Issue

The repo has two main places where vcvarsall.bat is called and therefore where the C++ environment is setup. These are:

• https://github.com/dotnet/runtime/blob/main/eng/native/init-vs-env.cmd
• https://github.com/dotnet/runtime/blob/main/src/coreclr/build-runtime.cmd

To summarize, vcvarsall.bat allows a parameter in the form of host_target and therefore x86_x64 is host=x86, target=x64.

Examples

In the case of init-vs-env it defaults to assuming that the host (that is the machine we are building on) is always x86 and therefore restricts us to using the 32-bit x86 versions of the compilers and related tools.

In the case of build-runtime it has some complex handling that ultimately defaults to host=x64, target=x64 and otherwise uses host=x86, target=* where typically target=%__HostArch%. __HostArch itself defaults to __TargetArch unless the user passes in -hostarch *. __TargetArch matches the default -arch command line passed in.

Solution - init-vs-env

For init-vs-env we should check %PROCESSOR_ARCHITECTURE% and default back to x86 if unrecognized. This winds up with the most portability but also the least amount of emulation on platforms like Arm/Arm64. It likewise means we can make full advantage of modern build machines.

if /i "%PROCESSOR_ARCHITECTURE%"=="AMD64" (
    if /i "%~1" == "x86"   (set __VCBuildArch=x64_x86)
    if /i "%~1" == "x64"   (set __VCBuildArch=x64)
    if /i "%~1" == "arm"   (set __VCBuildArch=x64_arm)
    if /i "%~1" == "arm64" (set __VCBuildArch=x64_arm64)
    if /i "%~1" == "wasm"  (set __VCBuildArch=x64)
) else if /i "%PROCESSOR_ARCHITECTURE%"=="ARM64" (
    if /i "%~1" == "x86"   (set __VCBuildArch=arm64_x86)
    if /i "%~1" == "x64"   (set __VCBuildArch=arm64_x64)
    if /i "%~1" == "arm"   (set __VCBuildArch=arm64_arm)
    if /i "%~1" == "arm64" (set __VCBuildArch=arm64)
    if /i "%~1" == "wasm"  (set __VCBuildArch=arm64_x64)
) else if /i "%PROCESSOR_ARCHITECTURE%"=="ARM" (
    if /i "%~1" == "x86"   (set __VCBuildArch=arm_x86)
    if /i "%~1" == "x64"   (set __VCBuildArch=arm_x64)
    if /i "%~1" == "arm"   (set __VCBuildArch=arm)
    if /i "%~1" == "arm64" (set __VCBuildArch=arm_arm64)
    if /i "%~1" == "wasm"  (set __VCBuildArch=arm_x64)
) else (
    if /i "%~1" == "x86"   (set __VCBuildArch=x86)
    if /i "%~1" == "x64"   (set __VCBuildArch=x86_x64)
    if /i "%~1" == "arm"   (set __VCBuildArch=x86_arm)
    if /i "%~1" == "arm64" (set __VCBuildArch=x86_arm64)
    if /i "%~1" == "wasm"  (set __VCBuildArch=x86_x64)
)

Solution - build-runtime

For build-runtime the fix should ultimately be similar. I don't think we need __HostArch at all and instead should just detect it implicitly, requiring users to run the batch script from the correct command line environment.

If we wanted to keep __HostArch, it should correctly default to matching PROCESSOR_ARCHITECTURE if otherwise unspecified. It should likewise be used for the host portion of host_target. __TargetArch should then be used for the target portion.