Debugging PHP.wasm Side Modules

Patterns for diagnosing and fixing issues with dynamic PHP extensions built as WASM side modules and loaded via dlopen.

_dlopen_js Must Be Synchronous

Emscripten marks _dlopen_js as async by default (isAsync = true). With JSPI, this wraps the import with WebAssembly.Suspending. Even when the implementation returns a plain value (not a Promise), the JSPI wrapper corrupts the WASM call stack — V8's native stack bookkeeping desynchronizes __stack_pointer in linear memory, causing heap corruption that manifests later as zend_mm_panic in _efree.

Fix: Set _dlopen_js__async: false in the Emscripten JS library (phpwasm-emscripten-library-dynamic-linking.js).