scripts/bootstrap.sh, binutils, gcc, musl: improve bootstrap

- requires new abuild (from git until 2.30 is tagged)
- properly build initial musl-dev before c-compiler is available
- mark core aports with options=toolchain, and fix all makedepends
- bootstrap.sh: reorganize and use set -e there
- bootstrap.sh: use new EXTRADEPENDS_* to pull in implicit dependencies
  during bootstrap to simplify the script

4 files changed, 128 insertions, 155 deletions

diff --git a/main/binutils/APKBUILD b/main/binutils/APKBUILD
index 8bacc931c21..09ea0962d68 100644
--- a/main/binutils/APKBUILD
+++ b/main/binutils/APKBUILD
@@ -5,6 +5,7 @@ pkgrel=1
 pkgdesc="Tools necessary to build programs"
 url="http://www.gnu.org/software/binutils/"
 depends=""
+options="toolchain"
 makedepends_build="bison flex texinfo"
 makedepends_host="zlib-dev"
 makedepends="$makedepends_build $makedepends_host"
diff --git a/main/gcc/APKBUILD b/main/gcc/APKBUILD
index 32b7fd2c9be..70610f0f47d 100644
--- a/main/gcc/APKBUILD
+++ b/main/gcc/APKBUILD
@@ -2,24 +2,23 @@
 pkgname=gcc
 pkgver=6.3.0
 _pkgbase=6.3.0
-_cross=""
-[ "$BOOTSTRAP" = "noheaders" ] && pkgname="gcc-pass1"
 [ "$BOOTSTRAP" = "nolibc" ] && pkgname="gcc-pass2"
-[ "$CHOST" != "$CTARGET" ] && _cross="-$CTARGET_ARCH"
+[ "$CBUILD" != "$CHOST" ] && _cross="-$CARCH" || _cross=""
+[ "$CHOST" != "$CTARGET" ] && _target="-$CTARGET_ARCH" || _target=""
 
-pkgname="$pkgname$_cross"
+pkgname="$pkgname$_target"
 pkgrel=1
 pkgdesc="The GNU Compiler Collection"
 url="http://gcc.gnu.org"
 arch="all"
 license="GPL LGPL"
 _gccrel=$pkgver-r$pkgrel
-depends="binutils$_cross isl"
-makedepends_build="paxmark bison flex texinfo gawk zip gmp-dev mpfr-dev mpc1-dev zlib-dev"
+options="toolchain"
+depends="binutils$_target isl"
+makedepends_build="gcc$_cross g++$_cross paxmark bison flex texinfo gawk zip gmp-dev mpfr-dev mpc1-dev zlib-dev"
 makedepends_host="linux-headers gmp-dev mpfr-dev mpc1-dev isl-dev zlib-dev !gettext-dev"
-makedepends="$makedepends_build $makedepends_host"
 subpackages=" "
-[ "$CHOST" = "$CTARGET" ] && subpackages="gcc-doc$_cross"
+[ "$CHOST" = "$CTARGET" ] && subpackages="gcc-doc$_target"
 replaces="libstdc++ binutils"
 
 : ${LANG_CXX:=true}
@@ -127,30 +126,31 @@ fi
 
 _languages=c
 if $LANG_CXX; then
-	subpackages="$subpackages libstdc++:libcxx:$CTARGET_ARCH g++$_cross:gpp"
+	subpackages="$subpackages libstdc++:libcxx:$CTARGET_ARCH g++$_target:gpp"
 	_languages="$_languages,c++"
 fi
 if $LANG_OBJC; then
-	subpackages="$subpackages libobjc::$CTARGET_ARCH gcc-objc$_cross:objc"
+	subpackages="$subpackages libobjc::$CTARGET_ARCH gcc-objc$_target:objc"
 	_languages="$_languages,objc"
 fi
 if $LANG_JAVA; then
-	subpackages="$subpackages libgcj::$CTARGET_ARCH gcc-java$_cross:java"
+	subpackages="$subpackages libgcj::$CTARGET_ARCH gcc-java$_target:java"
 	_languages="$_languages,java"
 fi
 if $LANG_GO; then
-	subpackages="$subpackages libgo::$CTARGET_ARCH gcc-go$_cross:go"
+	subpackages="$subpackages libgo::$CTARGET_ARCH gcc-go$_target:go"
 	_languages="$_languages,go"
 fi
 if $LANG_FORTRAN; then
-	subpackages="$subpackages libgfortran::$CTARGET_ARCH gfortran$_cross:gfortran"
+	subpackages="$subpackages libgfortran::$CTARGET_ARCH gfortran$_target:gfortran"
 	_languages="$_languages,fortran"
 fi
 if $LANG_ADA; then
-	subpackages="$subpackages libgnat::$CTARGET_ARCH gcc-gnat$_cross:gnat"
+	subpackages="$subpackages libgnat::$CTARGET_ARCH gcc-gnat$_target:gnat"
 	_languages="$_languages,ada"
-	makedepends="$makedepends gcc-gnat"
+	makedepends_build="$makedepends_build gcc-gnat$_cross"
 fi
+makedepends="$makedepends_build $makedepends_host"
 
 source="ftp://gcc.gnu.org/pub/gcc/releases/gcc-${_pkgbase:-$pkgver}/gcc-${_pkgbase:-$pkgver}.tar.bz2
 	ftp://sourceware.org/pub/java/ecj-4.9.jar
@@ -266,15 +266,8 @@ build() {
 	[ "$CHOST"  != "$CTARGET" ] && _cross_configure="--disable-bootstrap --with-sysroot=$CBUILDROOT"
 
 	case "$BOOTSTRAP" in
-	noheaders)
-		_bootstrap_configure="--with-newlib --without-headers --disable-shared --enable-threads=no"
-		;;
-	nolibc)
-		_bootstrap_configure="--with-newlib --disable-shared --enable-threads=no"
-		;;
-	*)
-		_bootstrap_configure="--enable-shared --enable-threads --enable-tls"
-		;;
+	nolibc)	_bootstrap_configure="--with-newlib --disable-shared --enable-threads=no" ;;
+	*)	_bootstrap_configure="--enable-shared --enable-threads --enable-tls" ;;
 	esac
 
 	$LIBGOMP	|| _bootstrap_configure="$_bootstrap_configure --disable-libgomp"
@@ -405,7 +398,7 @@ libatomic() {
 	replaces="gcc"
 
 	mkdir -p "$subpkgdir"/usr/lib
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}lib/libatomic.so.* "$subpkgdir"/usr/lib/ || \
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}lib/libatomic.so.* "$subpkgdir"/usr/lib/ || \
 		return 1
 }
 
@@ -414,7 +407,7 @@ libcxx() {
 	depends=
 
 	mkdir -p "$subpkgdir"/usr/lib
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}lib/libstdc++.so.* "$subpkgdir"/usr/lib/ || \
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}lib/libstdc++.so.* "$subpkgdir"/usr/lib/ || \
 		return 1
 }
 
@@ -423,14 +416,14 @@ gpp() {
 	depends="libstdc++=$_gccrel gcc=$_gccrel libc-dev"
 	mkdir -p "$subpkgdir/$_gcclibexec" \
 		"$subpkgdir"/usr/bin \
-		"$subpkgdir"/usr/${_cross:+$CTARGET/}include \
-		"$subpkgdir"/usr/${_cross:+$CTARGET/}lib \
+		"$subpkgdir"/usr/${_target:+$CTARGET/}include \
+		"$subpkgdir"/usr/${_target:+$CTARGET/}lib \
 
 	mv "$pkgdir/$_gcclibexec/cc1plus" "$subpkgdir/$_gcclibexec/"
 	paxmark -pmrs "$subpkgdir/$_gcclibexec/cc1plus" || return 1
 
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}lib/*++* "$subpkgdir"/usr/${_cross:+$CTARGET/}lib/ || return 1
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}include/c++ "$subpkgdir"/usr/${_cross:+$CTARGET/}include/ || return 1
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}lib/*++* "$subpkgdir"/usr/${_target:+$CTARGET/}lib/ || return 1
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}include/c++ "$subpkgdir"/usr/${_target:+$CTARGET/}include/ || return 1
 	mv "$pkgdir"/usr/bin/*++ "$subpkgdir"/usr/bin/ || return 1
 }
 
@@ -439,7 +432,7 @@ libobjc() {
 	replaces="objc"
 	depends=
 	mkdir -p "$subpkgdir"/usr/lib
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}lib/libobjc.so.* "$subpkgdir"/usr/lib/
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}lib/libobjc.so.* "$subpkgdir"/usr/lib/
 }
 
 objc() {
@@ -461,7 +454,7 @@ libgcc() {
 	depends=
 
 	mkdir -p "$subpkgdir"/usr/lib
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}lib/libgcc_s.so.* "$subpkgdir"/usr/lib/ || \
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}lib/libgcc_s.so.* "$subpkgdir"/usr/lib/ || \
 		return 1
 }
 
@@ -471,7 +464,7 @@ libgomp() {
 	replaces="gcc"
 
 	mkdir -p "$subpkgdir"/usr/lib
-	mv "$pkgdir"/usr/${_cross:+$CTARGET/}lib/libgomp.so.* "$subpkgdir"/usr/lib/
+	mv "$pkgdir"/usr/${_target:+$CTARGET/}lib/libgomp.so.* "$subpkgdir"/usr/lib/
 }
 
 java() {
diff --git a/main/musl/APKBUILD b/main/musl/APKBUILD
index d44e05ef2c3..81d951ba120 100644
--- a/main/musl/APKBUILD
+++ b/main/musl/APKBUILD
@@ -9,9 +9,14 @@ arch="all"
 license="MIT"
 depends=""
 depends_dev="!uclibc-dev"
+options="toolchain"
 makedepends="$depends_dev"
 subpackages="$pkgname-dev $pkgname-dbg libc6-compat:compat:noarch"
-[ "$BOOTSTRAP" != "nolibc" ] && subpackages="$subpackages $pkgname-utils"
+case "$BOOTSTRAP" in
+nocc)	pkgname="musl-dev"; subpackages="";;
+nolibc) ;;
+*)	subpackages="$subpackages $pkgname-utils";;
+esac
 source="http://www.musl-libc.org/releases/musl-$pkgver.tar.gz
 	0001-fix-strftime-y-for-negative-years.patch
 	0002-make-globfree-safe-after-failed-glob-from-over-lengt.patch
@@ -33,24 +38,11 @@ source="http://www.musl-libc.org/releases/musl-$pkgver.tar.gz
 
 builddir="$srcdir"/musl-$pkgver
 
-install_sysroot_headers() {
-	cd "$builddir"
-	[ -z "${CBUILDROOT}" ] && die "CBUILDROOT not set"
-	case "$CARCH" in
-	aarch64*) ARCH="aarch64" ;;
-	arm*) ARCH="arm" ;;
-	x86) ARCH="i386" ;;
-	x86_64) ARCH="x86_64" ;;
-	ppc) ARCH="powerpc" ;;
-	ppc64*) ARCH="powerpc64" ;;
-	mips*) ARCH="mips" ;;
-	esac
-	make ARCH="$ARCH" prefix=/usr DESTDIR="${CBUILDROOT}" install-headers || return 1
-}
-
 build() {
 	cd "$builddir"
 
+	[ "$BOOTSTRAP" == "nocc" ] && return 0
+
 	# provide minimal libssp_nonshared.a so we don't need libssp from gcc
 	${CROSS_COMPILE}gcc $CPPFLAGS $CFLAGS -c "$srcdir"/__stack_chk_fail_local.c -o __stack_chk_fail_local.o || return 1
 	${CROSS_COMPILE}ar r libssp_nonshared.a __stack_chk_fail_local.o || return 1
@@ -79,17 +71,32 @@ build() {
 
 package() {
 	cd "$builddir"
-	make DESTDIR="$pkgdir" install || return 1
 
-	cp libssp_nonshared.a "$pkgdir"/usr/lib || return 1
-
-	# make LDSO the be the real file, and libc the symlink
-	local LDSO=$(make -f Makefile --eval "$(echo -e 'print-ldso:\n\t@echo $$(basename $(LDSO_PATHNAME))')" print-ldso)
-	mv -f "$pkgdir"/usr/lib/libc.so "$pkgdir"/lib/"$LDSO" || return 1
-	ln -sf "$LDSO" "$pkgdir"/lib/libc.musl-${CARCH}.so.1 || return 1
-	ln -sf ../../lib/"$LDSO" "$pkgdir"/usr/lib/libc.so || return 1
-	mkdir -p "$pkgdir"/usr/bin || return 1
-	ln -sf ../../lib/"$LDSO" "$pkgdir"/usr/bin/ldd || return 1
+	if [ "$BOOTSTRAP" == "nocc" ]; then
+		case "$CARCH" in
+		aarch64*)	ARCH="aarch64" ;;
+		arm*)		ARCH="arm" ;;
+		x86)		ARCH="i386" ;;
+		x86_64)		ARCH="x86_64" ;;
+		ppc)		ARCH="powerpc" ;;
+		ppc64*)		ARCH="powerpc64" ;;
+		mips*)		ARCH="mips" ;;
+		esac
+
+		make ARCH="$ARCH" prefix=/usr DESTDIR="$pkgdir" install-headers || return 1
+	else
+		make DESTDIR="$pkgdir" install || return 1
+
+		cp libssp_nonshared.a "$pkgdir"/usr/lib || return 1
+
+		# make LDSO the be the real file, and libc the symlink
+		local LDSO=$(make -f Makefile --eval "$(echo -e 'print-ldso:\n\t@echo $$(basename $(LDSO_PATHNAME))')" print-ldso)
+		mv -f "$pkgdir"/usr/lib/libc.so "$pkgdir"/lib/"$LDSO" || return 1
+		ln -sf "$LDSO" "$pkgdir"/lib/libc.musl-${CARCH}.so.1 || return 1
+		ln -sf ../../lib/"$LDSO" "$pkgdir"/usr/lib/libc.so || return 1
+		mkdir -p "$pkgdir"/usr/bin || return 1
+		ln -sf ../../lib/"$LDSO" "$pkgdir"/usr/bin/ldd || return 1
+	fi
 
 	# remove libintl.h, currently we don't want by default any NLS
 	# and use GNU gettext where needed. the plan is to migrate to
diff --git a/scripts/bootstrap.sh b/scripts/bootstrap.sh
index b7e4f9cb7a1..a9fd7547b9e 100755
--- a/scripts/bootstrap.sh
+++ b/scripts/bootstrap.sh
@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -e
+
 TARGET_ARCH="$1"
 SUDO_APK=abuild-apk
 
@@ -10,7 +12,8 @@ KERNEL_PKG="linux-firmware linux-vanilla"
 [ -e /usr/share/abuild/functions.sh ] || (echo "abuild not found" ; exit 1)
 CBUILDROOT="$(CTARGET=$TARGET_ARCH . /usr/share/abuild/functions.sh ; echo $CBUILDROOT)"
 . /usr/share/abuild/functions.sh
-[ -z "$CBUILD_ARCH" ] && die "abuild is too old (use git snapshot from cross-build branch)"
+[ -z "$CBUILD_ARCH" ] && die "abuild is too old (use 2.29.0 or later)"
+[ -z "$CBUILDROOT" ] && die "CBUILDROOT not set for $TARGET_ARCH"
 
 # deduce aports directory
 [ -z "$APORTS" ] && APORTS=$(realpath $(dirname $0)/../)
@@ -27,100 +30,6 @@ msg() {
         printf "${prompt} ${name}: %s\n" "$1" >&2
 }
 
-setup_sysroot() {
-	[ -e "$CBUILDROOT" ] && return 0
-	msg "Creating sysroot in $CBUILDROOT"
-	mkdir -p "$CBUILDROOT/etc/apk/keys"
-	cp -a /etc/apk/keys/* "$CBUILDROOT/etc/apk/keys"
-	${SUDO_APK} add --quiet --initdb --arch $TARGET_ARCH --root $CBUILDROOT
-}
-
-create_cross_compiler() {
-	msg "Building cross-compiler"
-
-	# Prepare local build environment
-	apk info --quiet --installed build-base gcc-gnat || ${SUDO_APK} add build-base gcc-gnat
-
-	# Build and install cross binutils (--with-sysroot)
-	CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname binutils) abuild up2date >& /dev/null
-	if [ $? -ne 0 ]; then
-		CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname binutils) abuild -r || return 1
-		${SUDO_APK} add --repository "$REPODEST/main" binutils-$TARGET_ARCH || return 1
-	fi
-
-	# Build and install cross GCC
-	CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname gcc) abuild up2date >& /dev/null
-	if [ $? -ne 0 ]; then
-		# Build bootstrap C-library for target if needed
-		CHOST=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname musl) abuild up2date >& /dev/null
-		if [ $? -ne 0 ]; then
-			# musl does not need GCC for headers installation, skipped step.
-			# CTARGET=$TARGET_ARCH BOOTSTRAP=noheaders abuild
-
-			# Hack: Install C-library headers for target sysroot
-			CHOST=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname musl) abuild clean unpack prepare install_sysroot_headers || return 1
-
-			# Build minimal cross GCC (--with-newlib --enable-threads=no --disable-bootstrap)
-			CTARGET=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname gcc) abuild -r || return 1
-
-			# Cross build bootstrap C-library for the target
-			${SUDO_APK} --quiet del gcc-$TARGET_ARCH g++-$TARGET_ARCH gcc-gnat-$TARGET_ARCH
-			${SUDO_APK} add --repository "$REPODEST/main" gcc-pass2-$TARGET_ARCH || return 1
-			CHOST=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname musl) abuild -r || return 1
-			${SUDO_APK} --quiet del gcc-pass2-$TARGET_ARCH
-		fi
-
-		# Build cross GCC
-		apk info --quiet --installed --root "$CBUILDROOT" musl-dev || \
-			${SUDO_APK} --root "$CBUILDROOT" add --repository "$REPODEST/main" musl-dev \
-			|| return 1
-		CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname gcc) abuild -r || return 1
-		${SUDO_APK} add --repository "$REPODEST/main" gcc-gnat gcc-$TARGET_ARCH g++-$TARGET_ARCH gcc-gnat-$TARGET_ARCH \
-			|| return 1
-	fi
-}
-
-cross_compile_base() {
-	msg "Cross building base system"
-
-	# remove possible old pass2 gcc, and add implicit host prerequisite packages
-	apk info --quiet --installed gcc-pass2-$TARGET_ARCH && ${SUDO_APK} del gcc-pass2-$TARGET_ARCH
-	apk info --quiet --installed gcc-gnat gcc-$TARGET_ARCH g++-$TARGET_ARCH gcc-gnat-$TARGET_ARCH || \
-		${SUDO_APK} add --repository "$REPODEST/main" gcc-gnat gcc-$TARGET_ARCH g++-$TARGET_ARCH gcc-gnat-$TARGET_ARCH \
-		|| return 1
-	apk info --quiet --installed --root "$CBUILDROOT" libgcc libstdc++ musl-dev || \
-		${SUDO_APK} --root "$CBUILDROOT" add --repository "$REPODEST/main" libgcc libstdc++ musl-dev \
-		|| return 1
-
-	# ordered cross-build
-	for PKG in fortify-headers linux-headers musl libc-dev pkgconf zlib \
-		   busybox busybox-initscripts binutils make \
-		   libressl libfetch apk-tools \
-		   gmp mpfr3 mpc1 isl cloog gcc \
-		   openrc alpine-conf alpine-baselayout alpine-keys alpine-base build-base \
-		   attr libcap patch sudo acl fakeroot tar \
-		   pax-utils abuild openssh \
-		   ncurses util-linux lvm2 popt xz cryptsetup kmod lddtree mkinitfs \
-		   $KERNEL_PKG ; do
-
-		CHOST=$TARGET_ARCH BOOTSTRAP=bootimage APKBUILD=$(apkbuildname $PKG) abuild -r || exit 1
-
-		case "$PKG" in
-		fortify-headers | libc-dev | build-base)
-			# headers packages which are implicit but mandatory dependency
-			apk info --quiet --installed --root "$CBUILDROOT" $PKG || \
-				${SUDO_APK} --update --root "$CBUILDROOT" --repository "$REPODEST/main" add $PKG \
-				|| return 1
-			;;
-		musl | gcc)
-			# target libraries rebuilt, force upgrade
-			[ "$(apk upgrade --root "$CBUILDROOT" --repository "$REPODEST/main" --available --simulate | wc -l)" -gt 1 ] &&
-				${SUDO_APK} upgrade --root "$CBUILDROOT" --repository "$REPODEST/main" --available
-			;;
-		esac
-	done
-}
-
 if [ -z "$TARGET_ARCH" ]; then
 	local program=$(basename $0)
 	cat <<EOF
@@ -144,4 +53,67 @@ EOF
 	return 1
 fi
 
-setup_sysroot && create_cross_compiler && cross_compile_base
+if [ ! -d "$CBUILDROOT" ]; then
+	msg "Creating sysroot in $CBUILDROOT"
+	mkdir -p "$CBUILDROOT/etc/apk/keys"
+	cp -a /etc/apk/keys/* "$CBUILDROOT/etc/apk/keys"
+	${SUDO_APK} add --quiet --initdb --arch $TARGET_ARCH --root $CBUILDROOT
+fi
+
+msg "Building cross-compiler"
+
+# Build and install cross binutils (--with-sysroot)
+CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname binutils) abuild -r
+
+if ! CHOST=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname musl) abuild up2date 2>/dev/null; then
+	# C-library headers for target
+	CHOST=$TARGET_ARCH BOOTSTRAP=nocc APKBUILD=$(apkbuildname musl) abuild -r
+
+	# Minimal cross GCC
+	EXTRADEPENDS_HOST="musl-dev" \
+	CTARGET=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname gcc) abuild -r
+
+	# Cross build bootstrap C-library for the target
+	EXTRADEPENDS_BUILD="gcc-pass2-$TARGET_ARCH" \
+	CHOST=$TARGET_ARCH BOOTSTRAP=nolibc APKBUILD=$(apkbuildname musl) abuild -r
+fi
+
+# Full cross GCC
+EXTRADEPENDS_TARGET="musl musl-dev" \
+CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname gcc) abuild -r -k
+
+# Cross build-base
+CTARGET=$TARGET_ARCH APKBUILD=$(apkbuildname build-base) abuild -r
+
+msg "Cross building base system"
+
+# add implicit target prerequisite packages
+apk info --quiet --installed --root "$CBUILDROOT" libgcc libstdc++ musl-dev || \
+	${SUDO_APK} --root "$CBUILDROOT" add --repository "$REPODEST/main" libgcc libstdc++ musl-dev
+
+# ordered cross-build
+for PKG in fortify-headers linux-headers musl libc-dev pkgconf zlib \
+	   busybox busybox-initscripts binutils make \
+	   libressl libfetch apk-tools \
+	   gmp mpfr3 mpc1 isl cloog gcc \
+	   openrc alpine-conf alpine-baselayout alpine-keys alpine-base build-base \
+	   attr libcap patch sudo acl fakeroot tar \
+	   pax-utils abuild openssh \
+	   ncurses util-linux lvm2 popt xz cryptsetup kmod lddtree mkinitfs \
+	   $KERNEL_PKG ; do
+
+	CHOST=$TARGET_ARCH BOOTSTRAP=bootimage APKBUILD=$(apkbuildname $PKG) abuild -r
+
+	case "$PKG" in
+	fortify-headers | libc-dev | build-base)
+		# headers packages which are implicit but mandatory dependency
+		apk info --quiet --installed --root "$CBUILDROOT" $PKG || \
+			${SUDO_APK} --update --root "$CBUILDROOT" --repository "$REPODEST/main" add $PKG
+		;;
+	musl | gcc)
+		# target libraries rebuilt, force upgrade
+		[ "$(apk upgrade --root "$CBUILDROOT" --repository "$REPODEST/main" --available --simulate | wc -l)" -gt 1 ] &&
+			${SUDO_APK} upgrade --root "$CBUILDROOT" --repository "$REPODEST/main" --available
+		;;
+	esac
+done