[OE-core] [PATCH] kernel.bbclass: fix SOURCE_DATE_EPOCH for non-git kernel builds

[christopher.w.clark at gmail.com]

From: Christopher Clark <christopher.w.clark at gmail.com>

Only use git to set SOURCE_DATE_EPOCH if ${S} is the top level of a git
repository.

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.

Signed-off-by: Christopher Clark <christopher.w.clark at gmail.com>
---
 meta/classes/kernel.bbclass | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index 0eadd3efb8..2603f24709 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -296,10 +296,14 @@ kernel_do_compile() {
 		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}
+			# This kernel dir is not necessarily a git repo and we
+			# must ensure that git does not incorrectly query a
+			# repository in a parent directory.
+			GIT_TOP=`git rev-parse --show-toplevel 2>/dev/null || echo ""`
+			if [ "${S}" = "${GIT_TOP}" ]; then
+				SOURCE_DATE_EPOCH=`git log  -1 --pretty=%ct`
+			else
+				SOURCE_DATE_EPOCH="${REPRODUCIBLE_TIMESTAMP_ROOTFS}"
 			fi
 			cd $olddir
 		fi
-- 
2.17.1