Add USE_GIT_DATE=1 to make args to build repeatable images

Up until now, every image includes the time of compilation in the
build information. This makes it impossible to verify that a
particular image came from a particular source code snapshot.

With this change, specifying USE_GIT_DATE=1 to the make command
will use the author date of HEAD as the timestamp. That means
that successive builds from the same source will produce
bitwise-identical output (assuming the same toolchain, of
course).

BUG=none
BRANCH=none
TEST=manual

Do this twice:

  \rm -rf build
  make BOARD=cr50 USE_GIT_DATE=1
  md5sum build/cr50/ec.bin

The md5sum should be the same for both runs.

Change-Id: If64307101a453cb13c62fa003f1bf432f4998273
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/252751
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/util/getversion.sh b/util/getversion.sh
index c1da044690..798bb51448 100755
--- a/util/getversion.sh
+++ b/util/getversion.sh
@@ -31,6 +31,8 @@ fi
 
 ver="${BOARD}_${vbase}"
 
+gitdate=$(git log -1 --format='%ai' HEAD | cut -d ' ' -f '1 2')
+
 echo "/* This file is generated by util/getversion.sh */"
 
 echo "/* Version string for use by common/version.c */"
@@ -47,3 +49,8 @@ echo "/* Sub-fields for use in Makefile.rules and to form build info string"
 echo " * in common/version.c. */"
 echo "#define VERSION \"${ver}\""
 echo "#define BUILDER \"${USER}@`hostname`\""
+
+echo "/* Author date of last commit, in case compile-time is not used. */"
+echo "#ifndef DATE"
+echo "#define DATE \"${gitdate}\""
+echo "#endif"