[OE-core] [PATCH v2] 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>

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.

Signed-off-by: Christopher Clark <christopher.w.clark at gmail.com>
---
 meta/classes/kernel.bbclass | 12 ++++--------
 1 file 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`
-- 
2.17.1