[DTAccessibilityElement accessibilityFrame] Crash with SEGV_ACCERR

[Daemonson]

Hi there, our app recently encountered some crashes with users whose iPhone enabled the Accessibility functionality. Below are some crash Infos:

Device Top 5
iPhone 11 78.57%
iPhone 12 Pro Max 19.64%
iPhone 12 1.79%

iOS version Top 5
14.3 (18C66) 83.02%
14.2 (18B111) 13.21%
14.2 (18B92) 3.77%

0 libobjc.A.dylib | objc_retain + 16
-- | --
1 AppName | -[DTAccessibilityElement accessibilityFrame] (DTAccessibilityElement.m:34)
2 UIAccessibility | -[NSObject(AXPrivCategory) _iosAccessibilityAttributeValue:] + 5064
3 UIAccessibility | __copyMultipleAttributeValuesCallback + 544
4 AXRuntime | ____AXXMIGCopyMultipleAttributeValues_block_invoke + 64
5 AXRuntime | __handleNonMainThreadCallback + 68
6 AXRuntime | _AXXMIGCopyMultipleAttributeValues + 360
7 AXRuntime | __XCopyMultipleAttributeValues + 396
8 AXRuntime | _mshMIGPerform + 272
9 CoreFoundation | ___CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 60
10 CoreFoundation | ___CFRunLoopDoSource1 + 596
11 CoreFoundation | ___CFRunLoopRun + 2360
12 CoreFoundation | CFRunLoopRunSpecific + 600
13 GraphicsServices | GSEventRunModal + 164
14 UIKitCore | -[UIApplication _run] + 1072
15 UIKitCore | UIApplicationMain + 168
16 AppName | main (main.m:17)
17 libdyld.dylib | _start + 4

From the crash log, it seems like the parentView has been released somewhere. The parentView object is attributed by unsafe_unretained. When the parentView object has been released, it will be a bad access address. I think that's the point that caused this crash.

So, if it is possible to upgrade the project target version higher than iOS 4.3 and then replace the unsafe_unretained to weak? Thanks a lot.

[odrobnik]

We already have a macro to use weak if the OS supports it. I made the necessary change. Please test if that resolves the issue.

[Daemonson]

We already have a macro to use weak if the OS supports it. I made the necessary change. Please test if that resolves the issue.

❤️ Thanks a lot. I have found the macro. I will test it in my next released version. And I will give feedback then.

[Daemonson]

This DT_WEAK_PROPERTY does not seem to resolve the issue. This crash only happens on iOS 14.x. But I can't reproduce this crash on my devices when I enable the VoiceOver functionality.

#import <DTFoundation/DTWeakSupport.h>

static const CGPoint DTAccessibilityElementNullActivationPoint = {CGFLOAT_MAX, CGFLOAT_MAX};

@interface DTAccessibilityElement()
@property (nonatomic, DT_WEAK_PROPERTY) UIView *parentView;
@end

0 libobjc.A.dylib | objc_retain + 16
-- | --
1 AppName | -[DTAccessibilityElement accessibilityFrame] (DTAccessibilityElement.m:35)
2 UIAccessibility | -[NSObject(AXPrivCategory) _iosAccessibilityAttributeValue:] + 5064
3 UIAccessibility | __copyMultipleAttributeValuesCallback + 544
4 AXRuntime | ____AXXMIGCopyMultipleAttributeValues_block_invoke + 64
5 AXRuntime | __handleNonMainThreadCallback + 68
6 AXRuntime | _AXXMIGCopyMultipleAttributeValues + 360
7 AXRuntime | __XCopyMultipleAttributeValues + 396
8 AXRuntime | _mshMIGPerform + 272
9 CoreFoundation | ___CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 60
10 CoreFoundation | ___CFRunLoopDoSource1 + 596
11 CoreFoundation | ___CFRunLoopRun + 2360
12 CoreFoundation | CFRunLoopRunSpecific + 600
13 GraphicsServices | GSEventRunModal + 164
14 UIKitCore | -[UIApplication _run] + 1072
15 UIKitCore | UIApplicationMain + 168
16 AppName | main (main.m:17)
17 libdyld.dylib | _start + 4