We are facing an issue on Catalyst when building our app using Xcode 15.4. The issue is related to precompiled frameworks and seems to be widespread as it happens with multiple vendors (like Firebase or Braze). We are using SPM to add these dependencies, for instance: .package(url: "https://github.com/braze-inc/braze-swift-sdk", from: "8.2.1"), When building, we get the following error: clang:1:1: invalid version number in '-target arm64-apple-ios10.15-macabi' Our macOS deployment target is 12.3. Our iOS deployment target is 15.4. I will try to create a reproducer I can share but I wanted to share this in case there's a known workaround. Thanks in advance!

I regularly see questions from folks who’ve run into problems with their third-party IDE on macOS. Specifically, the issue is that their IDE is invoking Apple’s command-line tools — things like clang and ld — and that’s failing in some way. This post collects my ideas on how to investigate, and potentially resolve, issues like this. If you have any questions or comments, please put them in a new thread here on DevForums. Tag it appropriately so that I see it. Good tags include Compiler, Linker, LLVM, and Command Line Tools. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Investigating Third-Party IDE Integration Problems Many third-party IDEs rely on Apple tools. For example, the IDE might run clang to compile C code or run ld to link object files. These IDEs typically don’t include the tools themselves. Rather, they rely on you to install Xcode or Apple’s Command Line Tools package. These are available at Apple > Developer > Downloads Occasionally I see folks having problems with this. They most typically report that basic stuff, like compiling a simple C program, fails with some mysterious error. If you’re having such a problem, follow the steps below to investigate it. IMPORTANT Some IDEs come with their own tools for compiling and linking. Such IDEs are not the focus of this post. If you have problems with an IDE like that, contact its vendor. Select Your Tools macOS has a concept of the current command-line tools. This can either point to the tools within Xcode or to an installed Command Line Tools package. To see which tools are currently selected, run xcode-select with the --print-path argument. This is what you’ll see if you have Xcode installed in the Applications folder: % xcode-select --print-path /Applications/Xcode.app/Contents/Developer Note All of the tools I discuss here are documented in man pages. If you’re not familiar with those, see Reading UNIX Manual Pages. And this is what you’ll see with a Command Line Tools package selected. % xcode-select --print-path /Library/Developer/CommandLineTools There are two common problems with this: It points to something you’ve deleted. It points to something unexpected. Run the command above to see the current state. If necessary, change the state using the --switch option. For example: % xcode-select --print-path /Applications/Xcode.app/Contents/Developer % clang -v Apple clang version 14.0.3 (clang-1403.0.22.14.1) … % sudo xcode-select --switch ~/XcodeZone/Xcode-beta.app % clang -v Apple clang version 15.0.0 (clang-1500.0.38.1) … I have Xcode 14.3 in the Applications folder and thus clang runs Clang 14.0.3. I have Xcode 15.0b5 in ~/XcodeZone, so switching to that yields Clang 15.0.0. It’s possible to run one specific command with different tools. See Select Your Tools Temporarily, below. Run a Simple Test A good diagnostic test is to use the selected command-line tools to compile a trivial test program. Consider this C [1] example: % cat hello.c #include <stdio.h> int main(int argc, char ** argv) { printf("Hello Cruel World!\n"); return 0; } % clang -o hello hello.c % ./hello Hello Cruel World! IMPORTANT If possible, run this from Terminal rather than, say, over SSH. You may need to expand this test program to exercise your specific case. For example, if your program is hitting an error when it tries to import the Core Foundation framework, add that import to your test program: % cat hello.c #include <stdio.h> #include <CoreFoundation/CoreFoundation.h> int main(int argc, char ** argv) { printf("Hello Cruel World!\n"); return 0; } When you compile your test program, you might see one of these results: Your test program compiles. Your test program fails with a similar error. Your test program fails with a different error. I’ll explore each case in turn. [1] For a C++ example, see C++ Issues, below. If your test program compiles… If your test program compiles from the shell, that proves that your basic command-line tools setup is fine. If the same program fails to compile in your IDE, there’s something IDE-specific going on here. I can’t help you with that. I recommend that you escalate the issue via the support channel for your IDE. If your test program fails with a similar error… If your test program fails with an error similar to the one you’re seeing in your IDE, there are two possibilities: There’s a bug in your test program’s code. There’s an environmental issue that’s affecting your command-line tools setup. Don’t rule out the first possibility. I regularly see folks bump into problems like this, where it turns out to be a bug in their code. For a specific example, see C++ Issues, below. Assuming, however, that your test program’s code is OK, it’s time to investigate environmental issues. See Vary Your Environment, below. If your test program fails with a different error… If your test program fails with a different error, look at the test program’s code to confirm that it’s correct, and that it accurately reflects the code you’re trying to run in your IDE. Vary Your Environment If your test program fails with the same error as you’re seeing in your IDE, and you are sure that the code is correct, it’s time to look for environmental factors. I typically do this with the steps described in the next sections, which are listed from most to least complex. These steps only tell you where things are going wrong, not what is going wrong. However, that’s often enough to continue the investigation of your issue. Vary Your Shell Try running your commands in a different shell. macOS’s default shell is zsh. Try running your commands in bash instead: % bash … bash-3.2$ clang -o hello hello.c bash-3.2$ ./hello Hello Cruel World! Or if you’ve switched your shell to bash, try it in zsh. Vary Your User Account Some problems are caused by settings tied to your user account. To investigate whether that’s an issue here: Use System Settings > Users & Groups to create a new user. Log in as that user. Run your test again. Vary Your Mac Some problems are system wide, so you need to test on a different Mac. The easiest way to do that is to set up a virtual machine (VM) and run your test there. Or, if you have a separate physical Mac, run your test on that. Vary Your Site If you’re working for an organisation, they may have installed software on your Mac that causes problems. If you have a Mac at home, try running your test there. It’s also possible that your network is causing problems [1]. If you have a laptop, try taking it to a different location to see if that changes things. [1] I rarely see this when building a simple test program, but it do see it with other stuff, like code signing. C++ Issues If you’re using C++, here’s a simple test you can try: % cat hello.cpp #include <iostream> int main() { std::cout << "Hello Cruel World!\n"; } % clang++ -o hello hello.cpp % ./hello Hello Cruel World! A classic problem with C++ relates to name mangling. Consider this example: % cat hello.c #include <stdio.h> #include "hello-core.h" int main(int argc, char ** argv) { HCSayHello(); return 0; } % cat hello-core.cpp #include "hello-core.h" #include <iostream> extern void HCSayHello() { std::cout << "Hello Cruel World!\n"; } % cat hello-core.h extern void HCSayHello(); % clang -c hello.c % clang++ -c hello-core.cpp % clang++ -o hello hello.o hello-core.o Undefined symbols for architecture x86_64: "_HCSayHello", referenced from: _main in hello.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) The issue here is that C++ generates a mangled name for HCSayHello: % nm hello-core.o | grep HCSayHello 0000000000000000 T __Z10HCSayHellov whereas C uses the non-mangled name: % nm hello.o | grep HCSayHello U _HCSayHello The fix is an appropriate application of extern "C": % cat hello-core.h extern "C" { extern void HCSayHello(); }; Select Your Tools Temporarily Sometimes you want to temporarily run a command from a particular tools package. To continue my earlier example, I currently have Xcode 14.3 installed in the Applications folder and Xcode 15.0b5 in ~/XcodeZone. Xcode 14.3 is the default but I can override that with the DEVELOPER_DIR environment variable: % clang -v Apple clang version 14.0.3 (clang-1403.0.22.14.1) … % DEVELOPER_DIR=~/XcodeZone/Xcode-beta.app/Contents/Developer clang -v Apple clang version 15.0.0 (clang-1500.0.38.1) … Revision History 2025-01-27 Remove the full width characters. These were a workaround for a forums platform bug that’s since been fixed. Made other minor editorial changes. 2023-07-31 First posted.

Call to std::remainder(double(411.0), int(365)); results in a crash due to a nan in libsystem_m.dylib. MCVE program is provided + lldb backtrace and system report. $ clang++ -g -arch arm64 -std=c++20 main.cpp -o test $ ./test ori_fpcr=0, new_fpcr=1792 std::fmod(simTimeInDays, numDays) = 46 Illegal instruction: 4 main.cpp #include <cassert> #include <cfenv> #include <cmath> #include <iostream> #if !defined(__arm64__) || !defined(__APPLE__) # error "Meant to be run on arm64 apple" #endif inline int feenableexcept(unsigned int excepts) { static fenv_t fenv; if (std::fegetenv(&fenv) != 0) { return -1; } const unsigned long long old_fpcr = fenv.__fpcr; const unsigned int old_excepts = (old_fpcr >> 8u) & unsigned(FE_ALL_EXCEPT); // Check the bits passed are valid, and bit shift them const unsigned int new_excepts = excepts & unsigned(FE_ALL_EXCEPT); const unsigned long long new_fpcr = new_excepts << 8u; // Set the new bits fenv.__fpcr = fenv.__fpcr | new_fpcr; return (std::fesetenv(&fenv) != 0) ? -1 : static_cast<int>(old_excepts); } int main([[maybe_unused]] int argc, [[maybe_unused]] const char** argv) { constexpr unsigned int flags = FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW; static_assert(flags == 7); constexpr uint32_t fpcr_flags_shifted = flags << 8; constexpr uint32_t fpcr_flags = (__fpcr_trap_divbyzero | __fpcr_trap_invalid | __fpcr_trap_overflow); static_assert(fpcr_flags_shifted == fpcr_flags); static_assert(fpcr_flags_shifted == 1792); uint32_t ori_fpcr = __builtin_arm_rsr("fpcr"); feenableexcept(flags); uint32_t new_fpcr = __builtin_arm_rsr("fpcr"); // std::cout << "(FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW) = " << flags << '\n'; // std::cout << "((FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW) << 8) = " << fpcr_flags_shifted << '\n'; // std::cout << "(__fpcr_trap_divbyzero | __fpcr_trap_invalid | __fpcr_trap_overflow) = " << fpcr_flags << '\n'; std::cout << "ori_fpcr=" << ori_fpcr << ", new_fpcr=" << new_fpcr << '\n'; const double simTimeInDays = 411.0; const int numDays = 365; // This is fine std::cout << "std::fmod(simTimeInDays, numDays) = " << std::fmod(simTimeInDays, numDays) << '\n'; // This isn't std::cout << "std::fmod(simTimeInDays, numDays) = " << std::remainder(simTimeInDays, numDays) << '\n'; return 0; } backtrace: see attachment lldb_backtrace.txt $ system_profiler SPSoftwareDataType SPHardwareDataType Software: System Software Overview: System Version: macOS 13.2 (22D49) Kernel Version: Darwin 22.3.0 Boot Volume: Macintosh HD Boot Mode: Normal Secure Virtual Memory: Enabled System Integrity Protection: Enabled Time since boot: 7 hours, 58 minutes Hardware: Hardware Overview: Model Name: MacBook Pro Model Identifier: MacBookPro18,2 Model Number: Z14V000NBFN/A Chip: Apple M1 Max Total Number of Cores: 10 (8 performance and 2 efficiency) Memory: 64 GB System Firmware Version: 8419.80.7 OS Loader Version: 8419.80.7 Activation Lock Status: Enabled $ otool -L test test: /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1300.36.0) /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1319.0.0 $ clang++ --version Apple clang version 14.0.0 (clang-1400.0.29.202) Target: arm64-apple-darwin22.3.0 Thread model: posix InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Today I got stuck with a weird behaviour with my c++ project. There is the code which doesn't catch exception from standard library (the same snippet works well on intel mac and under linux machines). Code snippet: #include &lt;exception&gt; #include &lt;stdexcept&gt; #include &lt;iostream&gt; #include &lt;string&gt; int main() { try { std::stod("notanumber"); } catch (const std::invalid_argument&amp;) { std::cerr &lt;&lt; "Caught std::invalid_argument" &lt;&lt; std::endl; } } Compilation command: clang++ -fno-rtti main.cpp -o main &amp;&amp; ./main Clang versions: clang++ --version Homebrew clang version 15.0.3 Target: arm64-apple-darwin21.6.0 Thread model: posix InstalledDir: /opt/homebrew/opt/llvm/bin Also tried: Apple clang version 14.0.0 (clang-1400.0.29.102) Target: arm64-apple-darwin21.6.0 Thread model: posix InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin Output: libc++abi: terminating with uncaught exception of type std::invalid_argument: stod: no conversion [1] 65643 abort ./main Expected output: Caught std::invalid_argument Other info: Chip: Apple M1 OS: 12.6

I'm writing a simple Command line application on macOS with code using C++, using a API called 'std::to_chars' from charconv void foo(void) {   if (__builtin_available(macOS 10.15, *))   {     char buffer[10];     std::to_chars_result tcr = std::to_chars( buffer, buffer+5, 5 ); #pragma unused (tcr)   }else{     return;   }     } Since Xcode complains main.cpp:19:41: error build: 'to_chars<int, 0>' is unavailable: introduced in macOS 10.15 I wrapped the code with an availability check API in C++, __builtin_available(macOS 10.15, *)) But even with this availability check API, Xcode still failed to compile. Anyone knows why?

A few years ago [1] Xcode added new warnings that help detect a nasty gotcha related to the lifetime of unsafe pointers. For example: Initialization of 'UnsafeMutablePointer<timeval>' results in a dangling pointer Inout expression creates a temporary pointer, but argument 'iov_base' should be a pointer that outlives the call to 'init(iov_base:iov_len:)' I’ve seen a lot of folks confused by these warnings, and by the lifetime of unsafe pointers in general, and this post is my attempt to clarify the topic. If you have questions about any of this, please put them in a new thread in the Programming Languages > Swift topic. Finally, I encourage you to watch the following WWDC presentations: WWDC 2020 Session 10648 Unsafe Swift WWDC 2020 Session 10167 Safely manage pointers in Swift These cover some of the same ground I’ve covered here, and a lot of other cool stuff as well. Share and Enjoy — Quinn “The Eskimo!” Apple Developer Relations, Developer Technical Support, Core OS/Hardware let myEmail = "eskimo" + "1" + "@apple.com" [1] Swift 5.2.2, as shipped in Xcode 11.4. See the discussion of SR-2790 in Xcode 11.4 Release Notes. Basics In Swift, the ampersand (&) indicates that a parameter is being passed inout. Consider this example: func addVarnish(_ product: inout String) { product += " varnish" } var waffle = "waffle" addVarnish(&waffle) // line A print(waffle) // printed: waffle varnish On line A, the ampersand tells you that waffle could be modified by addVarnish(_:). However, there is another use of ampersand that was designed to help with C interoperability. Consider this code: var tv = timeval() gettimeofday(&tv, nil) print(tv) // printed: timeval(tv_sec: 1590743104, tv_usec: 77027) The first parameter to gettimeofday is an UnsafeMutablePointer<timeval>. Here the ampersand denotes a conversion from a timeval to an UnsafeMutablePointer<timeval>. This conversion makes it much easier to call common C APIs from Swift. This also works for array values. For example: var hostName = [CChar](repeating: 0, count: 256) gethostname(&hostName, hostName.count) print(String(cString: hostName)) // printed: slimey.local. In this code the ampersand denotes a conversion from [CChar] to an UnsafeMutablePointer<CChar> that points to the base of the array. While this is convenient, it’s potentially misleading, especially if you come from a C background. In C-based languages, using ampersand in this way yields a pointer to the value that’s valid until the value gets deallocated. That’s not the case in Swift. Rather, the pointer generated by the ampersand syntax is only valid for the duration of that function call. To understand why that’s the case, consider this code: struct TimeInTwoParts { var sec: time_t = 0 var usec: Int32 = 0 var combined: timeval { get { timeval(tv_sec: sec, tv_usec: usec) } set { sec = newValue.tv_sec usec = newValue.tv_usec } } } var time = TimeInTwoParts() gettimeofday(&time.combined, nil) // line A print(time.combined) // printed: timeval(tv_sec: 1590743484, tv_usec: 89118) print(time.sec) // printed: 1590743484 print(time.usec) // printed: 89118 Here combined is a computed property that has no independent existence in memory. Thus, it simply makes no sense to take the address of it. So, how does ampersand deal with this? Under the covers the Swift compiler expands line A to something like this: var tmp = time.combined gettimeofday(&tmp, nil) time.combined = tmp Once you understand this it’s clear why the resulting pointer is only valid for the duration of the call: As soon as Swift cleans up tmp, the pointer becomes invalid. A Gotcha This automatic conversion can be a nasty gotcha. Consider this code: var tv = timeval() let tvPtr = UnsafeMutablePointer(&tv) // line A // ^~~~~~~~~~~~~~~~~~~~~~~~~ // Initialization of 'UnsafeMutablePointer<timeval>' results in a dangling pointer gettimeofday(tvPtr, nil) // line B This results in undefined behaviour because the pointer generated by the ampersand on line A is no longer valid when it’s used on line B. In some cases, like this one, the later Swift compiler is able to detect this problem and warn you about it. In other cases you’re not so lucky. Consider this code: guard let f = fopen("tmp.txt", "w") else { … } var buf = [CChar](repeating: 0, count: 1024) setvbuf(f, &buf, _IOFBF, buf.count) // line A let message = [UInt8]("Hello Crueld World!".utf8) fwrite(message, message.count, 1, f) // line B fclose(f) // line C This uses setvbuf to apply a custom buffer to the file handle. The file handle uses this buffer until after the close on line C. However, the pointer created by the ampersand on line A only exists for the duration of the setvbuf call. When the code calls fwrite on line B the buffer pointer is no longer valid and things end badly. Unfortunately the compiler isn’t able to detect this problem. Worse yet, the code might actually work initially, and then stop working as you change optimisation settings, update the compiler, change unrelated code, and so on. Another Gotcha There is another gotcha associated with the ampersand syntax. Consider this code: class AtomicCounter { var count: Int32 = 0 func increment() { OSAtomicAdd32(1, &count) } } This looks like it’ll implement an atomic counter but there’s no guarantee that the counter will be atomic. To understand why, apply the tmp transform from earlier: class AtomicCounter { var count: Int32 = 0 func increment() { var tmp = count OSAtomicAdd32(1, &tmp) count = tmp } } So each call to OSAtomicAdd32 could potentially be operating on a separate copy of the counter that’s then assigned back to count. This undermines the whole notion of atomicity. Again, this might work in some builds of your product and then fail in other builds. Note The above discussion is now theoretical because Swift 6 added a Synchronization module that includes comprehensive support for atomics. That module also has a Mutex type (if you need a mutex on older platforms, check out OSAllocatedUnfairLock). These constructs use various different mechanisms to ensure that the underlying value has a stable address. Summary So, to summarise: Swift’s ampersand syntax has very different semantics from the equivalent syntax in C. When you use an ampersand to convert from a value to a pointer as part of a function call, make sure that the called function doesn’t use the pointer after it’s returned. It is not safe to use the ampersand syntax for functions where the exact pointer matters. It’s Not Just Ampersands There’s one further gotcha related to arrays. The gethostname example above shows that you can use an ampersand to pass the base address of an array to a function that takes a mutable pointer. Swift supports two other implicit conversions like this: From String to UnsafePointer<CChar> — This allows you to pass a Swift string to an API that takes a C string. For example: let greeting = "Hello Cruel World!" let greetingLength = strlen(greeting) print(greetingLength) // printed: 18 From Array<Element> to UnsafePointer<Element> — This allows you to pass a Swift array to a C API that takes an array (in C, arrays are typically represented as a base pointer and a length). For example: let charsUTF16: [UniChar] = [72, 101, 108, 108, 111, 32, 67, 114, 117, 101, 108, 32, 87, 111, 114, 108, 100, 33] print(charsUTF16) let str = CFStringCreateWithCharacters(nil, charsUTF16, charsUTF16.count)! print(str) // prints: Hello Cruel World! Note that there’s no ampersand in either of these examples. This technique only works for UnsafePointer parameters (as opposed to UnsafeMutablePointer parameters), so the called function can’t modify its buffer. As the ampersand is there to indicate that the value might be modified, it’s not used in this immutable case. However, the same pointer lifetime restriction applies: The pointer passed to the function is only valid for the duration of that function call. If the function keeps a copy of that pointer and then uses it later on, Bad Things™ will happen. Consider this code: func printAfterDelay(_ str: UnsafePointer<CChar>) { print(strlen(str)) // printed: 18 DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) { print(strlen(str)) // printed: 0 } } let greeting = ["Hello", "Cruel", "World!"].joined(separator: " ") printAfterDelay(greeting) dispatchMain() The second call to strlen yields undefined behaviour because the pointer passed to printAfterDelay(_:) becomes invalid once printAfterDelay(_:) returns. In this specific example the memory pointed to by str happened to contain a zero, and hence strlen returned 0 but that’s not guaranteed. The str pointer is dangling, so you might get any result from strlen, including a crash. Advice So, what can you do about this? There’s two basic strategies here: Extend the lifetime of the pointer Manual memory management Extending the Pointer’s Lifetime The first strategy makes sense when you have a limited number of pointers and their lifespan is limited. For example, you can fix the setvbuf code from above by changing it to: let message = [UInt8]("Hello Crueld World!".utf8) guard let f = fopen("tmp.txt", "w") else { … } var buf = [CChar](repeating: 0, count: 1024) buf.withUnsafeMutableBufferPointer { buf in setvbuf(f, buf.baseAddress!, _IOFBF, buf.count) fwrite(message, message.count, 1, f) fclose(f) } This version of the code uses withUnsafeMutableBufferPointer(_:). That calls the supplied closure and passes it a pointer (actually an UnsafeMutableBufferPointer) that’s valid for the duration of that closure. As long as you only use that pointer inside the closure, you’re safe! There are a variety of other routines like withUnsafeMutableBufferPointer(_:), including: The withUnsafeMutablePointer(to:_:) function The withUnsafeBufferPointer(_:), withUnsafeMutableBufferPointer(_:), withUnsafeBytes(_:), and withUnsafeMutableBytes(_:) methods on Array The withUnsafeBytes(_:) and withUnsafeMutableBytes(_:) methods on Data The withCString(_:) and withUTF8(_:) methods on String. Manual Memory Management If you have to wrangle an unbounded number of pointers — or the lifetime of your pointer isn’t simple, for example when calling an asynchronous call — you must revert to manual memory management. Consider the following code, which is a Swift-friendly wrapper around posix_spawn: func spawn(arguments: [String]) throws -> pid_t { var argv = arguments.map { arg -> UnsafeMutablePointer<CChar>? in strdup(arg) } argv.append(nil) defer { argv.forEach { free($0) } } var pid: pid_t = 0 let success = posix_spawn(&pid, argv[0], nil, nil, argv, environ) == 0 guard success else { throw NSError(domain: NSPOSIXErrorDomain, code: Int(errno), userInfo: nil) } return pid } This code can’t use the withCString(_:) method on String because it has to deal with an arbitrary number of strings. Instead, it uses strdup to copy each string to its own manually managed buffer. And, as these buffers are manually managed, is has to remember to free them. Change History 2024-12-11 Added a note about the Synchronization module. Made various editorial changes. 2021-02-24 Fixed the formatting. Added links to the WWDC 2021 sessions. Fixed the feedback advice. Minor editorial changes. 2020-06-01 Initial version.

My question set is fairly broad, but I can't seem to find any answers anywhere. As a fairly low-level developer, the vast majority of my work is done with Sublime Text, terminal-based compilers, IDEs like Coq's (coq.inria.fr), and code that has to be compiled by terminal. These projects are at the very fabric of what I do, and I fear that Rosetta 2 will be inadequate until LLVM and other systems are updated to run natively on Apple Silicon. Honestly, I can't really afford complex virtualization systems like Parallels or VMWare (not that they help much) and I'd rather not give up MacOS for my Ubuntu desktop. I was raised on MacOS and I can't imagine losing features like scenes or seamless integration with the rest of my electronics. I want to keep my initial post fairly simple and broad, but if anyone has any questions on what I need supported, feel free to ask. I am sure I'm not alone here.