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>

0 files changed, 0 insertions, 0 deletions