Node.js v10.x+ C++ plugin for the LLDB debugger.

The llnode plugin adds the ability to inspect JavaScript stack frames, objects, source code and more to the standard C/C++ debugging facilities when working with Node.js processes or core dumps in LLDB.

Demo

https://asciinema.org/a/29589

Quick start

Start an LLDB session with the llnode plugin automatically loaded:

npm install -g llnode
llnode `which node` -c /path/to/core/dump

• Never install llnode with sudo as it can easily lead to errors during installation and execution.
• For more details on starting llnode see the Usage section.
• To get started with the llnode commands see the Commands section.

Install Instructions

Prerequisites: Official, active Node.js version

llnode only supports currently active Node.js versions installed via official channels. We recommend installing Node.js with nvm as it allows users to install global packages without sudo by default, and it always installs the official executables from https://nodejs.org.

Do not install Node.js from the default Ubuntu/Debian apt repositories (or from the default repositories of other Linux distributions), llnode is not compatible with Node.js installed that way. If you still want to install Node.js via apt-get, take a look at nodesource/distributions.

Prerequisites: Install LLDB and its Library

To use llnode you need to have the LLDB debugger installed. The recommended version is LLDB 3.9 and above.

• OS X/macOS

  • You can install Xcode and use the LLDB that comes with it.

  • Optionally, you can install newer versions of lldb using Homebrew with

    brew update && brew install --with-lldb --with-toolchain llvm
    

    and make sure /usr/local/opt/llvm/bin gets searched before /usr/bin/ on your PATH. llnode will link to the LLDB installation returned by llvm-config if available.

• Linux

  • You can install the lldb package using the package manager of your distribution. You may need to install additional packages for liblldb as well.

  • For example, on Ubuntu 18.04 you can install the prerequisites with

    apt-get install lldb-8 liblldb-8-dev
    

• FreeBSD

  # Install llvm with lldb and headers
  pkg install llvm39
  rm -f /usr/bin/lldb
  ln -s /usr/local/bin/lldb39 /usr/bin/lldb
  

• Windows

  • You can install a binary distribution of LLVM directly or using Chocolatey:

    cinst -y visualstudio2017buildtools visualstudio2017-workload-vctools llvm git
    

    Visual Studio is required for MSBuild and headers when building llnode. Git is required to download the lldb headers.

• Android / Termux (Experimental)

  • Install Termux (https://termux.com)

  • Install Termux Packages

    • pkg install clang lldb lldb-dev make
    • pkg install nodejs-lts nodejs-lts-dev

  • To debug:

  llnode -- /data/data/com.termux/files/usr/bin/node --abort_on_uncaught_exception script.js
  (llnode) run
  

Install the Plugin

Install llnode globally via npm

If you have lldb available on your PATH, simply run:

npm install -g llnode

To build llnode against a specific lldb version matching an lldb executable, use the --lldb_exe npm option. For example, on Linux the executable on the PATH might be lldb-3.9:

npm install --lldb_exe=`which lldb-3.9` -g llnode

After installing with npm, llnode should be available on your PATH as a shortcut for running LLDB with the llnode plugin.

Optional: Install with Homebrew (OS X/macOS)

brew install llnode

Loading the llnode Plugin

There are several ways to load the llnode plugin:

1. Using the llnode shortcut

If you install llnode globally via npm (npm install -g llnode), you can use the llnode shortcut script. This starts lldb and automatically issues the plugin load command. All parameters to the llnode script are passed directly to lldb. If you it's not a local installation, the shortcut will be in node_modules/.bin/llnode.

2. Using ~/.lldbinit to load the Plugin Automatically

To tell LLDB to load llnode automatically regardless of the version of lldb that you are running, add this line to ~/.lldbinit:

plugin load /path/to/the/llnode/plugin

The path to the llnode plugin should be printed when the installation is finished. On OS X/macOS the plugin is typically node_modules/llnode/llnode.dylib, on Linux it's node_modules/llnode/llnode.so.

3. Loading the Plugin Manually

The llnode plugin can also be manually loaded into LLDB using the plugin load command within lldb.

It does not matter whether the plugin load command is issued before or after loading a core dump or attaching to a process.

4. Install the Plugin to the LLDB System Plugin Directory

Similar to the ~/.lldbinit approach, this way LLDB will also load the plugin automatically on start-up. Doing this may require additional permissions to be able to copy the plugin library to the system plugin directory.

On Linux, run make install-linux in the project directory, or if installing with npm, copy node_modules/llnode/llnode.so to /usr/lib/lldb/plugins or create a link there.

On OS X/macOS, run make install-osx in the project directory, or if installing with npm, copy node_modules/llnode/llnode.dylib to ~/Library/Application\ Support/LLDB/PlugIns/ or create a link there.

Usage

To use llnode with a core dump the core dump needs to be loaded into lldb along with the exact executable that created the core dump. The executable contains information that lldb and the llnode plugin need to make sense of the data in the core dump.

To load a core dump when starting llnode use:

llnode /path/to/bin/node -c /path/to/core

or to load the core dump after starting lldb:

(llnode) target create /path/to/bin/node -c /path/to/core

To use llnode against a live process:

llnode -- /path/to/bin/node script.js
(llnode) run

This is ideal for debugging an npm package with native code. To debug a Node.js crash on uncaught exception:

llnode -- /path/to/bin/node --abort_on_uncaught_exception script.js
(llnode) run

lldb will stop your process when it crashes. To see where it stopped use the v8 bt command. See the Commands section below for more commands.

Commands

(llnode) v8 help
     Node.js helpers

Syntax: v8

The following subcommands are supported:

      bt              -- Show a backtrace with node.js JavaScript functions and their args. An optional argument is accepted; if
                         that argument is a number, it specifies the number of frames to display. Otherwise all frames will be
                         dumped.

                         Syntax: v8 bt [number]
      findjsinstances -- List every object with the specified type name.
                         Use -v or --verbose to display detailed `v8 inspect` output for each object.
                         Accepts the same options as `v8 inspect`
      findjsobjects   -- List all object types and instance counts grouped by typename and sorted by instance count. Use
                         -d or --detailed to get an output grouped by type name, properties, and array length, as well as
                         more information regarding each type.
      findrefs        -- Finds all the object properties which meet the search criteria.
                         The default is to list all the object properties that reference the specified value.
                         Flags:

                          * -v, --value expr     - all properties that refer to the specified JavaScript object (default)
                          * -n, --name  name     - all properties with the specified name
                          * -s, --string string  - all properties that refer to the specified JavaScript string value

      getactivehandles  -- Print all pending handles in the queue. Equivalent to running process._getActiveHandles() on
                           the living process.

      getactiverequests -- Print all pending requests in the queue. Equivalent to running process._getActiveRequests() on
                           the living process.

      inspect         -- Print detailed description and contents of the JavaScript value.

                         Possible flags (all optional):

                          * -F, --full-string    - print whole string without adding ellipsis
                          * -m, --print-map      - print object's map address
                          * -s, --print-source   - print source code for function objects
                          * -l num, --length num - print maximum of `num` elements from string/array

                         Syntax: v8 inspect [flags] expr
      nodeinfo        -- Print information about Node.js
      print           -- Print short description of the JavaScript value.

                         Syntax: v8 print expr
      source list     -- Print source lines around the currently selected
                         JavaScript frame.
                         Syntax: v8 source list [flags]
                         Flags:
                         * -l