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diff --git a/Help/policy/CMP0123.rst b/Help/policy/CMP0123.rst new file mode 100644 index 0000000..e09b5ec --- /dev/null +++ b/Help/policy/CMP0123.rst @@ -0,0 +1,32 @@ +CMP0123 +------- + +.. versionadded:: 3.21 + +``ARMClang`` cpu/arch compile and link flags must be set explicitly. + +CMake 3.20 and lower automatically maps the :variable:`CMAKE_SYSTEM_PROCESSOR` +variable and an undocumented ``CMAKE_SYSTEM_ARCH`` to compile and link options +for ``ARMClang``. For example, the ``-mcpu=cortex-m33`` flag is added when +:variable:`CMAKE_SYSTEM_PROCESSOR` equals ``cortex-m33``. CMake requires +projects to set either variable or it raises a fatal error. However, the +project may need to additionally specify CPU features using e.g. +``-mcpu=cortex-m33+nodsp``, conflicting with the ``-mcpu=cortex-m33`` added +by CMake. This results in either link errors or unusable binaries. + +CMake 3.21 and above prefer instead to not add any cpu/arch compile and link +flags automatically. Instead, projects must specify them explicitly. +This policy provides compatibility for projects that have not been updated. + +The ``OLD`` behavior of this policy requires projects that use ``ARMClang`` +to set either :variable:`CMAKE_SYSTEM_PROCESSOR` or ``CMAKE_SYSTEM_ARCH`` +and it automatically adds a compile option ``-mcpu=`` or ``-march=`` and +a link option ``--cpu=`` based on those variables. The ``NEW`` behavior +does not add compile or link options, and projects are responsible for +setting correct options. + +This policy was introduced in CMake version 3.21. CMake version |release| +warns when the policy is not set and uses ``OLD`` behavior. Use the +:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly. + +.. include:: DEPRECATED.txt |