手册上是这么写的。
The backup domain includes 4Kbytes of backup SRAM accessible only from the CPU, and
 mode
address in 32-bit, 16-bit or 8-bit mode. Its content is retained even in Standby or V
BAT
when the low power backup regulator is enabled. It can be considered as an internal
 is always present.
EEPROM when VBAT is always present.
我如何才能把变量定义到这4K  SRAM

IAR有预定义命令，能够直接把变量定位到地址，可以看看IAR的文档，keil也有的。

看stm32的手册，没看到有讲Backup sram的具体地址分配