diff --git a/bare-metal-bsp/libwrap/sys/_exit.c b/bare-metal-bsp/libwrap/sys/_exit.c
index 9a5f484..7dab930 100644
--- a/bare-metal-bsp/libwrap/sys/_exit.c
+++ b/bare-metal-bsp/libwrap/sys/_exit.c
@@ -5,6 +5,7 @@
 
 extern volatile uint32_t tohost;
 extern volatile uint32_t fromhost;
+void write_hex(int fd, uint32_t hex);
 
 void __wrap__exit(int code)
 {
diff --git a/bare-metal-bsp/libwrap/sys/weak_under_alias.h b/bare-metal-bsp/libwrap/sys/weak_under_alias.h
new file mode 100644
index 0000000..7629353
--- /dev/null
+++ b/bare-metal-bsp/libwrap/sys/weak_under_alias.h
@@ -0,0 +1,7 @@
+#ifndef _BSP_LIBWRAP_WEAK_UNDER_ALIAS_H
+#define _BSP_LIBWRAP_WEAK_UNDER_ALIAS_H
+
+#define weak_under_alias(name) \
+  extern __typeof (__wrap_##name) __wrap__##name __attribute__ ((weak, alias ("__wrap_"#name)))
+
+#endif