WASM64 fixes

Author: tiran

Lib/test/test_warnings/__init__.py

@@ -487,7 +487,14 @@ def test_warn_explicit_non_ascii_filename(self):
                 module=self.module) as w:
             self.module.resetwarnings()
             self.module.filterwarnings("always", category=UserWarning)
-            for filename in ("nonascii\xe9\u20ac", "surrogate\udc80"):
+            filenames = ["nonascii\xe9\u20ac"]
+            if not support.is_emscripten:
+                # JavaScript does not like surrogates
+                # Invalid UTF-8 leading byte 0x80 encountered when
+                # deserializing a UTF-8 string in wasm memory to a JS
+                # string!
+                filenames.append("surrogate\udc80")
+            for filename in filenames:
                 try:
                     os.fsencode(filename)
                 except UnicodeEncodeError:

Tools/wasm/README.md

@@ -212,6 +212,15 @@ Node builds use ``NODERAWFS``.
 - Node RawFS allows direct access to the host file system without need to
   perform ``FS.mount()`` call.
 
+## wasm64-emscripten
+
+- wasm64 requires recent NodeJS and ``--experimental-wasm-memory64``.
+- ``EM_JS`` functions must return ``BigInt()``.
+- ``Py_BuildValue()`` format strings must match size of types. Confusing 32
+  and 64 bits types leads to memory corruption, see
+  [gh-95876](https://github.com/python/cpython/issues/95876) and
+  [gh-95878](https://github.com/python/cpython/issues/95878).
+
 # Hosting Python WASM builds
 
 The simple REPL terminal uses SharedArrayBuffer. For security reasons