[torch deploy] add support for Python C extension modules (#58117)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58117
Previously it was not possible to load C extension modules with deploy because extension
modules need to link against the Python.h API functions. Since
each libtorchdeploy_interpreter.so had its own copy of these functions, it is not possible
to tell dlopen to resolve symbols in a loaded SO from one of these libraries without exposing
its symbols globally.
This patch adds a custom ELF loader which does the custom loading of attaching c extension libraries
to the Python API that loaded the shared library. Simple use of numpy and regex modules appears to work.
This diff has some limitations:
* 64-bit Linux only. OSX and windows use different formats for shared libraries. 32-bit ELF files are not supported.
* debug info is not immediately availiable to debuggers. A script for lldb is provided which can be loaded
so that lldb knows about the libraries as they are loaded.
* shared libraries can directly use the Python API, but libraries they depend on
(via DT_NEEDED entries in their dynamic segment) may not use Python. In the future, we can
try to detect whether a sub library uses the Python API and load it with our customer loader.
* TLS initialization and library initialization may occur in a different order than what would happen with dlopen,
potentially leading to some issues running destructors in TLS segments. Use of this C++ features is relatively rare.
Test Plan: Imported from OSS
Reviewed By: suo
Differential Revision: D28435305
Pulled By: zdevito
fbshipit-source-id: 10f046053dd1d250e3c73f2cce8eb945eeba31b6
