kbuild: add script and target to generate pacman package

pacman is the package manager used by Arch Linux and its derivates.
Creating native packages from the kernel tree has multiple advantages:

* The package triggers the correct hooks for initramfs generation and
  bootloader configuration
* Uninstallation is complete and also invokes the relevant hooks
* New UAPI headers can be installed without any manual bookkeeping

The PKGBUILD file is a modified version of the one used for the
downstream Arch Linux "linux" package.
Extra steps that should not be necessary for a development kernel have
been removed and an UAPI header package has been added.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

.gitignore

@@ -92,6 +92,12 @@ modules.order
 #
 /tar-install/
 
+#
+# pacman files (make pacman-pkg)
+#
+/PKGBUILD
+/pacman/
+
 #
 # We don't want to ignore the following even if they are dot-files
 #

MAINTAINERS

@@ -11998,6 +11998,13 @@ F:	include/uapi/linux/nfsd/
 F:	include/uapi/linux/sunrpc/
 F:	net/sunrpc/
 
+KERNEL PACMAN PACKAGING (in addition to generic KERNEL BUILD)
+M:	Thomas Weißschuh <linux@weissschuh.net>
+R:	Christian Heusel <christian@heusel.eu>
+R:	Nathan Chancellor <nathan@kernel.org>
+S:	Maintained
+F:	scripts/package/PKGBUILD
+
 KERNEL REGRESSIONS
 M:	Thorsten Leemhuis <linux@leemhuis.info>
 L:	regressions@lists.linux.dev

Makefile

@@ -1489,7 +1489,7 @@ CLEAN_FILES += vmlinux.symvers modules-only.symvers \
 # Directories & files removed with 'make mrproper'
 MRPROPER_FILES += include/config include/generated          \
 		  arch/$(SRCARCH)/include/generated .objdiff \
-		  debian snap tar-install \
+		  debian snap tar-install PKGBUILD pacman \
 		  .config .config.old .version \
 		  Module.symvers \
 		  certs/signing_key.pem \

scripts/Makefile.package

@@ -141,6 +141,19 @@ snap-pkg:
 	cd $(objtree)/snap && \
 	snapcraft --target-arch=$(UTS_MACHINE)
 
+# pacman-pkg
+# ---------------------------------------------------------------------------
+
+PHONY += pacman-pkg
+pacman-pkg:
+	@ln -srf $(srctree)/scripts/package/PKGBUILD $(objtree)/PKGBUILD
+	+objtree="$(realpath $(objtree))" \
+		BUILDDIR="$(realpath $(objtree))/pacman" \
+		CARCH="$(UTS_MACHINE)" \
+		KBUILD_MAKEFLAGS="$(MAKEFLAGS)" \
+		KBUILD_REVISION="$(shell $(srctree)/scripts/build-version)" \
+		makepkg $(MAKEPKGOPTS)
+
 # dir-pkg tar*-pkg - tarball targets
 # ---------------------------------------------------------------------------
 
@@ -221,6 +234,7 @@ help:
 	@echo '  bindeb-pkg          - Build only the binary kernel deb package'
 	@echo '  snap-pkg            - Build only the binary kernel snap package'
 	@echo '                        (will connect to external hosts)'
+	@echo '  pacman-pkg          - Build only the binary kernel pacman package'
 	@echo '  dir-pkg             - Build the kernel as a plain directory structure'
 	@echo '  tar-pkg             - Build the kernel as an uncompressed tarball'
 	@echo '  targz-pkg           - Build the kernel as a gzip compressed tarball'

scripts/package/PKGBUILD

@@ -0,0 +1,108 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# Maintainer: Thomas Weißschuh <linux@weissschuh.net>
+# Contributor: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
+
+pkgbase=${PACMAN_PKGBASE:-linux-upstream}
+pkgname=("${pkgbase}" "${pkgbase}-api-headers")
+if grep -q CONFIG_MODULES=y include/config/auto.conf; then
+	pkgname+=("${pkgbase}-headers")
+fi
+pkgver="${KERNELRELEASE//-/_}"
+# The PKGBUILD is evaluated multiple times.
+# Running scripts/build-version from here would introduce inconsistencies.
+pkgrel="${KBUILD_REVISION}"
+pkgdesc='Upstream Linux'
+url='https://www.kernel.org/'
+# Enable flexible cross-compilation
+arch=(${CARCH})
+license=(GPL-2.0-only)
+makedepends=(
+	bc
+	bison
+	cpio
+	flex
+	gettext
+	kmod
+	libelf
+	openssl
+	pahole
+	perl
+	python
+	rsync
+	tar
+)
+options=(!debug !strip !buildflags !makeflags)
+
+build() {
+	# MAKEFLAGS from makepkg.conf override the ones inherited from kbuild.
+	# Bypass this override with a custom variable.
+	export MAKEFLAGS="${KBUILD_MAKEFLAGS}"
+	cd "${objtree}"
+
+	${MAKE} KERNELRELEASE="${KERNELRELEASE}" KBUILD_BUILD_VERSION="${pkgrel}"
+}
+
+_package() {
+	pkgdesc="The ${pkgdesc} kernel and modules"
+
+	export MAKEFLAGS="${KBUILD_MAKEFLAGS}"
+	cd "${objtree}"
+	local modulesdir="${pkgdir}/usr/${MODLIB}"
+
+	echo "Installing boot image..."
+	# systemd expects to find the kernel here to allow hibernation
+	# https://github.com/systemd/systemd/commit/edda44605f06a41fb86b7ab8128dcf99161d2344
+	install -Dm644 "$(${MAKE} -s image_name)" "${modulesdir}/vmlinuz"
+
+	# Used by mkinitcpio to name the kernel
+	echo "${pkgbase}" > "${modulesdir}/pkgbase"
+
+	echo "Installing modules..."
+	${MAKE} INSTALL_MOD_PATH="${pkgdir}/usr" INSTALL_MOD_STRIP=1 \
+		DEPMOD=true modules_install
+
+	if [ -d "${srctree}/arch/${SRCARCH}/boot/dts" ]; then
+		echo "Installing dtbs..."
+		${MAKE} INSTALL_DTBS_PATH="${modulesdir}/dtb" dtbs_install
+	fi
+
+	# remove build link, will be part of -headers package
+	rm -f "${modulesdir}/build"
+}
+
+_package-headers() {
+	pkgdesc="Headers and scripts for building modules for the ${pkgdesc} kernel"
+
+	export MAKEFLAGS="${KBUILD_MAKEFLAGS}"
+	cd "${objtree}"
+	local builddir="${pkgdir}/usr/${MODLIB}/build"
+
+	echo "Installing build files..."
+	"${srctree}/scripts/package/install-extmod-build" "${builddir}"
+
+	echo "Installing System.map and config..."
+	cp System.map "${builddir}/System.map"
+	cp .config "${builddir}/.config"
+
+	echo "Adding symlink..."
+	mkdir -p "${pkgdir}/usr/src"
+	ln -sr "${builddir}" "${pkgdir}/usr/src/${pkgbase}"
+}
+
+_package-api-headers() {
+	pkgdesc="Kernel headers sanitized for use in userspace"
+	provides=(linux-api-headers)
+	conflicts=(linux-api-headers)
+
+	export MAKEFLAGS="${KBUILD_MAKEFLAGS}"
+	cd "${objtree}"
+
+	${MAKE} headers_install INSTALL_HDR_PATH="${pkgdir}/usr"
+}
+
+for _p in "${pkgname[@]}"; do
+	eval "package_$_p() {
+		$(declare -f "_package${_p#$pkgbase}")
+		_package${_p#$pkgbase}
+	}"
+done