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Notes on llnode and lldb installation

What's all this?

lldb

It's a tool for analyzing low level diagnostics information from processes. Node.js in our case :)

llnode

It's a plugin to lldb that shows real names of references/functions in JavaScript in lldb (normally you'd only get names for C++ functions and objects)

It's great that lldb+llnode can be used to read diagnostics from node, it used to be that only mdb on solaris based operating system could do that.

Notes on installation

First install lldb using apt-get, then install the llnode plugin from npm:

https://npmjs.org/package/llnode

To install the plugin use npm install llnode or follow the build instructions in the github project.

Note that lldb supports the use of a system plugin directory (/usr/lib/lldb/plugins on Linux). By installing a plugin in the system plugin directory you avoid having to run the lldb plugin load llnode.so command in each lldb session. The npm install does not add the llnode plugin to the system plugin directory. You can either copy the plugin: sudo cp llnode.so /usr/lib/lldb/plugins or if you are building from the github repository, install it using the sudo make install-linux build step.

A global npm install of llnode, i.e. npm install -g llnode, does not work right now. Maybe we should raise an issue on llnode to have the -g install do the copy to the system plugin directory. It would need to run as sudo/root.

It should work on all flavors of ubuntu and most other distros with any version of lldb starting at 3.8. If you find out more, feel free to PR here

On 2017-02-03 I managed to install lldb-3.8 with latest llnode in xubuntu 16.04.1 kernel 4.4.0-62-generic x86_64

llnode commands

Once you install llnode, these commands become available in lldb.

v8 help Display the help

v8 nodeinfo Display Node.js information summary

Display the JavaScript and C++ stack

v8 bt [<number of frames>]

  • output includes source file, line number, object addresses
  • display source code using frame select <frame number> then v8 source list

List objects in the JavaScript heap

v8 findjsobjects

  • provides number of objects, total size and type name

Display JavaScript object/constructor/function

v8 print <object address>

v8 inspect <object address>

v8 inspect <buffer object address> Display raw address of buffer memory

v8 inspect [-m -s -F] <object address>

  • -m prints the object's map address
  • -s prints source code for function objects
    • see v8 bt above for source code of stackframe
  • -F prints full string values without truncation

Find JavaScript objects by type name

v8 findjsinstances [-m -s -F] <type name>

  • same output options as the v8 inspect

Find JavaScript objects by reference

v8 findrefs [-v -n -s]

  • -v <object address> (default) finds objects that reference a specified object
  • -n <name> finds objects that reference a specified property name
  • -s <string> finds objects that reference a specified string