Building runtime on Windows 11 ARM machine targetting x64

[quantumhu]

Hi!

I have a Surface ARM device running Windows 11. I read the docs explaining how to build from source and how to cross-compile but the cross-compile docs assume the Windows host machine is x64 and is targetting arm64. Is there a way to do the opposite? I tried passing the -x64 flag to the build.cmd command but I ran into several errors.

Thank you in advance!

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[huoyaoyuan]

Does -platform x64 work?

[quantumhu]

Hi, I tried build.cmd -s clr -arch x64 -platform x64 as well as build.cmd -s clr -platform x64 with a git clean -xdf in between, no luck.

[vcsjones]

I just gave this a shot on my DevKit with .\build.cmd -s clr -arch x64 and it failed with

  C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.39.33519\include\xmmintrin.h(27): fatal error C1189: #error:  This header is specific to X86, X64, ARM64, and ARM64EC targets
  [92/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\format1.cpp.obj
  [93/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\sha1.cpp.obj
  [94/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\prettyprintsig.cpp.obj
  [95/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\sigparser.cpp.obj
  [96/525] Building CXX object jit\CMakeFiles\clrjit_win_x64_arm64.dir\cmake_pch.cxx.obj
  [97/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\sigbuilder.cpp.obj
  [98/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\loaderheap.cpp.obj
  [99/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\sstring.cpp.obj
  [100/525] Building CXX object utilcode\CMakeFiles\utilcode_dac.dir\util_nodependencies.cpp.obj

...

E:\code\runtime\src\coreclr\runtime.proj(94,5): error MSB3073: The command ""E:\code\runtime\src\coreclr\build-runtime.
cmd" -cmakeargs "-DCLR_CROSS_COMPONENTS_BUILD=1" -x64 -release -os windows -hostarch arm64 -hostos windows -outputrid w
in-x64 -component crosscomponents" exited with code 1.

[quantumhu]

Yes thank you, that is the error I see. Are there any known workarounds?

[quantumhu]

Closing this because I found another solution. My main goal was to get x64 instructions generated on an arm64 device, but I thought the only way was to build the runtime as x64.

There is an AltJit functionality that allows arm64 hosts to generate x64 instructions:

set DOTNET_AltJit=<FuncName>
set DOTNET_AltJitName=clrjit_win_x64_arm64