kernel/reproducibility: kernel modules need SOURCE_DATE_EPOCH export

If CONFIG_IKHEADERS is set to =m, then reproducibility issues creep
into the modules build, since the variables we are setting for the
main kernel build are not present.

Since the source code must be available for a possibly git query
on the timestamp, there didn't seem to be an easy way to move the
environment variable setting to a common routine. As such, we
duplicate the block of code that exports the required variables for
reproducible builds. There is a maintenance risk to this, but any
issues should be easy enough to catch.

(From OE-Core rev: 82cdfcdccfedd320ebc0cdc778c7d4966198b96f)

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index 6846d6040d..0935196f6f 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -331,6 +331,21 @@ kernel_do_compile() {
 
 do_compile_kernelmodules() {
         unset CFLAGS CPPFLAGS CXXFLAGS LDFLAGS MACHINE
+        if [ "${BUILD_REPRODUCIBLE_BINARIES}" = "1" ]; then
+                # kernel sources do not use do_unpack, so SOURCE_DATE_EPOCH may not
+                # be set....
+                if [ "${SOURCE_DATE_EPOCH}" = "" -o "${SOURCE_DATE_EPOCH}" = "0" ]; then
+                        # The source directory is not necessarily a git repository, so we
+                        # specify the git-dir to ensure that git does not query a
+                        # repository in any parent directory.
+                        SOURCE_DATE_EPOCH=`git --git-dir="${S}/.git" log -1 --pretty=%ct 2>/dev/null || echo "${REPRODUCIBLE_TIMESTAMP_ROOTFS}"`
+                fi
+
+                ts=`LC_ALL=C date -d @$SOURCE_DATE_EPOCH`
+                export KBUILD_BUILD_TIMESTAMP="$ts"
+                export KCONFIG_NOTIMESTAMP=1
+                bbnote "KBUILD_BUILD_TIMESTAMP: $ts"
+        fi
         if (grep -q -i -e '^CONFIG_MODULES=y$' ${B}/.config); then
                 cc_extra=$(get_cc_option)
                 oe_runmake -C ${B} ${PARALLEL_MAKE} modules CC="${KERNEL_CC} $cc_extra " LD="${KERNEL_LD}" ${KERNEL_EXTRA_ARGS}