Multiple undefined reference during linking of a CMake project using ARM toolchain - cmake

Question

I'm developing a build system using CMake to build applications using the arm-none-eabi toolchain.
This is my folder structure:
project/
├── apps/
│ ├── test_app
│ │ ├── inc/
│ │ ├── src/
│ │ ├── CMakeLists.txt
├── arch/
│ ├── CMSIS/
│ ├── include/
│ ├── startup/
│ ├── CMakeLists.txt
├── cmake/
│ ├── toolchain-samd51.cmake
├── CMakeLists.txt
This is my top level CMakeLists.txt:
cmake_minimum_required(VERSION 3.17)
project(SMALL-FW LANGUAGES C)
add_subdirectory(arch)
add_subdirectory(apps/test_app)
This is the toolchain cmake file:
# Set target architecture
set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)
# Set compiler to use
set(CMAKE_C_COMPILER "arm-none-eabi-gcc")
#set(CMAKE_LINKER "arm-none-eabi-ld")
# Clear default compiler and linker flags.
set(CMAKE_C_FLAGS "")
set(CMAKE_C_LINK_FLAGS "")
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
# FIX - Bypass compiler check
set(CMAKE_C_COMPILER_FORCED TRUE)
# Define common compiler and linker flags
set(ARM_OPTIONS
-mthumb
-mabi=aapcs-linux
-mcpu=cortex-m4
-mfpu=fpv4-sp-d16
-mfloat-abi=softfp
--specs=nano.specs
-mlong-calls
-DSAMD51
)
# Define compiler specific flags
add_compile_options(
${ARM_OPTIONS}
-D__SAMD51J19A__
-ffunction-sections
-Wall
)
# Define linker specific flags
add_link_options(
${ARM_OPTIONS}
#--specs=nano.specs
LINKER:--gc-sections
)
This is the CMakeList.txt inside the arch folder:
add_library(asf OBJECT
startup/startup_samd51.c
startup/system_samd51.c
)
# Every target that links against asf needs to know where the ASF headers are.
target_include_directories(asf PUBLIC
${CMAKE_CURRENT_SOURCE_DIR}/CMSIS/Include
${CMAKE_CURRENT_SOURCE_DIR}/include
)
# Use the custom linker script provided with ASF.
target_link_options(asf PUBLIC
-T${CMAKE_CURRENT_SOURCE_DIR}/startup/samd51j19a_flash.ld
)
And this is the app CMakeLists.txt:
add_executable(APP)
target_sources(APP PRIVATE src/main.c src/module.c)
target_include_directories(APP PRIVATE inc/)
target_link_libraries(APP asf)
CMake is running fine when the CMAKE_C_COMPILER_FORCED options is set to true, but when I try to make the project it fails with multiple undefined references errors like the next one:
/build/arm-none-eabi-newlib/src/build-nano/arm-none-eabi/thumb/v7e-m+fp/softfp/newlib/libc/reent/../../../../../../../../newlib-4.2.0.20211231/newlib/libc/reent/sbrkr.c:51: undefined reference to _sbrk'`
I have tried using nosys.specs flag but similar errors occurs.

Answer 1

Try this, it looks like typo
# Define linker specific flags
add_link_options(
${ARM_OPTIONS}
--specs=nano.specs
--gc-sections
)