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source_location for methods written in C (Method#c_location)

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README.md

Given various assumptions about your setup, provides Method#c_location, which is the equivalent of Method#source_location for methods that were written in C.

Requirements

On Mac OS X, you will need the nm tool that's bundled with Xcode; and the gobjdump tool that you can get with brew install binutils.

On Linux you'll need the objdump tool, on Debian/Ubuntu it's obtainable with apt-get install binutils, I assume other distros are similar.

On all systems you'll need your Rubies compiled with debug information (seems to be the default on Linux). If you're using rvm add export rvm_configure_flags="CFLAGS=-g" to ~/.rvmrc.

If it still doesn't work — try running the commands that are found in lib/c_location/resolver.rb manually, and see where the problem is.

How does this even work?!

  1. Find a pointer to the C function that's behind a ruby method (most of the code in ext/c_location.c deals with doing this for various versions of Ruby — it's certainly not exposed in the API!)

  2. Find the shared object file that contains this C function, and the offset in that file that the function's compiled code resides. This is done using the non-standard (but widespread) dladdr() function. (See man dladdr).

  3. (Mac OS X only). Use nm to find the original library that the shared object file was built from. (This is because .bundle files don't contain the debugging information directly).

  4. use objdump to read the DWARF data embedded in the shared object file when it was compiled with the -g flag.

  5. Use some heuristics to guess the directories that might include that file based on the location of the object file on disk, and look for a correctly named file there.

(In short, lots and lots of string).

TODO

If possible, it'd be nice to have fewer external calls. Perhaps the data we're using nm for could be done in Ruby without too much help; we could even try bundling libdwarf to avoid the dependency on objdump.

It'd be really cool to make the Pry edit-method command work for C extensions. I think this is just a matter of writing more code: have edit-method work as normal, and then after closing the editor run make in the right directory; then copy the .so file into a new directory and then require it. (the Init_foo method should then just overwrite all the existing setup).

Meta-fu

Released under the MIT License. Bug reports and pull requests welcome.

Do not use this in production :p.

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