Refactor: Phase 2 Box化 - SuperSlab Lookup Box with multiple contract levels
Purpose: Formalize SuperSlab lookup responsibilities with clear safety guarantees Evolution: - Phase 12: UNSAFE mask+dereference (5-10 cycles) → 12% crash rate - Phase 1b: SAFE registry lookup (50-100 cycles) → 0% crash rate - Phase 2: Box化 - multiple contracts (UNSAFE/SAFE/GUARDED) Box Pattern Benefits: 1. Clear Contracts: Each API documents preconditions and guarantees 2. Multiple Levels: Choose speed vs safety based on context 3. Future-Proof: Enables optimizations without breaking existing code API Design: - ss_lookup_unsafe(): 5-10 cycles, requires validated pointer (internal use only) - ss_lookup_safe(): 50-100 cycles, works with arbitrary pointers (recommended) - ss_lookup_guarded(): 100-200 cycles, adds integrity checks (debug only) - ss_fast_lookup(): Backward compatible (→ ss_lookup_safe) Implementation: - Created core/box/superslab_lookup_box.h with full contract documentation - Integrated into core/superslab/superslab_inline.h - ss_lookup_safe() implemented as macro to avoid circular dependency - ss_lookup_guarded() only available in debug builds - Removed conflicting extern declarations from 3 locations Testing: - Build: Success (all warnings resolved) - Crash rate: 0% (50/50 iterations passed) - Backward compatibility: Maintained via ss_fast_lookup() macro Future Optimization Opportunities (documented in Box): - Phase 2.1: Hybrid lookup (try UNSAFE first, fallback to SAFE) - Phase 2.2: Per-thread cache (1-2 cycles hit rate) - Phase 2.3: Hardware-assisted validation (PAC/CPUID) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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Moe Charm (CI)
@ -11,27 +11,132 @@ void _ss_remote_drain_to_freelist_unsafe(SuperSlab* ss, int slab_idx, TinySlabMe
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// Optional debug counter (defined in hakmem_tiny_superslab.c)
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extern _Atomic uint64_t g_ss_active_dec_calls;
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// ========== Fast SuperSlab Lookup via Registry (Phase 12 fix) ==========
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// Purpose: Safe SuperSlab lookup that prevents SEGFAULT on arbitrary pointers
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// Original Phase 12: Tried mask+dereference (5-10 cycles) but caused 12% crash rate
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// Current Fix: Use registry-based lookup (50-100 cycles) for safety
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// ========== SuperSlab Lookup Box (Phase 2: Box化) ==========
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// Purpose: Formalize SuperSlab lookup contracts with clear safety guarantees
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//
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// BUGFIX (2025-11-29): Replaced unsafe mask+dereference with safe registry lookup
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// Root Cause: hak_tiny_free_fast_v2() can receive arbitrary pointers (stack, garbage, etc.)
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// Mask calculation could produce unmapped address → SEGFAULT on ss->magic read
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// Phase 1a: Tried range checks → insufficient (still 10-12% crash rate)
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// Phase 1b: Use hak_super_lookup() registry → 0% crash rate expected
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// Trade-off: Rollback Phase 12 optimization (5-10x slower) but crash-free
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// Evolution:
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// - Phase 12: UNSAFE mask+dereference (5-10 cycles) → 12% crash rate
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// - Phase 1b: SAFE registry lookup (50-100 cycles) → 0% crash rate
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// - Phase 2: Box化 - multiple contracts (UNSAFE/SAFE/GUARDED)
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//
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// Performance comparison:
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// - Phase 12 (unsafe): ~5-10 cycles, 12% crash rate
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// - Phase 1b (safe): ~50-100 cycles, 0% crash rate
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// - Still faster than mincore() syscall (5000-10000 cycles)
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// Box Pattern Benefits:
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// 1. Clear contracts: Each API documents preconditions and guarantees
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// 2. Multiple levels: Choose speed vs safety based on context
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// 3. Future-proof: Enables optimizations without breaking existing code
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//
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// Note: Implemented as macro to avoid circular include dependency
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// (superslab_inline.h ↔ hakmem_super_registry.h)
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// APIs:
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// - ss_lookup_unsafe() : 5-10 cycles, requires validated pointer
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// - ss_lookup_safe() : 50-100 cycles, works with arbitrary pointers
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// - ss_lookup_guarded() : 100-200 cycles, adds integrity checks
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// - ss_fast_lookup() : Backward compatible (→ ss_lookup_safe)
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//
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// Note: hak_super_lookup() is implemented in hakmem_super_registry.h as static inline
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// The circular dependency (this file ↔ hakmem_super_registry.h) is resolved because:
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// - hakmem_super_registry.h is included before this file in hakmem_tiny_superslab.h
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// - By the time functions here are instantiated, hak_super_lookup() is already defined
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// ============================================================================
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// Contract Level 1: UNSAFE - Fast but dangerous (internal use only)
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// ============================================================================
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//
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// Preconditions:
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// - ptr MUST be a valid Tiny allocation pointer (already validated)
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// - ptr MUST be within a mapped SuperSlab region
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// - Violation of preconditions → SEGFAULT
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//
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// Use cases:
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// - After header magic validation (LARSON_FIX paths)
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// - Internal paths where pointer origin is known
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//
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// Performance: ~5-10 cycles
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// Safety: ⚠️ UNSAFE - caller must ensure preconditions
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//
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static inline SuperSlab* ss_lookup_unsafe(void* ptr)
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{
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if (__builtin_expect(!ptr, 0)) return NULL;
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uintptr_t p = (uintptr_t)ptr;
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// Step 1: Mask with minimum SuperSlab size (1MB alignment)
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SuperSlab* ss = (SuperSlab*)(p & ~((uintptr_t)SUPERSLAB_SIZE_MIN - 1u));
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// Step 2: Validate magic (quick reject for non-SuperSlab memory)
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// ⚠️ DANGER: This dereference can SEGFAULT if preconditions not met
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if (__builtin_expect(ss->magic != SUPERSLAB_MAGIC, 0)) {
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return NULL;
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}
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// Step 3: Range check (ptr must be within this SuperSlab)
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size_t ss_size = (size_t)1 << ss->lg_size;
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if (__builtin_expect(p >= (uintptr_t)ss + ss_size, 0)) {
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return NULL;
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}
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return ss;
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}
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// ============================================================================
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// Contract Level 2: SAFE - Registry-based (recommended)
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// ============================================================================
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//
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// Preconditions: None (works with arbitrary pointers)
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//
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// Guarantees:
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// - Never dereferences unmapped memory
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// - Returns NULL for invalid pointers (stack, heap, garbage, etc.)
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// - Thread-safe (lock-free reads)
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//
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// Use cases:
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// - Free paths with arbitrary pointers (hak_tiny_free_fast_v2)
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// - External API boundaries
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// - Default choice for unknown pointer origin
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//
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// Performance: ~50-100 cycles (hash table + linear probing)
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// Safety: ✓ SAFE - guaranteed crash-free
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//
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// Note: Implemented as macro to avoid static/extern declaration conflicts
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// hak_super_lookup() is defined in hakmem_super_registry.h
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#define ss_fast_lookup(ptr) hak_super_lookup(ptr)
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#define ss_lookup_safe(ptr) hak_super_lookup(ptr)
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// ============================================================================
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// Contract Level 3: GUARDED - Full validation (debug builds only)
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// ============================================================================
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//
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// Note: This API is only available in debug builds to avoid circular dependency issues
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// In release builds, use ss_lookup_safe() directly
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//
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#if !HAKMEM_BUILD_RELEASE
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static inline SuperSlab* ss_lookup_guarded(void* ptr)
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{
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SuperSlab* ss = hak_super_lookup(ptr); // Direct call, not via macro
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if (!ss) return NULL;
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// Debug mode: additional integrity checks
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uint32_t refcount = atomic_load_explicit(&ss->refcount, memory_order_relaxed);
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if (refcount == 0 || refcount > 1000000) {
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fprintf(stderr, "[SS_LOOKUP_GUARDED] WARNING: ptr=%p ss=%p refcount=%u (suspicious)\n",
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ptr, (void*)ss, refcount);
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}
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if (ss->magic != SUPERSLAB_MAGIC) {
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fprintf(stderr, "[SS_LOOKUP_GUARDED] ERROR: ptr=%p ss=%p magic=%llx (corrupted!)\n",
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ptr, (void*)ss, (unsigned long long)ss->magic);
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return NULL;
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}
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return ss;
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}
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#else
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// Release build: ss_lookup_guarded() not available, use ss_lookup_safe() instead
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#define ss_lookup_guarded(ptr) ss_lookup_safe(ptr)
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#endif
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// ============================================================================
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// Backward Compatibility
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// ============================================================================
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// Legacy API: ss_fast_lookup() → ss_lookup_safe()
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#define ss_fast_lookup(ptr) ss_lookup_safe(ptr)
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// Return maximum number of slabs for this SuperSlab based on lg_size.
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static inline int ss_slabs_capacity(SuperSlab* ss)
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