Index: kernel/generic/include/printf/printf_core.h
===================================================================
--- kernel/generic/include/printf/printf_core.h	(revision 6ab8697dc506650b8712d1dc5e817cc473bf170a)
+++ kernel/generic/include/printf/printf_core.h	(revision a721f6a2c63802500636ecfd5e60b628b5bdce9c)
@@ -51,5 +51,5 @@
 } printf_spec_t;
 
-int printf_core(const char *fmt, printf_spec_t *ps, va_list ap);
+extern int printf_core(const char *fmt, printf_spec_t *ps, va_list ap);
 
 #endif