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Title: ProXPL Bug Fix Log 2026-04 Version: 1.0 Date: 2025-12-11 Author: ProgrammerKR

ProXPL VM Bug Fix Log - April 2026

This document details the comprehensive audit and subsequent fixes applied to the ProXPL Virtual Machine (src/runtime/vm.c) to improve memory safety, runtime stability, and semantic correctness.

Summary of Changes

A total of 15 bugs were addressed, ranging from critical memory corruption issues to logic errors in opcode implementations.

🔴 Critical Memory Safety Fixes

  1. Stack Overflow Protection: Added explicit exit(1) in the push() function to halt execution upon stack overflow, preventing out-of-bounds memory writes.
  2. Stack Underflow Guard: Implemented bounds checking in pop() to prevent the stack pointer from decrementing below the stack base.
  3. Runtime Error Frame Guard: Added a check in runtimeError() to ensure frameCount > 0 before accessing call frames, preventing crashes during early initialization or edge-case errors.
  4. Tensor Dimension Overflow: Increased the internal dims array size in OP_MAKE_TENSOR from 16 to 256 to accommodate the full range of uint8_t dimension counts.
  5. Sign Extension UB: Fixed undefined behavior in 32-bit integer reconstruction from bytecode by casting uint8_t reads to uint32_t before bitwise shifting.
  6. Use-After-Free in freeVM: Ensured initString is set to NULL before freeing objects to prevent the GC or free-loop from accessing a dangling pointer.
  7. resolveContextualMethod Tombstone Detection: Fixed a regression where tombstone entries in the context method table could cause crashes by restoring the IS_BOOL check.

🟠 Logic and Semantic Improvements

  1. Numeric Type Guards: Added IS_NUMBER checks to OP_GREATER, OP_LESS, OP_MODULO, and all bitwise opcodes (AND, OR, XOR, LSHIFT, RSHIFT) to ensure type safety before numeric extraction.
  2. Global Variable Semantics: Replaced the "insert-then-delete" hack in OP_SET_GLOBAL with a proper existence check via tableGet, ensuring standard Lox-style global variable behavior.
  3. Tombstone Handling: Fixed the tombstone detection logic in resolveContextualMethod() to correctly identify empty slots by checking for NULL keys.
  4. Module Loading Fix: Corrected OP_USE to actually push the loaded module onto the stack, allowing user scripts to interact with imported modules.
  5. Inheritance Stack Management: Fixed OP_INHERIT to only pop the subclass, keeping the superclass on the stack as required for super method lookups.
  6. Division/Modulo Safety: Implemented runtime error reporting for division and modulo by zero in scalar operations, matching existing tensor safety.
  7. Bitwise Shift Safety:
    • Added checks to OP_LEFT_SHIFT and OP_RIGHT_SHIFT to ensure shift amounts are between 0 and 31.
    • Implemented unsigned casts in OP_LEFT_SHIFT to prevent undefined behavior when shifting negative signed integers.
  8. Tensor Build Safety:
    • Implemented integer overflow protection for totalSize calculation in OP_MAKE_TENSOR.
    • Added stack underflow bounds checking before adjusting the stack pointer during tensor initialization.
    • Removed redundant dead code guards.

🟡 Structural and Minor Fixes

  1. Dead Code Elimination: Removed an unreachable DISPATCH() call at the end of the OP_CALL implementation.
  2. interpretChunk Safety:
    • Enhanced documentation and ensured initChunk calls in interpretChunk() safely detach transient function objects from caller-owned memory.
    • Added a GC guard (pvm->nextGC = SIZE_MAX) during interpretChunk execution to prevent the collector from freeing transient chunk data during the run.
  3. NaN Equality: Updated OP_EQUAL to respect IEEE 754 NaN semantics (NaN != NaN) for NaN-boxed numeric values.
  4. Foreign Function Safety: Added IS_STRING guards to OP_MAKE_FOREIGN to prevent crashes when non-string values are passed as library or symbol names.
  5. List Build Safety: Added a stack underflow check to OP_BUILD_LIST to prevent memory corruption from malformed bytecode.

System-Wide Fixes (CLI, API, & Build)

🔴 CLI & Lifecycle Security (src/main.c)

  1. Token Array Bounds: Implemented strict look-ahead bounds checking for token arrays in both REPL (256 tokens) and file execution (4096 tokens) to prevent buffer overflows.
  2. Buffer Security: Replaced unsafe sprintf calls with snprintf when generating UI transpilation output directories.
  3. Error Path Cleanup: Corrected the order of resource deallocation in runFile to ensure TypeChecker, StmtList, and source buffers are freed even on failure paths.
  4. CLI Extension Guard: Added length verification to argv indexing to prevent out-of-bounds reads on short filenames.
  5. ftell Sign Error: Added checks for negative return values from ftell() to prevent massive erroneous memory allocations on file I/O failure.

🟠 Public API & Integration (src/proxpl_api.c)

  1. Lifecycle Guards: Added NULL pointer verification to proxpl_vm_init, proxpl_vm_free, and proxpl_interpret_file for integration safety.
  2. Include Standardization: Reordered headers to ensure system libraries are prioritized over local project headers, preventing macro conflicts.

🟡 Build System & Workspace (Makefile, .gitignore)

  1. Strict Compilation: Enabled -Wpedantic and -Wno-unused-parameter to catch standards violations and silence intentional suppression warnings.
  2. Missing Sources: Added src/proxpl_api.c to the SOURCES list to ensure the public API is correctly linked into the binary.
  3. Workspace Hygiene: Updated .gitignore to track UI transpiler output (dist_*/) and PRM caches (.prm-cache/), and verified correct file naming.

Version Update: These fixes are included in ProXPL version 1.3.2. Date: April 26, 2026 Lead Engineer: Antigravity (AI Assistant)