Fix architecture detection to use correct function.

.github/workflows/build.yml

@@ -105,6 +105,34 @@ jobs:
         PYMSBUILD_LAYOUT_DIR: ${{ runner.temp }}/layout
         TEST_MSIX_DIR: ${{ runner.temp }}/test_msix
 
+    - name: 'Upload build output'
+      uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+      with:
+        name: packages
+        path: ${{ runner.temp }}/dist
+
+  test:
+    name: 'Test (${{ matrix.runner }})'
+    needs: build
+    strategy:
+      fail-fast: false
+      matrix:
+        runner:
+        - windows-latest
+        - windows-11-vs2026-arm
+    runs-on: ${{ matrix.runner }}
+
+    steps:
+    - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      with:
+        persist-credentials: false
+
+    - name: 'Download build output'
+      uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+      with:
+        name: packages
+        path: ${{ runner.temp }}/dist
+
     - name: 'Register unsigned MSIX'
       run: |
         $msix = dir "${env:PYMSBUILD_DIST_DIR}\*.msix" `

src/_native/misc.cpp

@@ -233,25 +233,24 @@ PyObject *broadcast_settings_change(PyObject *, PyObject *, PyObject *) {
     return Py_GetConstant(Py_CONSTANT_NONE);
 }
 
-typedef enum {
-    CPU_X86     = 0,
-    CPU_X86_64  = 9,
-    CPU_ARM     = 5,
-    CPU_ARM64   = 12,
-    CPU_UNKNOWN = 0xffff
-} CpuArchitecture;
+// We load IsWow64Process2 dynamically to avoid breaking on earlier OS than we
+// officially support. If the API doesn't exist, then we assume -64.
+typedef BOOL (*PIsWow64Process2)(HANDLE, USHORT*, USHORT*);
 
 PyObject *get_processor_architecture(PyObject *, PyObject *, PyObject *) {
-    SYSTEM_INFO system_info;
-    GetNativeSystemInfo(&system_info);
-
-    switch (system_info.wProcessorArchitecture) {
-        case CPU_X86: return PyUnicode_FromString("-32");
-        case CPU_X86_64: return PyUnicode_FromString("-64");
-        case CPU_ARM: return PyUnicode_FromString("-arm");
-        case CPU_ARM64: return PyUnicode_FromString("-arm64");
-        default: return PyUnicode_FromString("-64"); // x86-64
+    USHORT dummy, machine = IMAGE_FILE_MACHINE_AMD64;
+    HMODULE kernel32 = GetModuleHandleW(L"kernel32.dll");
+    if (kernel32) {
+        PIsWow64Process2 isWow64Process2 = (PIsWow64Process2)GetProcAddress(kernel32, "IsWow64Process2");
+        if (!isWow64Process2 || !isWow64Process2(0, &dummy, &machine)) {
+            machine = IMAGE_FILE_MACHINE_AMD64;
+        }
+    }
+    switch (machine) {
+        case IMAGE_FILE_MACHINE_I386: return PyUnicode_FromString("-32");
+        case IMAGE_FILE_MACHINE_ARM64: return PyUnicode_FromString("-arm64");
     }
+    return PyUnicode_FromString("-64");
 }
 
 }