bpo-42405: fix C extensions build on Windows ARM64

The following changes are required:

  * add a new platform win-arm64
  * replace the emulated compiler executable paths
  * bump the linker base addressed as ARM64 requires more memory
    this change might not be needed (investigation required)

On Windows 10 ARM64, VS compiler paths look like this:
C:\Program Files (x86)\Microsoft Visual
Studio\2019\Community\VC\Tools\MSVC\14.27.29110\bin\HostX86\ARM64\cl.exe
Note that the cl.exe for ARM64 is an x32 binary, which can run emulated
on Windows 10 ARM64 (it has builtin emulation for x32).

The rc.exe and mc.exe paths have to also be changed, as the initial
discovery has to be fixed.

Author: ader1990

Lib/distutils/msvc9compiler.py

@@ -54,6 +54,7 @@
 PLAT_TO_VCVARS = {
     'win32' : 'x86',
     'win-amd64' : 'amd64',
+    'win-arm64' : 'arm64',
 }
 
 class Reg:
@@ -342,7 +343,7 @@ def initialize(self, plat_name=None):
         if plat_name is None:
             plat_name = get_platform()
         # sanity check for platforms to prevent obscure errors later.
-        ok_plats = 'win32', 'win-amd64'
+        ok_plats = 'win32', 'win-amd64', 'win-arm64'
         if plat_name not in ok_plats:
             raise DistutilsPlatformError("--plat-name must be one of %s" %
                                          (ok_plats,))
@@ -371,6 +372,9 @@ def initialize(self, plat_name=None):
             vc_env = query_vcvarsall(VERSION, plat_spec)
 
             self.__paths = vc_env['path'].split(os.pathsep)
+            if plat_name == 'win-arm64':
+                self.__paths = (
+                    vc_env['path'].replace('HostX64', 'HostX86').split(os.pathsep))
             os.environ['lib'] = vc_env['lib']
             os.environ['include'] = vc_env['include']
 
@@ -385,6 +389,12 @@ def initialize(self, plat_name=None):
             self.lib = self.find_exe("lib.exe")
             self.rc = self.find_exe("rc.exe")   # resource compiler
             self.mc = self.find_exe("mc.exe")   # message compiler
+            if plat_name == 'win-arm64':
+                self.cc = self.cc.replace('HostX64', 'Hostx86')
+                self.linker = self.linker.replace('HostX64', 'Hostx86')
+                self.lib = self.lib.replace('HostX64', 'Hostx86')
+                self.rc = self.rc.replace('x64', 'arm64')
+                self.mc = self.mc.replace('x64', 'arm64')
             #self.set_path_env_var('lib')
             #self.set_path_env_var('include')
 
@@ -634,6 +644,17 @@ def link(self,
             if extra_postargs:
                 ld_args.extend(extra_postargs)
 
+            if get_platform() == 'win-arm64':
+                ld_args_arm = []
+                for ld_arg in ld_args:
+                    # VS tries to use the x86 linker
+                    ld_arg_arm = ld_arg.replace(r'\um\x86', r'\um\arm64')
+                    # A larger memory address is required on ARM64
+                    ld_arg_arm = ld_arg_arm.replace("0x1", "0x10")
+                    ld_args_arm += [ld_arg_arm]
+
+                ld_args = list(ld_args_arm)
+
             self.mkpath(os.path.dirname(output_filename))
             try:
                 self.spawn([self.linker] + ld_args)

Misc/NEWS.d/next/Windows/2020-11-23-10-14-03.bpo-42405.4vQUja.rst

@@ -0,0 +1 @@
+Fix C extensions build on Windows ARM64