enable crosscompiling aarch64 python wheels under dockcross manylinux…

… docker image

kokoro/release/python/linux/build_artifacts.sh

@@ -49,9 +49,23 @@ build_artifact_version() {
   sudo rm -rf $REPO_DIR
 }
 
+build_crosscompiled_aarch64_artifact_version() {
+  # crosscompilation is only supported with the dockcross manylinux2014 image
+  DOCKER_IMAGE=dockcross/manylinux2014-aarch64
+  PLAT=aarch64
+
+  # TODO(jtatermusch): currently when crosscompiling, "auditwheel repair" will be disabled
+  # since auditwheel doesn't work for crosscomiled wheels.
+  build_artifact_version $@
+}
+
 build_artifact_version 2.7
 build_artifact_version 3.5
 build_artifact_version 3.6
 build_artifact_version 3.7
 build_artifact_version 3.8
 build_artifact_version 3.9
+
+build_crosscompiled_aarch64_artifact_version 3.7
+build_crosscompiled_aarch64_artifact_version 3.8
+build_crosscompiled_aarch64_artifact_version 3.9

kokoro/release/python/linux/config.sh

@@ -6,15 +6,38 @@ function pre_build {
     # Runs in the root directory of this repository.
     pushd protobuf
 
-    yum install -y devtoolset-2-libatomic-devel
+    if [ "$PLAT" == "aarch64" ]
+    then
+      local configure_host_flag="--host=aarch64"
+    else
+      yum install -y devtoolset-2-libatomic-devel
+    fi
 
-    # Build protoc
+    # Build protoc and libprotobuf
     ./autogen.sh
-    ./configure
-
-    CXXFLAGS="-fPIC -g -O2" ./configure
+    CXXFLAGS="-fPIC -g -O2" ./configure $configure_host_flag
     make -j8
 
+    if [ "$PLAT" == "aarch64" ]
+    then
+      # we are crosscompiling for aarch64 while running on x64
+      # the simplest way for build_py command to be able to generate
+      # the protos is by running the protoc process under
+      # an emulator. That way we don't have to build a x64 version
+      # of protoc. The qemu-arm emulator is already included
+      # in the dockcross docker image.
+      # Running protoc under an emulator is fast as protoc doesn't
+      # really do much.
+
+      # create a simple shell wrapper that runs crosscompiled protoc under qemu
+      echo '#!/bin/bash' >protoc_qemu_wrapper.sh
+      echo 'exec qemu-aarch64 "../src/protoc" "$@"' >>protoc_qemu_wrapper.sh
+      chmod ugo+x protoc_qemu_wrapper.sh
+
+      # PROTOC variable is by build_py step that runs under ./python directory
+      export PROTOC=../protoc_qemu_wrapper.sh
+    fi
+
     # Generate python dependencies.
     pushd python
     python setup.py build_py
@@ -35,7 +58,20 @@ function bdist_wheel_cmd {
     # Modify build version
     pwd
     ls
-    python setup.py bdist_wheel --cpp_implementation --compile_static_extension
+
+    if [ "$PLAT" == "aarch64" ]
+    then
+      # when crosscompiling for aarch64, --plat-name needs to be set explicitly
+      # to end up with correctly named wheel file
+      # the value should be manylinuxABC_ARCH and dockcross docker image
+      # conveniently provides the value in the AUDITWHEEL_PLAT env
+      local plat_name_flag="--plat-name=$AUDITWHEEL_PLAT"
+
+      # override the value of EXT_SUFFIX to make sure the crosscompiled .so files in the wheel have the correct filename suffix
+      export PROTOCOL_BUFFERS_OVERRIDE_EXT_SUFFIX="$(python -c 'import sysconfig; print(sysconfig.get_config_var("EXT_SUFFIX").replace("-x86_64-linux-gnu.so", "-aarch64-linux-gnu.so"))')"
+    fi
+
+    python setup.py bdist_wheel --cpp_implementation --compile_static_extension $plat_name_flag
     cp dist/*.whl $abs_wheelhouse
 }
 
@@ -48,3 +84,12 @@ function run_tests {
     python --version
     python -c "from google.protobuf.pyext import _message;"
 }
+
+if [ "$PLAT" == "aarch64" ]
+then
+  # when crosscompiling for aarch64, override the default multibuild's repair_wheelhouse logic
+  # since "auditwheel repair" doesn't work for crosscompiled wheels
+  function repair_wheelhouse {
+      echo "Skipping repair_wheelhouse since auditwheel requires build architecture to match wheel architecture."
+  }
+fi

python/setup.py

@@ -18,6 +18,7 @@
 
 from distutils.command.build_py import build_py as _build_py
 from distutils.command.clean import clean as _clean
+from distutils.command.build_ext import build_ext as _build_ext
 from distutils.spawn import find_executable
 
 # Find the Protocol Compiler.
@@ -157,6 +158,22 @@ def find_package_modules(self, package, package_dir):
             if not any(fnmatch.fnmatchcase(fil, pat=pat) for pat in exclude)]
 
 
+class build_ext(_build_ext):
+  def get_ext_filename(self, ext_name):
+      # since python3.5, python extensions' shared libraries use a suffix that corresponds to the value
+      # of sysconfig.get_config_var('EXT_SUFFIX') and contains info about the architecture the library targets.
+      # E.g. on x64 linux the suffix is ".cpython-XYZ-x86_64-linux-gnu.so"
+      # When crosscompiling python wheels, we need to be able to override this suffix
+      # so that the resulting file name matches the target architecture and we end up with a well-formed
+      # wheel.
+      filename = _build_ext.get_ext_filename(self, ext_name)
+      orig_ext_suffix = sysconfig.get_config_var("EXT_SUFFIX")
+      new_ext_suffix = os.getenv("PROTOCOL_BUFFERS_OVERRIDE_EXT_SUFFIX")
+      if new_ext_suffix and filename.endswith(orig_ext_suffix):
+        filename = filename[:-len(orig_ext_suffix)] + new_ext_suffix
+      return filename
+
+
 class test_conformance(_build_py):
   target = 'test_python'
   def run(self):
@@ -291,6 +308,7 @@ def get_option_from_sys_argv(option_str):
       cmdclass={
           'clean': clean,
           'build_py': build_py,
+          'build_ext': build_ext,
           'test_conformance': test_conformance,
       },
       install_requires=install_requires,