+#elif __x86_64
+
+/* No way to cover x86_64 with a generic implementation, as it uses register-
+ based parameter passing. Using the GCC builtins here.
+*/
+typedef __builtin_va_list _PDCLIB_va_list;
+#define _PDCLIB_va_arg( ap, type ) ( __builtin_va_arg( ap, type ) )
+#define _PDCLIB_va_copy( dest, src ) ( __builtin_va_copy( dest, src ) )
+#define _PDCLIB_va_end( ap ) ( __builtin_va_end( ap ) )
+#define _PDCLIB_va_start( ap, parmN ) ( __builtin_va_start( ap, parmN ) )
+
+#else
+
+#error Please create your own _PDCLIB_config.h. Using the existing one as-is will not work.
+
+#endif
+