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Since commit b6c60f14b6 (macOS: Default to arm64 architecture on Apple
Silicon hosts, 2020-09-28, v3.19.0-rc1~63^2) we use `sysctl` to detect
that we are running on Apple Silicon in a way that pierces Rosetta.
This always sets `CMAKE_HOST_SYSTEM_PROCESSOR` to be `arm64` on such
hosts. However, macOS offers strong support for running processes under
an emulated `x86_64` architecture.
Teach CMake to select either `arm64` or `x86_64` as the host
architecture on Apple Silicon based on the architecture of its own
process. When CMake is built as a universal binary, macOS will select
whichever slice (architecture) is appropriate under the user's shell,
and `CMAKE_HOST_SYSTEM_PROCESSOR` will match.
Also offer a `CMAKE_APPLE_SILICON_PROCESSOR` variable and environment
variable to provide users with explicit control over the host
architecture selection regardless of CMake's own architecture.
Finally, if `CMAKE_OSX_ARCHITECTURES` is not set, pass explicit flags to
the toolchain to use selected host architecture instead of letting the
toolchain pick.
Fixes: #21554
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617 B
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617 B
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CMAKE_APPLE_SILICON_PROCESSOR
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.. versionadded:: 3.19.2
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On Apple Silicon hosts running macOS, set this variable to tell
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CMake what architecture to use for :variable:`CMAKE_HOST_SYSTEM_PROCESSOR`.
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The value must be either ``arm64`` or ``x86_64``.
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The value of this variable should never be modified by project code.
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It is meant to be set by a toolchain file specified by the
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:variable:`CMAKE_TOOLCHAIN_FILE` variable, or as a cache entry
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provided by the user, e.g. via ``-DCMAKE_APPLE_SILICON_PROCESSOR=...``.
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See also the :envvar:`CMAKE_APPLE_SILICON_PROCESSOR` environment variable.
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