GDB Remote debug: Why several "$Z0,address,length" msg when only set one breakpoint?

Hi,

Currently, I am hacking uboot arm kgdb and adding breakpoint support.

The steps is as following:
(gdb) b do_bootz
Breakpoint 1, do_bootz (cmdtp=0x8784ca14 <_u_boot_list_2_cmd_2_bootz>, flag=0, argc=1, argv=0xbf552a20) at common/cmd_bootm.c:1928
(gdb) c
Continuing.
Sending packet: $m87809580,4#7a...Ack
Packet received: f0452de9
Sending packet: $m87809580,4#7a...Ack
Packet received: f0452de9
Sending packet: $Z0,87809584,4#c7...Ack
Packet received: OK
Sending packet: $Hc0#db...Ack
Packet received: 
Sending packet: $c#63...Ack
Packet received: T050f:84958087;0d:a41355bf;
Sending packet: $z0,87809584,4#e7...Ack
Packet received: OK
Sending packet: $qTStatus#49...Ack
Packet received: 
Sending packet: $Z0,87800000,4#ad...Ack
Packet received: OK
Sending packet: $Z0,87809580,4#c3...Ack
Packet received: OK
Sending packet: $Hc0#db...Ack
Packet received: 
Sending packet: $c#63...Ack

Actually the breakpoint is at 0x87809580, but why first set breakpoint at 0x87809584 then remove it then set breakpoint at 0x87809580?

Also the first time set a breakpoint then continue.
(gdb) c
Continuing.
Sending packet: $qTStatus#49...Ack
Packet received: 
Sending packet: $Z0,87800000,4#ad...Ack
Packet received: OK
Packet Z0 (software-breakpoint) is supported
Sending packet: $Z0,87809580,4#c3...Ack
Packet received: OK
Sending packet: $vCont?#49...Ack
Packet received: 
Packet vCont (verbose-resume) is NOT supported
Sending packet: $Hc0#db...Ack
Packet received: 
Sending packet: $c#63...Ack

why two Z0 here? I only set break at 0x87809580, but gdb send a break set at 0x87800000 which is the beginning of the elf entry.

Thanks.
Peng.