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117 lines
4.1 KiB
117 lines
4.1 KiB
CMAKE_LINK_LIBRARY_<FEATURE>_ATTRIBUTES
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---------------------------------------
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.. versionadded:: 3.30
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This variable defines the behavior of the specified link library
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``<FEATURE>``. It specifies how the ``<FEATURE>`` interacts with other
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features, when the ``<FEATURE>`` should be applied, and aspects of how the
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``<FEATURE>`` should be handled when CMake assembles the final linker
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command line (e.g. de-duplication).
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The syntax of the linker flags for the ``<FEATURE>`` are controlled by the
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:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>` and
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:variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variables.
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The :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` and
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:variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` variables
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control whether the ``<FEATURE>`` is available at all.
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When linking for a particular language ``<LANG>``,
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``CMAKE_LINK_LIBRARY_<FEATURE>_ATTRIBUTES`` is ignored if the
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:variable:`CMAKE_<LANG>_LINK_LIBRARY_<FEATURE>_ATTRIBUTES` variable is also
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defined for the same ``<FEATURE>``.
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The value of ``CMAKE_LINK_LIBRARY_<FEATURE>_ATTRIBUTES`` and
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:variable:`CMAKE_<LANG>_LINK_LIBRARY_<FEATURE>_ATTRIBUTES` at the end of the
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directory scope in which a target is defined is what matters.
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Feature Attributes Definition
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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A feature attributes definition is a
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:ref:`semicolon-separated list <CMake Language Lists>` of
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``attribute=value(s)`` items. If an attribute has multiple values, those values
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must be comma-separated.
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The following attributes are supported:
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``LIBRARY_TYPE=<library-type-list>``
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Specify the library types supported by the feature. Supported values are:
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``STATIC``, ``SHARED``, ``MODULE``, and ``EXECUTABLE``.
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If this attribute is not specified, the default is
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``LIBRARY_TYPE=STATIC,SHARED,MODULE,EXECUTABLE``.
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If the feature is used with an unsupported library type, CMake will emit a
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developer warning and the feature will be ignored.
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``OVERRIDE=<feature-list>``
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Specify which features this one replaces in the event of a conflict.
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This override mechanism is superseded by
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:prop_tgt:`LINK_LIBRARY_OVERRIDE` or
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:prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>` target property definitions,
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if defined.
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If this attribute is not specified, the default is an empty list.
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``DEDUPLICATION=YES|NO|DEFAULT``
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Specify the de-duplication strategy for a library using this feature.
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``YES``
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The library is always de-duplicated. The default strategy CMake would
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normally apply is ignored.
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``NO``
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The library is never de-duplicated. The default strategy CMake would
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normally apply is ignored.
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``DEFAULT``
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Let CMake determine a de-duplication strategy automatically.
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If this attribute is not specified, ``DEFAULT`` will be used.
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Example
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^^^^^^^
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A common need is the loading of a full archive as part of the creation of a
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shared library. The built-in ``WHOLE_ARCHIVE`` feature can be used for that
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purpose. The implementation of that built-in feature sets the following
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link library feature attributes:
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.. code-block:: cmake
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set(CMAKE_LINK_LIBRARY_WHOLE_ARCHIVE_ATTRIBUTES
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LIBRARY_TYPE=STATIC
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OVERRIDE=DEFAULT
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DEDUPLICATION=YES
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)
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``LIBRARY_TYPE=STATIC``
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This feature is only meaningful for static libraries.
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``OVERRIDE=DEFAULT``
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The ``DEFAULT`` feature will be overridden by the ``WHOLE_ARCHIVE`` feature
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because they are compatible and enhance the user's experience: standard
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library specification and ``$<LINK_LIBRARY:WHOLE_ARCHIVE>`` can be used
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freely.
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``DEDUPLICATION=YES``
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When this feature is used, the linker loads all symbols from the static
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library, so there is no need to repeat the library on the linker
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command line.
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The ``WHOLE_ARCHIVE`` feature can be used like so:
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.. code-block:: cmake
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add_library(A STATIC ...)
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add_library(B STATIC ...)
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target_link_libraries(B PUBLIC A)
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target_link_libraries(A PUBLIC B)
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add_library(global SHARED ...)
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target_link_libraries(global PRIVATE $<LINK_LIBRARY:WHOLE_ARCHIVE,A>)
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The resulting link command will only have one instance of the ``A`` library
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specified, and the linker flags will ensure that all symbols are loaded from
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the ``A`` library.
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