include/kernel: add custom USER/DOMAIN config options

These allow the generated kernel's build metadata to be defined explicitly.
This metadata is reported, eg, at boot time and in `uname -a` on running
systems. If the variables aren't configured, the current build system username
and hostname are used as normal.

The motivation for this option is to achive reproducible (bit-for-bit
identical) kernel builds of official openwrt releases.

Signed-off-by: bryan newbold <bnewbold@robocracy.org>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 48541

config/Config-kernel.in

@@ -4,6 +4,22 @@
 # See /LICENSE for more information.
 #
 
+config KERNEL_BUILD_USER
+	string "Custom Kernel Build User Name"
+	default ""
+	help
+	  Sets the Kernel build user string, which for example will be returned
+	  by 'uname -a' on running systems.
+	  If not set, uses system user at build time.
+
+config KERNEL_BUILD_DOMAIN
+	string "Custom Kernel Build Domain Name"
+	default ""
+	help
+	  Sets the Kernel build domain string, which for example will be
+	  returned by 'uname -a' on running systems.
+	  If not set, uses system hostname at build time.
+
 config KERNEL_PRINTK
 	bool "Enable support for printk"
 	default y

include/kernel-defaults.mk

@@ -10,6 +10,8 @@ KERNEL_MAKEOPTS := -C $(LINUX_DIR) \
 	CROSS_COMPILE="$(KERNEL_CROSS)" \
 	ARCH="$(LINUX_KARCH)" \
 	KBUILD_HAVE_NLS=no \
+	KBUILD_BUILD_USER="$(call qstrip,$(CONFIG_KERNEL_BUILD_USER))" \
+	KBUILD_BUILD_HOST="$(call qstrip,$(CONFIG_KERNEL_BUILD_DOMAIN))" \
 	CONFIG_SHELL="$(BASH)" \
 	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='') \
 	$(if $(PKG_BUILD_ID),LDFLAGS_MODULE=--build-id=0x$(PKG_BUILD_ID))