luagc: Lua 5.1 tri-color GC with full forward barrier coverage

Major port of Lua 5.1 incremental GC patterns:

Tri-color system:
- Two-white (WHITE0/WHITE1) with currentwhite flip in atomic phase
- Objects born currentwhite via hooked luaC_link (0x6F7B20)
- String birth mark patched to currentwhite at each flip
- isDead: otherwhite check with FIXED exception for WoW
- makewhite on survivors (preserves KEYWEAK/VALUEWEAK/FIXED)
- Bootstrap: first cycle sets all existing objects to currentwhite

Mark system (5.1 reallymarkobject/propagatemark):
- Strings: stringmark inline (no gray stack)
- Userdata: go black inline, mark metatable
- Tables: gray2black, traverse, black2gray if weak
- Threads: NEVER black, always grayagain (re-traversed in atomic)
- Closures: go black normally

Forward barriers (5.1 luaC_barrierf at every write site):
- OP_SETUPVAL: VM patch at 0x6F8A97 with naked asm trampoline
- lua_setmetatable (0x6F4020): hooked, barrier on new metatable
- lua_setupvalue (0x6F47B0): hooked, barrier grays closure
- lua_setfenv (0x6F40D0): hooked, barrier grays object

Backward barriers (5.1 luaC_barrierback):
- lua_table_set_value (0x6FA840): black2gray + grayagain
- lua_table_set_int_key (0x6FAD80): black2gray + grayagain

Atomic phase (5.1 ordering):
- propagateall, re-traverse weak tables, mark running thread,
  grayagain drain, separateudata, marktmu, cleartable, flip white

Status: enters world successfully with CHUNK_SIZE=5000 (incremental).
Crashes on UI reload (different crash pattern -- NULL+8 deref in mark,
not the old hash chain crash). Progress from "crashes on enter world"
to "crashes on UI reload."

This commit is contained in:

MarcelineVQ

2026-04-09 23:50:37 -07:00

parent 54d1b69f0e

commit e996796d39

2 changed files with 640 additions and 273 deletions

src/luagc/luagc.zig

+597 -257

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