Arm backend: Add build support aarch64-linux-musl

Add support for aarch64-linux-musl as a toolchain in setup.sh and
building the executor_runner as a Linux binary used for direct drive.

To download the toolchain and setup the development environment:
examples/arm/setup.sh \
--i-agree-to-the-contained-eula \
--target-toolchain linux-musl

To build the binary:
backends/arm/scripts/build_executorch.sh \
--toolchain=aarch64-linux-musl-gcc --build_type=Debug

Signed-off-by: Per Held <per.held@arm.com>
Change-Id: If0335b41754be598647dfef08bf23aae1a72409f

Author: perheld

CMakePresets.json

@@ -285,6 +285,20 @@
         "EXECUTORCH_BUILD_PRESET_FILE": "${sourceDir}/tools/cmake/preset/arm_baremetal.cmake",
         "CMAKE_TOOLCHAIN_FILE": "${sourceDir}/examples/arm/ethos-u-setup/arm-none-eabi-gcc.cmake"
       }
+    },
+    {
+      "name": "arm-ethosu-linux",
+      "displayName": "Build ExecuTorch for Arm Ethos-U Linux",
+      "inherits": ["common"],
+      "cacheVariables": {
+        "EXECUTORCH_BUILD_ARM_ETHOSU_LINUX": "ON",
+        "EXECUTORCH_BUILD_EXECUTOR_RUNNER": "ON",
+        "EXECUTORCH_BUILD_KERNELS_QUANTIZED": "ON",
+        "CMAKE_C_FLAGS_RELEASE": "-UNDEBUG",
+        "CMAKE_CXX_FLAGS_RELEASE": "-UNDEBUG",
+        "_comment": "musl declares __assert_fail with int for line; avoid NDEBUG forward-decl mismatch in Release builds",
+        "CMAKE_TOOLCHAIN_FILE": "${sourceDir}/examples/arm/ethos-u-setup/aarch64-linux-musl-toolchain.cmake"
+      }
     }
   ],
   "buildPresets": [

backends/arm/runtime/EthosUBackend_Cortex_A.cpp

@@ -150,7 +150,12 @@ EthosULinuxDeviceCache& get_linux_device_cache() {
   return cache;
 }
 
-const char* inference_status_to_string(EthosU::InferenceStatus status) {
+/*
+ * Used for logging when building in Debug mode, but unused building
+ * for Release.
+ */
+[[maybe_unused]] const char* inference_status_to_string(
+    EthosU::InferenceStatus status) {
   switch (status) {
     case EthosU::InferenceStatus::OK:
       return "OK";
@@ -288,11 +293,10 @@ Error invoke_linux_driver(
 
     if (options.enable_cycle_counter) {
       try {
-        uint64_t cycles = inference->getCycleCounter();
         ET_LOG(
             Info,
             "Ethos-U Linux delegate cycle counter: %llu",
-            static_cast<unsigned long long>(cycles));
+            static_cast<unsigned long long>(inference->getCycleCounter()));
       } catch (const std::exception& e) {
         ET_LOG(Debug, "Failed to read Ethos-U cycle counter: %s", e.what());
       }

backends/arm/scripts/build_executor_runner.sh

@@ -50,7 +50,7 @@ help() {
     echo "  --output=<FOLDER>                    Output folder Default: <MODEL>/<MODEL>_<TARGET INFO>.pte"
     echo "  --et_build_root=<FOLDER>             Build output root folder to use, defaults to ${et_build_root}"
     echo "  --ethosu_tools_dir=<FOLDER>          Path to your Ethos-U tools dir if you not using default: ${ethosu_tools_dir}"
-    echo "  --toolchain=<TOOLCHAIN>              Toolchain can be specified (e.g. bare metal as arm-none-eabi-gcc or zephyr as arm-zephyr-eabi-gcc Default: ${toolchain}"
+    echo "  --toolchain=<TOOLCHAIN>              Toolchain can be specified (arm-none-eabi-gcc, arm-zephyr-eabi-gcc). Default: ${toolchain}"
     echo "  --select_ops_list=<OPS>              Comma separated list of portable (non delagated) kernels to include Default: ${select_ops_list}"
     echo "                                         NOTE: This is used when select_ops_model is not possible to use, e.g. for semihosting or bundleio."
     echo "                                         See https://docs.pytorch.org/executorch/stable/kernel-library-selective-build.html for more information."
@@ -82,6 +82,11 @@ if [[ ${toolchain} == "arm-none-eabi-gcc" ]]; then
     toolchain_cmake=${et_root_dir}/examples/arm/ethos-u-setup/${toolchain}.cmake
 elif [[ ${toolchain} == "arm-zephyr-eabi-gcc" ]]; then
     toolchain_cmake=${et_root_dir}/examples/zephyr/x86_64-linux-arm-zephyr-eabi-gcc.cmake
+elif [[ ${toolchain} == "aarch64-linux-musl-gcc" ]]; then
+    echo "Error: aarch64-linux-musl-gcc is not supported for this bare-metal runner."
+    echo "       Use executorch/backends/arm/scripts/build_executorch.sh with aarch64-linux-musl-gcc"
+    echo "       or run the direct drive CMake flow to build executor_runner for Linux."
+    exit 1;
 else
     echo "Error: Invalid toolchain selection, provided: ${toolchain}"
     echo "    Valid options are {arm-none-eabi-gcc, arm-zephyr-eabi-gcc}"

backends/arm/scripts/build_executorch.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Copyright 2025 Arm Limited and/or its affiliates.
+# Copyright 2025-2026 Arm Limited and/or its affiliates.
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
@@ -23,6 +23,7 @@ et_build_root="${et_root_dir}/arm_test"
 build_type="Release"
 build_devtools=OFF
 build_with_etdump=OFF
+is_linux_musl=0
 
 help() {
     echo "Usage: $(basename $0) [options]"
@@ -31,7 +32,7 @@ help() {
     echo "  --build_type=<TYPE>       Build with Release, Debug, RelWithDebInfo, UndefinedSanitizer or AddressSanitizer, default is ${build_type}"
     echo "  --devtools                Build Devtools libs"
     echo "  --etdump                  Adds Devtools etdump support to track timing, etdump area will be base64 encoded in the log"
-    echo "  --toolchain=<TOOLCHAIN>   Toolchain can be specified (e.g. bare metal as arm-none-eabi-gcc or zephyr as arm-zephyr-eabi-gcc Default: ${toolchain}"
+    echo "  --toolchain=<TOOLCHAIN>   Toolchain can be specified (arm-none-eabi-gcc, arm-zephyr-eabi-gcc, aarch64-linux-musl-gcc). Default: ${toolchain}"
     exit 0
 }
 
@@ -52,9 +53,12 @@ if [[ ${toolchain} == "arm-none-eabi-gcc" ]]; then
     toolchain_cmake=${et_root_dir}/examples/arm/ethos-u-setup/${toolchain}.cmake
 elif [[ ${toolchain} == "arm-zephyr-eabi-gcc" ]]; then
     toolchain_cmake=${et_root_dir}/examples/zephyr/x86_64-linux-arm-zephyr-eabi-gcc.cmake
+elif [[ ${toolchain} == "aarch64-linux-musl-gcc" ]]; then
+    toolchain_cmake=${et_root_dir}/examples/arm/ethos-u-setup/aarch64-linux-musl-toolchain.cmake
+    is_linux_musl=1
 else
     echo "Error: Invalid toolchain selection, provided: ${toolchain}"
-    echo "    Valid options are {arm-none-eabi-gcc, arm-zephyr-eabi-gcc}"
+    echo "    Valid options are {arm-none-eabi-gcc, arm-zephyr-eabi-gcc, aarch64-linux-musl-gcc}"
     exit 1;
 fi
 toolchain_cmake=$(realpath ${toolchain_cmake})
@@ -76,18 +80,40 @@ cd "${et_root_dir}"
     echo "Build ExecuTorch target libs ${build_type} into '${et_build_dir}'" ;
     echo "--------------------------------------------------------------------------------" )
 
-# Build
-cmake -DCMAKE_TOOLCHAIN_FILE=${toolchain_cmake} \
--DCMAKE_BUILD_TYPE=${build_type} \
--DEXECUTORCH_BUILD_DEVTOOLS=$build_devtools \
--DEXECUTORCH_BUILD_ARM_ETDUMP=$build_with_etdump \
---preset arm-baremetal -B${et_build_dir}
+cmake_args=(
+    -DCMAKE_TOOLCHAIN_FILE=${toolchain_cmake}
+    -DCMAKE_BUILD_TYPE=${build_type}
+    -DEXECUTORCH_BUILD_DEVTOOLS=${build_devtools}
+    -DEXECUTORCH_BUILD_ARM_ETDUMP=${build_with_etdump}
+)
+
+if [[ ${is_linux_musl} -eq 1 ]]; then
+    if [[ -z "${MUSL_TOOLCHAIN_ROOT:-}" ]]; then
+        echo "Error: MUSL_TOOLCHAIN_ROOT is required for aarch64-linux-musl-gcc."
+        echo "       Source ${setup_path_script} after running examples/arm/setup.sh --target-toolchain linux-musl."
+        exit 1
+    fi
+    cmake -S "${et_root_dir}" -B "${et_build_dir}" \
+        "${cmake_args[@]}" \
+        --preset arm-ethosu-linux \
+        -DPYTHON_EXECUTABLE=$(which python3)
+else
+    cmake "${cmake_args[@]}" --preset arm-baremetal -B${et_build_dir}
+fi
 
 parallel_jobs="$(get_parallel_jobs)"
 
-cmake --build ${et_build_dir} -j"${parallel_jobs}" --target install --config ${build_type} --
+if [[ ${is_linux_musl} -eq 1 ]]; then
+    cmake --build ${et_build_dir} -j"${parallel_jobs}" --target executorch_delegate_ethos_u executor_runner --config ${build_type} --
+else
+    cmake --build ${et_build_dir} -j"${parallel_jobs}" --target install --config ${build_type} --
+fi
 
 set +x
 
-echo "[$(basename $0)] Generated static libraries for ExecuTorch:"
-find ${et_build_dir} -name "*.a" -exec ls -al {} \;
+if [[ ${is_linux_musl} -eq 1 ]]; then
+    echo "[$(basename $0)] Built ExecuTorch targets in ${et_build_dir}"
+else
+    echo "[$(basename $0)] Generated static libraries for ExecuTorch:"
+    find ${et_build_dir} -name "*.a" -exec ls -al {} \;
+fi

backends/arm/scripts/toolchain_utils.sh

@@ -25,15 +25,18 @@ function gcc_select_toolchain() {
         toolchain_url="https://armkeil.blob.core.windows.net/developer/Files/downloads/gnu/13.3.rel1/binrel/arm-gnu-toolchain-13.3.rel1-x86_64-arm-none-eabi.tar.xz"
         toolchain_dir="arm-gnu-toolchain-13.3.rel1-x86_64-arm-none-eabi"
         toolchain_md5_checksum="0601a9588bc5b9c99ad2b56133b7f118"
+        toolchain_archive="${toolchain_dir}.tar.xz"
     elif [[ "${ARCH}" == "aarch64" ]] || [[ "${ARCH}" == "arm64" ]] ; then
         if [[ "${OS}" == "Darwin" ]]; then
             toolchain_url="https://armkeil.blob.core.windows.net/developer/Files/downloads/gnu/13.3.rel1/binrel/arm-gnu-toolchain-13.3.rel1-darwin-arm64-arm-none-eabi.tar.xz"
             toolchain_dir="arm-gnu-toolchain-13.3.rel1-darwin-arm64-arm-none-eabi"
             toolchain_md5_checksum="f1c18320bb3121fa89dca11399273f4e"
+            toolchain_archive="${toolchain_dir}.tar.xz"
         elif [[ "${OS}" == "Linux" ]]; then
             toolchain_url="https://armkeil.blob.core.windows.net/developer/Files/downloads/gnu/13.3.rel1/binrel/arm-gnu-toolchain-13.3.rel1-aarch64-arm-none-eabi.tar.xz"
             toolchain_dir="arm-gnu-toolchain-13.3.rel1-aarch64-arm-none-eabi"
             toolchain_md5_checksum="303102d97b877ebbeb36b3158994b218"
+            toolchain_archive="${toolchain_dir}.tar.xz"
         fi
     else
         # This should never happen, it should be covered by setup.sh but catch it anyway
@@ -52,20 +55,41 @@ function zephyr_select_toolchain() {
         toolchain_url="https://github.com/zephyrproject-rtos/sdk-ng/releases/download/v0.17.4/toolchain_linux-x86_64_arm-zephyr-eabi.tar.xz"
         toolchain_dir="arm-zephyr-eabi"
         toolchain_md5_checksum="68ae71edc0106c3093055b97aaa47017"
+        toolchain_archive="${toolchain_dir}.tar.xz"
     elif [[ "${ARCH}" == "aarch64" ]] || [[ "${ARCH}" == "arm64" ]] ; then
         toolchain_url="https://github.com/zephyrproject-rtos/sdk-ng/releases/download/v0.17.4/toolchain_linux-aarch64_arm-zephyr-eabi.tar.xz"
         toolchain_dir="arm-zephyr-eabi"
         toolchain_md5_checksum="d8a6dfd4314d55da713957d0b161d01f"
+        toolchain_archive="${toolchain_dir}.tar.xz"
     else
         # This should never happen, it should be covered by setup.sh but catch it anyway
         log_step "toolchain" "Error: Unsupported architecture ${ARCH}"
         exit 1
     fi
 }
 
+function musl_select_toolchain() {
+    if [[ "${OS}" != "Linux" ]] ; then
+        log_step "toolchain" "Error: Linux is required for musl toolchain support"
+        exit 1
+    fi
+
+    if [[ "${ARCH}" == "x86_64" ]] ; then
+        toolchain_url="https://musl.cc/aarch64-linux-musl-cross.tgz"
+        toolchain_dir="aarch64-linux-musl-cross"
+        toolchain_md5_checksum="a6bb806af217a91cf575e15163e8b12b"
+        toolchain_archive="${toolchain_dir}.tgz"
+    else
+        log_step "toolchain" "Error: Unsupported architecture ${ARCH} for musl toolchain"
+        exit 1
+    fi
+}
+
 function select_toolchain() {
     if [[ "${target_toolchain}" == "zephyr" ]]; then
         zephyr_select_toolchain
+    elif [[ "${target_toolchain}" == "linux-musl" ]]; then
+        musl_select_toolchain
     else
         gcc_select_toolchain
     fi
@@ -76,18 +100,28 @@ function setup_toolchain() {
     # Download and install the arm toolchain (default is arm-none-eabi)
     # setting --target-toolchain to zephyr sets this to arm-zephyr-eabi
     cd "${root_dir}"
-    if [[ ! -e "${toolchain_dir}.tar.xz" ]]; then
+    if [[ -z "${toolchain_archive}" ]]; then
+        log_step "toolchain" "Error: Toolchain archive not set"
+        exit 1
+    fi
+
+    if [[ ! -e "${toolchain_archive}" ]]; then
         log_step "toolchain" "Downloading ${toolchain_dir} toolchain"
-        curl --output "${toolchain_dir}.tar.xz" -L "${toolchain_url}"
-        verify_md5 ${toolchain_md5_checksum} "${toolchain_dir}.tar.xz" || exit 1
+        curl --output "${toolchain_archive}" -L "${toolchain_url}"
+        verify_md5 ${toolchain_md5_checksum} "${toolchain_archive}" || exit 1
     fi
 
     log_step "toolchain" "Installing ${toolchain_dir} toolchain"
     rm -rf "${toolchain_dir}"
-    tar xf "${toolchain_dir}.tar.xz"
+    tar xf "${toolchain_archive}"
 }
 
 function setup_path_toolchain() {
     toolchain_bin_path="$(cd ${toolchain_dir}/bin && pwd)"
     append_env_in_setup_path PATH ${toolchain_bin_path}
+
+    if [[ "${target_toolchain}" == "linux-musl" ]]; then
+        local toolchain_root_path="$(cd ${toolchain_dir} && pwd)"
+        set_env_in_setup_path MUSL_TOOLCHAIN_ROOT ${toolchain_root_path}
+    fi
 }

backends/arm/scripts/utils.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Copyright 2025 Arm Limited and/or its affiliates.
+# Copyright 2025-2026 Arm Limited and/or its affiliates.
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
@@ -138,6 +138,11 @@ function append_env_in_setup_path() {
     echo "set --path -agx $1 $2" >> ${setup_path_script}.fish
 }
 
+function set_env_in_setup_path() {
+    echo "export $1=$2" >> ${setup_path_script}.sh
+    echo "set -gx $1 $2" >> ${setup_path_script}.fish
+}
+
 function clear_setup_path() {
     # Clear setup_path_script
     echo "" > "${setup_path_script}.sh"

examples/arm/setup.sh

@@ -35,6 +35,7 @@ enable_mlsdk_pip_install=1
 toolchain_url=""
 toolchain_dir=""
 toolchain_md5_checksum=""
+toolchain_archive=""
 
 # Load logging helpers early so option parsing can emit status messages.
 source "$et_dir/backends/arm/scripts/utils.sh"
@@ -45,6 +46,7 @@ OPTION_LIST=(
   "--i-agree-to-the-contained-eula (required) Agree to the EULA"
   "--root-dir Path to scratch directory"
   "--enable-baremetal-toolchain Enable baremetal toolchain setup"
+  "--target-toolchain Select toolchain: gnu (default), zephyr, or linux-musl"
   "--enable-fvps Enable FVP setup"
   "--enable-vela Enable VELA setup"
   "--enable-model-converter Enable MLSDK model converter setup"