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 170332d3d135e4a1d5f7b7ffcec5cc352b6faa1b)
@@ -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