Async Await crash on iOS14 with Xcode 13.2.1

Douglas_Gregor · 2022-01-13T18:55:38.549Z

tera:

I managed to get this crash in Xcode:

In the debugger console, if you run image list does it show the libswift_Concurrency.dylib as being loaded?

Doug

tera · 2022-01-13T18:58:20.937Z

Nope, 264 items on the list but not that one. Tell me what to do while I am still in debugger.

btw, this is what it tries to de-mangle:

0x1008835d4 <+28>:  adr    x0, #0xa78c               ; demangling cache variable for type metadata for Swift.Optional<Swift.TaskPriority>

Douglas_Gregor · 2022-01-13T19:03:16.857Z

tera:

Nope, 264 items on the list but not that one. Tell me what to do while I am still in debugger.

That explains the crash, because the runtime is looking for a symbol in libswift_Concurrency.dylib, but that shared library hasn't been loaded. That means either it isn't there in the .app, or it's somehow invalid. If you look at the .app directory on disk, does it have libswift_Concurrency.dylib in its Frameworks directory? If so, is it ~1MB or is it ~11MB?

Doug

tera · 2022-01-13T19:07:57.448Z

Yes, it is (in the app that is in the build folder on mac). It is 1MB. I also see it mentioned in CodeResources.

From the build log:

Copying /Applications/Xcode-13.2.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift-5.5/iphoneos/libswift_Concurrency.dylib to /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
/Applications/Xcode-13.2.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/bitcode_strip /Applications/Xcode-13.2.1.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift-5.5/iphoneos/libswift_Concurrency.dylib -r -o /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
Probing signature of /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
/usr/bin/codesign -r- --display /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
/Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib: code object is not signed at all

Codesigning /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
/usr/bin/codesign --force --sign 2BBB636743121E376194A84FCD31546991DBFAB9 --verbose /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib

~~hmm.. "code object is not signed at all" ?~~
~~Can the issue be because the library is not signed?~~

~~(Note in this particular instance to help with debugging in Xcode I am building debug version.)~~

~~According to Xcode signing settings the signing is automatic for both debug and release, and it doesn't raise any flags.~~

hmm.. let me do this test again. I'll try release now.

tera · 2022-01-13T19:25:42.386Z

~~@Douglas_Gregor, I was puzzled by that "not signed at all" message. when I run it manually in terminal that's what I am getting:~~

/usr/bin/codesign -r- --display /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
Executable=/Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib
designated => identifier "com.apple.dt.runtime.swiftConcurrency" and anchor apple generic and certificate leaf[subject.CN] = "Apple Development: ***reducted***" and certificate 1[field.1.2.840.113635.100.6.2.1] /* exists */

no, probably red herring, as that's just the check. and it's getting signed the next line. something else.

jmuthialu · 2022-01-13T20:54:56.627Z

Just curious, how is it working for @Douglas_Gregor but for myself, @tera and others are experiencing/reproduce crash?

tera · 2022-01-13T21:22:56.256Z

No idea 🤔

I have several different Xcodes and often switch between them (I mean just launching different Xcodes, sometimes having two opened at once, I'm not doing anything fancy in terminal "to switch"). When installing new versions of Xcode (betas or releases) Xcode sometimes prompts me to install command line tools (or whatever that was named) which I do but I always wonder if switching between Xcode's is reliable. I also had Xcode 13 beta on this machine.

zavsby · 2022-01-13T21:42:03.866Z

I have only one Xcode installed (13.2.1) and only one command line tools installed (13.2.1 too).
Xcode was installed via XIP (not from store) btw.

tera · 2022-01-13T21:44:46.306Z

zavsby:

Xcode was installed via XIP (not from store) btw.

same here

jmuthialu · 2022-01-13T22:38:22.296Z

zavsby:

Xcode was installed via XIP (not from store)

Mine was installed from Appstore, if that helps.

tera · 2022-01-14T00:51:40.096Z

Anything suspicious here?

otool -L /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/CrashTest2 
/Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/CrashTest2:
	/System/Library/Frameworks/Foundation.framework/Foundation (compatibility version 300.0.0, current version 1856.105.0)
	/usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1311.0.0)
	/System/Library/Frameworks/UIKit.framework/UIKit (compatibility version 1.0.0, current version 5205.0.101)
	/usr/lib/swift/libswiftCore.dylib (compatibility version 1.0.0, current version 1300.0.46)
	/usr/lib/swift/libswiftCoreFoundation.dylib (compatibility version 1.0.0, current version 14.0.0, weak)
	/usr/lib/swift/libswiftCoreGraphics.dylib (compatibility version 1.0.0, current version 3.0.0, weak)
	/usr/lib/swift/libswiftCoreImage.dylib (compatibility version 1.0.0, current version 2.0.0, weak)
	/usr/lib/swift/libswiftDarwin.dylib (compatibility version 1.0.0, current version 0.0.0, weak)
	/usr/lib/swift/libswiftDataDetection.dylib (compatibility version 1.0.0, current version 697.1.0, weak)
	/usr/lib/swift/libswiftDispatch.dylib (compatibility version 1.0.0, current version 11.0.0)
	/usr/lib/swift/libswiftFileProvider.dylib (compatibility version 1.0.0, current version 378.62.1, weak)
	/usr/lib/swift/libswiftFoundation.dylib (compatibility version 1.0.0, current version 70.101.0)
	/usr/lib/swift/libswiftMetal.dylib (compatibility version 1.0.0, current version 258.14.0, weak)
	/usr/lib/swift/libswiftObjectiveC.dylib (compatibility version 1.0.0, current version 2.0.0, weak)
	/usr/lib/swift/libswiftQuartzCore.dylib (compatibility version 1.0.0, current version 3.0.0, weak)
	/usr/lib/swift/libswiftUIKit.dylib (compatibility version 1.0.0, current version 5100.0.0)
	@rpath/libswift_Concurrency.dylib (compatibility version 1.0.0, current version 1300.0.46, weak)

Keith · 2022-01-14T01:39:48.346Z

I think this looks fine as long as /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib exists and otool -l /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/CrashTest2 | grep -A2 RPATH shows something like this:

          cmd LC_RPATH
      cmdsize 32
         path /usr/lib/swift (offset 12)
--
          cmd LC_RPATH
      cmdsize 40
         path @executable_path/Frameworks (offset 12)

I am a bit surprised that the library is loaded weakly, I did some hacking on LD to make this not weak, and when reproducing this crash, instead of the reports we have above, I got:

Termination Description: DYLD, dependent dylib '@rpath/libswift_Concurrency.dylib' not found for '/private/var/containers/Bundle/Application/AF6C2EFE-2B61-48EF-9EF4-53B7C29B103D/crashtest.app/crashtest'. chained fixups, seg_count does not match number of segments

Which might lead us to something.

tera · 2022-01-14T01:54:55.879Z

Full otool output for those who can read it.

otool -l /Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/CrashTest2
/Users/tera/Library/Developer/Xcode/DerivedData/CrashTest2-dxpfkkbbfiopxcavapqahqofquyf/Build/Products/Release-iphoneos/CrashTest2.app/CrashTest2:

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      current version 1300.0.46
compatibility version 1.0.0
Load command 32
          cmd LC_RPATH
      cmdsize 32
         path /usr/lib/swift (offset 12)
Load command 33
          cmd LC_RPATH
      cmdsize 40
         path @executable_path/Frameworks (offset 12)
Load command 34
      cmd LC_FUNCTION_STARTS
  cmdsize 16
  dataoff 86560
 datasize 96
Load command 35
      cmd LC_DATA_IN_CODE
  cmdsize 16
  dataoff 86656
 datasize 0
Load command 36
      cmd LC_CODE_SIGNATURE
  cmdsize 16
  dataoff 119952
 datasize 20224

Keith · 2022-01-14T02:06:14.701Z

I was able to make this crash with the debugger attached in Xcode on an iOS 13 device by unchecking all the scheme options that lead to custom libraries being injected when launching the binary with DYLD_INSERT_LIBRARIES. Here is a project with that scheme shared GitHub - keith/backdeploy-concurrency-crash: https://forums.swift.org/t/async-await-crash-on-ios14-with-xcode-13-2-1/54541/33

My assumption based on my previous comment is DYLD changes behavior somehow based on those libraries being loaded as well. I would appreciate if someone could verify that running this project on their device also causes the crash even when attached in Xcode (you'll have to update provisioning info). I am testing on an iOS 13.6 device. In the crashed state image list does not show the concurrency library as loaded, but I assume since it's linked weakly that is accepted and leads to this crash later.

Keith · 2022-01-14T02:15:53.125Z

So I noticed in this case that the dylib bundled with the app contains multiple architectures:

DerivedData/CrashTest2/Build/Products/Debug-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib: Mach-O universal binary with 2 architectures: [arm64:Mach-O 64-bit dynamically linked shared library arm64] [arm64e:Mach-O 64-bit dynamically linked shared library arm64e]
DerivedData/CrashTest2/Build/Products/Debug-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib (for architecture arm64):     Mach-O 64-bit dynamically linked shared library arm64
DerivedData/CrashTest2/Build/Products/Debug-iphoneos/CrashTest2.app/Frameworks/libswift_Concurrency.dylib (for architecture arm64e):    Mach-O 64-bit dynamically linked shared library arm64e

If I explicitly remove the arm64e slice from this with:

lipo -remove arm64e /path/to/dylib -output foo
mv foo /path/to/dylib

And re-run without Xcode overwriting this, it works successfully on my 13.6 device. I guess I'm not sure if this would be the same behavior on 14.x given the minimum OS version of that slice specific says 14.0, but I don't have a device on that OS version to test.

tera · 2022-01-14T03:03:56.709Z

Keith:

by unchecking all the scheme options that lead to custom libraries being injected when launching the binary with DYLD_INSERT_LIBRARIES

What are those options?

I can confirm both your findings: launching your project in Xcode crashes it into debugger and stripping the architecture fixes the bug, so the app can now be opened on iPhone. Tested on iOS 14.5. Well done!

jmuthialu · 2022-01-14T03:10:14.084Z

@Keith - I took your project and ran lipo to remove arm64e and ran the build in my device running iOS14.8 and can confirm that it did not crash by running with Xcode and also by running from homescreen (without Xcode). Awesome!!

Keith · 2022-01-14T03:13:11.117Z

tera:

What are those options?

By default at least the main thread checker, and the the other options in the Options tab of the scheme editor. I didn't do them one by one to see which translate to injecting some libraries, but it did seem to require they all be disabled.

Please note that I'm not recommending any of these solutions, I'm just hoping this debugging is helpful for the folks who know more about all the moving pieces here.

Keith · 2022-01-14T03:13:34.636Z

Thank you both for testing it!

jmuthialu · 2022-01-14T03:17:32.046Z

So what happens next?