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#!/bin/bash
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#
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# Setup and configure qemu userspace emulator on kokoro worker so that we can seamlessly emulate processes running
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# inside docker containers.
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set -ex
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# show pre-existing qemu registration
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cat /proc/sys/fs/binfmt_misc/qemu-aarch64
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# Kokoro ubuntu1604 workers have already qemu-user and qemu-user-static packages installed, but it's and old version that:
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# * prints warning about some syscalls (e.g "qemu: Unsupported syscall: 278")
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# * doesn't register with binfmt_misc with the persistent ("F") flag we need (see below)
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#
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# To overcome the above limitations, we use the https://github.com/multiarch/qemu-user-static
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# docker image to provide a new enough version of qemu-user-static and register it with
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# the desired binfmt_misc flags. The most important flag we need is "F" (set by "--persistent yes"),
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# which allows the qemu-aarch64-static binary to be loaded eagerly at the time of registration with binfmt_misc.
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# That way, we can emulate aarch64 binaries running inside docker containers transparently, without needing the emulator
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# binary to be accessible from the docker image we're emulating.
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# Note that on newer distributions (such as glinux), simply "apt install qemu-user-static" is sufficient
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# to install qemu-user-static with the right flags.
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docker run --rm --privileged multiarch/qemu-user-static:5.2.0-2 --reset --credential yes --persistent yes
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# Print current qemu reqistration to make sure everything is setup correctly.
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cat /proc/sys/fs/binfmt_misc/qemu-aarch64
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