Orderfile: Treat unknown offsets as error

We found that encountering unknown offsets from profile information may
indicate that the data is seriously offset (pun intended). It does not
happen now on the orderfile bot, and we would like to know when it
happens next. Converting this situation to error.

Bug: 893981
Change-Id: Ibabe4b39886afa4e3a228f9e3910df5d0bcf91cf
Reviewed-on: https://chromium-review.googlesource.com/c/1340328Reviewed-by: Matthew Cary <mattcary@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608810}

tools/cygprofile/process_profiles.py

@@ -232,21 +232,15 @@ class SymbolOffsetProcessor(object):
     """
     dump_offset_to_symbol_info = self._GetDumpOffsetToSymbolInfo()
     logging.info('Offset to Symbol size = %d', len(dump_offset_to_symbol_info))
-    offsets_not_found = 0
     for i in items:
       dump_offset = get(i)
       idx = dump_offset / 2
       assert dump_offset >= 0 and idx < len(dump_offset_to_symbol_info), (
           'Dump offset out of binary range')
       symbol_info = dump_offset_to_symbol_info[idx]
-      if symbol_info is None:
-        offsets_not_found += 1
-        update(i, None)
-      else:
-        update(i, symbol_info.offset)
-    if offsets_not_found:
-      logging.warning('%d return addresses don\'t map to any symbol',
-                      offsets_not_found)
+      assert symbol_info, ('A return address (offset = 0x{:08x}) does not map '
+          'to any symbol'.format(dump_offset))
+      update(i, symbol_info.offset)
 
   def _GetDumpOffsetToSymbolInfo(self):
     """Computes an array mapping each word in .text to a symbol.