undefined reference to "MX_USB_DEVICE_Init" during Linker operation under System Workbench for STM32

Hi all,

I'm developping an application under system workbench for STM32. The compilation works fine, but when it comes to the Linker I get the following output :

16:08:46 **** Incremental Build of configuration Release for project Firmware ****
make all 
Building target: Firmware.elf
Invoking: MCU GCC Linker
arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 -specs=nosys.specs -specs=nano.specs -T"../STM32F412ZETx_FLASH.ld" -Wl,-Map=output.map -Wl,--gc-sections -o "Firmware.elf" @"objects.list" -lm
Src/main.o: In function `main':
D:\dev\AEL_FW\Firmware\Release/../Src/main.c:119: undefined reference to `MX_USB_DEVICE_Init'
Src/stm32f4xx_it.o: In function `OTG_FS_IRQHandler':
D:\dev\AEL_FW\Firmware\Release/../Src/stm32f4xx_it.c:282: undefined reference to `hpcd_USB_OTG_FS'
collect2.exe: error: ld returned 1 exit status
make: *** [Firmware.elf] Error 1
makefile:43: recipe for target 'Firmware.elf' failed
 
16:08:47 Build Finished (took 981ms)

I've tried to trace back the error :

main.c :

#include "usb_device.h" 
 
...
 
int main(void)
{
...
MX_USB_DEVICE_Init();
...
}

in usb_device.h :

void MX_USB_DEVICE_Init(void);

in usb_device.c

void MX_USB_DEVICE_Init(void)
{
 /* USER CODE BEGIN USB_DEVICE_Init_PreTreatment */
 
 /* USER CODE END USB_DEVICE_Init_PreTreatment */
 
 /* Init Device Library, add supported class and start the library. */
 if (USBD_Init(&hUsbDeviceFS, &FS_Desc, DEVICE_FS) != USBD_OK)
 {
 Error_Handler();
 }
 if (USBD_RegisterClass(&hUsbDeviceFS, &USBD_CDC) != USBD_OK)
 {
 Error_Handler();
 }
 if (USBD_CDC_RegisterInterface(&hUsbDeviceFS, &USBD_Interface_fops_FS) != USBD_OK)
 {
 Error_Handler();
 }
 if (USBD_Start(&hUsbDeviceFS) != USBD_OK)
 {
 Error_Handler();
 }
 
 /* USER CODE BEGIN USB_DEVICE_Init_PostTreatment */
 
 /* USER CODE END USB_DEVICE_Init_PostTreatment */
}

It also seems that FS_Desc cannot be resolved eventhough usbd_desc.h and usbd_desc.c are included and FS_Desc is declared and defined :

USBD_DescriptorsTypeDef FS_Desc =
{
 USBD_FS_DeviceDescriptor
, USBD_FS_LangIDStrDescriptor
, USBD_FS_ManufacturerStrDescriptor
, USBD_FS_ProductStrDescriptor
, USBD_FS_SerialStrDescriptor
, USBD_FS_ConfigStrDescriptor
, USBD_FS_InterfaceStrDescriptor
#if (USBD_LPM_ENABLED == 1)
, USBD_FS_USR_BOSDescriptor
#endif /* (USBD_LPM_ENABLED == 1) */
};

I've attached the whole project if you want to take a look at it.