It was required to compile older WebKit versions for other operating systems and was made available up until ~2020 by Apple under the url http://developer.apple.com/opensource/internet/webkit_sptlib_agree.html
However this site and file does not seem to be available anymore. Looking for someone who can provide this file.
I'd like to put this on archive.org for historic purposes.
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I have developed a Swift macro called @CodableInit in the SwiftCodableMacro module, and I’m able to use it successfully in my main project.
Here’s an example usage:
import SwiftCodableMacro
@CodableInit // This is for Codable macros
public class ErrorMonitoringWebPlugin {
public var identifier: UUID = UUID()
// MARK: - Codable
required public init(from decoder:Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
identifier = try values.decode(UUID.self, forKey: .identifier)
}
}
However, when I try to write a unit test for the ErrorMonitoringWebPlugin class, I encounter an issue. Here's the test case:
func testCodableSubjectIdentifierShouldEqualDecodedSubjectIdentifier() {
self.measure {
let encoder = JSONEncoder()
let data = try? encoder.encode(subject)
//Here I am getting this error
Class 'JSONEncoder' requires that 'ErrorMonitoringWebPlugin' conform to 'Encodable'
let decoder = JSONDecoder()
let decodedSubject = try? decoder.decode(ErrorMonitoringWebPlugin.self, from: data!)
XCTAssertEqual(subject.identifier, decodedSubject?.identifier)
}
}
The compiler throws an error saying:
Class 'JSONEncoder' requires that 'ErrorMonitoringWebPlugin' conform to 'Encodable'
Even though the @CodableInit macro is supposed to generate conformance, it seems that this macro-generated code is not visible or active inside the test target.
How can I ensure that the @CodableInit macro (from SwiftCodableMacro) is correctly applied and recognized within the XCTest target of my main project?
I work at a well-established university with a business journal that is over 25 years old. We have been waiting now for almost four months to have our Apple News account reviewed. In what world is this OK? No ability to communicate with anyone or have any updates except to log in once a month to see the 'under review' message still there. Seriously?
Was working ok, then after my latest attempt at submitting a .PKG it crashes right after displaying the list of previous submitted things.
This make it impossible to make progress with my project, unless there's another way of getting it to TestFlight (not using Xcode).
Transporter 1.3.2 on Intel Mac Sequoia 15.0
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!
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
Topic:
Developer Tools & Services
SubTopic:
General
I'm a newbie to on-demand resources and I feel like I'm missing something very obvious. I've successfully tagged and set up ODR in my Xcode project, but now I want to upload the assets to my own server so I can retrieve them from within the app, and I can't figure out how to export the files I need.
I'm following the ODR Guide and I'm stuck at Step #4, after I've selected my archive in the Archives window it says to "Click the Export button", but this is what I see:
As shown in the screenshot, there is no export button visible. I have tried different approaches, including distributing to appstore connect, and doing a local development release. The best I've been able to do is find a .assetpack folder inside the archive package through the finder, but uploading that, or the asset.car inside it, just gives me a "cannot parse response" error from the ODR loading code. I've verified I uploaded those to the correct URL.
Can anyone walk me through how to save out the file(s) I need, in a form I can just upload to my server?
Thanks,
Pete
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
We're facing critical stability issues with a Xamarin-based iOS warehouse management app and need expert validation of our crash log analysis.
We’re seeing recurring issues related to:
Auto Layout Threading Violations
Memory Pressure Terminations
CPU Resource Usage Violations
These are causing app crashes and performance degradation in production. We've attached representative crash logs to this post.
Technical Validation Questions:
Do the crash logs point to app-level defects (e.g., threading/memory management), or could user behavior be a contributing factor?
Is ~1.8GB memory usage acceptable for enterprise apps on iOS, or does it breach platform best practices?
Do the threading violations suggest a fundamental architectural or concurrency design flaw in the codebase?
Would you classify these as enterprise-grade stability concerns requiring immediate architectural refactoring?
Do the memory logs indicate potential leaks, or are the spikes consistent with expected usage patterns under load?
Could resolving the threading violation eliminate or reduce the memory and CPU issues (i.e., a cascading failure)?
Are these issues rooted in Xamarin framework limitations, or do they point more toward app-specific implementation problems?
Documentation & UX Questions:
What Apple-recommended solutions exist for these specific issues? (e.g., memory management, thread safety, layout handling)
From your experience, how would these issues manifest for users? (e.g., crashes, slow performance, logout events, unresponsive UI, etc.
JetsamEvent-2025-05-27-123434_REDACTED.ips
)
WarehouseApp.iOS.cpu_resource-2025-05-30-142737_REDACTED.ips
WarehouseApp.iOS-2025-05-27-105134_REDACTED.ips
Any insights, analysis, or references would be incredibly helpful.
Thanks in advance!
Topic:
Developer Tools & Services
SubTopic:
General
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!
Can someone please tell me if it possible to create and publish an ios app onto the app store from a windows device? If it possible then how do i do it?
Topic:
Developer Tools & Services
SubTopic:
General
Hi,
I'm generating MusicKit JWT tokens on my backend side and using it on the client side to query the Apple Music API. One concern I have is accidentally over issuing the scope of this JWT, resulting in accidental access more services than intended like DeviceCheck or APNS.
Other than using separate keys for MusicKit and other services, is there a way to limit the generated JWT to only the Apple Music API (https://api.music.apple.com/v1/*) using the JWT payload scope?
Topic:
Developer Tools & Services
SubTopic:
General
Tags:
Apple Music API
MusicKit
App Store Connect API
I already asked this, although I want to ask again so it boots and gets more people; When I try to run my project on the simulator, it tells me there is a bug. It is not in the code I wrote, but I believe in the compiler. It would work perfectly, say the build succeeded, but the phone turns white and stops there. I don't know how to debunk it, what to do!
Picture of what happens with the phone:
Picture of the debugging area:
Picture of my code:
If I need to add more things, please let me know.
Have a great day!
iphone 15 pro max
ios 26
Stuck at the developer mode startup interface and unable to swipe up.
I have two macOS applications: Application A, named My App.app with the bundle ID com.comp.myapp, and Application B, named My App.app with the bundle ID com.comp.myapp2. Both applications have the same name. Application A is installed at /Applications/My App.app. When I run the installer for Application B, it gets installed in a folder at /Applications/My App.localized/My App.app. Even if I remove Application A using the preinstall script of Application B's installer, the result remains the same.
Does the installer determine the installation path with the new folder before the preinstall script executes?
How can it be addressed so the new folder will not be created?
Notes:
We have a composite package that contains multiple components. Instead of just running pkgbuild, we use our own components.plist rather than a synthesized one. The components.plist is attached.
The PackageInfo for Application B is also attached.
components.plist
PackageInfo
packageInfo.xml
components.plist
Topic:
Developer Tools & Services
SubTopic:
General
Tags:
Developer Tools
InstallerJS
macOS
Command Line Tools
I am trying to get my app deployed to an iOs device (iphone 14) from Visual Studio on Windows 11. If the device I am trying to deploy to is included in https://developer.apple.com/account/resources/devices/list then I see below error in Visual Studio logs.
Xamarin.Messaging.IDB.AppleProvisioningManager Error: 0 : Xamarin.MacDev.AppleSigning.AppleServerException: A device with number '0000xxxx-0014093926Bxxxx' already exists on this team.
at Xamarin.MacDev.AppleSigning.AppStoreDeveloperPortal.d__42.MoveNext() in D:\a_work\1\s\External\maciostools\Xamarin.MacDev.AppleSigning\AppleDeveloperPortal\AppStoreDeveloperPortal.cs:line 913
If I disable it I see below error in Visual Studio logs:
Xamarin.Messaging.Client.MessagingClient Error: 0 : An error occurred on the receiver while executing a post for topic xvs/idb/auto-provision and client vs26896sv3
Xamarin.Messaging.Exceptions.MessagingRemoteException: An error occurred on client xxxxxxx while executing a reply for topic xvs/idb/auto-provision ---> Newtonsoft.Json.JsonSerializationException: Error converting value {null} to type 'System.DateTime'. Path 'data.attributes.addedDate', line 6, position 24
I am seeing no option to completely remove the device from the list. How can this issue be fixed?
Topic:
Developer Tools & Services
SubTopic:
General
I cannot find this specific KDK for my build 22H417. I need help locating and downloading this Developer Kit.
Error Domain=KMErrorDomain Code=34 "Missing Developer Kit: As of macOS 13.0, you will need to install a KDK matching your build 22H417 to rebuild kernel collections." UserInfo={NSLocalizedDescription=Missing Developer Kit: As of macOS 13.0, you will need to install a KDK matching your build 22H417 to rebuild kernel collections.}
I
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!
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在将游戏从 Nintendo Switch 移植到 Mac 的过程中使用 .NET (NativeAOT) 有哪些限制和注意事项(尽管两者都是 ARM)?
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