System preparation

Qemu

Emerge qemu with static-user USE enabled and your wanted architectures.

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app-emulation/qemu      QEMU_SOFTMMU_TARGETS: aarch64 arm x86_64
app-emulation/qemu      QEMU_USER_TARGETS: aarch64 arm x86_64

app-emulation/qemu      static-user
dev-libs/glib           static-libs
sys-apps/attr           static-libs
sys-libs/zlib           static-libs
dev-libs/libpcre2       static-libs

OpenRC

Enable qemu-binfmt:

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rc-update add qemu-binfmt default

Start qemu-binfmt:

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rc-service qemu-binfmt start

Chrooting

• select chroot location (eg /chroots/gentoo-arm64-musl-stable)
• unpack the desired rootfs
• create needed directories
  • mkdir -p /chroots/gentoo-arm64-musl-stable/var/cache/distfiles
• execute bwrap
  • with last ro-bind mount the qemu emulator binary (eg qemu-aarch64)
  • execute the mounted emulator binary giving it a shell program (eg bash)

Chroot with bwrap:

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bwrap                                                       \
    --bind /chroots/gentoo-arm64-musl-stable /              \
    --dev /dev                                              \
    --proc /proc --perms 1777                               \
    --tmpfs /dev/shm                                        \
    --tmpfs /run                                            \
    --ro-bind /etc/resolv.conf /etc/resolv.conf             \
    --bind /var/cache/distfiles /var/cache/distfiles        \
    --ro-bind /usr/bin/qemu-aarch64 /usr/bin/qemu-aarch64   \
    /usr/bin/qemu-aarch64 /bin/bash -l

User-mode

By default you would probably have something like this, the user-mode network:

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<interface type="user">
  <mac address="00:00:00:00:00:00"/>
  <model type="virtio"/>
  <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>
</interface>

Bridge

Bridges can be easily created using the NetworkManager’s TUI tool called nmtui.

Bridge XML configuration for Libvirt

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<interface type="bridge">
  <mac address="00:00:00:00:00:00"/>
  <source bridge="br1"/>
  <target dev="vnet2"/>
  <model type="virtio"/>
  <alias name="net0"/>
  <address type="pci" domain="0x0000" bus="0x06" slot="0x00" function="0x0"/>
</interface>

Sysctl options

Be sure the following options are enabled (1):

• net.ipv4.ip_forward
• net.ipv4.conf.all.send_redirects

and the following options are disabled (0):

• net.bridge.bridge-nf-call-iptables