+#if SIZEOF_VOID_P == 4 && G_HAVE_API_SUPPORT(HAVE_CLASSIC_WINAPI_SUPPORT)
+typedef BOOL (WINAPI *LPFN_ISWOW64PROCESS) (HANDLE, PBOOL);
+static gboolean is_wow64 = FALSE;
+#endif
+
+/* We do this at init time to avoid potential races with module opening */
+void
+mono_threads_platform_init (void)
+{
+#if SIZEOF_VOID_P == 4 && G_HAVE_API_SUPPORT(HAVE_CLASSIC_WINAPI_SUPPORT)
+ LPFN_ISWOW64PROCESS is_wow64_func = (LPFN_ISWOW64PROCESS) GetProcAddress (GetModuleHandle (TEXT ("kernel32")), "IsWow64Process");
+ if (is_wow64_func)
+ is_wow64_func (GetCurrentProcess (), &is_wow64);
+#endif
+}
+
+/*
+ * When running x86 process under x64 system syscalls are done through WoW64. This
+ * needs to do a transition from x86 mode to x64 so it can syscall into the x64 system.
+ * Apparently this transition invalidates the ESP that we would get from calling
+ * GetThreadContext, so we would fail to scan parts of the thread stack. We attempt
+ * to query whether the thread is in such a transition so we try to restart it later.
+ * We check CONTEXT_EXCEPTION_ACTIVE for this, which is highly undocumented.
+ */