Tighten the generated ESP-IDF component's sources and warnings

The generator vendored kernel util sources from KERNELS_UTIL_ALL_DEPS_SRCS,
which lacks stack_util.cpp and grid_sampler_2d_util.cpp, so a profile with
aten::stack.out failed to link with an undefined stack_out_impl. Both files are
added to the list, which also fixes CMake's selected_kernels_util_all_deps
library built from it, and the generator now globs the util directory so the
next new util file cannot go missing.

flatcc was vendored and compiled, but nothing in the component includes it, so
it is no longer shipped. Only internal headers (tensor_parser.h and the
generated schema headers) include flatbuffers, so it moves to priv_include,
out of consumers' include paths where it could collide with another
component's copy; FLATBUFFERS_MAX_ALIGNMENT becomes private with it.

The blanket per-source -Wno-error hid every warning class. With the log format
sites fixed in the previous commit, the vendored sources build clean under
ESP-IDF's -Werror for ESP32-S3 and ESP32-C6, so only deprecation warnings,
from ExecuTorch's own deprecated aliases, stay disabled. ET_OPTIMIZE_SIZE now
defaults to y, since -Os on the runtime saves about 72 KB of code in an -O2
application. It costs speed (the ESP32-S3 smoke model went from 7.4 to 10.9 ms
per frame), which the Kconfig help now says.

Newlib's nano printf (CONFIG_LIBC_NEWLIB_NANO_FORMAT) has no 64-bit integer
formats, and ExecuTorch's error messages print about 80 of them, so with it a
logged failure misprints or crashes the app. The component now compiles
ExecuTorch logging out under nano formatting and prints a CMake warning saying
so; CI checks the warning. Picolibc, ESP-IDF's default, and full newlib format
them correctly on Xtensa and RISC-V.

Authored with Claude Code.

Author: rascani

.ci/scripts/test_espressif_idf_component.sh

@@ -45,6 +45,22 @@ bash examples/espressif/build_idf_component.sh --profiles "${profiles}" \
     --out "${component_dir}" 2>&1 | tee "${build_dir}/generate.log"
 
 project=examples/espressif/idf_component_smoke
+
+# With newlib's nano printf, the component compiles ExecuTorch logging out and
+# says so.
+printf 'CONFIG_LIBC_NEWLIB=y\nCONFIG_LIBC_NEWLIB_NANO_FORMAT=y\n' > "${build_dir}/nano.defaults"
+idf.py -C "${project}" -B "${build_dir}/firmware-nano" -DIDF_TARGET=esp32s3 \
+    -DSDKCONFIG="${build_dir}/sdkconfig-nano" \
+    "-DSDKCONFIG_DEFAULTS=sdkconfig.defaults;${build_dir}/nano.defaults" \
+    -DET_COMPONENT_DIR="${component_dir}" -DET_SMOKE_PTE="${build_dir}/smoke.pte" \
+    reconfigure > "${build_dir}/firmware-nano.log" 2>&1
+# CMake wraps long messages, so match with whitespace runs collapsed.
+if ! tr -s ' \n' '  ' < "${build_dir}/firmware-nano.log" \
+    | grep -qF "ExecuTorch logging is DISABLED"; then
+    echo "FAIL: no nano printf warning; see ${build_dir}/firmware-nano.log" >&2
+    exit 1
+fi
+
 for profile in ${profiles//,/ }; do
     profile_upper=$(echo "${profile}" | tr '[:lower:]-' '[:upper:]_')
     firmware_dir="${build_dir}/firmware-${profile}"

examples/espressif/build_idf_component.sh

@@ -25,13 +25,14 @@
 #
 # Host requirements: python3 with ExecuTorch + torchgen importable (for
 # kernel codegen), cmake (to build flatc from third-party/flatbuffers
-# when no flatc is available), and git submodules third-party/flatcc +
+# when no flatc is available), and the git submodule
 # third-party/flatbuffers initialized. Consumers of the output need
 # only ESP-IDF. Set PYTHON=... / FLATC=... to override discovery.
 #
 # NOTE: This script is coupled to the ExecuTorch source tree layout, but
-# its source file lists come from the same build_variables.bzl the
-# CMake build uses, so upstream file moves are picked up automatically.
+# its runtime source lists come from the same build_variables.bzl the
+# CMake build uses and kernel util sources are globbed, so upstream file
+# moves are picked up automatically.
 # Consumer builds for Xtensa + RISC-V targets are the safety net.
 
 set -euo pipefail
@@ -106,12 +107,10 @@ if [[ ! "$ET_VERSION" =~ ^(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$ ]];
 fi
 ET_COMPONENT_VERSION="${ET_VERSION}~${PACKAGING_REV}"
 
-for dep in flatbuffers flatcc; do
-  if [ ! -f "$ET_ROOT/third-party/$dep/LICENSE" ]; then
-    echo "ERROR: third-party/$dep is empty. Run: git submodule update --init third-party/$dep" >&2
-    exit 1
-  fi
-done
+if [ ! -f "$ET_ROOT/third-party/flatbuffers/LICENSE" ]; then
+  echo "ERROR: third-party/flatbuffers is empty. Run: git submodule update --init third-party/flatbuffers" >&2
+  exit 1
+fi
 
 # Refuse to clobber a directory that is not a previous run's output.
 if [ -d "$OUT_DIR" ] && [ -n "$(ls -A "$OUT_DIR" 2>/dev/null)" ] \
@@ -473,26 +472,29 @@ echo "[2/6] Kernel registration generated for: ${PROFILES[*]}"
 
 # ─────────────────────────────────────────────────────────
 # 3. Vendor runtime + extension sources (build_variables.bzl
-#    lists) and the union of profile kernel sources.
+#    lists), kernel util sources and the union of profile kernel
+#    sources.
 #    Output mirrors upstream paths under src/executorch/.
 # ─────────────────────────────────────────────────────────
 : > "$SCRATCH/core_srcs.txt"
 
-copy_bzl_list() { # $1=bzl variable name; appends to core_srcs.txt
+copy_srcs() { # ET_ROOT-relative paths on stdin; appends to core_srcs.txt
   local f
-  bzl_list "$1" | while IFS= read -r f; do
+  while IFS= read -r f; do
     if [ ! -f "$ET_ROOT/$f" ]; then
-      echo "ERROR: build_variables.bzl lists missing file: $f" >&2; exit 1
+      echo "ERROR: missing source file: $f" >&2; exit 1
     fi
     mkdir -p "$OUT_DIR/src/executorch/$(dirname "$f")"
     cp "$ET_ROOT/$f" "$OUT_DIR/src/executorch/$f"
     echo "src/executorch/$f" >> "$SCRATCH/core_srcs.txt"
   done
 }
 
-copy_bzl_list EXECUTORCH_CORE_SRCS
-copy_bzl_list EXECUTORCH_SRCS # prim ops
-copy_bzl_list KERNELS_UTIL_ALL_DEPS_SRCS
+bzl_list EXECUTORCH_CORE_SRCS | copy_srcs
+bzl_list EXECUTORCH_SRCS | copy_srcs # prim ops
+# Globbed, so a util source missing from KERNELS_UTIL_ALL_DEPS_SRCS cannot
+# break the link.
+( cd "$ET_ROOT" && printf '%s\n' kernels/portable/cpu/util/*.cpp ) | copy_srcs
 
 # Kernel sources needed by at least one shipped profile.
 : > "$SCRATCH/kernel_srcs_by_profile.txt"
@@ -504,8 +506,8 @@ done < "$SCRATCH/kernel_union/files.txt"
 echo "[3/6] Runtime, extension and kernel sources copied"
 
 # ─────────────────────────────────────────────────────────
-# 4. Vendor headers: executorch/** (public), c10/torch,
-#    flatbuffers, flatcc (+ its C runtime).
+# 4. Vendor headers: executorch/** and c10/torch (public),
+#    flatbuffers (private: only internal headers include it).
 # ─────────────────────────────────────────────────────────
 copy_headers() { # $1=src dir under ET_ROOT, $2=dest under OUT/include
   local src_dir="$1" dest_dir="$2" f
@@ -561,16 +563,9 @@ if [ "$ANY_CADENCE" = true ]; then
   copy_headers backends/cadence/generic executorch/backends/cadence/generic
 fi
 
+mkdir -p "$OUT_DIR/priv_include"
 cp -r "$ET_ROOT/third-party/flatbuffers/include/flatbuffers" \
-      "$OUT_DIR/include/flatbuffers"
-mkdir -p "$OUT_DIR/include/flatcc" "$OUT_DIR/src/flatcc/runtime"
-cp "$ET_ROOT/third-party/flatcc/include/flatcc/"*.h "$OUT_DIR/include/flatcc/"
-cp -r "$ET_ROOT/third-party/flatcc/include/flatcc/portable" \
-      "$OUT_DIR/include/flatcc/"
-cp "$ET_ROOT/third-party/flatcc/src/runtime/"*.c "$OUT_DIR/src/flatcc/runtime/"
-for f in "$OUT_DIR/src/flatcc/runtime/"*.c; do
-  echo "src/flatcc/runtime/$(basename "$f")" >> "$SCRATCH/core_srcs.txt"
-done
+      "$OUT_DIR/priv_include/flatbuffers"
 
 echo "[4/6] Headers and third-party code copied"
 
@@ -588,9 +583,7 @@ cp "$ET_ROOT/LICENSE" "$OUT_DIR/LICENSE"
 
 LICENSES="$OUT_DIR/THIRD_PARTY_LICENSES"
 mkdir -p "$LICENSES"
-for dep in flatbuffers flatcc; do
-  cp "$ET_ROOT/third-party/$dep/LICENSE" "$LICENSES/$dep-LICENSE.txt"
-done
+cp "$ET_ROOT/third-party/flatbuffers/LICENSE" "$LICENSES/flatbuffers-LICENSE.txt"
 cat > "$LICENSES/README.md" <<'NOTICE'
 # Third-party licenses
 
@@ -599,8 +592,7 @@ ExecuTorch's own BSD license is in the LICENSE file at the root.
 
 | Component | Location in this component | License |
 |---|---|---|
-| FlatBuffers (Google) | `include/flatbuffers/` | Apache-2.0 — `flatbuffers-LICENSE.txt` |
-| flatcc (Mikkel F. Jorgensen) | `include/flatcc/`, `src/flatcc/` | Apache-2.0 — `flatcc-LICENSE.txt` |
+| FlatBuffers (Google) | `priv_include/flatbuffers/` | Apache-2.0 — `flatbuffers-LICENSE.txt` |
 | PyTorch c10 (Meta) | `include/c10/`, `include/torch/` | BSD-3-Clause, as exact copies from PyTorch core |
 
 `src/profiles/*/register_kernels.cpp` is generated by ExecuTorch's
@@ -674,7 +666,10 @@ KHEAD
         help
             When disabled, ET_LOG is compiled out entirely
             (ET_LOG_ENABLED=0). When enabled, messages go through
-            ESP_LOG under the "executorch" tag.
+            ESP_LOG under the "executorch" tag. Newlib's nano printf
+            (LIBC_NEWLIB_NANO_FORMAT) cannot format the 64-bit integers
+            in ExecuTorch's error messages, so with it logging is
+            compiled out regardless, with a build warning.
 
     choice ET_LOG_LEVEL
         prompt "ExecuTorch log level floor"
@@ -696,10 +691,11 @@ KHEAD
 
     config ET_OPTIMIZE_SIZE
         bool "Build the runtime with -Os"
-        default n
+        default y
         help
             Optimize the ExecuTorch runtime for size regardless of the
-            project's compiler optimization level.
+            project's compiler optimization level. This trades speed
+            for flash; turn it off when inference time matters more.
 
     config ET_PROGRAM_VERIFICATION
         bool "Compile in full .pte verification"

examples/espressif/idf_component_template/CMakeLists.txt

@@ -56,6 +56,8 @@ idf_component_register(
   "src/platform/esp_pal.cpp"
   INCLUDE_DIRS
   "include"
+  PRIV_INCLUDE_DIRS
+  "priv_include"
   PRIV_REQUIRES
   ${_et_requires}
   WHOLE_ARCHIVE
@@ -81,14 +83,13 @@ else()
   set(_et_program_verification 0)
 endif()
 
-# Consumers including <executorch/...> headers need the same c10 macro mode and
-# flatbuffers alignment the runtime was built with. __FUNCTION__ instead of
-# __builtin_FUNCTION() keeps log function names without full signatures.
+# Consumers including <executorch/...> headers need the same c10 macro mode the
+# runtime was built with. __FUNCTION__ instead of __builtin_FUNCTION() keeps log
+# function names without full signatures.
 target_compile_definitions(
   ${COMPONENT_LIB}
-  PUBLIC C10_USING_CUSTOM_GENERATED_MACROS FLATBUFFERS_MAX_ALIGNMENT=1024
-         ET_USE_BUILTIN_FUNCTION_NAME=0
-  PRIVATE MAX_KERNEL_NUM=${_et_max_kernel_num}
+  PUBLIC C10_USING_CUSTOM_GENERATED_MACROS ET_USE_BUILTIN_FUNCTION_NAME=0
+  PRIVATE FLATBUFFERS_MAX_ALIGNMENT=1024 MAX_KERNEL_NUM=${_et_max_kernel_num}
           ET_ENABLE_PROGRAM_VERIFICATION=${_et_program_verification}
 )
 
@@ -100,7 +101,18 @@ if(CONFIG_ET_OPTIMIZE_SIZE)
   target_compile_options(${COMPONENT_LIB} PRIVATE -Os)
 endif()
 
-if(NOT CONFIG_ET_ENABLE_LOGGING)
+# Newlib's nano printf cannot format 64-bit integers, which ExecuTorch's error
+# messages print, so logging one could crash the app.
+if(CONFIG_ET_ENABLE_LOGGING AND CONFIG_LIBC_NEWLIB_NANO_FORMAT)
+  message(
+    WARNING
+      "ExecuTorch logging is DISABLED: CONFIG_LIBC_NEWLIB_NANO_FORMAT selects "
+      "newlib's nano printf, which cannot format the 64-bit integers in "
+      "ExecuTorch's error messages. Use Picolibc (ESP-IDF's default) or turn "
+      "off nano formatting to keep ExecuTorch logging."
+  )
+endif()
+if(NOT CONFIG_ET_ENABLE_LOGGING OR CONFIG_LIBC_NEWLIB_NANO_FORMAT)
   target_compile_definitions(${COMPONENT_LIB} PUBLIC ET_LOG_ENABLED=0)
 endif()
 
@@ -126,11 +138,8 @@ target_compile_definitions(
   PRIVATE ET_ESP_LOG_LEVEL=${_et_esp_log_level}
 )
 
-# ESP-IDF builds with warnings-as-errors; upstream ExecuTorch sources are not
-# warning-clean under the IDF flag set, so demote for vendored sources only.
+# Vendored ExecuTorch sources use ExecuTorch's own deprecated aliases.
 set_source_files_properties(
-  ${_et_vendored_srcs}
-  PROPERTIES
-    COMPILE_OPTIONS
-    "-Wno-error;-Wno-deprecated-declarations;-Wno-unused-parameter;-Wno-sign-compare;-Wno-unused-variable"
+  ${_et_vendored_srcs} PROPERTIES COMPILE_OPTIONS
+                                  "-Wno-deprecated-declarations"
 )

examples/espressif/idf_component_template/idf_component.yml.in

@@ -3,7 +3,7 @@
 ## GENERATED by examples/espressif/build_idf_component.sh -- do not edit.
 ## Version is "<ExecuTorch release>~<packaging revision>"; see VERSION
 ## in this directory for the exact commit and op-set hashes. Vendored
-## third-party code (FlatBuffers, flatcc: Apache-2.0) is listed in
+## third-party code (FlatBuffers: Apache-2.0) is listed in
 ## THIRD_PARTY_LICENSES. No targets list: the runtime is portable
 ## across ESP targets.
 version: "@ET_COMPONENT_VERSION@"

shim_et/xplat/executorch/build/build_variables.bzl

@@ -251,6 +251,7 @@ KERNELS_UTIL_ALL_DEPS_SRCS = [
     "kernels/portable/cpu/util/delinearize_index.cpp",
     "kernels/portable/cpu/util/distance_util.cpp",
     "kernels/portable/cpu/util/dtype_util.cpp",
+    "kernels/portable/cpu/util/grid_sampler_2d_util.cpp",
     "kernels/portable/cpu/util/index_util.cpp",
     "kernels/portable/cpu/util/kernel_ops_util.cpp",
     "kernels/portable/cpu/util/matmul_ops_util.cpp",
@@ -260,6 +261,7 @@ KERNELS_UTIL_ALL_DEPS_SRCS = [
     "kernels/portable/cpu/util/repeat_util.cpp",
     "kernels/portable/cpu/util/select_copy_util.cpp",
     "kernels/portable/cpu/util/slice_util.cpp",
+    "kernels/portable/cpu/util/stack_util.cpp",
     "kernels/portable/cpu/util/upsample_util.cpp",
 ]