You're better off using debugger-ruby_core_source:

gem install debugger-ruby_core_source

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If you can't do this, try the following.

Here is how to fix the following error when installing the debugger gem fails:

Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension

Note: The following example is for a project using Ruby 1.9.3-p448 -- adjust accordingly for your project.

1. Fetch the source for your Ruby version, if you do not yet have it:

   rvm fetch ruby-1.9.3-p448
   

2. Install the gem by explicitly telling it where your Ruby's source is located:

   gem install debugger-linecache -v '1.1.2' -- --with-ruby-include=$rvm_path/src/ruby-1.9.3-p448
   

3. Resume what you were doing before (probably a bundle install).

Here is how the "full" error looks like when a Bundler installation fails.

Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /home/martin/.rvm/rubies/ruby-1.9.3-p448/bin/ruby extconf.rb 
checking for vm_core.h... no
checking for vm_core.h... no
Makefile creation failed
**************************************************************************
No source for ruby-1.9.3-p448 provided with debugger-ruby_core_source gem.
**************************************************************************
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/home/martin/.rvm/rubies/ruby-1.9.3-p448/bin/ruby
	--with-ruby-dir
	--without-ruby-dir
	--with-ruby-include
	--without-ruby-include=${ruby-dir}/include
	--with-ruby-lib
	--without-ruby-lib=${ruby-dir}/lib


Gem files will remain installed in /home/martin/.rvm/gems/ruby-1.9.3-p448/gems/debugger-linecache-1.1.2 for inspection.
Results logged to /home/martin/.rvm/gems/ruby-1.9.3-p448/gems/debugger-linecache-1.1.2/ext/trace_nums/gem_make.out

An error occurred while installing debugger-linecache (1.1.2), and Bundler cannot continue.
Make sure that `gem install debugger-linecache -v '1.1.2'` succeeds before bundling.