LLDB (Swift): Casting Raw Address into Usable Type

Question

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?

Solution 1

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)

Solution 2

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.

Solution 3

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)

Solution 4

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)

Solution 5

Objective-C version

po ((MKPinAnnotationView *)0x7df67c50).alpha

View more solutions

Comments

[jarrodparkes]

For the first statement i think you forgot the 'expr' or 'expression'. Otherwise it is working great!

[devios1]

I'm getting "error: use of undeclared identifier 'unsafeBitCast'" in Xcode 7.2.

[carlos_ms]

Besides that error (@devios) there's another error it shows in 7.3.1: "error: unknown type name 'let'"

[Lucas van Dongen]

This really shouldn't be so hard

[mfaani]

This was a little counter intuitive. I thought I didn't need to type the (lldb) in my console. But it didn't work without that.

[p0lAris]

Is there a way to do this in objective-c?

[Patrick Pijnappel]

Note that depending on context you might need to switch lldb to Swift mode first using (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

[Koen.]

I keep getting back at this. I probably should create a lldb alias for expr -l Swift -- ..

[Trev14]

This worked perfectly for me. In my case I was in the 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.

[Alexander Stepanishin]

I'm getting error: no such module "MyProjectName". Any thoughts how to fix this?

[Juanmi]

@AlexanderStepanishin try setting the thread/stack path, Example: "MyApp > Thread 1 > 12 main"

[tontonCD]

from your link, expression -l objc -O -- 0x76543210 is just the response for me, and it doesn't need to know the variable class from the adress!

[Max Desiatov]

As was mentioned in a different answer to this question, typing settings set target.language swift once is enough to avoid expr -l Swift -- in subsequent commands.

[Bogdan Razvan]

@AlexanderStepanishin you need to hit a breakpoint. It won't work if you interrupt the flow by pressing the Debug Memory Graph button in xCode.