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105 lines
3.3 KiB
105 lines
3.3 KiB
CMP0003
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-------
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Libraries linked via full path no longer produce linker search paths.
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This policy affects how libraries whose full paths are NOT known are
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found at link time, but was created due to a change in how CMake deals
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with libraries whose full paths are known. Consider the code
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::
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target_link_libraries(myexe /path/to/libA.so)
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CMake 2.4 and below implemented linking to libraries whose full paths
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are known by splitting them on the link line into separate components
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consisting of the linker search path and the library name. The
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example code might have produced something like
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::
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... -L/path/to -lA ...
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in order to link to library A. An analysis was performed to order
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multiple link directories such that the linker would find library A in
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the desired location, but there are cases in which this does not work.
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CMake versions 2.6 and above use the more reliable approach of passing
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the full path to libraries directly to the linker in most cases. The
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example code now produces something like
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::
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... /path/to/libA.so ....
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Unfortunately this change can break code like
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::
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target_link_libraries(myexe /path/to/libA.so B)
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where ``B`` is meant to find ``/path/to/libB.so``. This code is wrong
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because the user is asking the linker to find library B but has not
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provided a linker search path (which may be added with the
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link_directories command). However, with the old linking
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implementation the code would work accidentally because the linker
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search path added for library A allowed library B to be found.
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In order to support projects depending on linker search paths added by
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linking to libraries with known full paths, the ``OLD`` behavior for this
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policy will add the linker search paths even though they are not
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needed for their own libraries. When this policy is set to ``OLD``, CMake
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will produce a link line such as
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::
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... -L/path/to /path/to/libA.so -lB ...
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which will allow library B to be found as it was previously. When
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this policy is set to NEW, CMake will produce a link line such as
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::
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... /path/to/libA.so -lB ...
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which more accurately matches what the project specified.
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The setting for this policy used when generating the link line is that
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in effect when the target is created by an add_executable or
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add_library command. For the example described above, the code
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::
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cmake_policy(SET CMP0003 OLD) # or cmake_policy(VERSION 2.4)
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add_executable(myexe myexe.c)
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target_link_libraries(myexe /path/to/libA.so B)
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will work and suppress the warning for this policy. It may also be
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updated to work with the corrected linking approach:
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::
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cmake_policy(SET CMP0003 NEW) # or cmake_policy(VERSION 2.6)
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link_directories(/path/to) # needed to find library B
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add_executable(myexe myexe.c)
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target_link_libraries(myexe /path/to/libA.so B)
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Even better, library B may be specified with a full path:
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::
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add_executable(myexe myexe.c)
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target_link_libraries(myexe /path/to/libA.so /path/to/libB.so)
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When all items on the link line have known paths CMake does not check
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this policy so it has no effect.
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Note that the warning for this policy will be issued for at most one
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target. This avoids flooding users with messages for every target
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when setting the policy once will probably fix all targets.
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.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 2.6.0
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.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
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.. include:: STANDARD_ADVICE.txt
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.. include:: DEPRECATED.txt
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