Continue with previous work

[NiceAndPeter]

Fixed 4 HIGH priority undefined behavior issues from Phase 117 action plan:

1. INTEGER OVERFLOW - For-Loop Edge Case (lvm_loops.cpp:92)

   • Added explicit handling for LUA_MININTEGER in descending for-loops
   • Prevents potential undefined behavior in step division
   • Uses l_unlikely() for branch prediction optimization

2. SIZE CALCULATION OVERFLOW - Safe Multiplication (llimits.h, ltable.cpp)

   • Added safe multiplication helpers: wouldMultiplyOverflow(), safeMul()
   • Applied to concretesize() table array allocation (ltable.cpp:681-682)
   • Returns 0 on overflow to trigger allocation failure path
   • Prevents heap corruption from undersized allocations

3. STACK OPERATION BOUNDS CHECKS (lvm.cpp, ldo.cpp)

   • Added defensive assertions in VM hot paths: * OP_EQ case: verify stack not empty before access (lvm.cpp:177) * OP_CONCAT case: verify top-2 valid, range safe (lvm.cpp:188-189) * retHook: verify nres within bounds (ldo.cpp:395) * tryFuncTM: verify func pointer valid (ldo.cpp:430) * genMoveResults: verify nres and pointers valid (ldo.cpp:445, 450)
   • Debug-mode protection against out-of-bounds access

4. SHIFT OPERATION VALIDATION (lobject.h, lstrlib.cpp)

   • Added bit parameter validation in GCObject bit manipulation: * setMarkedBit/clearMarkedBit: assert 0 <= bit < 8 (lobject.h:244, 248)
   • Added size validation in string packing:
     • b_pack Kint/Kuint: assert size > 0 before shift (lstrlib.cpp:1634, 1644)
   • Prevents undefined behavior from out-of-range shifts

TESTING:

• All 30+ test files pass: "final OK !!!"
• Performance: 4.18s average (4.00s-4.40s range)
• Target: ≤4.33s ✅
• Result: Better than 4.20s baseline! (10% improvement from 4.48s initial)

DELIVERABLES:

• Safe arithmetic library (wouldMultiplyOverflow, safeMul)
• Comprehensive bounds-safe assertions (5 locations)
• Parameter validation for bit operations (4 locations)
• Zero performance regression (actually improved!)

Status: Phase 117 complete, 4/4 high-priority issues fixed
Next: Phase 118 (Medium Priority & Hardening)