为什么 link 一个图书馆反对自己是有意义的？

Question

检查 otool -L /System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO 输出的前两行表明该库显然与自身链接。这是有原因的吗？为什么这甚至有意义？

/System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO:
        /System/Library/Frameworks/ImageIO.framework/Versions/A/ImageIO (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/Accelerate.framework/Versions/A/Accelerate (compatibility version 1.0.0, current version 4.0.0)
        /System/Library/Frameworks/CoreGraphics.framework/Versions/A/CoreGraphics (compatibility version 64.0.0, current version 600.0.0)
        /System/Library/Frameworks/ApplicationServices.framework/Versions/A/ApplicationServices (compatibility version 1.0.0, current version 48.0.0)
        /System/Library/PrivateFrameworks/AppleVPA.framework/Versions/A/AppleVPA (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (compatibility version 300.0.0, current version 1252.0.0)
        /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1255.0.0)
        /System/Library/Frameworks/CoreServices.framework/Versions/A/CoreServices (compatibility version 1.0.0, current version 728.4.0)
        /System/Library/PrivateFrameworks/AppleJPEG.framework/Versions/A/AppleJPEG (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/ImageIO.framework/Versions/A/Resources/libJPEG.dylib (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/ImageIO.framework/Versions/A/Resources/libTIFF.dylib (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/ImageIO.framework/Versions/A/Resources/libPng.dylib (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/ImageIO.framework/Versions/A/Resources/libGIF.dylib (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/ImageIO.framework/Versions/A/Resources/libJP2.dylib (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/ImageIO.framework/Versions/A/Resources/libRadiance.dylib (compatibility version 1.0.0, current version 1.0.0)
        /usr/lib/libobjc.A.dylib (compatibility version 1.0.0, current version 228.0.0)
        /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.5)
        /System/Library/Frameworks/IOSurface.framework/Versions/A/IOSurface (compatibility version 1.0.0, current version 1.0.0)
        /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.1.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1225.1.1)

Answer 1

otool -L 输出的第一行只是它正在操作的文件的路径，如在命令行中传递的那样。

第二行（第一行缩进）不是依赖项。它显示了库的安装名称。换句话说，它显示的是 LC_ID_DYLIB 加载命令的值，而不是任何 LC_LOAD[_WEAK]_DYLIB 命令的值。

来自 otool 手册页（由于某种原因它不在 Apple 的在线参考库中）：

   -L     Display the names and version numbers of  the  shared  libraries
          that  the  object file uses, as well as the shared library ID if
          the file is a shared library.

注："as well as the shared library ID if the file is a shared library".

为什么 link 一个图书馆反对自己是有意义的？

Why can it make sense to link a library against itself?

macos

dylib

dynamic-linking