auditwheel-emscripten

auditwheel-like tool for wheels targeting Emscripten platform

$ pip install auditwheel-emscripten

What is this?

auditwheel-emscripten is a tiny tool to facilitate the creation of Python wheel packages for Emscripten. auditwheel-emscripten is originally created for Pyodide, but it can be used in any other projects that target Python-in-the-browser using Emscripten.

• pyodide auditwheel show: shows external shared libraries that the wheel depends on.
• pyodide auditwheel repair: copies these external shared libraries into the wheel itself, mangles copied names with a source-content hash, and updates the RPATH of the WASM module correspondingly.

Usage (CLI)

 Usage: pyodide auditwheel [OPTIONS] COMMAND [ARGS]...

 Auditwheel-like tool for emscripten wheels and shared libraries.

╭─ Options ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ --help          Show this message and exit.                                                                                         │
╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
╭─ Commands ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ copy      [Deprecated] Copy shared libraries to the wheel directory. Works same as repair. Use repair instead.          │
│ exports   Show exports of a wheel or a shared library file.                                                                         │
│ imports   Show imports of a wheel or a shared library file.                                                                         │
│ repair    Repair a wheel file: copy shared libraries to the wheel directory.   │
│ show      Show shared library dependencies of a wheel or a shared library file.                                                     │
╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

$ pyodide auditwheel show shapely-2.0.7-cp313-cp313-pyodide_2025_0_wasm32.whl
shapely/speedups/_speedups.cpython-310-wasm32-emscripten.so:
        libgeos_c.so

shapely/vectorized/_vectorized.cpython-310-wasm32-emscripten.so:
        libgeos_c.so

$ pyodide auditwheel repair --libdir <directory which contains libgeos_c.so> shapely-2.0.7-cp313-cp313-pyodide_2025_0_wasm32.whl
shapely/lib.cpython-313-wasm32-emscripten.so:
        libgeos_c-a1b2c3d4.so => shapely.libs/libgeos_c-a1b2c3d4.so

shapely/_geometry_helpers.cpython-313-wasm32-emscripten.so:
        libgeos_c-a1b2c3d4.so => shapely.libs/libgeos_c-a1b2c3d4.so

shapely/_geos.cpython-313-wasm32-emscripten.so:
        libgeos_c-a1b2c3d4.so => shapely.libs/libgeos_c-a1b2c3d4.so

shapely.libs/libgeos-e5f6a7b8.so:

shapely.libs/libgeos_c-a1b2c3d4.so:
        libgeos-e5f6a7b8.so => shapely.libs/libgeos-e5f6a7b8.so

Usage (API)

Listing shared library dependencies of a wheel file:

from auditwheel_emscripten import show
libs = show("Shapely-1.8.2-cp310-cp310-emscripten_3_1_14_wasm32.whl")
print(libs)
# {'shapely/vectorized/_vectorized.cpython-310-wasm32-emscripten.so': ['libgeos_c.so'], 'shapely/speedups/_speedups.cpython-310-wasm32-emscripten.so': ['libgeos_c.so']}

Copying shared libraries to the wheel:

from auditwheel_emscripten import repair, show
repaired_wheel = repair(
    "Shapely-1.8.2-cp310-cp310-emscripten_3_1_14_wasm32.whl",
    libdir="/path/where/shared/libraries/are/located",
    outdir="/path/to/output/directory",
)
libs = show(repaired_wheel)
print(libs)
# {'Shapely.libs/libgeos-e5f6a7b8.so.3.10.3': [], 'Shapely.libs/libgeos_c-a1b2c3d4.so': ['libgeos-e5f6a7b8.so.3.10.3'], 'shapely/speedups/_speedups.cpython-310-wasm32-emscripten.so': ['libgeos_c-a1b2c3d4.so'], 'shapely/vectorized/_vectorized.cpython-310-wasm32-emscripten.so': ['libgeos_c-a1b2c3d4.so']}

Implementation details / limitations

Dynamic linking in Emscripten

Dynamic linking is not in the WebAssembly specification, but Emscripten has its own dynamic linking support, which is required for building Python wheels targeting Emscripten platform.

This tool is based on:

• Loosely documented Emscripten dynamic linking specification: https://github.com/WebAssembly/tool-conventions/blob/main/DynamicLinking.md
• Emscripten's internal utility for inspecting WASM module: https://github.com/emscripten-core/emscripten/blob/main/tools/webassembly.py
• Emscripten dylink implementation: https://github.com/emscripten-core/emscripten/blob/main/src/library_dylink.js

auditwheel vs auditwheel-emscripten

auditwheel is a tool that helps repair and modify Python wheels (pre-compiled packages) to be compatible with a wide range of Linux distributions. It does this by copying external shared libraries into the wheel and repairing the RPATH (a file path that is used to locate shared libraries at runtime) of the ELF binary so that the Linux operating system can locate the library when the program is run.

auditwheel-emscripten is a variation of auditwheel that is specifically designed to work with Emscripten-generated WebAssembly (WASM) modules. Like auditwheel, it copies the required shared libraries into the wheel and patches the runtime search path of each WASM module so the dynamic linker can locate them at runtime. It does this by writing a RUNTIME_PATH entry (using $ORIGIN-relative paths) into the dylink.0 custom section of each module, which is the Emscripten equivalent of the ELF RPATH. Pyodide's dynamic linker reads this section to resolve library locations.

Unlike auditwheel on Linux, auditwheel-emscripten does not enforce compatibility between Emscripten versions, since no stable ABI exists for Emscripten-compiled shared libraries.