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| <div class="section" id="cmp0060"> |
| <span id="policy:CMP0060"></span><h1>CMP0060<a class="headerlink" href="#cmp0060" title="Permalink to this headline">ΒΆ</a></h1> |
| <div class="versionadded"> |
| <p><span class="versionmodified added">New in version 3.3.</span></p> |
| </div> |
| <p>Link libraries by full path even in implicit directories.</p> |
| <p>Policy <span class="target" id="index-0-policy:CMP0003"></span><a class="reference internal" href="CMP0003.html#policy:CMP0003" title="CMP0003"><code class="xref cmake cmake-policy docutils literal notranslate"><span class="pre">CMP0003</span></code></a> was introduced with the intention of always |
| linking library files by full path when a full path is given to the |
| <span class="target" id="index-0-command:target_link_libraries"></span><a class="reference internal" href="../command/target_link_libraries.html#command:target_link_libraries" title="target_link_libraries"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_link_libraries()</span></code></a> command. However, on some platforms |
| (e.g. HP-UX) the compiler front-end adds alternative library search paths |
| for the current architecture (e.g. <code class="docutils literal notranslate"><span class="pre">/usr/lib/<arch></span></code> has alternatives |
| to libraries in <code class="docutils literal notranslate"><span class="pre">/usr/lib</span></code> for the current architecture). |
| On such platforms the <span class="target" id="index-0-command:find_library"></span><a class="reference internal" href="../command/find_library.html#command:find_library" title="find_library"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">find_library()</span></code></a> may find a library such as |
| <code class="docutils literal notranslate"><span class="pre">/usr/lib/libfoo.so</span></code> that does not belong to the current architecture.</p> |
| <p>Prior to policy <span class="target" id="index-1-policy:CMP0003"></span><a class="reference internal" href="CMP0003.html#policy:CMP0003" title="CMP0003"><code class="xref cmake cmake-policy docutils literal notranslate"><span class="pre">CMP0003</span></code></a> projects would still build in such |
| cases because the incorrect library path would be converted to <code class="docutils literal notranslate"><span class="pre">-lfoo</span></code> |
| on the link line and the linker would find the proper library in the |
| arch-specific search path provided by the compiler front-end implicitly. |
| At the time we chose to remain compatible with such projects by always |
| converting library files found in implicit link directories to <code class="docutils literal notranslate"><span class="pre">-lfoo</span></code> |
| flags to ask the linker to search for them. This approach allowed existing |
| projects to continue to build while still linking to libraries outside |
| implicit link directories via full path (such as those in the build tree).</p> |
| <p>CMake does allow projects to override this behavior by using an |
| <a class="reference internal" href="../manual/cmake-buildsystem.7.html#imported-targets"><span class="std std-ref">IMPORTED library target</span></a> with its |
| <span class="target" id="index-0-prop_tgt:IMPORTED_LOCATION"></span><a class="reference internal" href="../prop_tgt/IMPORTED_LOCATION.html#prop_tgt:IMPORTED_LOCATION" title="IMPORTED_LOCATION"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">IMPORTED_LOCATION</span></code></a> property set to the desired full path to |
| a library file. In fact, many <a class="reference internal" href="../manual/cmake-developer.7.html#find-modules"><span class="std std-ref">Find Modules</span></a> are learning to provide |
| <a class="reference internal" href="../manual/cmake-buildsystem.7.html#imported-targets"><span class="std std-ref">Imported Targets</span></a> instead of just the traditional <code class="docutils literal notranslate"><span class="pre">Foo_LIBRARIES</span></code> |
| variable listing library files. However, this makes the link line |
| generated for a library found by a Find Module depend on whether it |
| is linked through an imported target or not, which is inconsistent. |
| Furthermore, this behavior has been a source of confusion because the |
| generated link line for a library file depends on its location. It is |
| also problematic for projects trying to link statically because flags |
| like <code class="docutils literal notranslate"><span class="pre">-Wl,-Bstatic</span> <span class="pre">-lfoo</span> <span class="pre">-Wl,-Bdynamic</span></code> may be used to help the linker |
| select <code class="docutils literal notranslate"><span class="pre">libfoo.a</span></code> instead of <code class="docutils literal notranslate"><span class="pre">libfoo.so</span></code> but then leak dynamic linking |
| to following libraries. (See the <span class="target" id="index-0-prop_tgt:LINK_SEARCH_END_STATIC"></span><a class="reference internal" href="../prop_tgt/LINK_SEARCH_END_STATIC.html#prop_tgt:LINK_SEARCH_END_STATIC" title="LINK_SEARCH_END_STATIC"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">LINK_SEARCH_END_STATIC</span></code></a> |
| target property for a solution typically used for that problem.)</p> |
| <p>When the special case for libraries in implicit link directories was first |
| introduced the list of implicit link directories was simply hard-coded |
| (e.g. <code class="docutils literal notranslate"><span class="pre">/lib</span></code>, <code class="docutils literal notranslate"><span class="pre">/usr/lib</span></code>, and a few others). Since that time, CMake |
| has learned to detect the implicit link directories used by the compiler |
| front-end. If necessary, the <span class="target" id="index-1-command:find_library"></span><a class="reference internal" href="../command/find_library.html#command:find_library" title="find_library"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">find_library()</span></code></a> command could be |
| taught to use this information to help find libraries of the proper |
| architecture.</p> |
| <p>For these reasons, CMake 3.3 and above prefer to drop the special case |
| and link libraries by full path even when they are in implicit link |
| directories. Policy <code class="docutils literal notranslate"><span class="pre">CMP0060</span></code> provides compatibility for existing |
| projects.</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior for this policy is to ask the linker to search for |
| libraries whose full paths are known to be in implicit link directories. |
| The <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior for this policy is to link libraries by full path even |
| if they are in implicit link directories.</p> |
| <p>This policy was introduced in CMake version 3.3. Unlike most policies, |
| CMake version 3.23.1 does <em>not</em> warn by default when this policy |
| is not set and simply uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior. See documentation of the |
| <span class="target" id="index-0-variable:CMAKE_POLICY_WARNING_CMP<NNNN>"></span><a class="reference internal" href="../variable/CMAKE_POLICY_WARNING_CMPNNNN.html#variable:CMAKE_POLICY_WARNING_CMP<NNNN>" title="CMAKE_POLICY_WARNING_CMP<NNNN>"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_POLICY_WARNING_CMP0060</span></code></a> |
| variable to control the warning.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is |
| <span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a> |
| and may be removed in a future version of CMake.</p> |
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