CI: Hack: Patch MicroPython to remove exception handling.

Force "-specs=nano.specs" on MicroPython builds and disable various stack unwinding and exception handling features for C++ modules.

Author: Gadgetoid

.github/workflows/micropython.yml

@@ -19,9 +19,9 @@ jobs:
       uses: actions/cache@v3
       with:
         path: ${{runner.workspace}}
-        key: workspace-micropython-${{env.MICROPYTHON_VERSION}}-pico
+        key: workspace-micropython-${{env.MICROPYTHON_VERSION}}-nano-specs
         restore-keys: |
-          workspace-micropython-${{env.MICROPYTHON_VERSION}}-pico
+          workspace-micropython-${{env.MICROPYTHON_VERSION}}-nano-specs
 
     # Check out MicroPython
     - name: Checkout MicroPython
@@ -129,18 +129,24 @@ jobs:
         echo "MICROPY_GIT_TAG=$MICROPYTHON_VERSION, ${{matrix.name}} ${{github.event.release.tag_name || github.sha}}" >> $GITHUB_ENV
         echo "MICROPY_GIT_HASH=$MICROPYTHON_VERSION-${{github.event.release.tag_name || github.sha}}" >> $GITHUB_ENV
 
-    - name: "HACK: Clean ports/rp2/modules"  # We should move to using manifest.py to include our custom modules
+    - name: "HACK: Clean ports/rp2/modules and ports/rp2/CMakeLists.txt"
       shell: bash
       working-directory: micropython/ports/rp2
       run: |
         rm -rf modules
         git checkout modules
   
-    - name: "HACK: Revert Pico SDK Patch"  # Avoid an already-patched MicroPython tree breaking our build
+    - name: "HACK: Revert Patches"  # Avoid an already-patched MicroPython tree breaking our build
       shell: bash
-      working-directory: micropython/lib/pico-sdk
+      working-directory: micropython
       run: |
-        git checkout .
+        git checkout lib/pico-sdk
+        git checkout ports/rp2/CMakeLists.txt
+
+    - name: "HACK: CMakeLists.txt Disable C++ Exceptions Patch"
+      shell: bash
+      working-directory: micropython
+      run: git apply $GITHUB_WORKSPACE/pimoroni-pico-${{ github.sha }}/micropython/micropython_nano_specs.patch
 
     - name: "HACK: Pico SDK Patch"
       if: matrix.patch == true

micropython/micropython_nano_specs.patch

@@ -0,0 +1,20 @@
+diff --git a/ports/rp2/CMakeLists.txt b/ports/rp2/CMakeLists.txt
+index 094031c6852a..5f268414c08f 100644
+--- a/ports/rp2/CMakeLists.txt
++++ b/ports/rp2/CMakeLists.txt
+@@ -374,6 +374,15 @@ target_compile_options(${MICROPY_TARGET} PRIVATE
+ target_link_options(${MICROPY_TARGET} PRIVATE
+     -Wl,--defsym=__micropy_c_heap_size__=${MICROPY_C_HEAP_SIZE}
+ )
++# Do not include stack unwinding & exception handling for C++ user modules
++target_compile_definitions(usermod INTERFACE PICO_CXX_ENABLE_EXCEPTIONS=0)
++target_compile_options(usermod INTERFACE $<$<COMPILE_LANGUAGE:CXX>:
++    -fno-exceptions
++    -fno-unwind-tables
++    -fno-rtti
++    -fno-use-cxa-atexit
++>)
++target_link_options(usermod INTERFACE -specs=nano.specs)
+ 
+ set_source_files_properties(
+     ${PICO_SDK_PATH}/src/rp2_common/pico_double/double_math.c