diff --git a/lib/gdbcommand.py b/lib/gdbcommand.py
index 7a150de..583b873 100644
--- a/lib/gdbcommand.py
+++ b/lib/gdbcommand.py
@@ -2,8 +2,36 @@
 
 from buildbot.status.builder import SUCCESS, WARNINGS, FAILURE, EXCEPTION
 from buildbot.steps.shell import ShellCommand
-from sumfiles import DejaResults
+from sumfiles import DejaResults, get_web_base
 from gdbgitdb import switch_to_branch
+from shutil import copyfile
+
+class CopyOldGDBSumFile (ShellCommand):
+    """Copy the current gdb.sum file into the old_gdb.sum file."""
+    name = "copy gdb.sum file"
+    command = [ '/bin/true' ]
+
+    def __init__ (self, **kwargs):
+        ShellCommand.__init__ (self, **kwargs)
+
+    def evaluateCommand (self, cmd):
+        rev = self.getProperty('got_revision')
+        builder = self.getProperty('buildername')
+        istry = self.getProperty('isTryBuilder')
+        branch = self.getProperty('branch')
+        wb = get_web_base ()
+        if branch is None:
+            branch = 'master'
+
+        # Switch to the right branch inside the BUILDER repo
+        switch_to_branch (builder, branch)
+
+        try:
+            copyfile ("%d/%d/gdb.sum" % (wb, builder),
+                      "%d/%d/previous_gdb.sum" % (wb, builder))
+        except IOError:
+            # If the dest file does not exist, ignore
+            pass
 
 class GdbCatSumfileCommand(ShellCommand):
     name = 'regressions'
@@ -27,20 +55,31 @@ class GdbCatSumfileCommand(ShellCommand):
         cur_results = parser.read_sum_text(self.getLog('stdio').getText())
         if not istry or istry == 'no':
             baseline = parser.read_baseline (builder, branch)
+            old_sum = parser.read_old_sum_file (builder, branch)
         else:
             baseline = parser.read_sum_file(builder, rev)
+            old_sum = parser.read_old_sum_file (builder, rev)
         result = SUCCESS
         if baseline is not None:
             report = parser.compute_regressions (builder, branch,
                                                  cur_results, baseline)
+            if report is not '':
+                self.addCompleteLog ('baseline_diff', report)
+                result = WARNINGS
+
+        if old_sum is not None:
+            report = parser.compute_regressions (builder, branch,
+                                                 cur_results, old_sum)
             if report is not '':
                 self.addCompleteLog ('regressions', report)
                 result = FAILURE
+
         if not istry or istry == 'no':
             parser.write_sum_file (cur_results, builder, branch)
             # If there was no previous baseline, then this run
             # gets the honor.
             if baseline is None:
                 baseline = cur_results
-            parser.write_baseline (baseline, builder, branch)
+            parser.write_baseline (baseline, builder, branch, rev)
+
         return result
diff --git a/lib/gdbgitdb.py b/lib/gdbgitdb.py
index 04714f8..2bbb4a7 100644
--- a/lib/gdbgitdb.py
+++ b/lib/gdbgitdb.py
@@ -133,6 +133,8 @@ class SaveGDBResults (ShellCommand):
             repo.index.add (['gdb.sum',
                              'gdb.log',
                              'baseline'])
+            if os.path.exists ("%s/previous_gdb.sum"):
+                repo.index.add (['previous_gdb.sum'])
             if repo.is_dirty ():
                 repo.index.commit ('Log files for %s -- branch %s' % (full_tag, branch))
                 repo.index.write ()
diff --git a/lib/sumfiles.py b/lib/sumfiles.py
index d448155..0887776 100644
--- a/lib/sumfiles.py
+++ b/lib/sumfiles.py
@@ -46,7 +46,8 @@ class DejaResults(object):
                 test_name = nname
             out_dict[test_name] = result
 
-    def _write_sum_file(self, sum_dict, subdir, rev_or_branch, filename):
+    def _write_sum_file(self, sum_dict, subdir, rev_or_branch, filename,
+                        header = None):
         global gdb_web_base
         if not rev_or_branch:
             bdir = os.path.join (gdb_web_base, subdir)
@@ -57,15 +58,21 @@ class DejaResults(object):
         fname = os.path.join (bdir, filename)
         keys = sum_dict.keys ()
         keys.sort ()
-        with open (fname, 'w') as f:
+        mode = 'w'
+        if header:
+            with open (fname, 'w') as f:
+                f.write (header)
+            mode = 'a'
+        with open (fname, mode) as f:
             for k in keys:
                 f.write (sum_dict[k] + ': ' + k + '\n')
 
     def write_sum_file(self, sum_dict, builder, branch):
         self._write_sum_file (sum_dict, builder, None, 'gdb.sum')
 
-    def write_baseline(self, sum_dict, builder, branch):
-        self._write_sum_file(sum_dict, builder, None, 'baseline')
+    def write_baseline(self, sum_dict, builder, branch, rev):
+        self._write_sum_file(sum_dict, builder, None, 'baseline',
+                             header = "### THIS BASELINE WAS LAST UPDATED BY COMMIT %s ###\n\n" % rev)
 
     # Read a .sum file.
     # The builder name is BUILDER.
@@ -98,6 +105,9 @@ class DejaResults(object):
         return self._read_sum_file (builder, os.path.join ('xfails', branch),
                                     'xfail')
 
+    def read_old_sum_file (self, builder, branch):
+        return self._read_sum_file (builder, None, 'previous_gdb.sum')
+
     # Parse some text as a .sum file and return the resulting
     # dictionary.
     def read_sum_text (self, text):
diff --git a/master.cfg b/master.cfg
index a774fbd..0f55c6a 100644
--- a/master.cfg
+++ b/master.cfg
@@ -24,7 +24,7 @@ from buildbot.steps.slave import RemoveDirectory
 from buildbot.changes.filter import ChangeFilter
 from buildbot.buildslave import BuildSlave
 from buildbot.status.results import SUCCESS, WARNINGS, FAILURE, EXCEPTION
-from gdbcommand import GdbCatSumfileCommand
+from gdbcommand import CopyOldGDBSumFile, GdbCatSumfileCommand
 from gdbgitdb import SaveGDBResults, get_builder_commit_id
 from urllib import quote
 
@@ -472,6 +472,7 @@ The parameters of the class are:
                                        descriptionDone = r"removed old build dir"))
         self.addStep (CloneOrUpdateGDBMasterRepo ())
         self.addStep (CloneOrUpdateGDBRepo ())
+        self.addStep (CopyOldGDBSumFile ())
 
         if not self.extra_conf_flags:
             self.extra_conf_flags = []