating the previous function).
- Sub-object body itself is zero-filled apart from the [+0]=vtable_ptr
write; round-19 disassembly confirms workers only touch slots 15/17.
Smoke (XENIA_SILPH_SYNTH=1, persistent cache, 5e7 instr):
- Lockstep: no crash, all 4 workers (tid=6/7/8/9) reach Ready in deep
worker-body PCs (0x825067xx/0x825089xx/0x825091xx). Verdict (D) —
workers run their idle loop returning NULL; existing silph waiters
(0x1020, 0x1090) remain <NO_SIGNALS_DESPITE_WAITS> because we
deliberately neutered productive work.
- Parallel: identical picture, no PC=0/PC=garbage fault anywhere.
No regression in 765-test suite.
Next round: feed real work-items into the intrusive ring at ctx+0x210
so workers' returned-NULL idle becomes returned-work productive; or
discover which sub-vtable slots actually need real callees (slot 15
worker drain, slot 17 producer).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
8683fb59ed