System Workbench for STM32

I forgot:

In your program you have to add syscalls.c (for GNU) and implement the function int __io_putchar(int ch).
Something like this:

int __io_putchar(int ch){
ITM_SendChar(ch);
return(ch);
}

ITM_SendChar(ch) is defined in core_cm4.h and core_cm3.h.