Add python3.8 aarch64 wheel distribtest (#26136)

* add python3.8 aarch64 distribtest

* register qemu emulator for linux distribtests

test/distrib/python/distribtest.py

@@ -18,4 +18,4 @@ import grpc
 # which is what we are testing here.
 channel = grpc.insecure_channel('localhost:1000')
 del channel
-print 'Success!'
+print('Success!')

tools/dockerfile/distribtest/python_python38_buster_aarch64/Dockerfile

@@ -0,0 +1,18 @@
+# Copyright 2021 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# this an aarch64 image, qemu emulator will be used to run the tests
+FROM arm64v8/python:3.8-buster
+
+RUN pip install virtualenv

tools/internal_ci/helper_scripts/prepare_qemu_rc

@@ -0,0 +1,37 @@
+#!/bin/bash
+# Copyright 2021 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Source this rc script to setup and configure qemu userspace emulator on kokoro worker so that we can seamlessly emulate processes running
+# inside docker containers.
+
+# show pre-existing qemu registration
+cat /proc/sys/fs/binfmt_misc/qemu-aarch64
+
+# Kokoro ubuntu1604 workers have already qemu-user and qemu-user-static packages installed, but it's and old version that:
+# * prints warning about some syscalls (e.g "qemu: Unsupported syscall: 278")
+# * doesn't register with binfmt_misc with the persistent ("F") flag we need (see below)
+#
+# To overcome the above limitations, we use the https://github.com/multiarch/qemu-user-static
+# docker image to provide a new enough version of qemu-user-static and register it with
+# the desired binfmt_misc flags. The most important flag we need is "F" (set by "--persistent yes"),
+# which allows the qemu-aarch64-static binary to be loaded eagerly at the time of registration with binfmt_misc.
+# That way, we can emulate aarch64 binaries running inside docker containers transparently, without needing the emulator
+# binary to be accessible from the docker image we're emulating.
+# Note that on newer distributions (such as glinux), simply "apt install qemu-user-static" is sufficient
+# to install qemu-user-static with the right flags.
+docker run --rm --privileged multiarch/qemu-user-static:5.2.0-2 --reset --credential yes --persistent yes
+
+# Print current qemu reqistration to make sure everything is setup correctly.
+cat /proc/sys/fs/binfmt_misc/qemu-aarch64

tools/internal_ci/linux/grpc_distribtests.sh

@@ -20,6 +20,11 @@ cd $(dirname $0)/../../..
 
 source tools/internal_ci/helper_scripts/prepare_build_linux_rc
 
+# some distribtests use a pre-registered binfmt_misc hook
+# to automatically execute foreign binaries (such as aarch64)
+# under qemu emulator.
+source tools/internal_ci/helper_scripts/prepare_qemu_rc
+
 set +ex
 [[ -s /etc/profile.d/rvm.sh ]] && . /etc/profile.d/rvm.sh
 set -e  # rvm commands are very verbose

tools/run_tests/artifacts/distribtest_targets.py

@@ -353,6 +353,7 @@ def targets():
         PythonDistribTest('linux', 'x64', 'arch'),
         PythonDistribTest('linux', 'x64', 'ubuntu1604'),
         PythonDistribTest('linux', 'x64', 'ubuntu1804'),
+        PythonDistribTest('linux', 'aarch64', 'python38_buster'),
         PythonDistribTest('linux', 'x64', 'alpine3.7', source=True),
         PythonDistribTest('linux', 'x64', 'jessie', source=True),
         PythonDistribTest('linux', 'x86', 'jessie', source=True),