CMake setup with crosscompilation, modules and libs - c++

Question

I am trying to write a proper CMake script for building an embedded project(STM32). Our project structure looks like this:
App/
....Module1/
....Module2/
Core/
....OwnFramework/
........CoreModule1/
........CoreModule2/
....CubeMXGeneratedCode/
........Core/ (there are more files and dirs, but they are not relevant)
...........Src/main.c (only important info is that main is here)
........Drivers/
....Libs/
........Lib1/ (for example ETL)
Right now there is one CMakeLists.txt file in root project dir, but this seems like a bad solution. I've tried adding CMakeLists into App/ and App/Module but then I would get linking errors (while looking at compile_commands I've seen that they were compiled with almost no flags).
./CMakeLists.txt (removed some non-important parts, like set variables that are obvious, so it's little bit shorter)
set(APP_INCLUDE_DIRECTORIES
${APP_DIR}/Module1
${APP_DIR}/Module2
)
set(CORE_INCLUDE_DIRECTORIES
${Core_DIR}/CoreModule1
${Core_DIR}/CoreModule2
)
set(FLAGS
"-Wl,--gc-sections")
set(CPP_FLAGS
"-fno-rtti -fno-exceptions -fno-threadsafe-statics")
set(CPU_PARAMETERS
-mcpu=cortex-m4
-mthumb
-mfpu=fpv4-sp-d16
-mfloat-abi=hard)
set(STARTUP_SCRIPT ${CUBEMX_DIR}/startup_stm32fxxxxx.s)
set(MCU_LINKER_SCRIPT ${CUBEMX_DIR}/STM32Fxxxxxxx_FLASH.ld)
set(CUBEMX_INCLUDE_DIRECTORIES
${CUBEMX_DIR}/Core/Inc
... and some more Inc dirs
set(PROJECT_INCLUDE_DIRECTORIES
${CMAKE_SOURCE_DIR}
${APP_INCLUDE_DIRECTORIES}
${CORE_INCLUDE_DIRECTORIES})
file(GLOB_RECURSE STM32CUBEMX_SOURCES
${CUBEMX_DIR}/Core/*.c
${CUBEMX_DIR}/Drivers/*.c
${CUBEMX_DIR}/Middlewares/Third_Party/FreeRTOS/Source/*.c)
file(GLOB_RECURSE PROJECT_SOURCES FOLLOW_SYMLINKS
${APP_DIR}/*.cpp
${APP_DIR}/*.c
${CORE_DIR}/*.cpp
${CORE_DIR}/*.c)
add_executable(${EXECUTABLE}
${STM32CUBEMX_SOURCES}
${PROJECT_SOURCES}
${STARTUP_SCRIPT})
target_compile_definitions(${EXECUTABLE} PRIVATE
${MCU_MODEL}
USE_HAL_DRIVER)
target_include_directories(${EXECUTABLE} PRIVATE
${CUBEMX_INCLUDE_DIRECTORIES}
${PROJECT_INCLUDE_DIRECTORIES})
target_compile_options(${EXECUTABLE} PRIVATE
${CPU_PARAMETERS}
${FLAGS}
-Wall
-Wextra
-Wpedantic
-Wno-unused-parameter
$<$<COMPILE_LANGUAGE:CXX>:
${CPP_FLAGS}
-Wno-volatile
-Wold-style-cast
-Wuseless-cast
-Wsuggest-override>
$<$<CONFIG:Debug>:-Og -g3 -ggdb>
$<$<CONFIG:Release>:-Og -g0>)
target_link_options(${EXECUTABLE} PRIVATE
-T${MCU_LINKER_SCRIPT}
${CPU_PARAMETERS}
-Wl,-Map=${CMAKE_PROJECT_NAME}.map
--specs=nosys.specs
-Wl,--start-group
-lc
-lm
-lstdc++
-lsupc++
-Wl,--end-group
-Wl,--print-memory-usage)
add_custom_command(TARGET ${EXECUTABLE} POST_BUILD
COMMAND ${CMAKE_SIZE} $<TARGET_FILE:${EXECUTABLE}>)
add_custom_command(TARGET ${EXECUTABLE} POST_BUILD
COMMAND ${CMAKE_OBJCOPY} -O ihex $<TARGET_FILE:${EXECUTABLE}>
${EXECUTABLE}.hex
COMMAND ${CMAKE_OBJCOPY} -O binary $<TARGET_FILE:${EXECUTABLE}>
${EXECUTABLE}.bin)
There is also toolchain file:
set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)
set(TOOLCHAIN_PREFIX arm-none-eabi-)
set(FLAGS
"-fdata-sections -ffunction-sections \
--specs=nano.specs -Wl,--gc-sections")
set(CMAKE_C_COMPILER ${TOOLCHAIN_PREFIX}gcc ${FLAGS})
set(CMAKE_ASM_COMPILER ${CMAKE_C_COMPILER})
set(CMAKE_CXX_COMPILER ${TOOLCHAIN_PREFIX}g++ ${FLAGS})
set(CMAKE_OBJCOPY ${TOOLCHAIN_PREFIX}objcopy)
set(CMAKE_SIZE ${TOOLCHAIN_PREFIX}size)
set(CMAKE_EXECUTABLE_SUFFIX_ASM ".elf")
set(CMAKE_EXECUTABLE_SUFFIX_C ".elf")
set(CMAKE_EXECUTABLE_SUFFIX_CXX ".elf")
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
I am building everything with this command:
cmake -B${workspaceFolder}/build -DCMAKE_TOOLCHAIN_FILE=gcc-arm-none-eabi.cmake -DCMAKE_BUILD_TYPE=Debug
And this setup works, but I have a feeling that this is a vary bad way of doing it. When I tried adding subdirectories in App and each module, I've got linking erros due to problems with compile flags (arm none eabi elf uses VFP register arguments linking error).
I am also not sure how well will it work when I start adding libs like Embedded Template Library.
So my question is, how do I add subdirectories so they compile the same way my root CMakeLists does? I've tried doing this following multiple guides and examples like this one: https://github.com/rgujju/STM32_Base_Project/blob/master/modules/simple_module/CMakeLists.txt.
But when I've put this in my App/Module/CMakeLists.txt
set(MODULE_NAME simple_module)
file(GLOB SOURCES ./*.c)
add_library(${MODULE_NAME} STATIC
${SOURCES}
)
target_include_directories(${MODULE_NAME}
PUBLIC
${CMAKE_CURRENT_LIST_DIR}
${PROJECT_SOURCE_DIR}/include
)
And added add_subdirectory(App) to main, my generated commands for modules where without most of my flags and didn't link.
If anyone has experience with dividing CMake project into modules, libs and subdirectories, I would gladly accept any help.