6410之重定位，清bss

代码如下：

relocate_code:adr r0,_start     //获取指令_start的当前地址ldr r1,=_start  //获取指令_start的链接地址ldr r2,=bss_startcmp r0,r1beq clean_bsscopy_loop:ldr r3,[r0],#4str r3,[r1],#4cmp r1,r2bne copy_loopclean_bss:ldr r0,=bss_startldr r1,=bss_endmov r2,#0clean_loop:str r2,[r0],#4cmp r0,r1bne clean_loop