Cannot debug Catalyst App: "Message from debugger: Process attach denied"

Question

Hi all,

I have a rather large iOS app that I enabled to run as a MacOS Catalyst App. I can run the app, but when I set the checkmark "debug executable" in the scheme, running the app fails with the following error message:

"Message from debugger: Process attach denied, possibly because System Integrity Protection is enabled and process does not allow attaching."

I'm using XCode 11.4.1.

In the Console log, you can see the following messages:

2020-05-10 10:56:19.787046 +0200	com.apple.dt.lldb	error	debugserver	error: MachTask::TaskPortForProcessID task_for_pid failed: ::task_for_pid ( target_tport = 0x0103, pid = 28030, &task ) => err = 0x00000005 ((os/kern) failure)
2020-05-10 10:56:19.787133 +0200	com.apple.dt.lldb	default	debugserver	10 +0.010309 sec [6d7f/0307]: error: ::task_for_pid ( target_tport = 0x0103, pid = 28030, &task ) => err = 0x00000005 ((os/kern) failure) err = ::task_for_pid ( target_tport = 0x0103, pid = 28030, &task ) => err = 0x00000005 ((os/kern) failure) (0x0000000
2020-05-10 10:56:19.799117 +0200	com.apple.dt.lldb	error	debugserver	error: MachTask::StartExceptionThread (): task invalid, exception thread start failed.
2020-05-10 10:56:19.799177 +0200	com.apple.dt.lldb	error	debugserver	error: MachProcess::AttachForDebug failed to start exception thread: unable to start the exception thread
2020-05-10 10:56:19.799398 +0200	com.apple.dt.lldb	error	debugserver	error: Attach failed because process does not allow attaching: "unable to start the exception thread".
2020-05-10 10:56:19.799437 +0200	com.apple.dt.lldb	default	debugserver	error: attach failed.
2020-05-10 10:56:19.800153 +0200	com.apple.dt.lldb	default	debugserver	11 +0.013004 sec [6d7f/2903]: error: ::read ( 6, 0x70000b99bb00, 1024 ) => -1 err = Bad file descriptor (0x00000009)
2020-05-10 10:56:19.800499 +0200	com.apple.dt.lldb	default	debugserver	Exiting.

If I create a fresh iOS app and enable Catalyst, everything works fine. So I guess it's something with the Build settings or similar.

Thanks,
Markus

Graphical Debugger

4.6k

Posted by

funcoder

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Answer 1

If I create a fresh iOS app and enable Catalyst, everything works fine. So I guess it's something with the Build settings or similar.

Right. This typically means that your app is missing the get-task-allow entitlement (

get-task-allow

on iOS,

com.apple.security.get-task-allow

on macOS). I’ve seen two causes for this:

The Code Signing Inject Base Entitlements (
```
CODE_SIGN_INJECT_BASE_ENTITLEMENTS
```
) build setting not being set
The Deployment Postprocessing (
```
DEPLOYMENT_POSTPROCESSING
```
) build setting being set

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Posted by

eskimo

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Answer 2

If I create a fresh iOS app and enable Catalyst, everything works fine. So I guess it's something with the Build settings or similar.

Right. This typically means that your app is missing the get-task-allow entitlement (

get-task-allow

on iOS,

com.apple.security.get-task-allow

on macOS). I’ve seen two causes for this:

The Code Signing Inject Base Entitlements (
```
CODE_SIGN_INJECT_BASE_ENTITLEMENTS
```
) build setting not being set
The Deployment Postprocessing (
```
DEPLOYMENT_POSTPROCESSING
```
) build setting being set

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Posted by

eskimo

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Answer 3

Thanks for your quick answer. Code Signing Inject Base Entitlements is set, but Deployment Postprocessing was also set. Unsetting it didn't help though.

I used your trick from another post to get the entitlements:

codesign -d --entitlements :- <pid>

and got the output

....

<key>com.apple.security.network.client</key>

<true/>

<key>get-task-allow</key>

<true/>

So it looks like the wrong "get-task-allow" is enabled, the iOS one instead of the MacOS one?

Posted by

funcoder

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Answer 4

So it looks like the wrong "get-task-allow" is enabled, the iOS one instead of the macOS one?

Right. I just created a simple test app here in my office and the Mac build definitely gets

com.apple.security.get-task-allow

. Given that you don’t see the problem with a new project, I presume that this will be the same at your end.

It’s seems likely that your main project has a lurking build setting that triggers this problem. I don’t have any other suggestions as to what that might be, but I can explain how I tracked this down the last time:

Create a new branch in your source control system for the purposes of this test.
Take your existing project and remove all the code and resources from it (other than a minimal
```
main
```
function).
Build it; it should build really quickly (-:
Confirm that it still reproduces the problem.
Commit this version of your project.
Compare its build settings to your new project and unify the most obvious discrepancies.
Repeat steps 3 through 6 until the problem goes away.
Look at your latest commit to see what you actually changed. If you changed multiple things, redo the above for once for each of those changes.
Switch back to your main branch and apply that change.
Profit!

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Posted by

eskimo

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Answer 5

Thanks for your instructions! Strange, when I was about to get started with them, I tried one more time and it worked! I swear it didn't work the day before and I did a clean build folder to make sure. In the end, it was the Deployment Postprocessing setting. Sorry for your extra time and thanks again.

Posted by

funcoder

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Cannot debug Catalyst App: "Message from debugger: Process attach denied"

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