Fix and tidy unstripped binary path resolution logic.

The code as checked in breaks on Swarming because it attempts to read
the stripped file, which is omitted on isolated builds.

This CL does the ELF check on the unstripped file instead, and
consolidates the logic within a function.

Bug: 792521
Change-Id: I0042bb9b234f34ebc65c6b3ab10c075771b777ef
Reviewed-on: https://chromium-review.googlesource.com/899677
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534112}

build/fuchsia/runner_v2/symbolizer.py

@@ -20,17 +20,32 @@ _BACKTRACE_ENTRY_RE = re.compile(
 
 
 def _GetUnstrippedPath(path):
-  """Computes the path to the unstripped binary stored at |path|."""
+  """If there is a binary located at |path|, returns a path to its unstripped
+  source.
+
+  Returns None if |path| isn't a binary or doesn't exist in the lib.unstripped
+  or exe.unstripped directories."""
 
   if path.endswith('.so'):
-    return os.path.normpath(
+    maybe_unstripped_path = os.path.normpath(
         os.path.join(path, os.path.pardir, 'lib.unstripped',
                      os.path.basename(path)))
   else:
-    return os.path.normpath(
+    maybe_unstripped_path = os.path.normpath(
         os.path.join(path, os.path.pardir, 'exe.unstripped',
                      os.path.basename(path)))
 
+  if not os.path.exists(maybe_unstripped_path):
+    return None
+
+  with open(maybe_unstripped_path, 'rb') as f:
+    file_tag = f.read(4)
+  if file_tag != '\x7fELF':
+    logging.warn('Expected an ELF binary: ' + maybe_unstripped_path)
+    return None
+
+  return maybe_unstripped_path
+
 
 def FilterStream(stream, manifest_path, output_dir):
   """Looks for backtrace lines from an iterable |stream| and symbolizes them.
@@ -48,23 +63,13 @@ class _SymbolizerFilter(object):
 
     # Compute remote/local path mappings using the manifest data.
     for next_line in open(manifest_path):
-      split = next_line.strip().split('=')
-
-      # Check that the file exists in the unstripped directories and
-      # that it is an executable binary (indicated by the existence of
-      # an ELF header.)
-      target = split[0]
-      source = os.path.join(output_dir, split[1])
-      with open(source, 'rb') as f:
-        file_tag = f.read(4)
-      if file_tag != '\x7fELF':
+      target, source = next_line.strip().split('=')
+      stripped_binary_path = _GetUnstrippedPath(os.path.join(output_dir, source))
+      if not stripped_binary_path:
         continue
-      source = _GetUnstrippedPath(source)
-      if not os.path.exists(source):
-        raise Exception('Unstripped binary not found at %s' % source)
 
-      self._symbols_mapping[os.path.basename(target)] = source
-      self._symbols_mapping[target] = source
+      self._symbols_mapping[os.path.basename(target)] = stripped_binary_path
+      self._symbols_mapping[target] = stripped_binary_path
       logging.debug('Symbols: %s -> %s' % (source, target))
 
   def _SymbolizeEntries(self, entries):