loader: nano_connect: fix linking error with picolibc

The Zephyr SDK's picolibc.specs file unconditionally injects --gc-sections
into the linker flags. --gc-sections removes any section not reachable from
an entry point. But boot_stage2.ld has no ENTRY() directive, so the linker
thinks everything is unreachable and discards all sections and then objcopy
fails with the input file 'boot_stage2' has no sections.

The fix overrides the default cmake configs with --no-gc-sections.

Signed-off-by: Gilberto Conti <g.conti@arduino.cc>

Author: gibix

loader/CMakeLists.txt

@@ -10,6 +10,10 @@ find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE} COMPONENTS yaml boards)
 set(DTC_OVERLAY_FILE ${CMAKE_CURRENT_LIST_DIR}/../variants/${NORMALIZED_BOARD_TARGET}/${NORMALIZED_BOARD_TARGET}.overlay)
 set(EXTRA_CONF_FILE ${CMAKE_CURRENT_LIST_DIR}/../variants/${NORMALIZED_BOARD_TARGET}/${NORMALIZED_BOARD_TARGET}.conf)
 
+# Register our project as a MODULE_EXT_ROOT so our module overrides
+# (e.g. modules/hal_rpi_pico) take precedence over zephyr's defaults.
+list(APPEND MODULE_EXT_ROOT ${CMAKE_CURRENT_LIST_DIR})
+
 find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
 
 project(app LANGUAGES C CXX)

loader/modules/hal_rpi_pico/CMakeLists.txt

@@ -0,0 +1,53 @@
+# SPDX-License-Identifier: Apache-2.0
+#
+# Override for hal_rpi_pico module: patches the boot_stage2 ExternalProject
+# to add -Wl,--no-gc-sections (picolibc.specs injects --gc-sections which
+# discards all sections because boot_stage2.ld has no ENTRY()).
+#
+# Instead of maintaining a full copy of the zephyr CMakeLists.txt, we read
+# the original, apply targeted patches, and include the patched version.
+
+set(_orig_dir ${ZEPHYR_BASE}/modules/hal_rpi_pico)
+set(_patch_dir ${CMAKE_CURRENT_BINARY_DIR}/_patched_hal_rpi_pico)
+
+# --- Patch the main CMakeLists.txt ---
+file(READ ${_orig_dir}/CMakeLists.txt _content)
+
+# Point the ExternalProject to our patched bootloader dir
+string(REPLACE
+  "SOURCE_DIR \${CMAKE_CURRENT_LIST_DIR}/bootloader"
+  "SOURCE_DIR ${_patch_dir}/bootloader"
+  _content "${_content}")
+
+# Fix remaining CMAKE_CURRENT_LIST_DIR refs (include dirs, linker scripts)
+string(REPLACE
+  "\${CMAKE_CURRENT_LIST_DIR}"
+  "${_orig_dir}"
+  _content "${_content}")
+
+# Fix relative linker script paths (resolved via CMAKE_CURRENT_SOURCE_DIR)
+string(REPLACE " timecritical.ld)" " ${_orig_dir}/timecritical.ld)" _content "${_content}")
+string(REPLACE " uninit_data.ld)" " ${_orig_dir}/uninit_data.ld)" _content "${_content}")
+
+file(WRITE ${_patch_dir}/CMakeLists.txt "${_content}")
+
+# --- Patch the bootloader CMakeLists.txt ---
+file(READ ${_orig_dir}/bootloader/CMakeLists.txt _boot_content)
+
+# Add --no-gc-sections after picolibc.specs
+string(REPLACE
+  "\"--specs=picolibc.specs\""
+  "\"--specs=picolibc.specs\"\n  \"-Wl,--no-gc-sections\""
+  _boot_content "${_boot_content}")
+
+# Fix ".." include dir to point to original zephyr module dir
+string(REPLACE
+  "\n  ..\n"
+  "\n  ${_orig_dir}\n"
+  _boot_content "${_boot_content}")
+
+file(MAKE_DIRECTORY ${_patch_dir}/bootloader)
+file(WRITE ${_patch_dir}/bootloader/CMakeLists.txt "${_boot_content}")
+
+# --- Include the patched version ---
+include(${_patch_dir}/CMakeLists.txt)

loader/modules/modules.cmake

@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: Apache-2.0
+# Override module cmake dirs with our local versions.
+
+file(GLOB cmake_modules "${CMAKE_CURRENT_LIST_DIR}/*/CMakeLists.txt")
+
+foreach(module ${cmake_modules})
+  get_filename_component(module_dir  ${module} DIRECTORY)
+  get_filename_component(module_name ${module_dir} NAME)
+  zephyr_string(SANITIZE TOUPPER MODULE_NAME_UPPER ${module_name})
+
+  set(ZEPHYR_${MODULE_NAME_UPPER}_CMAKE_DIR ${module_dir})
+endforeach()