Introspection of the interface of a shared library

Question

I have a problem with a library I'm working with for the first time ( it's Boost.Python but my question is much more general than this case).

As a consequence I need to check what is the interface of the library I have built: so as to check if I have at least built everything correctly.

(Python is complaining that he doesn't see my module, though I put the .so renammed in .pyd into its PYTHONPATH, so there's something wrong in my library)

I need to know all the names of the exposed functions of my .so library, and their prototype if possible.

Are there commands or package that I could install to achieve something like this ?

Answer 1

You can get information from an ELF file (executable or library) with readelf.

Looks like you're looking for the exported symbols, so use:

$ readelf --dyn-syms libyourthing.so

For C-type functions, you'll only get function names, not argument types or return values. For C++ functions, you'll get mangled names - pipe the output of that command through c++filt to get function names and argument types (still no return values though).
(Globals are also displayed in the output, with their names and size but not their type.)

Other useful tools are nm and objdump which provide similar information.

I'm not sure that'll help you though. You should also try strace to see if python is looking where you think it is. Something like:

$ strace -e trace=open python your_code_that_loads_your_lib.py

will show you all the open calls executed by python - look for your library name in there (there will be a lot logged by the above, filter it). Each call also shows the return code, so you might get a better idea about what is going on.

_{Oh, and do make sure you're not trying to load a 32bit library into a 64bit python runtime, or vice-versa.}