Is there an LLDB command that can cast a raw address into a usable Swift class?
For example:
(lldb) po 0x7df67c50 as MKPinAnnotationView
I know that this address points to a MKPinAnnotationView, but it is not in a frame that I can select. But, I want to cast the raw address into a MKPinAnnotationView so that I can examine its properties. Is this possible?
Under Xcode 8.2.1 and Swift 3, the lldb command po or p won't work with the typed variable. You will need to use the swift command print to examine the properties of the typed object instance. (Thanks to cbowns's answer!) E.g.:
expr -l Swift -- import UIKit
expr -l Swift -- let $pin = unsafeBitCast(0x7df67c50, to: MKPinAnnotationView.self)
expr -l Swift -- print($pin.alpha)
(lldb) in my console. But it didn't work without that.
expr -l Swift -- ..
settings set target.language swift once is enough to avoid expr -l Swift -- in subsequent commands.You can use Swift's unsafeBitCast function to cast an address to an object instance:
(lldb) e let $pin = unsafeBitCast(0x7df67c50, MKPinAnnotationView.self)
(lldb) po $pin
Then you can work with $pin as usual – access properties, call methods, etc.
Check out this article for more information: Swift Memory Dumping.
(lldb) settings set target.language swift. Also, in some cases (e.g. when breaking outside of your app's module while casting to a type from your app) you might need to follow that with a e import MyApp
The lldb format for expression seems to have changed in Xcode 7.3. The following got me started:
(lldb) expr -l Swift -- import UIKit
(lldb) expr -l Swift -- let $view = unsafeBitCast(0x7fb75d8349c0, UIView.self)
For Custom Classes you need to import your project
expr -l Swift -- import MyTestProject
expr -l Swift -- let $vc = unsafeBitCast(0x7fad22c066d0, ViewController.self)
expr -l Swift -- print($vc.view)
Objective-C version
po ((MKPinAnnotationView *)0x7df67c50).alpha
Debug View Hierarchy view, right clicked on a view, then selected Print description of.... That gave me a memory address and type I could drop into the code above. Nice to know that the visual debugger puts the console into an Obj-C frame.As of Xcode 8/Swift 3, here's what worked for me. (This is based off @sfaxon's answer.)
(lldb) expr -l Swift -- import UIKit
(lldb) expr -l Swift -- let $nav = unsafeBitCast(0x1030ff000, to: UINavigationController.self)
Thanks to all the answers above, unsafeBitCast also works well with Xcode 8.3.2 / Swift 3 / macOS / Cocoa Application.
Memorize an address of current instance
(lldb) p tabView.controlTint
(NSControlTint) $R10 = defaultControlTint
(lldb) p self
(LearningStoryboard.NSTabViewController) $R11 = 0x00006080000e2280 {
.....
Later, examine them
(lldb) p unsafeBitCast(0x00006080000e2280, to: NSTabViewController.self).tabView.controlTint
(NSControlTint) $R20 = graphiteControlTint
(lldb) p $R11.tabView.controlTint
(NSControlTint) $R21 = graphiteControlTint
If something like this happens
(lldb) p unsafeBitCast(0x00006080000e2280, to: NSTabViewController.self).tabView.controlTint
error: use of undeclared identifier 'to'
(lldb) p $R11.tabView.controlTint
error: use of undeclared identifier '$R11'
make sure that choose one of the stack frames of Swift source code rather than assembler one.
It is likely to happen when the application was paused by clicking a Pause button or stopped with an exception. By choosing a stack frame accordingly, let lldb infer a proper programing language.
It took me longer to figure out that I'd like to admit. It's similar to @afinlayson answer, but with better explanation (I hope!) and fixed syntax
If you want to check properties of an objects using Xcode’s view hierarchy debugger then this will work: You’re in objc context by default so you’ll have to switch it to Swift context
expr -l Swift -- import <YOUR PROJECT NAME>
expr -l Swift -- let $vc = unsafeBitCast(0x7fb7c51cb270, to: <YOUR PROJECT NAME>.<YOUR CUSTOM CLASS NAME>.self)
expr -l Swift -- print($vc.<PROPERTY NAME>)
Example:
expr -l Swift -- import Football
expr -l Swift -- let $vc = unsafeBitCast(0x7fb7c51cb270, to: Football.Ball.self)
expr -l Swift -- print($vc.velocity)
@Xi Chen's answer works perfectly when your LLDB session was started in a Swift context. However, in some cases you might have stopped in a breakpoint outside a Swift context; for example, when it's a symbolic breakpoint to Objective-C API, or when in Debug View Hierarchy mode (at least as of Xcode 11.4).
error: unknown type name 'let'
error: use of undeclared identifier 'unsafeBitCast'
In that case, you'll need to do it the old way using Objective-C:
e MKPinAnnotationView *$pin = (MKPinAnnotationView *)0x7df67c50
and now you can use $pin as you would.
The easiest way, swift 4
expr unsafeBitCast(0x7df67c50, to: MKPinAnnotationView.self)
po is an alias, which means it can be overridden. You can override po by handling hex addresses using objc:
command regex po
s/(0x[[:xdigit:]]+)/expression -l objc -O -- %1/
s/(.+)/expression -O -- %1/
To see what effect this has, you can tell lldb to expand these aliases:
(lldb) settings set interpreter.expand-regex-aliases true
Also I have created https://github.com/kastiglione/swift_po, which is a substitute po for Swift. It handles object addresses, and has a few other improvements too.
expression -l objc -O -- 0x76543210 is just the response for me, and it doesn't need to know the variable class from the adress!When in Swift lldb context and dealing with NSObject subclass such as MKPinAnnotationView it's arguably easier to deliberately switch back to obj-c lldb context using this 1-liner:
e -O -l objc -- 0x7df67c50
where e -O -- is equivalent to po in lldb when in obj-c context.
I managed to make it work using this command in my .lldbinit file:
command regex ps 's/^([^[:space:]]+)[[:space:]]+([^[:space:]]+)[[:space:]]+([^[:space:]]+)$/expression -l Swift -- import UIKit; let pointer = UnsafeRawPointer(bitPattern: %1)!; let this = unsafeBitCast(pointer, to: %2.self); print(%3)/'
And I'm using it like this:
(lldb) ps 0x6000007a5bc0 CAGradientLayer this
<CAGradientLayer: 0x6000007a5bc0>
() $R1 = {}
(lldb) ps 0x6000007a5bc0 CAGradientLayer this.bounds
(0.0, 0.0, 61.333333333333336, 22.666666666666668)
() $R0 = {}