I’m new to Cmake, and am a bit beaten by it.

In my main project I’m trying to fetchcontent a git Repo and add it to my main project as a lib.
The problem I have is that everything builds fine. however when I call the function int GetVersion(){return 2;} from the LIB, it simply returns 0.

I build a .elf for an STM32 Microcontroller using STM32CUBEIDE.
I already made a project without IDE and made .exe and… it works as expected it prints 3…

There are no errors or warning other that a = unused. But the optimizer is turned of and i can step through the code.
Since everything builds fine, I have a feeling it is not linking well.
Am I missing anything, what can I do to debug this further?

//Main.c
#include <stdint.h>
#include "ringbuff.h"

int main(void)
{
    static int a = 1;
    a = GetVersion(); // after this call a = 0
    for(;;);
}

//ringbuff.c from the lib.  The header contains: 'int GetVersion2();'
#include "ringbuff.h"

int GetVersion()
{
    return 3;
}

cMakelists of Main project. Everything is standard cmaketemplate from the IDE, I’ve added the part inbetween the Import Lib comments

cmake_minimum_required(VERSION 3.20)

set (PROJECT_NAME             "CM7")

# LIST SOURCE FILES HERE
set (PROJECT_SOURCES
    Startup/startup_stm32h755zitx.s
    Sources/system_stm32h7xx_dualcore_boot_cm4_cm7.c
    Sources/main.c
    Sources/syscalls.c
    Sources/sysmem.c
    )

# LIST COMPILER DEFINITIONS HERE
set (PROJECT_DEFINES
        CORE_CM7
        STM32H755xx
    ) 

# LIST INCLUDE DIRECTORIES HERE
set (PROJECT_INCLUDES
    Sources
      
    #STM32 HAL & CMSIS
    Drivers/STM32H7xx_HAL_Driver/Inc
    Drivers/STM32H7xx_HAL_Driver/Inc/Legacy
    Drivers/CMSIS/Device/ST/STM32H7xx/Include
    Drivers/CMSIS/Include
    )

project(${PROJECT_NAME})
enable_language(ASM)

add_executable(${PROJECT_NAME} ${PROJECT_SOURCES})
add_custom_command(TARGET ${CMAKE_PROJECT_NAME} POST_BUILD COMMAND ${CMAKE_SIZE} $<TARGET_FILE:${CMAKE_PROJECT_NAME}>)

################# Import module #####################
include(FetchContent)
Set(FETCHCONTENT_QUIET FALSE)
FetchContent_Declare(
  ringbuff
  GIT_REPOSITORY https://github.com/TESTMODULE.git
  GIT_TAG        V0.7
  GIT_PROGRESS   TRUE
)
FetchContent_MakeAvailable(ringbuff)

target_include_directories(${PROJECT_NAME}
    PUBLIC ${ringbuff_SOURCE_DIR}
)

target_link_libraries(${PROJECT_NAME} 
    PRIVATE ringbuff
)
#####################################################

target_compile_definitions(${PROJECT_NAME}
    PRIVATE ${PROJECT_DEFINES}
)
target_include_directories(${PROJECT_NAME}
    PUBLIC ${PROJECT_INCLUDES}
)

set (CMAKE_EXECUTABLE_SUFFIX ".elf")
set (CMAKE_STATIC_LIBRARY_SUFFIX ".a")
set (CMAKE_C_FLAGS "-mcpu=Cortex-M7 -O0 -std=gnu11 -mfpu=fpv5-d16 --specs=nano.specs -mthumb -Wall")
set (CMAKE_EXE_LINKER_FLAGS "-T../STM32H755ZITX_FLASH.ld --specs=nosys.specs -Wl,-Map=test.map -Wl,--gc-sections -static -Wl,--start-group -lc -lm -Wl,--end-group")
set (CMAKE_ASM_FLAGS "${CMAKE_C_FLAGS} -x assembler-with-cpp")

Cmakelist of the ringbuff lib

# Minimum version of CMake required
cmake_minimum_required(VERSION 3.20)

# Project name
project(RingBuffer C)

# Add the source files
add_library(ringbuff STATIC ringbuff.c)