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I am developing a Cocoa Application using the latest version of Xcode 4, I want to link dynamic libraries to my project (dylibs).
I read somewhere that adding the libraries in my project was not enough as I have to run install_name_tool and otool to make my project use the libraries that were bundled in my project.
I have read the manual pages for install_name_tool, but I do not understand WHY I have to do this.
How do libraries work? Especially interested in the part where the application and the libraries have paths that point to specific places in my machine, like /usr/local/lib/mylibrary.dylib when running otool -L
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The otool command displays specified parts of object files or libraries. If the -m option is not used the file arguments may be of the form libx. a(foo.o), to request information about only that object file and not the entire library.
In computing, rpath designates the run-time search path hard-coded in an executable file or library. Dynamic linking loaders use the rpath to find required libraries. Specifically, it encodes a path to shared libraries into the header of an executable (or another shared library).
The term install name refers to the exact path of the . dylib file in the end-user system so the runtime linker can find and load the dynamic library. The name can be either: Absolute, which is the case for system libraries. These are in the same place on both the end-user's and developer's system.
Apple has several ways of locating shared libraries:
@executable_path : relative to the main executable@loader_path : relative to the referring binary@rpath : relative to any of a list of paths.@rpath is the most recent addition, introduced in OS X 10.5.
If for instance you want to have your executable in Contents/MacOS and libraries in Contents/Libraries you could do the following:
install_name_tool -id @rpath/Libraries/lib_this.dylib builddir/lib_this.dylib and in the top-level executable set rpath with:
install_name_tool -add_rpath @loader_path/.. myexecutable and:
install_name_tool -change builddir/lib_this.dylib @rpath/Libraries/lib_this.dylib myexecutable Note: that the first path after -change must match exactly what is currently in the binary.
If you get lost otool -l -v myexecutable will tell you what load commands exactly are currently in the executable.
See man dyld and man install_name_tool for more information.
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