[3.11] gh-95853: Add script to automate WASM build (GH-95828, GH-95985, GH-96045, GH-96389, GH-96744) (GH-96749)

Automate WASM build with a new Python script. The script provides
several build profiles with configure flags for Emscripten flavors
and WASI. The script can detect and use Emscripten SDK and WASI SDK from
default locations or env vars.

``configure`` now detects Node arguments and creates HOSTRUNNER
arguments for Node 16. It also sets correct arguments for
``wasm64-emscripten``.

4 files changed, 997 insertions, 21 deletions

diff --git a/Tools/wasm/README.md b/Tools/wasm/README.md
index 6496a29e6f..fe9a1dc99b 100644
--- a/Tools/wasm/README.md
+++ b/Tools/wasm/README.md
@@ -1,11 +1,16 @@
 # Python WebAssembly (WASM) build
 
-**WARNING: WASM support is highly experimental! Lots of features are not working yet.**
+**WARNING: WASM support is work-in-progress! Lots of features are not working yet.**
 
 This directory contains configuration and helpers to facilitate cross
-compilation of CPython to WebAssembly (WASM). For now we support
-*wasm32-emscripten* builds for modern browser and for *Node.js*. WASI
-(*wasm32-wasi*) is work-in-progress
+compilation of CPython to WebAssembly (WASM). Python supports Emscripten
+(*wasm32-emscripten*) and WASI (*wasm32-wasi*) targets. Emscripten builds
+run in modern browsers and JavaScript runtimes like *Node.js*. WASI builds
+use WASM runtimes such as *wasmtime*.
+
+Users and developers are encouraged to use the script
+`Tools/wasm/wasm_build.py`. The tool automates the build process and provides
+assistance with installation of SDKs.
 
 ## wasm32-emscripten build
 
@@ -17,7 +22,7 @@ access the file system directly.
 
 Cross compiling to the wasm32-emscripten platform needs the
 [Emscripten](https://emscripten.org/) SDK and a build Python interpreter.
-Emscripten 3.1.8 or newer are recommended. All commands below are relative
+Emscripten 3.1.19 or newer are recommended. All commands below are relative
 to a repository checkout.
 
 Christian Heimes maintains a container image with Emscripten SDK, Python
@@ -35,7 +40,13 @@ docker run --rm -ti -v $(pwd):/python-wasm/cpython -w /python-wasm/cpython quay.
 
 ### Compile a build Python interpreter
 
-From within the container, run the following commands:
+From within the container, run the following command:
+
+```shell
+./Tools/wasm/wasm_build.py build
+```
+
+The command is roughly equivalent to:
 
 ```shell
 mkdir -p builddir/build
@@ -45,13 +56,13 @@ make -j$(nproc)
 popd
 ```
 
-### Fetch and build additional emscripten ports
+### Cross-compile to wasm32-emscripten for browser
 
 ```shell
-embuilder build zlib bzip2
+./Tools/wasm/wasm_build.py emscripten-browser
 ```
 
-### Cross compile to wasm32-emscripten for browser
+The command is roughly equivalent to:
 
 ```shell
 mkdir -p builddir/emscripten-browser
@@ -85,14 +96,21 @@ and header files with debug builds.
 ### Cross compile to wasm32-emscripten for node
 
 ```shell
-mkdir -p builddir/emscripten-node
-pushd builddir/emscripten-node
+./Tools/wasm/wasm_build.py emscripten-browser-dl
+```
+
+The command is roughly equivalent to:
+
+```shell
+mkdir -p builddir/emscripten-node-dl
+pushd builddir/emscripten-node-dl
 
 CONFIG_SITE=../../Tools/wasm/config.site-wasm32-emscripten \
   emconfigure ../../configure -C \
     --host=wasm32-unknown-emscripten \
     --build=$(../../config.guess) \
     --with-emscripten-target=node \
+    --enable-wasm-dynamic-linking \
     --with-build-python=$(pwd)/../build/python
 
 emmake make -j$(nproc)
@@ -100,7 +118,7 @@ popd
 ```
 
 ```shell
-node --experimental-wasm-threads --experimental-wasm-bulk-memory --experimental-wasm-bigint builddir/emscripten-node/python.js
+node --experimental-wasm-threads --experimental-wasm-bulk-memory --experimental-wasm-bigint builddir/emscripten-node-dl/python.js
 ```
 
 (``--experimental-wasm-bigint`` is not needed with recent NodeJS versions)
@@ -199,6 +217,15 @@ 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
@@ -235,6 +262,12 @@ The script ``wasi-env`` sets necessary compiler and linker flags as well as
 ``/opt/wasi-sdk`` or ``$WASI_SDK_PATH``.
 
 ```shell
+./Tools/wasm/wasm_build.py wasi
+```
+
+The command is roughly equivalent to:
+
+```shell
 mkdir -p builddir/wasi
 pushd builddir/wasi
 
@@ -308,26 +341,46 @@ if os.name == "posix":
 ```python
 >>> import os, sys
 >>> os.uname()
-posix.uname_result(sysname='Emscripten', nodename='emscripten', release='1.0', version='#1', machine='wasm32')
+posix.uname_result(
+    sysname='Emscripten',
+    nodename='emscripten',
+    release='3.1.19',
+    version='#1',
+    machine='wasm32'
+)
 >>> os.name
 'posix'
 >>> sys.platform
 'emscripten'
 >>> sys._emscripten_info
 sys._emscripten_info(
-    emscripten_version=(3, 1, 8),
-    runtime='Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:99.0) Gecko/20100101 Firefox/99.0',
+    emscripten_version=(3, 1, 10),
+    runtime='Mozilla/5.0 (X11; Linux x86_64; rv:104.0) Gecko/20100101 Firefox/104.0',
     pthreads=False,
     shared_memory=False
 )
+```
+
+```python
 >>> sys._emscripten_info
-sys._emscripten_info(emscripten_version=(3, 1, 8), runtime='Node.js v14.18.2', pthreads=True, shared_memory=True)
+sys._emscripten_info(
+    emscripten_version=(3, 1, 19),
+    runtime='Node.js v14.18.2',
+    pthreads=True,
+    shared_memory=True
+)
 ```
 
 ```python
 >>> import os, sys
 >>> os.uname()
-posix.uname_result(sysname='wasi', nodename='(none)', release='0.0.0', version='0.0.0', machine='wasm32')
+posix.uname_result(
+    sysname='wasi',
+    nodename='(none)',
+    release='0.0.0',
+    version='0.0.0',
+    machine='wasm32'
+)
 >>> os.name
 'posix'
 >>> sys.platform
@@ -418,7 +471,8 @@ embuilder build --pic zlib bzip2 MINIMAL_PIC
 
 **NOTE**: WASI-SDK's clang may show a warning on Fedora:
 ``/lib64/libtinfo.so.6: no version information available``,
-[RHBZ#1875587](https://bugzilla.redhat.com/show_bug.cgi?id=1875587).
+[RHBZ#1875587](https://bugzilla.redhat.com/show_bug.cgi?id=1875587). The
+warning can be ignored.
 
 ```shell
 export WASI_VERSION=16
@@ -443,6 +497,8 @@ ln -srf -t /usr/local/bin/ ~/.wasmtime/bin/wasmtime
 
 ### WASI debugging
 
-* ``wasmtime run -g`` generates debugging symbols for gdb and lldb.
+* ``wasmtime run -g`` generates debugging symbols for gdb and lldb. The
+  feature is currently broken, see
+  https://github.com/bytecodealliance/wasmtime/issues/4669 .
 * The environment variable ``RUST_LOG=wasi_common`` enables debug and
   trace logging.
diff --git a/Tools/wasm/wasi-env b/Tools/wasm/wasi-env
index 6c2d56e0e5..48908b02e6 100755
--- a/Tools/wasm/wasi-env
+++ b/Tools/wasm/wasi-env
@@ -72,4 +72,5 @@ export CFLAGS LDFLAGS
 export PKG_CONFIG_PATH PKG_CONFIG_LIBDIR PKG_CONFIG_SYSROOT_DIR
 export PATH
 
-exec "$@"
+# no exec, it makes arvg[0] path absolute.
+"$@"
diff --git a/Tools/wasm/wasm_assets.py b/Tools/wasm/wasm_assets.py
index 34a9bb5640..9b0bee33dc 100755
--- a/Tools/wasm/wasm_assets.py
+++ b/Tools/wasm/wasm_assets.py
@@ -116,6 +116,14 @@ OMIT_SUBDIRS = (
     "unittest/test/",
 )
 
+SYSCONFIG_NAMES = (
+    "_sysconfigdata__emscripten_wasm32-emscripten",
+    "_sysconfigdata__emscripten_wasm32-emscripten",
+    "_sysconfigdata__wasi_wasm32-wasi",
+    "_sysconfigdata__wasi_wasm64-wasi",
+)
+
+
 def get_builddir(args: argparse.Namespace) -> pathlib.Path:
     """Get builddir path from pybuilddir.txt
     """
@@ -128,7 +136,11 @@ def get_sysconfigdata(args: argparse.Namespace) -> pathlib.Path:
     """Get path to sysconfigdata relative to build root
     """
     data_name = sysconfig._get_sysconfigdata_name()
-    assert "emscripten_wasm32" in data_name
+    if not data_name.startswith(SYSCONFIG_NAMES):
+        raise ValueError(
+            f"Invalid sysconfig data name '{data_name}'.",
+            SYSCONFIG_NAMES
+        )
     filename = data_name + ".py"
     return args.builddir / filename
 
diff --git a/Tools/wasm/wasm_build.py b/Tools/wasm/wasm_build.py
new file mode 100755
index 0000000000..63812c6f31
--- /dev/null
+++ b/Tools/wasm/wasm_build.py
@@ -0,0 +1,907 @@
+#!/usr/bin/env python3
+"""Build script for Python on WebAssembly platforms.
+
+  $ ./Tools/wasm/wasm_builder.py emscripten-browser build repl
+  $ ./Tools/wasm/wasm_builder.py emscripten-node-dl build test
+  $ ./Tools/wasm/wasm_builder.py wasi build test
+
+Primary build targets are "emscripten-node-dl" (NodeJS, dynamic linking),
+"emscripten-browser", and "wasi".
+
+Emscripten builds require a recent Emscripten SDK. The tools looks for an
+activated EMSDK environment (". /path/to/emsdk_env.sh"). System packages
+(Debian, Homebrew) are not supported.
+
+WASI builds require WASI SDK and wasmtime. The tool looks for 'WASI_SDK_PATH'
+and falls back to /opt/wasi-sdk.
+
+The 'build' Python interpreter must be rebuilt every time Python's byte code
+changes.
+
+  ./Tools/wasm/wasm_builder.py --clean build build
+
+"""
+import argparse
+import enum
+import dataclasses
+import logging
+import os
+import pathlib
+import re
+import shlex
+import shutil
+import socket
+import subprocess
+import sys
+import sysconfig
+import tempfile
+import time
+import warnings
+import webbrowser
+
+# for Python 3.8
+from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, Union
+
+logger = logging.getLogger("wasm_build")
+
+SRCDIR = pathlib.Path(__file__).parent.parent.parent.absolute()
+WASMTOOLS = SRCDIR / "Tools" / "wasm"
+BUILDDIR = SRCDIR / "builddir"
+CONFIGURE = SRCDIR / "configure"
+SETUP_LOCAL = SRCDIR / "Modules" / "Setup.local"
+
+HAS_CCACHE = shutil.which("ccache") is not None
+
+# path to WASI-SDK root
+WASI_SDK_PATH = pathlib.Path(os.environ.get("WASI_SDK_PATH", "/opt/wasi-sdk"))
+
+# path to Emscripten SDK config file.
+# auto-detect's EMSDK in /opt/emsdk without ". emsdk_env.sh".
+EM_CONFIG = pathlib.Path(os.environ.setdefault("EM_CONFIG", "/opt/emsdk/.emscripten"))
+EMSDK_MIN_VERSION = (3, 1, 19)
+EMSDK_BROKEN_VERSION = {
+    (3, 1, 14): "https://github.com/emscripten-core/emscripten/issues/17338",
+    (3, 1, 16): "https://github.com/emscripten-core/emscripten/issues/17393",
+    (3, 1, 20): "https://github.com/emscripten-core/emscripten/issues/17720",
+}
+_MISSING = pathlib.PurePath("MISSING")
+
+WASM_WEBSERVER = WASMTOOLS / "wasm_webserver.py"
+
+CLEAN_SRCDIR = f"""
+Builds require a clean source directory. Please use a clean checkout or
+run "make clean -C '{SRCDIR}'".
+"""
+
+INSTALL_NATIVE = f"""
+Builds require a C compiler (gcc, clang), make, pkg-config, and development
+headers for dependencies like zlib.
+
+Debian/Ubuntu: sudo apt install build-essential git curl pkg-config zlib1g-dev
+Fedora/CentOS: sudo dnf install gcc make git-core curl pkgconfig zlib-devel
+"""
+
+INSTALL_EMSDK = """
+wasm32-emscripten builds need Emscripten SDK. Please follow instructions at
+https://emscripten.org/docs/getting_started/downloads.html how to install
+Emscripten and how to activate the SDK with "emsdk_env.sh".
+
+    git clone https://github.com/emscripten-core/emsdk.git /path/to/emsdk
+    cd /path/to/emsdk
+    ./emsdk install latest
+    ./emsdk activate latest
+    source /path/to/emsdk_env.sh
+"""
+
+INSTALL_WASI_SDK = """
+wasm32-wasi builds need WASI SDK. Please fetch the latest SDK from
+https://github.com/WebAssembly/wasi-sdk/releases and install it to
+"/opt/wasi-sdk". Alternatively you can install the SDK in a different location
+and point the environment variable WASI_SDK_PATH to the root directory
+of the SDK. The SDK is available for Linux x86_64, macOS x86_64, and MinGW.
+"""
+
+INSTALL_WASMTIME = """
+wasm32-wasi tests require wasmtime on PATH. Please follow instructions at
+https://wasmtime.dev/ to install wasmtime.
+"""
+
+
+def parse_emconfig(
+    emconfig: pathlib.Path = EM_CONFIG,
+) -> Tuple[pathlib.PurePath, pathlib.PurePath]:
+    """Parse EM_CONFIG file and lookup EMSCRIPTEN_ROOT and NODE_JS.
+
+    The ".emscripten" config file is a Python snippet that uses "EM_CONFIG"
+    environment variable. EMSCRIPTEN_ROOT is the "upstream/emscripten"
+    subdirectory with tools like "emconfigure".
+    """
+    if not emconfig.exists():
+        return _MISSING, _MISSING
+    with open(emconfig, encoding="utf-8") as f:
+        code = f.read()
+    # EM_CONFIG file is a Python snippet
+    local: Dict[str, Any] = {}
+    exec(code, globals(), local)
+    emscripten_root = pathlib.Path(local["EMSCRIPTEN_ROOT"])
+    node_js = pathlib.Path(local["NODE_JS"])
+    return emscripten_root, node_js
+
+
+EMSCRIPTEN_ROOT, NODE_JS = parse_emconfig()
+
+
+def read_python_version(configure: pathlib.Path = CONFIGURE) -> str:
+    """Read PACKAGE_VERSION from configure script
+
+    configure and configure.ac are the canonical source for major and
+    minor version number.
+    """
+    version_re = re.compile("^PACKAGE_VERSION='(\d\.\d+)'")
+    with configure.open(encoding="utf-8") as f:
+        for line in f:
+            mo = version_re.match(line)
+            if mo:
+                return mo.group(1)
+    raise ValueError(f"PACKAGE_VERSION not found in {configure}")
+
+
+PYTHON_VERSION = read_python_version()
+
+
+class ConditionError(ValueError):
+    def __init__(self, info: str, text: str):
+        self.info = info
+        self.text = text
+
+    def __str__(self):
+        return f"{type(self).__name__}: '{self.info}'\n{self.text}"
+
+
+class MissingDependency(ConditionError):
+    pass
+
+
+class DirtySourceDirectory(ConditionError):
+    pass
+
+
+@dataclasses.dataclass
+class Platform:
+    """Platform-specific settings
+
+    - CONFIG_SITE override
+    - configure wrapper (e.g. emconfigure)
+    - make wrapper (e.g. emmake)
+    - additional environment variables
+    - check function to verify SDK
+    """
+
+    name: str
+    pythonexe: str
+    config_site: Optional[pathlib.PurePath]
+    configure_wrapper: Optional[pathlib.PurePath]
+    make_wrapper: Optional[pathlib.PurePath]
+    environ: dict
+    check: Callable[[], None]
+    # Used for build_emports().
+    ports: Optional[pathlib.PurePath]
+    cc: Optional[pathlib.PurePath]
+
+    def getenv(self, profile: "BuildProfile") -> dict:
+        return self.environ.copy()
+
+
+def _check_clean_src():
+    candidates = [
+        SRCDIR / "Programs" / "python.o",
+        SRCDIR / "Python" / "frozen_modules" / "importlib._bootstrap.h",
+    ]
+    for candidate in candidates:
+        if candidate.exists():
+            raise DirtySourceDirectory(os.fspath(candidate), CLEAN_SRCDIR)
+
+
+def _check_native():
+    if not any(shutil.which(cc) for cc in ["cc", "gcc", "clang"]):
+        raise MissingDependency("cc", INSTALL_NATIVE)
+    if not shutil.which("make"):
+        raise MissingDependency("make", INSTALL_NATIVE)
+    if sys.platform == "linux":
+        # skip pkg-config check on macOS
+        if not shutil.which("pkg-config"):
+            raise MissingDependency("pkg-config", INSTALL_NATIVE)
+        # zlib is needed to create zip files
+        for devel in ["zlib"]:
+            try:
+                subprocess.check_call(["pkg-config", "--exists", devel])
+            except subprocess.CalledProcessError:
+                raise MissingDependency(devel, INSTALL_NATIVE) from None
+    _check_clean_src()
+
+
+NATIVE = Platform(
+    "native",
+    # macOS has python.exe
+    pythonexe=sysconfig.get_config_var("BUILDPYTHON") or "python",
+    config_site=None,
+    configure_wrapper=None,
+    ports=None,
+    cc=None,
+    make_wrapper=None,
+    environ={},
+    check=_check_native,
+)
+
+
+def _check_emscripten():
+    if EMSCRIPTEN_ROOT is _MISSING:
+        raise MissingDependency("Emscripten SDK EM_CONFIG", INSTALL_EMSDK)
+    # sanity check
+    emconfigure = EMSCRIPTEN.configure_wrapper
+    if not emconfigure.exists():
+        raise MissingDependency(os.fspath(emconfigure), INSTALL_EMSDK)
+    # version check
+    version_txt = EMSCRIPTEN_ROOT / "emscripten-version.txt"
+    if not version_txt.exists():
+        raise MissingDependency(os.fspath(version_txt), INSTALL_EMSDK)
+    with open(version_txt) as f:
+        version = f.read().strip().strip('"')
+    if version.endswith("-git"):
+        # git / upstream / tot-upstream installation
+        version = version[:-4]
+    version_tuple = tuple(int(v) for v in version.split("."))
+    if version_tuple < EMSDK_MIN_VERSION:
+        raise ConditionError(
+            os.fspath(version_txt),
+            f"Emscripten SDK {version} in '{EMSCRIPTEN_ROOT}' is older than "
+            "minimum required version "
+            f"{'.'.join(str(v) for v in EMSDK_MIN_VERSION)}.",
+        )
+    broken = EMSDK_BROKEN_VERSION.get(version_tuple)
+    if broken is not None:
+        raise ConditionError(
+            os.fspath(version_txt),
+            (
+                f"Emscripten SDK {version} in '{EMSCRIPTEN_ROOT}' has known "
+                f"bugs, see {broken}."
+            ),
+        )
+    if os.environ.get("PKG_CONFIG_PATH"):
+        warnings.warn(
+            "PKG_CONFIG_PATH is set and not empty. emconfigure overrides "
+            "this environment variable. Use EM_PKG_CONFIG_PATH instead."
+        )
+    _check_clean_src()
+
+
+EMSCRIPTEN = Platform(
+    "emscripten",
+    pythonexe="python.js",
+    config_site=WASMTOOLS / "config.site-wasm32-emscripten",
+    configure_wrapper=EMSCRIPTEN_ROOT / "emconfigure",
+    ports=EMSCRIPTEN_ROOT / "embuilder",
+    cc=EMSCRIPTEN_ROOT / "emcc",
+    make_wrapper=EMSCRIPTEN_ROOT / "emmake",
+    environ={
+        # workaround for https://github.com/emscripten-core/emscripten/issues/17635
+        "TZ": "UTC",
+        "EM_COMPILER_WRAPPER": "ccache" if HAS_CCACHE else None,
+        "PATH": [EMSCRIPTEN_ROOT, os.environ["PATH"]],
+    },
+    check=_check_emscripten,
+)
+
+
+def _check_wasi():
+    wasm_ld = WASI_SDK_PATH / "bin" / "wasm-ld"
+    if not wasm_ld.exists():
+        raise MissingDependency(os.fspath(wasm_ld), INSTALL_WASI_SDK)
+    wasmtime = shutil.which("wasmtime")
+    if wasmtime is None:
+        raise MissingDependency("wasmtime", INSTALL_WASMTIME)
+    _check_clean_src()
+
+
+WASI = Platform(
+    "wasi",
+    pythonexe="python.wasm",
+    config_site=WASMTOOLS / "config.site-wasm32-wasi",
+    configure_wrapper=WASMTOOLS / "wasi-env",
+    ports=None,
+    cc=WASI_SDK_PATH / "bin" / "clang",
+    make_wrapper=None,
+    environ={
+        "WASI_SDK_PATH": WASI_SDK_PATH,
+        # workaround for https://github.com/python/cpython/issues/95952
+        "HOSTRUNNER": (
+            "wasmtime run "
+            "--env PYTHONPATH=/{relbuilddir}/build/lib.wasi-wasm32-{version}:/Lib "
+            "--mapdir /::{srcdir} --"
+        ),
+        "PATH": [WASI_SDK_PATH / "bin", os.environ["PATH"]],
+    },
+    check=_check_wasi,
+)
+
+
+class Host(enum.Enum):
+    """Target host triplet"""
+
+    wasm32_emscripten = "wasm32-unknown-emscripten"
+    wasm64_emscripten = "wasm64-unknown-emscripten"
+    wasm32_wasi = "wasm32-unknown-wasi"
+    wasm64_wasi = "wasm64-unknown-wasi"
+    # current platform
+    build = sysconfig.get_config_var("BUILD_GNU_TYPE")
+
+    @property
+    def platform(self) -> Platform:
+        if self.is_emscripten:
+            return EMSCRIPTEN
+        elif self.is_wasi:
+            return WASI
+        else:
+            return NATIVE
+
+    @property
+    def is_emscripten(self) -> bool:
+        cls = type(self)
+        return self in {cls.wasm32_emscripten, cls.wasm64_emscripten}
+
+    @property
+    def is_wasi(self) -> bool:
+        cls = type(self)
+        return self in {cls.wasm32_wasi, cls.wasm64_wasi}
+
+    def get_extra_paths(self) -> Iterable[pathlib.PurePath]:
+        """Host-specific os.environ["PATH"] entries.
+
+        Emscripten's Node version 14.x works well for wasm32-emscripten.
+        wasm64-emscripten requires more recent v8 version, e.g. node 16.x.
+        Attempt to use system's node command.
+        """
+        cls = type(self)
+        if self == cls.wasm32_emscripten:
+            return [NODE_JS.parent]
+        elif self == cls.wasm64_emscripten:
+            # TODO: look for recent node
+            return []
+        else:
+            return []
+
+    @property
+    def emport_args(self) -> List[str]:
+        """Host-specific port args (Emscripten)."""
+        cls = type(self)
+        if self is cls.wasm64_emscripten:
+            return ["-sMEMORY64=1"]
+        elif self is cls.wasm32_emscripten:
+            return ["-sMEMORY64=0"]
+        else:
+            return []
+
+    @property
+    def embuilder_args(self) -> List[str]:
+        """Host-specific embuilder args (Emscripten)."""
+        cls = type(self)
+        if self is cls.wasm64_emscripten:
+            return ["--wasm64"]
+        else:
+            return []
+
+
+class EmscriptenTarget(enum.Enum):
+    """Emscripten-specific targets (--with-emscripten-target)"""
+
+    browser = "browser"
+    browser_debug = "browser-debug"
+    node = "node"
+    node_debug = "node-debug"
+
+    @property
+    def is_browser(self):
+        cls = type(self)
+        return self in {cls.browser, cls.browser_debug}
+
+    @property
+    def emport_args(self) -> List[str]:
+        """Target-specific port args."""
+        cls = type(self)
+        if self in {cls.browser_debug, cls.node_debug}:
+            # some libs come in debug and non-debug builds
+            return ["-O0"]
+        else:
+            return ["-O2"]
+
+
+class SupportLevel(enum.Enum):
+    supported = "tier 3, supported"
+    working = "working, unsupported"
+    experimental = "experimental, may be broken"
+    broken = "broken / unavailable"
+
+    def __bool__(self):
+        cls = type(self)
+        return self in {cls.supported, cls.working}
+
+
+@dataclasses.dataclass
+class BuildProfile:
+    name: str
+    support_level: SupportLevel
+    host: Host
+    target: Union[EmscriptenTarget, None] = None
+    dynamic_linking: Union[bool, None] = None
+    pthreads: Union[bool, None] = None
+    default_testopts: str = "-j2"
+
+    @property
+    def is_browser(self) -> bool:
+        """Is this a browser build?"""
+        return self.target is not None and self.target.is_browser
+
+    @property
+    def builddir(self) -> pathlib.Path:
+        """Path to build directory"""
+        return BUILDDIR / self.name
+
+    @property
+    def python_cmd(self) -> pathlib.Path:
+        """Path to python executable"""
+        return self.builddir / self.host.platform.pythonexe
+
+    @property
+    def makefile(self) -> pathlib.Path:
+        """Path to Makefile"""
+        return self.builddir / "Makefile"
+
+    @property
+    def configure_cmd(self) -> List[str]:
+        """Generate configure command"""
+        # use relative path, so WASI tests can find lib prefix.
+        # pathlib.Path.relative_to() does not work here.
+        configure = os.path.relpath(CONFIGURE, self.builddir)
+        cmd = [configure, "-C"]
+        platform = self.host.platform
+        if platform.configure_wrapper:
+            cmd.insert(0, os.fspath(platform.configure_wrapper))
+
+        cmd.append(f"--host={self.host.value}")
+        cmd.append(f"--build={Host.build.value}")
+
+        if self.target is not None:
+            assert self.host.is_emscripten
+            cmd.append(f"--with-emscripten-target={self.target.value}")
+
+        if self.dynamic_linking is not None:
+            assert self.host.is_emscripten
+            opt = "enable" if self.dynamic_linking else "disable"
+            cmd.append(f"--{opt}-wasm-dynamic-linking")
+
+        if self.pthreads is not None:
+            assert self.host.is_emscripten
+            opt = "enable" if self.pthreads else "disable"
+            cmd.append(f"--{opt}-wasm-pthreads")
+
+        if self.host != Host.build:
+            cmd.append(f"--with-build-python={BUILD.python_cmd}")
+
+        if platform.config_site is not None:
+            cmd.append(f"CONFIG_SITE={platform.config_site}")
+
+        return cmd
+
+    @property
+    def make_cmd(self) -> List[str]:
+        """Generate make command"""
+        cmd = ["make"]
+        platform = self.host.platform
+        if platform.make_wrapper:
+            cmd.insert(0, os.fspath(platform.make_wrapper))
+        return cmd
+
+    def getenv(self) -> dict:
+        """Generate environ dict for platform"""
+        env = os.environ.copy()
+        env.setdefault("MAKEFLAGS", f"-j{os.cpu_count()}")
+        platenv = self.host.platform.getenv(self)
+        for key, value in platenv.items():
+            if value is None:
+                env.pop(key, None)
+            elif key == "PATH":
+                # list of path items, prefix with extra paths
+                new_path: List[pathlib.PurePath] = []
+                new_path.extend(self.host.get_extra_paths())
+                new_path.extend(value)
+                env[key] = os.pathsep.join(os.fspath(p) for p in new_path)
+            elif isinstance(value, str):
+                env[key] = value.format(
+                    relbuilddir=self.builddir.relative_to(SRCDIR),
+                    srcdir=SRCDIR,
+                    version=PYTHON_VERSION,
+                )
+            else:
+                env[key] = value
+        return env
+
+    def _run_cmd(
+        self,
+        cmd: Iterable[str],
+        args: Iterable[str] = (),
+        cwd: Optional[pathlib.Path] = None,
+    ):
+        cmd = list(cmd)
+        cmd.extend(args)
+        if cwd is None:
+            cwd = self.builddir
+        logger.info('Running "%s" in "%s"', shlex.join(cmd), cwd)
+        return subprocess.check_call(
+            cmd,
+            cwd=os.fspath(cwd),
+            env=self.getenv(),
+        )
+
+    def _check_execute(self):
+        if self.is_browser:
+            raise ValueError(f"Cannot execute on {self.target}")
+
+    def run_build(self, *args):
+        """Run configure (if necessary) and make"""
+        if not self.makefile.exists():
+            logger.info("Makefile not found, running configure")
+            self.run_configure(*args)
+        self.run_make("all", *args)
+
+    def run_configure(self, *args):
+        """Run configure script to generate Makefile"""
+        os.makedirs(self.builddir, exist_ok=True)
+        return self._run_cmd(self.configure_cmd, args)
+
+    def run_make(self, *args):
+        """Run make (defaults to build all)"""
+        return self._run_cmd(self.make_cmd, args)
+
+    def run_pythoninfo(self, *args):
+        """Run 'make pythoninfo'"""
+        self._check_execute()
+        return self.run_make("pythoninfo", *args)
+
+    def run_test(self, target: str, testopts: Optional[str] = None):
+        """Run buildbottests"""
+        self._check_execute()
+        if testopts is None:
+            testopts = self.default_testopts
+        return self.run_make(target, f"TESTOPTS={testopts}")
+
+    def run_py(self, *args):
+        """Run Python with hostrunner"""
+        self._check_execute()
+        self.run_make(
+            "--eval", f"run: all; $(HOSTRUNNER) ./$(PYTHON) {shlex.join(args)}", "run"
+        )
+
+    def run_browser(self, bind="127.0.0.1", port=8000):
+        """Run WASM webserver and open build in browser"""
+        relbuilddir = self.builddir.relative_to(SRCDIR)
+        url = f"http://{bind}:{port}/{relbuilddir}/python.html"
+        args = [
+            sys.executable,
+            os.fspath(WASM_WEBSERVER),
+            "--bind",
+            bind,
+            "--port",
+            str(port),
+        ]
+        srv = subprocess.Popen(args, cwd=SRCDIR)
+        # wait for server
+        end = time.monotonic() + 3.0
+        while time.monotonic() < end and srv.returncode is None:
+            try:
+                with socket.create_connection((bind, port), timeout=0.1) as s:
+                    pass
+            except OSError:
+                time.sleep(0.01)
+            else:
+                break
+
+        webbrowser.open(url)
+
+        try:
+            srv.wait()
+        except KeyboardInterrupt:
+            pass
+
+    def clean(self, all: bool = False):
+        """Clean build directory"""
+        if all:
+            if self.builddir.exists():
+                shutil.rmtree(self.builddir)
+        elif self.makefile.exists():
+            self.run_make("clean")
+
+    def build_emports(self, force: bool = False):
+        """Pre-build emscripten ports."""
+        platform = self.host.platform
+        if platform.ports is None or platform.cc is None:
+            raise ValueError("Need ports and CC command")
+
+        embuilder_cmd = [os.fspath(platform.ports)]
+        embuilder_cmd.extend(self.host.embuilder_args)
+        if force:
+            embuilder_cmd.append("--force")
+
+        ports_cmd = [os.fspath(platform.cc)]
+        ports_cmd.extend(self.host.emport_args)
+        if self.target:
+            ports_cmd.extend(self.target.emport_args)
+
+        if self.dynamic_linking:
+            # Trigger PIC build.
+            ports_cmd.append("-sMAIN_MODULE")
+            embuilder_cmd.append("--pic")
+
+        if self.pthreads:
+            # Trigger multi-threaded build.
+            ports_cmd.append("-sUSE_PTHREADS")
+
+        # Pre-build libbz2, libsqlite3, libz, and some system libs.
+        ports_cmd.extend(["-sUSE_ZLIB", "-sUSE_BZIP2", "-sUSE_SQLITE3"])
+        # Multi-threaded sqlite3 has different suffix
+        embuilder_cmd.extend(
+            ["build", "bzip2", "sqlite3-mt" if self.pthreads else "sqlite3", "zlib"]
+        )
+
+        self._run_cmd(embuilder_cmd, cwd=SRCDIR)
+
+        with tempfile.TemporaryDirectory(suffix="-py-emport") as tmpdir:
+            tmppath = pathlib.Path(tmpdir)
+            main_c = tmppath / "main.c"
+            main_js = tmppath / "main.js"
+            with main_c.open("w") as f:
+                f.write("int main(void) { return 0; }\n")
+            args = [
+                os.fspath(main_c),
+                "-o",
+                os.fspath(main_js),
+            ]
+            self._run_cmd(ports_cmd, args, cwd=tmppath)
+
+
+# native build (build Python)
+BUILD = BuildProfile(
+    "build",
+    support_level=SupportLevel.working,
+    host=Host.build,
+)
+
+_profiles = [
+    BUILD,
+    # wasm32-emscripten
+    BuildProfile(
+        "emscripten-browser",
+        support_level=SupportLevel.supported,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.browser,
+        dynamic_linking=True,
+    ),
+    BuildProfile(
+        "emscripten-browser-debug",
+        support_level=SupportLevel.working,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.browser_debug,
+        dynamic_linking=True,
+    ),
+    BuildProfile(
+        "emscripten-node-dl",
+        support_level=SupportLevel.supported,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.node,
+        dynamic_linking=True,
+    ),
+    BuildProfile(
+        "emscripten-node-dl-debug",
+        support_level=SupportLevel.working,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.node_debug,
+        dynamic_linking=True,
+    ),
+    BuildProfile(
+        "emscripten-node-pthreads",
+        support_level=SupportLevel.supported,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.node,
+        pthreads=True,
+    ),
+    BuildProfile(
+        "emscripten-node-pthreads-debug",
+        support_level=SupportLevel.working,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.node_debug,
+        pthreads=True,
+    ),
+    # Emscripten build with both pthreads and dynamic linking is crashing.
+    BuildProfile(
+        "emscripten-node-dl-pthreads-debug",
+        support_level=SupportLevel.broken,
+        host=Host.wasm32_emscripten,
+        target=EmscriptenTarget.node_debug,
+        dynamic_linking=True,
+        pthreads=True,
+    ),
+    # wasm64-emscripten (requires Emscripten >= 3.1.21)
+    BuildProfile(
+        "wasm64-emscripten-node-debug",
+        support_level=SupportLevel.experimental,
+        host=Host.wasm64_emscripten,
+        target=EmscriptenTarget.node_debug,
+        # MEMORY64 is not compatible with dynamic linking
+        dynamic_linking=False,
+        pthreads=False,
+    ),
+    # wasm32-wasi
+    BuildProfile(
+        "wasi",
+        support_level=SupportLevel.supported,
+        host=Host.wasm32_wasi,
+    ),
+    # no SDK available yet
+    # BuildProfile(
+    #    "wasm64-wasi",
+    #    support_level=SupportLevel.broken,
+    #    host=Host.wasm64_wasi,
+    # ),
+]
+
+PROFILES = {p.name: p for p in _profiles}
+
+parser = argparse.ArgumentParser(
+    "wasm_build.py",
+    description=__doc__,
+    formatter_class=argparse.RawTextHelpFormatter,
+)
+
+parser.add_argument(
+    "--clean",
+    "-c",
+    help="Clean build directories first",
+    action="store_true",
+)
+
+parser.add_argument(
+    "--verbose",
+    "-v",
+    help="Verbose logging",
+    action="store_true",
+)
+
+parser.add_argument(
+    "--silent",
+    help="Run configure and make in silent mode",
+    action="store_true",
+)
+
+parser.add_argument(
+    "--testopts",
+    help=(
+        "Additional test options for 'test' and 'hostrunnertest', e.g. "
+        "--testopts='-v test_os'."
+    ),
+    default=None,
+)
+
+# Don't list broken and experimental variants in help
+platforms_choices = list(p.name for p in _profiles) + ["cleanall"]
+platforms_help = list(p.name for p in _profiles if p.support_level) + ["cleanall"]
+parser.add_argument(
+    "platform",
+    metavar="PLATFORM",
+    help=f"Build platform: {', '.join(platforms_help)}",
+    choices=platforms_choices,
+)
+
+ops = dict(
+    build="auto build (build 'build' Python, emports, configure, compile)",
+    configure="run ./configure",
+    compile="run 'make all'",
+    pythoninfo="run 'make pythoninfo'",
+    test="run 'make buildbottest TESTOPTS=...' (supports parallel tests)",
+    hostrunnertest="run 'make hostrunnertest TESTOPTS=...'",
+    repl="start interactive REPL / webserver + browser session",
+    clean="run 'make clean'",
+    cleanall="remove all build directories",
+    emports="build Emscripten port with embuilder (only Emscripten)",
+)
+ops_help = "\n".join(f"{op:16s} {help}" for op, help in ops.items())
+parser.add_argument(
+    "ops",
+    metavar="OP",
+    help=f"operation (default: build)\n\n{ops_help}",
+    choices=tuple(ops),
+    default="build",
+    nargs="*",
+)
+
+
+def main():
+    args = parser.parse_args()
+    logging.basicConfig(
+        level=logging.INFO if args.verbose else logging.ERROR,
+        format="%(message)s",
+    )
+
+    if args.platform == "cleanall":
+        for builder in PROFILES.values():
+            builder.clean(all=True)
+        parser.exit(0)
+
+    # additional configure and make args
+    cm_args = ("--silent",) if args.silent else ()
+
+    # nargs=* with default quirk
+    if args.ops == "build":
+        args.ops = ["build"]
+
+    builder = PROFILES[args.platform]
+    try:
+        builder.host.platform.check()
+    except ConditionError as e:
+        parser.error(str(e))
+
+    if args.clean:
+        builder.clean(all=False)
+
+    # hack for WASI
+    if builder.host.is_wasi and not SETUP_LOCAL.exists():
+        SETUP_LOCAL.touch()
+
+    # auto-build
+    if "build" in args.ops:
+        # check and create build Python
+        if builder is not BUILD:
+            logger.info("Auto-building 'build' Python.")
+            try:
+                BUILD.host.platform.check()
+            except ConditionError as e:
+                parser.error(str(e))
+            if args.clean:
+                BUILD.clean(all=False)
+            BUILD.run_build(*cm_args)
+        # build Emscripten ports with embuilder
+        if builder.host.is_emscripten and "emports" not in args.ops:
+            builder.build_emports()
+
+    for op in args.ops:
+        logger.info("\n*** %s %s", args.platform, op)
+        if op == "build":
+            builder.run_build(*cm_args)
+        elif op == "configure":
+            builder.run_configure(*cm_args)
+        elif op == "compile":
+            builder.run_make("all", *cm_args)
+        elif op == "pythoninfo":
+            builder.run_pythoninfo(*cm_args)
+        elif op == "repl":
+            if builder.is_browser:
+                builder.run_browser()
+            else:
+                builder.run_py()
+        elif op == "test":
+            builder.run_test("buildbottest", testopts=args.testopts)
+        elif op == "hostrunnertest":
+            builder.run_test("hostrunnertest", testopts=args.testopts)
+        elif op == "clean":
+            builder.clean(all=False)
+        elif op == "cleanall":
+            builder.clean(all=True)
+        elif op == "emports":
+            builder.build_emports(force=args.clean)
+        else:
+            raise ValueError(op)
+
+    print(builder.builddir)
+    parser.exit(0)
+
+
+if __name__ == "__main__":
+    main()