dyld3

dyld3 is the third major version of the dynamic linker for macOS and iOS. It was introduced with macOS Catalina and iOS 13. The primary goal of dyld3 is to improve the performance and security of the dynamic linking process, which is how an operating system loads and links shared libraries at runtime.

One of the key features of dyld3 is its use of pre-linking and code caching. Instead of dynamically resolving all symbols every time an application launches, dyld3 can pre-compute and cache the linking information for system libraries. This significantly speeds up application launch times, especially for applications that rely on many shared frameworks. The caching mechanism is designed to be secure, ensuring that the cached data has not been tampered with.

dyld3 also introduces changes to how dynamic linker information is stored and accessed. It utilizes a flatter and more efficient data structure for its caches. This optimization contributes to both faster loading and reduced memory footprint. Furthermore, dyld3 incorporates enhanced security measures to prevent code injection and other security vulnerabilities that could arise during the dynamic linking phase. The system is designed to verify the integrity of libraries before loading them.

The transition to dyld3 was a significant undertaking, requiring updates to the operating system and the toolchain. While it aims to be backward compatible with older applications, some very old executables might require adjustments to function correctly with dyld3. Overall, dyld3 represents a substantial advancement in the dynamic linking technology used by Apple's operating systems, focusing on speed, efficiency, and security.