René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ffi: SharedArrayBuffer pointer argument changes from rejected to accepted after optimization","articleBody":"### Version\n\nmain\n\n### Platform\n\n```text\nmacOS 26.6.0\n```\n\n### Subsystem\n\nffi\n\n### What steps will reproduce the bug?\n\n`repro.c`\n```c\n#include \u003cstdint.h>\n\nuint8_t first_byte(const uint8_t* pointer) {\n  return pointer[0];\n}\n```\n\n`repro.js`\n```js\nimport { DynamicLibrary, suffix } from 'node:ffi';\n\nconst lib = new DynamicLibrary(`./repro.${suffix}`);\nconst call = lib.getFunction('first_byte', {\n  arguments: ['pointer'],\n  return: 'u8',\n});\n\nconst regular = new ArrayBuffer(1);\nconst shared = new SharedArrayBuffer(1);\nnew Uint8Array(shared)[0] = 42;\n\nfunction printResult(label) {\n  try {\n    console.log(label, call(shared));\n  } catch (error) {\n    console.log(label, error.code, error.message);\n  }\n}\n\nprintResult('before optimization');\n\n%PrepareFunctionForOptimization(call);\ncall(regular);\n\n%OptimizeFunctionOnNextCall(call);\ncall(regular);\n\nprintResult('after optimization');\n\nlib.close();\n```\n\nCommands to run:\n```console\n$ cc -dynamiclib -o repro.dylib repro.c\n\n$ node --no-warnings --experimental-ffi --allow-natives-syntax repro.js\n```\n\n### How often does it reproduce? Is there a required condition?\n\nAlways\n\n### What is the expected behavior? Why is that the expected behavior?\n\nArgument validation and behavior should be identical regardless of optimization state. Either consistently reject SAB or consistently support it.\n\n### What do you see instead?\n\n```console\nbefore optimization ERR_INVALID_ARG_VALUE Argument 0 must be a buffer, an ArrayBuffer, a string, or a bigint\nafter optimization 42\n```\n\nThe unoptimized path rejects the direct `SharedArrayBuffer`, but the optimized Fast API path accepts the identical value and calls C\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/trivikr","@type":"Person","name":"trivikr"},"datePublished":"2026-08-12T07:01:33Z","url":"https://github.com/nodejs/node/issues/65232"}