Boehm's conservative pointer scan cannot recognize lumbda's Value
layout — heap pointers live in the low 48 bits with QNAN + tag bits
in the upper mantissa, so a raw word never looks like a heap address.
Until now main.c neutralized this with GC_disable(): every allocation
leaked, OOMing any long-running workload.
Add precise tracing via a custom Boehm kind:
- New c/gc.c: mark proc walks 8-byte words in mixed mode — when the
QNAN bits are set with a pointer-bearing tag (0/2/4/5/6) extract
the low-48 pointer; otherwise fall through to raw-pointer
validation. GC_set_push_other_roots callback decodes NaN-boxed
Values on the C stack via setjmp anchor + scan up to the stack
base captured at process start.
- Allocations holding Values (Pair, Env bindings, ValueStack data,
ULVector data, HTEntry, Proc params + body, FullCont stack,
CodeObj instrs, SymbolEntry) route through lumbda_value_malloc.
Pure-byte sites (bignum limbs, char buffers, source files) stay
on regular GC_MALLOC.
- main.c / test.c / bench.c capture stack-base then drop GC_disable.
types.c also zeros popped slots on the value stack so stale pointers
do not survive a vs_pop and pin freed objects — independent
correctness fix that pays off once GC actually runs.
Build: USE_GC=1 (default when /usr/include/gc.h exists).
Tests with GC enabled:
- 88/88 c-test
- 4/4 regression-named-let-leak (test that motivated GC_disable)
- 205/205 functional (Python + C)
- zoe-favorites all tiers (Python + C + asm + asm-full)
alloc-test 1M cons drop-loop:
- Before: 0.60s wall, 156 MB RSS, leaks every cell
- After: 0.37s wall, 4 MB RSS, ~1500 GC cycles each freeing ~370 KB
russell@unturf.com
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