Hangs in vsprintf()

Question

I'm programming on stm32f407 and using vsprintf to access all the the arguments assigned to argv such as:

va_list argv;

va_start(argv, __format);


vsprintf(buffer, __format, argv);


va_end(argv);

But the program hangs in vsprintf. I modified stm32_flash.ld :

      ._user_heap_stack :
  {
    . = ALIGN(4);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    PROVIDE ( __end__ = . ); 
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(4);
  } >RAM

And Cpu flags in Makefile:

CFLAGS += --specs=rdimon.specs -Wl,--start-group -lgcc -lc -lm -lrdimon -Wl,--end-group

Does anyone know how to solve this issue? Please help me. Thanks so much.