kbuild: deb-pkg: improve the usability of source package

Improve the source package support in case the dpkg-buildpackage is
directly used to build binary packages.

For cross-compiling, you can set CROSS_COMPILE via the environment
variable, but it is better to set it automatically - set it to
${DEB_HOST_GNU_TYPE}- if we are cross-compiling but not from the top
Makefile.

The generated source package may be carried to a different build
environment, which may have a different compiler installed.
Run olddefconfig first to set new CONFIG options to their default
values without prompting.

Take KERNELRELEASE and KBUILD_BUILD_VERSION from the version field of
debian/changelog in case it is updated afterwards.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/package/deb-build-option

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+# Set up CROSS_COMPILE if we are cross-compiling, but not called from the
+# kernel toplevel Makefile
+if [ -z "${CROSS_COMPILE}${cross_compiling}" -a "${DEB_HOST_ARCH}" != "${DEB_BUILD_ARCH}" ]; then
+	echo CROSS_COMPILE=${DEB_HOST_GNU_TYPE}-
+fi
+
+version=$(dpkg-parsechangelog -S Version)
+version_upstream="${version%-*}"
+debian_revision="${version#${version_upstream}}"
+debian_revision="${debian_revision#*-}"
+
+echo KERNELRELEASE=${version_upstream}
+echo KBUILD_BUILD_VERSION=${debian_revision}

scripts/package/mkdebian

@@ -90,10 +90,8 @@ rm -rf debian
 version=$KERNELRELEASE
 if [ -n "$KDEB_PKGVERSION" ]; then
 	packageversion=$KDEB_PKGVERSION
-	revision=${packageversion##*-}
 else
-	revision=$($srctree/init/build-version)
-	packageversion=$version-$revision
+	packageversion=$version-$($srctree/init/build-version)
 fi
 sourcename=${KDEB_SOURCENAME:-linux-upstream}
 
@@ -244,8 +242,9 @@ srctree ?= .
 
 build-indep:
 build-arch:
-	\$(MAKE) KERNELRELEASE=${version} ARCH=${ARCH} \
-	KBUILD_BUILD_VERSION=${revision} -f \$(srctree)/Makefile
+	\$(MAKE) -f \$(srctree)/Makefile ARCH=${ARCH} \
+	\$(shell \$(srctree)/scripts/package/deb-build-option) \
+	olddefconfig all
 
 build: build-arch