Chisel
Chisel is a collection of LLDB commands to assist in the debugging of iOS apps.
[Installation • Commands • Custom Commands • Development Workflow Contributing • License]
For a comprehensive overview of LLDB, and how Chisel complements it, read Ari Grant's Dancing in the Debugger — A Waltz with LLDB in issue 19 of objc.io.
Installation
brew update
brew install chisel
if .lldbinit file doesn't exist you can create it & open it by tapping on the terminal
touch .lldbinit
open .lldbinit
Then add the following line to your ~/.lldbinit file.
# ~/.lldbinit
...
command script import /usr/local/opt/chisel/libexec/fbchisellldb.py
Alternatively, download chisel and add the following line to your ~/.lldbinit file.
# ~/.lldbinit
...
command script import /path/to/fbchisellldb.py
The commands will be available the next time Xcode starts.
Commands
There are many commands; here's a few: (Compatibility with iOS/Mac indicated at right)
| Command | Description | iOS | OS X |
|---|---|---|---|
| pviews | Print the recursive view description for the key window. | Yes | Yes |
| pvc | Print the recursive view controller description for the key window. | Yes | No |
| visualize | Open a UIImage, CGImageRef, UIView, CALayer, NSData (of an image), UIColor, CIColor, or CGColorRef in Preview.app on your Mac. |
Yes | No |
| fv | Find a view in the hierarchy whose class name matches the provided regex. | Yes | No |
| fvc | Find a view controller in the hierarchy whose class name matches the provided regex. | Yes | No |
| show/hide | Show or hide the given view or layer. You don't even have to continue the process to see the changes! | Yes | Yes |
| mask/unmask | Overlay a view or layer with a transparent rectangle to visualize where it is. | Yes | No |
| border/unborder | Add a border to a view or layer to visualize where it is. | Yes | Yes |
| caflush | Flush the render server (equivalent to a "repaint" if no animations are in-flight). | Yes | Yes |
| bmessage | Set a symbolic breakpoint on the method of a class or the method of an instance without worrying which class in the hierarchy actually implements the method. | Yes | Yes |
| wivar | Set a watchpoint on an instance variable of an object. | Yes | Yes |
| presponder | Print the responder chain starting from the given object. | Yes | Yes |
| ... | ... and many more! |
To see the list of all of the commands execute the help command in LLDB or go to the Wiki.
(lldb) help
The following is a list of built-in, permanent debugger commands:
...
The following is a list of your current user-defined commands:
...
The bottom list contains all the commands sourced from Chisel.
You can also inspect a specific command by passing its name as an argument to the help command (as with all other LLDB commands).
(lldb) help border
Draws a border around <viewOrLayer>. Color and width can be optionally provided.
Arguments:
<viewOrLayer>; Type: UIView*; The view to border.
Options:
--color/-c <color>; Type: string; A color name such as 'red', 'green', 'magenta', etc.
--width/-w <width>; Type: CGFloat; Desired width of border.
Syntax: border [--color=color] [--width=width] <viewOrLayer>
All of the commands provided by Chisel come with verbose help. Be sure to read it when in doubt!
Custom Commands
You can add local, custom commands. Here's a contrived example.
#!/usr/bin/python
# Example file with custom commands, located at /magical/commands/example.py
import lldb
import fbchisellldbbase as fb
def lldbcommands():
return [ PrintKeyWindowLevel() ]
class PrintKeyWindowLevel(fb.FBCommand):
def name(self):
return 'pkeywinlevel'
def description(self):
return 'An incredibly contrived command that prints the window level of the key window.'
def run(self, arguments, options):
# It's a good habit to explicitly cast the type of all return
# values and arguments. LLDB can't always find them on its own.
lldb.debugger.HandleCommand('p (CGFloat)[(id)[(id)[UIApplication sharedApplication] keyWindow] windowLevel]')
Then all that's left is to source the commands in lldbinit. Chisel has a python function just for this, loadCommandsInDirectory in the fbobjclldb.py module.
# ~/.lldbinit
...
command script import /path/to/fbobjclldb.py
script fbobjclldb.loadCommandsInDirectory('/magical/commands/')
There's also builtin support to make it super easy to specify the arguments and options that a command takes. See the border and pinvocation commands for example use.
Development Workflow
Developing commands, whether for local use or contributing to Chisel directly, both follow the same workflow. Create a command as described in the Custom Commands section and then
- Start
LLDB - Reach a breakpoint (or simply pause execution via the pause button in
Xcode's debug bar orprocess interruptif attached directly) - Execute
command source ~/.lldbinitin LLDB to source the commands - Run the command you are working on
- Modify the command
- Optionally run
script reload(modulename) - Repeat steps 3-6 until the command becomes a source of happiness
Contributing
Please contribute any generic commands that you make. If it helps you then it will likely help many others! :D See CONTRIBUTING.md to learn how to contribute.
License
Chisel is MIT-licensed. See LICENSE.
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