Add an rpi4ub-armv8 build variant

doc/BUILDING.rst

@@ -213,6 +213,27 @@ The path of the system tree can be overridden from the default values defined in
    cd ../STT/native_client
    make TARGET=<system> stt
 
+RPi4 ARMv8 (Ubuntu 21.10)
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+We support cross-compilation from Linux hosts. The following ``--config`` flags can be specified when building with bazel:
+
+* ``--config=rpi4ub-armv8_opt`` for Ubuntu / ARM64
+
+Your command line should look like:
+
+.. code-block::
+
+   bazel build --workspace_status_command="bash native_client/bazel_workspace_status_cmd.sh" -c opt --config=rpi4ub-armv8_opt //native_client:libstt.so
+
+The ``stt`` binary can also be cross-built, with ``TARGET=rpi4ub-armv8``. This might require you to setup a system tree using the tool ``multistrap`` and the multistrap configuration file: ``native_client/multistrap-ubuntu64-impish.conf``.
+The path of the system tree can be overridden from the default values defined in ``definitions.mk`` through the ``RASPBIAN`` ``make`` variable.
+
+.. code-block::
+
+   cd ../STT/native_client
+   make TARGET=rpi4ub-armv8 stt
+
 Building ``libstt.so`` for Android
 ----------------------------------
 

native_client/BUILD

@@ -19,6 +19,13 @@ config_setting(
     },
 )
 
+config_setting(
+    name = "rpi4ub-armv8",
+    define_values = {
+        "target_system": "rpi4ub-armv8"
+    },
+)
+
 genrule(
     name = "workspace_status",
     outs = ["workspace_status.cc"],

native_client/definitions.mk

@@ -112,6 +112,28 @@ NODE_PLATFORM_TARGET := --target_arch=arm64 --target_platform=linux
 TOOLCHAIN_LDD_OPTS   := --root $(RASPBIAN)/
 endif # ($(TARGET),rpi3-armv8)
 
+# Custom: RPi 4, Ubuntu 21.10, Arm v8 (64-bit)
+ifeq ($(TARGET),rpi4ub-armv8)
+TOOLCHAIN_DIR ?= ${TFDIR}/bazel-$(shell basename "${TFDIR}")/external/LinaroAarch64Gcc72/bin
+TOOLCHAIN   ?= $(TOOLCHAIN_DIR)/aarch64-linux-gnu-
+RASPBIAN    ?= $(abspath $(NC_DIR)/../multistrap-ubuntu64-impish)
+CFLAGS      := -march=armv8-a -mtune=cortex-a72 -D_GLIBCXX_USE_CXX11_ABI=0 --sysroot $(RASPBIAN)
+CXXFLAGS    := $(CFLAGS)
+LDFLAGS     := -Wl,-rpath-link,$(RASPBIAN)/lib/aarch64-linux-gnu/ -Wl,-rpath-link,$(RASPBIAN)/usr/lib/aarch64-linux-gnu/
+
+SOX_CFLAGS  := -I$(RASPBIAN)/usr/include
+SOX_LDFLAGS := $(RASPBIAN)/usr/lib/aarch64-linux-gnu/libsox.so
+
+PYVER := $(shell python -c "import platform; maj, min, _ = platform.python_version_tuple(); print(maj+'.'+min);")
+PYTHON_PACKAGES      :=
+PYTHON_PATH          := PYTHONPATH=$(RASPBIAN)/usr/lib/python$(PYVER)/:$(RASPBIAN)/usr/lib/python3/dist-packages/
+PYTHON_SYSCONFIGDATA := _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata_m_linux_aarch64-linux-gnu
+NUMPY_INCLUDE        := NUMPY_INCLUDE=$(RASPBIAN)/usr/include/python3.9/
+PYTHON_PLATFORM_NAME := --plat-name linux_aarch64
+NODE_PLATFORM_TARGET := --target_arch=arm64 --target_platform=linux
+TOOLCHAIN_LDD_OPTS   := --root $(RASPBIAN)/
+endif # ($(TARGET),rpi4ub-armv8)
+
 ifeq ($(TARGET),ios-simulator)
 CFLAGS          := -isysroot $(shell xcrun -sdk iphonesimulator13.5 -show-sdk-path)
 SOX_CFLAGS      :=

native_client/multistrap_ubuntu64_impish.conf

@@ -0,0 +1,14 @@
+[General]
+arch=arm64
+noauth=false
+unpack=true
+debootstrap=Debian
+aptsources=Debian
+cleanup=true
+
+[Debian]
+packages=apt libc6 libc6-dev libstdc++-7-dev linux-libc-dev libffi-dev libpython3.9-dev libsox-dev python3-numpy python3-setuptools
+source=http://ports.ubuntu.com/ubuntu-ports
+keyring=ubuntu-keyring
+components=main universe
+suite=impish