Use git rev-parse --short=8 to get rev

enter_chroot.sh

 #!/bin/bash
 
 # Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Script to enter the chroot environment
 
 # Load common constants.  This should be the first executable line.
 # The path to common.sh should be relative to your script's location.
@@ skipping 229 matching lines @@
 # the wrong version, which would mess up the .git directories.
 #
 # Note that this fixes $CHROMEOS_REVISION at the time the chroot is
 # entered.  That's ok for the main use case of automated builds,
 # which pass each command line into a separate call to enter_chroot
 # so always have up-to-date info.  For developer builds, there may not
 # be a single revision, since the developer may have
 # hand-sync'd some subdirs and edited files in others.
 # In that case, check against origin/HEAD and mark** revision.
 # Use git:8 chars of sha1
-REVISION=$(git rev-parse HEAD)
-ORIGIN_REVISION=$(git rev-parse origin/HEAD)
-# Do not check for clean revision on official builds.  They are coming directly
-# from a branch rev and cannot compare to origin/HEAD.
-if [ $FLAGS_official_build != $FLAGS_TRUE ] && \
-   [ "$REVISION" != "$ORIGIN_REVISION" ]
-then
-  # Mark dirty tree with "**"
-  REVISION="${REVISION:0:8}**"
-else
-  REVISION="${REVISION:0:8}"
-fi
+REVISION=$(git rev-parse --short=8 HEAD)
 CHROOT_PASSTHRU="CHROMEOS_REVISION=$REVISION BUILDBOT_BUILD=$FLAGS_build_number CHROMEOS_OFFICIAL=$CHROMEOS_OFFICIAL"
 
 # Run command or interactive shell.  Also include the non-chrooted path to
 # the source trunk for scripts that may need to print it (e.g.
 # build_image.sh).
 sudo chroot "$FLAGS_chroot" sudo -i -u $USER $CHROOT_PASSTHRU \
   EXTERNAL_TRUNK_PATH="${FLAGS_trunk}" LANG=C "$@"
 
 # Remove trap and explicitly unmount
 trap - EXIT
 teardown_env