kernel.bbclass: fix SOURCE_DATE_EPOCH for non-git kernel builds

The source directory is not always a git repository, so when querying
git for data to set SOURCE_DATE_EPOCH, specify ${S}/.git as the git
directory to prevent retrieving incorrect data from any parent directory.

Fixes the following errors with the prior logic when building a kernel
that is not obtained from a git repository:

1. With TMPDIR set to a directory outside any git repository on a
mounted filesystem, reproducible builds fail in do_compile with this git
error:

  fatal: not a git repository (or any parent up to mount point <abspath>)
  Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).

aborting before the error handling logic.

2. With TMPDIR located within a subdirectory of a git repository, the
SOURCE_DATE_EPOCH timestamp would be that of said repository rather than
that of the kernel.

(From OE-Core rev: 270ae94fe345b9ce98d822034cbfad7e24c5f393)

Signed-off-by: Christopher Clark <christopher.w.clark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 4 insertions, 8 deletions

diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index 0eadd3efb8..a724645466 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -294,14 +294,10 @@ kernel_do_compile() {
                 # kernel sources do not use do_unpack, so SOURCE_DATE_EPOCH may not
                 # be set....
                 if [ "${SOURCE_DATE_EPOCH}" = "" -o "${SOURCE_DATE_EPOCH}" = "0" ]; then
-                        olddir=`pwd`
-                        cd ${S}
-                        SOURCE_DATE_EPOCH=`git log  -1 --pretty=%ct`
-                        # git repo not guaranteed, so fall back to REPRODUCIBLE_TIMESTAMP_ROOTFS
-                        if [ $? -ne 0 ]; then
-                                SOURCE_DATE_EPOCH=${REPRODUCIBLE_TIMESTAMP_ROOTFS}
-                        fi
-                        cd $olddir
+                        # The source directory is not necessarily a git repository, so we
+                        # specify the git-dir to ensure that git does not query a
+                        # repository in any parent directory.
+                        SOURCE_DATE_EPOCH=`git --git-dir="${S}/.git" log -1 --pretty=%ct 2>/dev/null || echo "${REPRODUCIBLE_TIMESTAMP_ROOTFS}"`
                 fi
 
                 ts=`LC_ALL=C date -d @$SOURCE_DATE_EPOCH`