External lib error - file format not recognized

[d-soliveira]

Hi there,

I want to use a JSON external library, and I'm following the samples/application_development/external_lib example.

For some reason I'm getting the error error adding symbols: file format not recognized which I guess is related with cross-compiler.
Am I missing some CMake flag or other configuration?

Thank you

The error:

[ 89%] Linking CXX static library app/libapp.a
[ 94%] Built target app
[ 95%] Linking CXX executable zephyr_prebuilt.elf
/home/vm20/zephyr-sdk-0.12.4/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/10.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd: /home/vm20/git/S/zephyr2/json/libjson-c.a: error adding symbols: file format not recognized
collect2: error: ld returned 1 exit status
make[2]: *** [zephyr/CMakeFiles/zephyr_prebuilt.dir/build.make:101: zephyr/zephyr_prebuilt.elf] Error 1
make[1]: *** [CMakeFiles/Makefile2:2973: zephyr/CMakeFiles/zephyr_prebuilt.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

My CMakeLists.txt:

zephyr_get_include_directories_for_lang_as_string(       C includes)
zephyr_get_system_include_directories_for_lang_as_string(C system_includes)
zephyr_get_compile_definitions_for_lang_as_string(       C definitions)
zephyr_get_compile_options_for_lang_as_string(           C options)

set(external_project_cflags
  "${includes} ${definitions} ${options} ${system_includes}"
  )

include(ExternalProject)

ExternalProject_Add(
  json_project                 # Name for custom target
  PREFIX     ${json_build_dir} # Root dir for entire project
  SOURCE_DIR ${json_src_dir}
  BINARY_DIR ${json_src_dir}
  GIT_REPOSITORY https://github.com/json-c/json-c
  GIT_TAG master
  CONFIGURE_COMMAND ""    # Skip configuring the project, e.g. with autoconf
  BUILD_COMMAND cmake ../${json_folder_name} && ${submake}
  CC=${CMAKE_C_COMPILER}
  AR=${CMAKE_AR}
  CFLAGS=${external_project_cflags}
  INSTALL_COMMAND ""      # This particular build system has no install command
  BUILD_BYPRODUCTS ${JSON_LIB_DIR}/libjson-c.a
  )

  # Create a wrapper CMake library that our app can link with
add_library(json_lib STATIC IMPORTED GLOBAL)
add_dependencies(
  json_lib
  json_project
  )
 
set_target_properties(json_lib PROPERTIES IMPORTED_LOCATION             ${PROJECT_SOURCE_DIR}/${json_folder_name}/libjson-c.a)
set_target_properties(json_lib PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${JSON_LIB_DIR})

target_link_libraries(app PUBLIC json_lib)