The Buckblog

In his usual inimitable fashion, _why raised his hand in the comments to Inspecting a live ruby process and asked “I wonder if this could be wrapped up into an extension?” Intriguing idea!

I played around with it a bit over the weekend, and came up with a relatively simple script that wraps the GDB console, using popen to communicate with it from Ruby. It lets you do some fun stuff, but it’s still kind of fragile. I’m releasing it into the public domain, in the hopes that someone will take the idea and run with it, since I don’t really have any more time to play with it.

You can grab it here.

Basic usage:

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require 'gdb'

# create a new GDB::Ruby instance and attach it to
# pid 12345
gdb = GDB::Ruby.new(12345)

# print the (ruby) backtrace of the remote process
gdb.backtrace.each { |line| puts line }

# show the current local variables, and their values
p gdb.local_variables

# evaluate arbitrary ruby code in the remote process
p gdb.eval('%(pid #{$$})')

# show how many instances of each class exist in the
# remote process
p gdb.object_space

# raise an exception in the remote process
gdb.raise Exception, "go boom!"

# close the connection to the remote process
gdb.quit

As I said, it’s a little fragile; it doesn’t really do much in the way of error handling. Also, I’ve noticed that it will occassionally kill the process it attaches to (I suspect some bad interaction with garbage collection, but I haven’t dug much into it). For the curious, it uses the C API to work its magic, rather than the eval-based approach described by Mauricio. A more robust implementation could possibly be created using eval.

So, forgive the unoriginal name and the spotty implementation. It’s a fun experiment, nonetheless. Let me know what you think!