I have existing code in production that links against the mach-o library, and uses the following code: NSData *data = [NSData dataWithBytes: getsectiondata(&_mh_execute_header, "__TEXT", "__somePlist_plist", &len) length:len]; In order for this to compile with Sequoia Beta 4 and Xcode 16 beta 4, I have to replace _mh_execute_header with _mh_dylib_header. If I don't, the compiler raises the following error: ld: Undefined symbols: __mh_execute_header, referenced from: -[MyClass init] in MyClass.o clang: error: linker command failed with exit code 1 (use -v to see invocation) Any idea why the linking behavior might have changed? Should I file a bug? (I realize this is a C issue, not Objective-C - but didn't find a tag for that) Thanks!

I think I found a bug in the Objective-C++ compiler, linker, or runtime. Here’s the scenario: We have a macOS app written in Swift. To control hardware from a 3rd party manufacturer, we use a couple SDKs provided by the manufacturer. The SDKs use dynamically loaded libraries and the interface is defined in C++ headers. To bridge between our Swift code and the C++ APIs we have a private Cocoapod that wraps the 3rd party interface with Objective-C++ classes. The two SDKs each provide an interface for discovering attached devices using a callback class that the programmer provides. By accident we named both callback implementations DiscoveryCallback, but this was not a compiler error because neither class was publicly declared, and each was defined in the .mm file where it was used. However, the problem we’re seeing is this: We want to discover Videohub devices, so we register a new instance of DiscoveryCallback (defined in the same .mm file as this code) with the Videohub SDK. A Videohub device is connected and the SDK calls a method on our callback. Surprise! The callback we registered in step 1 was actually the one intended for Decklink devices, defined in a completely different .mm file. This violates all sorts of assumptions and our app quickly crashes. The funny thing is, the two implementations of DiscoveryCallback have completely different method names. The Videohub SDK is supposed to be calling NewVideohubDevice, yet somehow it successfully calls DeckLinkDeviceArrived on an instance of a class it shouldn’t even know about. So the compiler has checked that our intended DiscoveryCallback matches the protocol that the SDK expects, but at runtime the compiled code instantiates a completely different implementation of DiscoveryCallback and somehow doesn’t immediately fail; we still call a method on it that doesn’t even share a name with the intended target. I imagine at this point the method names are long forgotten and are just pointers in a table. I don’t know if this is a bug in the compiler, the Objective-C++ runtime, or if this is just “working as designed” undefined behavior that I should have avoided by not giving two private classes the same name. I know it’s possible to use a private API simply by redeclaring it in my own code, and this seems related to that, but I feel like the compiler or linker should have warned me that I had two implementations of the same class, or if that is not an error, then the runtime should have instantiated the class that was privately defined in the same source file where it was used. Obviously I can’t share our entire project; I’d like to provide some sample code that replicates the issue, but I don’t have time to do that right now. I’m posting this to see if other developers have had a similar experience.

I'm unable to run my app with ASAN enabled when targeting a physical iOS device. Simulator targets do work. With Xcode 12 and an iPad mini 4 running iOS 14 beta 1 I get the following error during app launch ==750==ERROR: AddressSanitizer failed to allocate 0xffffffffff9fc000 (-6307840) bytes at address 2db624000 (errno: 22) ==750==ReserveShadowMemoryRange failed while trying to map 0xffffffffff9fc000 bytes. Perhaps you're using ulimit -v With Xcode 11.5 and an iPad Air 2 running OS 12.4.1 the error is ==2177==Unable to find a memory range after restricting VM. ==2177==AddressSanitizer CHECK failed: /BuildRoot/Library/Caches/com.apple.xbs/Sources/clangcompilerrt/clang-1103.0.32.62/compiler-rt/lib/asan/asanmac.cc:92 "((0 && "cannot place shadow after restricting vm")) != (0)" (0x0, 0x0) <empty stack>==2177==AddressSanitizer CHECK failed: /BuildRoot/Library/Caches/com.apple.xbs/Sources/clangcompilerrt/clang-1103.0.32.62/compiler-rt/lib/asan/../sanitizercommon/sanitizermallocmac.inc:143 "((!asaninitisrunning)) != (0)" (0x0, 0x0) warning: could not execute support code to read Objective-C class data in the process. This may reduce the quality of type information available. AddressSanitizer report breakpoint hit. Use 'thread info -s' to get extended information about the report. (lldb) thread info -s thread #1: tid = 0x1076c2, 0x000000011531e984 libclangrt.asaniosdynamic.dylib`__asan::AsanDie() My coworker is able to use ASAN with the same App using iPad Pro 10.5, iPadOS 13.5.1, Xcode 11.5 Are there any configuration changes I need to make to be able to use ASAN on my devices?