Use absolute paths for bootloader binaries

Author: theotherjimmy

tools/config/__init__.py

@@ -17,7 +17,7 @@
 
 from copy import deepcopy
 import os
-from os.path import dirname, abspath, exists
+from os.path import dirname, abspath, exists, join
 import sys
 from collections import namedtuple
 from os.path import splitext, relpath
@@ -526,11 +526,11 @@ def regions(self):
             raise ConfigException(
                 "Bootloader build requested but no bootlader configuration")
 
-    @staticmethod
-    def _generate_booloader_build(target_overrides, rom_start, rom_size):
+    def _generate_booloader_build(self, target_overrides, rom_start, rom_size):
         start = 0
         if 'target.bootloader_img' in target_overrides:
-            filename = target_overrides['target.bootloader_img']
+            basedir = abspath(dirname(self.app_config_location))
+            filename = join(basedir, target_overrides['target.bootloader_img'])
             if not exists(filename):
                 raise ConfigException("Bootloader %s not found" % filename)
             part = intelhex_offset(filename, offset=rom_start)