Safety fix: ss_fast_lookup masks pointer to 1MB boundary and reads
memory at that address. If called with arbitrary (non-Tiny) pointers,
the masked address could be unmapped → SEGFAULT.
Changes:
- tiny_free_fast(): Reverted to safe hak_super_lookup (can receive
arbitrary pointers without prior validation)
- ss_fast_lookup(): Added safety warning in comments documenting when
it's safe to use (after header magic 0xA0 validation)
ss_fast_lookup remains in LARSON_FIX paths where header magic is
already validated before the SuperSlab lookup.
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Co-Authored-By: Claude <noreply@anthropic.com>
Replaces expensive hak_super_lookup() (registry hash lookup, 50-100 cycles)
with fast mask-based lookup (~5-10 cycles) in free hot paths.
Algorithm:
1. Mask pointer with SUPERSLAB_SIZE_MIN (1MB) - works for both 1MB and 2MB SS
2. Validate magic (SUPERSLAB_MAGIC)
3. Range check using ss->lg_size
Applied to:
- tiny_free_fast.inc.h: tiny_free_fast() SuperSlab path
- tiny_free_fast_v2.inc.h: LARSON_FIX cross-thread check
- front/malloc_tiny_fast.h: free_tiny_fast() LARSON_FIX path
Note: Performance impact minimal with LARSON_FIX=OFF (default) since
SuperSlab lookup is skipped entirely in that case. Optimization benefits
LARSON_FIX=ON path for safe multi-threaded operation.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Optimized HAKMEM_SFC_DEBUG environment variable handling by caching
the value at initialization instead of repeated getenv() calls in
hot paths.
Changes:
1. Added g_sfc_debug global variable (core/hakmem_tiny_sfc.c)
- Initialized once in sfc_init() by reading HAKMEM_SFC_DEBUG
- Single source of truth for SFC debug state
2. Declared g_sfc_debug as extern (core/hakmem_tiny_config.h)
- Available to all modules that need SFC debug checks
3. Replaced getenv() with g_sfc_debug in hot paths:
- core/tiny_alloc_fast_sfc.inc.h (allocation path)
- core/tiny_free_fast.inc.h (free path)
- core/box/hak_wrappers.inc.h (wrapper layer)
Impact:
- getenv() calls: 7 → 1 (86% reduction)
- Hot-path calls eliminated: 6 (all moved to init-time)
- Performance: 15.10M ops/s (stable, 0% CV)
- Build: Clean compilation, no new warnings
Testing:
- 10 runs of 100K iterations: consistent performance
- Symbol verification: g_sfc_debug present in hakmem_tiny_sfc.o
- No regression detected
Note: 3 additional getenv("HAKMEM_SFC_DEBUG") calls exist in
hakmem_tiny_ultra_simple.inc but are dead code (file not compiled
in current build configuration).
Files modified: 5 core files
Status: Production-ready, all tests passed
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Root Cause:
- TINY_ALLOC_FAST_POP_INLINE returned USER pointer (base+1), but all other
frontend layers return BASE pointer → HAK_RET_ALLOC wrote header/region
at wrong offset (off-by-one)
- tiny_free_fast_ss() performed BASE conversion twice (ptr-1 then base-1)
→ Corrupted TLS SLL chain, causing SEGV at iteration 66151
Fixes:
1. tiny_alloc_fast_inline.h (Line 62):
- Change POP macro to return BASE pointer (not USER)
- Update PUSH macro to convert USER→BASE and restore header at BASE
- Unify all frontend layers to "BASE world"
2. tiny_free_fast.inc.h (Line 125, 228):
- Remove double conversion in tiny_free_fast_ss()
- Pass BASE pointer from caller (already converted via ptr-1)
- Add comments to prevent future regressions
Impact:
- Before: Crash at iteration 66151 (stack corruption)
- After: 100K iterations ✅ (1.95M ops/s), 1M iterations ✅ (840K ops/s)
Verified: Random mixed benchmark (WS=256, seeds 42-44), all tests pass.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
CRITICAL BUG FIX: Phase E1 introduced 1-byte headers for ALL size classes (C0-C7),
changing the pointer contract. However, many locations still called slab_index_for()
with USER pointers (storage+1) instead of BASE pointers (storage), causing off-by-one
slab index calculations that corrupted memory.
Root Cause:
- USER pointer = BASE + 1 (returned by malloc, points past header)
- BASE pointer = storage start (where 1-byte header is written)
- slab_index_for() expects BASE pointer for correct slab boundary calculations
- Passing USER pointer → wrong slab_idx → wrong metadata → freelist corruption
Impact Before Fix:
- bench_random_mixed crashes at ~14K iterations with SEGV
- Massive C7 alignment check failures (wrong slab classification)
- Memory corruption from writing to wrong slab freelists
Fixes Applied (8 locations):
1. core/hakmem_tiny_free.inc:137
- Added USER→BASE conversion before slab_index_for()
2. core/hakmem_tiny_ultra_simple.inc:148
- Added USER→BASE conversion before slab_index_for()
3. core/tiny_free_fast.inc.h:220
- Added USER→BASE conversion before slab_index_for()
4-5. core/tiny_free_magazine.inc.h:126,315
- Added USER→BASE conversion before slab_index_for() (2 locations)
6. core/box/free_local_box.c:14,22,62
- Added USER→BASE conversion before slab_index_for()
- Fixed delta calculation to use BASE instead of USER
- Fixed debug logging to use BASE instead of USER
7. core/hakmem_tiny.c:448,460,473 (tiny_debug_track_alloc_ret)
- Added USER→BASE conversion before slab_index_for() (2 calls)
- Fixed delta calculation to use BASE instead of USER
- This function is called on EVERY allocation in debug builds
Results After Fix:
✅ bench_random_mixed stable up to 66K iterations (~4.7x improvement)
✅ C7 alignment check failures eliminated (was: 100% failure rate)
✅ Front Gate "Unknown" classification dropped to 0% (was: 1.67%)
✅ No segfaults for workloads up to ~33K allocations
Remaining Issue:
❌ Segfault still occurs at iteration 66152 (allocs=33137, frees=33014)
- Different bug from USER/BASE conversion issues
- Likely capacity/boundary condition (further investigation needed)
Testing:
- bench_random_mixed_hakmem 1K-66K iterations: PASS
- bench_random_mixed_hakmem 67K+ iterations: FAIL (different bug)
- bench_fixed_size_hakmem 200K iterations: PASS
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Co-Authored-By: Claude <noreply@anthropic.com>
