bpo-40280: Add --enable-wasm-dynamic-linking (GH-32253)

Author: tiran

Doc/using/configure.rst

@@ -52,11 +52,13 @@ General Options
    Set the Python executable suffix to *SUFFIX*.
 
    The default suffix is ``.exe`` on Windows and macOS (``python.exe``
-   executable), ``.wasm`` on Emscripten (``python.wasm`` executable), and
-   an empty string on other platforms (``python`` executable).
+   executable), ``.js`` on Emscripten node, ``.html`` on Emscripten browser,
+   ``.wasm`` on WASI, and an empty string on other platforms (``python``
+   executable).
 
    .. versionchanged:: 3.11
-      The default suffix on Emscripten platform is ``.wasm``.
+      The default suffix on WASM platform is one of ``.js``, ``.html``
+      or ``.wasm``.
 
 .. cmdoption:: --with-tzpath=<list of absolute paths separated by pathsep>
 
@@ -141,6 +143,27 @@ General Options
 
    .. versionadded:: 3.11
 
+WebAssemby Options
+------------------
+
+.. cmdoption:: --with-emscripten-target=[browser|node]
+
+   Set build flavor for ``wasm32-emscripten``.
+
+   * ``browser`` (default): preload minimal stdlib, default MEMFS.
+   * ``node``: NODERAWFS and pthread support.
+
+   .. versionadded:: 3.11
+
+.. cmdoption:: --enable-wasm-dynamic-linking
+
+   Turn on dynamic linking support for WASM.
+
+   Dynamic linking enables ``dlopen``. File size of the executable
+   increases due to limited dead code elimination and additional features.
+
+   .. versionadded:: 3.11
+
 
 Install Options
 ---------------

Misc/NEWS.d/next/Build/2022-04-02-17-52-38.bpo-40280.U8Dd0H.rst

@@ -0,0 +1,2 @@
+Add configure option :option:`--enable-wasm-dynamic-linking` to enable
+``dlopen`` and MAIN_MODULE / SIDE_MODULE on ``wasm32-emscripten``.

Tools/wasm/README.md

@@ -81,24 +81,31 @@ node --experimental-wasm-threads --experimental-wasm-bulk-memory builddir/emscri
 
 ## wasm32-emscripten limitations and issues
 
+- Heap and stack are limited.
 - Most stdlib modules with a dependency on external libraries are missing:
   ``ctypes``, ``readline``, ``sqlite3``, ``ssl``, and more.
 - Shared extension modules are not implemented yet. All extension modules
   are statically linked into the main binary.
+  The experimental configure option ``--enable-wasm-dynamic-linking`` enables
+  dynamic extensions.
 - Processes are not supported. System calls like fork, popen, and subprocess
   fail with ``ENOSYS`` or ``ENOSUP``.
+- Only ``AF_INET`` and ``AF_INET6`` with ``SOCK_STREAM`` (TCP) or
+  ``SOCK_DGRAM`` (UDP) are available. ``AF_UNIX`` is not supported.
+- ``socketpair`` does not work.
 - Blocking sockets are not available and non-blocking sockets don't work
   correctly, e.g. ``socket.accept`` crashes the runtime. ``gethostbyname``
   does not resolve to a real IP address. IPv6 is not available.
 - The ``select`` module is limited. ``select.select()`` crashes the runtime
   due to lack of exectfd support.
-- The ``*at`` variants of functions (e.g. ``openat``) are not available.
-  The ``dir_fd`` argument of *os* module functions can't be used.
 - Signal support is limited. ``signal.alarm``, ``itimer``, ``sigaction``
   are not available or do not work correctly. ``SIGTERM`` exits the runtime.
 - Most user, group, and permission related function and modules are not
   supported or don't work as expected, e.g.``pwd`` module, ``grp`` module,
-  ``os.setgroups``, ``os.chown``, and so on.
+  ``os.setgroups``, ``os.chown``, and so on. ``lchown`` and `lchmod`` are
+  not available.
+- ``umask`` is a no-op.
+- hard links (``os.link``) are not supported.
 - Offset and iovec I/O functions (e.g. ``os.pread``, ``os.preadv``) are not
   available.
 - ``os.mknod`` and ``os.mkfifo``
@@ -108,17 +115,9 @@ node --experimental-wasm-threads --experimental-wasm-bulk-memory builddir/emscri
 - ``mmap`` module is unstable. flush (``msync``) can crash the runtime.
 - Resource-related functions like ``os.nice`` and most functions of the
   ``resource`` module are not available.
-- Some time and datetime features are broken. ``strftime`` and ``strptime``
-  have known bugs, e.g.
-  [%% quoting](https://github.com/emscripten-core/emscripten/issues/16155),
-  [%U off-by-one](https://github.com/emscripten-core/emscripten/issues/16156).
-  Extended glibc formatting features are not available.
+- glibc extensions for date and time formatting are not available.
 - ``locales`` module is affected by musl libc issues,
   [bpo-46390](https://bugs.python.org/issue46390).
-- ``uuid`` module is affected by
-  [memory leak](https://github.com/emscripten-core/emscripten/issues/16081)
-  and crasher in Emscripten's ``freeaddrinfo``,
-- Recursive ``glob`` leaks file descriptors.
 - Python's object allocator ``obmalloc`` is disabled by default.
 - ``ensurepip`` is not available.
 

Tools/wasm/config.site-wasm32-emscripten

@@ -91,7 +91,3 @@ ac_cv_func_linkat=no
 
 # alarm signal is not delivered, may need a callback into the event loop?
 ac_cv_func_alarm=no
-
-# To use dlopen, you need to use Emscripten's linking support,
-# see https://emscripten.org/docs/compiling/Dynamic-Linking.html
-ac_cv_func_dlopen=no