Correct some warnings

core/stack.c

@@ -74,7 +74,7 @@ void stackSymbolSetup(multiboot_info_t *mbi)
 }
 
 /** Look up an address in symbols map and return its function name or NULL. */
-static const char *lookupSymbolName(uint32_t addr)
+const char *lookupSymbolName(uint32_t addr)
 {
     size_t symtab_len = elfSymtabSize / sizeof(Elf32_Sym_t);
 

drivers/keyboard.c

@@ -460,7 +460,7 @@ void keyboard_do_irq()
     }
 
     if (key){
-        printf(key);
+        putc(*key);
         ringbufferEnqueue(buf, *key);
     }
 }