仅在阿拉伯语等RTL语言下App触发EXC_BAD_ACCESS崩溃求助

问题 #

App仅在RTL（从右到左）模式下触发EXC_BAD_ACCESS异常崩溃，LTR（从左到右）模式运行正常。测试时通过以下方式强制开启RTL：
Edit Scheme -> Run -> Option -> App Language -> Right to Left Pseudo Language

崩溃发生在UIApplicationMain中，汇编堆栈跟踪：

0x12495a1bb <+94>:  movq   0x47896(%rip), %rsi       ; "overflowEngineVarIndexForEngine:"
    0x12495a1c2 <+101>: movq   %r14, %rdi
    0x12495a1c5 <+104>: movq   %rbx, %rdx
    0x12495a1c8 <+107>: callq  *0x3d022(%rip)            ; (void *)0x0000000113ecd7c0: objc_msgSend
    0x12495a1ce <+113>: jmp    0x12495a1d5               ; <+120>
    0x12495a1d0 <+115>: movl   $0xffffffff, %eax         ; imm = 0xFFFFFFFF 
    0x12495a1d5 <+120>: movq   0xc0(%rbx), %rcx
    0x12495a1dc <+127>: movl   %eax, %eax
    0x12495a1de <+129>: movq   %rax, %rdx
    0x12495a1e1 <+132>: shrq   $0x6, %rdx
->  0x12495a1e5 <+136>: movq   (%rcx,%rdx,8), %rcx     Thread 1: EXC_BAD_ACCESS (code=2, address=0x6190201a4f78)
    0x12495a1e9 <+140>: andl   $0x3f, %eax
    0x12495a1ec <+143>: shlq   $0x5, %rax
    0x12495a1f0 <+147>: leaq   (%rcx,%rax), %r15

完整崩溃日志：

Thread 0::  Dispatch queue: com.apple.main-thread
0   ???                                    0x110739ad8 ???
1   ???                                    0x111e93948 ???
2   CoreAutoLayout                         0x128b4e3e9 -[NSISEngine negativeErrorVarForBrokenConstraintWithMarker:errorVar:] + 89
3   CoreAutoLayout                         0x128b5716f -[NSISEngine removeConstraintWithMarker:] + 1102
4   CoreAutoLayout                         0x128b6ca30 -[NSLayoutConstraint _removeFromEngine:] + 209
5   UIKitCore                              0x13ecd4dd0 -[UIView _layoutEngine_willRemoveLayoutConstraint:] + 80
6   UIKitCore                              0x13ecd589c -[UIView(UIConstraintBasedLayout) nsli_removeConstraint:] + 90
7   CoreAutoLayout                         0x128b6de31 __55+[NSLayoutConstraint _addOrRemoveConstraints:activate:]_block_invoke + 53
8   CoreAutoLayout                         0x128b5458f -[NSISEngine withBehaviors:performModifications:] + 84
9   CoreAutoLayout                         0x128b6dd0a +[NSLayoutConstraint _addOrRemoveConstraints:activate:] + 398
10  UIKitCore                              0x13ece22f8 -[UIView(AdditionalLayoutSupport) _withUnsatisfiableConstraintsLoggingSuspendedIfEngineDelegateExists:] + 580
11  UIKitCore                              0x13ece344d -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededWithViewForVariableChangeNotifications:] + 154
12  UIKitCore                              0x13ece4556 -[UIView(AdditionalLayoutSupport) _updateConstraintsAtEngineLevelIfNeededWithViewForVariableChangeNotifications:] + 374
13  UIKitCore                              0x13ede1561 -[UIView _updateConstraintsAsNecessaryAndApplyLayoutFromEngine] + 352
14  UIKitCore                              0x13edf559f -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 2305
15  QuartzCore                             0x11b49302c CA::Layer::layout_if_needed(CA::Transaction*) + 526
16  QuartzCore                             0x11b49e5b9 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 65
17  QuartzCore                             0x11b3afb0c CA::Context::commit_transaction(CA::Transaction*, double, double*) + 626
18  QuartzCore                             0x11b3e769b CA::Transaction::commit() + 735
19  QuartzCore                             0x11b3e8b64 CA::Transaction::flush_as_runloop_observer(bool) + 60
20  CoreFoundation                         0x11f3df055 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
21  CoreFoundation                         0x11f3d99c2 __CFRunLoopDoObservers + 515
22  CoreFoundation                         0x11f3d9f0d __CFRunLoopRun + 1161
23  CoreFoundation                         0x11f3d96a7 CFRunLoopRunSpecific + 560
24  GraphicsServices                       0x12793128a GSEventRunModal + 139
25  UIKitCore                              0x13e7c2ad3 -[UIApplication _run] + 994
26  UIKitCore                              0x13e7c79ef UIApplicationMain + 123
27  libswiftUIKit.dylib                    0x1267f3c72 UIApplicationMain(_:_:_:_:) + 98
28  Bookings                               0x105de34c0 main + 560 (main.swift:12)
29  dyld_sim                               0x1170582bf start_sim + 10
30  dyld                                   0x20cd81310 start + 2432

已尝试的排查手段：

• 启用Constraint Error Breakpoint、Exception Breakpoint和Run Time Issue Breakpoint，未捕获有效线索
• 用Instruments检测内存泄漏，无泄漏提示

从日志判断问题出在AutoLayout引擎，但App约束数量庞大，无法逐一排查，需要定位根因并解决。

排查与解决建议 #

1. 聚焦RTL特有的约束逻辑 #

RTL模式下系统会自动翻转leading/trailing等布局属性，优先检查代码中手动处理RTL的逻辑：

• 排查是否存在重复添加/移除约束的情况：比如RTL时重复激活同一约束，或移除已被释放的约束
• 检查约束激活状态是否与布局方向绑定错误：比如LTR激活A约束、RTL激活B约束时出现状态混淆

2. 启用AutoLayout详细日志 #

在main.swift中添加以下代码，开启AutoLayout详细日志，从控制台输出中定位RTL模式下的约束冲突或异常操作：

UserDefaults.standard.set(true, forKey: "NSConstraintBasedLayoutLogUnsatisfiable")
UserDefaults.standard.set(true, forKey: "NSLayoutConstraintLogDebug")

重点关注崩溃前的约束添加/移除记录，以及RTL特有的约束冲突日志。

3. 逐步隔离排查 #

• 按页面缩小范围：暂时注释部分页面的初始化代码，逐步定位到触发崩溃的特定页面
• 按组件排查：针对可疑页面，逐个移除自定义组件或复杂布局模块，找到问题组件
• 临时禁用自动翻转：在Info.plist中添加UIApplicationSupportsIndirectInputEvents并设为NO，或给特定视图设置semanticContentAttribute = .forceLeftToRight，验证是否是自动翻转导致的问题

4. 检查约束生命周期 #

崩溃发生在约束移除流程中，重点排查以下场景：

• 是否存在约束被多次移除的情况：比如在deinit和updateConstraints中重复移除同一约束
• 是否存在弱引用约束被提前释放：如果约束是弱引用，RTL布局变化时可能已被释放，导致移除操作访问野指针
• 检查updateConstraints逻辑：确保只在该方法中更新约束，不进行多余的添加/移除操作，且必须调用super.updateConstraints()

5. 针对NSISEngine崩溃的特殊处理 #

从堆栈看崩溃源于AutoLayout引擎的内存访问错误，尝试以下操作：

• 清理项目中的无效约束：比如Storyboard/XIB中的废弃约束，或代码中创建但未正确管理的约束
• 更新Xcode和iOS SDK：旧版本AutoLayout引擎可能存在RTL相关bug，升级到最新稳定版本尝试修复

内容的提问来源于stack exchange，提问作者Jaffer Sheriff