[source] kernel: allow reproducable builds

[LEDE Commits]

jogo pushed a commit to source.git, branch master:
https://git.lede-project.org/?p=source.git;a=commitdiff;h=5fe923b15d94e27fa6db863a6d994bfb4355e4cb

commit 5fe923b15d94e27fa6db863a6d994bfb4355e4cb
Author: Jonas Gorski <jonas.gorski at gmail.com>
AuthorDate: Sat Aug 13 11:29:46 2016 +0200

    kernel: allow reproducable builds
    
    Similar how we fix the file times in the filesystems, fix the build time
    of the kernel, and make the build number static. This should allow the
    kernel build to be reproducable when combined with setting the
    KERNEL_BUILD_USER and _DOMAIN in case of different machines.
    
    The reproducability only applies to non-initramfs kernels, those still
    require additional changes.
    
    Signed-off-by: Jonas Gorski <jonas.gorski at gmail.com>
---
 include/kernel-defaults.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/kernel-defaults.mk b/include/kernel-defaults.mk
index 11dff75..534699b 100644
--- a/include/kernel-defaults.mk
+++ b/include/kernel-defaults.mk
@@ -12,6 +12,8 @@ KERNEL_MAKEOPTS := -C $(LINUX_DIR) \
 	KBUILD_HAVE_NLS=no \
 	KBUILD_BUILD_USER="$(call qstrip,$(CONFIG_KERNEL_BUILD_USER))" \
 	KBUILD_BUILD_HOST="$(call qstrip,$(CONFIG_KERNEL_BUILD_DOMAIN))" \
+	KBUILD_BUILD_TIMESTAMP="$(shell date -u --date="@$(SOURCE_DATE_EPOCH)")" \
+	KBUILD_BUILD_VERSION="0" \
 	CONFIG_SHELL="$(BASH)" \
 	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='') \
 	$(if $(PKG_BUILD_ID),LDFLAGS_MODULE=--build-id=0x$(PKG_BUILD_ID))