Where is M4 hardware breakpoint address?

Hi I'm learning cortex m4 debug feature, 

I'm using stm32f407 discovery with openocd in ubuntu

I'm trying to understad breakpoint feature,

I can set breakpoint address in openocd and chip will stop when pc run to that address

like main function is at 0x8008000,

I guess there must be a register to store this address(0x8008000), but I cannot find wher is this register from all information I can get

can anyone tell me where to learn relative info, thanks :)