CInvoke

Description

CInvoke is a way to call your C functions from Python. It is similar to ctypes in concept, but implemented very differently.

The package features:

• cinvoke: The Python/C pipe-based bridge.
• DataTypes: Some very generic code I would like to see built into Python. Until then, I use it from here. I narrowed it down to the minimal subset used by CInvoke, for distribution purposes.
• DataTypes.CDataTypes: A powerful replacement for the built-in struct module. A generic c-type library that is used with CInvoke.
• OSUtils.Executables: A library to parse executables. Currently it is a very limited implementation that uses "readelf" to parse only ELF formats. In the future, real DWARF parsing and hopefully COFF parsing will be implemented.

CInvoke

• Uses a socket/pipe to control the C side, allowing it to control multiple processes.
• Cannot cause segmentation faults in the hosting Python interpreter process. At worst, the controlled process dies, and the pipe to it is closed.
• Can control processes on remote computers.
• Can be used side-by-side a mainloop of an existing C program.
• Allows testing C programs in a more "realistic" environment, without the Python interpreter around it (This is relevant if your program installs signal handlers, manages its memory space, etc).
• Allows nesting request handling loops inside stubbed (replaced) functions. This allows for very powerful error injection, controlling the execution of these replaced functions from Python. It is also useful to halt the C process in a specific point, in which time the Python can command other C processes.
• Limitation: CInvoke requires building your program differently (With symbol information and a custom main() or server call code). Hopefully, I will find a way to use ldpreload or other tricks in order to avoid the main() replacement, and ease replacing of functions with stubs. In any case, compilation with Symbols will still be required. Note that compiling with -g and using strip is possible, in order to create both a stripped and non-stripped version of the same executable.
• Limitation: CInvoke currently uses readelf to extract the symbols and debug information from the executable. This means CInvoke is currently ELF-only. In the future, I plan to create and use a Pythonic executable parsing library or wrap an existing one and support many executable and debug information formats.

DataTypes

• Various small and useful modules, required by the above libraries. Probably worth a look, if you are a Pythoneer.

DataTypes.CDataTypes

• Support for all basic C types, Unions, Structs, Enums, Arrays, and Pointers.
• Pointer dereference semantics are defined by the user. Dereferences can be defined to access any arbitrary address space, for example: A remote C process's address space, a file address space, a mutable string, ...

Download

CInvoke can be downloaded here.

A simple example can be found inside the Example directory.

The current installer is very lame, and does not install the C code anywhere, I have only had about 15 minutes to work the setup.py and installation so far, sorry! :-) For now you can just use "make" inside the server directory to make a linkable server, or use "make" inside the example directory to make the example.

Bug reports

Please report bugs to Eyal Lotem.

Note that the "assertion failed" in the end of the "test" is not a bug, but the current way to handle errors in the server. Assertion failures are much easier to debug than bad return codes and more useful for unit tests, and currently this happens in EOF too. In the future assertion failures will be an optional way to error handle, and EOF will definitely not be an error.