How python library is linked?

[zhqrbitee]

Hi,
In my project, I need to create a type_caster for int128_t, so I'm using some private python APIs: _PyLong_AsByteArray and _PyLong_FromByteArray.

However, it causes link issue when compiled using nanobind_add_module:

Undefined symbols for architecture arm64:
  "__PyLong_AsByteArray", referenced from:
      ...
  "__PyLong_FromByteArray", referenced from:
      ...

I guess it is because nanobind_add_module doesn't add link to python library?

I can work around by adding below line after nanobind_add_module:

    target_link_options(${TARGET_NAME} PRIVATE "-Wl,-undefined,dynamic_lookup")

But want to know is there any recommended way to solve this?

[wjakob]

You will only have this issue on macOS, and -Wl,-undefined,dynamic_lookup is a reasonable workaround. The (very tiny) downside is that the build then won't use the new dynamic fixups feature, causing the resulting binary to be slightly larger. Alternatively, you could create a PR to add these private symbols to cmake/darwin-ld-cpython.sym and cmake.darwin-ld-pypy.sym. But private symbols are all going away soon as part of Python C API cleanups, so this is not future-proof.

A more portable way is described here: https://docs.python.org/3/c-api/long.html#c.PyLong_FromString: call the Python from/to_bytes function.