Ruby GDB introspection

Attaching to the process with GDB

Populate your .gdbinit and .gdb directories

In ~/.gdbinit:

define session-ruby
  source ~/.gdb/ruby
end

Next, you need to download http://eigenclass.org/hiki.rb?c=plugin;plugin=attach_download;p=ruby+live+process+introspection;file_name=ruby

And place it in ~/.gdb/ruby.

$ mkdir -p ~/.gdb
$ wget 'http://eigenclass.org/hiki.rb?c=plugin;plugin=attach_download;p=ruby+live+process+introspection;file_name=ruby'
$ mv ruby ~/.gdb

Attach to the process, load the ruby helpers, and redirect stdout:

$ ps ax | grep ruby
  845 s000  S+     0:00.91 /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby /usr/bin/chef-indexer -l debug
  932 s001  R+     0:00.00 grep ruby
  842 s002  S+     0:00.44 /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby /usr/bin/stompserver


The important part here is the very first segment of the line (the PID).

$ gdb /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby 845

The first argument to gdb should be the full path to the ruby executable that is running the process.

Start your debug session

From above, you should see a bunch of output like this:

...
Loaded symbols for /srv/ruby/1.8.6/lib/ruby/1.8/i686-linux/nkf.so
0xbfffe402 in +kernel_vsyscall ()

And then you'll wind up at...

(gdb)

First things first, load up the ruby helpers.

(gdb) session-ruby

Then, redirect stdout to a file, so we can capture the output for later.

(gdb) redirect_stdout

Open up a second terminal, and you can watch the output from your debug session:

$ tail -f /tmp/ruby-debug.PID

Where PID above is equal to the PID you attached to with gdb.

Now that you are watching, flip back to your gdb session and..

Get some data

(gdb) eval "caller" 
(gdb) rb_object_counts
(gdb) eval "total = ObjectSpace.each_object {|x| if x.class.to_s =~ /Puppet/; puts '---'; puts x.inspect; end }; puts \"---\nTotal Objects: #{total}\"" 

Or, for arrays only:
(gdb) eval "total = ObjectSpace.each_object(Array){|x| puts '---'; puts x.inspect }; puts \"---\nTotal Arrays: #{total}\"" 

You should see a stack trace, a long count of the number of objects in the system.