Script to compare global variables between two PDBs

This script relies on having the recently added ShowGlobals.exe built
and in your path.

R=stanisc@chromium.org
BUG=630755

Review-Url: https://codereview.chromium.org/2592323002
Cr-Commit-Position: refs/heads/master@{#440764}

tools/win/pdb_compare_globals.py

+# Copyright (c) 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""
+This script uses ShowGlobals.exe to compare two PDBs to see what interesting
+globals are present in one but not the other. You can either pass in a .pdb file
+or you can pass in a .txt file that contains the results of calling ShowGlobals.
+This helps when investigating size regressions. Often code-size regressions are
+associated with global variable changes, and those global variables can be
+easier to track and investigate than the code.
+
+Typical output from ShowGlobals.exe is lines like these:
+
+  #Dups   DupSize   Size  Section Symbol name     PDB name
+
+  0       0       122784  2       kBrotliDictionary       chrome.dll.pdb
+  1       1824    0       0       LcidToLocaleNameTable   chrome.dll.pdb
+"""
+
+import os
+import subprocess
+import sys
+
+
+def LoadSymbols(pdb_name):
+  result = {}
+  extension = os.path.splitext(pdb_name)[1].lower()
+  if extension in ['.pdb']:
+    command = 'ShowGlobals.exe "%s"' % pdb_name
+    lines = subprocess.check_output(command).splitlines()
+  elif extension in ['.txt']:
+    lines = open(pdb_name).readlines()
+  else:
+    print 'Unrecognized extension in %s' % pdb_name
+    return result
+  for line in lines:
+    parts = line.split('\t')
+    if len(parts) >= 5 and not line.startswith('#'):
+      # Put the first four columns (the numerical data associated with a symbol)
+      # into a dictionary indexed by the fifth column, which is the symbol name.
+      symbol_name = parts[4]
+      result[symbol_name] = parts[:4]
+  return result
+
+
+def ShowExtras(symbols_A, symbols_B, name_A, name_B):
+  print 'Symbols that are in %s but not in %s' % (name_A, name_B)
+  for key in symbols_A:
+    if not key in symbols_B:
+      # Print all the numerical data, followed by the symbol name, separated by
+      # tabs.
+      print '\t'.join(symbols_A[key] + [key])
+  print
+
+
+def ShowDifferences(symbols_A, symbols_B, name_A, name_B):
+  print 'Symbols that are changed from %s to %s' % (name_A, name_B)
+  for key in symbols_A:
+    if key in symbols_B:
+      value_a = symbols_A[key]
+      value_b = symbols_B[key]
+      if value_a != value_b:
+        # Print the symbol name and then the two versions of the numerical data,
+        # indented.
+        print '%s changed from/to:' % key
+        print '\t' + '\t'.join(value_a)
+        print '\t' + '\t'.join(value_b)
+  print
+
+
+def main():
+  symbols_1 = LoadSymbols(sys.argv[1])
+  symbols_2 = LoadSymbols(sys.argv[2])
+
+  if len(symbols_1) == 0:
+    print 'No data found in %s - fastlink?' % sys.argv[1]
+    return
+  if len(symbols_2) == 0:
+    print 'No data found in %s - fastlink?' % sys.argv[2]
+    return
+
+  print ('%d interesting globals in %s, %d interesting globals in %s' %
+         (len(symbols_1), sys.argv[1], len(symbols_2), sys.argv[2]))
+
+  ShowExtras(symbols_1, symbols_2, sys.argv[1], sys.argv[2])
+  ShowExtras(symbols_2, symbols_1, sys.argv[2], sys.argv[1])
+  ShowDifferences(symbols_1, symbols_2, sys.argv[1], sys.argv[2])
+
+
+if __name__ == '__main__':
+  sys.exit(main())