I am running Appium tests on an iOS 18 simulator, and I am encountering an intermittent issue where the device screen gets locked unexpectedly during the tests. The Appium logs show no errors or unusual activity, and all commands appear to be executed successfully. However, upon reviewing the device logs, I see entries related to the lock event, but the exact cause remains unclear. SpringBoard: (SpringBoard) [com.apple.SpringBoard:Common] lockUIFromSource:Boot options:{ SBUILockOptionsLockAutomaticallyKey: 1, SBUILockOptionsForceLockKey: 1, SBUILockOptionsUseScreenOffModeKey: 0 } SpringBoard: (SpringBoard) [com.apple.SpringBoard:Common] -[SBTelephonyManager inCall] 0 SpringBoard: (SpringBoard) [com.apple.SpringBoard:Common] LockUI from source: Now locking Has anyone experienced similar behavior with Appium on iOS 18, or could there be a setting or configuration in the simulator that is causing this issue?

For the Linux version of my application which is written in C++ using Qt, I display the CHM format help files with this code: QString helpFile{ QCoreApplication::applicationDirPath() + "/Help/" + tr("DeepSkyStacker Help.chm","IDS_HELPFILE") }; QString program{ "kchmviewer" }; QStringList arguments{ "-token", "com.github.deepskystacker", helpFile }; helpProcess->startDetached(program, arguments); (helpProcess is a pointer to a QProcess object) The -token com.github.deepskystackerpart of that ensures that only a single instance of the viewer is used for any code that uses that invocation. Are there any chm file viewers for macOS that are capable of that sort of trick? The ones I've found on the App Store give minimal information and appear to be very simple minded tools that are not not intended for integration into an application as above. I know that MacPorts offers ports of kchmviewer but I'd prefer not to use either that or HomeBrew ... David

Hello Everyone, (and I hope folks at Apple are listening) So around a year ago, I decided to take on the challenge of creating my own Iphone App from scratch. I am an engineer by trade, and thought it would be a fun interesting experience, and maybe make some money on the side. So I bought a macbook, and focused on learning Swift for the next few months. Lots of really great developer folks helped me along the way. And I could not have been successful without so much help. It is very much appreciated. So I finished the app, created my own company. And deployed it to the Istore. Unfortunately, just no interest, I think I sold like 4 copies. No problem, still got to learn a lot along the way. So when it came time to renew my developer licence, I let it expire. Just did not make any sense to drop another $100 into it, since only 4 copies had sold in a year. And then..... this happened!!!! I attempted to use the App that was installed on my own Iphone.... and got the message "My Apps Name" is no longer Available. and it stops... The code is on my phone. I am fully aware that I can no longer use xcode to put anything else on my iphone without a developer licence. But for Apple to reach into my own Iphone, and deny my access to something that I already created, (and in theory already paid for) is just infuriating!!! I checked, and even though it no longer exists in the IStore, purchased copies still seem to function. (one person that bought a copy was a friend of mine). So do I really need to drop another $100, puchase an actual copy of MY OWN APP from the app store, just to have it on my own phone again???!!! So much money and time went into this, that I am considering just smashing every apple product I own, and go with Android instead. I am a single person developer. Almost no one does this sort of thing anymore. Apple used to be the place where innovators could come to try to make something cool and fun to use. I guess not any more. Dan

Windows 10 使用 VirtualBox 创建的 Monterey 12.6.7 macOS 虚拟机不能识别到 iPhone 7 手机。 iPhone 7 已经连接到电脑主机 (win 10) 的 USB 3.0 口子，手机已经信任电脑。 在 win 10，我看到了 “此电脑\Apple iPhone”，就是说，宿主机识别到了 手机。 现在，开启macOS 虚拟机，虚拟机右下角的 usb 图标，显示并且勾选到了 "Apple Inc. iPhone [0901]"，但虚拟机还是没看到手机设备，导致 Xcode 也看不到手机设备。 虚拟机运行后，插拔 iPhone 7 手机，通过 sudo log show --predicate 'eventMessage contains "usbmuxd"' --info 看到了报错信息： 2025-02-13 10:31:06.541201+0800 0xa3c Error 0x0 0 0 kernel: (Sandbox) 1 duplicate report for System Policy: usbmuxd(22583) deny(1) file-write-mode /private/var/db/lockdown 2025-02-13 10:31:07.090321+0800 0xf807 Error 0x0 140 0 sandboxd: [com.apple.sandbox.reporting:violation] System Policy: usbmuxd(22583) deny(1) file-write-mode /private/var/db/lockdown Violation: deny(1) file-write-mode /private/var/db/lockdown Process: usbmuxd [22583] Path: /usr/local/sbin/usbmuxd Load Address: 0x10564b000 Identifier: usbmuxd Version: ??? (???) Code Type: x86_64 (Native) Parent Process: sudo [22582] Responsible: /System/Applications/Utilities/Terminal.app/Contents/MacOS/Terminal User ID: 0 Date/Time: 2025-02-13 10:31:06.793 GMT+8 OS Version: macOS 12.6.7 (21G651) Release Type: User Report Version: 8 MetaData: {"vnode-type":"DIRECTORY","hardlinked":false,"pid":22583,"process":"usbmuxd","primary-filter-value":"/private/var/db/lockdown","platform-policy":true,"binary-in-trust-cache":false,"path":"/private/var/db/lockdown","primary-filter":"path","action":"deny","matched-extension":false,"process-path":"/usr/local/sbin/usbmuxd","file-flags":0,"responsible-process-path":"/System/Applications/Utilities/Terminal.app/Contents/MacOS/Terminal","flags":21,"platform-binary":false,"rdev":0,"summary":"deny(1) file-write-mode /private/var/db/lockdown","target":"/private/var/db/lockdown","mount-flags":76582912,"profile":"platform","matched-user-intent-extension":false,"apple-internal":false,"storage-class":"Lockdown","platform_binary":"no","operation":"file-write-mode","profile-flags":0,"normalized_target":["private","var","db","lockdown"],"file-mode":448,"errno":1,"build":"macOS 12.6.7 (21G651)","policy-description":"System Policy","responsible-process-signing-id":"com.apple.Terminal","hardware":"Mac","uid":0,"release-type":"User"} Thread 0 (id: 63477): 0 libsystem_kernel.dylib 0x00007ff80d8368ae __chmod + 10 1 usbmuxd 0x000000010565584e main + 3582 (main.c:816) 2 dyld 0x0000000114e3f52e start + 462 Binary Images: 0x10564b000 - 0x10565afff usbmuxd (0) <0fc9b657-d311-38b5-bf02-e294b175a615> /usr/local/sbin/usbmuxd 0x114e3a000 - 0x114ea3567 dyld (960) <2517e9fe-884a-3855-8532-92bffba3f81c> /usr/lib/dyld 0x7ff80d832000 - 0x7ff80d869fff libsystem_kernel.dylib (8020.240.18.701.6) /usr/lib/system/libsystem_kernel.dylib 2025-02-13 10:35:39.751714+0800 0x27f Default 0x0 0 0 kernel: (Sandbox) Sandbox: usbmuxd(119) allow iokit-get-properties kCDCDoNotMatchThisDevice 2025-02-13 10:35:45.025063+0800 0x27f Default 0x0 0 0 kernel: (Sandbox) Sandbox: usbmuxd(119) allow iokit-get-properties kCDCDoNotMatchThisDevice

Hi Would someone happen to know how to solve the problem when installing Concorde.jl in julia: (@v1.11) pkg> add Concorde Resolving package versions... No Changes to ~/.julia/environments/v1.11/Project.toml No Changes to ~/.julia/environments/v1.11/Manifest.toml Precompiling project... ✗ Concorde 0 dependencies successfully precompiled in 2 seconds. 238 already precompiled. 1 dependency errored. For a report of the errors see julia> err. To retry use pkg> precompile (@v1.11) pkg> build Concorde Building Concorde → ~/.julia/scratchspaces/44cfe95a-1eb2-52ea-b672-e2afdf69b78f/5d9f1b1a480235ffdd3c8ab8cab011aa9afe81af/build.log ERROR: Error building Concorde, showing the last 100 of log: x ./concorde/TOOLS/prob2tsp.c x ./concorde/TOOLS/showres.c ... x ./concorde/VERIFY/Makefile.in x ./concorde/README loading cache ./config.cache checking host system type... Invalid configuration darwin': machine darwin' not recognized checking for prespecified compiler options... no checking for gcc... (cached) gcc checking whether the C compiler (gcc -fPIC -O2 -g ) works... no configure: error: installation or configuration problem: C compiler cannot create executables. ERROR: LoadError: failed process: Process(bash -c "CFLAGS='-fPIC -O2 -g' ./configure --with-qsopt=/Users/poss/.julia/packages/Concorde/VRfqN/deps/qsopt --host=darwin", ProcessExited(1)) [1] It seems to be related to the M3 processor as I have the same error on another Mac with that processor, while the M2 I tried on could install the package properly. It is related to my C compiler, but the latter works, despite the error "checking whether the C compiler (gcc -fPIC -O2 -g ) works... no" poss@Mac-de-Michael ~ % gcc --version Apple clang version 16.0.0 (clang-1600.0.26.6) Target: arm64-apple-darwin24.1.0 Thread model: posix InstalledDir: /Library/Developer/CommandLineTools/usr/bin poss@Mac-de-Michael ~ % gcc -fPIC -O2 -g test.c Best, Michaël.

Hi everyone. I’m working on an iOS app that uses Firebase Cloud Messaging (FCM) to send push notifications. I’m encountering an issue when trying to send notifications either from Firebase Functions or directly using the FCM token with the Firebase Admin SDK and REST API. Error Message: FirebaseMessagingError: Auth error from APNS or Web Push Service code: 'messaging/third-party-auth-error' message: 'Auth error from APNS or Web Push Service' What I’ve Set Up: iOS App Registered in Firebase Bundle ID: Kilovative-Designs.ParkAware APNs Key downloaded from Apple Developer Portal Team ID and Key ID correctly entered in Firebase Console Firebase Admin SDK Service Account setup and used for sending Device is successfully receiving FCM tokens Subscribed to topics and calling Messaging.messaging().subscribe(toTopic:) works Using firebase-admin to send FCM messages via sendToDevice or sendToTopic What I’ve Tried: Tested push via firebase-admin in Node.js (got same APNs auth error) Tested with both topic-based and direct token-based push Confirmed the .p8 key is uploaded in Firebase, with correct Key ID and Team ID Tried generating a new APNs Auth Key Firebase Admin SDK is initialized with the correct service account Using Node.js firebase-admin with a known good FCM token, and sending this payload: { notification: { title: "Test Notification", body: "This is a direct FCM test" }, token: "cxleOwi73EhFh9C5_V4hED:APA91bE3W..." } Returns: FirebaseMessagingError: Auth error from APNS or Web Push Service Questions: Are there known conditions under which Firebase throws this error even if the APNs Auth Key is present? Does the Bundle ID need to start with com. in the Apple Developer Portal and Firebase for APNs authentication to work? Could this be a certificate or provisioning profile mismatch issue (even when using a .p8 key)? Is there a way to manually validate APNs authentication from Firebase outside of actual push delivery? Any insight or guidance would be incredibly helpful. I’m new to developing and have tried repeated efforts to fix this issue but still haven’t resolved it. Thanks in advance!

如何在没有电脑的情况下启用开发者模式 please reply me in Chinese

Merhaba, iOS üzerinde bir sözleşme onay uygulaması geliştiriyorum. Kullanıcıların dijital ortamda sözleşmeleri okuyup onaylaması gerekiyor. Ancak hukuki geçerlilik konusunda bazı tereddütlerim vardı. Bursa’da yaşayan biri olarak bu konuda bir avukata danışmam gerekti. Şans eseri https://www.avukatcanata.com ile karşılaştım ve hem bireysel hem ticari sözleşmeler konusunda gerçekten çok net açıklamalar sundular. Özellikle elektronik imza ve KVKK uyumu hakkında verdikleri bilgiler sayesinde projemi yasal zemine oturtabildim. Eğer bu tarz uygulamalar geliştiriyorsanız, mutlaka bir hukukçu görüşü alın. Yanlış bir adım size veya kullanıcınıza ciddi sonuçlar doğurabilir. Teşekkürler 🍏

iPhone does not show Xcode app when plugged to MacBook. Anybody know something about viewing your app on your iPhone? Thanks

Hi everyone, I'm working on an NFC-related app using CoreNFC with APDU commands to read and write tags. I’ve encountered an issue when trying to handle the scenario where the user cancels the NFC session. Here’s what’s happening: When a user cancels the NFC session manually (e.g., by tapping "Cancel"), I see an error log indicating tagReaderSession|userCancelled. However, when I explicitly call session.invalidate(errorMessage: "No NFC tag found") in my code to handle a scenario where no tag is detected, the session still shows the error as userCancelled instead of my custom error message. This behavior is confusing both in terms of debugging and for providing feedback to users, as I expect my custom message to appear instead of the generic "user cancelled" message. func tagReaderSessionDidBecomeActive(_ session: NFCTagReaderSession) { // Session becomes active } func tagReaderSession(_ session: NFCTagReaderSession, didDetect tags: [NFCTag]) { // Handle tag detection logic } func tagReaderSession(_ session: NFCTagReaderSession, didInvalidateWithError error: Error) { print("Session invalidated with error: \(error.localizedDescription)") } func handleNoTagDetected(session: NFCTagReaderSession) { session.invalidate(errorMessage: "No NFC tag found") } I call handleNoTagDetected(session:) explicitly when no tag is detected, expecting the custom error message to show. However, the system still shows the cancellation error. Has anyone else experienced this behavior? Is this the intended behavior for CoreNFC, or am I missing something in my implementation? Any guidance would be appreciated. Thanks in advance!

Hello, I have created a .NET MAUI application in Windows Visual Studio 2022. Also I have a MAC fully configured with latest Visual Studio for MAC and Xcode Installed. When pairing the MAC for windows machine I am able to run the simulators for various IPhone devices(as they are attached to MAC) but when I try to run for the MacCatalyst from my Windows machine it doesnt work. Is it possible to create a build for the MAUI application for MacCatalyst from my windows machine.The build should be created in my Windows folder directory.?

I have received email about your development certificate has been revoked, but couldn't identify who did that, due to this revocation one of our enterprise application stopped working. So posting here to seek some suggestion on following 1.) Identification of Revoking Party: Though I have already raised a support ticket to Apple still waiting for their reply. Is it possible for Apple to send logs or account activity logs that from which account or who did the revocation? 2.) How much does Apple take to reply to the support tickets. 3.) No one else received email in my development team. Is it because the certificate which I created is revoked that's the reason only I have received email? 4.) May I know what are the other scenarios that certificate can be revoked other than a human error? 5.) Is there a way for us to internally monitor activity within our developer account, such as identifying who has been actively logged in and updating certificates?

I admit I am doing something unusual, and I would not be surprised if it didn't work. I am surprised, however, because after performing the equivalent operations on four bundles, all of the bundles work fine on macOS 15.6.1, but only two of them work on macOS 26.1 (beta 2). I don't know what causes the different outcomes. What I am trying to do is get Java to pass the macOS 26 AppKit UI SDK linkage checking without having to rebuild the JDK using Xcode 26. Rebuilding works for the latest SDK, but it is very inconvenient and may not work for older JDKs. It usually takes a while before the JDK build team successfully transitions to a new Xcode release. My approach is to use vtool to update the sdk version in the LC_BUILD_VERSION load command of $JAVA_HOME/bin/java, which is the launching executable for the JDK. I performed this operation on four JDKs: 25, 21, 17, and 11. (I ran vtool on macOS 15.) It was completely successful on JDK 25 and 21. The JDK launches correctly on macOS 15 and macOS 26. On macOS 26, AppKit uses the new UI, which is the desired outcome. The JDK runs despite that fact that I signed the modified $JAVA_HOME/bin/java with my developer ID, which is inconsistent with the JDK bundle signature. (Redoing the bundle signing is part of the JDK build process; if that were necessary, I would stick with rebuilding the JDK.) The operation was not successful on JDK 17 and 11. I noticed two problems, which are not obviously related. When vtool created the new version of the java program, it lost the tool definition. $ vtool -show-build-version java java: Load command 10 cmd LC_BUILD_VERSION cmdsize 32 platform MACOS minos 11.0 sdk 11.1 ntools 1 tool LD version 609.8 $ vtool -set-build-version 1 10.0 26.0 -output a.out java /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/vtool warning: code signature will be invalid for a.out $ vtool -show-build-version a.out a.out: Load command 22 cmd LC_BUILD_VERSION cmdsize 24 platform MACOS minos 10.0 sdk 26.0 ntools 0 Adding back the tool definition didn't seem to matter. When I try to run the revised executable (in the context of the JDK bundle), it works on macOS 15, but on macOS 26, it is rejected as damaged. If I run the revised executable outside the JDK bundle, it runs (but fails because it can't find the rest of the JDK, which is expected). In all cases, GateKeeper rejects the revised executable because it has not been notarized, but that doesn't seem to stop the program from executing.

Hi all, I'm trying to integrate Apple’s DeviceCheck API into my Flutter iOS app. I already have everything set up on the backend — the Apple private key, key ID, team ID, and DeviceCheck capability. The backend is generating and signing the JWT correctly and making requests to Apple. However, I’m currently stuck on the frontend (Flutter): 👉 How can I generate the device_token required by the DeviceCheck API (via DCDevice.generateToken) in a Flutter iOS app? I understand that DCDevice.generateToken() must be called from native Swift code. I previously attempted to use a MethodChannel to bridge this in Swift, but would prefer not to write or maintain native Swift code if possible. I've looked for a prebuilt Flutter package to handle this, but nothing exists or is up-to-date on pub.dev. Main Question: Is there any Apple-supported way to generate the device_token for DeviceCheck from a Flutter app without writing Swift code manually? If not, is DCDevice.generateToken() the only possible approach, and must I implement this via Swift and Flutter platform channels? Thanks!

I have opened a case with the apple developer support a month ago and they have not replied, since then I sent multiple other emails and opened more cases requesting them to get a status update about my case. So far I am being ignored, no reply or anything it is very frustrating, what can I do to get someone to help me with the apple developer team?

Hi, I really appreciate the C++ binding provided. I got the metal-cpp source code from the website at Getting Started. However, I could not find the same for metal-cpp-extensions. Is it not available or do we have to always extract it from the sample code? Thanks.

Under macOS 26 and iPadOS, the Help menu in many cases has a menu item for "App Help". This item has the following icon: I need to use this in my own app. I am unable to find this icon in SF Symbols 7 beta. I've scanned all of the icons under "What's New". I've searched for "help", "light", and "bulb" and this icon does not appear. Does anyone know if it's even a new SF Symbol? Or does anyone know of a way to use this icon?

am I correct in thinking that local agentsic coding is going to come to Xcode at some point ? I'm thinking cursor ai or windsurf / cline style.

After combing the forums and release nodes, here are some extra notes to help other developers using Apple-Hosted Background Assets. I don't promise I got this perfect, but it may help direct you. AssetPack.Status is an OptionSet (not an enum!) - Critical API detail missing from guide It's a bitmask where values can be combined 2⁰ (1) = available to download 2¹ (2) = update available 2² (4) = up to date 2⁶ (64) = downloaded Example: status value 69 = 0b1000101 = available + up to date + downloaded Use .contains() method to check specific flags AssetPack.version property - Undocumented feature Auto-assigned by App Store Connect for Apple-hosted packs Increments with each upload of same asset pack ID No file deduplication across asset packs Same file in two packs = counts twice toward 200GB limit Best practice: create separate pack for shared files Shared namespace path requirements Asset pack ID is NOT part of file path Each file must have unique relative path across ALL app's asset packs Example: Foo/10/239/414.png and Bar/10/239/414.png are distinct and won't collide Additional url(for:) bugs beyond iOS 26.1 fix iOS 26 Beta 5: "item with same name already exists" error Workaround: Request URL for directory, then manually append filename TestFlight-only availability - Major limitation not mentioned! Apple-hosted packs currently ONLY work for internal testers on TestFlight or from App Store. Won't work from Xcode until "later this year" HTTP 400 errors expected for non-TestFlight installs ba-serve port workaround URL override port bug exists on multiple device types Use ba-serve -p 443 instead of custom ports

This posts collects together a bunch of information about the symbols found in a Mach-O file. It assumes the terminology defined in An Apple Library Primer. If you’re unfamiliar with a term used here, look there for the definition. If you have any questions or comments about this, start a new thread in the Developer Tools & Services > General topic area and tag it with Linker. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Understanding Mach-O Symbols Every Mach-O file has a symbol table. This symbol table has many different uses: During development, it’s written by the compiler. And both read and written by the linker. And various other tools. During execution, it’s read by the dynamic linker. And also by various APIs, most notably dlsym. The symbol table is an array of entries. The format of each entry is very simple, but they have been used and combined in various creative ways to achieve a wide range of goals. For example: In a Mach-O object file, there’s an entry for each symbol exported to the linker. In a Mach-O image, there’s an entry for each symbol exported to the dynamic linker. And an entry for each symbol imported from dynamic libraries. Some entries hold information used by the debugger. See Debug Symbols, below. Examining the Symbol Table There are numerous tools to view and manipulate the symbol table, including nm, dyld_info, symbols, strip, and nmedit. Each of these has its own man page. A good place to start is nm: % nm Products/Debug/TestSymTab U ___stdoutp 0000000100000000 T __mh_execute_header U _fprintf U _getpid 0000000100003f44 T _main 0000000100008000 d _tDefault 0000000100003ecc T _test 0000000100003f04 t _testHelper Note In the examples in this post, TestSymTab is a Mach-O executable that’s formed by linking two Mach-O object files, main.o and TestCore.o. There are three columns here, and the second is the most important. It’s a single letter indicating the type of the entry. For example, T is a code symbol (in Unix parlance, code is in the text segment), D is a data symbol, and so on. An uppercase letter indicates that the symbol is visible to the linker; a lowercase letter indicates that it’s internal. An undefined (U) symbol has two potential meanings: In a Mach-O image, the symbol is typically imported from a specific dynamic library. The dynamic linker connects this import to the corresponding exported symbol of the dynamic library at load time. In a Mach-O object file, the symbol is undefined. In most cases the linker will try to resolve this symbol at link time. Note The above is a bit vague because there are numerous edge cases in how the system handles undefined symbols. For more on this, see Undefined Symbols, below. The first column in the nm output is the address associated with the entry, or blank if an address is not relevant for this type of entry. For a Mach-O image, this address is based on the load address, so the actual address at runtime is offset by the slide. See An Apple Library Primer for more about those concepts. The third column is the name for this entry. These names have a leading underscore because that’s the standard name mangling for C. See An Apple Library Primer for more about name mangling. The nm tool has a lot of formatting options. The ones I use the most are: -m — This prints more information about each symbol table entry. For example, if a symbol is imported from a dynamic library, this prints the library name. For a concrete example, see A Deeper Examination below. -a — This prints all the entries, including debug symbols. We’ll come back to that in the Debug Symbols section, below. -p — By default nm sorts entries by their address. This disables that sort, causing nm to print the entries in the order in which they occur in the symbol table. -x — This outputs entries in a raw format, which is great when you’re trying to understand what’s really going on. See Raw Symbol Information, below, for an example of this. A Deeper Examination To get more information about each symbol table, run nm with the -m option: % nm -m Products/Debug/TestSymTab (undefined) external ___stdoutp (from libSystem) 0000000100000000 (__TEXT,__text) [referenced dynamically] external __mh_execute_header (undefined) external _fprintf (from libSystem) (undefined) external _getpid (from libSystem) 0000000100003f44 (__TEXT,__text) external _main 0000000100008000 (__DATA,__data) non-external _tDefault 0000000100003ecc (__TEXT,__text) external _test 0000000100003f04 (__TEXT,__text) non-external _testHelper This contains a world of extra information about each entry. For example: You no longer have to remember cryptic single letter codes. Instead of U, you get undefined. If the symbol is imported from a dynamic library, it gives the name of that dynamic library. Here we see that _fprintf is imported from the libSystem library. It surfaces additional, more obscure information. For example, the referenced dynamically flag is a flag used by the linker to indicate that a symbol is… well… referenced dynamically, and thus shouldn’t be dead stripped. Undefined Symbols Mach-O’s handling of undefined symbols is quite complex. To start, you need to draw a distinction between the linker (aka the static linker) and the dynamic linker. Undefined Symbols at Link Time The linker takes a set of files as its input and produces a single file as its output. The input files can be Mach-O images or dynamic libraries [1]. The output file is typically a Mach-O image [2]. The goal of the linker is to merge the object files, resolving any undefined symbols used by those object files, and create the Mach-O image. There are two standard ways to resolve an undefined symbol: To a symbol exported by another Mach-O object file To a symbol exported by a dynamic library In the first case, the undefined symbol disappears in a puff of linker magic. In the second case, it records that the generated Mach-O image depends on that dynamic library [3] and adds a symbol table entry for that specific symbol. That entry is also shown as undefined, but it now indicates the library that the symbol is being imported from. This is the core of the two-level namespace. A Mach-O image that imports a symbol records both the symbol name and the library that exports the symbol. The above describes the standard ways used by the linker to resolve symbols. However, there are many subtleties here. The most radical is the flat namespace. That’s out of scope for this post, because it’s a really bad option for the vast majority of products. However, if you’re curious, the ld man page has some info about how symbol resolution works in that case. A more interesting case is the -undefined dynamic_lookup option. This represents a halfway house between the two-level namespace and the flat namespace. When you link a Mach-O image with this option, the linker resolves any undefined symbols by adding a dynamic lookup undefined entry to the symbol table. At load time, the dynamic linker attempts to resolve that symbol by searching all loaded images. This is useful if your software works on other Unix-y platforms, where a flat namespace is the norm. It can simplify your build system without going all the way to the flat namespace. Of course, if you use this facility and there are multiple libraries that export that symbol, you might be in for a surprise! [1] These days it’s more common for the build system to pass a stub library (.tbd) to the linker. The effect is much the same as passing in a dynamic library. In this discussion I’m sticking with the old mechanism, so just assume that I mean dynamic library or stub library. If you’re unfamiliar with the concept of a stub library, see An Apple Library Primer. [2] The linker can also merge the object files together into a single object file, but that’s relatively uncommon operation. For more on that, see the discussion of the -r option in the ld man page. [3] It adds an LC_LOAD_DYLIB load command with the install name from the dynamic library. See Dynamic Library Identification for more on that. Undefined Symbols at Load Time When you load a Mach-O image the dynamic linker is responsible for finding all the libraries it depends on, loading them, and connecting your imports to their exports. In the typical case the undefined entry in your symbol table records the symbol name and the library that exports the symbol. This allows the dynamic linker to quickly and unambiguously find the correct symbol. However, if the entry is marked as dynamic lookup [1], the dynamic linker will search all loaded images for the symbol and connect your library to the first one it finds. If the dynamic linker is unable to find a symbol, its default behaviour is to fail the load of the Mach-O image. This changes if the symbol is a weak reference. In that case, the dynamic linking continues to load the image but sets the address of the symbol to NULL. See Weak vs Weak vs Weak, below, for more about this. [1] In this case nm shows the library name as dynamically looked up. Weak vs Weak vs Weak Mach-O supports two different types of weak symbols: Weak references (aka weak imports) Weak definitions IMPORTANT If you use the term weak without qualification, the meaning depends on your audience. App developers tend to assume that you mean a weak reference whereas folks with a C++ background tend to assume that you mean a weak definition. It’s best to be specific. Weak References Weak references support the availability mechanism on Apple platforms. Most developers build their apps with the latest SDK and specify a deployment target, that is, the oldest OS version on which their app runs. Within the SDK, each declaration is annotated with the OS version that introduced that symbol [1]. If the app uses a symbol introduced later than its deployment target, the compiler flags that import as a weak reference. The app is then responsible for not using the symbol if it’s run on an OS release where it’s not available. For example, consider this snippet: #include <xpc/xpc.h> void testWeakReference(void) { printf("%p\n", xpc_listener_set_peer_code_signing_requirement); } The xpc_listener_set_peer_code_signing_requirement function is declared like so: API_AVAILABLE(macos(14.4)) … int xpc_listener_set_peer_code_signing_requirement(…); The API_AVAILABLE macro indicates that the symbol was introduced in macOS 14.4. If you build this code with the deployment target set to macOS 13, the symbol is marked as a weak reference: % nm -m Products/Debug/TestWeakRefC … (undefined) weak external _xpc_listener_set_peer_code_signing_requirement (from libSystem) If you run the above program on macOS 13, it’ll print NULL (actually 0x0). Without support for weak references, the dynamic linker on macOS 13 would fail to load the program because the _xpc_listener_set_peer_code_signing_requirement symbol is unavailable. [1] In practice most of the SDK’s declarations don’t have availability annotations because they were introduced before the minimum deployment target supported by that SDK. Weak definitions Weak references are about imports. Weak definitions are about exports. A weak definition allows you to export a symbol from multiple images. The dynamic linker coalesces these symbol definitions. Specifically: The first time it loads a library with a given weak definition, the dynamic linker makes it the primary. It registers that definition such that all references to the symbol resolve to it. This registration occurs in a namespace dedicated to weak definitions. That namespace is flat. Any subsequent definitions of that symbol are ignored. Weak definitions are weird, but they’re necessary to support C++’s One Definition Rule in a dynamically linked environment. IMPORTANT Weak definitions are not just weird, but also inefficient. Avoid them where you can. To flush out any unexpected weak definitions, pass the -warn_weak_exports option to the static linker. The easiest way to create a weak definition is with the weak attribute: __attribute__((weak)) void testWeakDefinition(void) { } IMPORTANT The C++ compiler can generate weak definitions without weak ever appearing in your code. This shows up in nm like so: % nm -m Products/Debug/TestWeakDefC … 0000000100003f40 (__TEXT,__text) weak external _testWeakDefinition … The output is quite subtle. A symbol flagged as weak external is either a weak reference or a weak definition depending on whether it’s undefined or not. For clarity, use dyld_info instead: % dyld_info -imports -exports Products/Debug/TestWeakRefC Products/Debug/TestWeakDefC [arm64]: … -imports: … 0x0001 _xpc_listener_set_peer_code_signing_requirement [weak-import] (from libSystem) % dyld_info -imports -exports Products/Debug/TestWeakDefC Products/Debug/TestWeakDefC [arm64]: -exports: offset symbol … 0x00003F40 _testWeakDefinition [weak-def] … … Here, weak-import indicates a weak reference and weak-def a weak definition. Weak Library There’s one final confusing use of the term weak, that is, weak libraries. A Mach-O image includes a list of imported libraries and a list of symbols along with the libraries they’re imported from. If an image references a library that’s not present, the dynamic linker will fail to load the library even if all the symbols it references in that library are weak references. To get around this you need to mark the library itself as weak. If you’re using Xcode it will often do this for your automatically. If it doesn’t, mark the library as optional in the Link Binary with Libraries build phase. Use otool to see whether a library is required or optional. For example, this shows an optional library: % otool -L Products/Debug/TestWeakRefC Products/Debug/TestWeakRefC: /usr/lib/libEndpointSecurity.dylib (… 511.60.5, weak) … In the non-optional case, there’s no weak indicator: % otool -L Products/Debug/TestWeakRefC Products/Debug/TestWeakRefC: /usr/lib/libEndpointSecurity.dylib (… 511.60.5) … Debug Symbols or Why the DWARF still stabs. (-: Historically, all debug information was stored in symbol table entries, using a format knows as stabs. This format is now obsolete, having been largely replaced by DWARF. However, stabs symbols are still used for some specific roles. Note See <mach-o/stab.h> and the stab man page for more about stabs on Apple platforms. See stabs and DWARF for general information about these formats. In DWARF, debug symbols aren’t stored in the symbol table. Rather, debug information is stored in various __DWARF sections. For example: % otool -l Intermediates.noindex/TestSymTab.build/Debug/TestSymTab.build/Objects-normal/arm64/TestCore.o | grep __DWARF -B 1 sectname __debug_abbrev segname __DWARF … The compiler inserts this debug information into the Mach-O object file that it creates. Eventually this Mach-O object file is linked into a Mach-O image. At that point one of two things happens, depending on the Debug Information Format build setting. During day-to-day development, set Debug Information Format to DWARF. When the linker creates a Mach-O image from a bunch of Mach-O object files, it doesn’t do anything with the DWARF information in those objects. Rather, it records references to the source objects files into the final image. This is super quick. When you debug that Mach-O image, the debugger finds those references and uses them to locate the DWARF information in the original Mach-O object files. Each reference is stored in a stabs OSO symbol table entry. To see them, run nm with the -a option: % nm -a Products/Debug/TestSymTab … 0000000000000000 - 00 0001 OSO …/Intermediates.noindex/TestSymTab.build/Debug/TestSymTab.build/Objects-normal/arm64/TestCore.o 0000000000000000 - 00 0001 OSO …/Intermediates.noindex/TestSymTab.build/Debug/TestSymTab.build/Objects-normal/arm64/main.o … Given the above, the debugger knows to look for DWARF information in TestCore.o and main.o. And notably, the executable does not contain any DWARF sections: % otool -l Products/Debug/TestSymTab | grep __DWARF -B 1 % When you build your app for distribution, set Debug Information Format to DWARF with dSYM File. The executable now contains no DWARF information: % otool -l Products/Release/TestSymTab | grep __DWARF -B 1 % Xcode runs dsymutil tool to collect the DWARF information, organise it, and export a .dSYM file. This is actually a document package, within which is a Mach-O dSYM companion file: % find Products/Release/TestSymTab.dSYM Products/Release/TestSymTab.dSYM Products/Release/TestSymTab.dSYM/Contents … Products/Release/TestSymTab.dSYM/Contents/Resources/DWARF Products/Release/TestSymTab.dSYM/Contents/Resources/DWARF/TestSymTab … % file Products/Release/TestSymTab.dSYM/Contents/Resources/DWARF/TestSymTab Products/Release/TestSymTab.dSYM/Contents/Resources/DWARF/TestSymTab: Mach-O 64-bit dSYM companion file arm64 That file contains a copy of the the DWARF information from all the original Mach-O object files, optimised for use by the debugger: % otool -l Products/Release/TestSymTab.dSYM/Contents/Resources/DWARF/TestSymTab | grep __DWARF -B 1 … sectname __debug_line segname __DWARF … Raw Symbol Information As described above, each Mach-O file has a symbol table that’s an array of symbol table entries. The structure of each entry is defined by the declarations in <mach-o/nlist.h> [1]. While there is an nlist man page, the best documentation for this format is the the comments in the header itself. Note The terms nlist stands for name list and dates back to truly ancient versions of Unix. Each entry is represented by an nlist_64 structure (nlist for 32-bit Mach-O files) with five fields: n_strx ‘points’ to the string for this entry. n_type encodes the entry type. This is actually split up into four subfields, as discussed below. n_sect is the section number for this entry. n_desc is additional information. n_value is the address of the symbol. The four fields within n_type are N_STAB (3 bits), N_PEXT (1 bit), N_TYPE (3 bits), and N_EXT (1 bit). To see these raw values, run nm with the -x option: % nm -a -x Products/Debug/TestSymTab … 0000000000000000 01 00 0300 00000036 _getpid 0000000100003f44 24 01 0000 00000016 _main 0000000100003f44 0f 01 0000 00000016 _main … This prints a column for n_value, n_type, n_sect, n_desc, and n_strx. The last column is the string you get when you follow the ‘pointer’ in n_strx. The mechanism used to encode all the necessary info into these fields is both complex and arcane. For the details, see the comments in <mach-o/nlist.h> and <mach-o/stab.h>. However, just to give you a taste: The entry for getpid has an n_type field with just the N_EXT flag set, indicating that this is an external symbol. The n_sect field is 0, indicating a text symbol. And n_desc is 0x0300, with the top byte indicating that the symbol is imported from the third dynamic library. The first entry for _main has an n_type field set to N_FUN, indicating a stabs function symbol. The n_desc field is the line number, that is, line 22. The second entry for _main has an n_type field with N_TYPE set to N_SECT and the N_EXT flag set, indicating a symbol exported from a section. In this case the section number is 1, that is, the text section. [1] There is also an <nlist.h> header that defines an API that returns the symbol table. The difference between <nlist.h> and <mach-o/nlist.h> is that the former defines an API whereas the latter defines the Mach-O on-disk format. Don’t include both; that won’t end well!