Posted on 2012-04-18 06:14
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@executable path, @load path and @rpath
Note: this article is actually about the @executable_path, @load_path and @rpath install paths used by the linker on Mac OS X; wiki titles can't include underscores, however, because they are ambiguous with spaces.
Absolute paths
Useful for frameworks installed in shared locations. Example:
- Install path:
/Library/Frameworks/Foo.framework/Versions/A/Foo
@executable_path
Useful for frameworks embedded inside applications, because it allows you to specify the location of the framework relative to the application's executable:
- Install path:
@executable_path/../Frameworks/Foo.framework/Versions/A/Foo - Application location:
/Applications/Foo.app - Executable path:
/Applications/Foo.app/Contents/MacOS - Framework location:
/Applications/Foo.app/Contents/Frameworks/Foo.framework - Linker puts all this together to figure out that the framework binary can be found at:
/Applications/Foo.app/Contents/MacOS/../Frameworks/Foo.framework/Versions/A/Foo
@loader_path
Available from Mac OS X 10.4 Tiger onwards; useful for frameworks embedded inside plug-ins, because it allows you to specify the location of the framework relative to the plug-in's code (remember, plug-ins may not actually know where they are going to be installed, relative to the application, so knowing @executable_path doesn't help us in this case):
- Install path:
@loader_path/../Frameworks/Foo.framework/Versions/A/Foo - Application location:
/Applications/Foo.app - Plug-in location:
/Library/Application Support/Foo/Plug-Ins/Bar.bundle - Executable path:
/Applications/Foo.app/Contents/MacOS - Loader path:
/Library/Application Support/Foo/Plug-Ins/Bar.bundle/Contents/MacOS - Framework location:
/Library/Application Support/Foo/Plug-Ins/Bar.bundle/Contents/Frameworks/Foo.framework - Linker puts all this together to figure out that the framework binary can be found at:
/Library/Application Support/Foo/Plug-Ins/Bar.bundle/Contents/MacOS/../Frameworks/Foo.framework/Versions/A/Foo
Note that if the "loader" is an application rather than a plug-in, the @loader_path ends up being equivalent to @executable_path.
@rpath
New in Mac OS X 10.5 Leopard is @rpath. Key points:
@rpath instructs the dynamic linker to search a list of paths in order to locate the framework- critically, this list is embedded in the loading application
- this means that a single framework with
@rpath/Foo.framework/Versions/A/Foo can be made to work in a number of different ways; that is, you are effectively no longer limited by the choice of specifying your "install path" using either @executable_path or @loader_path - the down side: you now have to pass additional linker flags when building the host application (eg.
-rpath @executable_path/../Frameworks or /Library/Frameworks; note that specifying both will cause the dynamic linker to try looking in both locations)
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