CMP0123ΒΆ
New in version 3.21.
ARMClang cpu/arch compile and link flags must be set explicitly.
CMake 3.20 and lower automatically maps the 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
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 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 3.25.3
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy() command to set it to OLD or NEW explicitly.
Note
The OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.