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?

score 215 · Accepted Answer · edited Oct 17 '19 at 00:06

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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)

edited Oct 17 '19 at 00:06

cbowns

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answered Mar 13 '17 at 14:34

Xi Chen

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This really shouldn't be so hard – Lucas van Dongen Nov 07 '17 at 22:24
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. – mfaani Dec 13 '17 at 16:53
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Is there a way to do this in objective-c? – p0lAris May 11 '18 at 01:43
I keep getting back at this. I probably should create a lldb alias for `expr -l Swift -- `.. – Koen. Dec 03 '18 at 19:48
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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. – Max Desiatov Jan 17 '22 at 13:44
I was just passing by and wanted to share my little observation with you: the `print` function is redundant there! it will print `() $R0 = {}` which means that expression executed and return nothing. Well I personally have no idea where it was printed, but not in this stupid debugger. So you should write just `expr -l Swift -- $pin.alpha` to see its value on next line – vlastachu Sep 08 '22 at 12:33

gregheo · Answer 2 · 2015-04-04T04:13:34.940

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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.

edited Apr 04 '15 at 04:13

answered Apr 04 '15 at 03:43

gregheo

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For the first statement i think you forgot the 'expr' or 'expression'. Otherwise it is working great! – jarrodparkes Apr 04 '15 at 04:13
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I'm getting "error: use of undeclared identifier 'unsafeBitCast'" in Xcode 7.2. – devios1 Mar 04 '16 at 17:47
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Besides that error (@devios) there's another error it shows in 7.3.1: "error: unknown type name 'let'" – carlos_ms Apr 22 '16 at 20:10
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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` – Patrick Pijnappel Nov 14 '18 at 05:27
That doesn't seem to work for tagged pointers. Short NSString, NSIndexPath, NSNumber etc. are implemented as tagged pointers where the content is part of the pointer itself. – Ortwin Gentz Nov 23 '22 at 16:59

score 28 · Answer 3 · edited Jun 10 '19 at 06:21

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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)

edited Jun 10 '19 at 06:21

pkamb

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answered Aug 11 '16 at 20:28

sfaxon

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score 23 · Answer 4 · edited May 10 '23 at 10:23

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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)

edited May 10 '23 at 10:23

Iulian Onofrei

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answered Oct 10 '17 at 19:17

afinlayson

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I'm getting error: no such module "MyProjectName". Any thoughts how to fix this? – Alexander Stepanishin Aug 07 '19 at 11:23
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@AlexanderStepanishin try setting the thread/stack path, Example: "MyApp > Thread 1 > 12 main" – Juanmi Feb 10 '20 at 17:42
@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. – Bogdan Razvan Jan 31 '22 at 13:14

score 22 · Answer 5 · answered May 15 '18 at 12:25

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Objective-C version

po ((MKPinAnnotationView *)0x7df67c50).alpha

answered May 15 '18 at 12:25

rockhard

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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. – Trev14 Jan 18 '19 at 21:09

score 13 · Answer 6 · edited May 23 '17 at 11:47

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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)

edited May 23 '17 at 11:47

Community

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answered Jan 27 '17 at 23:12

cbowns

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Tora · Answer 7 · 2017-06-04T09:07:48.373

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.

score 8 · Answer 8 · answered Aug 14 '19 at 08:37

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

First import your project (if you want to use some of the classes defined there)

expr -l Swift -- import <YOUR PROJECT NAME>

Cast object using it’s memory address to whatever class you want

expr -l Swift -- let $vc = unsafeBitCast(0x7fb7c51cb270, to: <YOUR PROJECT NAME>.<YOUR CUSTOM CLASS NAME>.self)

Access any value you want from the object

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)

Gobe · Answer 9 · 2020-04-01T17:34:02.680

@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.

Kingsley Mitchell · Answer 10 · 2023-08-26T22:47:00.510

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The easiest way, swift 4

expr unsafeBitCast(0x7df67c50, to: MKPinAnnotationView.self)

Answer by : https://www.kproapps.com

edited Aug 26 '23 at 22:47

answered Sep 06 '18 at 02:13

Kingsley Mitchell

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score 3 · Answer 11 · answered Nov 05 '18 at 22:55

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.

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! — tontonCD, Mar 24 '20 at 16:48

score 1 · Answer 12 · answered Aug 04 '21 at 10:23

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.

LLDB (Swift): Casting Raw Address into Usable Type

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