build: more on cross-building using qemu

README.md

@@ -130,6 +130,18 @@ A virtual machine disk image is created using:
 
     # make vm
 
+Cross-building for other architecures
+=====================================
+
+This feature is currently experimental.  It requires
+to install a qemu package for user mode emulation:
+
+    # pkg install qemu-user-static
+
+The current target is the Raspberry Pi 1 / 2 using the
+option ARCH=arm:armv6 and is supposed to run best on
+i386 for a matching 32 bit size.
+
 About other scripts and tweaks
 ==============================
 

build/common.sh

@@ -43,14 +43,15 @@ usage()
 while getopts a:C:c:d:f:K:k:L:l:m:n:o:P:p:R:S:s:T:t:U:u:v: OPT; do
 	case ${OPT} in
 	a)
-		case "${OPTARG}" in
-		amd64|i386)
+		case ${OPTARG} in
+		amd64|i386|arm:armv6)
 			export PRODUCT_TARGET=${OPTARG%%:*}
 			export PRODUCT_ARCH=${OPTARG##*:}
+			export PRODUCT_HOST=$(uname -m)
 			SCRUB_ARGS=${SCRUB_ARGS};shift;shift
 			;;
 		*)
-			echo "ARCH wants amd64 or i386" >&2
+			echo "ARCH wants amd64, arm:armv6 or i386" >&2
 			exit 1
 			;;
 		esac
@@ -303,9 +304,18 @@ setup_chroot()
 {
 	echo ">>> Setting up chroot in ${1}"
 
+	if [ ${PRODUCT_HOST} != ${PRODUCT_ARCH} ]; then
+		# additional emulation layer so that chroot
+		# looks like a native environment later on
+		mkdir -p ${1}/usr/local/bin
+		cp /usr/local/bin/qemu-${PRODUCT_TARGET}-static \
+		    ${1}/usr/local/bin
+		/usr/local/etc/rc.d/qemu_user_static onerestart
+	fi
+
 	cp /etc/resolv.conf ${1}/etc
 	mount -t devfs devfs ${1}/dev
-	chroot ${1} /etc/rc.d/ldconfig start
+	chroot ${1} /bin/sh /etc/rc.d/ldconfig start
 }
 
 setup_marker()

build/ports.sh

@@ -57,8 +57,13 @@ fi
 trap : 2
 
 if ! chroot ${STAGEDIR} /bin/sh -es << EOF; then SELF=; fi
-# overwrites the ports tree variable, behaviour is unwanted...
+# overwrites the ports tree variable, behaviour is unwanted:
 unset STAGEDIR
+# clobbers build for pkg(8) at least, since ARCH= is in there:
+unset MAKEFLAGS
+
+export TARGET_ARCH=${PRODUCT_ARCH}
+export TARGET=${PRODUCT_TARGET}
 
 if pkg -N; then
 	# no need to rebuild
@@ -99,7 +104,8 @@ trap - 2
 
 echo ">>> Creating binary packages..."
 
-chroot ${STAGEDIR} /bin/sh -es << EOF && bundle_packages ${STAGEDIR} ${SELF} plugins core
+chroot ${STAGEDIR} /bin/sh -es << EOF && \
+    bundle_packages ${STAGEDIR} ${SELF} plugins core
 pkg autoremove -y
 pkg create -nao ${PACKAGESDIR}/All -f txz
 EOF