如何在构建时设置cdll搜索路径

Question

我在非标准文件夹中有一个分解库libcustom.so，还有一个使用ctypes.cdll.LoadLibrary("libcustom.so")的python包。

如何在构建时设置libcustom.so路径(类似于rpath(？

env LD_LIBRARY_PATH=/path/to/custom/lib python3 -c "import mypackage"

这很好，但我不想使用全局LD_LIBRARY_PATH，也不想在运行时设置库路径。

python3 -c "import mypackage"

导致错误：

OSError:libcustum.so:无法打开共享对象文件：没有这样的文件或目录

Answer 1

我找到的唯一解决方案(肯定有更好的解决方案(是创建一个python模块来封装dlopen调用。因此，可以在编译时插入rpath以在运行时解析动态链接。

/* _custom.c */
#include <Python.h>
#include <dlfcn.h>
static struct PyModuleDef _custommodule = {
PyModuleDef_HEAD_INIT,
.m_name = "_custom",
.m_doc = "Convenience module, libcustom.so wrapper",
.m_size = -1
};
PyMODINIT_FUNC
PyInit__custom(void)
{
PyObject *self = NULL, *ctypes = NULL, *cdll = NULL, *lib = NULL;
/* We must import the library a first time here to allow the use
of rpath. Otherwise `ctypes.cdll.LoadLibrary` uses dlopen from
an internal python module, and the internal module's rpath will
be used for link resolution instead of our. */
if (! dlopen("libcustom.so", RTLD_NOW | RTLD_LOCAL)) {
PyErr_SetString(PyExc_ImportError, dlerror());
return NULL;
}
if (! (self = PyModule_Create(&_custommodule))) goto fail;
if (! (ctypes = PyImport_ImportModule("ctypes"))) goto fail;
if (! (cdll = PyDict_GetItemString(PyModule_GetDict(ctypes), (char*) "cdll"))) goto fail;
if (! (lib = PyObject_CallMethod(cdll, "LoadLibrary", "s", "libcustom.so"))) goto fail;
if (PyModule_AddObject(self, "_lib", lib) < 0) goto fail;
Py_DECREF(ctypes);
Py_DECREF(cdll);
return self;
fail:
PyErr_SetString(PyExc_ImportError, "Internal error");
Py_XDECREF(self);
Py_XDECREF(ctypes);
Py_XDECREF(cdll);
Py_XDECREF(lib);
return NULL;
}

然后我们将这个扩展添加到python包中：

# setup.py
setup(
ext_modules=[Extension("mypackage._custom", ["_custom.c"])],
...
)

然后，在构建包时，我们可以插入rpath：

python3 setup.py build_ext --rpath /path/to/custom/lib
python3 setup.py install

它只剩下用importlib.import_module("mypackage._custom")._lib代替ctypes.cdll.LoadLibrary("libcustom.so")。

Answer 2

Listing[Python.Docs]：ctypes-Python的外部函数库。

您可以将完整的.dll名称传递给CDLL(或CDLL.LoadLibrary(。

code00.py：

#!/usr/bin/env python
import ctypes as ct
import os
import sys
from custom_dll_path import CUSTOM_DLL_PATH

DLL_NAME = "dll00.{:s}".format("dll" if sys.platform[:3].lower() == "win" else "so")

def main(*argv):
if argv:
dll_name = DLL_NAME
else:
dll_name = os.path.join(CUSTOM_DLL_PATH, DLL_NAME)
print("Attempting to load: {:s}".format(dll_name))
dll00 = ct.CDLL(dll_name)

if __name__ == "__main__":
print("Python {:s} {:03d}bit on {:s}n".format(" ".join(elem.strip() for elem in sys.version.split("n")),
64 if sys.maxsize > 0x100000000 else 32, sys.platform))
rc = main(*sys.argv[1:])
print("nDone.")
sys.exit(rc)

设置.py：

#!/usr/bin/env python
import sys
from setuptools import Command, setup

class SetDllPath(Command):
user_options = [
("path=", "p", "Dll path"),
]
def initialize_options(self):
self.path = ""
def finalize_options(self):
pass
def run(self):
with open("custom_dll_path.py", "w") as f:
f.write("CUSTOM_DLL_PATH = "{:s}"n".format(self.path))

setup(
name="custom_project",
cmdclass={
"set_dll_path": SetDllPath,
},
#  Other stuff ...
)

输出：

[cfati@cfati-5510-0:/mnt/e/Work/Dev/StackOverflow/q070640586]> ~/sopr.sh
### Set shorter prompt to better fit when pasted in StackOverflow (or other) pages ###
[064bit prompt]> ls
code00.py  setup.py
[064bit prompt]> echo "int f() { return 0; }" > dll00.c
[064bit prompt]> gcc -fPIC -shared -o dll00.so dll00.c
[064bit prompt]> ls
code00.py  dll00.c  dll00.so  setup.py
[064bit prompt]>
[064bit prompt]> python3.9 setup.py set_dll_path -p $(pwd)
running set_dll_path
[064bit prompt]> ls
code00.py  custom_dll_path.py  dll00.c  dll00.so  setup.py
[064bit prompt]> cat custom_dll_path.py
CUSTOM_DLL_PATH = "/mnt/e/Work/Dev/StackOverflow/q070640586"
[064bit prompt]>
[064bit prompt]> python3.9 code00.py dummy args to fail
Python 3.9.9 (main, Nov 16 2021, 03:08:02) [GCC 9.3.0] 064bit on linux
Attempting to load: dll00.so
Traceback (most recent call last):
File "/mnt/e/Work/Dev/StackOverflow/q070640586/code00.py", line 24, in <module>
rc = main(*sys.argv[1:])
File "/mnt/e/Work/Dev/StackOverflow/q070640586/code00.py", line 18, in main
dll00 = ct.CDLL(dll_name)
File "/usr/lib/python3.9/ctypes/__init__.py", line 374, in __init__
self._handle = _dlopen(self._name, mode)
OSError: dll00.so: cannot open shared object file: No such file or directory
[064bit prompt]>
[064bit prompt]> python3.9 code00.py
Python 3.9.9 (main, Nov 16 2021, 03:08:02) [GCC 9.3.0] 064bit on linux
Attempting to load: /mnt/e/Work/Dev/StackOverflow/q070640586/dll00.so
Done.