In iOS application development, XCODE is a widely used integrated development environment (IDE), and linkers are one of the key components of building applications. In Xcode, we often come across two important concepts: ld64 and -ld classic. They represent the choice of the default linker and the classic linker, respectively. This article will detail what LD64 and -LD Classic mean, what they do, and how to configure them in Xcode.
What are LD64 and -LD Classic?
LD64 is the default linker in Xcode and is used to link applications. The purpose of a linker is to combine multiple objects and library files into a final executable or dynamic library. ld64 is responsible for linking the compiled object files and the dependent library files to generate executable files or dynamic libraries. -ld classic is a linking option that specifies the use of a classic linker instead of the default ld64. Classic linkers are linkers used in earlier versions of Xcode and have some of the features and limitations of traditional linkers.
What LD Classic does:
Compatibility: For some cases where older projects or third-party libraries may still be linked using the classic linker, the -ld classic option can be used to maintain compatibility. This way, you can continue to use these projects or libraries in Xcode without having to make modifications. Classic linkers may have some special features or behaviors that are suitable for some specific projects. If your project needs to take advantage of these features to meet your needs, you can choose to use the -ld classic option. It's important to note that while the classic linker may have some peculiarities, it also has some limitations and drawbacks. In most cases, it is recommended to link with the default ld64 as it is the latest linker for Xcode with better performance and support.
How to use the -ld classic option:
To use the -ld classic option in Xcode, you can configure it by following these steps:
Open your Xcode project.
Select your project in the left navigation.
Select the Build Settings tab in the right panel.
Enter "other linker flags" in the search bar.
Add "-LD classic" to the "Other linker flags" column.
Save and rebuild your project.
By properly configuring XCODE's build settings, you can choose to link using LD64 or a classic linker to meet the needs of your project. This way, Xcode will do the linking work with the specified linker.
Limitations of the classic linker:
While there are some advantages to the classic linker, there are also some limitations and disadvantages. Here are some of the main limitations of the classic linker:
Unable to handle larger libraries: Classic linkers can have performance bottlenecks and limitations for very large libraries. If your project needs to work with larger libraries, it is recommended to use the default ld64 for linking.
Can't handle dynamic libraries: Classic linkers can't handle dynamic libraries, which means you can't package them as dynamic libraries for distribution and use. If you need to create a dynamic library, you must link it with the default ld64.
Compatibility issues: The classic linker may not be compatible with some new compilation technologies and language features, which can lead to some compilation errors and linking issues. If your project needs to use the latest compilation techniques and language features, it is recommended to use the default ld64 for linking.
Lacks some of the features of a modern linker: The classic linker lacks some of the features of a modern linker, such as incremental linking, quick linking, etc. This can affect link speed and performance. If you need to take advantage of these features to improve linking performance and efficiency, it is recommended to use the default ld64 for linking.
How to choose the right linker:
When choosing the right linker, you need to consider the following factors:
If you need to maintain compatibility, you can use the -ld classic option to select a classic linker to link to. Otherwise, it is recommended to use the default ld64 for linking. Your project needs to take advantage of the classic linker features to meet your needs, and you can choose to use the -ld classic option. Otherwise, it is recommended to use the default ld64 for linking. If your library is very large, it is recommended to link with the default ld64 for better performance and efficiency. If you need to create a dynamic library, you must link it with the default ld64.
In iOS development, linkers are one of the important parts of building apps. LD64 is the default linker in Xcode and is responsible for linking compiled objects and library files. -ld classic is a linking option that specifies linking with a classic linker instead of ld64. By properly configuring the build settings for Xcode, we can choose to link using LD64 or Classic Linker to meet the needs of the project. The right linker needs to be selected on a case-by-case basis, and its characteristics and limitations need to be weighed.