python3生成.so动态库&执行exec函数的兼容问题

通过生成.so文件可以加密python项目，破解难度较大，但是会有代码兼容问题，并且在新系统下需要重新编译

整理一些python中执行exec函数编译为.so动态库之后碰到的问题

测试代码执行环境:

centos:centos7 镜像
Python 3.6.8
gcc version 4.8.5 20150623 (Red Hat 4.8.5-44) (GCC)

因为我这用的空的centos7环境所以安装东西比较多，正常比如使用macOS可能只需要安装Cython就可以了
安装:

yum -y install python3
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
python3 get-pip.py
pip3 install Cython
yum -y install gcc
yum -y install python3-devel

生成.so的代码(gen-so.py):

#!/usr/bin/env python3

import sys 
from distutils.core import setup
from Cython.Build import cythonize

setup(ext_modules = cythonize([sys.argv[1]], compiler_directives={'language_level' : "3"}), script_args=['build_ext', '-b', './build', '-t', './tmp'])

举一个简单的例子：
python文件(demo.py)：

def run():
    print('run')

生成.so文件, 运行命令：

python3 gen-so.py demo.py

生成后文件结构:

.
|-- build
|   `-- demo.cpython-36m-x86_64-linux-gnu.so
|-- demo.c
|-- demo.py
|-- gen-so.py
`-- tmp
    `-- demo.o

2 directories, 5 files

调用.so文件，这里方便起见就直接通过python -c调用了:

python3 -c "from build import demo;demo.run()"

会输出"run"，没问题

调用exec函数编译为动态库后表现不一致的情况

1. exec中使用实例变量
demo.py

class Demo():
    def __init__(self):
        self.a = 1
        exec('self.b=2')
        print(self.b)    

def run():
    Demo()
    

生成.so文件后，分别执行Python和.so的代码:

[root@6d819d145bf6 demo]# python3 -c "import demo; demo.run()"
2
[root@6d819d145bf6 demo]# python3 -c "from build import demo; demo.run()"
Traceback (most recent call last):
  File "", line 1, in 
  File "demo.py", line 8, in demo.run
    Demo()
  File "demo.py", line 4, in demo.Demo.__init__
    exec('self.b="2"')
  File "", line 1, in 
NameError: name 'self' is not defined

修改exec('self.b=2')为self.__dict__['b'] = 2或者exec('self.b=2',locals())

2. exec中使用局部变量
demo.py

class Demo():
    def __init__(self):
        self.a = 1
        local_c = 'lc'
        exec('local_d = "ld"')
        print(locals())    

def run():
    Demo()

分别执行python和.so:

[root@6d819d145bf6 demo]# python3 -c "import demo; demo.run()"
{'local_c': 'lc', 'self': , 'local_d': 'ld'}
[root@6d819d145bf6 demo]# python3 -c "from build import demo; demo.run()"
{'local_c': 'lc', 'self': }

可以看到Python能拿到exec中的局部变量local_d，但是.so动态库中不能拿到

3. exec中动态调用方法
demo.py

class Demo():
    def __init__(self):
        self.a = 1
        import math
        func_name = "log"
        exec("log10 = math."+ func_name + "(10)")
        print(log10)

def run():
    Demo()
    

编译失败：

[root@6d819d145bf6 demo]# python3 gen-so.py demo.py
Compiling demo.py because it changed.
[1/1] Cythonizing demo.py

Error compiling Cython file:
------------------------------------------------------------
...
    def __init__(self):
        self.a = 1
        import math
        func_name = "log"
        exec("log10 = math."+ func_name + "(10)")
        print(log10)
             ^
------------------------------------------------------------

demo.py:7:14: undeclared name not builtin: log10
Traceback (most recent call last):
  File "gen-so.py", line 7, in 
    setup(ext_modules = cythonize([sys.argv[1]], compiler_directives={'language_level' : "3"}), script_args=['build_ext', '-b', './build', '-t', './tmp'])
  File "/usr/local/lib64/python3.6/site-packages/Cython/Build/Dependencies.py", line 1102, in cythonize
    cythonize_one(*args)
  File "/usr/local/lib64/python3.6/site-packages/Cython/Build/Dependencies.py", line 1225, in cythonize_one
    raise CompileError(None, pyx_file)
Cython.Compiler.Errors.CompileError: demo.py

因为上面的log10是局部变量，所以通过locals()中也获取不到

修改exec("log10 = math."+ func_name + "(10)")为log10 = getattr(math, func_name)(10)
直接运行.so:

[root@6d819d145bf6 demo]# python3 -c "from build import demo; demo.run()"
2.302585092994046

运行正确

4. exec代码内list使用局部变量
参考： listcomp unable to access locals defined in code called by exec if nested in function

这段代码在python和.so方式下都正常执行：

code = """
g = 5
x = [g for i in range(5)]
print(x)
"""
exec(code)

def run():
    pass

执行后正确输出[5, 5, 5, 5, 5]

下面这段代码在Python版执行报错，但是.so动态库执行成功：

def run():
    code = """
g = 5
x = [g for i in range(5)]
print(x)
"""
    exec(code)

python版报错，.so执行成功：

[root@6d819d145bf6 demo]# python3 -c "import demo; demo.run()"
Traceback (most recent call last):
  File "", line 1, in 
  File "/opt/demo/demo.py", line 7, in run
    exec(code)
  File "", line 3, in 
  File "", line 3, in 
NameError: name 'g' is not defined
[root@6d819d145bf6 demo]# python3 -c "from build import demo; demo.run()"
[5, 5, 5, 5, 5]

修改exec(code)为exec(code, globals())后，python也运行正确，和.so表现一致