Missing CMAKE_SYSTEM_PROCESSOR variable in cross-compiling

[shibayan]

CMAKE_SYSTEM_PROCESSOR is not set when building an ARM / ARM64 target, so configure does not work correctly with some libraries. (e.g opencv)

For ARM64 Windows 10 (not UWP), CMAKE_SYSTEM_PROCESSOR and CMAKE_CROSSCOMPILING is not set.

Proposed solution

Set CMAKE_SYSTEM_PROCESSOR and CMAKE_CROSSCOMPILING when building ARM / ARM64 target using toolchain file.

I created a branch to check the operation.

• Explicitly set CMAKE_SYSTEM_PROCESSOR only for ARM / ARM64
• For ARM64 Windows 10 (not UWP), set CMAKE_SYSTEM_NAME and CMAKE_SYSTEM_VERSION
  • (to set CMAKE_SYSTEM_PROCESSOR and CMAKE_CROSSCOMPILING)
• Turn off CMAKE_CROSSCOMPILING for x86 / x64 UWP

https://github.com/shibayan/vcpkg/tree/crosscompile

Additional context

Share the OpenCV 4 configure log. In the modified toolchains, the CPU is correctly detected.

command : vcpkg install opencv4[core]:arm64-uwp

Configure log with master branch

-- Detecting C compile features
-- Detecting C compile features - done
-- Detected processor: 
-- Performing Test HAVE_CXX11 (check file: cmake/checks/cxx11.cpp)
-- Performing Test HAVE_CXX11 - Success

Configure log with crosscompile branch

-- Detecting C compile features
-- Detecting C compile features - done
-- Detected processor: ARM64
-- Performing Test HAVE_CXX11 (check file: cmake/checks/cxx11.cpp)
-- Performing Test HAVE_CXX11 - Success

Rel #3036 #4907

[driver1998]

We should probably turn off CMAKE_SYSTEM_CROSSCOMPILING when running vcpkg on ARM64 (if vcpkg actually works on a ARM64 machine).

actually:
ARM64/ARM/x86 on ARM64 -> CMAKE_SYSTEM_CROSSCOMPILING off
x64 on ARM64 -> CMAKE_SYSTEM_CROSSCOMPILING on