Index: /trunk/src/kmk/variable.c
===================================================================
--- /trunk/src/kmk/variable.c	(revision 3420)
+++ /trunk/src/kmk/variable.c	(revision 3421)
@@ -1652,5 +1652,5 @@
     define_variable_cname ("KBUILD_HOST", val, o_default, 0);
   if (!envvar2)
-    define_variable_cname ("BUILD_PLATFORM", val, o_default, 0);
+    define_variable_cname ("BUILD_PLATFORM", "$(KBUILD_HOST)", o_default, 1);
 
   envvar1 = lookup_variable (STRING_SIZE_TUPLE ("KBUILD_HOST_ARCH"));
@@ -1662,5 +1662,5 @@
     define_variable_cname ("KBUILD_HOST_ARCH", val, o_default, 0);
   if (!envvar2)
-    define_variable_cname ("BUILD_PLATFORM_ARCH", val, o_default, 0);
+    define_variable_cname ("BUILD_PLATFORM_ARCH", "$(KBUILD_HOST_ARCH)", o_default, 1);
 
   envvar1 = lookup_variable (STRING_SIZE_TUPLE ("KBUILD_HOST_CPU"));
@@ -1672,5 +1672,5 @@
     define_variable_cname ("KBUILD_HOST_CPU", val, o_default, 0);
   if (!envvar2)
-    define_variable_cname ("BUILD_PLATFORM_CPU", val, o_default, 0);
+    define_variable_cname ("BUILD_PLATFORM_CPU", "$(KBUILD_HOST_CPU)", o_default, 1);
 
   /* The host kernel version. */