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macOS 上的 .so 和 .dylib 有什么区别？

发布于 2024-08-22 15:14:15 字数 229 浏览 7 评论 0原文

.dylib 是 macOS 上的动态库扩展，但我一直不清楚什么时候我不能/不应该使用传统的 unix .so 共享对象。

我的一些问题：

在概念层面上，.so 和 .dylib 之间的主要区别是什么？
我什么时候可以/应该使用其中一种而不是另一种？
编译技巧&提示（例如，替换 gcc -shared -fPIC，因为它在 osx 上不起作用）

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吖咩 2024-08-29 15:14:15

Mac OS X 用于可执行文件和库的 Mach-O 目标文件格式区分共享库和动态加载模块。使用otool -hv some_file查看some_file的文件类型。

Mach-O 共享库的文件类型为 MH_DYLIB 并带有扩展名 .dylib。它们可以与通常的静态链接器标志链接，例如 libfoo.dylib 的 -lfoo。它们可以通过将 -dynamiclib 标志传递给编译器来创建。（-fPIC 是默认值，无需指定。）

可加载模块在 Mach-O 语言中称为“包”。它们的文件类型为 MH_BUNDLE。他们可以携带任何扩展；扩展名 .bundle 是 Apple 推荐的，但大多数移植软件出于兼容性考虑而使用 .so。通常，您将使用扩展应用程序的插件捆绑包。在这种情况下，捆绑包将链接到应用程序二进制文件，以获得对应用程序导出的 API 的访问权限。它们可以通过将 -bundle 标志传递给编译器来创建。

dylib 和bundle 都可以使用dl API（例如dlopen、dlclose）动态加载。不可能像共享库一样链接到捆绑包。然而，捆绑包可能链接到真正的共享库；这些将在加载包时自动加载。

从历史上看，差异更为显着。在 Mac OS X 10.0 中，无法动态加载库。 10.1 中引入了一组 dyld API（例如 NSCreateObjectFileImageFromFile、NSLinkModule）来加载和卸载包，但它们不适用于 dylib。 10.3 中添加了与捆绑包一起使用的 dlopen 兼容性库；在 10.4 中，dlopen 被重写为 dyld 的本机部分，并添加了对加载（但不卸载）dylib 的支持。最后，10.5 添加了对 dylib 中使用 dlclose 的支持，并弃用了 dyld API。

在 Linux 等 ELF 系统上，两者都使用相同的文件格式；任何共享代码都可以用作库并用于动态加载。

最后，请注意，在 Mac OS X 中，" “bundle”也指的是具有标准化结构的目录，其中包含可执行代码和该代码使用的资源。有一些概念上的重叠（特别是像插件这样的“可加载包”，它们通常包含 Mach-O 包形式的可执行代码），但它们不应该与上面讨论的 Mach-O 包混淆。

其他参考文献：

Fink 移植指南，此答案的基础（虽然已经过时了，因为它是为 Mac OS X 10.3 编写的）。
ld(1) 和dlopen(3)
< a href="http://developer.apple.com/Mac/library/documentation/DeveloperTools/Conceptual/DynamicLibraries/000-Introduction/Introduction.html" rel="noreferrer">动态库编程主题
Mach-O 编程主题

The Mach-O object file format used by Mac OS X for executables and libraries distinguishes between shared libraries and dynamically loaded modules. Use otool -hv some_file to see the filetype of some_file.

Mach-O shared libraries have the file type MH_DYLIB and carry the extension .dylib. They can be linked against with the usual static linker flags, e.g. -lfoo for libfoo.dylib. They can be created by passing the -dynamiclib flag to the compiler. (-fPIC is the default and needn't be specified.)

Loadable modules are called "bundles" in Mach-O speak. They have the file type MH_BUNDLE. They can carry any extension; the extension .bundle is recommended by Apple, but most ported software uses .so for the sake of compatibility. Typically, you'll use bundles for plug-ins that extend an application; in such situations, the bundle will link against the application binary to gain access to the application’s exported API. They can be created by passing the -bundle flag to the compiler.

Both dylibs and bundles can be dynamically loaded using the dl APIs (e.g. dlopen, dlclose). It is not possible to link against bundles as if they were shared libraries. However, it is possible that a bundle is linked against real shared libraries; those will be loaded automatically when the bundle is loaded.

Historically, the differences were more significant. In Mac OS X 10.0, there was no way to dynamically load libraries. A set of dyld APIs (e.g. NSCreateObjectFileImageFromFile, NSLinkModule) were introduced with 10.1 to load and unload bundles, but they didn't work for dylibs. A dlopen compatibility library that worked with bundles was added in 10.3; in 10.4, dlopen was rewritten to be a native part of dyld and added support for loading (but not unloading) dylibs. Finally, 10.5 added support for using dlclose with dylibs and deprecated the dyld APIs.

On ELF systems like Linux, both use the same file format; any piece of shared code can be used as a library and for dynamic loading.

Finally, be aware that in Mac OS X, "bundle" can also refer to directories with a standardized structure that holds executable code and the resources used by that code. There is some conceptual overlap (particularly with "loadable bundles" like plugins, which generally contain executable code in the form of a Mach-O bundle), but they shouldn't be confused with Mach-O bundles discussed above.

Additional references:

Fink Porting Guide, the basis for this answer (though pretty out of date, as it was written for Mac OS X 10.3).
ld(1) and dlopen(3)
Dynamic Library Programming Topics
Mach-O Programming Topics

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千寻… 2024-08-29 15:14:15

Mac OS X 上的 .dylib 和 .so 之间的区别在于它们的编译方式。对于 .so 文件，您使用 -shared；对于 .dylib，您使用 -dynamiclib。 .so 和 .dylib 都可以作为动态库文件互换，并且类型均为 DYLIB 或 BUNDLE。这是显示这一点的不同文件的读数。

libtriangle.dylib:
Mach header
      magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64  X86_64        ALL  0x00       DYLIB    17       1368   NOUNDEFS DYLDLINK TWOLEVEL NO_REEXPORTED_DYLIBS



libtriangle.so:
Mach header
      magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64  X86_64        ALL  0x00       DYLIB    17       1256   NOUNDEFS DYLDLINK TWOLEVEL NO_REEXPORTED_DYLIBS

triangle.so:
Mach header
      magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64  X86_64        ALL  0x00      BUNDLE    16       1696   NOUNDEFS DYLDLINK TWOLEVEL

两者在 Mac OS X 上等效的原因是为了向后兼容编译为 .so 文件类型的其他 UNIX 操作系统程序。

编译注意事项：无论编译.so文件还是.dylib文件，都需要在链接步骤中将正确的路径插入到动态库中。您可以通过将 -install_name 和文件路径添加到链接命令来完成此操作。如果您不这样做，您将遇到本文中看到的问题：Mac 动态库疯狂（可能仅限 Fortran）。

The difference between .dylib and .so on mac os x is how they are compiled. For .so files you use -shared and for .dylib you use -dynamiclib. Both .so and .dylib are interchangeable as dynamic library files and either have a type as DYLIB or BUNDLE. Heres the readout for different files showing this.

libtriangle.dylib:
Mach header
      magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64  X86_64        ALL  0x00       DYLIB    17       1368   NOUNDEFS DYLDLINK TWOLEVEL NO_REEXPORTED_DYLIBS



libtriangle.so:
Mach header
      magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64  X86_64        ALL  0x00       DYLIB    17       1256   NOUNDEFS DYLDLINK TWOLEVEL NO_REEXPORTED_DYLIBS

triangle.so:
Mach header
      magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64  X86_64        ALL  0x00      BUNDLE    16       1696   NOUNDEFS DYLDLINK TWOLEVEL

The reason the two are equivalent on Mac OS X is for backwards compatibility with other UNIX OS programs that compile to the .so file type.

Compilation notes: whether you compile a .so file or a .dylib file you need to insert the correct path into the dynamic library during the linking step. You do this by adding -install_name and the file path to the linking command. If you dont do this you will run into the problem seen in this post: Mac Dynamic Library Craziness (May be Fortran Only).

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