{"record":{"id":"8092dc5c23a184c4","repo":"xai-org/x-algorithm","slug":"async-emb-arena-alignment-overflow","errorCode":null,"errorMessage":"async_emb arena alignment overflow","messagePattern":"async_emb arena alignment overflow","errorType":"exception","errorClass":"std::overflow_error","httpStatus":null,"severity":"critical","filePath":"phoenix/xrex/cuda/async_emb/src/async_emb_comm.cc","lineNumber":40,"sourceCode":"constexpr size_t kAlign = 128;\nconstexpr int kNcclMinCtas = 1;\nconstexpr int kNcclMaxCtas = 4;\nconstexpr std::chrono::minutes kNcclReadyTimeout{5};\n\nsize_t checkedProduct(std::initializer_list<size_t> factors) {\n  size_t result = 1;\n  for (size_t factor : factors) {\n    if (factor != 0 && result > std::numeric_limits<size_t>::max() / factor) {\n      throw std::overflow_error(\"async_emb arena size overflow\");\n    }\n    result *= factor;\n  }\n  return result;\n}\n\nsize_t alignUp(size_t value) {\n  if (value > std::numeric_limits<size_t>::max() - (kAlign - 1)) {\n    throw std::overflow_error(\"async_emb arena alignment overflow\");\n  }\n  return (value + kAlign - 1) / kAlign * kAlign;\n}\n\nstd::runtime_error ncclError(const char* operation, ncclResult_t result) {\n  return std::runtime_error(\n      std::string(\"NCCL \") + operation + \" failed: \" + ncclGetErrorString(result)\n  );\n}\n\nvoid requireEnvironment(const char* name, const char* expected) {\n  const char* value = std::getenv(name);\n  if (value == nullptr || std::strcmp(value, expected) != 0) {\n    throw std::runtime_error(\n        \"async_emb requires \" + std::string(name) + \"=\" + expected + \" before process startup\"\n    );\n  }\n}","sourceCodeStart":22,"sourceCodeEnd":58,"githubUrl":"https://github.com/xai-org/x-algorithm/blob/24c60942c5c5fdad3a6addffb4c6e6d2f228f04f/phoenix/xrex/cuda/async_emb/src/async_emb_comm.cc#L22-L58","documentation":"alignUp rounds arena offsets up to kAlign; if value is within kAlign-1 of SIZE_MAX, rounding would overflow, so std::overflow_error('async_emb arena alignment overflow') is thrown. Like checkedProduct, this guards the arena layout computation in ArenaLayout::build against size_t wraparound.","triggerScenarios":"Building a context whose accumulated arena size is so close to SIZE_MAX that adding the alignment mask overflows — practically only reachable via corrupted/overflowing spec inputs (see also 'async_emb arena size overflow').","commonSituations":"Same class as the product overflow: negative or uninitialized spec dimensions reinterpreted as huge unsigned values; chained large-allocation requests from a bad config.","solutions":["Fix the upstream spec/config producing absurd sizes (validate all dimensions positive and bounded)","Treat this and error 817 together: whichever fires first indicates the same oversized-arena root cause","Add pre-creation assertions on spec magnitudes from the Python side"],"exampleFix":"# before\nspec.num_unique = 2**63          # absurd\nctx = async_emb.create_context(spec)  # layout build throws\n\n# after\nassert spec.num_unique < 10**9\nctx = async_emb.create_context(spec)","handlingStrategy":"validation","validationCode":"total = world_size * spec.tokens_per_rank * spec.shard_width\nassert 0 < total < 2**62, f\"arena too large: {total}\"","typeGuard":null,"tryCatchPattern":"try:\n    ctx = async_emb.create_context(spec)\nexcept OverflowError as e:\n    if \"alignment overflow\" in str(e) or \"arena size overflow\" in str(e):\n        raise ValueError(\"reduce spec dimensions / shard the table\") from e\n    raise","preventionTips":["Same root cause as size overflow: bound all spec inputs","Add upper-bound assertions to config loading"],"tags":["async-emb","cpp","integer-overflow","memory-layout","cuda"],"backgroundTag":"integer-overflow-guard","analyzedSha":"24c60942c5c5fdad3a6addffb4c6e6d2f228f04f","analyzedAt":"2026-08-28T11:40:14.686Z","schemaVersion":2},"datasetVersion":"2026-08-28T16:17:29.566Z"}