Clean up chroot/QEMU logic
The logic that sets up the QEMU static binary to permit running alien binary formats is quite complex. This commit cleans up a lot of the logic around this and adds a huge number of comments to try and clarify why things happen when they do. Ultimately this commit provides a lot of the ground work to factor out all of the chroot setup into a seperate shell file that can be sourced by other mklive tasks that need to operate inside of a chroot with a possibly alien executable format.
This commit is contained in:
Michael Aldridge
parent
a7ba42f7ec
commit
10568660ac
176
mkrootfs.sh.in
176
mkrootfs.sh.in
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@ -69,14 +69,30 @@ _EOF
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}
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mount_pseudofs() {
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# This function ensures that the psuedofs mountpoints are present
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# in the chroot. Strictly they are not necessary to have for many
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# commands, but bind-mounts are cheap and it isn't too bad to just
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# mount them all the time.
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for f in dev proc sys; do
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# In a naked chroot there is nothing to bind the mounts to, so
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# we need to create directories for these first.
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[ ! -d "$ROOTFS/$f" ] && mkdir -p "$ROOTFS/$f"
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mount -r --bind /$f "$ROOTFS/$f"
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if ! mountpoint -q "$ROOTFS/$f" ; then
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# It is VERY important that this only happen if the
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# pseudofs isn't already mounted. If it already is then
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# this is virtually impossible to troubleshoot because it
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# looks like the subsequent umount just isn't working.
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mount -r --bind /$f "$ROOTFS/$f"
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fi
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done
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}
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umount_pseudofs() {
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umount -f /proc/sys/fs/binfmt_misc >/dev/null 2>&1
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# This function cleans up the mounts in the chroot. Failure to
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# clean up these mounts will prevent the tmpdir from being
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# deletable instead throwing the error "Device or Resource Busy".
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# The '-f' option is passed to umount to account for the
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# contingency where the psuedofs mounts are not present.
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if [ -d "${ROOTFS}" ]; then
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for f in dev proc sys; do
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umount -f "$ROOTFS/$f" >/dev/null 2>&1
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@ -107,25 +123,118 @@ run_cmd() {
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eval "$@"
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}
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run_cmd_chroot() {
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# General purpose chroot function which makes sure the chroot is
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# prepared. This function takes 2 arguments, the location to
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# chroot to and the command to run.
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# This is an idempotent function, it is safe to call every time
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# before entering the chroot. This has the advantage of making
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# execution in the chroot appear as though it "Just Works(tm)".
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register_binfmt
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# Before we step into the chroot we need to make sure the
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# pseudo-filesystems are ready to go. Not all commands will need
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# this, but its still a good idea to call it here anyway.
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mount_pseudofs
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# With assurance that things will run now we can jump into the
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# chroot and run stuff!
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chroot "$1" sh -c "$2"
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}
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cleanup_chroot() {
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# This function cleans up the chroot shims that are used by QEMU
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# to allow builds on alien platforms. It takes no arguments but
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# expects the global $ROOTFS variable to be set.
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# Un-Mount the pseudofs mounts if they were mounted
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umount_pseudofs
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# If a QEMU binary was copied in, remove that as well
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if [ -x "$ROOTFS/usr/bin/$QEMU_BIN" ] ; then
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rm "$ROOTFS/usr/bin/$QEMU_BIN"
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fi
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}
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# TODO: Figure out how to register the binfmt for x86_64 and for i686
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# to facilitate building on alien build systems.
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register_binfmt() {
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mountpoint -q /proc/sys/fs/binfmt_misc || modprobe -q binfmt_misc; mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc 2>/dev/null
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case "${QEMU_BIN}" in
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qemu-arm-static)
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echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm-static:' > /proc/sys/fs/binfmt_misc/register 2>/dev/null
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# This function sets up everything that is needed to be able to
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# chroot into a ROOTFS and be able to run commands there. This
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# really matters on platforms where the host architecture is
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# different from the target, and you wouldn't be able to run
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# things like xbps-reconfigure -a. This function is idempotent
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# (You can run it multiple times without modifying state). This
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# function takes no arguments, but does expect the global variable
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# $XBPS_TARGET_ARCH to be set.
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# This select sets up the "magic" bytes in /proc that let the
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# kernel select an alternate interpreter. More values for this
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# map can be obtained from here:
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# https://github.com/qemu/qemu/blob/master/scripts/qemu-binfmt-conf.sh
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case "${XBPS_TARGET_ARCH}" in
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armv*)
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_cpu=arm
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_magic="\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00"
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_mask="\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff"
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QEMU_BIN=qemu-arm-static
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;;
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qemu-aarch64-static)
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echo ':arm64:M::\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/bin/qemu-aarch64-static:' > /proc/sys/fs/binfmt_misc/register 2>/dev/null
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aarch64*)
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_cpu=aarch64
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_magic="\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7"
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_mask="\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff"
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QEMU_BIN=qemu-aarch64-static
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;;
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qemu-mipsel-static)
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echo ':mipsel:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x08\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-mipsel-static:' > /proc/sys/fs/binfmt_misc/register 2>/dev/null
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mipsel*)
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_cpu=mipsel
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_magic="\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x08\x00"
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_mask="\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff"
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QEMU_BIN=qemu-mipsel-static
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;;
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*86*)
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info_msg "FIXME: Assuming that x86 instructions are native"
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QEMU_BIN=NATIVE
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;;
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*)
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die "Unknown target architecture!"
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;;
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esac
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cp -f "$(which "$QEMU_BIN")" "$ROOTFS/usr/bin" || die "failed to copy $QEMU_BIN to the ROOTFS"
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# In the special case where the build is native we can return
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# without doing anything else
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if [ "$QEMU_BIN" = "NATIVE" ] ; then
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return
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fi
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# For builds that do not match the host architecture, the correct
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# qemu binary will be required.
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if ! $QEMU_BIN -version >/dev/null 2>&1; then
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die "$QEMU_BIN binary is missing in your system, exiting."
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fi
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# In order to use the binfmt system the binfmt_misc mountpoint
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# must exist inside of proc
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if ! mountpoint -q /proc/sys/fs/binfmt_misc ; then
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modprobe -q binfmt_misc
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mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc 2>/dev/null
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fi
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# Only register if the map is incomplete
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if [ ! -f /proc/sys/fs/binfmt_misc/qemu-$_cpu ] ; then
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echo ":qemu-$_cpu:M::$_magic:$_mask:$QEMU_BIN:" > /proc/sys/fs/binfmt_misc/register 2>/dev/null
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fi
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# If the static binary isn't in the chroot then the chroot will
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# fail. The kernel knows about the map but without the static
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# version there's no interpreter in the chroot, only the
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# dynamically linked one in the host. To simplify things we just
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# use the static one always and make sure it shows up at the same
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# place in the host and the chroot.
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if [ ! -x "$ROOTFS/usr/bin/$QEMU_BIN" ] ; then
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cp -f "$(which "$QEMU_BIN")" "$ROOTFS/usr/bin" ||
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die "Could not install $QEMU_BIN to $ROOTFS/usr/bin/"
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fi
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}
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#
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@ -156,18 +265,6 @@ if [ -z "$XBPS_TARGET_ARCH" ]; then
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usage; exit 1
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fi
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# This select maps the architectures to the appropriate QEMU binaries
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# since this mapping isn't something that can just be subbed in for
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# easily.
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case "$XBPS_TARGET_ARCH" in
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i686*) QEMU_BIN=qemu-i386-static ;;
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x86_64*) QEMU_BIN=qemu-x86_64-static ;;
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armv*) QEMU_BIN=qemu-arm-static ;;
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aarch64*) QEMU_BIN=qemu-aarch64-static ;;
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mipsel*) QEMU_BIN=qemu-mipsel-static ;;
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*) die "Unknown target architecture" ;;
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esac
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# If the repository hasn't already been set, we set it to a sane value
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# here. These should all resolve even if they won't have the
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# appropriate repodata files for the selected architecture.
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@ -186,12 +283,6 @@ for f in chroot tar xbps-install xbps-reconfigure xbps-query; do
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fi
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done
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# For builds that do not match the host architecture, the correct qemu
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# binary will also be required.
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if ! $QEMU_BIN -version >/dev/null 2>&1; then
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die "$QEMU_BIN binary is missing in your system, exiting."
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fi
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# We need to operate on a tempdir, if this fails to create, it is
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# absolutely crucial to bail out so that we don't hose the system that
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# is running the script.
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@ -248,22 +339,16 @@ case "$XBPS_TARGET_ARCH" in
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run_cmd "XBPS_ARCH=${XBPS_TARGET_ARCH} xbps-reconfigure -r $ROOTFS base-files"
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;;
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*)
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# This case handles configuration of the system when it won't
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# work directly with the host ELF infrastructure. Before
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# continuing its necessary to determine the correct magic
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# numbers and load them into the kernel so that it will defer
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# to the appropriate interpreter as defined by $QEMU_BIN
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register_binfmt
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# This step sets up enough of the base-files that the chroot
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# will work and they can be reconfigured natively. Without
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# this step there isn't enough configured for ld to work.
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# This step runs as the host architecture.
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run_cmd "xbps-reconfigure -r $ROOTFS base-files"
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# Now running as the target system, this step reconfigures the
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# base-files completely. Certain things just won't work in
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# the first pass, so this cleans up any issues that linger.
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run_cmd "chroot $ROOTFS env -i xbps-reconfigure -f base-files"
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run_cmd_chroot "$ROOTFS" "env -i xbps-reconfigure -f base-files"
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# TODO: determine why these lines are here. What is the harm
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# in having them and what do they remove. Do they interact
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@ -275,11 +360,12 @@ esac
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# Once base-files is configured and functional its possible to
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# configure the rest of the system.
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run_cmd "chroot $ROOTFS xbps-reconfigure -a"
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run_cmd_chroot "$ROOTFS" "xbps-reconfigure -a"
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# At this point we're done running things that needed to be done with
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# the pseudo filesystems to be mounted, so we can clean that up.
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umount_pseudofs
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# At this point we're done running things in the chroot and we can
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# clean up the shims. Failure to do this can result in things hanging
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# when we try to delete the tmpdir.
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cleanup_chroot
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# Set the default password. Previous versions of this script used a
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# chroot to do this, but that is unnecessary since chpasswd
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@ -295,12 +381,6 @@ rm -f "$ROOTFS/etc/.pwd.lock"
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# only for it to be out of date, we remove it now.
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rm -rf "$ROOTFS/var/cache/*" 2>/dev/null
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# If we needed to copy in a QEMU_BIN executable, that needs to be
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# removed before packaging up the shiny new ROOTFS. This could be
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# wrapped in a conditional, but its much easier to just remove the
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# binary location on the off chance its there.
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rm -f "$ROOTFS/usr/bin/$QEMU_BIN"
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# Finally we can compress the tarball, the name will include the
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# architecture and the date on which the tarball was built.
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tarball=void-${XBPS_TARGET_ARCH}-ROOTFS-$(date '+%Y%m%d').tar.xz
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