kbuild: add debug package to pacman PKGBUILD

Add a new debug package to the PKGBUILD for the pacman-pkg target. The
debug package includes the non-stripped vmlinux file with debug symbols
for kernel debugging and profiling. The file is installed at
/usr/src/debug/${pkgbase}, with a symbolic link at
/usr/lib/modules/$(uname -r)/build/vmlinux. The debug package is built
by default.
Signed-off-by: Jose Fernandez <jose.fernandez@linux.dev>
Reviewed-by: Peter Jung <ptr1337@cachyos.org>
Acked-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/package/PKGBUILD

@@ -5,7 +5,7 @@
 pkgbase=${PACMAN_PKGBASE:-linux-upstream}
 pkgname=("${pkgbase}")
 
-_extrapackages=${PACMAN_EXTRAPACKAGES-headers api-headers}
+_extrapackages=${PACMAN_EXTRAPACKAGES-headers api-headers debug}
 for pkg in $_extrapackages; do
 	pkgname+=("${pkgbase}-${pkg}")
 done
@@ -111,6 +111,19 @@ _package-api-headers() {
 	${MAKE} headers_install INSTALL_HDR_PATH="${pkgdir}/usr"
 }
 
+_package-debug(){
+	pkgdesc="Non-stripped vmlinux file for the ${pkgdesc} kernel"
+
+	local debugdir="${pkgdir}/usr/src/debug/${pkgbase}"
+	local builddir="${pkgdir}/usr/${MODLIB}/build"
+
+	_prologue
+
+	install -Dt "${debugdir}" -m644 vmlinux
+	mkdir -p "${builddir}"
+	ln -sr "${debugdir}/vmlinux" "${builddir}/vmlinux"
+}
+
 for _p in "${pkgname[@]}"; do
 	eval "package_$_p() {
 		$(declare -f "_package${_p#$pkgbase}")